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The Effect of Microelement and Heat Treatment on Shape MemoryEffect and Mechanical Properties of Copper-based Shape Memory Alloys

Author: ShenANi
Tutor: LiNing
School: Sichuan University
Course: Materials Processing Engineering
Keywords: Shape memory alloy Shape memory effect Thermoelastical martensite Betatizing treatment Aging Mechanical properties
CLC: TG139.6
Type: Master's thesis
Year: 2002
Downloads: 163
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Abstract


The crucial parameters Sbr engineering application of copper-based shape memory alloys (SMA) are the stability of their shape memory effect(SME) and mechanical properties. This paper emplcnyed a certain microelement Zr to explore how to enhance their mechanical properties, namely failer strength and extensibility besides how to stablize their shape memory effect. Such indexes as phase transformation temperatures, shape recovery rate, tensile strength and ductility of the alloys were measured.The experimental results indicated that with higher betatizing temperatures and longer betatizing duration, phase transformation temperatures of the alloys became higher.It was found through comparation that after being betatized at different temperatures for 15min and- up quenched, then deformed at room temperature, 2-3 alloy had the best SME at 72 0C, while shape recovery of 2-1 alloy was mainly due to super elastic recovery.Experimental results also showed that after betatized at 850C for different duration, 2-1 alloy, compared with 2-3 and l-7,had the best SME when being deformed at -20C and the best PME(psuedoelasticity) when being deformed at 24 C. 1 -7 alloy had better SME tham 2-3 alloy, which was heat treated in the same way as that of 1-7. This can be explained by the difference between their phase transformationtemperatures and deforming temperatures, the growth behaviors of their grains and the structure changes of their martensites.2-1 alloy existed in a complete shape recovery temperature when being deformed at -20, therefore showed the best SME. While it existed in super elastic recovery temperature when being deformed at 24, therefore showed the best PME.1-7 alloy lied both in shape recovery temperatures when being deformed and showed a stable SME. With the increase of betatizing duration, ordered martensite plates, which were uniformly oriented,appeared followed by striped and spear-like martensites, all these thermo elastic martensites ensured its SME. The microelement Zr made its SME behavior more complicated. The alloy obviously had the best duration span. When being deformed at -20C, the best betatizing duration span is 20min, while at room temperature 24C, 40min instead. This could be explained through its complicated phases and structure change of martensites, etc.Aging also had some influence on SME of alloys. After being betatized at 850癈 for 5 minutes and up-quenched, SME of 1 -7 alloy was measured after being aged at parental phase. The result showed that with the increase of aging duration, ductility of the alloy came to the highest at first and lowered down afterward. When aged at room temperature for a certain time, SME of the alloy degraded furtherly.Alloy 2-3 with Zr had higher tensile strength and ductility than 2-1 free of Zr under the same thermo treatment, and 2-3 was considerably sensitive to betatizing temperatures. With the highering of betatizing temperature, the tensile strength and ductility of the alloy both decreased. After repeated extention, strength of the alloy increased with the increase of deformation cycles, so did super elastic recovery. Some residual strain kept.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Other special nature of the alloy > Shape Memory Alloys
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