جستجوی مقالات مرتبط با کلیدواژه « zro2 » در نشریات گروه « مواد و متالورژی »

In the present study, friction stir process (FSP) was used to produce AL/ZrO2/ZrSiO4 surface hybrid composite at a fixed rotation speed of 1400 rpm and traverse speeds of 20, 25, 31.5 and 40 mm/min. Therefore, the purpose of the mentioned study is to investigate the effect of tool traverse speed on the microstructure, hardness and wear behavior of the above-mentioned surface hybrid composite and compare it with base material aluminum 5052. Investigations showed that as a result of FSP operation, a fine-grained structure is created, which improves the hardness and wear resistance of the samples compared to the base sample with the presence of ZrO2 and ZrSiO4 particles. Also, the results showed that among the FSP samples, the sample with a speed of 20 mm/min has the highest hardness and wear resistance. The reason for this is that in this sample, due to the lower traverse speed compared to other samples, more heat has been generated, which has led to more suitable particle distribution and more fine particles. Therefore, in the sample with the traverse speed of 20 mm/min, the hardness and wear resistance increases by 27.3% and 68.9% respectively compared to the base material sample. Also, the examination of the wear surfaces of the samples showed that the wear mechanism in the base sample is strong adhesive wear, and as a result of the FSP operation and surface compositing due to the fineness of the grains and the increase in hardness, the wear mechanism has become weak adhesive, so the wear resistance of the sample is FSPs have been improved.

Austenitic stainless steels are high performance steels that have various applications in solid oxide fuel cells and boiler tubes under high temperature operating conditions. The Cr2O3 oxide layer formed on the steel surface becomes unstable at high temperatures and reduces the oxidation resistance of the steel. Therefore, protection of these steels at high temperatures is essential. Therefore, one of the best effective ways to extend the life of these components against oxidation is by applying protective coatings. In this research, Ni-Co-CeO2-ZrO2 composite coating was created by direct electrodeposition on the surface of AISI 304 austenitic stainless steel. In order to obtain proper coating, the effect of current density, pH and concentration of ZrO2 in the bath was investigated. To create the optimum deposition, the bath parameters were investigated. Influence of ZrO2 content (5, 10 and 25 g/L), current density (15, 20, 25 and 30 mA/cm-2) and pH (3, 3.5, 4 and 4.5) on the deposition amount of ceramic particles and microstructure of the coating has been investigated. Scanning electron microscopy (SEM) and EDX analysis were used to determine the morphology. The results showed that with increasing ZrO2, the amount of ZrO2 deposition increased and the amount of CeO2 deposition decreased. Also, with increasing current density and pH, the amount of ZrO2 and CeO2 particles decreased.

Composite coatings with nickel matrix and ceramic reinforcement particles have high ability to improve surface properties, such as good corrosion and abrasion resistance. In this study, Ni-P composite coating was coated with ZrO2 and TiO2 ceramic particles on the AISI 316 steel substrate through direct current plating method. The effect of the current densities of 20, 30, 40 and 50 mA/cm2 on the microstructure and corrosion resistance was investigated. Scanning electron microscopy (SEM) was used to investigate the microstructure. In order to investigate the corrosion behavior of the coatings, potentiodynamic polarization test was used in aqueous NaCl solution of 3.5%. The results of SEM and EDX analysis showed that the coating produced at current density of 40 mA/cm2 was more uniform and had more deposition of titanium oxide and zirconium oxide particles. Also, the polarization results showed that the corrosion resistance of the coated specimen in the current density of 40 mA/cm2 (Rp = 12.3030 MΩ) was higher than that of the coated in current density of 20 (Rp = 12.1950 KΩ), 30 (Rp = 22.2710KΩ) and 50 mA/cm2 (Rp = 8.34020 KΩ). In the higher or less current densities, the coatings were not uniform.

The present study aimed to investigate the synthesis, microstructural and mechanical properties of alumina/zirconia-cobalt composite. The compositions containing 5, 10, 20 Vol.% of the sum of ZrO2 and Co were studied. The composite powders were prepared through mixing of alumina powder with partially stabilized zirconia and cobalt sulfate powders followed by calcination treatment at 1100 for 3h and reduction of cobalt by aluminum powder additive, in carbon bed at 950 for 3h. The XRD analysis showed the presence of Al2O3, t-ZrO2, Co and a little m-ZrO2. In order to investigate the properties of Al2O3/ZrO2-Co composite, composite powders were pressed uniaxial followed by Cold Isostatic Pressing (CIP) at 400MPa. The prepared discs were sintered in carbon bed at 1550 1600 , 1650 for 5h. The alumina specimen was also prepared with the same procedure. The final results showed that the highest relative density value was 83.9% obtained for the specimen with the composition containing 5vol.% ZrO2 and 5vol.% Co densified at 1650 for 5h. The bending strength and hardness of this specimen was 322MPa and 11.95MPa.m1/2 respectively. So 20.15% increment of bending strength and 15.96% decrease of hardness was observed compare to monolithic alumina. The decrease of hardness was due to the lower hardness of metallic phase and the increase of bending strength is occurred because of presence of zirconia and cobalt particles which prevent of alumina grains growth.

Thermal shock behaviour of thermal sprayed ZrO2-8%Y2O3 coating on aluminized superalloy In-738LC has been investigated. Thermal shock experiments consisted of rapid thermal cycling between 1100 ºC and 300 ºC. Visual observations were conducted after each cycle in order to identify macroscopic features such as macrocraking and spallation. Coating characterization before and after the thermal cycling was conducted by means of optical and scanning electron microscopes as well as EDS analysis. The results demonstrated that the coating response to the thermal cycling was consisted of TGO thickening، extending of the interdiffusion zone and transformation of β-NiAlγ''-Ni3Al in the aluminide coating. In addition، failure of the coating system comprised of pitting oxidation at aluminide topcoat، nucleation of cracks in TGO، and finally cracks propagation into the ceramic layer.