Journal of Welding Science

In this research, the transient liquid phase bonding of St52 carbon steel to WC-Co cermet using a copper interlayer with 50 μm thickness was done. For this purpose, samples were jointed to each other at a constant temperature of 1100 ºC and bonding times of 1, 15, 30, and 45 min. The microstructure of the joints was examined using an optical microscope and scanning electron microscope equipped with energy-dispersive X-ray spectroscopy. XRD analysis was also used to investigate the effect of bonding on the phase changes of the bonding area. Microhardness and tensile shear tests were also conducted to study the mechanical properties of the samples. Microstructural investigations showed the formation of three different zones including isothermal and athermal solidification zones and DAZ in the WC-Co base material side, which determine the characteristics of the samples. The isothermal solidification zone contained a Fe-rich solid solution and the athermal solidification zone contained a Cu-rich solid solution. η phase was not formed in the DAZ of WC-Co cermet at bonding times of 1 and 15 min. This phase was formed in the DAZ of WC-Co cermet by increasing the bonding time to 30 and 45 min. The microhardness studies showed that all samples had the same trend. Maximum microhardness was 1100 HV which was related to WC-Co base cermet and the lowest microhardness was about 220 HV which was related to steel base metal. Also, the maximum tensile-shear strength of the bonded samples was about 180 MPa for a bonded sample at a bonding time of 15 min, which was due to the increase in the volume fraction of iron-rich solid solution, as well as proper microstructural continuity and the presence of an optimal amount of copper-rich phase in the microstructure.

The dissimilar joint of alumina to copper with active filler metals Ag-Cu-Ti-Sn and Ag-Cu-Ti-Sn-%3.5Zr were done using the induction brazing process at temperatures of 840 and 860 ℃ for 15 minutes. The microstructures of joints were evaluated using optical microscope (OM) and scanning electron microscope (SEM). Vickers hardness test and shear tensile strength test were used to evaluate the mechanical properties. The results of the microstructural studies showed that the Al2O3/Cu joints using Ag-Cu-Ti-Sn and Ag-Cu-Ti-Sn-%3.5Zr fillers contain a reaction layer at the interface between alumina and the filler metal. At the area of the reaction layer with Ag-Cu-Ti-Sn filler metal, two TiO and Cu3Ti3O phases were observed, and also at the reaction layer with Ag-Cu-Ti-Sn-%3.5Zr filler metal, two TiO and ZrO2 phases were observed. The results of the shear strength test showed that due to the greater thickness of the filler metal and the lower thickness of the reaction layer, the joint with the filler metal Ag-Cu-Ti-Sn-%3.5Zr (14 MPa) has a higher shear strength as compared with the joint with filler metal Ag-Cu-Ti- Sn (9 MPa).

Soldering plays a crucial role in the electronics industry, driving the need for constant improvements in physical and mechanical properties and the management of intermetallic compound formation. Research in composite materials aims to achieve a uniform distribution of reinforcing particles within solder matrix to enhance their performance. This study investigates the integration of cobalt microparticles into SAC0307 lead-free soft solder alloy using the accumulative roll bonding (ARB) method. Microstructural analysis confirmed a homogeneous dispersion of cobalt particles within the solder after three ARB passes. Moreover, increasing cobalt content led to a reduction in the size of Cu₆Sn₅ intermetallic compounds, from 9 µm to 5 µm with 1% cobalt by weight. Examination of β-Sn grain morphology revealed the impact of cobalt particles on recovery and recrystallization kinetics in the solder. Mechanical testing indicated a 20% decrease in interlayer strength within composite solder sheets. Tensile tests showed a 28% increase in strength and a 31% decrease in elongation for composite solder alloy containing 1% cobalt. Differential scanning calorimetry (DSC) results revealed minimal change in the melting temperature of composite solder foil.
 

In this research, the influence of friction stir welding parameters (tool traverse speed ranging from 50 to 150 mm/min, and tool rotational speed ranging from 300 to 1100 rpm) was investigated on the microstructure and mechanical properties of AA5052 aluminum/PP-Z30S polypropylene joint. Results showed that joint formation was accompanied by the formation of mechanical locks in the shape of anchor-like aluminum pieces. Decreasing the heat input (either by increasing the tool traverse speed or decreasing the tool rotational speed) resulted in the formation of larger anchors. The results of tensile-shear test showed that increasing the tool traverse speed from 50 to 100 mm/min led to an enhancement in the fracture load (by ~10%), while at higher traverse speeds, the fracture load decreased (from 235 to 181 N) due to the formation of defects and voids at the joint interface. An increase in the tool rotational speed from 300 to 900 rpm resulted in a superior fracture load (by 70%) due to the formation of anchors perpendicular to the polymer surface with greater penetration depth.

