Characterization of innovative rotary swaged Cu-Al clad composite wire conductors

Cu/Al composites are perspective for applications in a wide range of industrial and commercial branches, from transportation to elecatrotechnics. This study focuses on Cu/Al clad composite wires with 5 mm diameter featuring unique sequencing produced via the technology of rotary swaging at the processing temperatures of 20 degrees C and 250 degrees C. During the swaging process, we continuously acquired samples for investigations and used our own KOMAFU S600 system for dynamic detection of swaging forces. The composite wires subjected to electrical resistivity measurement were further analysed via electron microscopy, neutron diffraction, and mechanical testing. The results showed that both the total imposed strain (swaging degree) and swaging temperature influenced the investigated parameters non-negligibly. The samples subjected to high reduction ratios (swaging degree > 3) at the temperature of 250 degrees C exhibited formation of intermetallics at the interfaces, which deteriorated the electric conductivity. However, the conductivity was also affected by structural phenomena, such as work hardening, texture development, dislocations density, and recrystallization. All the final 5 mm samples exhibited sufficient bonding of both the components and recrystallized ultra-fine grained structures providing them with the ultimate tensile strength of >200 MPa.Web of Science16083582

Texture evolution in biocompatible Mg-Y-Re alloy after friction stir processing

The presented study deals with the investigation of biocompatible WE 43 Mg-based alloy processed via the combination of rotary swaging (RS) and friction stir processing (FSP) at three different rotational speeds of 400 RPM, 800 RPM, and 1200 RPM. The structure observations primarily focused on texture development and characterizations of grain sizes and grain boundaries. The results showed that swaging plus processing at 400 RPM and 1200 RPM lead to substantial recrystallization and grain refinement. The fractions of low angle grain boundaries within the 400 RPM and 1200 RPM samples were approximately 11%, while for the 800 RPM sample exhibiting secondary recrystallization it was about 22%. The grains were also the finest in the 1200 RPM sample (average grain diameter of 1.8 mu m). The processed structures exhibited a slight tendency to form the {10-10} preferential fiber texture (especially the 800 RPM sample). Tensile testing showed the FSP to have positive influence on the ultimate tensile stress, as well as ductility of all the samples; the mechanical properties improved with increasing FSP rate.Web of Science911art. no. 118

Optimizing thermomechanical processing of bimetallic laminates

Thermomechanical processing combining plastic deformation and heat treatment is a favorable way to enhance the performance and lifetime of bimetallic laminates, especially those consisting of metals, which tend to form intermetallic layers on the interfaces when produced using methods involving increased temperatures. The presented work focuses on optimizing the conditions of thermomechanical treatment for an Al + Cu bimetallic laminate of innovative design involving a shear-strain-based deformation procedure (rotary swaging) and post-process heat treatment in order to acquire microstructures providing advantageous characteristics during the transfer of direct and alternate electric currents. The specific electric resistivity, as well as microhardness, was particularly affected by the structural features, e.g., grain size, the types of grain boundaries, and grain orientations, which were closely related to the applied thermomechanical procedure. The microhardness increased considerably after swaging (up to 116 HV02 for the Cu components), but it decreased after the subsequent heat treatment at 350 ◦C. Nevertheless, the heat-treated laminates still featured increased mechanical properties. The measured electric characteristics for DC transfer were the most favorable for the heat-treated 15 mm bimetallic laminate featuring the lowest measured specific electric resistivity of 22.70 × 10−9 Ωm, while the 10 mm bimetallic laminates exhibited advantageous behavior during AC transfer due to a very low power loss coefficient of 1.001.Web of Science169art. no. 348

Predvidanje deformacije i temperature metodom konačnih elemenata (MKE) tijekom valjanja cijevi na pilger – stanu

3D - FEM simulation was used as an efficient tool for description of stress-deformation thermal field at rolling of tubes on a pilgrim mill. The monitored objectives comprised also behaviour of working tools at this rolling. This paper assumes rolling of already pierced thick-walled blank, which passes through the pilgrim stand at simultaneous reduction of thickness of inside and outside diameters at the expense of elongation of initial length. Main attention is focused on the mentioned parameters with respect to various conditions of rolling, such as different heat transfer, different friction or different distance of insertion of the rolled product into the gauge. The input data used at simulation were derived from real conditions of tubemaking.Za prikaz termičkog polja naprezanje – deformacija tijekom valjanja cijevi na pilger - stanu učinkovito je rabljena trodimenzijska metoda konačnih elemenata (3D – MKE). U radu je razmatrano i ponašanje alata tijekom izrade cijevi valjanjem. Pretpostavljeno je valjanje šuplje debelostjene cijevnice na pilger stanu uz istovremeno smanjenje vanjskog i unutrašnjeg promjera na uštrb produljenja početne duljine. Rad se fokusira na navedene parametre obzirom na promjenjive režime valjanja poput različitog prijenosa topline, različitog trenja ili različite udaljenosti uvodenja valjanog proizvoda u uredaj. Ulazni podaci rabljeni u simulaciji odgovaraju onima iz realnog procesa valjanja cijevi

Affecting structure characteristics of rotary swaged tungsten heavy alloy via variable deformation temperature

