Evaluation of Ultrasonic Cleaning and Glass Bead Blasting as Surface Preparation Techniques for Manganese Phosphating of SAE 4140 Low Alloy Steel for Small Arms Components

Evaluation of Ultrasonic Cleaning and Glass Bead Blasting as Surface Preparation Techniques for Manganese Phosphating of SAE 4140 Low Alloy Steel for Small Arms Components | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Evaluation of Ultrasonic Cleaning and Glass Bead Blasting as Surface Preparation Techniques for Manganese Phosphating of SAE 4140 Low Alloy Steel for Small Arms Components Major Ameya Prashant Joshi, Captain Manuj Chamoli This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9649913/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The corrosion resistance of small arms components depend largely upon the integrity of their surface treatments. Traditional overhaul protocols for ferrous components of small arms typically involve a multi-bath chemical pre-treatment process followed by Manganese Phosphating, which presents significant challenges regarding coating consistency as well as operator and environmental safety at field level. This research investigates the efficacy of replacing hazardous chemical pre-treatments such as Trichloroethylene, Caustic Soda and Hydrochloric Acid with a combined protocol of ultrasonic cleaning and glass bead blasting. Experimental results on SAE 4140 steel coupons indicate that the proposed mechanical-ultrasonic approach yields a superior coating thickness of 2.60 µm compared to the 2.22 µm achieved by legacy chemical methods for the same Manganese Phosphating process. Scanning Electron Microscope analysis reveals a significantly denser, fine-grained crystalline morphology in the sample with the proposed pre-treatment protocol, which also translates to enhanced performance in accelerated salt spray testing over 72 hours. This study validates a safer, more efficient metallurgical standard for re-phosphating of small arms components during overhaul operations. Mechanical Engineering Manganese Phosphating Ultrasonic Cleaning Glass Bead Blasting Surface Preparation Corrosion Resistance Defence Metallurgy Figures Figure 1 Figure 2 Figure 3 Figure 4 INTRODUCTION Manganese Phosphating, colloquially known as "Parkerizing" in defence equipment contexts, is a crucial and popular thermochemical process used to improve the corrosion resistance, wear resistance and anti-galling properties of moving parts in small arms [ 1 ]. The process involves the formation of a layer of insoluble tertiary manganese phosphates on the ferrous substrate, which provides a porous base for supplemental lubricants and corrosion-inhibitive oils [ 2 ]. Current maintenance and overhaul practices for small arms in many defence facilities rely on a multi-bath preparation sequence for Manganese Phosphating. This legacy protocol involves de-greasing and de-rusting for surface preparation with chlorinated hydrocarbons (like Trichloroethylene), alkaline cleaning (Caustic Soda) and acid pickling (HCl). While effective at removing oils, greases and surface impurities including oxides, these chemicals pose severe health risks to operators and require complex effluent treatment systems. Furthermore, inconsistent bath chemistry often leads to sludging and coarse crystal growth on the small arm components, which compromises the overall protective quality of the phosphate layer [ 3 ]. Objectives of the Study This research seeks to evaluate a technologically advanced pre-treatment alternative for Manganese Phosphating that integrates ultrasonic cleaning and glass bead blasting for surface preparation. While ultrasonic cleaning is carried out to achieve microscopic cleaning without use of hazardous chemicals, while glass bead blasting is done to modify surface topography and increase the density of nucleation sites for phosphate crystal growth. The primary objective of the research is to compare the resulting coating thickness, crystal morphology and corrosion resistance against the established legacy standard. MATERIALS AND METHODS Sample Preparation SAE 4140 steel coupons were utilized to simulate the metallurgical properties of standard small arms ferrous components [ 4 ]. The coupons were precision-cut to ensure uniform surface area for comparative analysis. One face of the coupons was treated for Chrome plating to imitate a small arms barrel with Chrome plated inner layer and a phosphate outer layer [ 5 ]. The research is based on experimentation on the phosphate side of the coupon samples. Composition of the SAE 4140 Steel coupons is as given in Table 1 . Table 1 Composition of SAE 4140 Steel Coupons C % Cr % Mn % Mo % Si % P % S % Ni % Cu % W % 0.38–0.43 0.80–1.10 0.75 -1.0 0.15–0.25 0.15–0.35 0.025 max 0.025 max 0.25 max 0.35 max 0.10 max The study utilised two distinct preparation protocols for the coupon samples before undergoing an identical four-bath Manganese Phosphating process. Sample-A was pre-processed using ultrasonic cleaning followed by mechanical glass bead blasting while Sample-B was pre-processed using multi-bath chemical process involving Trichloroethylene, Caustic Soda and Hydrochloric Acid. Process Parameters Ultrasonic cavitation cleaning operates in the frequency range 20–40 kHz. In an aqueous medium, these sound waves create alternating cycles of high and low pressure, leading to formation and asymmetric collapse of microscopic vacuum bubbles - a phenomenon known as cavitation. When these bubbles implode near a solid boundary (the small arms component), they generate high-energy micro-jets and localised shockwaves. This energy dislodges carbon residues, sticky oils and lubricants from high-precision geometries, such as internal bores, blind holes and threads, which are inaccessible to mechanical scrubbing or simple chemical immersion. For ultrasonic cleaning, sample coupons were immersed in a mild alkali based bath and subjected to high-frequency sound waves (~ 40 kHz) for a time period of 10 minutes. The cavitation cleaning achieves effective oil and grease removal from old and used components of small arms. Glass bead blasting is a mechanical surface conditioning method using spherical soda-lime glass particles. Unlike angular abrasives (such as aluminium oxide or blasting sand), spherical beads do not remove base metal via a cutting action. Instead, they operate on the principle of Hertzian contact theory, where the spherical impact induces a controlled peening effect. This creates a uniform, matte micro-roughness and introduces beneficial compressive residual stresses into the surface layer. This mechanical activation removes tenacious oxides and scale without altering dimensional tolerances or creating sharp stress concentrations, which are commonly associated with angular media. The transition from cleaning to phosphating is governed by the Gibbs free energy of nucleation [ 6 ]. Mechanical roughening via glass bead blasting increases the surface energy and the density of active sites. This reduces the critical radius required for crystal formation. Consequently, the phosphate crystals form more rapidly and closer together, resulting in a fine-grained, dense morphology. As per the legacy methodology for surface preparation, the coupon sample was pre-treated through a multi-chemical bath process starting with a dip in Trichloroethylene, which is a potent solvent for removing petroleum based preservatives which are applied on the small arms components during deep preservation in depots. It is followed by a dip in hot Alkali bath containing 2% Soda Ash, 1% Sodium Phosphate Tribasic and 0.5% Soda Caustic dissolved in water and maintained at 90-95 O C for 10 minutes to emulsify remaining organic soils. Thereafter pickling in 10% Hydrochloric Acid bath is carried out to remove mill scale and rust. Multiple hot and cold water rinsing is done between each chemical dip to prevent cross-contamination of the chemical baths. Manganese Phosphating is a popular crystalline conversion coating that involves a chemical reaction between the ferrous substrate and a heated phosphoric acid solution containing manganese and phosphate ions. The reaction proceeds via an initial acid attack on the base steel, which raises the local pH at the metal-liquid interface. This pH shift triggers the precipitation of insoluble manganese phosphate crystals on the steel surface. Unlike electroplating, the Manganese Phosphate layer is an integral part of the substrate's surface, giving superior mechanical anchoring and oil-retention properties through its inherent micro-porous structure. Both coupon samples were then processed in a standard four bath Manganese Phosphating procedure involving surface activation, phosphating, rinsing and passivation, with the most crucial step being the phosphating bath which was maintained at 90–95°C for a duration of 30 minutes. TESTING & RESULTS Coating Thickness Analysis The thickness of the phosphate coating is a primary indicator of its potential for oil retention and corrosion protection. Coating thickness measurement was carried out as per ASTM B-487-20 [ 7 ] using an optical microscope by a NABL accredited laboratory. As shown in Table 2 , Sample-A demonstrated a higher deposition in comparison with Sample-B. Table 2 Comparative Phosphate Coating Thickness of Samples Readings Sample A Coating