Papers by Keyword: Alloys

Abstract: The data on the occurrence of martensitic transformation in steel under the action of a magnetic field were obtained by the electric resistivity method. The obtained data indicate the possibility of stress-assisted martensite formation in the temperature range of M_s-M_d (in which superplasticity of austenite is observed). This possibility is due to the magnetic heterogeneity of austenite. Nanosized regions with a ferromagnetic order are present in the paramagnetic matrix. They can perceive the energy of the external magnetic field through the magnetostrictive stresses and change the fields of the elastic forces in the crystal lattice. All this leads to a decrease in the energy of formation of the nucleation center.

Abstract: The necessity of finding scientifically grounded methods for the development of new heat-resistant, wear-resistant and corrosion-resistant aluminum alloys is presented in the present work. For this purpose, the analysis of modern methods for computer calculation of phase diagrams in multicomponent metal systems using the Thermo-Calc program was carried out. Therefore, a quantitative analysis of the phase diagram the Al-Cu-Mn-Zr system was carried out, as the basis of deformable high-temperature aluminum alloys. Isothermal and polythermal sections of the phase diagram were calculated in this system. The temperatures of phase transformations were calculated. The mass and volume fractions of the phases in the studied alloys were calculated. The range of concentrations and temperatures at which the maximum amount of dispersoids Al₂₀Cu₂Mn₃ may be achieved, was defined. The minimum amount of Al₂Cu phase is calculated, which should correspond to the best heat resistance of alloys. It is substantiated that in the alloys of a new generation of ALTEK type, the use of homogenization and quenching operations is inexpedient, which implies the possibility of a significant reduction in the cost of heat treatment in comparison with industrial alloys, such as 1201.

Abstract: The paper presents data on investigation of the microstructure of the surface of EI893 alloy samples on a Jeol JSM-6390A scanning electron microscope after different types of processing: annealing, thermoplastic hardening and surface plastic deformation. The change of structure and thickness of the hardened layer is shown, depending on the type of surface treatment

Abstract: It is advantageous to use the method of surface plastic deformation in order to get high-quality surfaces that meet increased requirements for strength and reliability. For efficient process of surface plastic deformation, it is required to define a set of conditions to provide minimum roughness of a machined surface. The paper addresses the problem of experimental search of optimal burnishing modes using the simplex design to minimize roughness of a machined surface. The significance of variable factor ranking was observed for this technique. A specific set of tests resulted in decrease in the initial surface roughness almost by 15 times in the specimens made of aluminum alloy after burnishing with the steel indenter. It was established that the surface quality was significantly affected by a new factor – angle of indenter contact with the machined surface, which had a damping effect on the machine-fixture-tool-workpiece system. The experiments showed that polished indenter balls significantly lowered the roughness grade of the machined surface under the same conditions.

Abstract: Introduction of refractory elements into alumina ceramics to improve its properties, is usually carried out by mixing the alumina with oxides of refractory metals. In this work this problem has been solved by pre-alloying refractory element with aluminum and subsequent dispersion of alloy in aqueous alkaline solutions. Characteristics of microstructure, phase composition and rheological properties of powders obtained by chemical dispersion of alloys Al-Mo, Al-V and Al-Zr with 10 wt.% refractory element in 20% aqueous sodium hydroxide solution, as well as the impact of heat treatment at 1250 oC on these properties, have been discussed. On the basis of X-Ray analysis (XRA) and electron microscopy the conclusion was adopted that heat treatment of powder leads to significant phase and structural transformations of such powders and is a necessary stage of preparation for sintering.

Abstract: The investigations of ultrasound Rayleigh wave parameters changing depending on localized plastic strain in AlCu4MgSi alloy and austenitic stainless steel AISI 304 are presented in this paper. Measurements of the ultrasound parameters and localized strain bands motion were carried out in-situ during the tensile tests of the specimens at the constant rate and room temperature. It has been found that the measurement of ultrasound velocity allows detecting the initiation of a localized strain band and its location relative to the acoustic measurement area independently of the deformation mechanism.

Abstract: A new method for non-destructive evaluation of the mechanical properties of structural materials has been developed. This is based on measurements of the ultrasound propagation velocity in deforming materials. Preliminarily investigations were carried out in order to relate the ultrasound propagation velocity to the mechanical characteristics of the deforming material. A detailed description of suitable devices intended for ultrasound propagation velocity measurement with high accuracy is presented. Using Zr-based alloys as an example, it is shown that the method can be used for the monitoring of zirconium billets from which nuclear reactor fuel cladding is fabricated by cold rolling.

Abstract: The microstructural properties and intermetallic (IMC) formation of Sn-Ag-Cu (SAC) through varying amounts of zinc were examined in this study while having tin held at constant composition. Samples were prepared and heated in a furnace for 168 hours to achieve complete solidification and homogenization. Results showed relatively fine microstructure primarily containing Sn dendrites, eutectic, and pro-eutectic phases. Microstructures for each alloy was similar for which majority of them formed copper-based IMCs and Sn dendrites. The alloy (0.7Sn-0.15Ag-0.1Cu-0.05Zn) containing minimal amount of zinc with high amount of Ag resulted to high Vickers hardness number. Structural analysis showed that these group of alloys composed mainly of β-Sn, Cu₆Sn₅, and Ag₃Sn.

Abstract: Developments in synchrotron and home laboratory X-ray sources and fast low noise X-ray imaging detectors over the last 15-20 years has enabled real time X-radiography of alloy solidification from the melt. These investigations have been an important tool for in–situ investigations of dendrite-, eutectic and monotectic growth, dendrite fragmentation etc. At the same time, the techniques have allowed studies of phenomena in the melt such as convection, formation of solute boundary layers and minority phase droplet interactions. The article will review the X-radiography techniques and some of the results with emphasis on studies of phenomena in alloy melts.

Abstract: The crystallization kinetics of melt-spun Cu_64.5Zr_35.5 amorphous alloy ribbons was investigated using differential scanning calorimetry (DSC) at different heating rates. Besides, the Kissinger and isoconversional approaches were used to obtain the crystallization kinetic parameters. As shown in the results, the activation energies for glass transition and crystallization process at the onset, peak and end crystallization temperatures were obtained by means of Kissinger equation to be 577.65 ± 34, 539.86 ± 54, 518.25 ± 20 and 224.84 ± 2 kJ/mol, respectively. The nucleation activation energy E_nucleation is greater than grain growth activation energy E_growth, indicating that the nucleation process is harder than grain growth. The local activation energy E_α decreases in the whole crystallization process, which suggests that crystallization process is increasingly easy.