Creep deformation behavior of a Ni-Fe-Cr based alloy: Key influences of phosphorus microalloying

Abstract

The effects of P on the creep deformation behavior for a Ni-Fe-Cr based alloy were studied by interrupted creep test. The results show that the P-doping can suppress the growth of M₂₃C₆, but has no effect on coarsening rate of γ’ during creep deformation. And the addition of P can not only retard the pile-up of dislocation near grain boundary, but also increase the stress concentration limit of grain boundary. First of all, P can retard the movement of grain boundary and dislocation by increasing grain boundary cohesion. Therefore, the grain rotation to 〈111〉 orientation and the appearance of hard grains are inhibited, which decreases the geometrically necessary dislocation density near the grain boundary and delays the creep damage process during creep deformation. Then, the granular M₂₃C₆ in the P-containing alloy can improve the deformation coordination between the adjacent grains, which increases the fraction of hard grains with <111> orientation after creep failure fracture. Hence, the addition of P increases the stress concentration limit of grain boundary and extends the creep damage process. Based on the two effects of P mentioned above, phosphorus microalloying can transform the creep damage type from microcracks to creep cavities and increase the creep strength and ductility for the Ni-Fe-Cr based alloy.