Abstract
Co-Cr-Mo alloys are widely used for biomedical implant materials such as artificial hip and knee joints owing to their excellent corrosion and wear resistance as well as higher strengthening properties. However, the alloys exhibits sever brittle nature under an as-cast condition. It is generally recognized that refinement of the grain size of the metallic materials by means of hot-forging processes is an effective methodology to strengthen the alloy. Dynamic recrystallization (DRX) is an effective metallurgical process for grain refinement during hot deformation. However, there are few studies on the hot deformation behavior of Co-Cr-Mo alloy, especially grain refinement through DRX. In the present study, DRX and grain refinement during hot deformation of Co-29Cr-6Mo alloy has been investigated under various conditions such as deformation temperature and strain rate.
Although at strain of 5% hot deformed microstructure maintains the original grains, the grain size decreases with increasing the strain and exhibits the average grain size of approximately 2μm at strain of 60%. Ultra fine grained microstructure with the grain size of approximately 0.5 μm was obtained under deformation at a 1323 K at a strain rate of 0.1s-1. The original grains are broken up into different grains due to the new boundary formation not only near the initial boundaries but also in the interior of the grains at large strain. This grain fragmentation without bulging in the course of hot deformation is associated with considerably low stacking fault energy (SFE) of the Co-29Cr-6Mo alloy even at the deformation temperatures.
