Stress relief and plastic flow in nickel oxide at elevated temperatures

Abstract

Stress relief and plastic flow modes in nickel oxide over the temperature range 1323–1473 K have been studied, involving an assessment of its creep-in-bend behavior in the form of small sintered beams, of average grain sizes in the range 2–10 μ, and of densities of ∼70% of the theoretical maximum; conditions of three-point loading were adopted involving a range of maximum fiber stress of 2 × 106 −8×107 N · m−2, that is, of the magnitudes likely to arise during the growth of nickel oxide scales on metallic nickel. After subtraction of any observed threshold stresses, most specimens were found to exhibit a stress index of about unity. The grain-size index was determined to be −2.5. It is believed that the dominant creep mechanism was probably that of Nabarro-Herring.