Development of graded Ni-YSZ composite coating on Alloy 690 by Pulsed Laser Deposition technique to reduce hazardous metallic nuclear waste inventory

Alloy 690 based ‘nuclear waste vitrification furnace’ components degrade prematurely due to molten glass-alloy interactions at high temperatures and thereby increase the volume of metallic nuclear waste. In order to reduce the waste inventory, compositionally graded Ni-YSZ (Y₂O₃ stabilized ZrO₂) composite coating has been developed on Alloy 690 using Pulsed Laser Deposition technique. Five different thin-films starting with Ni80YSZ20 (Ni 80 wt% + YSZ 20 wt%), through Ni60YSZ40 (Ni 60 wt% + YSZ 40 wt%), Ni40YSZ60 (Ni 40 wt% + YSZ 60 wt%), Ni20YSZ80 (Ni 20 wt% + YSZ 80 wt%) and Ni0YSZ100 (Ni 0 wt% + YSZ 100 wt%), were deposited successively on Alloy 690 coupons. Detailed analyses of the thin-films identify them as homogeneous, uniform, pore free and crystalline in nature. A comparative study of coated and uncoated Alloy 690 coupons, exposed to sodium borosilicate melt at 1000 °C for 1-6 h suggests that the graded composite coating could substantially reduced the chemical interactions between Alloy 690 and borosilicate melt.