Abstract: Numerical simulation of a mass-diffusion analysis requires several parameters in order to comply with experimental method of gas – carburizing of iron powder compacts. Among the known parameters of mass-diffusion process, the diffusivity is an uncertain parameter in terms of its value. Different formulas can be found in literature but most of them are empirical determined since different results of carbon content are obtained by numerical mass-diffusion analysis. For iron powder compacts with rectangular shape subjected to gas – carburizing – sintering process it was determined the average carbon content in several layers. Based on these determinations and on the characteristics of mass diffusion analysis using Abaqus software it was empirically determined the diffusivity dependency on the carburizing time.
Abstract: This research focuses on Ag-Cu powder particles processing by mechanical alloying (MA) route. The powder mixture is representative for the eutectic composition, respectively 72%wt. Ag + 28% wt. Cu. The milling process is developed in high energy ball mill Pulverisette 6, using different size for the milling balls, in wet conditions for 80 hours. One of the most important parameter studied in this research is the particle size distribution of the processed powder mixture. Thus, it changes along the milling time, from 10…75 µm at the beginning of MA process up to (60 – 80) nm at 80 h. The milling parameters will be optimized in future research depending on the particle size distribution related with thermophysical and thermodynamic properties focused on electrical and optical properties improvement.
Abstract: The aim of this work is to obtain sintered porous membranes with graded structure for microfiltration by sedimentation and sintering of metallic powders. Our previous studies have demonstrated the possibility of obtaining sintered porous materials with graded structure by sedimentation. In this paper, irregular nickel particles were used having a grain size in the 2-90 µm range evaluated using scanning electron microscopy and laser scattering particle size analyzer. The powders were sedimented into a sintering die in a sedimentation medium consisting of water and dispersant agent. After drying, the samples were sintered at 1000°C for 10 minutes in vacuum (~1•10-3 Pa). The structures obtained were characterized by scanning electron microscopy and mercury porosimetry. The pore size distribution was between 5-72 µm. The flow rate - pressure drop curves were experimentally determined and the viscous permeability coefficient was calculated using Darcy’s law (Ψv=0.14•10-12 m2). The absolute filtration fineness measured was 20 µm and the relative filtration fineness (95%) obtained for our membranes was 11 µm respectively. The possible applications for the studied membrane are: water microfiltration, environmental technologies, filtering lubricants and cleaning agents
Abstract: In this paper are presented the experimental results regarding the elaboration of electrical contacts using W-Cu composite powders obtained by mechanical alloying (MA) process. For the research commercial powders with a particle size between [10-80] µm were used. Three types of mixtures with different concentrations as follow: 90W-10Cu; 80W-20Cu; 70W-30Cu were mechanically alloyed for 2 up to 6 hours using a planetary ball mill. The mixtures obtained after MA process were pressed in a cylindrical die at 400 respective 600 MPa. The evolution of green densities function the compaction pressure and Cu content was studied. The green billets were sintered in an electrical furnace at 1180 oC and maintained 60 minutes at the sintering temperature in argon atmosphere. The evolution of densities, microstructures and electrical properties of the sintered samples function the Cu content and compaction pressure were studied.
Abstract: This paper presents an experimental study about the influence of the Selective Laser Sintering process parameters on the surface and cross-section porosity of parts sintered in polyamide PA2200 material two times recycled. Using of recycled powder affects the part structure and mechanical properties. Therefore, the paper aims to develop a suitable strategy to improve the part structure by controlling the most important SLS process parameters. The main process parameter whose influence was studied is the energy density of the laser beam. Special sample was designed and prototyped using EOS P100 prototyping machine. Three repetition jobs with different energy density of the laser beam were performed. Scanning Electron Microscopy was used to analyze the surface morphology and microstructure of the sintered benchmark parts. The relationship between the SLS parameters and part quality will extend the use of PA2200 recycled material.
Abstract: Reverse Engineering is a technique that is based on creating virtual models from existing products, is used to enhance or reproduce the look/function/role of the original part. It is used for shape design applications in different domains: aerospace, automotive, manufacturing, civil engineering, architecture, medicine, etc. For many years were used contact acquisition devices because of their ability to collect data with high accuracy, but this devices are slow during the acquisition process and constrained in digitization of small size objects. Thanks to the computer industry development and improvements in laser technology, in recent years have appeared scanning devices and scanning machine which have a smaller data acquisition time, and are able to scan a large variety of objects, whatever the size, shape or material. The advantages and disadvantages using scanning devices will be presented in the paper. In this paper we present an experiment conducted on Roland Laser Scanning Machine LPX-600, in which we want to determine factors influencing the surface quality of virtual models, obtained after scanning. For this experiment we used plastic and aluminum parts, cylindrical and prismatic shapes, both rotary scanning and plane scanning strategies and different scanning resolution. The results were processed and analyzed using Minitab.
