Study on Multi Stage Forging Process with Combination of Different Strain Rate and Temperature Regime in IMI 685 Forging

Abstract IMI 685, a near alpha Ti alloy has been used as high pressure compressor discs for aero engine application due to its high strength to weight ratio and high creep resistance. Compressor disc is a very critical component in an aero engine and manufacturing process plays an important role in obtaining the required mechanical properties. Generally due to a highly complex and critical product, its manufacturing process is not available in open literatures. Currently, isothermal forging is used and which is time consuming and not cost effective. Hence, in this paper non-isothermal approach of manufacturing compressor disc using a combination of hydraulic press and pneumatic hammer have been explored as an alternate. Simulation studies have been carried out using DEFORM 3D FEM software for the prediction of temperature distribution, strain and strain rate experienced during forging. Forging has been carried out in two stages, hydraulic press used for upsetting and hammer used for die forging in partial α-b / b temperature range and beta solutionised followed by aging. Extensive mechanical testing such as room temperature tensile test, hot tensile test, notch tensile test, creep, post creep tensile test and micro structural characterization has been performed. From the mechanical and metallurgical analysis it was found that processing in partial α-b / b temperature range resulted in higher creep strain rate with acicular / needle alpha platelets with a basket weave structure. This experiment has proven with a proper selection of thermo mechanical process parameter, required creep properties can be met with the non-isothermal processing route.