Thickness (µm) Sample B Coating Thickness (µm) Reading 1 3.93 1.72 Reading 2 2.21 2.22 Reading 3 2.21 2.46 Reading 4 1.96 2.46 Reading 5 2.70 2.22 Average 2.60 2.22 The higher coating thickness in Sample-A (greater by 14.6%) over that of Sample-B suggests that glass bead blasting creates a higher surface-to-volume ratio, allowing for a more robust chemical reaction during the phosphating phase and better deposition on the surface. Crystalline Morphology (SEM) The protective quality of a phosphate coating is highly dependent on the grain size of the deposition. Coarse, large crystals often leave micro-gaps that allow moisture to reach the substrate and initiate corrosion. SEM imaging of Sample-B pre-treated with legacy multi-bath chemical process revealed a coarse, irregular crystal morphology when observed at 500x, 1000x, 3000x and 5000x under a Scanning Electron Microscope Phenom XL G2 (Thermo Fischer Scientific India Pvt Ltd) as per ASM Handbook Vol 9 [ 8 ]. The structure showed prominent inter-crystalline gaps and high porosity, which serve as pathways for corrosive electrolytes. It is evident from the experimental results that the legacy chemical preparation, while effective at cleaning, does not provide the specific surface energy required for high-density nucleation. The morphology as observed for Sample-A was characterised by a fine, dense and compact crystalline structure at 500x, 1000x, 3000x and 5000x under the same SEM. The crystals are tightly interlocked with minimal porosity, creating a superior physical barrier and increasing the corrosion protection of the substrate. The abrasive mechanical impact of the glass beads likely created numerous high-energy active centres on the metal surface, which acted as nucleation sites for the phosphate crystal deposition. Corrosion Resistance (Salt Spray Test) The samples were further tested for corrosion resistance in a salt spray chamber as per ASTM B 117 − 19 [ 9 ] using a 5% NaCl with a specific gravity of 1.032 maintained at 35 o C. Both the samples were exposed for 72 hours and observations were recorded at every 24 hour interval. The results were categorized by the appearance of red rust on the phosphated side of the samples [ 10 ] [ 11 ]. Red rust started appearing on both the samples after an exposure to the salt spray after 24 hours, however there was significant visible difference in the appearance of the rust on both the samples. After 24 hours, Sample-A was largely unaffected, while rust was showing on a considerable portion of Sample-B, while after an exposure of 48 hours, rusting of Sample-B seemed to rapidly increase whereas there was comparatively minor increase in the rust observed in Sample-A. At the end of 72 hour exposure, the surface of Sample-B was largely rusted, while rust on surface of Sample-A was significantly lower. It can be derived from the observations that the refined crystalline structure of the coating on Sample-A acts as a more effective physical barrier, significantly slowing the rate of electrolyte penetration to the base metal, hence retarding the rate of corrosion. Conclusion This study confirms that the integration of ultrasonic cleaning and glass bead blasting represents a significant advancement in surface preparation of SAE 4140 steel components for Manganese Phosphating. The proposed surface preparation protocol produced a thicker and more compact phosphate layer than that produced with surface preparation using traditional chemical methods. Fine-grained crystalline morphology in the sample treated with the proposed protocol directly correlates to increased corrosion resistance in accelerated salt spray environments. The transition from coarse grains to a dense morphology for phosphate layer is fundamentally a kinetic phenomenon. By replacing chemical etching with glass bead blasting, we increase the surface energy of the substrate. In the initial seconds of the phosphating reaction, this higher surface energy lowers the energy barrier for nucleation, allowing crystals to form simultaneously across the entire surface. Because the nucleation density is high, the growing crystals impinge upon one another early, preventing the growth of large, irregular grains and resulting in the observed fine-grained, compact structure. Further, shifting away from hazardous chemicals like Trichloroethylene and HCl reduces the environmental footprint of small arms overhaul processes and improves operator safety. In conclusion, the combination of ultrasonic cavitation cleaning and glass bead blasting is a viable and superior alternative to the multi-bath chemical preparation, offering enhanced component longevity and modernised