Formation of NiWO₄ during high temperature oxidation of cube textured Ni-3%W substrates

Cube textured Ni-3 at.% W tapes were heated to temperatures in the range 800-1200 degrees C in flowing oxygen and either air-quenched or held for 1 h and furnace cooled. Cross-sectional backscattered electron images (BSEIs) and energy dispersive x-ray (EDX) analysis showed the formation of the ternary oxide NiWO4 at temperatures greater than 1000 degrees C in addition to the usual NiO. The nickel tungstate phase appeared first as a layer at the metal/NiO interface and then as internal oxides within the substrate. At some temperatures, the presence of this phase was observed to cause buckling and catastrophic spallation of the oxide.