In-situ SR-XRD Examination of Phase and Oxide Growth during a High Temperature Cycle with Short Isothermal Holds of a NiTi-20 at.% Zr HTSMA

Ternary additions to binary NiTi shape memory alloys (SMAs) are known to significantly affect the characteristic martensite to austentite phase transformation, i.e. decrease or increase transformation temperatures (TTs). High temperature shape memory alloys (HTSMAs), in which the austenitic transformation is above 115 °C, can be created by adding Au, Pt, Pd, Hf, or Zr to binary NiTi in appropriate amounts. However the majority of these ternary additions are exceedingly expensive, unfortunately making them impractical for most commercial applications. Zr is the exception of the group, but it is often disregarded because of its poor workability and thermal stability. In an effort to find a temperature range that allows for the potential workability of NiTiZr alloys and to gain understanding as to the cause of failure during processing, a NiTi-20 at.% Zr was subjected to a thermal cycle ranging from RT to 1000 °C with short 15 minute holds at select temperatures during both heating and cooling while simultaneously collecting high energy synchrotron radiation X-ray diffraction measurements (SR-XRD) every 30 seconds. Through this experiment valuable insight is gained as to when precipitate, in this case (Ti,Zr)₂Ni, and oxide formation begins and when these phases begin to grow rapidly. In addition, hot rolling of the alloy is performed at various temperatures with different degrees of success.