Senior Heat Treatment Technician

Author: Chief Editor: Yu Fengying
Publisher:
Publish Date: 1999-06-01
Features:
Segment: Basic knowledge training requires understanding the phase structure of alloys, metal diffusion phenomena, and the plastic deformation process of metals. It also involves mastering the types and performance characteristics of common metal compounds in steel, as well as the factors affecting metal diffusion and the changes in the microstructure and properties of cold-worked metals before and after heating. Section Alloy Phase Structure Most metal materials are alloys. Alloys not only possess the basic properties of pure metals but also exhibit higher mechanical properties, and some even have certain special physical and chemical properties. Therefore, they are widely used in industry. The performance of alloys is primarily determined by the composition phases, relative amounts, sizes, shapes, and distributions of the phases. Thus, it is necessary to understand the phase structure of alloys. The composition phases of alloys are diverse, and in general, they can be classified into two major categories: solid solutions and metal compounds.
I. Solid Solutions
A solid solution is a homogeneous crystalline phase formed when solute atoms dissolve into a solid solvent while maintaining the solvent's crystal lattice type. It is an important composition phase in alloys. Most actual metal materials used are single-phase solid solution alloys or multiphase alloys based on solid solutions. According to the positions occupied by solute atoms in the solvent lattice, solid solutions can be classified into substitutional solid solutions and interstitial solid solutions.
1. Substitutional Solid Solutions
A substitutional solid solution is formed when solute atoms occupy the lattice sites of the solvent. In substitutional solid solutions, the dissolution of solute atoms causes lattice distortion, as shown in Figure 1-1, which illustrates the lattice distortion in substitutional solid solutions. If the diameter of the solute atom is larger than that of the solvent atom, the lattice constant of the solid solution will increase; conversely, it will decrease. Moreover, the degree of lattice distortion increases with the concentration of solute atoms, and the effect of solid solution strengthening becomes more pronounced. The variation patterns of lattice constants for substitutional solid solutions based on commonly used aluminum, copper, and iron are shown in Figure 1-2.