On characterisation of wire-arc–plasma-sprayed Ni on alumina substrate

A study was carried out on metal–ceramic bonding produced by the technique of wire-arc–plasma spraying of Ni on Al2O3 substrate. The Ni layer and the Ni/Al2O3 interface were characterised using optical and electro-optic techniques. The plasma-deposited Ni layer shows a uniform lamellar microstructure throughout the cross-section. The metal–ceramic interface was found to be well bonded with no pores, flaws or cracks in the as-sprayed condition. The optical metallography and concentration profiles established with the help of an electron probe microanalyser confirmed the absence of any intermediate phase at the interface. An annealing treatment at 1273 K for 24 h on the plasma-coated samples did not result in formation of any intermetallic compound or spinel at the Ni/Al2O3 interface. This indicates that the oxygen picked up by Ni during the spraying operation is less than the threshold value required to form the spinel NiAl2O4.