Papers by Keyword: Intermetallic Phases

Abstract: The operational reliability of rolling production tools depends on the heat resistance of the steel from which they are made. To increase the performance of the rolls, a hardening surfacing with wear-resistant alloys is used. The effectiveness of the applied hardening technology depends on the functional characteristics of the deposited metal. The aim of the work is to study the tempering resistance in the state after heat treatment of the deposited steel (Fe-C-Ni-Mn-Mo-V-Ti-Nb system). It was established that the thermal resistance coefficient of steel 15N8G6M3FTB at temperatures from 650 to 800 °C varies from 0.76 to 0.66, which exceeds the heat resistance of steel 30Kh2V8F by 1.5 times. It is shown that in the fine structure of such a metal after tempering at 800 °C, large amounts of finely dispersed precipitates are observed. These precipitates have a rounded shape up to 100 nm in size and belong to the Laves phases - Fe₂Mo, Fe₂Nb, and Fe₂Ti. The obtained high heat resistance values of 15N8G6M3FTB steel make it possible to recommend it for creating surfacing materials. Flux-cored wire based on this steel can be used for hardfacing hardening of tools operating at temperatures up to 800 °C inclusive.

Abstract: The article deals with the use of newly developed hypoeutectic silumin type AlSi9NiCuMg0.5 in manufacturing practice. This type of silumin has been produced and patented by a team of workers at the Faculty of Mechanical Engineering at the University of J. E. Purkyně in Ústí nad Labem, Czech Republic. This alloy was developed and tested directly for the technical practice where the special mechanical and technological properties of the alloy were required [1]. The experiment, which is presented in this paper, focuses on the cause of the castings cracking in operating conditions. When the material was put into practice, castings were produced and subsequently used for breaking and cracking across the entire casting section. AlSi9NiCuMg0.5 alloy castings were manufactured using low-pressure technology. The research is focused on the observation of the fracture surface, identification of microstructure of AlSi9NiCuMg0.5 alloy casting and determination of the chemical composition of structural components on the surface of fracture by EDS analysis. Fractional field research has measured the chemical composition and it has been compared with the required declared alloy. Increased iron content and associated intermetallic phases were identified in the alloy. Evaluating of the obtained results can identify the cause of the premature cracking of the castings made from the newly developed hypoeutectic silumin.

Abstract: Under the current conditions, the consumption of special purpose alloys or steels is growing. This is due to the development of the import substitution program. It should be noted, that such materials possess specific deformation behavior, which requires providing particular conditions of a hot rolling process. One of the characteristics of the deformation behavior is the narrow thermal plastic range. Therefore, it is necessary to conduct a hot rolling in several stages, which include interchange of heating and rolling processes. For the purpose to resolve the issue, the experience of the multilayer hot rolling of plates has been investigated where all advantages of this way of a hot rolling process were used. Based on the method of the multilayer hot rolling, the pack rolling has been developed which gives the possibility of production of hot-rolled plates from special purpose alloys or steels.

Abstract: The silicides and aluminides particles precipitation in near α-and two-phase (α + β) titanium – alloys has been investigated. It is shown that in Ti-Al-Si-Zr alloys three different types of particles are precipitated: (Ti,Zr)₅Si₃ (S₁), (Ti,Zr)₆Si₃ (S₂), (Ti,Zr)₂Si (S₃). The types of precipitated particles depend on the heat treatment modes and an alloying elements ratio. The investigation of silicide particles influence on the mechanical properties of the alloys has shown that silicides S₁ reduced viscosity characteristics. While silicides S₂ and S₃ were found to reduce the heat resistance due to the depletion of solid solution by Al and Si and to impede the formation of α₂ - phase particles. Microstructural investigation has been performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The orientation relationships between silicides and matrix phase were identified by electron diffraction. Based on obtained results the schematic TTT-diagram of intermetallic phases formation has been suggested.

