Yielding and Deformation Behavior of the Single Crystal Nickel-Base Superalloy PWA 1480
GEORGIA INST OF TECH ATLANTA SCHOOL OF MATERIALS ENGINEERING
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Interrupted tensile tests were conducted to fixed plastic strain levels in 001 oriented single crystals of the nickel-base superalloys PWA 1480. Testing was done in the range from 20-1093 C, at strain rates of 0.5 and 50min. The yield strength was constant from 20-760 C, above which the strength dropped rapidly and became a strong function of strain rate. The high temperature data could be represented very well by an Arrhenius-type equation, which resulted in three distinct temperature regimes. The deformation substructures could be grouped in the same three regimes, indicating that there was a fundamental relationship between the deformation mechanisms and activation energies. At low temperatures, the activation energy for yielding was zero, and deformation occurred by gamma prime shearing by pairs of a2110 dislocations on octahedral planes. At high temperatures, the true activation energy for yielding was indicative of a diffusion-controlled process, and deformation occurred by gamma prime by-pass. Intermediate temperatures exhibited transitional behavior. Models of the yielding process were considered, and it was found that no currently available model was fully applicable to this alloy. It was also demonstrated that the initial deformation mechanism during yielding was frequently different from that which would be inferred by examining specimens which had been tested to failure.
- Metallurgy and Metallography