熱循環及時效對鈦鎳基形狀記憶合金麻田散體變態影響之研究

Abstract

本文研究經固溶處理的Ti50Ni50、Ti40.5Ni49.5Hf10及Ti50Ni50-xYx (Y= Fe、Pd、Cu) SMAs，以及固溶再經時效處理的極富鎳SMAs，經50次熱循環後探討在不同的麻田散體變態下其變態溫度所受的影響，發現變態剪應變s值越大，在熱循環時變態溫度被壓抑的也越大，同時Ti3Ni4的析出可有效阻止此種壓抑，但Ti2Ni3者則不能。本文同時研究極富鎳Ti47.8Ni52.2 (A合金)及Ti47.6Ni52.4 (B合金)在固溶處理後於300~600°C時效之相變態行為，發現A、B兩合金的相變態行為很相近，但B合金的Ni含量較高，而有較寬的變態峰，較低的ΔH值及較高的變態溫度遲滯。同時其變態行為可依時效溫度及時間分成三個階段，Period I時僅有Ti3Ni4析出，在Period II為Ti2Ni3析出並在其附近有Ti3Ni4空乏區，Period III時Ti3Ni4完全消失只剩Ti2Ni3析出。在300~500°C時效時，A/B合金都處於Period I，並為B2↔R或B2↔R↔B19’相變態，但在500°C 250hr以上進入Period II。在550°C時效25~1000hr時為在Period II的B21↔R1↔B19’1(與Ti3Ni4相關) + B22↔R2↔B19’2(與Ti2Ni3相關)四階相變態；在600°C的短時間時效為Period I的B21↔B19’1，中期時間時效為Period II的B21↔B19’1 + B22↔R2↔B19’2三階相變態，在長時間時效後為Period III的B22↔R2↔B19’2相變態。

Transformation temperatures of solid-solution(SS) treated Ti50Ni50, Ti40.5Ni49.5Hf10, Ti50Ni50-xYx (Y= Fe、Pd、Cu) SMAs and aged Ni-rich TiNi SMAs are characterized by 50 times thermal cycles. Experimental results indicate that the martensitic transformation exhibited higher shear strain value causes larger depression on transformation temperature during thermal cycling. In aged Ni-rich TiNi SMAs, Ti3Ni4 precipitates(ppts) can inhibit the depression of transformation temperature, while Ti2Ni3 ppts can’t. The transformation characteristics of aged Ni-rich Ti47.8Ni52.2 (A alloy) and Ti47.6Ni52.4 (B alloy) SMAs are also investigated. Both alloys are SS and then aged at 300 ºC to 600°C and exhibit similar phase transformation behavior. With higher Ni content, B alloy has broader transformation peak, lower ΔH value and higher thermal hysteresis. Periods I~III are observed when both alloys are aged at different temperature and time. In period I, only Ti3Ni4 ppts distribute homogeneously in the alloy. In period II, the Ti2Ni3 ppts form and the Ti3Ni4 depletion zone appear around Ti2Ni3 plates. In period III, more Ti2Ni3 ppts form and grow and Ti3Ni4 ppts dissolve entirely. During aging from 300 ºC to 500°C, A/B alloys are almost in period I and behave a B2↔R or B2↔R↔B19’ transformation. When aging at 500°C for more than 250hrs, A/B alloys are in period II. When aging at 550°C for 25~1000hrs, A/B alloys are in period II and a four-stage transformation B21↔R1↔B19’1 (related to Ti3Ni4 ppts) + B22↔R2↔B19’2 (related to Ti2Ni3 ppts) occurs. When aging at 600°C for the early aging time, A/B alloys are in period I, a single-stage transformation B21↔B19’1 occurs. For the middle aging time, A/B alloys are in period II, a three-stage transformation (B21↔B19’1) + (B22↔R2↔B19’2) occurs. For the longer aging time, A/B alloys are in period III, and a two-stage transformation B22↔R2↔B19’2 appears.