- 學位論文
熱處理對TiNiHf塊材及TiNiCu薄帶形狀記憶合金變態行為之研究
Heat Treatment on Transformation Behavior of TiNiHf Bulk and TiNiCu Ribbon Shape Memory Alloys
摘要
在Ti50.5-XNi49.5HfX（X＝5,10）合金之研究中，發現兩合金皆為B2←→B19’一階相變態，且Hf含量多者其相變態溫度越高，其中，TiNiHf10合金之形狀回復率可高達90％以上。兩合金之相變態溫度在熱循環次數20次內均快速下降，但高於20次後，即不再有太大的變化；少數的熱循環次數會使合金由一階相變態轉變為二階，但隨次數增加，又由二階轉為一階，此變態行為之改變與熱循環後合金內雙晶模式由TypeⅡ<011>M雙晶轉變為（001）M Compound雙晶有關。在冷加工後退火處理對兩合金之影響上，發現在低溫或短時間下，退火對合金之影響為消除殘留應力及缺陷，並造成變態溫度的快速上升；當高溫或長時間退火後，退火對合金之影響轉為回復、再結晶及成長，使變態溫度不再上升。而時效處理對兩合金相變態行為之影響則較小，顯示合金中第二相相當穩定，不因時效而改變。在研究退火處理對富鈦之Ti50Ni40Cu10薄帶之影響上，發現冷卻銅輪的轉速越快，其變態溫度及潛熱越低。薄帶之微結構在快速冷卻端是不具方向性之細小晶粒，但在空冷自由端則是具方向性之柱狀晶。退火處理可使薄帶之缺陷與殘留應力消除並提升變態溫度與潛熱；但短時間之退火會有不均勻的Ti2Ni析出，造成變態點降低與變態峰分離。而700℃以上退火者除Ti2Ni外，尚有TiNi2Cu相之析出。
並列摘要
Thermal cycling effect on transformation behavior and microstructure of Ti40.5Ni49.5Hf10 shape memory alloy (SMAs) is investigated. Experimental results show that Ti40.5Ni49.5Hf10 SMA exhibits one-stage transformation of B2 ↔B19’ to two–stage one of B2←→B19’1 and B2←→B19’2 within 10 thermal cycles. Transformation temperature rapidly decreases during the early 20 cycles and then keeps almost constant for the further cycles. The evolution of transformation behavior and the decrease of transformation temperature can be ascribed to the dislocations induced by thermal cycling, which can suppress the transformation temperature and cause (001)M micro-twins to replace <011>M Type II twins in B19’ martensite. The formation mechanism of (001)M micro-twins associated with the thermal cycling is also proposed. Aging effect on transformation behavior of Ti50Ni40Cu10 ribbons is also investigated. Experimental results show that aging treatment can eliminate the defect and retained strain induced by RSP and increases quickly the transformation temperature. However, at the same time, aging treatment can cause Ti2Ni precipitation inside grains which can lower the Ti content in matrix and result in the decreases of transformation temperature. Low temperature aging or aging for short period would induce multi-stage B2←→B19 transformation owing to composition deviation generated by non-uniform Ti2Ni precipitation inside the grains. The multi-stage transformation would merge to one stage with high temperature aging or aging for long period due to the homogeneous composition caused by uniform precipitation. When aging temperature is above 500oC, Ti2Ni particles precipitate inside grains and cause the multi-stage transformation during short period aging, while, except Ti2Ni, TiNi2Cu particles also precipitate at 700oC aging with homogeneous matrix composition.