This study focuses on numerical prediction and experimental investigation of deformation behaviour of a tungsten heavy alloy prepared via powder metallurgy and subsequent cold (20 degrees C) and warm (900 degrees C) rotary swaging. Special emphasis was placed on the prediction of the effects of the applied induction heating. As shown by the results, the predicted material behaviour was in good correlation with the real experiment. The differences in the plastic flow during cold and warm swaging imparted differences in structural development and the occurrence of residual stress. Both the swaged pieces exhibited the presence of residual stress in the peripheries of W agglomerates. However, the NiCO matrix of the warm-swaged piece also exhibited the presence of residual stress, and it also featured regions with increased W content. Testing of mechanical properties revealed the ultimate tensile strength of the swaged pieces to be approximately twice as high as of the sintered piece (860 MPa compared to 1650 MPa and 1828 MPa after warm and cold swaging, respectively).Web of Science1224art. no. 420

Correlating microstrain and activated slip systems with mechanical properties within rotary swaged WNiCo pseudoalloy

Due to their superb mechanical properties and high specific mass, tungsten heavy alloys are used in demanding applications, such as kinetic penetrators, gyroscope rotors, or radiation shielding. However, their structure, consisting of hard tungsten particles embedded in a soft matrix, makes the deformation processing a challenging task. This study focused on the characterization of deformation behavior during thermomechanical processing of a WNiCo tungsten heavy alloy (THA) via the method of rotary swaging at various temperatures. Emphasis is given to microstrain development and determination of the activated slip systems and dislocation density via neutron diffraction. The analyses showed that the grains of the NiCo2W matrix refined significantly after the deformation treatments. The microstrain was higher in the cold swaged sample (44.2 x 10(-4)). Both the samples swaged at 20 degrees C and 900 degrees C exhibited the activation of edge dislocations with {110} or {111} slip systems, and/or screw dislocations with slip system in the NiCo2W matrix. Dislocation densities were determined and the results were correlated with the final mechanical properties of the swaged bars.Web of Science131art. no. 20

Effects of sintering conditions on structures and properties of sintered tungsten heavy alloy

Probably the most advantageous fabrication technology of tungsten heavy alloys enabling the achievement of required performance combines methods of powder metallurgy and processing by intensive plastic deformation. Since the selected processing conditions applied for each individual processing step affect the final structures and properties of the alloys, their optimization is of the utmost importance. This study deals with thorough investigations of the effects of sintering temperature, sintering time, and subsequent quenching in water on the structures and mechanical properties of a 93W6Ni1Co tungsten heavy alloy. The results showed that sintering at temperatures of or above 1525 degrees C leads to formation of structures featuring W agglomerates surrounded by the NiCo matrix. The sintering time has non-negligible effects on the microhardness of the sintered samples as it affects the diffusion and structure softening phenomena. Implementation of quenching to the processing technology results in excellent plasticity of the green sintered and quenched pieces of almost 20%, while maintaining the strength of more than 1000 MPa.Web of Science1310art. no. 233

Matematické modelování proudění spalin včetně přestupu tepla ve spirálovém výměníku tepla

The paper presents the numerical solution of gas flow in a spiral heat exchanger, which flowing water is heated. Gaseous combustion products are derived from the combustion of natural gas in micro-turbine, which reaches tens of power [kW]. The paper defines a mathematical model of gas flow in the exchanger, including consideration of heat transfer through the conductive spiral heat exchanger. Conductive heat exchanger areas are different wall and the insulation layer that surrounds the heat exchanger itself. Inlet boundary conditions for gas and water were got from the experimental measurements. Then defined mathematical model was solved numerically in programming software ANSYS Fluent13. The results of numerical simulations are presented in the basic distribution of current values in the individual sections of exchanger. Subsequently, variables are evaluated to determine the energy analysis of the heat exchanger.Příspěvek prezentuje numerické řešení proudění spalin ve spirálovém výměníku tepla, kterým se ohřívá proudící voda. Plynné spaliny jsou získány ze spalování zemního plynu V mikroturbíně, která dosahuje výkonu řádově desítky [kW]. V příspěvku je definován matematický model proudění spalin ve výměníku včetně uvažování přestupu tepla skrz vodivé oblasti spirálového výměníku. Vodivými oblastmi výměníku tepla jsou jednotlivé stěny a vrstva izolace, která obklopuje samotný výměník. Vstupní okrajové podmínky pro spaliny a vodu byly získány na základě experimentálního měření. Definovaný matematický model byl následně řešen numericky V programovém prostředí ANSYS Fluent13. Výsledky numerické simulace jsou prezentovány rozložením základních proudových veličin V jednotlivých řezech výměníkem. Následně jsou vyhodnoceny veličiny K stanovení energetické analýze výměníku tepla

Microstructure and mechanical properties of sintered and heat-treated HfNbTaTiZr high entropy alloy

High entropy alloys (HEAs) have attracted researchers' interest in recent years. The aim of this work was to prepare the HfNbTaTiZr high entropy alloy via the powder metallurgy process and characterize its properties. The powder metallurgy process is a prospective solution for the synthesis of various alloys and has several advantages over arc melting (e.g., no dendritic structure, near net-shape, etc.). Cold isostatic pressing of blended elemental powders and subsequent sintering at 1400 degrees C for various time periods up to 64 h was used. Certain residual porosity, as well as bcc2 (Nb- and Ta-rich) and hcp (Zr- and Hf-rich) phases, remained in the bcc microstructure after sintering. The bcc2 phase was completely eliminated during annealing (1200 degrees C/1h) and subsequent water quenching. The hardness values of the sintered specimens ranged from 300 to 400 HV10. The grain coarsening during sintering was significantly limited and the maximum average grain diameter after 64 h of sintering was approximately 60 mu m. The compression strength at 800 degrees C was 370 MPa and decreased to 47 MPa at 1200 degrees C. Porosity can be removed during the hot deformation process, leading to an increase in hardness to similar to 450 HV10.Web of Science912art. no. 132