National Repository of Grey Literature 8 records found  Search took 0.00 seconds. 
Microstructure of commercially pure titanium after cryogenic milling and spark Plasma sintering
Kozlík, J. ; Harcuba, P. ; Stráský, J. ; Chráska, Tomáš ; Janeček, M.
Commercially pure titanium was prepared by advanced powder metallurgy methods with the aim to produce the ultra-fine grained material. Cryogenic attritor milling was used as a first step to refine the microstructure at liquid argon temperatures to suppress recovery and dynamic recrystallization. Spark plasma sintering was subsequently employed to produce bulk material, exploiting its ability to achieve fully dense structure in short time and thus to reduce the grain growth. In order to understand the undergoing microstructural changes during the process, detailed investigation was performed after each preparation step. Powder morphology was changed significantly after milling, while particle fragmentation was only limited. Grain size after sintering was in micrometer scale, relatively independent of sintering conditions.
The Study of Phase Transformation in Titanium Alloys
Zháňal, Pavel ; Harcuba, Petr (advisor) ; Kalvoda, Ladislav (referee) ; Strunz, Pavel (referee)
In this work phase transformations in metastable β (primarily Ti-15Mo) alloys were studied utilizing electrical resistance, dilatometry, transmission electron microscopy and X-ray and neutron diffraction. The materials Ti-15Mo, Ti-6.8Mo-4.5Fe-1.5Al (LCB), Ti-5Al-5V-5Mo-3Cr (Ti-5553), Ti-29Nb-1Fe-0.5Si (TNFS), Ti-15Mo-3Nb-3Al-0.2Si (Timetal 21S) and Ti-13Cr-1Fe-3Al (TCFA) (in wt. %) - were subjected to a solution treatment at a temperature above β transus and quenched into water. In this condition, the microstructure of the investigated materials consists of β matrix and ω particles. Samples quenched from important temperatures determined from in-situ electrical resistance and dilatometry measurements were studied by post-mortem TEM. In-situ X-ray and neutron diffraction provided direct observations of microstructure of Ti-15Mo alloy during linear heating and confirmed statements based on results of indirect methods, such as: the decrease of volume fraction of ω phase during heating at low temperatures (up to 250 ◦ C), complete dissolution of ω phase at 560 ◦ C and precipitation of α phase without ω particles serving as its direct precursors. X-ray diffraction experiment allowed to determine relative evolution of the size of ω particles while phase fraction evolution was derived from neutron diffraction. The...
Physical and mechanical properties of lead-free solder joints
Harcuba, Petr ; Janeček, Miloš (advisor) ; Drozd, Zdeněk (referee) ; Očenášek, Vladivoj (referee)
Title: Physical and mechanical properties of lead-free solder joints Author: Petr Harcuba Department: Department of Physics of Materials Supervisor: prof. RNDr. Miloš Janeček, CSc., Department of Physics of Materials Abstract: Due to recent restriction of the classical Sn-Pb solder alloy, lead-free solders became an extensively investigated class of materials. This thesis focused on selected Sn-Cu based alloys. The influence of Cu content and minor additions of Ni and P on IMC layers morphology and reliability of simulated solder joints were investigated. The growth kinetics of IMC layers and mechanical properties of solder joints were studied after reaction of molten solders with Cu substrate at various times and temperatures, and after subsequent ageing at elevated temperatures. Detailed analysis of the evolution of IMC layers morphology was performed using EBSD. Higher Cu concentration in solders decreased the dissolution rate of Cu substrate. It was shown that the addition of 0.1 at.% of Ni significantly changed the morphology of IMC layers and improved mechanical properties of solder joints. Addition of P had only a minor effect on the IMC growth and the solder joint reliability. Keywords: Lead-free solders, intermetallic compound layers, growth kinetics, reliability of solder joints
Study of Phase Transformations in Ti Alloys
Zháňal, Pavel ; Harcuba, Petr (advisor)
In this work phase transformations in metastable β Ti-15Mo alloy were stud- ied using electrical resistivity measurements. The alloy was subjected to a solu- tion treatment at a temperature higher than β-transus and quenched in water. In this condition, the microstructure of Ti-15Mo alloy consists of a metastable β-matrix and ω phase particles. During in-situ electrical resistivity measurement in a specially designed furnace, significant temperature points which indicate phase transformations in the material were detected. The dependence of elec- trical resistivity on the temperature changes during heating between increasing and decreasing according to the ongoing phase transformation. The changes were observed at temperatures 225, 356 and 560 ◦ C. A further study of these phase transformations using electrical resistivity measurements was performed on var- ious heat treated specimens. In order to control the microstructure evolution in the material, scanning and transmission electron microscopy was used. Mecha- nical properties were studied using Vickers microhardness testing. The obtained results serve to identify the type and sequence of phase transformations which take place in the Ti-15Mo alloy.
Studium fázových transformací ve slitinách Ti
Zháňal, Pavel ; Harcuba, Petr (advisor) ; Vlach, Martin (referee)
In this work phase transformations in metastable β Ti-15Mo alloy were studied using electrical resistivity measurements. The alloy was subjected to a solution treatment at a temperature higher than β- transus and quenched in water. In this condition, the microstructure of Ti-15Mo alloy consists of a metastable β - matrix and ω-phase particles. During in-situ electrical resistivity measurement in a specially designed furnace, significant temperature points which indicate phase transformations in the material were detected. The dependence of electrical resistivity on the temperature changes during heating between increasing and decreasing according to the ongoing phase transformation. The changes were observed at temperatures 225, 356 and 560 řC. A further study of these phase transformations using electrical resistivity measurements was performed on various heat treated specimens. In order to control the microstructure evolution in the material, scanning and transmission electron microscopy was used. Mechanical properties were studied using Vickers microhardness testing. The obtained results serve to identify the type and sequence of phase transformations which take place in the Ti-15Mo alloy. Powered by TCPDF (www.tcpdf.org)
Study of properties of Titanium prepared by SPD methods
Zháňal, Pavel ; Harcuba, Petr (advisor) ; Král, Robert (referee)
In present work the properties of comercially pure titanium fouth grade processed by equal channel angular pressing (ECAP) were studied. Experimental techniques such as Vickers microhardness, measurement of electrical resistivity, light and electron microscopy were used in this research. The dependence of the degree of the strain imposed by ECAP on microhardness of the material was measured. Microhardness measurement was used to indirectly investigate thermal stability of the prepared material, which is essential for ultra fine grained (UFG) materials. That was also the reason for establishing dependence of the electrical resistivity on the temperature. This method allows to detect changes in the material microstructure. Using scanning electron microscopy (SEM) the results obtained by previous methods were confirmed. It was found that the UFG titanium processed by ECAP is thermally stable aproximatelly up to 450řC. At this temperature begins recovery of the material which results in a decrease of the microhardness values and electrical resitivity. For the temperatures higher than 520řC material recrystalization begins.

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3 Harcuba, Petr
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