Some features of the energy dissipation in the course of plastic deformation of iron and niobium

Abstract

Introduction. In recent years, a deformed metal crystal has frequently been considered as a nonequilibrium self-organizing system and the plastic flow is described in terms of the dissipative structure evolution during deformation in various scales [1, 2]. However, the number of experimental investigations of the laws of dissipative processes accompanying the plastic deformation is still very restricted. Using the results of calorimetric measurements, we have obtained quantitative estimates of the heat dissipated in bcc metals and the energy stored in these metals in the course of deformation. Experimental. The flat plates of technical-purity iron and niobium (with dimensions of the working part 10 〈 3.5 〈 0.3 mm) were annealed for 1 h at 1220 K (Fe) and 1470 K (Nb). Then the samples were deformed by uniaxial tension at a rate of 8.3 〈 10 ‐4 s ‐1 at 293 K inside a microcalorimeter cell. This procedure was performed in a setup combining a microtesting machine and a differential Calvet calorimeter, which was specially designed for studying thermal effects accompanying the process of plastic deformation [3]. Upon processing of the simultaneously measured stress‐strain diagrams (plotted in the coordinates of force F versus elongation Δ l ) and DSC thermograms (plotted as the heat evolution rate dQ / dt versus time t ), we determined the mechanical characteristics (yield stress σ y , ultimate strength σ u , proportional elongation e p , and relative elongation at break e b ) and the energy parameters