workflow for re-phosphating of SAE 4140 steel components during overhaul operations of small arms. References Department of Defense (n.d.). MIL-DTL-16232G: Detail Specification: Phosphate Coating, Heavy, Manganese or Zinc Base ASM International (1994) ASM Handbook, Volume 5: Surface Engineering . Materials Park, OH Duszczyk J, Siuzdak K, Klimczuk T, Strychalska-Nowak J, Zaleska-Medynska A (2018) Manganese Phosphatizing Coatings: The Effects of Preparation Conditions on Surface Properties. Materials 11(12):2585. https://doi.org/10.3390/ma11122585 Klein M, Eifler D (2010) Influences of the manufacturing processes on the surface integrity and the resulting fatigue behavior of quenched and tempered SAE 4140. Procedia Eng 2(1):2239–2247. https://doi.org/10.1016/j.proeng.2010.03.240 Akhtar MN, Lohchab A, Singh D, Kumar RR, Gaur P, Yadav BK (2023) Experimental studies on the effect of chromium plating on the mechanical properties of SAE 4140 steel. Materials Today: Proceedings, 72 (4), 2488–2496. https://doi.org/10.1016/j.matpr.2022.09.527 Middelburg JJ (2024) The Gibbs Free Energy. In: Thermodynamics and Equilibria in Earth System Sciences: An Introduction (SpringerBriefs in Earth System Sciences). Springer, Cham. https://doi.org/10.1007/978-3-031-53407-2_4 ASTM International (2024) ASTM B 487 – 20: Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section . West Conshohocken, PA ASM International (2004) ASM Handbook, Volume 9: Metallography and Microstructures . Materials Park, OH ASTM International (2019) ASTM B117-19: Standard Practice for Operating Salt Spray (Fog) Apparatus. West Conshohocken, PA ASM International (2003) ASM Handbook, Volume 13A: Corrosion: Fundamentals, Testing, and Protection . Materials Park, OH Baboian R (2022) NACE Corrosion Engineer's Reference Guide, 4th edn. NACE International Additional Declarations The authors declare no competing interests. Supplementary Files SampleBSaltSpray.pdf SampleACoatingSEM.pdf SampleACoatingThickness.pdf SampleASaltSpray.pdf SampleBCoatingSEM.pdf SampleBCoatingThickness.pdf Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Process\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9649913/v1/87b4cd72292b0f222f18638c.png"},{"id":108940554,"identity":"0b915b38-96fc-4298-9129-5bc44348dcae","added_by":"auto","created_at":"2026-05-11 05:17:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":621809,"visible":true,"origin":"","legend":"\u003cp\u003eCoating Thickness Measurements of Samples for Phosphate Coating\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-9649913/v1/fae911e04d9a09cc2e00844d.png"},{"id":108940556,"identity":"86b7540c-fd2c-4b8b-85ba-b4263861a29f","added_by":"auto","created_at":"2026-05-11 05:17:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1309228,"visible":true,"origin":"","legend":"\u003cp\u003eSEM Micrographs (1000x and 3000x Magnification) comparing Fine Grains of 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The process involves the formation of a layer of insoluble tertiary manganese phosphates on the ferrous substrate, which provides a porous base for supplemental lubricants and corrosion-inhibitive oils [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCurrent maintenance and overhaul practices for small arms in many defence facilities rely on a multi-bath preparation sequence for Manganese Phosphating. This legacy protocol involves de-greasing and de-rusting for surface preparation with chlorinated hydrocarbons (like Trichloroethylene), alkaline cleaning (Caustic Soda) and acid pickling (HCl). While effective at removing oils, greases and surface impurities including oxides, these chemicals pose severe health risks to operators and require complex effluent treatment systems. Furthermore, inconsistent bath chemistry often leads to sludging and coarse crystal growth on the small arm components, which compromises the overall protective quality of the phosphate layer [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e\n\u003ch3\u003eObjectives of the Study\u003c/h3\u003e\n\u003cp\u003eThis research seeks to evaluate a technologically advanced pre-treatment alternative for Manganese Phosphating that integrates ultrasonic cleaning and glass bead blasting for surface preparation. While ultrasonic cleaning is carried out to achieve microscopic cleaning without use of hazardous chemicals, while glass bead blasting is done to modify surface topography and increase the density of nucleation sites for phosphate crystal growth.\u003c/p\u003e \u003cp\u003eThe primary objective of the research is to compare the resulting coating thickness, crystal morphology and corrosion resistance against the established legacy standard.