Weldability of Materials. Approaches, Evaluations, Definitions

Modern structural materials, such as metals, ceramics, polymers, composites etc., are continually becoming more and more complex in their composition, properties and application fields. Many materials are not just welded, but also used for deposition of coatings or other processing methods. An important characteristic of materials in both similar and dissimilar combinations as to their chemical composition, structure and properties is their ability to form a permanent joint.

The paper studies the problem of evaluation of weldability of materials and analyses criteria of their sensitivity to hot and cold cracking, as well as embrittlement, by using different technological strength determination methods. Physics and fracture mechanics approaches are used to consider changes in a material taking place during the process of formation of a joint. Micro and macro discontinuities formed as a result of the segregation processes are indicative of a change, i.e. degradation, in properties of a material during welding. Degradation of a material under certain conditions of a temperature-force effect, which is characteristic of welding, leads to reaching the limiting state by a material and, as a result, to fracture. This is related to a change in the Gibbs energy of a system and decrease in the critical energy causing degradation, which is estimated by characteristics of the fracture energy and level of mechanical and structural stability. The degree of degradation serves as an indicator that determines weldability of a material and, in fact, performance and quality of a joint. On a example of several type of materials it is shown and suggested that weldability of a material should be regarded as its individual property, which depends on the service conditions and can be controlled through the welding technology.