Solid State Phenomena Vol. 197

Abstract: The main objective of this study was to analyze the evolution of the microstructure (morphology, composition and distribution of intermetallic phases) in the 2024 aluminium alloy cooled with different cooling rates after solidification process. A few techniques: optical light microscopy (LM), scanning (SEM) electron microscopy combined with an energy dispersive X-ray microanalysis (EDS), X-ray diffraction (XRD) were used to identify intermetallics in the examined alloy. The results show that the microstructure of 2024 aluminum alloys in as-cast condition consisted following intermetallic phases: Al2Cu, Al2CuMg, Al7Cu2Fe, Al4Cu2Mg8Si7, AlCuFeMnSi and Mg2Si.

Abstract: Properties of the alloys Zn-Al-Cu can be improved by partial or total replacement of copper with silicon. The previous studies of the current authors have shown that in alloys with silicon addition its precipitates are not evenly distributed. This can lead to uneven wear of parts made of the Zn-Al-Cu alloy. The study of phenomena occurring during the crystallization of the ZnAl40Cu3Si alloy with ATD methods have shown that silicon does not form compounds and solid solutions with Zn and Al. In the examined alloy silicon is released as the primary even before the actual solidification of dendrites. It is not possible to reduce the uneven distribution of precipitates through heat treatment. Therefore it is important to assure the uniform distribution of precipitates of silicon already on the crystallization stage, e.g. by addition of rare earth elements. The purpose of this study was to determine the effect of rare earth elements on the morphology of silicon precipitates in the ZnAl40Cu3Si alloy. The investigated material were alloys containing 40 wt% Al, 3 wt% Cu and 1.5 wt% Si (Zn - remaining). The samples have been taken from the top, middle and bottom of the ingot. In order to determine the morphological characteristics of silicon precipitates a computer program Met-Ilo developed in the Department of Materials Science, Silesian University of Technology was used. Changes of the volume fraction and shape of precipitates in particular areas of the ingot were the subject of analysis in this work.

Abstract: The objective of the study as described in this paper is to analyse the effect of processing conditions as: volumetric content of TiB2 powders and the time of milling them on the parameters of microstructure of particulate composite with a SiC matrix and 10 or 20 vol.% of the TiB2 as dispersed phase. From the initial research conducted by the authors, as well as from the data contained in the reference literature, it is known that the SiC-TiB2 composite is a potential material to be applied in the manufacture of cutting tool inserts. To manufacture composites, SiC powders (Starck, UF-15) and TiB2 powders (Momentive, HCT-30) were used; they were milled for 15 or 30 h in a vibrating-rotating mill with silicon carbide balls as grinding media. The SiC-TiB2 composite was manufactured using a hot pressing method under the following conditions: temperature: 2120 oC; pressure: 25 MPa; and sintering time: 30 min. Under the stereological analysis of SiC-TiB2 some selected microstructural parameters were measured, i.e.: volume fraction of TiB2, average size of TiB2 particles, mean diameter of particles (D), shape factor of TiB2 particles, α, as well as NA and NV parameters that determine the quantity of TiB2 particles contained in the composite. Computer-aided analysis of microstructure of the SiC-TiB2 composites and analysis of results of measurements of mechanical properties of these composites prove their the microstructure and properties depend on the volumetric content of TiB2 dispersed phase, and this dependence is significant.