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Measurement of oxygen activity in ferro-alloys
Žák, Štěpán ; Čamek, Libor (referee) ; Záděra, Antonín (advisor)
The thesis deals with determination of the oxygen content in ferro-alloys with emphasis on direct oxygen activity measurement in the meltage. The practical part of the thesis contains statistical analysis of oxygen activity values measured in austenitic and duplex stainless steel meltages. The measurements were done in vacuum furnace before vacuuming and afterwards. Statistically significant dependency of oxygen activity on the temperature of meltage was discovered among the values measured after the vacuuming. Therefore, its value can be predicted based just on the temperature of the meltage. No statistically significant dependency was found among the values measured before vacuuming (except for the low Chromium austenitic stainless steel meltages). Hence, other factors need to be considered when predicting oxygen activity before vacuuming.
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The influence of mechanical alloying on contamination of powder mixtures and bulk materials
Kubíček, Antonín ; Hadraba, Hynek (referee) ; Moravčík, Igor (advisor)
This thesis deals with the influence of process parameters on the contamination level of powder materials produced by mechanical alloying (MA) technology. For this purpose austenitic stainless steel 316 L and equiatomic CoCrFeNi high-entropy alloy (HEA) were prepared by high-energy ball milling. Both materials were milled in argon and nitrogen atmospheres from 5 to 30 hours. Spark plasma sintering method (SPS) was then used for consolidation of chosen powder samples. Chemical analysis of contamination within MA was carried out using combustion analysers for determination of carbon, oxygen, and nitrogen contents after different lengths of milling. Also differences in chemical composition of powder and corresponding bulk samples were measured. The microstructure analysis using scanning electron microscopy (SEM) of both powder and bulk materials was executed with focus on oxide and carbide presence and dispersion. Increasing content of carbon with increasing milling time was observed across all measured samples. This contamination is attributed to using milling vial made of tool steel AISI D2 (containing 1,55 wt. % of carbon). Increase of carbon content within consolidation using SPS was also observed. Milling of specimens using N2 as milling atmosphere caused higher contamination level in both AISI 316 L and HEA compared to milling in argon.
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Measurement of oxygen activity in ferro-alloys
Žák, Štěpán ; Čamek, Libor (referee) ; Záděra, Antonín (advisor)
The thesis deals with determination of the oxygen content in ferro-alloys with emphasis on direct oxygen activity measurement in the meltage. The practical part of the thesis contains statistical analysis of oxygen activity values measured in austenitic and duplex stainless steel meltages. The measurements were done in vacuum furnace before vacuuming and afterwards. Statistically significant dependency of oxygen activity on the temperature of meltage was discovered among the values measured after the vacuuming. Therefore, its value can be predicted based just on the temperature of the meltage. No statistically significant dependency was found among the values measured before vacuuming (except for the low Chromium austenitic stainless steel meltages). Hence, other factors need to be considered when predicting oxygen activity before vacuuming.
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The influence of mechanical alloying on contamination of powder mixtures and bulk materials
Kubíček, Antonín ; Hadraba, Hynek (referee) ; Moravčík, Igor (advisor)
This thesis deals with the influence of process parameters on the contamination level of powder materials produced by mechanical alloying (MA) technology. For this purpose austenitic stainless steel 316 L and equiatomic CoCrFeNi high-entropy alloy (HEA) were prepared by high-energy ball milling. Both materials were milled in argon and nitrogen atmospheres from 5 to 30 hours. Spark plasma sintering method (SPS) was then used for consolidation of chosen powder samples. Chemical analysis of contamination within MA was carried out using combustion analysers for determination of carbon, oxygen, and nitrogen contents after different lengths of milling. Also differences in chemical composition of powder and corresponding bulk samples were measured. The microstructure analysis using scanning electron microscopy (SEM) of both powder and bulk materials was executed with focus on oxide and carbide presence and dispersion. Increasing content of carbon with increasing milling time was observed across all measured samples. This contamination is attributed to using milling vial made of tool steel AISI D2 (containing 1,55 wt. % of carbon). Increase of carbon content within consolidation using SPS was also observed. Milling of specimens using N2 as milling atmosphere caused higher contamination level in both AISI 316 L and HEA compared to milling in argon.
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