Welding in the World最新文献

The reduction of CO₂ emissions is closely linked to the development of highly efficient and economical steel components in plant and process engineering. To withstand the high combined corrosive, tribological, thermal, and mechanical stresses, wear-resistant coatings tailored to the application and steel grade are used. In addition to the increasing demand to substitute conventional cobalt alloys with nickel alloys, there is also a growing need for defined or functional surfaces of high integrity. Due to high tool wear, milling operations required to produce the complex geometries of the components are often not economically feasible for SMEs. By means of alloy modification of the filler metals for nickel-based plasma build-up welded wear-resistant coatings and by the use of innovative ultrasonic-assisted milling processes more favourable machinability shall be achieved without reducing the wear protection potential. In this paper, the influence of the microstructure and precipitation morphology adjusted by means of alloy modification on the machinability is investigated. This is done based on a wear protection alloy NiCrMoSiFeB (trade name: Colmonoy 56 PTA) typically used for screw machines, which substitutes conventional CoCr alloys (Stellite). Metallurgical investigations and in-situ measurements of occurring process forces and temperatures at the tool cutting edge during milling as well as subsequent investigations of tool wear and surface integrity allow a detailed analysis and correlation between microstructural properties and machinability. For the cast samples, a clear change in the microstructure and hardness can be seen through the addition of Al, Ti, or Nb. These differences lead to an improvement in the machining process for Nb. Al and Ti cause long-needled or star-shaped precipitations and hardness increases, which lead to higher cutting forces and increased tool wear.

In the welded joints, fatigue failures typically originate from defects or notch-like geometries under cyclic loading. This study investigates the impact of stress relief grooves (SRG) on the fatigue performance of butt-welded cast steel to ultra-high-strength steel components using experimental fatigue tests and finite element method. The experiments examined the fatigue properties of hybrid joints between G26CrMo4 cast steel (t = 20 mm) and S960 steel plate (t = 6 mm) with and without SRG. Gas metal arc welding process was used to weld the butt joints that had a permanent root backing machined on the cast steel part, causing a crack-like defect to the weld root. Additionally, the top surfaces of the welded parts were aligned, resulting in a significant axial misalignment in the butt joint. The SRG, positioned close to the weld root, was found to have a beneficial influence on the joint’s fatigue performance by a factor of 1.2 when using the nominal stress criterion. However, the fatigue capacity was still roughly 35% lower compared to the symmetrical equivalent due to the secondary bending stress, caused by axial misalignment. The finite element analyses indicated that the SRG reduces the amount of secondary stresses at the weld root leading to lower total structural stress. The study recommends using the FAT80 (m = 3) design curve in the structural stress method, for similar butt-welds having a crack-like defect, parallel to the loading direction, at the weld root. However, for welded joints with crack-like defects, it is advisable to use linear elastic fracture mechanics rather than relying solely on stress-based local approaches.

Duplex stainless steels (DSS) in wire and arc additive manufacturing (WAAM) have attracted significant research attention due to their mechanical properties and corrosion resistance. This study uses conventional and nanomechanical testing methods to compare the mechanical and microstructural behaviors at macroscopic and microscopic length scales. Macro hardness (HV10) testing yielded 259 and 249 in low and high heat input (HI) samples, respectively, while ferrite content averaged 52.7 and 48.5%. However, these results fail to provide conclusive insight into the potential influence of microstructural variations at the macroscopic level, likely due to the composite response of the material. To overcome this limitation, the mechanical response of the DSS samples is assessed at the grain level via high throughput nanoindentation mapping with image processing to track the location of each indent. This approach enabled differentiating the indents landing on ferrite and austenite phases as well as those landing on the interfaces. The results showed that the austenite phase had higher hardness (4.30 and 4.35 GPa) than the ferrite phase (3.89 GPa and 4.03 GPa) for high and low HI samples, respectively. The observed differences in hardness between the phases can be attributed to higher nitrogen content in the austenitic phase.

This research studies the influence of high-peak loads on local relaxation of residual stress and fatigue damage in high-strength steel welded joints treated by high-frequency mechanical impact (HFMI) treatment. The joint behavior is simulated with elastic–plastic finite element analyses that account for the combined effect of geometry, residual stress, and material properties. This simulation uses two treated geometry models: with or without surface roughness on HFMI groove, and two material properties: S690QL and AH36 structural steels. The results show that surface roughness and load history, including high-peak loads, significantly influence fatigue response. It is revealed that the model neglecting the surface roughness cannot represent the amount of residual stress change and fatigue damage at less than 100 µm depth from the surface. In addition, the local yield strength in the HFMI-treated zone affects the plasticity behavior near the surface imperfection under the high-peak loads, which provides comparatively different fatigue damage between S690QL and AH36 in some cases. As a result, this study provides the further understanding needed to develop a robust modeling approach to the fatigue life estimation of HFMI-treated welds subjected to high-peak loads.

