Advance Materials - Process Optimization, Microstructure and Hardness of Additively Manufactured Co-Cr Aerospace Alloy

Abstract

In the current study, the effect of carefully designed Powder Bed Fusion (PBF) laser parameters on the microstructure and hardness of Co-Cr alloy straight, thin-wall additively manufactured test coupons that are asbuilt or have undergone Hot Isostatic Pressing (HIP) was investigated. For enhanced productivity, it is important to evaluate the relationship between energy density (ED) input (laser power, scan speed) and the microstructure developed in the Co-Cr alloy coupons for an aerospace application. Both the High ED and Low ED input processing laser parameters induce a higher percent (%) volume of defects in the as-built coupons when compared to the manufacturer recommended benchmark parameters. However, after HIP, the % volume fraction of defects reduces significantly, and the microstructure is homogenized. Furthermore, the strength of the test coupons manufactured using the manufacturer recommended laser parameters is comparable to those obtained in the low ED input test coupons after HIP; which invariably could be utilized to enhance productivity significantly. In addition, the surface roughness of the Low ED input parameter coupons after HIP is similar to the coupons produced using the manufacturer recommended laser parameters assessed with light optical magnification image evaluation. Hot Isostatic Pressing is therefore an excellent post-processing method to reduce internal defects for a given range of laser energy densities in metal additive manufacturing at increased build speeds.