Welding of high entropy alloys: Progresses, challenges and perspectives

The effects of different transient liquid phase (TLP) bonding times on the microstructure and mechanical properties of Hastelloy X joints made by Ni–Cr–B–Si–Fe filler alloy were investigated. The specimens were TLP bonded at 1070 °C for holding times of 5, 20, 80, 320, and 640 min. The electron probe microanalysis (EPMA) results revealed that the main eutectic phases observed at the joints following incomplete isothermal solidification were Ni-rich borides, Ni-rich silicides, Ni–Si eutectic, and some Cr-rich borides. A high density of plate-like, blocky, and acicular (Mo and Cr)-rich borides were observed in the diffusion-affected zone (DAZ) of the samples; however, increasing the holding time decreased the contents of these phases. The solid-state diffusion was found to be a more effective transportation phenomenon than base metal dissolution at longer holding times. The increased DAZ thickness and the complete isothermal solidification as a result of the improved solid-state diffusion helped increase the uniformity of the hardness profile of the TLP bond at higher holding times (320 and 640 min). The results showed reverse relationship between the athermally solidified zone (ASZ) width and the bonding strength. The highest tensile strength (∼617 MPa) was achieved for the sample bonded at a holding time of 320 min; this strength was more than 80% of the base metal strength. A fractographic analysis of the tensile failure revealed a cellular fracture surface, exhibiting the characteristics of both brittle and ductile fractures. The sites prone to stress concentration and crack initiation were reduced with the completion of isothermal solidification.

Influence of bonding time on the transient liquid phase bonding behavior of Hastelloy X using Ni-Cr-B-Si-Fe filler alloy

Effect of transient liquid phase bonding time on the microstructure, isothermal solidification completion and the mechanical properties during bonding of Inconel 625 superalloy using Cr-Si-B-Ni filler metal

Microstructures and mechanical properties evolution of IN939 alloy during electron beam selective melting process

Phase formation during dissimilar transient liquid phase (TLP) bonding of IN939 to IN625 using a Ni-Cr-Fe-Si-B interlayer

High-strength low alloy (HSLA) S500MC steel is widely used for chassis components, structural parts, and pressure vessels. In this study, the effects of heat input during automatic gas tungsten arc welding (GTAW) on microstructure and mechanical properties of thermomechanically controlled processed (TMP) S500MC steel were investigated. A butt joint configuration was used, and welding was performed in autogenous mode. Six different levels of heat input namely 1.764 kJ/mm, 1.995 kJ/mm, 2.035 kJ/mm, 2.132 kJ/mm, 2.229 kJ/mm, and 2.33 kJ/mm were considered. Microstructural investigations revealed a different microstructure than base metal in the fusion zone (FZ) of all welded joints which was most likely due to a lath martensitic microstructure surrounded by retained austenite. With increased heat input, the amount of retained austenite and the size of packets increased. In the heat-affected zone (HAZ), two distinct regions of coarse grain (CG-HAZ) and fine grain (FG-HAZ) were observed. Due to the presence of carbides in the HAZ, mostly a martensitic microstructure with smaller packets, compared to FZ, was formed. By increasing the heat input and through the dissolution of carbides, the dimension of packets increased. Due to microstructural changes and grain growth, in both the FZ and the HAZ, the mechanical properties produced by TMP were lost in these regions. However, failure occurred in the base metal of all samples with a maximum tensile strength of 690 MPa. Thus, tensile strength in the weld zone and HAZ were higher than the base metal even for the highest heat input indicating the formation of a good joint between S500MC plates with GTAW, regardless of heat input.

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Influence of Heat Input on Microstructure and Mechanical Properties of Gas Tungsten Arc Welded HSLA S500MC Steel Joints

