Research On The Erosive Properties Of NiTi Shape Memory Alloy

Some components of water turbine fall under serious erosion because of big mass percents of sand in the river of our nation. Using NiTi weld coating to protect the components is a viable way to solve the problem. 4 NiTi alloys with different heat treatment program and NiTi coating's erosive properties were investigated comparing with 1Cr18Ni9Ti stainless steel in the similar environments of water turbine.NiTi alloys and coating's erosive properties were tested using a slurry pot that is self-made. Four NiTi alloys and 1Cr18Ni9Ti stainless steel's erosive volume loss increase with erosive time erosive velocity mass ratio of sand to water and sand size. It is found that heat treatment cannot influence the erosive properties of NiTi alloys too much, 500℃ mid-temperature heat treatment sample have better erosive properties in comparing and all the NiTi alloys are better than 1Cr18Ni9Ti stainless steel obviously.Five samples micro-hardness were tested with the MH-6 tester, then the morphologies of indentation and erosive surface were observed by Xl-30 SEM. The indentation shape of NiTi alloys like a star, while the lCrl8Ni9Ti stainless steel is square, which show that the NiTi alloys have better recover abilities. The surface morphologies exhibit deformation wear in the middle and micro cutting wear in the sides, which indicate that all the samples exhibit ductile material characteristics in the erosion.The mechanical properties of NiTi alloys and lCr18Ni9Ti stainless steel were tested changing with the loading speed step-load and mechanical cycling. The experiment results show that the superelasticity of NiTi-1 can reach 10% and the superplasticity of NiTi-2 NiTi-3 and NiTi-4 is good enough to 60-80%. The liner superelasticity of NiTi-2 NiTi-3 and NiTi-4 can reach 4. 5%, 5.5% 3.5% after cycling. It is found that NiTi-3's erosive property is better than NiTi-1, the conclusion can be drawn that not only the pseudoelastic NiTi have the smart tribological characteristics but also the pseudoplastic NiTi with heat treatment.All the stress-induced martensitic transformation and Superelasticity of NiTi parent phase, variants accommodation and Superplasticity of NiTi martensite, fatigue resistance, work hardening of NiTi alloys make important contributions to the slurry erosion resistance of NiTi alloys.NiTi coating has good erosive properties, the erosive volume loss of which is only third of lCrl8Ni9Ti coating.