Microstructure And Properties Of Solid Solution Cocrmo Alloy After High Pressure Torsion And High Pressure Heat Treatment

In this paper,the solution treatment of Co-28Cr-6Mo alloy and the microstructure and properties of solid solution Co-28Cr-6Mo alloy after high pressure torsion?HPT?and high pressure heat treatment are investigated.The precipitated in the studied Co-28Cr-6Mo alloy was carbides precipitated,and the complete solid solution time was60 min at a temperature of 1250°C.The solution treatment can promote the martensitic transformation and increase the hardness value.After high pressure torsion,the austenite phase in solution treated Co-28Cr-6Mo alloy transformed into martensite under the shear stress.This can be owing to the increasing torsional angle and equivalent strain?_eq.The greater the degree of deformation,the finer the grain size of the Co-28Cr-6Mo alloy,and the higher the hardness value and yield strength.Austenite recrystallization and phase transformation occurred after high-pressure heat treatment.When?_eq?2.25,the larger the value of?_eq,the finer the grain size,the higher the degree of austenite recrystallization and relative content of austenite.When?_eq>2.25,due to the pinning action of the precipitated phase at the grain boundary,the degree of recrystallization of the austenite phase is very low,and the cooled martensite grains retain a certain degree of deformation orientation.The hardness and yield strength of the Co-28Cr-6Mo alloy after high pressure heat treatment decreased when compared with the samples after HPT,but the tensile ductility was improved.The HPT Co-28Cr-6Mo alloy get best properties after high pressure heat treatment at 5GPa and 1000°C.Compared with the solid solution Co-28Cr-6Mo alloy,after high pressure heat treatment,the Co-28Cr-6Mo alloy with equivalent strain?_eq=2.25 has a hardness value increment from 340 to 400 and a yield strength increment from 480 MPa to 746 MPa.