2, Global Research & Innovation Technology Center GRIT, Hitachi Metals Ltd., Kumagaya, Saitama, Japan
A CoCrFeNiTiMo-based high entropy alloy (HEA) powder was used to successfully print near-net-shape hardware and test-blocks for examination of selective laser melting (SLM) materials properties. Additive manufacturing (AM) has enabled the manufacture of this difficult-to-process material. By simultaneously exploiting the fast cooling rate of the AM process with the uniformity of compositionally controlled powder, it is possible to reduce the chemical segregation seen in cast-wrought alloys. An anticipated benefit of reduced chemical segregation is improved corrosion resistance.
All specimens received a post-processing heat treatment which precipitated the strengthening phase gamma prime (γ’) and the intermetallic phases eta (η acicular morphology and sigma (σ globular morphology). The resultant microstructures and mechanical properties were evaluated as a function of build orientation. Results so far suggest the build orientation and location on the build plate have little effect on properties and microstructure.
A bimodal grain size distribution exists in the non-HIP and heat-treated condition (C1). Mechanical properties for C1 at room temperature (20C) yield the following: impact energy measured by instrumented Charpy testing is 39.7-40.9 J, yield strength is 890-892 MPa, and the UTS is 1420 – 1459 MPa. A KQ was measured using J-R fracture toughness testing with no build orientation effects observed. Additional work is ongoing to evaluate the aqueous corrosion resistance of the SLM specimens compared to industry standard cast and wrought alloys.