Strain Hardening and Recovery in High-Temperature Deformation by Pure-Metal Mode

Abstract

By a new method using the stress relaxation test, the coefficient of strain hardening without recovery (h) and the rate of recovery without strain hardening (r) are estimated in high-temperature deformation of fcc aluminum and bcc iron, where the internal stress is confirmed to be nearly 100% of the flow stress. Both h and r are dependent on applied stress σ and temperature T in a steady-state deformation, and are represented by h=h₀(σ⁄E)^mexp(−Q_h⁄RT) and r=r₀(σ⁄E)^lexp(−Q_r⁄RT), where h₀ and r₀ are constants, E is Young’s modulus and m=−0.88(−1.5), l=4.3(3.2), Q_h=−22(−76) kJ/mol, Q_r=88(132) kJ/mol for aluminum (iron). During a transient state of tensile deformation in the constant strain-rate test, h and r are nearly independent of strain. The activation energy for recovery (Q_r) is found to be appreciably smaller than that of self-diffusion, and then possible roles of pipe-diffusion and strain-enhanced diffusion in dynamic recovery are discussed.