Abstract: Selective laser sintering (SLS) is a manufacturing technique that uses a high power laser to fuse small particles of metal powders into a mass representing a desired 3-dimensional object. The topography of the dental restoration is designed by numerical monitoring after having scanned devised prostheses. In our application the alloy consists of 64-67% Co, 28-30% Cr and 5-6% Mo, and has at equilibrium of a γ monophasic structure. Evaluation and characterisation was made by: Microstructure analysis; Corrosion resistance evaluation; Polarization test; Crevice corrosion test; Release of cations. Dimensional observations of Co-Cr restorations show that adjustment leads to satisfactory clinical results with a precision of 25 μm. The metallographic observations show a slight porosity in the horizontal plan. Punctual analysis shows a high regularity of the local chemical composition. Potentiodynamic polarization curves confirm the presence of the porosity in the structure of the restoration. The technique of manufacturing by selective laser sintering allows obtaining prosthetic elements of high dimensional precision which present mechanical properties in agreement with the clinical requirements. However, the residual porosity inherent to the sintering process may present a risk for fracture and crevice corrosion.
Abstract: Thermal spray coatings, and in particular those applied by HVOF process, are being used in a diverse range of engineering applications to extend component life by retarding wear and corrosion degradation . Coatings performance is strongly dependent on microstructure . The mechanical properties are a complex function of carbide size, shape and distribution, matrix hardness and toughness and the presence of various reaction products. This paper is focused on the wear resistance of WC-based coatings containing 10 mass% Co and 4 mass% Cr as the metallic binder, involving a heat-treated steel rings as substrate, a hot rolled product of structural steel in accordance with DIN EN 10113-2 for steel construction, detaining a tensile strength about 520-680 N/mm2. A feedstock powder of WC-CoCr 86 10 4 agglomerated/sintered was used for coatings production. It has good properties, such as: high resistance against oxidation and corrosion (due to the metallic component), good wear resistance (due to the ceramic component) and with a hardness in range of 1000-1300HV. The coatings have been produced by HVOF spraying of four different WC-CoCr grain size of powder particles, such as:sample 1 (-45+22µm), sample2 (-22+5µm), sample 3 (-10+2µm) and sample 4 (-2+0.5µm), using an ID CoolFlow mono gun developed especially for internal surfaces. This type of gun is a HP HVOF system for high pressure, but cold internal HVOF spraying. The morphology and the structure of the sprayed coatings were investigated by means of scanning electron microscopy (SEM/EDS) and the qualitative and quantitative phase composition of those coatings were determined applying the x-ray diffraction technique (XRD). In order to determine the sliding wear resistance of the coated samples, it was used the pin on ring test method under dry condition, with and without compressed air. This method consists into a stationary ball loaded against a ring sample in relative motion. The sliding wear rate of the tested samples was calculated from the volume of material lost during the test. The investigated samples were examined by means of stereo and light microscopy before and after exposure to wear tests. Based on the obtained results it was demonstrated that the coatings obtained from -10+2µm powder particles exhibit an optimal wear behavior when exposed to severe conditions.
Abstract: The aim of the work was to study the microstructure and wear properties of fine-structured HVOF and HVAF sprayed WC-10Co-4Cr coatings prepared from powder having submicron-sized tungsten carbides. The coatings were deposited by HVOF (High Velocity Oxygen Fuel) and HVAF (High Velocity Air Fuel) using propane as a fuel gas in both processes, and using oxygen or air as oxidizing gas for combustion, respectively. Nitrogen was used as carrier gas for the powder. Commercially available agglomerated and sintered cermet powder with main carbide sizes under 500 nm was used in this study. Scanning electron microscopy (SEM) and X-ray diffraction were performed in order to characterize the powder and the microstructures formed during the spraying processes. The microhardness HV0.3 of the coatings was investigated and the pin on disk test was used to determine the sliding wear behaviour. The rubber wheel abrasion test was performed in order to determine the abrasion wear resistance of the coatings.
Abstract: The paper presents a research about influence of nitrocarburizing on wear resistance of metal coating layer. The research was made using six types of electrodes (El CrMn2, ElCrW8Co, El CrW2, E Cr25Ni20R, E 3161, El 62 H) for metal coating. After metal coating, were applied three variants of plasma nitrocarburizing, and was study their influence on wear resistance. Evaluation of results was made by weighing loss of samples after wearing.