Abstract: Within the scope of the Collaborative Research Centre (CRC) 1153 novel process chains for the production of hybrid solid components by Tailored Forming are developed at the Leibniz Universität Hannover. The combination of e. g. aluminium with steel allows to produce hybrid compounds with wear-resistant functional surfaces and reduced weight. In these process chains, joining takes place as the first step to produce hybrid semi-finished products by friction welding, cladding, ultrasonic assisted laser welding or co-extrusion, which are subsequently subjected to various forming processes such as forging or impact extrusion. The coaxially joined hybrid semi-finished components investigated in this work were produced by means of the lateral angular co-extrusion (LACE) process using the aluminium alloy EN AW-6082 and the case-hardening steel 20MnCr5. These semi-finished products shall be suited to produce hybrid bearing bushings by die forging in a subsequent process step. Initial investigations for the determination of the process parameters and the appropriate tool geometry were made using a steel rod. In future investigations, a steel tube will replace the steel rod in order to produce hybrid semi-finished products, which can be fully integrated into the process chain. The mechanical properties of the profile were determined at different positions along its length. For this purpose, the quality of the joining zone between aluminium and steel as a function of the profile position was examined by means of push-out tests. Moreover, the mechanical properties of the aluminium component’s longitudinal weld seam were determined by micro-tensile-tests.

Abstract: Present work is focused on study of the effect of Sr-modification (0 %; 0.03 % and 0.05 %) on the microstructure and mechanical properties of recycled AlSi8Cu2Mn cast alloy. For study and identification of intermetallic phases’ were utilized standard, colour and deep etching in order to reveal the three-dimensional morphology of the silicon particles and intermetallic phases. For element composition of the specimen was used X-ray analysis. Finally, the effect of modification on silicon morphology, mechanical properties (UTS, ductility, hardness and impact energy) was examined.The results show that the addition of Sr into AlSi8Cu2Mn cast alloy should act as a modifier, so it supposes to change the eutectic Si-morphology. However, its effect as a Si-modifier is not as significant as we have expected. Strontium refined and changed morphology of Si and thereby improves mechanical properties, first of all ductility and impact energy.

Abstract: Aluminum and titanium alloys are among the most important and the most frequently used construction materials due to their physical and mechanical properties. Especially in the automotive and aerospace industry these materials allow to reduce the weight of structure which leads to reducing fuel consumption and environment pollution. These materials are often used together which leads to problems with junction between these materials. In addition to the mechanical joints, there is an effort to produce quality welded joints. Series of works focused to welding of Al/Ti joints by conventional and nonconventional welding methods were published [1, 4, 5, 6, 7]. By reduction of dimensions of molten material is possible to reduce the amount of emerging intermetallic phases and welding defects. Electron beam welding appears as suitable method for welding Al/Ti joints because it allows production of very narrow welds. The benefit is also necessity to perform electron beam welding in vacuum which is required for decrease energy losses of incident beam and simultaneously prevents reaction of molten metal with ambient atmosphere. This paper is focused to determine of appropriate parameters for electron beam welding of heterogeneous welds of titanium alloy Ti-6Al-4V and aluminum alloy 6061. Metallographic evaluation, analysis of chemical and phase composition were performed on the test welds for purpose to describing present phases. On the selected welds was evaluated the influence of intermetallic phases on the mechanical properties. The obtained results will be used for further experiments focused to optimize the process of electron beam welding of Al/Ti alloys.

Abstract: Al containing intermetallic phases have been evaluated in various bcc and fcc steels. Attractive application options have been derived for hot working tools steels with respect to a reduction of resource critical alloying elements and in cold formable steels by the combined density reduction and strength increase.

Abstract: The implicit difference scheme has been suggested for the solution of diffusion-kinetic problem describing the ion implantation by intermetallic phase formation. The model corresponds to irreversible conditions and includes finite relaxation times for mass fluxes. The linear difference equations are solved by double-sweep method. The result illustrates the convergence of difference scheme at variation of its parameters. Qualitative picture of phase evolution in the surface layer is obtained different for problem with finite relaxation times and for zero relaxation times.

Abstract: This paper presents the results of an investigation using transmission electron microscopy concerning the structure of AlSi7Cu2 cast aluminium alloy after alloying and remelting with a high power diode laser (HPDL). In particular, the changes in the particle/precipitation type, size and shape were determined, concerning especially the SiC and TiC particles added to the initial material. The aim of this work was also to present the laser treatment technology which will be used for further alloying and remelting with ceramic powders – especially carbides and oxides. The innovatory arrangement of this investigation is based on the mixing of two different powders, which were fed simultaneously to the laser-treated aluminium surface. The overview focuses on the laser power required to achieve good layer hardness to prevent hot work tool steel from losing its work stability and to make the tool surface more resistant to action in external conditions.