Study On Microstructures And Properties Of Cobalt Alloy After High Pressure Heat Treatment And Hot Compression Deformation

In this thesis,The microstructure and properties of cobalt alloy?Co-28Cr-6Mo?were investigated,which treated by atmospheric heat treatment,high pressure heat treatment and thermal compression deformation.Microstructure performances of cobalt alloy?Co-28Cr-6Mo?were finished by optical microscope,X-ray diffraction and electron backscatter diffraction analyzer.Microhardness tester and universal tensile testing machine were used to test the mechanical properties.The experimental results show that,the properties could be obtained which the yield strength is 311-465Mpa,tensile strength is 797-1078Mpa and elongation is 14.3-17.30%after atmospheric heat treatment at 1050?and 10-60min.The effect of holding time on the austenite volume fraction and microhardness was not significant.Grain size of cobalt alloy can be refined after high pressure heat treatment at 3-5Gpa and 1050?.The phase compositions are?-austenite and?-martensite,but relative amounts are related to the heat treatment conditions.Controlling pressure and holding time can improve the strength of the cobalt alloy,but the ductility change is not obvious.The tensile property of yield strength608MPa,tensile strength 1287MPa and elongation 37.88%were obtained by high pressure heat treatment which under the condition of 5Gpa,1050?and 10min.After the hot compression deformation at the temperature of 1100?and the strain rate of 10^-1s^-1,the yield strength and tensile strength gradually increased with the reduction from22%to 70%.The elongation also showed an increasing trend.The microhardness value first decreased and then increased.When the compression deformation is 70%,the tensile properties of yield strength 608MPa,tensile strength 1287MPa and elongation 37.88%could be obtained.The phase compositions of cobalt alloy are still?-austenitic and?-martensite after hot compression deformation at 1000-1200?,strain rate 10^-3s^-1 and 70%reduction.With the increase of deformation temperature,the grain size increased;the austenitic content gradually decreased;the microhardness,yield strength and tensile strength all showed a decreasing trend and the elongation first increased and then decreased.It is the best ductility,elongation is 40.35%,which cobalt alloy had got at the hot compression deformation temperature 1050?.