THE INFLUENCE OF STRAIN-RATE, AMPLITUDE AND TEMPERATURE ON THE HYSTERESIS OF A PSEUDOELASTIC Cu-Zn-Al SINGLE CRYSTAL

The hysteresis loop, described during the formation of stressinduced pseudoelastic martensite in a Cu-Zn-Al betaphase single crystal, was studied as a function of strain-rate, deformation amplitude and temperature. The σp→m, the stress at which the transformation starts at a given constant temperature, is strain-rate independent but the hysteresis described by the stress-strain curve shows a maximum at intermediate strain-rates (3.3 x 10-3 sec-1). For very low strain rates (3.3 x 10-5 sec-1) the relative energy-loss (ƊW/W) was independent of amplitude. The amplitude-dependence was the strongest at intermediate strain-rates. The absolute hysteresis, i.e. energy loss, measured at constant strain-rate seems to be independent of temperature in the region (Ms+60, Ms+110). The change in hysteresis as a function of strain-rate can be attributed to the heating and cooling of the sample due to the exothermic character of the beta-martensite transformation and the reverse endothermic transformation. At very low strain-rates the transformation occurs isothermally so that nearly no hysteresis is found. Only at very high strain-rates the sample is deformed adiabatically