Papers by Keyword: Remelting

Abstract: The most popular spraying technologies include: flame spraying, arc spraying and plasma spraying. Spraying technologies allow for the formation of coatings with a desired chemical composition and thickness. However, such coatings characterize by numerous imperfections associated with the nature of the process itself. It is obvious that some of imperfections in thermal spraying coatings can be eliminated by choosing the right parameters of the process. However, in order to improve the properties and eliminate material discontinuous, it is necessary to conduct the remelting process. Research in most cases, showed that the reduction of porosity and simultaneous increase in hardness are possible only by remelting the coating using different heat sources. By adjusting the technological parameters and remelting speed, it is possible to precisely control the depth of the remelted material and thus the properties of final coatings. The paper presents the remelting processes of thermal spraying coatings in relation to technologies, properties and applications.

Abstract: The investigation results on the problem of the reliability of high-strength low-carbon maraging steel products have been generalized. The influence of a method for remelting on the reliability behavior is shown and the ways for the reliability behavior improvement are suggested. The study of the reasons for decreasing KCU during heat treatment shows that in addition to the precipitation of phases causing brittleness at cooling, chromium zones at heating, and formation of chemical and structure inhomogeneity in the two-phase region, the main reason is the remelting method with the parameters which predetermine the variation in grain size in the structure, a small number of interstitial elements (IE), retained austenite in the structure, and lower level of KCU of the steel prepared by VAR both after quenching and after TST. Shows influence of the quenching temperature on the amount of retained austenite and level of impact strength (KCU), of the time of aging on the work of the crack development (KCV) at the temperature of maximal development of brittleness in steel 08Cr15Ni5Cu2Ti and on the position of brittleness transition temperature prepared by ESR and VAR. After cooling down to the liquid nitrogen temperature, the VAR-steel is less liable to brittle fracture after maximal strengthening aging and more reliable after 1.5h-aging (KCV is twice as much as that in ESR-steel despite the low KCU level). The science-based regimes are developed for stamped semi-finished items from steel 08Cr15Ni5Cu2Ti allowing guaranteeing the proper quality and reliability of functioning of the items made from them.

Abstract: The paper presents the effect of alloying with WC and TaC powders on structure and mechanical properties of the X40CrMoV5-1 steel surface layer using the HPDL (High Power Diode Laser). The metallographic investigations on light microscope show that during alloying the X40CrMoV5-1 hot work tool steel with the WC and TaC powder the obtained run face is characteristic of the high roughness, multiple pores, irregularity, and flashes at the borders. The changes of the surface layers hardness formed as a result of alloying with ceramic powders containing carbides are accompanied with the increased tribological properties. The microstructure of the alloyed layers which were formed on the surface of the investigated hot work steel was examined using optical microscope. The tribological wear relationships using pin-on-disc test were specified for surface layers subject to laser treatment, determining the friction coefficient, and mass loss of the investigated surfaces.

Abstract: The specimens in the present study were prepared by air plasma spraying of NiCrAlY coatings onto the INCONEL 713LC nickel-based superalloy substrate surface. Subsequently an aluminium sheet was cladded onto the coating surface by means of uniaxial cold pressing. After that the specimens were annealed at temperatures of 650, 850 and 1000°C for two hours in argon-flow atmosphere. The remelted NiCrAlY coating specimens were annealed at a temperature of 800°C for fifty hours in ambient atmosphere. A scanning electron microscope was used to record the changes in the modified coating microstructure. Chemical composition was measured by means of energy dispersive microanalysis. Qualitative and quantitative x-ray diffraction analysis was used for the final determination of phases. The microhardness of remelted air-plasma-sprayed NiCrAlY coatings before and after short thermal exposure was also measured.

