A hydroxyapatite (HAp) layer was deposited on the surface of an NiTi alloy using a spark plasma technique. The effects of spraying conditions on the martensitic transformation were investigated in three heat-affected zones: the zone under the handle, the transition zone and in a representative zone with HAp coverage. In the representative area, a reduction in the amount of non-transformable phases was observed. A part of the sublayer showed a nanocrystalline or completely amorphous structure. This sublayer was approximately 30 µm thick. Structural changes contributed to the reduction of the temperature of the reverse martensitic transition down to 25°C. Moreover, modification of the surface revealed a positive influence on the transformation course by narrowing its temperature range and increasing its enthalpy.
This paper is part of a thematic issue on Titanium.
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