Ti50Ni50-XPdX ( X=15∼30 at％)高溫形狀記憶合金中Cu取代Pd之研究

Abstract

本研究針對TiNiPd高溫SMAs中的Pd由Cu部分取代，探討不同取代量對合金之變態行為、加工性、形狀記憶效應、顯微組織等之影響，並將合金冷加工後，經不同的退火溫度及退火時間，了解其變態行為及SME的改變情形。研究結果得知，TiNiPdCu合金系統在900℃固溶處理1小時後為一階的B2←→B19相變態，隨著Cu取代量的增加，其冷軋延加工性會變差，M*、A*、ΔHh、ΔHc亦會呈一線性下降，而其SME性質，可隨著循環次數的增加而獲得改善。TiNiPdCu合金系統經冷軋延後，在500℃短時間退火下變態溫度和潛熱其值較佳，隨著退火時間的增長，會造成富銅之析出物析出，使相變態行為受到壓抑。而在650℃短時間退火下就能消除冷加工的影響，且隨著退火時間增長，其相變態溫度和潛熱之增加減緩並趨於穩定。本研究同時發現Cu取代Pd的量不要超過10﹪為佳。

Ti50Ni50-x(Pd,Cu)x high temperature shape memory alloys (SMAs) with Pd substituted by Cu are studied. The effect of Cu content on SMAs’ transformation behavior, workability, shape memory effect (SME) and microstructure is also investigated. Specimens are hot-rolled and solution-treated, or cold-rolled and annealed at various temperatures and times. Experimental results show that, after solution-treated at 900℃ for 1 hour, TiNiPdCu SMAs are one stage B2←→B19 transformation. With increasing the Cu content, the cold-rolling ability of TiNiPdCu SMAs reduces and their transformation temperature and latent heat decrease linearly. The SME can be improved by increasing the number of thermal cycles. When annealing at 500℃ for a short time, transformation temperature and latent heat of specimens are near the solution-treated ones. On the other hand, the martensitic transformation of TiNiPdCu SMAs is suppressed due to the formation of Cu-rich precipitates for long annealing time. The effect of cold-rolling can be eliminated when TiNiPdCu SMAs are annealing at 650℃ in short time. When annealing time is prolonged, their transformation temperature and latent heat become stable. The up limit of the amount of Pd substituted by Cu in TiNiPdCu SMAs is suggested to be 10％.