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Microstructure stability of electron beam welds
Rončák, Ján ; Havlík, Petr (referee) ; Jan, Vít (advisor)
The aim of this bachelor thesis is an evaluation of microstructure and functionality of welded joints by using methods of material engineering. At first, there are various methods of welding described in the theoretical part. In the second part, the thesis introduces every material that is used to create a welded joint. The final part then offers an explanation of every method used to analyse the process of welding. The joints were created on two specimens without any filler material and at the machine that uses electron beam. The first joint is a combination of austenitic hadfield steel with ferrite-perlite carbon steel and in the second case combined with stainless ferritic steel with high amount of chromium.
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Experimental manufacturing of multiphase Ni-Si based layers
Rončák, Ján ; Moravčík, Igor (referee) ; Jan, Vít (advisor)
The diploma thesis deals with the preparation of the composite material based on the NiSi system using powder metallurgy supplemented by the sintering with the usage of SPS method (spark plasma sintering). Theoretical part contains general information about the mechanical-chemical process and sintering, while materials and methods used for experimental observation are explained in a separate chapter. Experimental part explains the procedure of the experiment and selected parameters of individual processes. In the experiment, two powder mixtures were created in order to form the NiSi phase in the maximum possible amount of powder material. After successfully reaching presence of the NiSi phase in the range of 87 to 89 wt. %, both mixtures were used to produce sintered samples at temperatures from 700 to 900 °C. Experiments showed the best results for sample number 2, which was sintered at 900 °C for 4 minutes. Resulting porosity was 0.9 % and hardness reached a maximum value of 718 HV 1. However, all sintered samples show cracks at room temperature associated with increased brittleness of the material.
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