Analysis of effect of dynamic compositional fluctuation on weld metal creep based on laminate composite simulation

The high temperature properties of wrought materials of uniform composition are different from those of materials exhibiting compositional fluctuation , which is generally caused by differences in materials processing. Roll bo nded laminate composites of nickel with Cu-Ni solid solutions containing 8. 9, 18.9, 28.6, 37.3, and 48.3 at.-%Cu were fabricated to simulate physicall y the microsegregation occurring in solidified Monel 400 weld metal. The re sults shaw that the creep behaviour is strongly influenced by the degree of interdiffusion and amplitude of the compositional fluctuation, as a result of the driving force of the simulated microsegregation. The apparent activ ation energy Q is dependent on the applied stress. As stresses increase, th e deformation mechanisms suggested vary from short circuit diffusion, to th ermal lattice selfdiffusion, to high atomic mobility selfdiffusion which is attributed to the athermal excess vacancies. Changes in stress Exponent n, Q, and the structure dependent constant A with time are correlated with th e dynamic interdiffusion due to the homogenisation process.