Characterization of 3R martensite in a Ni–40Al–15Pt bulk alloy

As Pt promotes the reversible martensite transformation, the aim of this study was to assess the influence of Pt on the crystallography of (β′) martensite, in terms of ordering adapted, twinning and stacking faults. The focused ion beam (FIB) milling process was used to prepare transmission electron microscopy (TEM) samples of the NiAlPt bulk alloys, whereby 3R, L10 ordering of the martensite was confirmed. The addition of Pt, coupled with high temperature oxidation resulted in more stacking faults, due to greater Pt diffusion and subsequent enrichment in martensite. For Pt diffusion the temperature must be in excess of 900 °C, both for isothermal and cyclic oxidation. When the favorable temperature environment is achieved Pt can diffuse preferentially allowing for promotion of the transformation to martensite.

► Three alloys of same composition but different thermal histories are investigated.
► Inform the scientific community about martensite crystallography (3R) in NiAlPt.
► Show how different the martensite composition is to adjacent untransformed β-NiAl.
► Show that cyclic and/or isothermal oxidation offer chemically different martensite.
► Pt needs high temperatures in excess of 900 ̊C for its thermal activation.