ADIABATIC CALORIMETRIC STUDY ON SHAPE-MEMORY ALLOYS - HEAT-CAPACITIESAND MARTENSITIC PHASE-TRANSFORMATION OF NI47TI44NB9 AND NB80TI14NI6 ALLOYS

A low-temperature precision adiabatic calorimeter for heat capacity me asurements has been constructed, The heat capacities of a shape memory alloy (Ni47Ti44Nb9) and a normal reference alloy (Nb80Ti14Ni6) have b een measured in the temperature range from 60 to 350 K with this calor imeter, The heat capacity curve of the normal alloy is smooth and cont inuous over the whole temperature range, An anomaly, indicating the ma rtensitic phase transformation, in the heat capacity curve of the shap e memory alloy was observed at T = 234.0 +/- 0.5 K with a maximum, whe re C-p,C-m = 34.86 +/- 0.21 J K-1 mol(-1). The molar enthalpy and mola r entropy associated with the martensitic transformation were determin ed as Delta(trs)H(m) degrees = 411.9 +/- 2.5 J mol(-1)and Delta(trs)S( m) degrees = 1.76 +/- 0.01 J K-1 mol(-1), respectively.