• The applicability of a blue laser system for welding Ni-coated copper and mild steel. • Blue laser welding of cylindrical cell terminals for the first time. • Effects of process parameters on microstructure and mechanical properties. • Effect of corrosive environment on joint strength. Modern advancements in blue lasers offer a promising alternative to conventional infrared laser welding of highly-reflective battery materials. In this study, a high-power blue laser system was used to weld the low thickness Ni-coated copper and mild steel used in 18650-type cylindrical cells. The effect of laser power on the penetration depth, interface width, and weld bead quality was studied. The weld microstructure was characterized by employing optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The mechanical performance of the welds was evaluated through peel testing and microhardness measurements. The results show that the penetration depth and weld width increased with laser power. Increasing the laser power to more than 1.3 kW resulted in a damaging effect on weld bead quality creating defects such as crack, under-fill, and distortion due to excessive heat input. Weld samples fractured in the heat-affected zone of Ni-coated copper during peel testing due to grain growth in copper. The maximum peel strength of 158.8 N was achieved for the 1.2 kW sample. The formation of a composite microstructure between Cu and Fe with a higher hardness than parent metals was observed inside the weld nugget. The hardness of this zone increased with the laser power due to an increase in the amount of Fe, reaching 185 HK for the 1.5 kW sample. By exposure to a corrosive environment, the peel strength drastically decreased and the failure occurred at the weld interface. For the 1.2 kW sample, the peel strength was reduced to around 57 N. The process initially developed for coupons of Ni-coated copper and mild steel was further tested on the positive and negative tabs of 18650-type cylindrical cells. The weld microstructure showed a lack of defects. However, due to varying thicknesses and associated heat sinks further process refinement is required for optimum joint quality. 

Blue laser welding of low thickness Ni-coated copper and mild steel for electric vehicle (EV) battery manufacturing

Laser beam welding of copper (Cu) using near-infrared radiation is extremely challenging due to its high thermal conductivity and large laser reflectivity. In the present study, the challenges and benefits of using spatial beam oscillation during quasi-continuous wave (QCW) pulsed laser beam welding of 0.4 mm Cu to 1 mm Cu in lap joint configuration are presented. This work demonstrates how laser beam oscillating parameters can be used to control the laser weld quality and laser weld dimensions for Cu-Cu joining. Compared to a non-oscillated laser beam, welds made using laser beam oscillation showed fewer spatters, porosities, and better surface quality. Four levels of oscillating amplitudes (0.2 mm, 0.4 mm, 0.6 mm, and 0.8 mm) and oscillating frequencies (100 Hz, 200 Hz, 300 Hz, and 400 Hz) were compared to reveal the effect of beam oscillation parameters. The weld width was mainly controlled by oscillating amplitude, while weld penetration was affected by both oscillating amplitude and frequency. As the oscillating amplitude increased, the weld width increased while the weld penetration decreased. Increasing the oscillating frequency reduced the weld penetration but had a negligible effect on the weld width. The maximum tensile force of approximately 1944 N was achieved for the joint with a high width-to-depth ratio with an oscillating amplitude of 0.8 mm and an oscillating frequency of 200 Hz.

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Quasi-Continuous Wave Pulsed Laser Welding of Copper Lap Joints Using Spatial Beam Oscillation

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Correction to: Effects of laser process parameters on the hardness profile of AISI 4340 cylindrical samples: statistical and experimental analyses

In the present paper, continuous Ytterbium Laser Systems (YLS) fiber laser hardening of cylindrical AISI 4340 steel specimens was studied using experimental and statistical analyses. Three laser parameters, namely laser power, laser feed speed, and sample rotation speed were selected to evaluate their influence on the depth of the hardened zone and the maximum surface hardness. Mathematical models were developed as a function of these three parameters and the analysis of variance (ANOVA) was used to conduct the statistical study. Microhardness measurements revealed three distinct regions in the heat-affected zone (HAZ) of all samples: the hardened zone (Z1) near the surface, with the highest value of hardness, the hardness loss zone (Z2), where hardness had started to decrease, and the overheated zone (Z3) adjacent to the core, with hardness values that were less than those of the base metal. Based on experimental measurements, a maximum surface hardness of 60.8 HRC was attained. Furthermore, the maximum depth of the hardened zone was observed as 500 µm. The microstructures of laser-hardened samples were studied using optical and scanning electron (SEM) microscopes. The hardened region appeared to have a hard martensitic microstructure. By comparing the predicted and measured data for maximum microhardness values, it was revealed that the models represent the experimental values with correlations close to 100%. 

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Amirhossein Sadeghian

Papers

Influence of Heat Input on Microstructure and Mechanical Properties of Gas Tungsten Arc Welded HSLA S500MC Steel Joints

Blue laser welding of low thickness Ni-coated copper and mild steel for electric vehicle (EV) battery manufacturing

Quasi-Continuous Wave Pulsed Laser Welding of Copper Lap Joints Using Spatial Beam Oscillation

Correction to: Effects of laser process parameters on the hardness profile of AISI 4340 cylindrical samples: statistical and experimental analyses

Effects of laser process parameters on the hardness profile of AISI 4340 cylindrical samples: statistical and experimental analyses