G. Kostiuková’s research while affiliated with VSB - Technical University of Ostrava and other places

New types of lead-free solders on the base of tin with addition of metals Ag, Al, Bi, Cu, In, Mg, Sb, Zn were studied. Various alloys were experimentally prepared by smelting of metals in an inert atmosphere or in vacuum in resistance furnace. Purity of metals was minimally 4N. The specimens of solders were studied metallographically including the micro-hardness measurements, complete chemical analysis (ICP-AES, OES), X-ray micro-analysis of alloys by SEM and EDX in order to determine the composition and identification of individual phases. Significant temperatures and enthalpies of phase transformations were determined by DTA. After long-term annealing of selected alloys in vacuum followed by quenching the structural and chemical microanalyses of the present phases and their limit concentrations were carried out. The achieved results were compared with the thermodynamic modelling of the ternary systems (ThermoCalc, Pandat, MTDATA and databases CALPHAD, COST 531 and COST MP0602). Electrical resistivity, density, magnetic susceptibility and wettability of solders were measured as well.

The Sn–Zn–Al alloys are one of significant candidates in the proposal of alternative lead-free solders for higher temperature soldering. This paper deals with the study of the aluminum–tin–zinc system. Twenty Sn–Zn–Al alloys together with six binary Sn–Zn alloys were prepared and studied experimentally. Alloys were prepared from pure Sn, Zn and Al (melting and cooling in a vacuum resistance furnace). The specimens were studied metallographically including the micro-hardness measurements, complete chemical analysis (ICP-AES, OES), X-ray micro-analysis of alloys by SEM and EDX in order to determine the composition and identification of individual phases. Significant temperatures and enthalpies of phase transformations were determined by DTA. After long-term annealing of selected alloys in vacuum followed by quenching the structural and chemical microanalyses of the present phases and their limit concentrations were carried out. The achieved results were compared with the thermodynamic modelling of the ternary Sn–Zn–Al system (computer programs THERMOCALC, MTDATA, PANDAT and databases CALPHAD, COST). Electrical resistivity, density, magnetic susceptibility and wettability of Sn–Zn–Al solders were measured as well.

The influence of rare earth metals (REM) addition on solidification structure of the low-carbon 42CrMo4 steel was investigated. Alloys were prepared by means of a centrifugal casting. The addition of cerium, praseodymium or mischmetal in the steel produced greatly improved solidification structure with a suppressed columnar grain zone, finer grain size in the equiaxed grain zone. The additions occurred in the steel bath in the form of REM oxide and/or oxide-sulphide inclusions and as dissolved REM segregated along with other elements at prior grain boundaries and interdendritic spaces. Microstructure (light microscope), SEM/EDX chemical microanalysis, and TOF-SIMS analysis – mapping of elements in the structure of alloys were obtained.

The results of an experimental study on influence of cerium addition on structural characteristics of 42CrMo4 steel are presented. Alloying with cerium was carried out using profile filled with powdered mixture of mischmetal. The samples were taken from two ingots cast in the VHM's steelworks with standard time of casting of about 14 minutes. Three steel bars from one of the produced ingots were prepared by forging. Chemical composition, macro- and microstructure, X-ray EDX chemical microanalysis, hardness of the all steel samples were obtained. Cerium addition resulted in the formation of micrometer size inclusions which can be utilized for controlling the grain size structure of steel castings. The majority of the particles have settled at the bottom part of the casting, indicating that the convection flow during solidification was very weak. The cerium addition slightly diminished hardness of the steel. A segregation phenomenon causing inhomogeneous distribution of cerium over entire volume of as-cast samples after relatively rapid crystallization process of the steel was revealed.

Thirteen ternary Al-Sn-Zn alloys with various contents of elements were prepared experimentally. The alloys were studied metallographically after casting and after long-time annealing in vacuum. X-ray structural and chemical micro-analyses (EDX, WDX) of the phases were measured. Temperatures and latent heats of characteristic phase transitions (liquidus, solidus, invariant reactions etc.) were obtained with use of the DTA method. Experiments were performed with SETARAM SETSYS 18TM experimental laboratory system for thermal analysis. Resulting experimental data were compared with data of known Sn-Zn binary system and Al-Sn-Zn ternary system. For the modelling of phase equilibria from critically assessed data software packages were used MTDATA, PANDAT and Thermo-Calc. Experimental results of the studied alloys from the point of view to measured structural and physico-chemical characteristics were compared with thermodynamic calculations. The result will be present in the form of isothermal and poly-thermal sections of the Al-Sn-Zn ternary system.

Theoretical and experimental study on influence of addition of selected non-ferrous metals and mischmetal on microstructural characteristics in special Cr–Mo steels were performed. A number of binary iron-admixture systems were theoretically studied and equilibrium distribution coefficients were recently computed. Cast samples of Cr–Mo steel with Ce addition were prepared using a plasma furnace and an induction furnace. Microstructure investigations of the cast steel samples revealed that the addition of rare-earth metals (REM) to liquid steels brought about formation of cerium oxy-sulfide inclusions prior to steel solidification. The inclusions have acted as active heterogeneous nucleation sites for grain nucleation during solidification processes and grain structure in final as-cast microstructure was remarkably refined. The performed REM addition produced positive effects on grain structure of the cast steel samples.

Problems of reactive diffusion at the interface solid phase - melt were studied theoretically and experimentally. A theoretical description of the kinetics of dissolution of the solid phase in the melt is presented for the case of planar dissolution. The main intention was to study experimentally the copper dissolution in melts of various solder alloys and the related reactive diffusion. We used pure Sn and Sn-Cu, Sn-Ag-Cu, Sn-Sb, Sn-Zn alloys as solder materials. Experiments aimed at the study of a Cu plate dissolving in the solder melt were carried out at various conditions. Concentration profiles of elements and thickness of layers of phases were determined by SEM and X-ray microanalyses (WDX, EDX) of specimens after their heating.