In situ formation of Al-Si-Mg based composite coating by different reactive thermal spray processes

Reactively sprayed coatings based on in-process reactions during flight and after impingement offer superior properties compared with conventional coatings as it has in-situ formed fine and uniformly dispersed stable hard phases. In the present work, composite powder composed of plated nickel, fine SiO2 particulates and Al-Si-Mg core particles with water glass binder (SiO2/Ni/Al-Si-Mg) was deposited onto an aluminum substrate to fabricate the composite coatings by using HVOF, RF and DC plasma spraying methods. The amount and constituents of the phases formed during reactive spraying were found to be different depending upon the methods used where in-process reactions differently proceed. Consequently, reactively sprayed composite coatings mainly consist of Mg2Si, MgAl2O4, NiAl3, and Al-Si matrix through the exothermic reaction of SiO2 with molten Al-Si-Mg alloy. The depletion of magnesium in the composite powder is responsible for the obtained lower hardness of composite coatings sprayed by RF plasma spraying which offers the highest molten droplet temperature.