Influence of Heat Treatment on Dynamic Properties of Tin-Free Bronze. Multifractal Parameterization of the Structures of Destroyed Samples

Abstract

The results of experimental studies of the dynamic characteristics of tinless bronze of the BrAZhNMts 9-4-4-1 brand of two types (in cold-rolled and annealed states) at different strain rates are presented. An experimental determination of the dynamic characteristics of bronze was carried out using a modification of the Kolsky method for dynamic tension using a split Hopkinson pressure bar. Tests were carried out with different strain rates up to rupture of the samples. It has been found that for both states, an increase in the strain rate leads to a significant change in the mechanical characteristics. The material after annealing showed a decrease in strength properties compared to the initial state by 20–22%. Compared to the static standard characteristics, the dynamic reduction in area has increased for both types of metal condition, and the dynamic reduction in area in the annealed state is 18–25% higher than the reduction in the cold-rolled state, i.e. in the annealed state, bronze is more ductile, which fits into the traditional theory of heat treatment. After dynamic testing, the fractured specimens were cut along the central tensile axis along the diameter so that the analytical sections (surfaces of the specimens that are ground, polished and chemically etched to reveal the structure or defectiveness of the specimens) were perpendicular to the fractures. The microstructural analysis of the destroyed samples and multifractal parametrization of their structures were carried out. On the basis of multifractal analysis in terms of the latent ordering parameter, it was found that the annealed state is less resistant to structural phase transition than the cold-rolled state. In annealed samples, a larger number of excited local regions appear, in which the hydrodynamic nature of the flow is possible and, as a result, such samples are more plastic.