A STUDY OF ELECTRICAL-RESISTIVITY, INTERNAL-FRICTION AND SHEAR MODULUS ON AN AGED TI49NI51 ALLOY

The 400°C aged Ti49Ni51 alloy can exhibit the transformation sequence of B2 →r premartensite R-phase →r martensite. In the early aging stage, only the premartensitic transformation is observed due to the Ms point being deeply depressed by the coherent stress of Ti11Ni14 precipitates. In the later aging stage, internal friction peaks associated with premartensitic and martensitic transformations are all observed on both heating and cooling. The sharp peaks associated premartensitic transformation on heating is believed to be related to the "bias" effect of the coherent stress induced by the Ti11Ni14 precipitates. The serrations of internal friction appearing significantly in the temperature around -30 to -80°C are found to be caused by the stress induced accomodation of R-phase or martensite variants, and are not associated with the transformation. The Ti11Ni14 precipitates can enhance the amount of martensite formed by unit of temperature or time during the martensitic transformation. © 1990.