Microstructure Features and High Temperature Oxidation Resistance of In-Situ TiN-Ti Composite Coatings by Plasma Transferred Arc Welding

In order to improve the high temperature oxidation resistance of Ti6Al4V alloy, the in-situ TiN-Ti composite coatings were prepared with Ti-Cr-Ni-Nb powders by plasma transferred arc welding. Nitrogen gas was used as the transport gas and provided N source for the formation reaction of TiN. Microstructure features and high temperature oxidation behaviors of the composite coatings were studied. The phases in the composite coatings were TiN, Ti, CrN, and NiTi. It was clearly observed that in-situ TiN particles were evenly distributed in the Ti matrix. A little Nb atom dissolved in TiN particles, and others dissolved in the Ti matrix. By comparing the curve of Ti6Al4V alloy to that of the composite coatings, the oxidation mass gain of the composite coatings was comparatively less. The oxidation film of the composite coatings was smooth and compact, and no crack was visibly observed. Based on the results of the high temperature tests, the composite coatings exhibited superior high temperature oxidation resistance than Ti6Al4V alloy both at 650 degrees C and at 850 degrees C.