Krzysztof Ziewiec

Formation and Properties of Amorphous/Crystalline Ductile Composites in Ni-Ag-P Immiscible Alloys

The aim of the work was to investigate the influence of silver as a modifying constituent on structure formation in Ni-P based glass forming matrix. Nickel-phosphorus-based Ni80P20, Ni78Ag2P20 and Ni76Ag4P20 alloys were prepared from 99.95 wt % Ni, 99.95 wt % Ag, and Ni-P master alloy. The alloys were melt-spun in helium. The microstructure of the melt-spun ribbons was investigated by XRD, a light microscope and a transmission electron microscope. Then the tensile tests were performed. The alloys with silver show lower tensile strength with respect to the fully amorphous Ni80P20 ribbon. The ductility of the amorphous matrix melt-spun Ni78Ag2P20 and Ni76Ag4P20 alloys was improved by addition of silver forming fcc-Ag precipitates in comparison with Ni80P20amorphous alloy. SEM observations of the fracture surfaces show different character of the fractured samples. The pattern and the number of the crack lines changes, depending on the silver content. For the fully amorphous Ni80P20 alloy simple brittle cracks are observed, however the alloys with silver content show more developed surfaces near the fractured regions and form crack lines arranged 60° with loading direction.

Properties and microstructure of the (Fe, Ni)-Cu-(P, Si, B) melt-spun alloys.

The work presents the microstructure characterization of the new (Fe, Ni)–Cu–(P, Si, B) melt‐spun glass forming alloys investigated by means of transmission electron microscope. The results are compared with the data obtained by other complementary methods such as XRD and Mössbauer spectroscopy. The phases occurring during the crystallization of the glassy matrix are identified and characterized in terms of a long‐range order and a short‐range order. The thermal stability of the alloy is characterized by differential scanning calorimetry. The study describes the mechanical and magnetic properties of the new alloys at room temperature as well as characteristics resulting from heating the as‐cast melt‐spun alloy at elevated temperatures. The changes of the properties of the alloy at elevated temperatures are correlated with the microstructural changes.

Microstructure of the Fe-Ni-P Melt-Spun Ribbons Produced from the Single-Chamber and from the Double-Chamber Crucibles

The aim of the work was to investigate the influence of the processing on the final microstructure of the melt-spun Ni-Fe-P ribbons. The melt-spinning was carried out in two ways. For the first one the alloy was molten in a simple single-chamber crucible and for the second one double-chamber crucible was used. The chemical composition of the alloy molten in the single chamber was Ni40Fe40P20. The two component melt-spinning was made starting from the Ni80P20 and Fe80P20 alloys. All of the three alloys were molten in titanium gettered argon atmosphere starting from 99.95 wt % Ni, 99.95 wt % Fe, Ni-P and Fe-P master alloys in the arc melting furnace. The alloys were melt-spun in helium. The phase composition and the microstructure of the melt-spun ribbons were investigated by X-ray diffraction (XRD), a transmission electron microscope (TEM), respectively. The fracture of the specimens were observed with use of scanning electron microscope (SEM). SEM observations of the fracture surfaces show different character of the fractured samples.

Devitrification and Nano-Crystalline/Amorphous Composite Formation in Ni64Cu9Fe8P19 Glassy Alloy at Elevated Temperatures

The Ni64Cu9Fe8P19 alloy was prepared using 99.95 wt % Ni, 99.95 wt % Cu, 99.95 wt % Fe and Ni-P master alloy. The melt spun ribbon in as-cast state was characterized using of transmission electron microscope (TEM) and X-ray diffraction (XRD). The amorphous alloy was subjected to DTA and resistivity measurement in order to determine the thermal stability at elevated temperatures. The melt spun ribbon had a negative TCR=-2.23·10-6K-1 that is stable up to the Tg-dep=511K. At higher temperature Tg-int=560K the relative resistance starts to decrease and between 573K and 591K the rate of the decrease reaches TRC=-480.096 K-1. After the heating cycle to 633K, during cooling the alloy has a positive TRC=6.03·105 K-1. DTA curve presents the three exothermal stages with the onsets and peak values at I: Tx1=564K and T1=611K, II: Tx2=655K and T2=662K, III: Tx3=697K and T3=715K, respectively. The melting stage can be characterized by endothermic peak with Tm=1149K and Tl=1174K. On the base of the measurements the amorphous alloy was heated to the temperatures where subsequent transformations occurred. TEM study delivered information about formation of the M3P type tetragonal phosphide (a=9.040Å, c=4.462Å) nanocrystals within the amorphous matrix after the first stage of crystallization.

Positron annihilation and tribological studies of nano-embedded Al alloys

Positron annihilation studies of aluminium alloys with nanodispersions of insoluble elements, i.e., In, Sn, Pb and Au were reported. The alloys were obtained using a rapid solidification process. For all alloys, except that with Au, the average diameter of nanoparticles in aluminium matrix was 100 nm, and variance of the size distribution was above 50 nm. Positron annihilation studies reveal the presence of monovacancies or divacancies, which were located at the interface between nanoparticles and the matrix. In the as-cast reference pure aluminium sample as well as the aluminium and gold alloy dislocations were identified as well. The isothermal annealing of the obtained alloys and measurement of the annihilation characteristic, i.e., S-parameter, allow us to determine the activation energy of grain boundary migration, which for the alloys was higher by the factor of four than for the reference sample. The measurements of friction parameters for the alloys confirmed the results reported by the other authors that, the friction coefficient was lower by the factor of about two and the specific wear rate was by the factor of about fifty higher than the reference sample. The present study confirmed the attractive positron affinity of the nanoparticles of In, Sn, Pb and Au compared to aluminium matrix.

Structure and Properties of the Melt-Spun Fe41Ni39P10Si5B5 Alloy Heat Treated at Elevated Temperatures

The aim of the work was to provide information on structure development and change of properties at elevated temperatures in Fe41Ni39P10Si5B5 amorphous alloy. The alloy was characterized by X-ray diffraction. The changes of properties were characterized with use of dynamic mechanical thermal analysis (DMTA) and the resistivity measurements at elevated temperatures. The microstructure of the melt spun ribbon was investigated with use of transmission electron microscope (TEM) at different stages of phase transformations after heating to different temperatures. The initially amorphous structure undergoes phase transformations due to glass transition and crystallization of the alloy. The appearance of glass transition region results in decrease of storage modulus and in a reversible change of temperature coefficient of resistivity (TCR). The phases are characterized with use of TEM. The crystallization was found to have the two stages. Formation of bcc crystals and Ni12P5 is followed by transformation of the products into fcc crystals and Ni3P. Temporary changes of the storage modulus and elongation of the sample suggest formation of hard phases during crystallization.