Investigation of physical properties of tungsten-based single crystals using an ultrasonic method

Using an ultrasonic method, the measurement of longitudinal and transversal velocities v of ultrasonic waves in the major crystallographic directions of pure-tungsten single crystals and tungsten single crystals alloyed with Ta and Mo was performed. Single crystals with a [110] crystallographic orientation were prepared by plasma-arc melting. Crystal density was also measured. Crystal elastic constants Cij, anisotropy factors A, Young’s modulus E, shear modulus G and bulk modulus B for the given crystallographic directions, and the mean values of the longitudinal and transversal velocities of the ultrasound according to the Fochtu-Roisu-Chilly method, Young’s modulus, shear modulus, Poisson’s ratio and Debye temperature were calculated from the obtained data. The measurement of ultrasound rates was realized by means of a pulse apparatus with a frequency of 10 MHz to 30 MHz. It was found that the alloying of pure tungsten with the elements such as tantalum and molybdenum led to a decrease in the average magnitudes of v, Cij, and B over various crystallographic and polarization directions, as well as the magnitude of . The effects of the alloying elements on the elastic properties of tungsten crystals were identical. It may be concluded on the basis of the obtained results that the ultrasonic method can be used for the quality control of the purity of tungsten single crystals and tungsten low-alloyed alloys by measuring the attenuation effects of ultrasound waves in various parts of the tested samples.Web of Science48682682

PhD students´day FMST 2023

The authors gave oral presentations of their work online as part of a Doctoral Students’ Day held on 15 June 2023, and they reflect the challenging work done by the students and their supervisors in the fields of metallurgy, materials engineering and management. There are 82 contributions in total, covering a range of areas – metallurgical technology, thermal engineering and fuels in industry, chemical metallurgy, nanotechnology, materials science and engineering, and industrial systems management. This represents a cross-section of the diverse topics investigated by doctoral students at the faculty, and it will provide a guide for Master’s graduates in these or similar disciplines who are interested in pursuing their scientific careers further, whether they are from the faculty here in Ostrava or engineering faculties elsewhere in the Czech Republic. The quality of the contributions varies: some are of average quality, but many reach a standard comparable with research articles published in established journals focusing on disciplines of materials technology. The diversity of topics, and in some cases the excellence of the contributions, with logical structure and clearly formulated conclusions, reflect the high standard of the doctoral programme at the faculty.Ostrav

Application of a Dy3Co0.6Cu0.4Hx addition for controlling the microstructure and magnetic properties of sintered Nd-Fe-B magnets

The focus of new technologies on the formation of inhomogeneous distributions of heavy rare-earth metals (REMs) in hard magnetic Nd-Fe-B materials is of scientific importance to increase their functional properties, along with preserving existing sources of heavy REMs. This paper focused on the coercivity enhancement of Nd2Fe14B-based magnets by optimizing the microstructure, which includes the processes of grain boundary structuring via the application of a Dy3Co0.6Cu0.4Hx alloy added to the initial Nd-Fe-B-based powder mixtures in the course of their mechanical activation. We have studied the role of alloying elements in the formation of phase composition, microstructure, the fine structure of grains, and the hysteretic properties of hard magnetic Nd(R)(2)Fe14B-based materials. It was shown that the Dy introduction via the two-component blending process (the hydrogenated Dy3Co0.6Cu0.4 compound is added to a powder mixture) resulted in the formation of the core-shell structure of 2-14-1 phase grains. The efficient improvement of the coercivity of Nd(RE)-Fe-B magnets, with a slight sacrifice of remanence, was demonstrated.Web of Science1224art. no. 423

Metallurgical preparation of Nb-Al and W-Al intermetallic compounds and characterization of their microstructure and phase transformations by DTA technique

The possibilities of metallurgical preparation of 40Nb-60Al and 15W-85Al intermetallic compounds (in at.%) by plasma arc melting (PAM) and vacuum induction melting (VIM) were studied. Both methods allow easy preparation of Nb-Al alloys; however, significant evaporation of Al was observed during the melting, which affected the resulting chemical composition. The preparation of W-Al alloys was more problematic because there was no complete re-melting of W during PAM and VIM. However, the combination of PAM and VIM allowed the preparation of W-Al alloy without any non-melted parts. The microstructure of Nb-Al alloys consisted of Nb2Al and NbAl3 intermetallic phases, and W-Al alloys consisted mainly of needle-like WAl4 intermetallic phase and Al matrix. The effects of melting conditions on chemical composition, homogeneity, and microstructure were determined. Differential thermal analysis was used to determine melting and phase transformation temperatures of the prepared alloys.Web of Science258art. no. 200

Influence of heat treatment on the structural and magnetic characteristics of (NdxPr1-x)(2)Fe14B-based magnetic material for low-temperature application

Sintered Pr-Nd-Fe-B-based permanent magnets with 10 and 13 wt. % of Pr were prepared by traditional technology and then subjected to various heat treatments. Stoichiometric composition of the matrix grains corresponds to (Pr0.3Nd0.7)2Fe14B and (Pr0.4Nd0.6)2Fe14B compounds, respectively. Conducted thermomagnetic analysis to samples of these magnets showed the presence of spin-reorientation transition in temperature 95 and 75 K, respectively. This makes the magnet potentially applicable for low temperatures. For these compounds, we have determined the optimum heat-treatment conditions. The magnetic domain structure of the magnet subjected to an optimum heat treatment has been studied. The effect of different low-temperature heat treatments on the magnetic properties of magnets has been demonstrated.Web of Science55462462

Komplexní charakterizace monokrystalů nízkolegovaných slitin wolframu a molybdenu, připravených elektronovým zonálním tavením a plazmovou metalurgií

Import 09/12/2014Prezenční637 - Katedra neželezných kovů, rafinace a recyklaceNeuveden

Study of macro- and micro-segregation of iridium in molybdenum single crystals after electron beam zone melting

The aim of the work was to study the creation of micro- and macro-segregation of iridium in low-alloyed molybdenum single crystals after electron beam zone melting (floating zone technique) depending on various conditions of crystallization. In order to evaluate relations between the chemical inhomogeneity and structural defects and their influence on properties of single crystals, the dependence of concentration and character of distribution of admixtures under „various crystallization conditions on the origin of concentration undercooling and dislocation substructure of molybdenum single crystals prepared by electron beam floating zone melting was experimentally investigated.Web of Science1041646

Structural changes of single crystals of low-alloyed tungsten alloys at thermal cycling

Parameters of sub-structure of single crystals of low-alloyed tungsten alloys from the system W-Nb and W-Mo were investigated after thermal cycling in argon protective atmosphere. The mode of thermal cycling of tungsten based single crystals consisted of heating to the temperature of 2500 °C and of cooling to the temperature of 500 °C with dwell of 3.5 s at those temperature. It was established with use of X-ray topography, OLM and SEM, that after 100 thermocycles dislocations were re-distributed, sub-boundaries of the 2nd order were “washed away” (disappeared), and the size of sub-grains of the 1st order and their angle disorientations increased – as a result of heat stresses. After 500 thermocycles formation of new boundaries was observed in the structure as a result of polygonisation, i.e. by ordering of dislocations of the same sign. Application of 2000 thermocycles led to an increase of size of new grains and that of their angle disorientations. All the tested samples preserved at the thermal cycling within the interval from 0 to 2000 thermocycles their single crystalline structure. Formation of oxides on the surface of single crystals is connected with residual content of oxygen in argon.Web of Science32656

Den doktorandů 2022

Ostrav

Nanoindentation testing of low-alloyed molybdenum single crystals

Web of Science106suppl. 3s536s53