Study On The Microstructure And Properties Of Co-Al Shape Memory Alloys

The fabricating process,microstructure,phase structure,magnetic properties, shape memory effect and mechanical properties of Co-Al alloys have been studied by means of optical microscope,XRD,DSC,PPMS and tensile test at room temperature.The influence of composition and aging temperature on the microstructure and properties of Co-Al alloys was revealed as a result.The investigation showed that the microstructure of annealed Co-Al alloys consisted of austenite and martensite phase at room temperature.The content of martensite phase increased with the increase of Al content.The investigation also showed that.the microstructure of aging Co-Al alloys consisted of austenite and martensite phase at room temperature.The content of martensite phase increased with the increase of aging temperature.The collected data were further used to calculate deformation stacking fault probability and growth stacking fault probability.The results showed that deformation stacking fault probability increased with the Al content and the ageing temperature.The FCC-HCP martensitic transformation and its reverse transformation occurred during heating and cooling respectively.The transformation temperature decreased with Al content.The mechanical test of annealed sample showed that the tensile strength increased with the increase of Al content at room temperature,where as the tensile strength of aged sample decreased with the increase of aging temperature.Shape memory effect measurement of Co-Al alloys showed that strain recovery ratio increased significantly with the increase of Al content and ageing temperature. The magnetic properties of Co-Al alloys showed soft magnetism feature.The saturation magnetization decreased with the increase of Al content indicated that the addition of Al weakened the ferromagnetism of Co-Al.Through the research work,we concluded that Co-Al alloy is a good shape memory alloy.Further study on composition and heat-treatment effect on shape memory properties is expected to exploit it to be an excellent high temperature shape memory alloy.