Microshear banding in shock-consolidated microcrystalline alloy powders

Abstract

Microshear bands (<0.02–0.03 μm thick), formed as a result of inhomogeneous plastic deformation within heavily deformed powder particle interiors, are observed during shock consolidation of microcrystalline Markomet 1064 (Ni_(55.8) Mo_(25.7) Cr_(9.7) B_(8.8)), and nickel based superalloys Pyromet 718 and Rene 95. Although part of the shock energy is utilized in melting of particle surfaces due to preferential plastic deformation near interfaces, a nonnegligible amount of energy is dissipated in plastic deformation within particle interiors. This involves localized regions of shear which are manifested as fine microshear bands of heavily twinned material, confined within individual powder particles. The thickness and length of the microshear bands is more than several orders of magnitude smaller than that in the macroscopic bands observed in materials subjected to unconstrained high-strain-rate deformation. The small size of the shear bands is attributed to the fact that the particle strain is limited, as individual powder particles are deformed to conform to their neighbors in the shock consolidation process.

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