Mechanism of reaction of molten NiTi with EBM graphite crucible

Ultra clean NiTi shape memory alloy was produced by electron beam melting of Ni rich vacuum inductionally melted butts together with pure Ti chunks in both condensed and electrographite crucibles. A hollow cathode discharge gun was used for heating up to 1623, 1653 and 1693 K and holding the charge materials under vacuum for 300, 600, 900 and 1200 s. Effects of temperature, time and compactness of the crucible on formation/disappearance of the hard compounds like Ni3Ti, Ti4Ni2O, Ti4Ni2C, Ti3Ni2OC and TiC were determined by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. A combination of the experimental results with the kinetic rate equations indicated that the reaction between NiTi and the crucible obeyed first order transfer kinetics with carbon intake activation energy of 225.8 kJ mol(-1) for the NiTi shape memory alloy melt.