Effects of Nb, Si additions on the Cu-Al-Be Alloys' phase transformation anad high temperature SME
Date Issued
2005
Date
2005
Author(s)
Tsai, Yan-Min
DOI
zh-TW
Abstract
In this experiment, the Cu-11.55wt% Al-0.32wt% Be shape memory alloy was firstly melted at 1100℃ in a evacuated quartz capsule. After homogenization, the ingot was cut into three equal parts, and two of them were added small amount of Nb and Si by VAR. After hot rolled, the specimen were quenched into water from 850℃ and aged at 300℃.The characteristics of these specimens were investigated by DSC, tension test, thermal cycling test and shape memory recovery tests. The microstructure and crystal structure of aged specimens were analyzed by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD).The purpose of present study is to discuss the influence of Nb and Si addition on the shape memory recovery and phase transformation of Cu-11.55wt%Al-0.32wt%Be alloy.
The results show that the three alloys have stabilization phenomenon after solution treatments and they must be performed with the reordering treatment in order to obtain shape memory effect. However, Nb and Si additions will induce the residual phases formed in the matrix, it can restrain the growth of martensite and contribute to fine grains that improve mechanical and shape recovery properties. The superelastic test shows that the alloy with higher reverse transformation temperature (Af), the better it’s shape recovery ability at 250℃. Besides, the main precipitates of each alloy after aging are α1-plate and a few γ2(Cu9Al4). Moreover, the residual phases have growth and segregation phenomenons during aging, so it causes the gradual degredation of high temperature shape memory effect. TEM and X-Ray diffraction analysis show that martensite and α1-plate are M18R structure and γ2 is D83 structure. Finally, TEM results prove that the reduce of shape recovery ability is due to the present of dislocations after 100th thermal cycling.
Subjects
形狀回復率
形狀記憶效應
超彈性拉伸
shape memory recovery
shape memory effect
superelastic test
Type
thesis
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