Papers by Keyword: Surface Alloying

Abstract: The technology of formation of high-carbon layers on the pipes of low-carbon steel using non-vacuum electron beam cladding is analyzed. Carbon fiber fabrics are used as a carbon source. High-carbon layers are formed on the surfaces of steel pipes due to the electron beam impact. The carbon concentration in high-carbon layers reaches 5.5 wt. % and decreases toward the base metal. The hardness of the obtained coatings reaches 8 GPa. Cladding of high-carbon layers allows increasing wear resistance of the material by 23 % compared to cemented and quenched steel.

Abstract: This paper is devoted to the investigation of structure and properties of Ti-Ta-Mo layers produced on the surface of commercially pure (cp) titanium using non-vacuum electron beam processing. Due to electron-beam surface alloying, a thick defect-free layer with increased hardness was produced. The average concentration of Ta and Mo was 22 % (wt.) and 9 % (wt.) respectively, which led to the formation of the β-Ti matrix with nanoscale precipitation of the ω-phase. The electron backscatter diffraction (EBSD) study revealed the formation of a cubic texture along the <100>direction ofβ-Ti normal to the sample surface, during crystallization of the surface layer. The results of this study can be used to predict the properties, particularly, the Young modulus of surface alloyed titanium, which may be of interest for biomedical application.

Abstract: Inthepresent paper wereporton surface alloyingof cylindrical substrateswithcarbonbynon-vacuumelectron-beamprocessing. A carbon fabric was used as a source of carbon. The electron-beam processing of the carbon fiber wrapped around the cylinders led to the formation of carbon-rich layer on the surface of the samples. Thehighestconcentrationofcarbonwasreacheddirectly on thesurface of the samples and was equal to ~4.3 % (wt.). The concentration of carbon gradually decreased to ~0.8 % (wt.) towards the substrate.The surface of the reinforced material had a high level of hardness (up to 750 HV). Wear resistance,underconditions of abrasive particleimpact, increased by 15% compared to wear resistanceof the sample produced by pack carburization and quenching.

Abstract: The mixture powder of Cr, Ni, Mo and Cu were deposited evenly on a ductile iron with ferrite matrix and treated by plasma transferred arc (PTA). The microstructure and hardness distribution of the PTA-alloyed layers were investigated by using scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and microhardness tester, respectively. Results show that the cross-section consists of four regions: alloyed zone, melted zone, heat affected zone and unaffected substrate. The maximum microhardness of PTA-alloyed sample is measured to be as high as 1077 HV_0.2, which is approximately 4.4 times higher than that of substrate. The improvement is attributed to the formation of mixed hard-phases such as Cr₇C₃, C₂₃C₆, martensite, cementite under nonequilibrium solidification, and the solution strengthening by the alloying elements as well as grain refining via the rapid cooling.

Abstract: Hydroxyapatite (HA) is bioactive and biocompatible bioceramics that is commonly used as a filler to replace amputated bone or as a coating to promote bone ingrowth into prosthetic implants. The need to overcome biocompatibility problems and improve the bone bonding ability enforced the researchers to develop suitable coating techniques. Feasibility of Powder Mixed Electrical Discharge Machining of Ti-6Al-4V alloy with HA additives in water dielectric liquid is studied as an alternative coating technique. Machined samples are analyzed by means of optical, scanning electron microscopy and energy dispersive spectroscopy. The experimental results have revealed that it is possible to deposit HA powders onto the work material surface by using the process. The morphology of the deposited material signified the dependency with respect to the operational parameters such as pulse on duration and current. Moderate pulse currents together with low pulse on duration were found to be the plausible choices for HA coating applications.

Abstract: The role of suspended particles on Ti-6Al-4V surface in Powder Mixed Electrical Discharge Machining (PMEDM) is studied using SiC powder mixing in water dielectric liquid. Surface modifications due to the additives in dielectric liquid are investigated by means of optical, scanning electron microscopy and energy dispersive spectroscopy. The attachment of added powders and surface topographies interrelated with powder suspension concentration, particle size and electrical parameters such as pulse on duration and current. The influence on discharge transitivity with respect to SiC additives is noticed with pock like features on the surface. The geometry and size of these features indicated a robust dependency with respect to operational parameters and indicated the role of secondary discharges during PMEDM. SiC particles severely transferred from di-electric liquid to machined surface at critical operational parameters and implied that the process could be also used as a surface alloying technique.

Abstract: Titanium and its alloys are widely used in the fields of chemistry, aerospace, biomedicine, automobile manufacturing, ship industry, and so on, due to the properties of light weight, high strength, high thermal stability and corrosion resistance. However, the shortcomings of Titanium and its alloys are prominent as well, such as unsatisfactory corrosion resistance in reducing acid, insufficient wear resistance and serious oxidation at high temperature. Surface modification can solve the problems effectively. In this paper, the recent researches of some surface modification techniques such as plasma spraying, surface alloying, magnetron sputtering and vacuum depositing to improve the corrosion resistant of titanium and its alloys are summarized. The characteristics of structures and properties of the coatings are introduced. And the future prospect of further investigations is presented.

Abstract: Local surface alloying of metallic materials by laser is an issue of interest in the scientific world and materials engineering. Laser surface alloying technology allows diffusion of alloying elements which add special features into the surface of a base material with modest properties but a low price. This paper presents the results of experimental research regarding the process of alloying on steel ST37-2 and the effects obtained after laser surface alloying.

Abstract: W-Mo-Dy alloying layer were prepared on the surface of different carbon content of steel by plasma alloying technique and the optimum parameters were obtained under the experimental conditions. The optimal process parameters are as follows: Source material is Φ 5mm × 30mm tungsten and molybdenum wire, the number of W:Mo is 2:8, spacing is 10~15mm; Rare earth Dy using an independent plate source and evenly arranged on the Φ 100mm the barrel auxiliary cathode; the source voltage is-850~-900V, the cathode voltage is-700~-750V, the limit vacuum is 2Pa; the working pressure is argon gas, gas pressure is 30pa, the insulation temperature is 1020°C; the holding time is 4.5h. Available to meet the test requirement and obtain the alloying layer thickness is 128um.

Abstract: CrN coating was deposited on 3Cr2W8V alloy by PVD and then processed with electron beam surface alloying process. The pulsed times of HCPEB was changed from 1 to 25 to prepare different specimens. Microstructures were investigated by optical metallurgical microscopy (OM), results show that the particles located in surface layer were obviously refined and the thickness of coating film has important influence to surface alloying . When the coating film is very thick, the heat-affect areas which are made by electron beam do not influence the matrix a lot. Microhardness, friction coefficient, amount of wear of electron beam treated specimens were determined. It is shown that the coating has an average microhardness of approximately HV630, the friction coefficient of electron beam irradiation treated specimens is considerably lower than that of CrN coating. When the electron beam irradiate times is appropriate, the roughness of surface will much lower, and it will achieve polishing effects. The corrosion behavior of the composite coating in 3.5% NaCl solution at room temperature was also determined using a potentiont state system. By comparing the electron beam treated specimen of 3Cr2W8V alloy to that of the primary 3Cr2W8V dendrites, the corrosion potentials of CrN coating and electron beam treated specimen are increased respectively. The electron beam treated specimen has the lowest corrosion current density as well as the highest corrosion potential showing an improved corrosion resistance compared with 3Cr₂W8V alloy.