R-Phase

The R-phase is a phase found in nitinol, a shape-memory alloy. It is a martensitic phase in nature, but is not the martensite that is responsible for the shape memory and superelastic effect. Figure 1: The R-Phase distortion of the B2 austenitic structureFigure 2: The trigonal representation of the R-phaseFigure 3: Free energy, strain, and calorimetry curves typical of the symmetric Austenite-R-Martensite transformation, in which R-phase is found during both cooling and heating.Figure 4: Free energy, strain, and calorimetry curves typical of the asymmetric Austenite-R-Martensite transformation, in which R-phase is found only upon cooling. The R-phase is a phase found in nitinol, a shape-memory alloy. It is a martensitic phase in nature, but is not the martensite that is responsible for the shape memory and superelastic effect. In connection with nitinol, 'martensite' normally refers to the B19' monoclinic martensite phase, rather than the R-phase. The R-phase competes with martensite, is often completely absent, and often appears during cooling before martensite, then giving way to it upon further cooling. In the same way, it can be observed during heating prior to reversion to austenite, or may be completely absent.