Microstructural and wear characteristics of HVOF-sprayed nanocrystalline NiAl coating

In this research, the microstructure and dry sliding friction and wear behavior of nanocrystalline NiAl coatings were investigated. Toward this purpose, nanocrystalline NiAl powders were initially prepared by mechanical alloying (MA) and deposited on low carbon steel substrate by high velocity oxygen fuel (HVOF) thermal spray process with two sets of spray parameters. The coatings were characterized with respect to their microstructure and phase compositions using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffractometry (XRD). In addition, the friction and wear behavior of coating were tested under three loads of 30, 60 and 90 N. Microstructural observations showed that the as-sprayed coatings include mainly NiAl intermetallic compound with a crystallite size of ~20 nm, although there exist some Al2O3 and Ni phases. HVOF spraying at higher fuel/oxygen ratio caused higher amounts of non-NiAl phases and lower hardness and wear resistance. The wear mechanisms and friction behavior of nanocrystalline NiAl coatings were evaluated and discussed in detail.