In this study, 316L stainless steel and WC-10Co cermet were bonded by transient liquid phase process with BNi-2 interlayers with different thicknesses of 25 and 50 μm. The bonding process was conducted at 1050 °C for 1, 15, and 30 min. After bonding, the microstructure of the joints was examined using optical microscopy and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. Microhardness and tensile-shear tests were also performed to study the mechanical properties of the bonded samples. Microstructural analyses revealed that the formation mechanism of the solidified region in all samples was isothermal solidification, resulting in an isothermal solidification zone upon bonding. Additionally, the only phase present in the isothermal solidification zone was a nickel-based solid solution. In the diffusion-affected zone of the steel base material, complex borides formed regardless of the interlayer thickness. In the diffusion-affected zone of the WC-Co material, a brittle eta phase formed. Microhardness tests indicated that the maximum hardness in all samples was approximately 1100 Vickers, which was attributed to the presence of hard WC particles in the WC-Co base material. Furthermore, the highest tensile-shear strength, approximately 240 MPa, was observed in the bonded sample for 15 min with 50 μm thickness interlayer.

In this research, the effect of heat input on the microstructure and mechanical properties of the joint of two dissimilar steels D6AC and VCN 200 steel was investigated. For this purpose, the samples were welded with the current intensity of 130, 145 and 160 Ampers by GTAW process and using ER120 SG welding wire with a diameter of 2.4 mm. The metallographic results showed that the microstructure of the weld metal consisted of  lath martensite and acicular ferrite phases, which increased the volume fraction of ferrite from 5 to 32% with the increase of heat input, and the morphology of the ferrite changed from acicular to polygonal ferrite due to the decrease in the cooling rate. The HAZ area microstructure consist of bainite, lath martenrite and ferrite. The highest strength value was obtained in the welded sample with low heat input. With the increase of heat input, the tensile strength has decreased from 1154 to 965 MPa. Also, with the increase of heat input, the impact energy has increased in the welding zone due to the increase of stable phases, and in the HAZ zone due to the growth of the primary austenite grains and the reduction of the grain boundary locking effect. The results of the fracture analysis showed that the fracture occurred in the weld zone with low heat input, brittle fracture, and in the HAZ area, combination of ductil and brittle fracture occurred. With the increase in heat input, dutil fracture occurred in the welding zone and brittle fracture occurred in the HAZ zone due to grain growth.

In this research, copper/silver-silicon carbide Cu-Ag-SiC composite was prepared by the friction stir processing (FSP). For this purpose, nanometer and micrometer SiC particles were used as reinforcing particles. In order to evaluate the microstructural properties, X-ray diffraction (XRD) analysis, scanning electron microscope and optical microscope were employed. Evaluation of mechanical properties through microhardness measurement, tensile test and pin on disc test were utilized to evaluate the wear behavior of the composite. The results of X-ray analysis revealed the presence of two phases of CuAg solid solution along with SiC particles, which indicated the formation of Cu-Ag-SiC composite. The addition of nano-particles led to a significant decrease in the intensity of peaks compared to micro-particles. This indicated a decrease in the grain size of the CuAg matrix. Using the FSP in the presence of reinforcing particles and without it led to a decrease in the crystal size and average grain size compared to the sample without FSP. So that the grain size of the sample without FSP and the FSPed sample without reinforcing particles and with nano-reinforcing particles were found to be about 46.3, 19.2 and 3.6 µm, respectively. The wear mechanism in the sample before FSP was adhesive wear due to its soft nature of the matrix, and after FSP in the sample without reinforcing particles, the adhesive wear decreased and due to the addition of silicon carbide micro and nano- particles reinforcement, the wear mechanism in entirely altered to abrasive wear. Overall, it can be stated that the addition of silicon carbide nanoparticles by FSP leads to the fabrication of  Cu-Ag-SiC composite with high mechanical properties.

In this study, the effect of friction stir welding on the microstructure and mechanical properties of Fe-24Ni-4Cr austenitic steel was investigated. For this purpose, a sheet with a thickness of 1 mm was subjected to friction stir welding using a WC-5%Co tool at a traverse speed of 100 mm/min and a tool rotational speed of 450 rpm. Electron backscatter diffraction (EBSD) analysis revealed that this process led to grain refinement and an increase in high-angle grain boundaries in the stir zone, attributed to dynamic recrystallization during welding. Phase maps indicated an increase in the BCC phase fraction in the stir zone compared to the base metal. Given the high strain rate and the presence of stabilizing elements, this phase was primarily strain-induced martensite. Mechanical property assessments showed a significant increase in the tensile strength of the stir zone (450 MPa) compared to the base metal (350 MPa). Moreover, the yield strength of the stir zone (388 MPa) was substantially higher than that of the base metal (145 MPa), which can be attributed to grain refinement, an increase in high-angle grain boundaries, a higher dislocation density, and martensite formation. However, the ductility of the stir zone decreased due to higher stress concentration and dislocation density in this region. These findings suggest that friction stir welding can be an effective method for enhancing the strength and hardness of austenitic steels, but process conditions must be carefully controlled to prevent reductions in toughness and ductility.

