Journal of Welding Science and Technology of Iran

Investigation and analysis of the effect of TiO2 flux in activated gas tungsten arc welding (A-GTAW) of inconel 738LC nickel-based superalloy

R. Ashiri

Nickel-based superalloys are among the most critical materials used in high-temperature components of gas turbines, where their replacement costs and potential turbine damage necessitate effective protection and repair strategies. Optimizing repair methods to enhance efficiency and reduce costs has therefore been a continuous focus. The aim of this study is to improve the repair process of Inconel 738LC superalloy by reducing the susceptibility to liquation cracking. Activated tungsten inert gas (A-TIG) welding was performed on Inconel 738LC using a welding current of 60 A. Titanium dioxide (TiO₂) powder was employed as an activating flux, and weldments with four flux concentrations were examined. The microstructure was characterized using optical microscopy and scanning electron microscopy. The results revealed that flux concentration had a significant influence on penetration depth, with a concentration of 1 g/mL producing the maximum effect. At this concentration, weld penetration increased by 68% and weld pool volume by 63%, while the heat-affected zone width decreased by 12%. Arc imaging and quantitative/qualitative analysis demonstrated a constricted and focused plasma arc column in the presence of TiO₂ flux. Microstructural examinations further revealed suppression of columnar dendrite growth. It was found that TiO₂ flux enhances weld penetration and pool volume by constricting the arc and activating a reversed Marangoni flow, while simultaneously reducing HAZ width. However, the increased weld pool volume also intensified contraction stresses, leading to liquation cracking in the weld with the largest pool volume.

Optimization of process map and prediction of single-pass properties of Inconel 738LC by selective laser melting method with regression and genetic algorithm

R. Shoja Razavi

Selective laser melting (SLM) has been considered as a method for manufacturing large and complex industrial parts. Considering that structural defects are generally caused by process parameters, the optimal evaluation of parameter selection to minimize localized defects has been of interest. Therefore, a model was presented to predict the optimal single-pass geometric characteristics based on the main process parameters, namely laser power and scanning speed, to prevent defects in single-pass Inconel 738LC on Inconel 738 casting substrate. An optimal process map was obtained based on the use of linear regression method combined with genetic optimization algorithm with optimal combination parameters (PαVβ). Finally, based on the geometric characteristics of single-passes, an optimal region was identified on the process map. At a power of 325 W and a laser scanning speed of 800 mm/s, due to the decrease in the G/R ratio, the microstructure from the junction to the substrate to the top of the single pass has changed from columnar to coaxial dendritic.

Microstructural engineering of crack-free and corrosion-resistant weld interfaces in gray cast iron surface repairs using IP-GMAW

H. Hamed Zargari

Welding is one of the methods of surface repair of cast irons. In this study, surface repair of gray cast iron was first performed by gas metal arc welding method with ER70S-6 welding wire under inter-pulse current, heat input of 393 J/mm and dilution of 17%. Also, to compare the results, two samples were welded with ENi-CI and E6013 covered electrodes. Microstructural studies showed that the microstructure of the interface of the sample is composed of martensite with fine lathes and upper bainite. Despite the presence of cementite (Fe₃C) next to alpha iron (α-Fe) in the interface area, the formation of incomplete mixing zone with bainite lathes in the ferrite zone has led to increased toughness and prevented crack formation. The hardness of the ER70S-6 sample was similar to that of the E6013 sample at the interface, at about 809 Vickers, which is 334 Vickers higher than the hardness of the ENi-CI sample. The results of the open circuit potential and potentiodynamic polarization tests showed that the ER70-CI sample, with a corrosion potential and current of -653 mV and 6.8 μA/cm², had a higher polarization resistance and was more resistant to galvanic corrosion than the ENi-CI sample (-622 mV and 8.9 μA/cm²).

Investigation of the effect of explosive parameters on the interface, mechanical properties and corrosion behavior of heterogeneous joints of phosphor bronze and St37 steel using explosive welding process

S. A. A. Akbari Mousavi

In this study, the metallurgical and mechanical properties of the interface obtained by explosive welding of 8-92 phosphor bronze to St37 carbon steel were investigated. The effects of explosive welding parameters such as explosive charge amount and stand-off distance on the shape and microstructure of the interface, mechanical properties and corrosion behavior were investigated. The results showed that with increasing stand-off distance and explosive charge amount, the velocity and angle of impact increased, and this phenomenon led to the interface transforming from a smooth to a wavy state and resulting in melted and separated regions. The results obtained from scanning electron microscope (SEM) images showed that with increasing stand-off distance and explosive charge amount and consequently increasing impact velocity, the length and height of the waves created at the interface increased. Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis showed that no intermetallic compounds were formed at the joint interface. The results of the microhardness test also indicated that the hardness around the joint interface increased by 25% due to plastic deformation and work hardening caused by the intense impact of the base and flying plates. By performing shear strength tests, it was found that in all samples, failure occurred in the phosohor bronze layer and no failure occurred due to separation of the samples from the interface. By performing tensile tests, it was found that the ultimate tensile strength increased from 430 to 488 MPa with increasing stand-off distance and explosive load. Polarization acquisition and impedance spectroscopy (EIS) tests showed that with increasing impact energy, the corrosion potential decreased and the corrosion current density increased significantly from 5.5 to 13.2 μA/cm².

