Abstract
Residual stress measurements using X-ray diffractometry have been carried out on nickel oxide scales formed at 1000°C on pure nickel and nickel containing 0·5 wt-% alloying additions of yttrium, hafnium, cerium, or zirconium. The residual stresses present in nickel oxide scales formed on the alloys containing the additions are significantly higher than those in the nickel oxide scale formed on pure nickel. It is proposed that the principal cause of this increase in stress is associated with oxide grain refinement due to the presence of the added elements in the parent metal. The eventual consequence of these high stress levels is the formation of a weak porous inner oxide that is susceptible to cracking and dramatic stress relief on cooling, leading ultimately to scale decohesion and spalling.
MST/1472
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