论文标题:镍钛形状记忆合金冲蚀性能的研究
Research on the Erosive Properties of NiTi Shape Memory Alloy
论文作者
论文导师 徐久军；孙玉清,论文学位 硕士,论文专业 轮机工程
论文单位 大连海事大学,点击次数 122,论文页数 76页File Size13433k
2006-02-01论文网 http://www.lw23.com/lunwen_982186147/
NiTi Alloy;Heat treatment;Slurry Erosion;Superelasticity and Superplasticity;Welding
我国大部分河流含沙量大,水轮机过流部件受到严重的冲蚀磨损。为解决水轮机过流部件冲蚀磨损问题,采用NiTi涂层是可行的方案之一。本文模拟水轮机过流部件工作环境,以水轮机过流部件常用材料1Cr18Ni9Ti为对比,重点研究了经不同条件热处理的NiTi合金丝及NiTi合金堆焊涂层的冲蚀磨损性能。 采用自制的浆罐式砂水冲蚀磨损试验装置研究NiTi合金丝及其涂层的冲蚀磨损性能。研究发现,4种经不同条件热处理的NiTi合金与1Cr18Ni9Ti的冲蚀磨损量随着冲蚀时间、冲蚀速度、砂水比及砂粒度的增大而增大。热处理对NiTi合金的冲蚀磨损性能影响不大,4种NiTi合金的冲蚀磨损性能相近,相比较而言,500℃中温热处理试样表现出较好的冲蚀磨损性能,4种NiTi合金的冲蚀性能均明显优于1Cr18Ni9Ti的冲蚀性能。 采用MH-6型显微硬度计测量5种试样显微硬度,采用XL-30型扫描电子显微镜观察压痕形貌及冲蚀磨损后试样的表面形貌。NiTi合金压痕呈星形,1Cr18Ni9Ti不锈钢压痕呈方形,表明NiTi合金具有很好的弹性恢复能力。合金丝试样中部为变形磨损,侧面为微切削磨损,表现为典型的韧性材料冲蚀磨损特性。 采用自制的拉伸试验装置测量了4种NiTi合金丝及1Cr18Ni9Ti合金丝的力学性能随加载速度、阶梯加载及机械循环的变化情况。试验结果表明,NiTi-1的超弹性可达10%左右,NiTi-2、NiTi-3及NiTi-4具有很好的塑性变形能力,最大变形量可达60～80%。经机械循环后,NiTi-2、NiTi-3及NiTi-4的线性超弹性分别为4.5%、5.5%、3.5%。NiTi-3的冲蚀性能优于NiTi-1,可见,不仅是超弹态的NiTi合金具有机敏的摩擦学特性,热处理后处于超塑性状态的NiTi合金同样具有优良的冲蚀性能和机敏摩擦学特性。 超弹性、超塑性、马氏体变体的自适应性及择优取向、耐疲劳性及加工硬化性能在不同的条件及受力阶段,均对提高NiTi合金的冲蚀性能起很大作用。 NiTi合金堆焊涂层具有很好的冲蚀磨损性能,其冲蚀磨损量仅为1Cr18Ni9Ti涂层的1/3左右。
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.
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