Effect of particle size and shielding gas flow rate on composition of functionally graded materials fabricated by pre-mixed powder in laser directed energy deposition process

Abstract Functionally Gradient Material (FGM) is attaining more and more interests recently due to its outstanding feature of possessing benefits of physical and mechanical properties of two materials in one part. One of the common processes to fabricate FGM is laser directed energy deposition of pre-mixed powder of two materials. However, it is challenging to achieve accurate and consistent composition from blended powders having different characteristics. The focus of this study is experimentally investigating two parameters effecting FGM composition: powder size and axial shielding gas flow rate. The pre-mixed powders used was the combination of WC with SS316L and 309L. The deposited layers were cut in different locations along deposition direction. Composition in each section was surveyed by the aid of SEM photos and ImageJ software. The result of experiments showed that the desired and consistent composition of two materials, is reachable if the ratio of powder size of two materials is equal to reverse square root of their density ratio. Moreover, In LDED of FGM, increasing axial shielding gas flow rate causes the lighter particles fall out of meltpool and consequently the presence of lighter material in deposited layer would be less than expected.