Experimental comparison of extruded and 3D-printed copper parts for manufacturing induction hardening coils

M. Safari

Copper coils are essential components of induction hardening machines. The traditional manufacturing process of these coils utilizes extruded copper profiles. In this study, the production of copper profiles using metal 3D printing was experimentally investigated. Two copper samples with hollow square cross-sections, produced by extrusion and metal 3D printing, were evalated for the purpose of manufacturing induction hardening coils. Density, electrical conductivity, hardness, and surface roughness tests were performed in accordance with the relevant standards. The quantitative results for the extruded and 3D-printed samples were, respectively: density of 99% and 93% of the theoretical density of copper; electrical conductivity of 100.8% and 99.1% relative to the annealed copper standard; Brinell hardness of 50 and 59 HB; and surface roughness (Ra) of 0.324-0.533 and 11.949-13.194. The results indicated that the extruded sample possessed higher density, superior electrical conductivity, and a smoother surface, whereas the 3D-printed sample exhibited higher hardness, lower density, and greater surface roughness. These findings demonstrate that metal 3D printing can be utilized for the manufacturing of induction hardening coils.

A novel approach to enhance the joints performance of AA1100 joints fabricated by friction stir welding (FSW)

Gh. Azimiroeen

In this study, the effect of an additional pass using a pinless tool on the microstructure and mechanical properties of friction stir welding (FSW) AA1100 butt joints was investigated. The microstructure was characterized using optical microscopy and scanning electron microscopy (SEM), while the mechanical properties were evaluated by tensile and Vickers microhardness tests. The results indicated that applying additional passes led to grain refinement of the microstructure and a reduction in grain size to approximately 1 µm in the stir zone. Moreover, the microhardness in the upper stir zone increased from about 30 HV in the initial joint to nearly 55 HV in the processed sample. Tensile test results also revealed an improvement in mechanical properties, with the ultimate tensile strength (UTS) increasing from 86 MPa to 101 MPa, corresponding to an enhancement of approximately 17%. This improvement was mainly attributed to grain refinement and the increased grain boundary density.

Microstructural characterization, solidification behavior, and mechanical properties of 316L stainless steel fabricated by wire and arc additive manufacturing

S. G. Shabestari

In the present study, 316L stainless steel walls were fabricated using the WAAM process under controlled primary parameters including welding current, voltage, torch travel speed, and wire feed rate. The solidification behavior, microstructural evolution, and mechanical performance of the WAAM-produced 316L stainless steel were systematically investigated. Microstructural observations revealed that the final structure consists of a γ austenitic matrix containing approximately 8.5% δ ferrite. Tensile testing demonstrated the simultaneous achievement of high strength and ductility. Specimens extracted perpendicular to the build direction exhibited an ultimate tensile strength of about 569 MPa, a yield strength of 378 MPa, and an elongation of approximately 69%. Mechanical anisotropy was estimated to be around 7.5%, attributed to the directional growth of columnar grains. The enhanced ductility compared to conventional cast steels is associated with the fully austenitic matrix, the controlled amount of δ ferrite, the refined dendritic microstructure, and the localized annealing effect resulting from the deposition of successive layers. Microhardness measurements along the build height indicated a gradual decrease in hardness with increasing distance from the substrate, caused by grain coarsening due to heat accumulation and the lower cooling rates in the upper layers. Overall, the findings demonstrate that the WAAM process is capable of producing 316L stainless steel with a balanced combination of high strength and ductility, provided that solidification behavior and thermal history are properly controlled. These results may serve as a basis for microstructure optimization and anisotropy reduction in industrial additive manufacturing applications.

