Papers by Author: Witold K. Krajewski

Abstract: Doping high-zinc aluminium alloys with Ti builds in-situ composites reinforced with ternary aluminides Ti (Al,Zn)₃ with a significantly grain-refined matrix. In a series of studies, Ti was introduced with Al-6 wt% Ti (AlTi6) and Zn-4 wt% Ti (ZnTi4) master alloys in amount to contribute about 3 wt% Ti in the examined alloys. The alloy microstructure has been studied using light microscopy, SEM / EDS and XRD measurements. The observed significant refinement of the alloys matrix should lead to improvement in ductility, while the in-situ reinforcement should improve tensile strength and wear properties.

Abstract: Structural modification of ternary aluminium – zinc – coper alloys influences their wear properties. In a series of studies, Al – 30 wt. % Zn – 3 wt. % Cu alloy (Al-30Zn-3Cu) has been doped with 1 wt.% Mn introduced with AlMn-based master alloys. The alloy microstructure and mechanical properties have been studied using light and SEM/EBSD microscopy, and measurements of wear resistance and dimensional changes. Reducing Cu content to 3 wt.% and doping with 1 wt.% Mn allows obtaining alloy of significantly refined grains, improved wear resistance and preserved high dimensional stability.

Abstract: Microstructure and mechanical properties of NiAlV alloys of the composition belonging to the pseudo-binary Ni₃Al-Ni₃V cross-section were investigated. The samples were prepared by the cold crucible levitation melting (CCLM) and by re-melting and crystallizing in the small volume copper mould. The phase composition of the samples, with should result from the eutectoidal decomposition was not found. Instead the Ni₃(Al,V) and Ni(Al,V) solid solution or seldom disordered solid solution were retained due to the relatively high cooling rates. In the compression test the NiAlV alloys crystallized in the copper mould revealed high ductility and strength.

Abstract: The paper brings data about heat balance of the killed steel ingot head. The balance is obtained on basis of the temperature measurement in the system: ingot body - ingot head - ingot mould - insulating sleeves – radiation shield - ambient. The measurements were performed using model sys-tem (1:5) of the 20000 kg flat ingot. The balance shows that about 86% of the heat issued during solidification of the ingot head is transferred to the ingot mould through the insulating sleeves. In order to decrease this heat, insulating sleeves of low thermal conductivity are required, which should allow reducing dimensions of the ingot head and increasing the metal yield.

Abstract: The presented work is aimed at determining thermal diffusivity, thermal conductivity and heat capacity of insulating sleeves used in Polish metallurgical/foundry practice. On basis of the theory elaborated in [1] the mean values of thermophysical properties for temperatures range of about 150-1000 oC were obtained. The results obtained during the examinations presented in the paper can be helpful when formulating boundary conditions during the computer aided simulation of the processes of heat and mass transfer in the system: casting (ingot) – mould riser (ingot head) – ambient, which uses the investigated insulating sleeves [2, 3]. The method of determining thermal properties can be also used for other foundry materials, e.g. sands or cores.

Abstract: The atoms site preference in the Al₃Ti-Zn system has been studied using H. Rietveld method. The L12 Ti(Al, Zn)₃ particles evolve in a ZnAl25 melt from the L1₂TiZn₃ particles in the ZnTi4 master alloy. It is found that Zn is replaced by Al during the transformation TiZn₃ → Ti(Al, Zn)₃. In the evolving fcc L12 Ti(Al, Zn)₃ phase Ti occupies (0, 0, 0) position while Al and Zn occupy (0, 0.5, 0.5) position, similarly to Al and X in the Al₃Ti-X systems, where X = Ni, Cr, Mn, Cu, Ag, Pd [1, 2].

Abstract: The microstructure of cast Zn-25wt%Al alloy inoculated by addition of a Zn-4wt%Ti master alloy (ZnTi4) has been studied using scanning electron microscopy and electron back-scatter diffraction (EBSD). It is found that Ti(Al,Zn)₃ particles act as nucleation centres for grains of the primary solid solution of Zn in Al (α' phase). The Ti(Al,Zn)₃ particles evolve in melt from the TiZn₃ particles in the ZnTi4 master alloy. EBSD shows that α' phase dendrites are in the same crystallographic orientation as the Ti(Al,Zn)₃ particles on which they nucleate. It is also found that some of the Ti(Al,Zn)₃ particles do not have any well-defined crystallographic orientation relationship with the α' phase. These particles were probably pushed and then engulfed by growing α' grains which had already nucleated on other particles.