Influence of a Tensile Stress on the Thermodynamics of Martensitic Transformations: Frictional Work and Stored Elastic Energy Calculations in Polycrystalline Alloys

Abstract

The influence of a tensile stress on the thermodynamics of martensitic transformations inpolycrystalline samples has been studied. The presentation of a thermodynamic frameworkfrom the principles of thermodynamics allowed the calculation of frictional work and storedelastic energy as functions of applied stress. The framework was used to analyze the martensitictransformations of a sputter-deposited Ni46:3Ti51:5Co2:2 (at. pct) thin film, with a microstructurecharacterized by Guinier–Preston zones and oriented Ti2Ni precipitates inside grains. Fromexperimental results of thermal cycles at different constant stresses, frictional work and storedelastic energy were calculated. The frictional work showed a constant behavior with appliedstress in both B2$R and R$B19’ transformations in the analyzed stress range. The storedelastic energy showed a decreasing behavior with applied stress in the B2 R transformation,and a constant behavior in the R$B19’ transformation. It was found that the temperatureinterval of martensitic transformations is no longer an indicator of the stored elastic energymagnitude when a tensile stress is applied. The observed decrease of the thermal hysteresis as theapplied stress increases was analyzed in terms of the stored elastic energy dissipation.Complementary, the utilization of a Clausius–Clapeyron-like equation in polycrystalline alloyshas been discussed.