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eSample Preparation\u003c/h2\u003e \u003cp\u003eSAE 4140 steel coupons were utilized to simulate the metallurgical properties of standard small arms ferrous components [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The coupons were precision-cut to ensure uniform surface area for comparative analysis. One face of the coupons was treated for Chrome plating to imitate a small arms barrel with Chrome plated inner layer and a phosphate outer layer [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The research is based on experimentation on the phosphate side of the coupon samples. Composition of the SAE 4140 Steel coupons is as given in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposition of SAE 4140 Steel Coupons\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCr %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMn %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMo %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSi %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eP %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eS %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eNi %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCu %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eW %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.38\u0026ndash;0.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.80\u0026ndash;1.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.75 -1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.15\u0026ndash;0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.15\u0026ndash;0.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.025 max\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.025 max\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.25 max\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.35 max\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.10 max\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe study utilised two distinct preparation protocols for the coupon samples before undergoing an identical four-bath Manganese Phosphating process. Sample-A was pre-processed using ultrasonic cleaning followed by mechanical glass bead blasting while Sample-B was pre-processed using multi-bath chemical process involving Trichloroethylene, Caustic Soda and Hydrochloric Acid.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eProcess Parameters\u003c/h3\u003e\n\u003cp\u003eUltrasonic cavitation cleaning operates in the frequency range 20\u0026ndash;40 kHz. In an aqueous medium, these sound waves create alternating cycles of high and low pressure, leading to formation and asymmetric collapse of microscopic vacuum bubbles - a phenomenon known as cavitation. When these bubbles implode near a solid boundary (the small arms component), they generate high-energy micro-jets and localised shockwaves. This energy dislodges carbon residues, sticky oils and lubricants from high-precision geometries, such as internal bores, blind holes and threads, which are inaccessible to mechanical scrubbing or simple chemical immersion.\u003c/p\u003e \u003cp\u003eFor ultrasonic cleaning, sample coupons were immersed in a mild alkali based bath and subjected to high-frequency sound waves (~\u0026thinsp;40 kHz) for a time period of 10 minutes. The cavitation cleaning achieves effective oil and grease removal from old and used components of small arms.\u003c/p\u003e \u003cp\u003eGlass bead blasting is a mechanical surface conditioning method using spherical soda-lime glass particles. Unlike angular abrasives (such as aluminium oxide or blasting sand), spherical beads do not remove base metal via a cutting action. Instead, they operate on the principle of Hertzian contact theory, where the spherical impact induces a controlled peening effect. This creates a uniform, matte micro-roughness and introduces beneficial compressive residual stresses into the surface layer. This mechanical activation removes tenacious oxides and scale without altering dimensional tolerances or creating sharp stress concentrations, which are commonly associated with angular media.\u003c/p\u003e \u003cp\u003eThe transition from cleaning to phosphating is governed by the \u003cem\u003eGibbs free energy of nucleation\u003c/em\u003e [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Mechanical roughening via glass bead blasting increases the surface energy and the density of active sites. This reduces the critical radius required for crystal formation. Consequently, the phosphate crystals form more rapidly and closer together, resulting in a fine-grained, dense morphology.