Welding in the World最新文献

Herein, diamond and diamond/WC composite coating were deposited on the surface of 45 steel by induction brazing. The microstructures of the composite coating were studied by scanning electron microscope, energy dispersive spectrometer, and X-ray diffractometer, and the wear resistance of the composite coating was assessed by rubber wheel abrasion test. The microstructure investigation indicates that both Cr₃C₂ and Cr₇C₃ carbides are formed at the interface between the diamond and BNi-2 alloy matrix, and Ni₂W₄C and NiW was formed at the interface between WC and BNi-2 alloy matrix. When WC is added to the diamond coating, the microhardness of the BNi-2 alloy matrix increases, and the microhardness of the BNi-2 alloy matrix reaches 583 HV0.2, which is 7.6% higher than that of the coating without WC. In addition, after 120 min wear test, the wear loss of the diamond WC composite coating is 0.337g, which is reduced by 31.5%. In the wear tests, abrasive wear was the main wear mechanism for composite coating. WC particles in diamond/WC composite coating improved the wear resistance and hardness of the alloy matrix.

Graphical Abstract

A novel Ti₅₀Zr₃₀Cu₈Co₇Fe₅ (at.%) amorphous/nanocrystalline brazing filler metal (BFM) with low Cu content and low liquidus temperature (1154 K) was developed and prepared into a flexible ribbon by melt-spinning for brazing Ti-6Al-4V (Ti64) alloy. The effects of vacuum brazing temperature and holding time on the microstructure and mechanical properties of the joints were investigated. For the joint brazed at a low brazing temperature of 1173 K for 15 min, a messy segregated layer consisted of α-Ti, β-Ti, and Ti₂Cu intermetallic compound was formed in the center of the braze zone, resulting in relatively low tensile shear strength (~ 310 MPa) of the joint. With the brazing temperature increasing up to 1233 K, the joints exhibited uniform Widmanstätten structure mainly consisting of acicular α-Ti, β-Ti, and sporadic Ti₂Cu intermetallic compound without segregated layer. The Ti64 joint brazed at 1233 K for 15 min possesses an improved tensile shear strength of ~ 400 MPa. By extending the holding time to 30 min and 45 min at the brazing temperature of 1233 K, the amount of Ti₂Cu intermetallic compound in the braze zone decreased, leading to the high strength of the joints up to ~ 446 and ~ 491 MPa, respectively.

This investigation focused on the welding of Q690 bainitic steel using vacuum electron beam welding with currents of 350 and 500 mA, yielding samples with diverse microstructures and distinct fusion and heat-affected zones. Additionally, H₂S immersion tests were conducted to evaluate the susceptibility of the welded microstructure to hydrogen embrittlement. The results indicated different fracture sites in the samples welded under currents of 350 and 500 mA. Under the 350-mA welding current, fracture occurred in the coarse-grain heat-affected zone (CGHAZ) because of the high dislocation density in the bainitic ferrite plates and the low concentration of retained austenite in the CGHAZ. Under the 500-mA current, hydrogen embrittlement and fracture occurred in the upper bainite of the fusion zone because of the high welding-induced heat input that led to coarse precipitation and micro-void coalescence.

Rotary friction welding is a fast and efficient joining process with the possibility to join materials that are not weldable by conventional GMAW-processes. If done properly, the welds have a static and fatigue strength higher than the base material. However, in literature, there exists only sparse information on the design and assessment of these joints in terms of fatigue. The fatigue strength of two material combinations, S355-S355 and S355-1.4301, is investigated based on two specimen conditions, (1) with flash and (2) with flash mechanically removed. In the majority of tests, failure occurred outside the weld zone, in the base material. The derived endurable nominal stresses are compared to the design S-N curve of conventionally welded specimens and show a more than 50% higher fatigue strength.

Fatigue life evaluation of welded joints under multiaxial loading usually refers to stresses normal to the weld and shear stresses. Stresses parallel to the weld are not considered in most experiments or the well-known Gough-Pollard criterion. Hence, the Gough-Pollard criterion has recently been extended to include all stress components at the weld surface. In this paper, both the original and, for the first time, the extended Gough-Pollard criterion are applied to different welded specimens under multiaxial loading that includes stresses parallel to the weld. As shown, the original criterion is insufficient to evaluate such stress states. This is because the calculated fatigue life becomes less conservative as the stresses parallel to the weld become more significant. The extended criterion, on the other hand, shows greatly improved accuracy while significantly reducing the likelihood of non-conservative results. In conclusion, the extended Gough-Pollard criterion can describe fatigue life under multiaxial loading better than the original version and provides reliable and conservative results for welded joints. The main findings are valid for the nominal, the hot spot, and the notch stress concept.

