β-grainsize Effects on the 18R-martensite Microstructure in Cu-based SMA

Abstract

A systematic experimental analysis based on the assessment of the mean martensite plate size in sub-grain domains was implemented to characterize the martensitic microstructure morphology in polycrystalline Cu-based shape memory alloys. Experimental data was collected by light and electron microscopy, analysing polycrystalline materials of grain size (d) in a wide range: from fine-grained material with grain size of about 500nm (ribbons and strips obtained by rapid solidification techniques) to single crystals of 6mm diameter (grown by the Bridgman method). In the d range below 100μm, a lineal relationship between the average width of the martensite plates (hplate) and the mean grain size was obtained for thermal-induced martensite transformation (TMT). Above this value (d> 100μm), such relation is no longer valid, and hplate becomes independent of grain size.