f. kermani

In this study, the effects of friction stir welding (FSW) parameters on the properties of dissimilar joints formed between 5083 aluminum alloys and 316L austenitic stainless steel, with a thickness of 4 mm, are investigated. The tool speed is varied in the range of 16 to 25 mm/min, while the tool rotation speed is maintained at a constant value of 250 rpm. To examine the microstructure of different weld regions, both optical and scanning electron microscopes are employed. To assess the mechanical properties, hardness and tensile tests are conducted. The results shows the formation of a composite region characterized by steel reinforcement particles dispersed within an aluminum matrix. At the steel-aluminum interface, a single layer of discontinuous intermetallic composition with a thickness of approximately 2 micrometers is observed. Notably, when the rotation speed is set to 250 rpm and the tool speed is 16 mm/min, a tensile strength of 298 MPa and ductility of 26% (93% of the tensile strength and 50% of the ductility of the 5083 aluminum alloy) are achieved.

Inconel 713LC super alloy is one of the most widely used high-temperature alloys. Due to the high level of gamma prime phase caused by Ti and Al alloy more than a critical value, this alloy is considered as one of the non-weldable alloys. One of the basic repair methods of this series of superalloys is laser cladding methods. In this research, the IN713LC  substrate was reconstructed with Inconel 625 powder by a direct laser deposition system. To characterize, optical and electron microscopy tests, porosity measurement, and XRD were carried out; The results showed that the R (growth rate of the dendrite tip) increases at high speeds of laser cladding; as a result, the G/R (combined solidification point) ratio decreases, and the structure tends towards the coaxial dendritic direction. For this reason, by increasing the speed of laser scanning from 4 to 6 mm/s, the coaxial dendritic structure increases. The hardness measurement results indicate a decrease in the hardness up to the junction area from 430 to 370 Vickers and fluctuations of about 50 Vickers. Due to the high solidification speed, the average distance between the secondary dendritic arm space was 0.8 at the bottom, 1.01 in the middle, and 1.75 micrometers at the top of the sample. Due to the high cooling speed, only carbides and lava phases are formed. Also, the porosity measurement results of the cladding indicate a maximum porosity of 0.1 percent.

Due to the efficiency of 17-4PH steel in gas turbines and contact with external particles such as dust and foreign objects, physical deposits such as oil vapors will undergo cracks, wear, and chemical corrosion during operation and will be removed from the cycle of use. Part replacement is not cost-effective due to the high cost of raw materials. In this research, the corrosion resistance of 17-4PH steel cladding and stellite6 on 17-4PH steel substrate was investigated by the Tafel polarization test; In the cyclic polarization curve for 17-4PH steel, the direct scan current density is lower than the reverse scan, and positive hysteresis is seen in the cyclic polarization curve. Also the partially formed passive layer is unstable and fragile. In the 17-4PH cladding, the direct scan current density is lower than the reverse scan, and positive hysteresis is observed in the polarization curve. Also the formed passive layer is resistant to the formation of new holes. In the cover of stellite6, according to the shape of this cover, it has high pitting corrosion resistance in this solution; It forms a negative hysteresis curve and its inverse curve is located in a lower current density than the straight curve; Therefore, the corroded areas can repair themselves by forming a passive layer. By examining the results, it was found that the corrosion rate of stellite6 and stainless steel claddings has decreased by 91% and 50% compared to the substrate.

The purpose of this research is to laser cladding of stellite6 and stainless steel 17-4PH powders on the substrate of stainless steel 17-4PH, and investigate its solidification microstructure. The results showed that the microstructure of the stellite6 cladding has a cobalt solid solution ground phase with an FCC structure and Cr7C3 and Cr23C6 carbides. Also, the values ​​of the primary dendrite distance and the distance of the secondary dendrite arm have decreased by moving away from the interface; The reason for this is related to the difference in the cooling rate in different parts of the coating. The microstructure of 17-4PH stainless steel coating includes martensitic, ferritic, and austenitic phases; Due to the same chemical composition of the substrate and the cladding, the weight percentage of elements such as iron, nickel, chromium, and copper did not change from the cladding to the interface. It indicates the uniformity of the chemical composition of the cladding and the substrate. The calculated microhardness for the cladding of stellite6, the substrate and the cladding of stainless steel 7-4PH is about 480, 350, and 350 respectively. The reason for the higher microhardness of the cladding is the presence of chromium carbides (Cr7C3 and Cr23C6) formed in the cobalt field and the cobalt solid solution field of the cladding.