\u003c/p\u003e \u003cp\u003eAs per the legacy methodology for surface preparation, the coupon sample was pre-treated through a multi-chemical bath process starting with a dip in Trichloroethylene, which is a potent solvent for removing petroleum based preservatives which are applied on the small arms components during deep preservation in depots. It is followed by a dip in hot Alkali bath containing 2% Soda Ash, 1% Sodium Phosphate Tribasic and 0.5% Soda Caustic dissolved in water and maintained at 90-95\u003csup\u003eO\u003c/sup\u003eC for 10 minutes to emulsify remaining organic soils. Thereafter pickling in 10% Hydrochloric Acid bath is carried out to remove mill scale and rust. Multiple hot and cold water rinsing is done between each chemical dip to prevent cross-contamination of the chemical baths.\u003c/p\u003e \u003cp\u003eManganese Phosphating is a popular crystalline conversion coating that involves a chemical reaction between the ferrous substrate and a heated phosphoric acid solution containing manganese and phosphate ions. The reaction proceeds via an initial acid attack on the base steel, which raises the local pH at the metal-liquid interface. This pH shift triggers the precipitation of insoluble manganese phosphate crystals on the steel surface. Unlike electroplating, the Manganese Phosphate layer is an integral part of the substrate's surface, giving superior mechanical anchoring and oil-retention properties through its inherent micro-porous structure.\u003c/p\u003e \u003cp\u003eBoth coupon samples were then processed in a standard four bath Manganese Phosphating procedure involving surface activation, phosphating, rinsing and passivation, with the most crucial step being the phosphating bath which was maintained at 90\u0026ndash;95\u0026deg;C for a duration of 30 minutes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"TESTING \u0026 RESULTS","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eCoating Thickness Analysis\u003c/h2\u003e \u003cp\u003eThe thickness of the phosphate coating is a primary indicator of its potential for oil retention and corrosion protection. Coating thickness measurement was carried out as per ASTM B-487-20 [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] using an optical microscope by a NABL accredited laboratory. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Sample-A demonstrated a higher deposition in comparison with Sample-B.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparative Phosphate Coating Thickness of Samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReadings\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSample A\u003c/p\u003e \u003cp\u003eCoating Thickness (\u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSample B\u003c/p\u003e \u003cp\u003eCoating Thickness (\u0026micro;m)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReading 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReading 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReading 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReading 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.46\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReading 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAverage\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e2.60\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e2.22\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe higher coating thickness in Sample-A (greater by 14.6%) over that of Sample-B suggests that glass bead blasting creates a higher surface-to-volume ratio, allowing for a more robust chemical reaction during the phosphating phase and better deposition on the surface.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eCrystalline Morphology (SEM)\u003c/h2\u003e \u003cp\u003eThe protective quality of a phosphate coating is highly dependent on the grain size of the deposition. Coarse, large crystals often leave micro-gaps that allow moisture to reach the substrate and initiate corrosion.\u003c/p\u003e \u003cp\u003eSEM imaging of Sample-B pre-treated with legacy multi-bath chemical process revealed a coarse, irregular crystal morphology when observed at 500x, 1000x, 3000x and 5000x under a Scanning Electron Microscope Phenom XL G2 (Thermo Fischer Scientific India Pvt Ltd) as per ASM Handbook Vol 9 [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The structure showed prominent inter-crystalline gaps and high porosity, which serve as pathways for corrosive electrolytes. It is evident from the experimental results that the legacy chemical preparation, while effective at cleaning, does not provide the specific surface energy required for high-density nucleation.