Nanocrystalline NiAl Coating Prepared by HVOF Thermal Spraying

Abstract

Nanocrystalline NiAl intermetallic powder was prepared by mechanical alloying (MA) of Ni 50 Al 50 powder mixture and then deposited on low carbon steel substrates by high velocity oxy fuel (HVOF) thermal spray technique using two sets of spraying parameters. X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), differential scanning calorimetry (DSC), and hardness test were used to characterize the prepared powders and coatings. The MA of Ni 50 Al 50 powder mixture led to the formation of NiAl intermetallic compound. The resulting powder particles were three dimensional in nature with irregular morphology and a crystallite size of~10 nm. This powder was thermally sprayed by HVOF technique to produce coating. The deposited coating had a nanocrystalline structure with low oxide and porosity contents. The hardness of coatings was in the range of 5.40-6.08 GPa, which is higher than that obtained for NiAl coating deposited using conventional powders.

KCl-Induced High-Temperature Corrosion Behavior of HVAF-Sprayed Ni-Based Coatings in Ambient Air

“…No feedstock oxidation and/or elemental loss related to the spray method was observed. This was in contrast to the phase change previously reported in the HVOF deposition of Ni-based powders (Ref 34,35) and represented a specific advantage of the HVAF technique, characterized by lower temperatures and higher particle velocities. Thus, the good interlamellar cohesion discussed in Characterization of Coatings and Feedstock Powders section could be also attributed to the lower oxidation state of the splashed particles during the spray process.…”

Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings

“…The XRD results proved that the HVAF process did not affect the phase composition of the feedstock powders. Formation of few in situ oxides could likely be due to; a) the powder particles being exposed to high temperature in oxidizing ambient air environment during the spraying process [30][31] and/or b) because of pre-existing oxygen in the feedstock material [32]. The influence of the former is minimal in the investigated samples, as the dwell time in the HVAF process is small and the temperature is also very low [19].…”

A study on nanostructured in-situ oxide dispersed NiAl coating and its high temperature oxidation behavior

“…To evaluate the changes that occurred during milling, sampling was done at 5-hour intervals. The average of crystallite size was estimated by Williamson-Hall method [10,11].…”