單晶CuAl17Mn10Ni1.5和單晶CuAl17Mn11Cr0.65形狀記憶合金之擬彈性和彈熱效應研究

Abstract

本研究以循環熱處理製成晶粒方位分別接近[ 0 0 1 ]、[ 1 0 1 ]和[ 1 1 1 ]之CuAl17Mn10Ni1.5單晶與CuAl17Mn11Cr0.65單晶六種形狀記憶合金塊材，研究晶粒方位對擬彈性和彈熱效應之影響，並以接近[ 0 0 1 ]、[ 1 0 1 ]和[ 1 1 1 ]之CuAl17Mn10Ni1.5單晶在不同操作溫度下之彈熱效應。實驗結果顯示，在晶粒方位相似的狀態下，CuAl17Mn10Ni1.5單晶之臨界應力較CuAl17Mn11Cr0.65單晶大，透過Clausius-Clapeyron方程式可以得知，當晶粒方位相似時，操作溫度和Ms溫度之差與相變態臨界應力的大小有明顯影響。相變態臨界應力和擬彈性應變對晶粒方位具有很高的依賴性，晶粒方位接近[ 0 0 1 ]的臨界應力最小，擬彈性應變最大，而晶粒方位接近[ 1 1 1 ]的臨界應力最大，擬彈性應變最小。[ 0 0 1 ]和[ 1 0 1 ]試片的卸載溫度場分布較[ 1 1 1 ]試片均勻，且卸載溫度場分布的變化與DIC之卸載應變分布變化基本相同，可以觀察到[ 1 1 1 ]試片之卸載降溫溫差集中於逆變態之區域，[ 1 1 1 ]試片測得之降溫溫差較低，因此除了晶粒方位、施加應變大小，試片相變態分布是否均勻也是影響卸載降溫溫差的重要因素。晶粒方位接近[ 0 0 1 ]的試片和接近[ 1 0 1 ]試片的卸載降溫溫差相近，且接近[ 1 0 1 ]試片的耗散能較小，因此效能係數(COP)最高，最適合應用於固態冷媒，晶粒方位接近[ 0 0 1 ]則因耗散能為三個方向中最大的，適合用於製作阻尼器。CuAl17Mn10Ni1.5單晶在-40°C~應力誘發麻田散體和應力誘發差排滑移之臨界溫度的操作區間中，[ 0 0 1 ]和[ 1 0 1 ]試片具有較大的溫差和穩定的COP，因而彈熱效應表現較好；[ 1 0 1 ]可能較不易抵抗塑性變形導致在循環使用中容易產生功能劣化；[ 1 1 1 ]試片除了相變態不均勻的原因導致卸載降溫溫差較低外，可能還受到塑性變形影響而使COP性能表現並不穩定。

In this study, cyclic heat treatment was used to prepare CuAl17Mn10Ni1.5 and CuAl17Mn11Cr0.65 bulk single-crystal shape memory alloy with grain orientation close to [001], [101], and [111] respectively. The influence of grain orientation on psuedoelasticity and elastocaloric effect of CuAl17Mn10Ni1.5 single-crystal with orientations close to [001], [101] and [111] under different operating temperatures were also investigaed. The results show that the critical stress to induce martensitic transformation of CuAl17Mn10Ni1.5 single-crystal is larger than that of the CuAl17Mn11Cr0.65 one. When the grain orientations are similar, the different between the operating temperature and Ms temperature has a significant effect on the critical stress, as predicted by Clausius-Clapeyron equation. The critical stress and psuedoelasticity are highly dependent on grain orientation. The critical stress is smallest and the psuedoelastic strain is largest when the grian orientation is closes to [001]. On the other hand, the critical stress is largest and the psuedoelastic strain is smallest when the grian orientation is closes to [111]. For the elastocaloric effect, the distributions of temperature after unloading of [001] and [101] specimens are more uniform than that of the [111] one. It is noted that, the unloading temperature drop of [111] specimen is concentrated in the area where the reverse martensitic transformation occurred, and the measured value of unloading temperature drop of [111] specimen is lower than the calculated value. Therefore, the factors affecting the unloading temperature drop are not only the grain orientation and the magnitude of the applied strain, but also the uniformity of the phase transformation distribution. The unloading temperature drop of specimens with grain orientation close to [001] and [101] are similar. At the same time, the dissipation energy of [101] specimen is the lowest, so the coefficient of efficiency (COP) of the [101] orientated one is the highest, and is considered suitable for use in solid refrigerant. The dissipation energy of [001] specimen is the largest, so it’s considered suitable for dampering applications. In the operating range of CuAl17Mn10Ni1.5 single-crystal form -40°C to the critical temperature of stress-induced dislocaltion slip, the elastocaloric effect of specimens with grain orientation close to [001] and [101] are better than that of the [111] one because they have larger temperature drops and stable COPs. However, the [101] specimen may be less resistant to plastic deformation, which may cause functional degradation during cycling compression test. Similarly, plastic deformation is easily introduced into the [111] specimen due to its higher stress for trigging martensitic transformation.Additionally, the [111] sample shows unstable COP at differet operating temperature and uneven phase transformation behavior.