Plasma-sprayed alumina coating on Inconel 600 for fast reactor neutron detector application

Alumina coating, with high electrical resistivity, has been proposed over Inconel 600 rings for application in fission chamber neutron detectors, operating at 923 K in fast breeder reactor. For improving the thermal cycling life and adhesion strength of alumina coating, selection of the suitable coating technique and bond coat, with appropriate spray parameters was pursued. In the present study, Ni–50%Cr bond coat was deposited over Inconel 600 by the high velocity oxygen fuel technique, while the top alumina coat was deposited using air plasma spray process. A dense coating with minimum porosity and a stable insulation resistance (600 V DC) of ∼10 ¹¹ ohm at room temperature and ∼10 ⁸ ohm at 923 K was achieved. Thermal cycling studies on coated samples and rings showed good thermal cycle life tested up to 100 cycles. The coating exhibited good bond strength and only marginal decrease in bond strength was observed with increase in thermal cycling.