Effect of Strain Rate on the Dislocation Substructure in Deformed Niobium Single Crystals

Abstract

This paper describes an investigation of the relationship between mechanical properties and dislocation substructure in the strain rate range 10⁻⁴ to 10⁴ sec⁻¹. The relationship between lower yield stress τ_yield and strain rate ε follows two consecutive semi-logarithmic relationships of the form τ_yield = α + β log ε with a break at a strain rate of approximately 10 sec⁻¹. The dislocation configurations produced by deformation in these two regions have been investigated at strain rates of 1.2 × 10⁻⁴ sec⁻¹ and 1.5 × 10³ sec⁻¹ using transmission electron microscopy techniques. The relationship between dislocation density, flow stress, and plastic strain has been determined and is discussed in terms of the dislocation structures observed.