Khalil-Allafi, Jafar; Eggeler, Gunther; Schmahl, Wolfgang W.; Sheptyakov, Denis
Quantitative phase analysis in microstructures which display multiple step martensitic transformations in Ni-rich NiTi shape memory alloys.
In: Materials Science and Engineering A-Structural Materials Properties Microstructure and Processing, Vol. 438, No. SI: pp. 593-596
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In the present study, we investigate a microstructure which shows athree-step martensitic transformation on cooling from the hightemperature regime and two DSC peaks on heating. Using in situ neutrondiffraction phase analysis based on Rietveld full profile fitting it isshown how the volume fractions of B2, R and B19’ phases evolve duringthe three step transformation on cooling and the reverse transformationon heating. We used TEM as a complementary method to support our neutrondiffraction findings. The first DSC peak on cooling is related to acomplete transformation of the B2 matrix to R phase and the second andthird peak on cooling are associated with the formation of B19’ in twostages. On heating also, the B19’ -> R transformation is accumulating intwo stages, with the second stage overlapping with the R -> B2transition.