The Strengthening Mechanism in Consolidated Rapidly Solidified Alloys

Abstract

ABSTRACTAttempts have been made to study mechanisms of strengthening in the Ni68W22C8B2 and the Ni45CO20 Cr10MO4Fe5B16 alloy systems during their amorphous crysialline transitions. In the Ni68W22C8B2 system where amorphous particulates of varying sizes have been cons Ti a ed at high pressure and low temperature (3.6 MPa, and 673°K respectively), the initial stage of crystallization is marked by transformation of the localized regions of the specimen. These crystallized regions contain microcracks and voids. Microhardness measurements from the consolidated specimens indicate an increasing trend in the microhardness with decreasing particulate sizes. Premature failures of the consolidated specimen during tensile stress measurements have been attributed to the presence of microcracks and voids in these specimens. In the Ni45Co20Crl0Mo4Fe5B16 alloy system isothermal annealing of an initially amorphous alloy has been allowed to produce grains of varying sizes. The tensile stress measurements from these thermally annealed ribbons indicate two distinctly different functional relationships between the strength, σ, and the grain size parameter, λ. In the early stage of transformation where grain reach a maximum growth of up to 400 Å, the functional form of the strength, σ, with the grain parameter, λ, is σ = σ + K Log λ, where σO and K are constants. During latter stages of transformation, where grains larger than 400 Å have been formed, the strength, σ, varies with the inverse square root of the grain sizes. This latter relationship is analogous with the well known Hall-Petch relationships, which describes the strength, σ, as a function of the grain sizes in conventionally processed alloys.