20th International Forgemasters Meeting - IFM 2017

Recently, Co-Al-W alloys with a new γ’ phase consisting of Co₃(Al,W) have been found. Since the Co-Al-W-based alloys show the γ/γ’ microstructure similar to the Ni-based superalloys and flow stress anomaly, it is expected that the Co₃(Al,W) strengthening Co-based superalloys would be able to be applied to higher temperature applications. However, the hot workability is one of the main concerns that should be addressed. In this work, we optimized the chemical compositions to improve the hot workability without deteriorating the high-temperature strength at service temperatures. Finally, Co-Ni-Al-W-Cr alloys was determined for wrought materials. Developed alloy COWALOY(Co-47.5%Ni-3.7%Al-16%W-15%Cr-0.01%C(mass%)) achieved excellent high temperature strength and superior hot workability than Alloy520(Ni-14%Cr-12%Co-6%Mo-3%Ti-2%Al-1W-0.05%C(mass%)) which is known well as a forging Ni-based superalloy with high temperature strength. In the trial production of COWALOY, VIM-ESR process was applied to homogenize the compositions in the ingot. Subsequently, a radial forging machine (12MN) was used for forging to make a billet of 95 mm in square. Moreover, the forged billet was rolled into a wire rod of 5.5 mm in diameter and the rolled wire was wire drawn to fine wire to approximately 1mm in diameter successfully. As the result of trial, it was confirmed that the common manufacturing process for Ni-based alloys can be applied for COWALOY without additional special process. It is expected that COWALOY can be applied in a wide range of high temperature applications such as exhaust valves in automobile, heat resistant wires and plant parts.