Observations on the Mechanical Properties of Nickel Oxide Scales

The mechanical properties of NiO scales produced by the complete oxidation of high-purity (grade-1) Ni and commercial-purity (grade-A) Ni have been investigated at 700 to 1000 degrees C. The modulus of elasticity of both grades of oxide decreased with increasing temperature, whereas the modulus of rupture for grade-A oxide exhibited a maximum at 850 degrees C and that for grade-1 oxide decreased with increasing temperature. At 700 degrees C, elastic deformation to fracture occurred with both oxides, whereas, at temperatures >= 850 degrees C, plasticity was also observed. The plasticity of grade-1 oxide was similar to 3 times greater than that of grade-A oxide. Creep behaviour of the oxides was studied at 900 and 1000 degrees C. Primary and secondary creep was observed and, in both oxides, the creep rates increased with increasing temperature and load. The creep rate of grade-1 oxide was 10 to 20 times greater than that for grade-A oxide.