Abstract

Laser Powder Bed Fusion (L-PBF) processes are becoming more viable in place of traditional castings in a variety of industries. To compete, novel material grades are being considered with additive manufacturing (AM). In maximizing performance and manufacturing efficiency through AM, a novel approach to heat treatment and Hot Isostatic Pressing (HIP) processing needs to be considered. It has been shown that combining key heat treatment processes with (HIP) by utilizing fast cooling rates can benefit static properties as well as improve turn-around time for HIP processing [1,2]. Argon pressures up to 207 MPa with cooling rates above 170°C per minute are now available in production sized HIP systems to design ideal HIP cycles for high pressure heat treatment. Additive manufacturing with high pressure heat treatment is in need of further investigation for establishing new qualification standards. This study investigates designed High-Pressure Heat Treatment cycles to consider mechanical performance on LPBF CoCr. The combined cycles investigate possible alternatives to historically accepted two step HIP then heat treat processing by combining densification with homogenization treatment into one step. Tensile, fatigue, hardness, microstructure and Charpy impact performance are explored to seek optimal properties and with streamlined thermal processing. It was found that all trial conditions exceeded Electron Beam Melted (EBM) AM CoCr expectation, but traditional processing provided a slight advantage in ultimate tensile stress. One of the novel processes explored, “common” was found to provide a slight improvement on yield stress and direct hardness. Published fatigue data is rare for CoCr, however data generated from this study showed a slight advantage to the “common” HPHT process primarily for lower applied stress levels. Microstructures were comparable across all trial processes. It is recommended that each novel processing route be considered as viable alternatives to traditional processing, but that the “common” processing may prove advantageous for both mechanical properties and streamlined manufacturing.

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