Welding titanium to aluminum alloys is difficult and challenging due to the differences in their chemical and physical properties. The aim of this research is to investigate the effect of integrating a pure copper (Cu) interlayer on the mechanical behavior and the microstructure of the dissimilar TA6V/AU4G Rotary Friction Weld (RFW) joints. Tensile tests and microhardness measurements were conducted to demonstrate the mechanical behavior of the RFW joints. Microscopic observations were carried out to identify the structural nuances and quality of the weld joint. Energy Dispersive X-Ray (EDX) analysis was performed to reveal the interdiffusion phenomenon at the weld interfaces, and the present phases were identified through X-Ray Diffraction (XRD) analysis. The results suggest that adding a Cu-interlayer changes the flow direction of thermoplastically deformed material, leading to an increase in the Ultimate Tensile Strength (UTS) value up to 393.34 MPa. The microhardness profile of the TA6V/Cu/AU4G RFW joint is similar to that of the TA6V/AU4G joint, except for noticeable difference at the interface. In addition, the use of a Cu-interlayer has been shown to be more effective in preventing the formation of brittle TiAl₃ intermetallic compounds (IMCs) compared to direct TA6V/AU4G welds. The inclusion of a Cu-interlayer results in a significant improvement in joint efficiency by 105.32%, demonstrating the effectiveness of the Cu-interlayer in enhancing the mechanical properties of the dissimilar TA6V/AU4G RFW joints.

This study compares the paste/slurry formed by different filler mixing ratios (filler metal powder: DM water [wt.%/wt.%]) used to fabricate dip-brazed joints for Al-64430. Eight different filler ratios were selected, namely 1:5, 1:4, 1:3, 1:2, 1:1, 5:4, 2:1 and 3:1. The fabricated samples were tested for bump test, microhardness, tensile strength and surface deformation. Maximum microhardness and tensile strength were observed at a 5:4 mixing ratio. Both the values increased until the 5:4 mixing ratio (450% increase in microhardness and a 5400% increase in tensile strength compared to a 1:4 mixing ratio sample), after which they declined (3% decrease in microhardness and a 35% decrease in tensile strength). Surface deformation of the samples remained almost constant throughout, although these values were 10–20 times less than those of samples produced by conventional welding operations. Microstructural analysis revealed dendrite formation at the brazed joints. Voids and cracks were also detected in some samples. Al-Si eutectic matrix and (alpha)-aluminium were visible at the joint. SEM analysis was carried out to determine the silicon state in the matrix, which displayed the presence of both primary and eutectic silicon. EDX analysis showed that the silicon concentration at the joint increased as the filler ratio increased, and this silicon concentration played a major role in determining the strength and hardness of the joints.

Laser-MIG hybrid multi-layer welding was performed upon the 20-mm thick 6082-T6 aluminum alloy butt-joints. The weld formation, microstructure, and mechanical properties of the welded joints were studied in details. The results indicated that the well-formed weld without obvious incomplete fusion and cracks could be obtained by using the optimal welding parameters, only very few porosities appeared in the filling layer and covering layer. The equiaxed crystals and columnar crystals were respectively observed in the weld center and near the fusion in the weld metal; their sizes and widths of each layer were different. The microhardness values of the weld metal and heat-affected zone are lower than those of the base metal; the lowest microhardness value appeared in the heat affected zone. The order of microhardness values in the weld center from high to low was filling layer, backing layer, and covering layer; their microhardness values were 74 HV, 70 HV, and 67 HV, respectively. The average tensile strength of the joints reached up to 235.2 MPa, which was 79.7% of the base metal. The tensile specimen fractured near the fusion line in the heat affected zone and the fracture propagated approximately parallel to the fusion line, and the tensile fracture showed a typical plastic fracture mode. The median fatigue limit and safety fatigue limit of the welded joints were 99 MPa and 93 MPa, respectively. The fatigue specimen fractured in the weld metal, and the crack initiated in the backing layer.