Wire-arc additive manufacturing (WAAM) is a prominent technique for producing large metallic components due to its high deposition rate. Utilizing austenitic stainless steels in this process not only reduces production costs but also provides greater design freedom. Among these steels, SS310, known as heat-resistant steel in the industry, offers excellent oxidation resistance and high-temperature performance. However, it is highly susceptible to hot cracking during welding and additive manufacturing processes. In this study, the microstructure and mechanical properties of SS310 fabricated using WAAM with Cold Metal Transfer (CMT) and Gas Metal Arc Welding (GMAW) processes were compared. The results revealed that the CMT process, due to its lower heat input, effectively reduces the susceptibility of SS310 to hot cracking compared to the GMAW process. These findings emphasize the importance of selecting an appropriate process to achieve high-quality components and minimize structural defects.

This research looks at how microstructure and mechanical properties change in resistance spot welds of QP980 advanced high-strength steel. It specifically focuses on the effects of zinc coating and how it influences weld nugget formation, mechanical properties, and fracture behavior. The study involved microscopic examinations, mechanical tests, and finite element simulations to determine the thermal history of different weld zones. A key finding was that rapid cooling during the welding process led to the formation of, metastable phases, such as martensite, in both the weld nugget and the heat-affected zone. A finite element model of the welding process was used to simulate heat distribution and analyze the microstructure in various weld regions. This model showed that reaching the peak temperature during four-pulse resistance spot welding is delayed. This delay, along with proper hold times, helps prevent the formation of voids. The simulated thermal history and the rapid heating/cooling conditions effectively predicted the evolution and transformation of the microstructure in different weld areas. It was found that the presence of a zinc coating, and the resulting reduction in electrical contact resistance, delayed the formation of the weld nugget at lower welding currents. However, at higher currents, the primary source of heat generation shifted from contact resistance to bulk resistance within the steel sheet. This led to larger weld nuggets in coated samples compared to uncoated ones. While uncoated samples showed higher weld nugget hardness (512 Vickers) and greater tensile-shear strength (with a maximum load-bearing capacity of 28.1 kN in uncoated samples versus 24 kN in coated samples), coated samples were able to achieve the critical weld nugget size for a change in fracture mode at lower welding currents (9 kA compared to 9.5 kA).

This study experimentally investigates the repair of surface grooves on pure magnesium samples using the surface friction stir processing (SFSP). Grooves with depths of 0.5, 1, and 1.5 mm were created and subsequently repaired under constant parameters of 1400 rpm rotational speed and 40 mm/min travel speed. The results revealed that the stir zone (SZ) exhibited fine equiaxed grains due to complete dynamic recrystallization, leading to significant improvements in tensile strength and hardness compared to the base metal. The highest ultimate tensile strength of 66.1 MPa and hardness of 60 HV were achieved in the 1 mm groove sample. Additionally, partial dynamic recrystallization was observed in the thermo-mechanically affected zone (TMAZ), and complete elimination of grooves was confirmed in all samples. These findings demonstrate that the SFSP is highly effective for localized repair and enhancement of mechanical properties in magnesium components, offering a promising solution to extend the service life of damaged magnesium parts.

In this study, laser direct deposition was employed to fabricate a functionally graded transition between 17‑4PH stainless steel and Stellite 6. Specimens were designed and produced such that the chemical composition varied incrementally from 100% 17‑4PH to 100% Stellite 6, with each step involving a 25% decrease in the 17‑4PH content and a corresponding 25 % increase in Stellite 6. Microstructural evolution and elemental distribution were characterized by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), while mechanical properties were assessed via Vickers microhardness testing and uniaxial tensile tests. The microstructural analysis revealed a needle‑like martensitic matrix in the substrate, which transformed into cellular dendrites upon reaching the 25% Stellite 6 layer. As the Stellite 6 fraction increased, along with corresponding rises in Cr and W content, grain boundaries broadened and carbides accumulated within interdendritic regions. At the 50% composition, oriented columnar dendrites became prominent, and at higher Stellite 6 levels the dendritic structure refined further, ultimately evolving into an equiaxed morphology. Microhardness measurements showed a continuous increase from approximately 300 HV in the 17‑4PH substrate to 490 HV in the pure Stellite 6 layer. Tensile testing demonstrated that both yield strength (σᵧ) and ultimate tensile strength (σᵤ) remained within 1102–1159 MPa across all compositions, with no evidence of brittle phases or manufacturing defects. Elongation increased from 7% in pure Stellite 6 to 19% in pure 17‑4PH, with the 50%–50% gradient exhibiting an optimal balance of strength and ductility (14.5% elongation).

