The surface hardening of Haynes ۲۵ super alloy using sever surface plastic deformation method

Co-Cr-W-Ni super alloy (Haynes ۲۵) was subjected to severe surface plastic deformation by friction sliding method and the microstructure and hardness of its surface were investigated. Friction hardening was performed by sliding a flat-head tungsten carbide pin with a diameter of ۱۵ mm under a load of ۶۰۰ N. The sliding was conducted at ۹۰, ۱۸۰ and ۳۶۰ mm/min for ۳۰ and ۶۰ passes. According to the results, the sliding friction in addition to surface work hardening promotes martensitic transformation (changing the crystal structure of the surface from FCC to HCP). However, it seems that due to the removal of the surface layers during the sliding process, the surface hardness of the alloy is increased mainly by the formation of martensitic phase. Under the optimum conditions (sliding speed of ۹۰ mm/min and ۳۰ passes), the formation of HCP martensite leads to ۱۰۰% increase in surface hardness (from about ۳۰۰ HV to more than ۶۰۰ HV). Increasing the sliding speed (from ۹۰ to ۳۶۰ mm/min) does not have appreciable effect on surface hardness.

Keywords:

Haynes ۲۵” , “Severe plastic deformation” , “Friction hardening” , “Martensite” , “Hardness”