Vliv krystalizačních procesů na strukturu a vlastnosti intermetalických sloučenin na bázi Ti-Al

Abstract

This PhD thesis entitled "Effect of crystallisation processes on the structure and properties of inter-metallic TiAl based compounds” deals primarily with the possibilities of metallurgical preparation of alloys based on -TiAl, possibly with the most economic metallurgical processes, including precision casting technology using a corundum crucible coated mechanically by paint Y2O3 or graphite crucibles, as well as technology of plasma melting in water-cooled copper mould. Special attention is in the presented work paid particularly to the influence of technology and homogeneity, and also to the content of impurities and of interstitial elements and their influence on the micro-structure and mechanical properties. The work is, however, aimed also at assessment of the effect of pure metallic yttrium as alloying element. The aim of the work is primarily to compare the possibilities of refinement of micro-structure by yttrium alloying for several -TiAl alloys of different composition and with different types of micro-structures that were formed by heat treatment under different conditions, and to determine the effect of alloying by this additive on mechanical properties. The work is divided into four main chapters. The first chapter summarises the literature findings concerning possible or already used applications of these alloys, it describes the basic methods of their preparation, it characterises development of these alloys, basic types of micro-structures and describes the impact of selected alloying elements. The second chapter deals with the objectives of this dissertation. The third chapter describes the used input materials and it describes the equipment, procedures and methods that were used during this work. The last chapter describes the achieved results. It was established that the micro-structure and properties of the prepared alloys are highly influenced by the technology used for their preparation. Advantages and disadvantages of individual technologies were characterised and effect of the used technology on the course of solidification, homogeneity, micro-structural characteristics and mechanical properties were determined. The influence of yttrium on the micro-structure of several different alloys was also determined and possibilities of structure refinement by additions of this element were characterised.