This study investigated the effects of pulsed current and constant current on the microstructure and mechanical properties of Hastelloy X superalloy welds produced by Gas Tungsten Arc Welding (GTAW), using ERNiCrMo-2 filler metal. Key microstructural parameters, such as elemental segregation, dendrite refinement, and weld metal uniformity, along with changes in weld strength and hardness, were examined and compared between the two welding modes. Microstructural evaluations were conducted using optical microscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) for phase identification. Pulsed current welding resulted in a finer microstructure with more equiaxed dendrites, reduced elemental segregation, and a more uniform distribution of M₆C carbides. Furthermore, this process led to significant improvements in hardness, impact toughness, and tensile strength of the weld metal compared to constant current welding. Fracture analysis confirmed ductile fracture behavior in all specimens, consistent with the microstructural and mechanical findings. The results of this research highlight the importance of using pulsed current in GTAW as an effective method for controlling the microstructure and enhancing the mechanical properties of Hastelloy X alloy joints. 

The friction stir spot welding (FSSW) process is a solid-state welding technique recognized as one of the most significant advancements in metal joining over the past decade. In this study, the effects of rotational speed and tool contact time, with a unique design different from previous research, on the microstructure and mechanical properties of 5754 series aluminum alloy were investigated. The workpiece was clamped using a specialized fixture on a radial drilling machine, and welding operations were performed using a FSSW machine at different rotational speeds and various tool contact times. Subsequently, the microstructure, microhardness, and tensile-shear strength of the welded spot region were evaluated. The results showed that increasing the tool rotational speed and prolonging the tool contact time led to an improvement of approximately 105% in the tensile-shear strength. According to statistical analyses, the factors of rotational speed and tool contact time significantly affected the shear strength with a confidence level greater than 95%; however, statistical analyses revealed different results regarding the relationship between rotational speed, contact time, and hardness.

The Ti-6242 alloy is of particular significance in additive manufacturing due to its high thermal resistance. However, components fabricated from this alloy using the electron beam powder bed fusion (EB-PBF) process often exhibit poor surface quality, primarily resulting from the layer-by-layer fabrication nature and and the presence of partially melted powder particles. In this study, laser polishing was employed to enhance the surface characteristics of EB-PBF fabricated Ti-6242 specimens using three laser powers (195, 260, and 325 W) and two scanning speeds (4.5 and 3 mm/s). The effects of these parameters on surface roughness, microstructure, and mechanical properties were evaluated through surface profilometry, metallography, hardness, and wear tests. The results indicated that the average surface roughness decreased by up to 93%, from 9.36 µm to 0.61 µm. Moreover, the initial α and β phases transformed into a fine, martensitic α′ phase within the polished layer, leading to a 33% increase in hardness—from 380 to 506 HV—and a significant improvement in wear resistance. Consequently, optimal adjustment of laser polishing parameters can simultaneously reduce surface roughness and enhance the mechanical performance of Ti-6242 components.

In this study, a novel two-step heating strategy was investigated for transient liquid-phase (TLP) bonding of the IN-738LC superalloy. The bonding process consisted of an initial heating at 1150 °C for 5 seconds, followed by holding at 1110–1130 °C for 3 to 40 minutes. The microstructural evolution during the process, as well as the interface morphology, was characterized and compared with conventional TLP joints. This approach significantly reduced the time required to complete isothermal solidification; the width of the central eutectic zone decreased from 45 µm at 3 minutes to 19 µm at 12 minutes, and the eutectic zone was completely eliminated after 40 minutes. Microstructural examinations revealed that the initial step of the two-step heating process produced a cellular–dendritic solidification interface, leading to a non-uniform distribution of porosity along the bond region. Subsequent homogenization removed boride precipitates and resulted in the formation of uniformly distributed γ′ precipitates similar to those in the base metal. These findings provide practical and microstructural insights into the influence of thermal profiles on interfacial evolution and offer a pathway for improving joint quality in nickel-based superalloys.

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.

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.

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.

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.