Journal of Welding Science

This research examines the microstructure and microhardness in the additive manufacturing process using the laser metal deposition method with the deposition of Inconel 718 powder on the Inconel 738 substrate. For this purpose, deposition with different laser power was performed on different substrates, and the microstructure and hardness of the layers were studied. Three layers of Inconel 718 powder were deposited on the substrates. The results show that the laser power parameter in the deposition process significantly affects the microstructure of the samples. By increasing the laser power by 100 W, the distance between the phases γ' in the substrate and γ'' in the layers decreased significantly. With increasing laser power, an increase in the geometric dimensions and volume percentage of the γ'' phase was also observed. In addition, increasing the laser power decreased the volume percentage of the Laves phase. By measuring the microhardness of the deposition layers, it was found that the hardness of the third layer decreases with increasing laser power.
 

In Wire and arc additive manufacturing (WAAM) based on Gas metal arc welding (GMAW) is one of the methods of manufacturing metal layer by layer. One of this method's basic steps is predicting the welding geometry created in each welding step. In the current research, an experimental study was conducted in this field considering the effective parameters of welding geometry. For this purpose, three parameters of voltage, welding speed, and wire feeding speed were considered as effective parameters on the welding geometry of the process. The width and height of the weld bead was selected as the answer according to the type and application of the research. The least squares support vector machine was used to model the welding geometry in the process. The results obtained from the regression (R2) of train, test, validation, and total were 0.945, 0.793, 0.894, and 0.881 respectively. The comparison between the experimental data and the model data shows the significance of the proposed model.

This study aimed to investigate the effect of electron beam welding parameters on the microstructural characteristics and mechanical properties of the dissimilar joint between 17-4PH stainless steel and Ti6Al4V alloy. For this purpose, the welding of these two alloys was performed with an copper interlayer with a thickness of 1 mm. Two different welding speeds of 0.7 and 0.9 m/min with four levels of beam offset  (0, 0.2, 0.4 and 0.6 mm) from the center of the interlayer towards the steel were used to accomplish the experiments. The results show that by using the copper interlayer with thickness of 1 mm, the cracks caused by the formation of intermetallic compounds are removed from the weld pool. At the interface between the titanium and the weld pool, at the beam offset  of 0 and 0.2 mm, a solid solution of copper and TiCu2 intermetallic compounds is formed, while at the beam offset  of 0.4 and 0.6 mm, a solid solution of copper and TiCu intermetallic compounds is formed. The weld pool, at the beam offset  of 0 and 0.2 mm, consists of TiCr2+TiFe2 intermetallic compounds while at the beam offset  of 0.4 and 0.6 mm, solid solution of iron (α-Fe), solid solution of copper and TiCu intermetallic compounds are formed. The highest value of hardness is observed at the interface between the weld pool and the titanium alloy, as well as at the interface between the weld pool and the steel, which is due to the presence of intermetallic compounds with high hardness in these regions. By increasing the welding speed and the beam offset, the hardness value decreases, which is due to the reduction of brittle intermetallic compounds in the joint structure. By increasing the beam offset from 0.4 mm to 0.6 mm at the speed of 0.7 m/min, the shear strength increases from 180 MPa to 210 MPa and at the speed of 0.9 m/min, the shear strength raises from 230 MPa to 250 MPa. The welded sample with the welding speed of 0.9 m/min and the beam offset of 0.6 mm has the highest shear strength equal to 250 MPa. The failure in all samples happened at the interface between the weld pool and the titanium alloy, which shows that the weakest region in the joint is this interface.

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.

In this study, gas-tungsten arc welding was used for the cladding of two high entropy alloys of AlCoCrFeNi (Al1) and Al0.7CoCrFeNi (Al0.7) onto plain carbon steel plates. The welding process was carried out at a welding current of 180 A and a welding speed of 1.4 mm/s. The microstructures, craking behavior, phase composition, and hardness of the clads were characterized using various methods, such as optical microscopy (OM), field emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD) analysis, and microhardness measurements. The results indicated that the Al1 clad had a petal-like structure of the BCC and Cr-rich phases. Both intergranular and transgranular cracks were identified in the Al1 alloy, which were recognized to be solidification cracks. Thermal stress and brittleness of the BCC phase promote cracking of the Al1. On the other hand, in the Al0.7 alloy, in addition to the BCC phase, a new FCC phase was  formed with various Widmanstatten and dendritic morphologies in the clad microstructure and the Cr-rich phase was not observed. Furthermore, in this alloy with lower Al content, a crack-free clad was obtained. The crack prevention in the Al0.7 alloy was attributed to a combination of factors, including a decrease in the solidification range, formation of the FCC phase, and reduction in hardness.

Reconstruction of parts using direct laser deposition can create a combination of high wear resistance properties, good toughness, and  corrosion resistance. In this research, the wear properties of Inconel 625 powder cladding on the same substrate have been investigated; For this purpose, room temperature and high temperature wear tests have been used. Mass reduction, friction coefficient, width and depth of wear penetration have been measured. Also, a scanning electron microscope with an energy disspersive spectroscopy system was used to evaluate the cladding surface. The results showed that the mass reduction due to wear at Inconel 625 cladding compared to Inconel 625 substrate has decreased by 7% and 52%, respectively, at temperatures of 25°C and 620°C. Also, the wear mechanism of the room temperature of the cladding is mainly scratchy, and the wear mechanism of high temperature is mainly sticky.

5xxx and 6xxx series alloys are among the most widely used aluminum alloys in various industries, including automobile, shipbuilding and aviation industries. In this research, the joint of two alloys AA6061-T6 and AA5052-H12 was investigated at 4 transmission speeds of 60, 90, 120 and 180 mm/min and 3 rotation speeds of 600, 800 and 1000 rpm. These investigations were carried out in the condition that each of the two alloys was placed in two progressive and regressive sides. The results of these studies showed that the highest tensile strength is when the AA5052 sample is placed on the advancing side and the transfer speed is 90 mm/min and the rotation speed is 600 rpm, and in this case, the final tensile strength value is equal to 197 MPa. In addition, the results showed that, generally, the tensile strength decreases with an increase in the transmission speed at a constant rotational speed, and with an increase in the rotational speed at a constant transmission speed, the tensile strength increases. In addition, microscopic and macroscopic examination of the sections of all samples was performed and various areas and defects were examined. According to the investigations carried out on the microstructure, the grain size in the weld nugget compared to the base metal, HAZ and TMAZ decreases. The grain size in HAZ is the largest in all samples, and this causes a decrease in weld strength in this zone.

In this study, non-homogenous welding of nimonic 75 superalloy to Monel 400 with 1 mm thickness was investigated with pulsed Nd:YAG laser welding. The mechanical properties of the joint were analyzed with optical and scanning electron microscope, X-ray diffraction, micro-hardness test and tensile test. In the case of non-homogeneous welding of Nimoinc 75 superalloy to Monel 400, defects such as liquation cracks and porosity in the welded samples were observed. these defects were removed with increasing the preheating temperature and decreasing the heat input. The results showed the voltage, pulse width, pulse frequency and welding speed should be selected as 500 volts, 9 milliseconds, 3 Hz and 0.9 mm/s respectively to reach the proper penetration depth. Also, the investigations show that the welding structure is composed of austenitic matrix containing columnar dendrites and some cellular areas. The mechanical properties of the weld metal were reduced after joining and segregation causes a change in the amount of elements and the appearance of intermetallic compounds in the spaces between dendrites and cells. All non-homogeneous samples broke during the tensile test from the weld metal area.

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.