جستجوی مقالات مرتبط با کلیدواژه « Micro-hardness » در نشریات گروه « فنی و مهندسی »

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.

Previous studies have shown that thermal spraying methods on steels have extensive applications in various industries to increase high-quality wear-resistance coatings. One of these coatings, which is important in diverse industries and has been studied, is tungsten carbide. One of the methods of coating is the high-velocity oxygen fuel (HVOF) process. Scanning electron microscopy (SEM) was used to examine the microstructure of the coatings and also by examining SEM images from the lateral surface of the coated sample, the thickness and quality of the coating were examined. Additionally, X-ray diffraction (XRD) was used to determine the formed phases before and after the coating process and the results of the presence of WC and W6C2.54 carbides were confirmed.The wear test results showed that coated samples demonstrated higher wear resistance than the sample without coating (control). Meanwhile, the sample with spraying pressure of 7.2 Bar and a feeding powder rate of 72 g/min (W2) exhibited the best wear resistance among other coatings due to the more uniform distribution of tungsten carbide (WC) and less porosity. As a result, it was obtained that the spraying pressure in the process of HVOF process was more effective than the feeding rate of coating powders and a sample with the spray pressure of 7.2 Bar and powders feeding rate of 72 g/min (W2) was introduced as the optimal sample among all coatings with the highest abrasion wear resistance.

In this research, friction stir spot welding on aluminum plates 7075 and 6061 was performed. The purpose of this work is to investigate the impact of the tool's hardness and its rotational speed by changing the layout of the plates on the mechanical properties of the made welds. Two tools were made of H13 steel, with different hadness was used. The mechanical properties of the weld were studied for shear strength and microhardness. The results showed that when the 6061 aluminum plate is located on top of the layout, the shear tensile strengths are less than the 7075 aluminum plate. Also, with the increase in the speed of the tool, the shear force force values have undergone a downward trend. The microhardness of the heat treatment device is higher than the microhardness of the raw material. Also, with increasing speed of tool, the obtained microconstability has a rising trend. This is due to the increased frictional heat transferred by the very high speed of the tool, which increased the hardness of the boiling region. The optimum mode is achieved at a speed of 1000 rpm and in a position where aluminum 7075 was placed on top of the plates. 

In this research, the effect of bonding temperature on the microstructure and mechanical properties of Inconel 939 super alloy by transient liquid phase bonding method. For this purpose, the middle layer of MBF20 with a thickness of 50 microns and three temperatures of 1060 °C, 1120 °C, 1180 °C and a time of 45 minutes have been used. In order to evaluate the microstructure, a scanning electron microscope equipped with an elemental analysis system has been used. Vickers hardness test and shear strength test have been used to evaluate the mechanical properties. The research findings showed that with increasing temperature from 1060 °C to 1120 °C, the width of the athermal solidification zonedecreased from 38µm to 35µm and with increasing temperature at 1180 °C, the athermal solidification zone was completely removed and isothermal solidification zone was replaced. In addition, with increasing temperature, the hardness in the joint center decreases and the shear strength increases.

In this study, the aluminum oxide coating was applied on 5083 Aluminum alloy by hard anodizing method in sulfuric acid. M icrostructural investigations showed that anodizing process leads to the formation of porous amorphous alumina coating on the surface of 5083 aluminum alloy. The porosity of the coating surface increases by increasing the anodizing voltage, leading to an increment in the surface roughness. In addition, as the voltage increased, the thickness and hardness of the coating increased due to the higher dissolution rate of the 5083 Al alloy substrate. M icroscopic examinations were indicant of appropriate adhesion of the aluminum oxide coatings. The anodizing process significantly improved the tribological behavior (at least more than 20 times) of 5083 aluminum alloy. M icroscopic analysis showed that the main wear mechanisms of 5083 aluminum alloy were abrasion and delamination and the dominant wear mechanisms in aluminum oxide coatings were adhesive and delamination.

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.

The effect of different amounts of ZnO on structural properties of SiO2-Al2O3-p < sub>2O5-CaF2-CaO-K2O-Na2O-xZnOglasses was studied. The effect of ZnO addition on glass transition and crystallization temperatures were studied by DTA. FTIR and RAMAN were used to study the characteristic bands of prepared glasses. All samples were heat treated at two different temperatures of 750 and 1100°C. XRD analysis showed that anorthite and calciumphosphate were the main crystalline phases. Based on DTA and XRD results, samples with higher amounts of ZnO were crystallized at higher temperatures. No significant band changes were detected as a result of ZnOaddition as spectroscopic results showed. Vickers microhardness numbers showed that ZnO addition up to 2gr lead to a significant (p < 0.05) improvement in microhardness values.

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.

The surface of continuous casting moulds with high number of castings may be worn or destructed. As result, an approach for increasing these moulds life is necessary. In this project, the goal is the restoration of the DHP copper sample. In this project, the destruction of the copper sample is done by creation of groove using a CNC machine. The restoration of the sample is done using OAW and filler to fill groove area. In this project, the effect of preheating temperature, filler type and heat treatment of welding area on hardness, microstructure, chemical analyses of welding area and thermal conductivity of the weld are investigated. The preheating temperature range of 300 to 450oC was selected. The Cu-P and Cu-Ag-P fillers were chosen to fill the groove of the weld area. The scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDS), micro hardness tester, optical microscope and thermal conductivity meter were employed for evaluation of the results in this project. The results showed that the increase of preheating temperature creates oxide layers and the decrease of preheating temperature causes the incomplete filling of the welding area. Finally, the preheating temperature of 400 oC was a proper choice considering the above mentioned factors. The stress relieving operation to decrease stress and preserve the mechanical properties in the temperature of 250 to 400 oC and duration two hours was carried out. The result demonstrated that the selected temperature causes no unwanted decrease on the hardness. It was also found that increasing the annealing duration, decreases the hardness of weld for Cu-P filler for Cu-Ag-P filler increasing the annealing duration, first decreases the weld hardness and then increases the weld hardness. The Cu-P filler was compared with Cu-Ag-P filler. The results showed that the Cu-Ag-P filler has less hardness (around 10 percent) than the filler without silver. On the other hand, the thermal conductivity of the Cu-Ag-P filler was around 10 percent more than the thermal conductivity of the Cu-P. It is obvious that the selection of the filler type depends on the type of base metal and its geometry. The results showed that the segregation in the Cu-P filler with 7.2 percent phosphorous, because of the proximity of the weld structure to the eutectic point, has slightly happened; while, the selection of the Cu-Ag-P filler with 6 percent silver caused severe segregation of silver to 90 percent silver at the center of weld at the non-dendrite area