\u003c/p\u003e \u003cp\u003eThe morphology as observed for Sample-A was characterised by a fine, dense and compact crystalline structure at 500x, 1000x, 3000x and 5000x under the same SEM. The crystals are tightly interlocked with minimal porosity, creating a superior physical barrier and increasing the corrosion protection of the substrate. The abrasive mechanical impact of the glass beads likely created numerous high-energy active centres on the metal surface, which acted as nucleation sites for the phosphate crystal deposition.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eCorrosion Resistance (Salt Spray Test)\u003c/h3\u003e\n\u003cp\u003eThe samples were further tested for corrosion resistance in a salt spray chamber as per ASTM B 117\u0026thinsp;\u0026minus;\u0026thinsp;19 [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] using a 5% NaCl with a specific gravity of 1.032 maintained at 35\u003csup\u003eo\u003c/sup\u003eC. Both the samples were exposed for 72 hours and observations were recorded at every 24 hour interval. The results were categorized by the appearance of red rust on the phosphated side of the samples [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRed rust started appearing on both the samples after an exposure to the salt spray after 24 hours, however there was significant visible difference in the appearance of the rust on both the samples. After 24 hours, Sample-A was largely unaffected, while rust was showing on a considerable portion of Sample-B, while after an exposure of 48 hours, rusting of Sample-B seemed to rapidly increase whereas there was comparatively minor increase in the rust observed in Sample-A. At the end of 72 hour exposure, the surface of Sample-B was largely rusted, while rust on surface of Sample-A was significantly lower.\u003c/p\u003e \u003cp\u003eIt can be derived from the observations that the refined crystalline structure of the coating on Sample-A acts as a more effective physical barrier, significantly slowing the rate of electrolyte penetration to the base metal, hence retarding the rate of corrosion.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study confirms that the integration of ultrasonic cleaning and glass bead blasting represents a significant advancement in surface preparation of SAE 4140 steel components for Manganese Phosphating.\u003c/p\u003e \u003cp\u003eThe proposed surface preparation protocol produced a thicker and more compact phosphate layer than that produced with surface preparation using traditional chemical methods. Fine-grained crystalline morphology in the sample treated with the proposed protocol directly correlates to increased corrosion resistance in accelerated salt spray environments.\u003c/p\u003e \u003cp\u003eThe transition from coarse grains to a dense morphology for phosphate layer is fundamentally a kinetic phenomenon. By replacing chemical etching with glass bead blasting, we increase the surface energy of the substrate. In the initial seconds of the phosphating reaction, this higher surface energy lowers the energy barrier for nucleation, allowing crystals to form simultaneously across the entire surface. Because the nucleation density is high, the growing crystals impinge upon one another early, preventing the growth of large, irregular grains and resulting in the observed fine-grained, compact structure.\u003c/p\u003e \u003cp\u003eFurther, shifting away from hazardous chemicals like Trichloroethylene and HCl reduces the environmental footprint of small arms overhaul processes and improves operator safety.\u003c/p\u003e \u003cp\u003eIn conclusion, the combination of ultrasonic cavitation cleaning and glass bead blasting is a viable and superior alternative to the multi-bath chemical preparation, offering enhanced component longevity and modernised workflow for re-phosphating of SAE 4140 steel components during overhaul operations of small arms.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDepartment of Defense (n.d.). \u003cem\u003eMIL-DTL-16232G: Detail Specification: Phosphate Coating, Heavy, Manganese or Zinc Base\u003c/em\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eASM International (1994) \u003cem\u003eASM Handbook, Volume 5: Surface Engineering\u003c/em\u003e. Materials Park, OH\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDuszczyk J, Siuzdak K, Klimczuk T, Strychalska-Nowak J, Zaleska-Medynska A (2018) Manganese Phosphatizing Coatings: The Effects of Preparation Conditions on Surface Properties. Materials 11(12):2585. