V.V. Cheverikin

Prediction of solidification behaviour and microstructure of Ni based alloys obtained by casting and direct additive laser growth

Numerical tools are now used widely in the prediction of material properties necessary in order to gain a better understanding of the relationship between material properties and performance, to improve the reliability of processes and the quality of the final product, and to reduce costs, waste and energy use. In this paper, the solidification properties and the microstructure of some commercial Ni based alloys were analysed and predicted numerically using the ProCAST software. The microstructure of a sample obtained by the direct additive laser growth, a new additive manufacturing technique based on the selective laser melting, is presented and discussed. Numerical approaches and software packages that can be used to model additive manufacturing processes are discussed and critically analysed.

Effect of Al3Ni and Mg2Si Eutectic Phases on Casting Properties and Hardening of an Al-7% Zn-3% Mg Alloy

The formation of eutectics in Al–Zn–Mg–Ni and Al–Zn–Mg–Si systems is studied by means of metallography, DSC, EPMA, X-ray spectroscopy and thermodynamical calculations. Polythermal sections of the corresponding phase diagrams are constructed. The concentrations and temperatures of binary eutectic reactions L → (Al) + Al3Ni and L → (Al) + Mg2Si in quaternary alloys are determined. Nonequilibrium solidification in Al–7% Zn–3% Mg-based alloys ceases at approximately 480 °C. The alloys close by composition to binary eutectics have considerably improved casting properties as compared to the base Al–7% Zn–3% Mg composition. In particular, hot tearing susceptibility is much less in alloys with Al3Ni or Mg2Si. These results are corroborated by measurements of thermal contraction during solidification. The alloys containing binary eutectics exhibit much lower temperatures of contraction onset and less thermal strain is accumulated in the solidification range. Fine eutectic morphology enables fragmentation and spheroidization of intermetallic particles during annealing. The presence of Al3Ni and Mg2Si particles does not decrease the precipitation hardening effect associated with precipitation of the T′ (AlMgZn) phase. Improved casting properties and good mechanical properties of castings allow the application of Al–Zn–Mg alloys with binary eutectics formed by Al3Ni or Mg2Si as foundry alloys.

Interaction of Zn and Zn–4Al, Zn–15Al (wt-%) solder alloys with aluminium

The interaction of pure zinc and Zn–4Al, Zn–15Al (wt-%) solder alloys with aluminium has been investigated. Two different experimental techniques were used: (i) the aluminium samples soldering and (ii) the holding of liquid solder alloys inside the hollow in an aluminium base. The aluminium content was determined in samples after contact with aluminium at various temperatures and various holding times. It is shown that in soldered seams and solder alloys that had been held inside the aluminium base, the content of the aluminium was higher than at the points on the liquidus line on the Zn–Al equilibrium phase diagram at the corresponding temperatures and increases along with an increase in the holding time. This was apparently due to isothermal solidification.

Experimental Investigation and Modeling of Copper Smelting Slags

Effective extraction of copper from sulfide ores requires careful operation of a copper smelter, which in turn depends very much on chemistry of the feed and resulted slag and matte. For example, chemical composition of copper smelting slags has to be in a certain range to ensure that their properties are within specific limits. Disobeying these rules may lead to complications in smelting operation, poor quality of the copper products, and premature shutdown of the copper smelter. In the present paper the microstructure and phase composition of slags from the Almalyk copper flash smelter were investigated experimentally and then modeled thermodynamically to evaluate potential ways of improvement and optimization of the copper smelting process and its products. The slag samples were taken at different stages of the copper smelting process: on slag tapping, after slag transportation to a deposition site, and at the site. Experimental investigation included the XRD, XRF, and SEM techniques, which were also confirmed by the traditional wet chemistry analysis. Thermodynamic modeling was carried out using thermochemical software package MTDATA, which enables thermodynamic and physical properties of the matte, slag, and gas phases to be calculated in a wide range of temperatures, pressures, and chemical compositions. In addition, slag viscosities and corresponding matte settling rates were estimated using the modified Urbain and Utigard–Warczok models, and the Hadamard–Rybczynski equation, respectively. It was found that the copper content in the slags may vary significantly depending on the location of slag sampling. Cu was found to be present as sulfide particles, almost no Cu was found to be dissolved in the slag. Analysis of microstructure and phase composition showed that major phase found in the samples is fayalite, while other phases are complex spinels (based on magnetite), different sulfides, and a glass-like phase. Thermodynamic calculations demonstrated the presence of these phases, their compositions, and optimal ranges of operating conditions. Potential ways of improving the matte grade and optimizing the smelting process were suggested on the basis of the calculations.

Oxide formation during electric resistance welding of low carbon steels

The influence of Mn and Cr on the formation of surface oxides and their entrapment during electric resistance welding of Si containing low carbon steels was studied using thermodynamic calculations and experimental investigation of the microstructure of the different oxide inclusions within welds on electric resistance welding-fabricated pipes. The process of oxidation during the welding process, its dependence on oxygen content, temperature of oxidation and the composition of ferrite within the parent steel were analysed. It was shown that the most important influence on the type of oxide inclusions formed during welding is the Mn/Si ratio, while Cr has an indirect influence via carbide formation, which increases the relative content of Mn in ferrite.

Superplastic Deformation Mechanisms in High Magnesium Contenting Aluminum Alloy

The evolution of surface, grains and dislocation structures during superplastic deformation was studied in Al–6.8%Mg–0.6%Mn–0.25%Cr alloy by SEM, EBSD, TEM techniques. The effective activation energy of superplastic deformation was calculated. Contribution of grain boundary sliding was defined during superplastic deformation. Low value of grain boundary sliding, significant dynamic grain growth in stress direction, high dislocations activity and permanent continuous formation of sub-grain boundaries during superplastic deformation were found.

Optimization of Regimes of Thermodeformation Treatment of High-Strength Aluminum Alloy 019705

The effect of regimes of thermodeformation treatment of high-strength aluminum alloy 019705 developed at the department of physical metallurgy of nonferrous metals of NITU “MISiS” is studied. The modes of fabrication of semiproducts are optimized using a “Gleeble System 380” (Hydrawedge II) facility for physical simulation of thermomechanical processes at deformation rates 0.01 – 10 sec – 1 in a temperature range of 200 – 450 °C. The scheme of fabrication of deformed semiproducts (pressing, rolling) and the rates and temperatures of the deformation are shown to be interrelated.

Transforming of the Morphology of Iron Phases in Aluminum Alloys

Iron containing phases with unfavorable morphology almost always exist in commercial aluminum alloys. The attempt to change morphology of the iron containing phase by addition of different alloying elements was made in present work. Experimental and thermodynamic studies of multicomponent phase diagrams with additions of refining elements were carried using ThermoCalc software and analysis of microstructures of the alloys in as-cast and annealed states. The possibility to obtain iron containing phases with almost spherical morphology, which allows to neutralize negative influence of iron on ductility and fracture strength of alloy, was presented in the work.

Analysis of multicomponent aluminum-based alloys with a high volume fraction of three-phase eutectics

Fragments of the Al-Zn-Mg + (Ni, Fe, Mn, Cr) phase diagrams are analyzed using both experimental techniques and calculation with the ThermoCalc software package. The structures of ternary eutectics are analyzed in the as-cast and annealed states. Alloy compositions with a high content of disperse eutectics forming at a moderate cooling rate are found. The intermetallic phases in eutectics are shown to be fragmented and spheroidized during homogenizing annealing before quenching.