Effect of increase in Nano-particle addition on mechanical and microstructural behaviour of HVOF and Cold-Spray Ni-20Cr coatings on boiler steels

Abstract

In the present work, Micron and nano-sized powders of Ni and Cr were blended in various proportions by mechanical milling, maintaining Ni (wt.% 80) and Cr (wt.% 20) as the overall weight %, to produce three different grain sized Ni-Cr nano-crystalline alloy powders. These in-house prepared nanocrystalline powders were sprayed on chosen SA 516 boiler steels in this study, using high-velocity oxy-fuel (HVOF) and cold spray (CS) processes. All the deposited coatings were found to have the nano-sized grains. Further the effect of different weight percentages of nanoparticles on the microhardness and scratch resistance of coatings was studied. It was concluded that on enhancement in weight % nano-particle, the microhardness of the coatings enhanced. The maximum hardness was found to be 525 Hv and 601 Hv respectively for HVOF and CS coatings. XRD analysis was used to identify phases, SEM/EDS for microstructure analysis and X-ray mapping for elemental distribution in case of all the developed coatings.