Papers by Keyword: Phases

Abstract: Ti-based intermetallic compounds are characterized by low machinability, therefore, to obtain accurate dimensions and shape of the surface grinding and Wire EDM are used. The unique properties of NiTi intermetallic alloys are largely influenced by structural phase transformations and variations in microhardness caused by processing accompanied by thermal phenomena. Having an understanding of the physics of the process, it is possible to counteract negative effects, which helps to preserve thermomechanical properties of the final NiTi products. Accumulation of knowledge about the quality of processing with various abrasive tools is part of the larger research presented in this article. Samples of titanium nickelide with a temperature A_f=+25 ⁰С were abraded with ordinary and high porosity SiC wheels. The article studied phase transformations using X-ray diffraction analysis and microhardness. The experimental data were processed using mathematical statistics. X-ray diffraction patterns and microhardness analysis showed that a significant effect on the structural transformation and corresponding increase in microhardness is exerted by grinding with green SiC wheels with normal porosity caused by an increased thermal effect on the surface. Simultaneously, the impact of Wire EDM process on microhardness in preparing workpieces for grinding was evaluated. It was established that grinding of Ti-based intermetallic compounds with memory effect should be performed by SiC wheels with an open structure of high porosity.

Abstract: The paper gives an assessment of the possibility of using local mineral raw materials to create foundry alloys that are operated under natural low temperatures. The feasibility of using iron ores of the Lena ore field (Yakutia, North-East of Russia) for the development of new cold resistant and high strength steels is analyzed. The chemical composition and microstructure of the melted alloy were studied. Also the phase composition of the alloy by X-ray diffraction method is analyzed. The alloy with respect to the chemical composition is naturally doped Mn, W, V, which are well preserved in the preparation of the iron semi-finished product by direct reduction technology. The obtained sample after processing has acquired a uniform structure, typical for tool carbon steel after forging. Elemental analysis data indicate a uniform distribution of iron, carbon, manganese, sulfur and phosphorus in the alloy.

Abstract: Triaxial ceramics are multiphased materials produced from natural raw material. That a small modification as much concerning in the composition from raw material a ceramic mass, may change several properties from ceramics. Thus, was included into the ceramic mass Al₂O₃ and Fe₂O₃, however both originated from pectin citrus plus salt the intended respective metal source. These oxides have a particular physical characteristic as high softness and high porosity. In addition to the ceramic mass containing 10% of clay, 25% kaolin, 35% feldspar and 30% of alumina (Ind. Alcoa) was inserted 6% of Fe₂O₃ and the full replacement of commercial alumina by Al₂O_3(pec). The result from these oxides are satisfactory mainly. Influencing in thermal contraction, in the reduction of the residual porosity and changing the final color inthe product.

Abstract: Advantage of Al-Mg₂Si metal matrix composite (MMC) is due to the particulate reinforced Mg₂Si in the Al matrix that has improved mechanical properties of the in situ composite. In particular, the composite has been chosen as the structural material for automotive and aerospace components. The hypereutectic Al-Mg₂Si composite should be comprised of two morphologies, namely primary Mg₂Si and pseudo-eutectic Al-Mg₂Si phase. However, as-received commercial Al-20Mg₂Si-2Cu in situ composite contained a wide range of elements that affect the resultant microstructure of the in situ composite. In fact, four different morphologies have been identified in the in situ composites. The first phase is dark facet primary Mg₂Si particles, surrounded by pseudo-eutectic Al-Mg₂Si phase in lamellar structure. Along the eutectic boundary is the formation of needle-like Al₅FeSi intermetallic and the phase is surrounded by Al₅Mg₈Si₆Cu₂+Al₂Cu as last phase nucleated. Optical micrograph, SEM imaging, EDX analysis and elemental mapping have revealed these phases correspond to shape of morphologies and respective molecular compound.

Abstract: According to literature, a High Entropy Alloy (HEA) has close to equimolar composition and forms mostly fcc and/or bcc phases as well as solid solutions, i.e. the elements take random occupations on available lattice sites. In this paper we report studies on HEAs of the CoCrFeNiPd system. All alloys have been found to, contrary to what has been reported earlier in literature, consist of four different phases, three of them of fcc type. The relative amounts of the different phases depend on Pd concentration. The different phases seem to be fully interconnected.

Abstract: This research penetrated on the transformation of phases in the microstructures of austempered ductile iron with respect to different austempering holding times. Ductile iron samples were constituted in form of Y block double cylinder with dimension of 300m x Ø25mm through CO2 sand casting process in 60 kg capacity furnace. Austempering process were conducted by first austenitizing the samples at temperature of 900°C for 1 hour. The process continues by rapidly quenched the samples inside salt bath furnace at 350°C for three different holding times of 1 hour, 2 hours and 3 hour. Samples were then taken out and cooled at room temperature. Samples were then prepared in accordance to standard metallographic process and observed using Tabletop Scanning Electron Microscopy (SEM) model Hitachi TM3000. Phases were then verified through X-Ray Diffraction analysis (XRD) test by Rigaku diffractometer. The phase structures of as cast ductile iron mainly consisted of graphite nodules embedded in ferrite and pearlite phases Austempering the samples for 1 hour holding time promoted the structures of ferrite platelets and bainitic structures surrounding the graphite. Longer austempering holding times resulted in coarsening of the ferrite platelets structures and transformation from lower bainite to upper bainite structures.

Abstract: This article describes the flexibility and the potentials of the most important finish for aluminium-based materials. After a suggestion for the classification of anodizing processes, the historical development of the electrolytic anodic oxidation (EAO) and the plasma-electrolytic anodic oxidation (PAO) are presented. In the following section the focus is given on selected topics concerning the process parameters, the microstructure including the layer composition and properties. The variability of the anodizing process parameters and the used materials provide this variety of application. Furthermore, both differences and similarities of the EAO and PAO processes are shown. The conclusion of this review emphasizes that there is still some need for further research especially in the interaction of the process, the formed microstructure and the resulted properties determining the final application. Hence new possibilities for this surface treatment will be open.

Abstract: The role of bismuth (50 to 9000 ppm) and calcium (50 to 200 ppm) additions on the microstructural characteristics in Sr-modified 319 alloys (with/without 0.4 wt% Mg addition) were investigated using optical and electron microscopy, and image analysis. It was found that the modification effect of Sr continuously diminished with Bi addition up to ~3000 ppm Bi; further Bi addition led to the modification of the Si particles due to the presence of Bi. In the Ca-containing alloys, a coarse eutectic Si structure resulted with Ca additions of 50 ppm, due to the formation of Alx(Ca,Sr)Siy compounds. Increased Ca additions (up to 200 ppm) did not alter the Si particle size. The Alx(Ca,Sr)Siy phase particles appeared in rod-like form in the Sr-modified alloys and in plate-like form in the 319+0.4 wt% Mg alloys. MgO, Al2O3, and AlP particles appear to act as nucleants for the precipitation of the plate-like Alx(Ca,Sr)Siy phase.