Study of Martensitic Phase Transformation in a NiTiCu Thin-Film Shape-Memory Alloy Using Photoelectron Emission Microscopy

Authors


  • This work was supported in part by the Department of Energy, Office of Science, Division of Chemical Sciences, under Grant DE-FG03-02ER45988. The PEEM and UPS studies were performed at the W. R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the US Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Pacific Northwest National Laboratory is operated for the US Department of Energy by Battelle under Contract DE-AC06-76RLO 1830. Supporting Information is available online from Wiley Interscience or from the author and can be downloaded at http://www.wsu.edu/∼langford.

Abstract

Thermally induced martensitic phase transformation in a polycrystalline NiTiCu thin-film shape-memory alloy is probed using photoelectron emission microscopy (PEEM). In situ PEEM images reveal distinct changes in microstructure and photoemission intensity at the phase-transition temperatures. In particular, images of the low-temperature, martensite phase are brighter than that of the high-temperature, austenite phase, because of the lower work function of the martensite. UV photoelectron spectroscopy shows that the effective work-function changes by about 0.16 eV during thermal cycling. In situ PEEM images also show that the network of trenches observed on the room-temperature film disappears suddenly during heating and reappears suddenly during subsequent cooling. These trenches are also characterized using atomic force microscopy at selected temperatures. The implications of these observations with respect to the spatial distribution of phases during thermal cycling in this thin-film shape-memory alloy are discussed.

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