Papers by Keyword: Micro Hardness

Abstract: The paper is focused on the elaboration of some sintered steels with Cr concentration between (1-2 %) wt., carbon as graphite with a concentration of 0,4% wt. and Fe for the balance. The samples were die pressed at 600 MPa and sintered at 1150 °C in argon atmosphere. The samples were studied from the point of view of wear behavior against three types of counter balls, alumina (Al₂O₃), steel (100Cr6) and stainless steel 440C. The results shows that the lowest value for the friction coefficient was attained for the steel with 1,5% Cr. Also, microhardness tests were performed and reveal that the highest value was equal to 229 HV_05.

Abstract: The present investigation aims at studying the effect of carbon nanotubes dispersion on the surface hardness of carbon fiber-reinforced polymer composites, manufactured by means of compression resin transfer molding. The influence of the weight fraction of nanofiller, distributed in the epoxy matrix, on the Vickers hardness values was investigated. Furthermore, the evaluation of carbon nanotubes filtering effect was also taken into account by comparing the hardness values measured at the top and bottom surfaces of the laminate composites. It was observed that the different weight loads affect the surface properties of the nano-composites, both in terms of hardness and filtering effect.

Abstract: It was shown that under dry contact conditions, under normal load of to 2 MPa, all coatings demonstrated a significant increase in wear resistance compared to that of the substrate. However, among them, the Mo coating showed the highest wear resistance: ~20 times higher than that of the uncoated steel. That was caused not only by the Mo high microhardness and the lowest initial roughness, but also by the structure of this coating. Meanwhile, the Ti + SiC samples displayed the highest microhardness among investigated coatings. A correlation was established between the microhardness of the coating and the friction coefficient: the larger the microhardness of the coating, the higher is the coefficient of friction. An X-ray analysis of the coatings obtained by ESA on steel with compositions (Ti + Al + C), (Ti + AlN) and (Ti + SiC) revealed phases of titanium carbide, titanium nitride, intermetallic compound AlFe₃, and small amounts of aluminum nitride, silicon dioxide and titanium dioxide. This could explain the high microhardness (from 6.8 up to 13.8 GPa) of the obtained coatings.

Abstract: Metallographic studies of structural-phase states formed in the section of the flange of the wheel band during surface plasma hardening were conducted. It is shown that the formation of several structural zones of different micro hardness is distinctly observed in the depth of hardening, which indicates the formation of a graded-layered structure. It has been confirmed that at superfast heating rates that occur during surface plasma quenching, phase and structural transformations are shifted to high temperatures, greatly changing the kinetics of nucleation and growth of the new phase (austenite). This forms a fine-grained austenite, which turns into a highly disperse martensitic structure, unattainable by traditional methods of heat treatment. It is shown that the main factor leading to strong hardening of the surface layer during plasma treatment is the formation in the near-surface zone of a nonequilibrium metastable structure, which goes over to a narrow zone of complete and incomplete quenching with an inhomogeneous and distorted structure of highly disperse martensite with a high level of internal stresses. The complete wear of the unstressed flange of the tire wheel band is 1.9 mm in 1.1 years, and for hardened flanges, wear is 0.7 mm for 2.6 years.

Abstract: Composites are the combination of materials that are mixed together to achieve specific structural properties. Teflon (Polytetrafluoroethylene PTFE) consists of long-chain molecular structure. Its monomer consists of two carbon atoms each of them having flourine atoms attached. Bonds within each chain are strong covalent bonds where as the secondary bonds between two chains are weaker. By raising temperature, the distance between the chains increases providing good adjustment of the atoms of other materials due to anisotropy of its mechanical properties. Powder metallurgy technique using hot isostatic pressing, a hybrid densification process in which pressure and temperature are applied at the same time, has been used to develop a teflon-copper composite material. Three samples were prepared by changing the teflon-copper composition as 60:40%, 65:35% and 70:30% by weight. Commercially available powders of teflon and copper of grain size ~ 40 μm was used. The aim to develop this type of material was to increase its density (~ 4 g/cm³), and hardness. The commercial applications of such type of composite material are solid lubricants, sleeves, bearings etc. In this paper the effect of composition on hardness, tensile strength and surface roughness is studied.

Abstract: The article describes the methods of laser cementation of the edge wood-cutting tools. There are the results of the experimental study of the described methods in the article. The most acceptable method of treatment from the point of view of the results reproducibility and the possibility of industrial use are determined.

Abstract: The results of the experimental study of the influence of micro-arc oxidation (MAO) on the corrosion resistance of aluminum alloy samples AK12D are presented in this paper. The description of the research methodology, including the formation of the hardened layer on the surface of laboratory samples by MAO under various process conditions and the study of their corrosion resistance are given. The studies were conducted in accordance with the experimental design theory for fractional factorial experiment 2^3-1. The MAO process was carried out using an alkaline electrolyte. MDO process factors were chosen according to an electrolyte concentration of the components (caustic potash - KOH and water glass - Na2SiO3) and electrical parameters of the process determined by the capacitors capacitance. In addition to corrosion resistance of the samples, the thickness, porosity, and microhardness of MAO layer were determined. Regression equations and conclusions about the degree of influence of modes of micro-arc oxidation on the corrosion resistance of the samples were compiled on the basis of the data obtained. The results showed that the MAO process regimes have a significant effect on the corrosion resistance of the samples. Regression equations describing the effect of the thickness and porosity of the surface on the corrosion rate are derived. It has been found that the greatest influence on the corrosion resistance renders the mean value of porosity. With an increase of this parameter there is an increase in the corrosion resistance of the coating. To account for this effect, it has been suggested that the corrosion resistance of the MAO layer should not correlate with the porosity but with the absolute volume occupied by the pores in the coating. The study was conducted to investigate the prospects for the use of the MAO method for improving the corrosion properties of parts and details made of Al-Si aluminum alloys.

Abstract: This work considers the questions of low-alloy tool steel cementation by laser treatment. The model of surface layer carbon saturation from the laser-induced plasma is shown. It is described that the diffusion process in the laser treatment can not be explained only by the influence of temperature gradient. The results of the experimental work confirmed the increasing intensity of the process surface layer saturation with carbon. The work describes the influence of the laser emission power on surface layer microstructure formation. The test results of the hardened samples showed an approximately two-time increase in durability.

Abstract: A well-designed experimental were conducted with L₁₈ Orthogonal Array (OA) based on the Taguchi method with input factors discharge current, pulse on time, lift time and flushing pressure. Micro hardness was measured and the mean of the observed values were plotted. The factors effecting the micro-hardness of the work-piece has been obtained. It is inferred that micro-hardness value increases with increase in discharge current and decreases with increase in Pulse on Time. The optimal condition for minimum hardness was found to be discharge current (Ip) = 2A, pulse on time (Ton) = 500μs, lift time (Tup)= 1.4 ms and flushing pressure (Fp)= 0.2 kgf/cm².

Abstract: In this research work, the effects of heat transfer on microhardness, microstructures of friction stir welded AA 6061-T6 Aluminum alloy butt joints advancing side and retreating side are analyzed. A three dimensional finite element model is developed to study the thermal history in the butt welding of AA 6061 aluminum alloy using ANSYS package. Solid 70 elements are used to develop the model and a moving co-ordinate has been introduced to model the three-dimensional heat transfer process because it reduces the difficulty of modeling the moving tool. In this model, the main parameter considered is the heat input from the tool shoulder and tool pin. As a result, the temperature distributions of the weld at a welding speed of 1.25mm/sec were obtained.