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

In this research, the new high entropy alloy of Al0.5CoCrFeNiNb0.5-Si0.1 was synthesized by mechanical alloying process. Then, the synthesized powder was deposited on Inconel 718 through direct laser deposition process. The effect of process parameters of laser cladding, such as laser power, powder feeding rate and scanning speed was investigated with 24 experiments for forming the optimized single-track claddings. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) were used to characterize the synthesized powders. Also, Optical Microscopy (OM) was used for investigation of geometry features and dilution of single-track clads. The XRD patterns of powder demonstrated that a singlephase solid solution (BCC) was formed after 30 hours of milling. SEM micrographs indicated the formation of solid solution after 30 hours. Also, the EDS results confirmed the compatibility of the chemical composition of the desired alloy with synthesized sample. OM images and geometrical calculations demonstrated that increasing the laser power and reducing the scanning speed led to increasing the width of single-track clad. The thickness or the height of single-track clads also was increased by reducing the scanning speed and increasing the feeding rate. Moreover, it was investigated that the laser power had the most effect on the penetration depth and dilution. The optimal conditions for direct laser deposition of synthesized powder on Inconel 718 was laser power of 500 W, feeding rate of 100 mg/s and laser scanning speed of 4 mm/s.

The aim of this study is to provide the characteristics of laser cladding and its application in three areas of coating, repair and prototyping. Among the innovations of this research, we can compare the features and advantages of laser coating with other conventional methods such as tags, etc. by mentioning sample studies. Also, the study of the areas of coating, repair / reconstruction and prototyping of laser coating with mentioning an objective industrial example in order to understand the exact application of other innovations of the present study is considered. In other words, the innovation of this research is the presentation of features and application of laser coating in three areas of coating, reconstruction and prototyping of industrial parts in comparison with other methods that were not addressed in a study. In this regard, the benefits of this technology will be presented first. Details of the laser coating process of the brake discs are given. How to repair the gas turbine fuel nozzle and rebuild the locomotive engine body by laser method will also be introduced. A prominent example of laser prototyping is the production of a helicopter engine combustion chamber. For a better understanding, a comprehensive overview of previous studies will be provided. Finally, the speed and capabilities used in each of the three areas of coating, reconstruction and laser prototyping are introduced.

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.

In this research, the microstructure of Inconel 625 cladded layer on ASTM A575 steel has been investigated. By examining different parameters, the optimal single-pass sample with the least amount of dilution, porosity and fusion and suitable wetting angle was determined. Then cladding process with the optimal parameter was performed. The microstructure of the cladding layer was evaluated from the base metal to the top. Due to different cooling rates, dendritic morphologies were observed at different distances. Also, the cladding layer was free of any cavities, porosity and cracks and its thickness was 0.9 mm (900 micrometers). The results of (XRD) and (EDS) analyzes indicate thatthe γphase is formed and there is a relatively uniform distribution of elements in the cladding layer. These results also indicate that no change in the chemical composition of the substrate surface was achieved near the interface.The hardness test results also show that the hardness starts from 450 VHN at the top surface and reaches to 135 VHN in the base metal with a gentle slope. This slope of hardness can be attributed to the cooling or heating rates of the substrate.

In this study, the effect of overlapping percentage on microstructure and mechanical properties of a single-pass coating by Inconel 625 powder laser has been investigated for quench-tempered ASTM A592 steel. In order to have a structural analysis, the inter dendritic distance was evaluated. For this purpose, scanning electron microscopy (FESEM) and Digimizer software were adopted. In order to investigate mechanical properties, elastic modulus, toughness, and micro hardness were evaluated. For the evaluation of elastic modulus, Noop indentation method was used, and for toughness studies, Evans method was applied. After the investigation, it was found that in the overlapping of single-pass 50% coatings, the heat input value is lower than overlapping in single-pass 75% coatings. It also contains a finer structure with much higher mechanical properties. This is in such a way that the inter dendritic distance in single-pass 50% coatings is about 0.91 µm. The average diameter of the dendritic columns is about 0.32 µm, hardness value is about 10%, Knoop hardness is about 9 units, elastic modulus is about 37 GPa, and toughness is about 9 MPa m1/2 higher in comparison with the 75% overlapping case.

Synthesis of a hard layer on the surface of mild steel is a proper way to rise its performance. Titanium carbide is among the preferred wear-resistant materials. In this research, the carbothermal synthesis of TiC via pulsed laser is studied. Ilmenite is used, as an economic raw material, for in-situ synthesis of TiC. However, the conversion of FeTiO3 to TiC in the short period of laser processing is challenging. Therefore two solutions were accompanied: the applied carbon content was more than the stoichiometry of reduction, while the blended ilmenite and graphite powders were mechanically activated. The increase of activation time to 200 hours was investigated via X-ray diffraction analysis. Afterward, a layer of the powder was preplaced on the substrate and the laser cladding was conducted. The effect of mechanical activation on the formation of the dispersed particles is studied, especially considering the transformation of oxides to TiC. SEM with EDS analyzer and XRD analysis were applied for this aim. The morphology of TiC particles and the microstructure of the matrix were also deliberated. The characteristic microstructure of directional solidification with equiaxed, cellular, dendritic and eutectic regions was observed. Otherwise, the Vickers microhardness measurements represented a gradual increase from the substrate toward the surface, which has reached to 1600 HV. It is confirmed that the synthesis of a composite layer with gradual dispersion of TiC particles via laser reduction of ilmenite is a feasible process.

Inconel 738 superalloy is widely used for hot-section components of gas turbines. These hot-section components are exposed to an extremely oxidative environment at high temperatures and consequently their life span is dramatically decreased. Considering this problem, NiCrAlY coatings can be effectively used to protect the hotsection components. In this study, laser cladding process was used to coat a NiCrAlY alloy on the surface of Inconel 738 substrate for the purpose of improving the high-temperature oxidation resistance. In order to compare the oxidation behavior, oxidation tests at temperature of 1200 ˚C were individually conducted on Inconel 738 substrate and freestanding laser-cladded NiCrAlY coating. Laser cladding of NiCrAlY alloy resulted in the formation of hypo-eutectic dendritic γ/β structure. Moreover, the results of oxidation tests showed that the oxidation resistance of the laser-cladded coating was significantly better than that of Inconel 738 substrate and this coating can be an effective choice for protecting the hot-section components made of Inconel 738 superalloy.