THE ISOTHERMAL COMPRESSION RESPONSE OF A NEAR GAMMA-TIAL+W INTERMETALLIC

Hot isostatically pressed Ti-48%Al-2%W powder compacts were isothermally compressed between 900-degrees-C and 1200-degrees-C, and at constant strain rate in the range 10(-1) to 10(-4) s-1. The deformation processes occurring are determined by correlation of the stress-strain response, strain rate sensitivity exponent m and activation energy, with the deformed microstructures. The resulting ''deformation map'' indicates that at low temperatures and high strain rates, mechanical twinning and dislocation generation cause a high flow stress, low m and high activation energy. Increasing compression temperature causes dynamic recrystallization, flow softening and increased m. Concurrent dynamic recrystallization and superplasticity can occur, with m as high as 0.44. At high temperatures and strain rates < 10(-3) s-1, superplastic deformation is accompanied by grain coarsening. A ''forging map'' indicates that cracking after 120% engineering strain can be avoided if appropriate compression parameters are applied.