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/ma11122585\u003c/span\u003e\u003cspan address=\"10.3390/ma11122585\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKlein M, Eifler D (2010) Influences of the manufacturing processes on the surface integrity and the resulting fatigue behavior of quenched and tempered SAE 4140. Procedia Eng 2(1):2239\u0026ndash;2247. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.proeng.2010.03.240\u003c/span\u003e\u003cspan address=\"10.1016/j.proeng.2010.03.240\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAkhtar MN, Lohchab A, Singh D, Kumar RR, Gaur P, Yadav BK (2023) Experimental studies on the effect of chromium plating on the mechanical properties of SAE 4140 steel. \u003cem\u003eMaterials Today: Proceedings, 72\u003c/em\u003e(4), 2488\u0026ndash;2496. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matpr.2022.09.527\u003c/span\u003e\u003cspan address=\"10.1016/j.matpr.2022.09.527\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMiddelburg JJ (2024) The Gibbs Free Energy. In: \u003cem\u003eThermodynamics and Equilibria in Earth System Sciences: An Introduction\u003c/em\u003e (SpringerBriefs in Earth System Sciences). Springer, Cham. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/978-3-031-53407-2_4\u003c/span\u003e\u003cspan address=\"10.1007/978-3-031-53407-2_4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eASTM International (2024) \u003cem\u003eASTM B 487\u0026thinsp;\u0026ndash;\u0026thinsp;20: Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section\u003c/em\u003e. West Conshohocken, PA\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eASM International (2004) \u003cem\u003eASM Handbook, Volume 9: Metallography and Microstructures\u003c/em\u003e. Materials Park, OH\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eASTM International (2019) ASTM B117-19: Standard Practice for Operating Salt Spray (Fog) Apparatus. West Conshohocken, PA\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eASM International (2003) \u003cem\u003eASM Handbook, Volume 13A: Corrosion: Fundamentals, Testing, and Protection\u003c/em\u003e. Materials Park, OH\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBaboian R (2022) NACE Corrosion Engineer's Reference Guide, 4th edn. NACE International\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Manganese Phosphating, Ultrasonic Cleaning, Glass Bead Blasting, Surface Preparation, Corrosion Resistance, Defence Metallurgy","lastPublishedDoi":"10.21203/rs.3.rs-9649913/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9649913/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe corrosion resistance of small arms components depend largely upon the integrity of their surface treatments. Traditional overhaul protocols for ferrous components of small arms typically involve a multi-bath chemical pre-treatment process followed by Manganese Phosphating, which presents significant challenges regarding coating consistency as well as operator and environmental safety at field level. This research investigates the efficacy of replacing hazardous chemical pre-treatments such as Trichloroethylene, Caustic Soda and Hydrochloric Acid with a combined protocol of ultrasonic cleaning and glass bead blasting. Experimental results on SAE 4140 steel coupons indicate that the proposed mechanical-ultrasonic approach yields a superior coating thickness of 2.60 \u0026micro;m compared to the 2.22 \u0026micro;m achieved by legacy chemical methods for the same Manganese Phosphating process. Scanning Electron Microscope analysis reveals a significantly denser, fine-grained crystalline morphology in the sample with the proposed pre-treatment protocol, which also translates to enhanced performance in accelerated salt spray testing over 72 hours. This study validates a safer, more efficient metallurgical standard for re-phosphating of small arms components during overhaul operations.\u003c/p\u003e","manuscriptTitle":"Evaluation of Ultrasonic Cleaning and Glass Bead Blasting as Surface Preparation Techniques for Manganese Phosphating of SAE 4140 Low Alloy Steel for Small Arms Components","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-11 05:17:06","doi":"10.21203/rs.3.rs-9649913/v1","editorialEvents":[{"type":"communityComments","content":5}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0331976c-ce98-4304-99b0-1ff35eb26dbb","owner":[],"postedDate":"May 11th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":67761569,"name":"Mechanical Engineering"}],"tags":[],"updatedAt":"2026-05-11T05:17:06+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-11 05:17:06","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9649913","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9649913","identity":"rs-9649913","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}