The optimum structures of alloys with high strength and crack resistance

Abstract

All of these indices are structurally sensitive and therefore may be improved only by directed production actions for the optimum structures of the alloys. The relationship of the different properties of any alloy to its structure is complex. The changes in yield strength and crack resistance such as in refinement of the phases of the alloy are opposite while in the fatigue limit it is unsteady. In addition, it is important to correctly determine the type and scale of the structure of the alloy for adoption of a decision on the advisability of one hardening method or another. Plastic deformation of metals may be considered as macro-, micro-, or submicroprocesses. Macroprocesses cover significant volumes comparable to the dimensions of the objects. These phenomena are investigated and described by the mathematical appartus of mechanics, the theories of elasticity and plasticity, and fracture mechanics. Being the foundation for engineering calculations of strength, mechanics may not serve as predictions of increasing the strength of metals, the creation of new alloys, or improvement of the structure and chemical composition of existing ones since it does not take into consideration the real structure of metals and alloys and the form and dimensions of actual defects of their internal structure. Submicroprocesses develop in individual crystalline cells (or point defects) or propagate along certain crystallographic planes. These phenomena are investigated by experimental metallographic methods and are described by the theory of dislocations, which, considering and quantitatively evaluating~the different experimental models of retarding of moving dislocations, has become the basis of the scientific search for optimum solutions to the problem of increasing the strength of metals and alloys. Discovery of the mechanism of increasing strength by the creation of obstacles in the path of dislocations has, on the one hand, explained known processes of strengthening (such as the aging of duralumin, the high strength of martensite, etc.) and, on the other, has served as the cornerstone for development of new