Effect of feedstock particle size on microstructure of APS coatings prepared from mechanically alloyed nickel–titanium powders

Abstract

Ni–Ti coatings were deposited using APS process. In this regard, mechanically activated Ni–Ti powders with amorphous/nanocrystalline structure were used. Two different sieved powders, one of nominal size range of (–63 to +20 μm) and the other of nominal size of (–125 to +63 μm), were employed in the experiments. The phase composition and microstructure of the coatings were examined by X-ray diffraction, optical microscopy and scanning electron microscopy. The results indicated that for coating produced using finer powder, increasing plasma power has caused severe cracking of the coatings whereas using the minimum power a coating with better quality can be deposited. In contrast, for coating produced using coarser powder, by selecting the medium power a coating with better quality can be deposited. Based on results of X-ray diffraction, the phase composition of coatings consists of NiTi, Ni₄Ti₃, Ni and some oxides.