Varivost kovin in lomne lastnosti zvarnih spojev (Slovene)

The research program is dealing with the joining of technical metals by using welding and development of new materials and technologies. a) Satisfactory weldability is prerequisite for joining by welding of metals for long term use, but not the only one base of weld joint strength. Fusion welded joints are never totally isotropic and homogeneous in the sense of defectiveness and mechanical properties. Additional stresses are present in the weld joints not caused by external loading (residual stresses). Possible existence of LBZ (local brittle zone) and crack-like defects interacting with stresses are of an extreme importance. To overcome this problem over-matched joints are often used in technically very demanding equipment. Measure of weld joint mis-matching is ratio of weld and base metal yield strengths (M). Fracture toughness testing can reveal brittle parts of weld joint more reliably than Charpy-impact testing but they have to be hit (sampled) by the crack. Through-thickness crack in the full-thickness specimen including the joint is usually prepared by controlled fatigue loading. Crack positioned in the weld metal and in HAZ is usualy practiced. The result of crack existence in the thick specimen under loading is constraint and three-axiallity of stresses. Three-axial stress state is increasing possibility of brittle fracture occurance on LBZs because of their low toughness. All findings can be after testing proved by metallography and fractography (post-testing sectioning). Mutual relationships exist between material fracture toughness and Charpy-impact toughness of isotropic polycrystalline metallic materials. The aim of this research program is to find by experiments such a relationship valid for an over-matched weld joint (M?1,25). b) The research programme at development of new materials and technologies is directed toward (1) manufacturing of alloys with special microstructures and properties with continuous casting technologies, and (2) manufacturing of discontinuously reinforced MMC composites (especially aluminium and copper base composites). The focus is given to the study of physical and chemical processes taking place in liquid, semi-solid and solid state. The fundamental understanding of the processes not only enables attainment of desired structures and properties of materials, but also contributes to the development of manufacturing technologies.