Papers by Keyword: Intermediate Phase

Abstract: The study deals with the material survey of a raw material, bronze axe and sickle from the Late Bronze Age. Artefacts were chosen from a set of about thirty objects, which were found in a ceramic pot near to Křenovice in the South Bohemia. The ancient technology of the axe and the sickle production was determined by the evaluating of structural properties using prepared metallographic sections. The chemical composition of a metal matrix and intermediate phases were determined using a scanning electron microscope with an EDS analyzer and X-ray fluorescence. The corrosion products of the artefacts were analyzed by X-ray diffraction. The results showed that the axe was made from partly wrought bronze (CuSn10) processed by subsequent recrystallization annealing. The bronze sickle (CuSn11) was a cast without any further mechanical processing or heat treatment. The material of the a raw material was found to be an arsenical copper alloy (CuAs1), which was probably used as a starting material for the bronze alloy production.

Abstract: The impact welding was performed for several kinds of metal plate couples. The joint interface exhibited a sinusoidal wave form when two metal plates with the same or similar density (e.g. Al/Al, Cu/Cu and Cu/Ni) were impact-welded by high-speed oblique collision. In contrast, as for dissimilar metal plate couples with large density difference such as Al/Cu, an asymmetric wavy interface was obtained. In order to make clear the reason for morphological difference, a computer simulation of the collision behavior was performed using SPH (Smooth Particle Hydrostatic) method. The simulation results revealed that the wave form was controlled by the interaction between the emitted metal jet and metal plate surfaces ahead of the collision point. For Al/Al and Cu/Ni, the emitted metal jet hit each surface alternatively and this resulted in symmetrical wavy interface formation. While, for Al/Cu, the metal jet was emitted to the direction parallel to the Cu plate, and the interaction took place between the metal jet and the Cu plate surface. The metal jet emission and wavy interface formation mechanism were also investigated.

Abstract: On the basis of the discovered phenomenon of phase and structure formation of metallic materials being electrodeposited through a stage of liquid state it was predicted and experimentally proved the following: a) formation of intermediate phases in the form of intermetallides in electrodeposited metallic alloys during the electrochemical crystallization of a liquid phase of two metals of different valences; b) formation of intermediate phases with complex crystal lattices in the form of carbides during solidification of a liquid phase of a transition metal alloyed with carbon; and c) formation of eutectics in electrodeposited metallic alloys as a result of decomposition of a liquid phase into two separate solid phases during its solidification. Intermetallides Cu5Zn8 and Cu6Sn5 in electrodeposited alloys of Cu-Zn and Cu-Sn systems, carbides Fe3C and Cr3C2 in electrodeposited iron and chromium alloyed with carbon, and eutectics in electrodeposited alloys of Sn-Zn and Pb-Cu systems were found.

Abstract: The mechanical properties and the oxidation resistance of -TiAl at elevated temperatures have to be improved to be used in the severe environmental conditions. It has become clear that the addition of more than 4at.%Ta in TiAl demonstrates a superior oxidation to the other TiAl-X compounds, according to the weight gain results of cyclic oxidation experiments at 1173 and 1273K. Oxidation behaviors are strongly influenced by the Ta concentration in TiAl. XRD, SEM-EDS, and TEM-EDS observations have been carried out to determine the microstructures and the surface compositions of multi-layered oxide scales. It was revealed that a protective intermediate phase simultaneously formed between the substrate γ-TiAl and the oxide scale layer. The Ti53Al32Ta15 ternary compound exists as an equilibrium phase at 1373K, according to the published Ti-Al-Ta ternary phase diagram. This ternary compound can work as a barrier to some extent. It contributes to decelerating the diffusion of Ti and Al atoms and to decreasing the oxidation rate. The formation mechanism of the intermediate phase has been discussed in conjunction with diffusion in TiAl.

Abstract: To respond the need of industries to the new materials with higher specific modulus and lower density than those of the older Al alloys, aluminum- lithium alloys have been invented and improved. Aging process is one of the most important methods to improve the mechanical properties of aluminum- lithium alloys which are in the heat treatable category of aluminum alloys. Low temperature and natural aging processes cause the "short range diffusion" of Cu atoms in the aluminum and the formation of the GP zones. In this research, stability of GP zones and the effects of these areas on physical and mechanical properties of AA2090 alloy were investigated by hardness, electrical resistance, DSC (differential scanning calorimetric) and tensile tests. Results show that endothermic effect in the DSC diagrams of AA2090 alloy at 180°C to 240°C can be related to the enthalpy of GP zones dissolution. Formation of GP zones in the structure increases hardness, tensile strength and electrical resistance of Al- Li C u (2090) alloys.

Abstract: Intermediate phase growth in Mg-Al diffusion couples were studied with different intensity of a strong static magnetic field from 0 to 10 Tesla. Thickness measurement of the intermediate phases (Mg17Al12 and Al3Mg2) shows that with the increasing of magnetic field intensity, the growth rate of both intermediate phases is retarded. The decrease of the phase growth rate is ascribed to the suppressed Al, Mg atom interdiffusion in the diffusion couple under the static magnetic field. It is also found that the orientation relationship between couple interface and magnetic field direction has no influence on the growth of intermediate phases.

Abstract: Application of magnesium alloy is restricted by its bad formability and low corrosion resistance. In order to resolve these problems, rolling-bonding has been tried as a new method. Pre-heating, rolling and annealing were used in the process of bonding, and aluminum cladding magnesium alloys obtained. The effects of many parameters in the processes of pre-heating, rolling and heat-treatment on bonding strength have been analyzed, and the mechanism of rolling-bonding been studied. It was found that intermediate phase played an important role in the bonding. Good bonding of aluminum cladding magnesium alloys achieved after annealing at 200oC for 1 hour.

Abstract: BaTiO3 powder was synthesized from BaCO3 and TiO2 using a domestic microwave oven. The samples were synthesized under different temperatures with various holding times. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the phase compositions and morphologies of the result samples. The main phase obtained at 950°C was BaTiO3, and the intermediate phases Ba2TiO4 and Ba4TiO9 were also detected. The pure, well-crystallized BaTiO3 powder could be obtained at 1050°C within 10 minutes and the particle size ranged from 300~500nm. In comparison with conventional synthesis, faster speed and finer grains could be achieved through microwave heating.