Abstract: Laser surface hardening of cast iron is not trivial due to the material’s heterogeneity and coarse-grained microstructure, particularly in massive castings. Despite that, hardening of heavy moulds for automotive industry is in high demand. The present paper summarises the findings collected over several years of study of materials structure and surface properties. Phase transformations in the vicinity of graphite are described using examples from production of body parts in automotive industry. The description relates to formation of martensite and carbide-based phases, which leads to hardness values above 65 HRC and to excellent abrasion resistance.

Abstract: The regular pattern of evolution of TiC and TiAl₃ during the remelting process of Al-Ti-C alloy wires was analyzed and the impact mechanism was discussed. The results show that: when the temperature of the remelting mass is at 730°C, with the increase of the heat preservation time of remelting, the degree of agglomeration of the original dispersed TiC will increase, and they are pushed toward crystal boundaries by α-Al during the solidification process, while TiAl₃ will dissolve, aggregate, and grow. When the remelting temperature is at 1000°C, as the heat preservation time increases, not only the agglomeration degree of TiC increases significantly compared to that at 730 °C and the sizes and shapes of TiAl₃ change significantly as well. The morphology of TiAl₃ will change from being lump-and-short-rod-like to needle-and-flake-like. Before and after remelting, the Al-Ti-C alloys are both composed of TiAl₃ and TiC, with no other phases formed.

Abstract: The CDC (Cast-Decant-Cast) Process is novel semi-solid processing method for joining two alloys, allowing the production of components from two or more alloys. The process produces a functionally gradient material (FGM) which, instead of having a sharp interface between the two alloys, features a transition region exhibiting a smooth gradient in concentration, microstructure and properties. Functionally gradient materials provide engineers with the flexibility to design components with different material properties at different locations. The details of the CDC Process are described. This paper, for the first time, provides information regarding the fabrication of functionally gradient castings from steels, cast irons and cobalt alloys. The first example involves the production of functionally gradient castings from a Ni-Hard cast iron + mild steel. The second example describes the production of functionally gradient castings from Stellite + mild steel. Processing parameters are documented and microstructures of the castings described.

Abstract: Laser surface remelting and alloying of sintered stainless steel type 410L with FeNi and Ni have been studied for improvement of corrosion resistance and hardness increase. The influences of high power diode laser (HPDL) processing conditions, laser power in range 0.7-2.1 kW on the microstructure and properties of alloyed surface layer have been evaluated. The FeNi alloyed layer shows microstructure composed of austenite and martensite formed, due to high cooling rate in laser remelting process, with average Ni content in range of 39 to 8% depending on laser processing conditions. The Ni alloyed layer was composed of austenitic microstructure with Ni content from 65% to 33%. The improvement in microhardness was achieved by laser surface alloying and remelting. Excellent corrosion properties were observed for such remelted and alloyed layers in salt spray test.

Abstract: In semi-solid remelting process, the various stages of reheating temperature and isothermal holding time must be accurately controlled in order to obtain the uniformly distributed and small equiaxed grains microstructure. In this paper, a temperature control program was developed and the remelting process for Al-7Si-2RE aluminum alloy was carried out. The results showed that with the raise of reheating temperature and the extension of isothermal holding time, the liquid fraction increases, α-phase grain grows and becomes rounding in the process of Al-7Si-2RE alloy semi-solid remelting. The most reasonable process parameter of reheating temperature is at 585~590°C and its appropriate isothermal holding time are about 10~15min for the semi-solid Al-7Si-2RE alloy.

Abstract: The Electro-Slag-Remelting (ESR) is an advanced technology for the production of components of e.g. high quality steels. In the present study a comprehensive computational model using the VOF technique for the prediction of the slag/pool interface is presented for axisymmetric and steady state conditions. In this model the distribution of the electric current is not constant in time, but is dynamically computed according to the evolution of the slag and steel phase distribution. The turbulent flow, created by the Lorentz and buoyancy forces, is computed by solving the time-averaged mass and momentum conservation equations. The turbulence effect is modelled by using a k-model. Two numerical simulations were performed, one assuming a flat interface, and a second leaving the interface free to find an equilibrium shape. The results are then analysed and compared for both cases.