CRYSTAL STRUCTURE CHANGES IN THE SURFACE LAYERS OF NICKEL SAMPLES INFLUENCED BY PERIODIC HEAT-TREATMENT (KRISTALLOSTRUKTURNYE IZMENENIYA V POVERKHNOSTNYKH SLOYAKH NIKELEVYKH OBRAZTSOV, PROISKHODYASHCHIE POD VLIYANIEM PERIODICHESKIKH TEPLOVYKH NAGRUZHENII),
FOREIGN TECHNOLOGY DIV WRIGHT-PATTERSON AFB OHIO
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Specimens of electrolytically pure nickel were annealed for 30 min at 500C to remove the surface work hardness resulting from their preparation, some of the specimens were polished mechanically, and all were subjected to thermal treatment which consisted in heating to 900C, holding for 5 min, and cooling in water 25C. The specimens were then analyzed by x-ray diffraction and electron microscopy. The results indicate that the mechanisms of failure of thin and massive nickel specimens are substantially different In the case of failure of thin specimens, a predominant role is played by a vacancy mechanism, whereas in massive specimens at considerable heating and cooling rates the thermal stresses produced are large enough to activate the dislocatory process of failure.
- Metallurgy and Metallography