جستجوی مقالات مرتبط با کلیدواژه « micro hardness » در نشریات گروه « مکانیک »

Waspaloy is a type of nickel-based superalloy that is mainly used in aircraft turbine parts, compressor disks, shafts, and turbine parts. Waspaloy, like many nickel base superalloys, is difficult to machine at room temperature (conventional turning). In this paper, the cutting and feeding forces and cutting temperature have been evaluated by changing rotational speed, feed rate and constant depth of cut, in the dry oblique turning process of Waspaloy. The workpiece's diameter and hardness were 25 mm and 385±10 Vickers, respectively. In order to investigate of the cutting force, temperature and the surface roughness, a full factorial design experiment was used, and a regression model of the influencing factors was presented. Moreover, the surfaces roughness and micro hardness of the machined parts were evaluated. The results showed that the hardness on the surface of the workpiece increases with the increase of the cutting depth and the feed rate.

In this paper, laser cladding of Inconel 713 LC was performed by using Metco 81VF powder and 400 W pulsed Nd:YAG laser. The effect of laser parameters including laser frequency, pulse width, and laser scanning speed was investigated on the microstructure characteristics and microhardness of coating. The results showed that by increasing the laser frequency and pulse width or decreasing the laser scanning speed, the heat input increases and therefore, the resultant dilution ratio raises. The clad zone of the samples with a high dilution ratio consists of a eutectic structure (γ and Cr7C3). However, the clad zone of specimens with a low dilution ratio is composed of a hypereutectic structure of Cr7C3+(γ+Cr7C3). Increasing the laser frequency and pulse width (increasing the dilution ratio and removal of primary carbides in the microstructure) causes the decrease in microhardnes of the clad zone, but increasing the laser scanning speed has an opposite effect and causes the increases in microhardness of the clad zone. The optimal sample was selected with a laser frequency of 18.4 Hz, a pulse width of 11.2 ms and a laser scanning speed of 2.8 mm/s. This sample, in addition to the acceptable dilution ratio and appearance, has a remarkable hardness of 1204 Vickers, which is about 3 times the hardness of the base metal.

Parameters of core roughness are important in the determination of contact area and performance of engaged surfaces which can be modified using finishing processes. Burnishing is a mechanical behavior on the surface to enhance surface characteristics and work hardening which can change core roughness parameters. In this research, a comprehensive study on the surface roughness parameters especially, peak and valley core roughness, before and after of ball burnishing process is presented on the copper cylindrical parts. Initial surface roughness and a tool with different balls are important inputs of the current research which are studied besides other parameters such as burnishing force and feed. Results showed that the burnishing process has reduced surface roughness by about 90 to 96 percent. Also, ball diameter of 20 mm decreased Ra about 20% in comparison to ball diameter of 12 mm. Peak core roughness (Rpk) and valley core roughness (Rvk) presented decreasing of 80% to 90% and 20% to 80%, respectively which prove lower effectiveness of burnishing process on the Rvk. Hence, an initial condition especially the initial surface roughness has a great effect on the Rvk. Considering other parameters, initial surfaces prepared using sandpaper with a grit size of 60 and turning with a feed of 0.24 mm/rev which associated with the highest surface roughness, presented a significant reduction of roughness parameters after the ball burnishing process.

Due to the needs of different industries to produce high precision dimensional products and desirable surface properties and the highest effect of final surface quality on product performance, selection of effective and suitable polishing processes for production of quality products is important. Among different methods of polishing, the burnishing process due to low cost, the possibility of installation on different machines and the polishing without chip has been consideration. Therefore, in this study, due to the widespread application of ductile cast iron in various industries, after preparing the samples of ductile cast iron, making the roller burnishing tools and mounting it on the lathe machine, experiments were carried out in accordance to experimental design table and the effect of burnishing force, feed rate and number of passes, on microhardness and surface roughness of samples were evaluated. For statistical analysis, the results of minitab software and response surface methodology (RSM) were used and the statistical analysis performed with the confidence level of 95%, the most effective parameters and their desirable values to increase the microhardness and quality of samples were introduced. The results showed that the effect of the burnishing force, had the greatest impact on the microhardness and roughness of samples and the optimization of samples by (RSM), optimum value for surface roughness and microhardness of specimens, respectively, 0.562 μm and 203.20 Vickers were obtained in comparison with the values for the initial sample, the surface roughness of samples about 58% reduction and microhardness of samples were increased about 12%.

Today, a variety of implants with different applications are used to replace or support a damaged biological structure, the most common of which are dental and orthopedic implants. Due to the widespread use of stainless steel 316 L in the manufacture of implants and the occurrence of cracks and residual stresses during the process of electrical discharge machining for the production of these products, the use of effective and economical polishing methods such as burnishing in It is effective in increasing the surface properties and compatibility of these products with living tissue. In this study, after performing the electrical discharge machining process on the surface of the sample and making the ball burnishing, the burnishing operations were performed by changing the input parameters and in accordance with the experiments designed using the mini tab software. Thus, the effect of variable burnishing force, feed speed and number of tool passes on surface roughness properties, micro-hardness and corrosion resistance of the final surface of the work piece were investigated. During the optimization of the response surface methodology, the optimal value for surface roughness, micro-hardness and surface corrosion rate of the samples were obtained, respectively, 0.108 μm, 435.34 Vickers and 2.18*105 respectively. Compared to the control sample, the surface roughness of the samples decreased by about 97% and the micro-hardness and corrosion resistance of the samples increased by about 2 and 11 times, respectively.

Among various manufacturing processes, the use of cold press- sintering has been considered with low cost, high efficiency, and the ability to produce components with the appropriate dimensional accuracy. In this method, at least two components of the alcoholic solution are used in granulation and milling steps. Removing the solutions is accompanied with energy consumption, as well as, an increment in probability of crack initiation, which may limited the widespread utilization of press-sintering process. Therefore, in the present study, the soluble component in the milling step was removed. In following just using PVA as a soluble component in the granulation step, the ceramic / ceramic composite was made. Doing this, samples based on NiO and YSZ were made with different weight percentages of the reinforcement component (25, 30 and 35% wt. zirconia-stabilized yttrium), and then their microstructure, density and micro-hardness were investigated. Microstructural studies indicate that the amount and distribution of porosity, surface quality and depth of cracks in the samples are depended on reinforcement weight. In detailed, at the surface of green tables, no deep crack was observed. In sintered specimens, the best distribution of the gas phase was observed in NiO- 30% wt. YSZ, which results in maximum micro-hardness. Also, the radiography results provided by the above samples indicated that deep crack in the discs is not visible. Therefore, it seems that the starch as a pore former displayed the beset role via porosity distribution and lessening crack nucleation in sample having 30% reinforcement.

In this research, deposition of AA7075-T6 coatings on AA2024-T351 substrates was studied. In order to investigate the influence of process parameters on the mechanical properties and microstructure, the experiments were performed based on design of experiments using Response Surface Methodology (RSM). Rotational speed (1200-1600 rpm), axial force (320-640 Kg) and feed rate (100-300 mm/min) were considered as input parameters, while coating width (w), coating thickness (t) and hardness of coating (HC), were raised as process outputs. The results reveal that joining of these two materials was done without any porosity at the interface. Hardness of coating showed a 30% decrease compared to the consumable rod in average. Thickness of deposition is decreased by increasing rotational speed, feed rate and axial force. If axial force is excessively increased, it results in development of an arc toward the plate along deposition. Microstructure of deposition turned into a totally fine-grained homogeneous structure in comparison with rod and plate microstructure.