The solubility and the diffusion coefficient of hydrogen were determined in the austenitic (cubic) high-temperature phase of the shape-memory alloy NiTi. The measurements were made between 500 and 950 "C, with hydrogen gas pressures of up to 1.3 bar, and with hydrogen-to-NiTi ratios of up to 0.027. The hydrogen was in interstitial solid solution. The absorption process is exothermic. The enthalpy of solution per hydrogen atom is -183 2 40 meV. The diffusion coefficient can be described by an Arrhenius relation with an activation energy E = 480 -+ 50 meV and a pre-exponential factor Do = (4.7 s) x cmz s-'.NiTi hydride was synthesised in experiments with a higher hydrogen gas pressure ( p = 150 bar, T = 500 K). Because of its brittleness, the hydride is readily pulverised by mechanical methods. This yields, after extraction of the hydrogen, NiTi powder which is difficult to prepare by other experimental techniques.

The solution behaviour of hydrogen in the A-15 compounds V3Ga and Ti& was studied by hydrogen absorption and x-ray diffraction measurements. It was found that the presence of the hydrogen did not change the structure of the A-15 host crystals. The lattice parameter, the partial enthalpy of solution and the partial entropy of solution were determined for both compounds investigated as a function of the hydrogen content.

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