Comparison of mechanical and microstructural properties of parts welded with dissimilar alloys AA5052-AA3105 using friction stir welding and TIG

H.R. Rezaei Ashtiani

The joining of dissimilar aluminum sheets is an important issue in the optimization of industrial joints due to the differences in physical, mechanical and metallurgical properties. In this study, the mechanical behavior and microstructural changes of bimetallic joints made of AA5052 and AA3105 alloys joined by two methods of TIG welding (TIG) and friction stir welding (FSW) were investigated and compared. First, preliminary experiments were carried out to optimize the parameters of the friction stir welding and TIG welding processes and to select appropriate levels of the process parameters. The results of mechanical experiments showed that in the FSW welded samples, the failure occurred mainly in the weld zone, but in the TIG welded samples, the failure occurred in the base metal. The tensile test results showed that the AA5052 sample had the highest tensile strength (273 MPa) and the highest elongation percentage (20%), and the F 3-5 welded sample with a strength of 89 MPa and 6% elongation performed worse than the T 3-5 welded sample and fractured in the weld area. The microhardness test results showed that the TIG welded sample had a higher hardness in the weld area than the FSW method due to the use of 5356 ER filler. Finally, by analyzing and comparing the results obtained from the tests related to the mechanical properties obtained from each method, it was found that the TIG method performed better than FSW in joining some alloys.

Effect of forge pressure on microstructure and mechanical properties of rotary friction welding of SS 304 to different plain carbon steels

S. R. Elmi Hosseini

In this research, the influence of various forge pressure values and also the chemical composition of different carbon steels on rotary friction welding of SS 304 to carbon steels has been investigated. The steel rods of AISI 1015, 1030, and 1045 have been RFWed to SS 304 using 20, 40, and 80 bar forge pressure. Results indicated the 40 bar forge pressure as the optimum value, and by applying pressures below this number, the material flow in the weld interface would be tackled, resulting in improper mechanical values. By exceeding the optimum forge pressure, most of the viscoplastic material inside the weld interface would be rejected from that area in the form of flash, causing the weld to be done at a relatively low temperature. Microstructural investigation has been done by optical and scanning electron microscopes. Results showed that the weld zone is extremely fine due to DRX, and in the interface, a pro-eutectoid ferrite layer is formed, which has an increasing width when the heat input increases. Tensile test results showed that the optimum weld specimen is the RFW of AISI 1030 to SS 304 using 40 bar forge pressure, 40 bar friction pressure, 5s friction time, and 1500 RPM rotational speed. This specimen has shown 116 % joint efficiency and 715 MPa ultimate tensile strength.

Effect of welding parameters on energy absorption and fracture mode in resistance spot welding of DP and HSLA automotive steels

R. Ashiri

In this study, the effects of welding current intensity (9 and 10 kA) and holding time (5 and 40 cycles) on the energy absorption and failure mode of a dissimilar joint between DP590 and HSLA440 steels in the resistance spot welding process were investigated. For this purpose, four parameter combinations were prepared, and a tensile–shear test was performed on each sample. The results showed that increasing the current from 9 to 10 kA at a holding time of 5 cycles led to an increase of about 1 kN in strength; however, at a hold time of 40 cycles, changing the current resulted in a decrease of approximately 1.6 kN in strength. Therefore, the role of current is limited and dependent on the saturation of the weld nugget diameter. In contrast, increasing the hold time from 5 to 40 cycles had the most significant effect, increasing the energy absorption by about 217 J. Failure mode analysis also revealed that samples with longer hold times predominantly exhibited pull-out failure (PF), absorbing significantly more energy compared to interfacial failure (IF). Overall, the results indicate that controlling cooling through increasing the holding time is the most effective factor in enhancing absorbed energy and altering the failure mode in DP590/HSLA440 joints.

Microstructure and mechanical properties of thin-walled SS316L fabricated by IP-GMAW-based via WAAM

H. Hamed Zargari

Wire and Arc Additive Manufacturing (WAAM) is one of the modern methods of fabrication parts by arc welding under shielding gas. In this research, the thin-wall of austenitic stainless steel 316L was fabricated via WAAM based on inter-pulse current; accordingly, a thin-wall was fabricated in 25-layers using two different strategies with a reciprocating torch movement pattern. Considering the equivalent chromium and nickel content in the Scheffler diagram, it was predicted that the microstructure solidification was done in the austenitic-ferritic (AF) state. Microstructural examination by optical microscopy and X-ray diffraction confirmed the presence of austenite matrix phase alongside ferrite dendrites (about 5%). The tensile test results showed that samples extracted in the vertical direction with an average tensile strength of 454 MPa had about 12% higher strain rates than horizontal samples with a tensile strength of 436 MPa. Also, examination of fine and coarse indentations on the fracture surface of tensile test specimens by scanning electron microscopy showed that the fracture of the specimens was of the ductile type. The hardness of the fabricated thin-wall was measured in the range of 200 to 265 Vickers with an average of 234 Vickers.