A strong effort has continued to optimize friction stir lap welding (FSLW) process and to achieve high strength of dissimilar metal welds. For more than a decade, various studies have shown that Al-to-Ti FSL welds can be strong under quasi-static loading. Recently, Al-to-Ti FSL welds have also been shown to be strong under cyclic loading, due to the unique and thin diffusion bonding layer formed at the interface. In this study, how readily high fatigue strength of AA2024-to-Ti6Al4V FSL welds can be achieved is assessed. First, the effect of increasing the pin size on the fatigue strength of the welds has been evaluated. Second, fatigue testing has been conducted on the welds of which diffusion bonding is more ascertained by the use of an interlayer. It has been found that the fatigue strength of the welds is insensitive to the pin size. This will be shown to be the result of the width of the diffusional bond to be insensitive to the use of a larger pin or whether the pin has penetrated to the bottom plate. Simulation has suggested that stress concentration in locations of lapping ends is not significantly affected by the increase of the metallurgically welded width, explaining that pin size and penetration-dependent weld width do not affect the fatigue strength. It has also been shown that interlayer assisted diffusion bonding has affected insignificantly the fatigue strength of the welds. Thus, the high fatigue strength is insensitive to process variation.

In the present study, laser welding of additively manufactured AlSi10Mg was undertaken with AlSi10Mg (similar) and Al6061 (dissimilar) alloy. The aim was to understand the laser weldability of selective laser melting (SLM)-printed AlSi10Mg alloy without filler material. The similar and dissimilar type of butt joints were  prepared, and it is found that dissimilar weldments had better mechanical properties than similar weldments. The heat treatment on these welded plates also improved their mechanical properties. The precipitation of Mg₂Si particles was evident from the XRD and TEM analysis. The as-built cellular structure was broken due to heat treatment and also near the weld zone in the as-welded plate. It was observed that microhardness increased with increase in Mg₂Si content after the heat treatment process. The strength of welded samples was less than that of the base metals. The heat treatment results in ~ 20% increase in the tensile strength of the welded samples with significant increase in elongation.

The serviceability of cladding layers manufactured by laser depends on the microstructure formed by the metallurgical solidification. The microstructure in the clad layer is influenced by several factors. Among them, the elemental distribution state of the molten powder in the molten pool plays a dominant role. The diffusion distribution of elements is closely related to the non-equilibrium metallurgical behavior in the additive manufacturing process. Therefore, it is important to conduct an in-depth study on the multi-field coupling behavior and the heat and mass transfer mechanism in laser additive manufacturing process. In this study, a coupled thermal-fluid–solid multi-physical field numerical model for the laser cladding of 316L stainless steel powder on 45 steels was developed. The transient change patterns of the temperature, flow and stress fields for the cladding process were quantitatively revealed. The diffusion process of the powder elements within the molten pool was considered to reveal the element distribution law in the clad layer. The effects of the surface tension, buoyancy for molten pool, and Marangoni convection on the flow field also were considered, and the validity of the numerical model was verified. This study provides a theoretical basis for optimizing the laser cladding process.

The influences of different laser beam offsets (LBOs) on the microstructures and mechanical performance of the welded joints were studied. In joints with LBO = +0.3, LBO = 0, and LBO = −0.3, the widths of fusion zones (FZs) are 0.98, 1.03, and 1.21 mm, respectively. Additionally, the equivalent grain diameters in the FZs are measured to be 45.3, 44.1, and 19.6 μm, respectively. The FZ of the joint with LBO = 0 contains β-Ti and Nb solid solution, as well as a small amount of α' phases. The FZ of the joint with LBO = +0.3 mainly consists of Nb solid solution and β-Ti phase. In contrast, the FZ of the joint with LBO = −0.3 is mainly composed of Nb solid solution as well as ω, α′, and α″ phases. The FZ of the joint with LBO = 0 shows the lowest Vickers microhardness (149.2 ± 10.4 HV on average), which decreases by 18.9% and 40.0% when composed with those of joints with LBO = +0.3 and LBO = −0.3. The joint with LBO = 0 is found to have the smoothest transition of the microhardness from the FZ to the base metal, which favors the performance of the joints. The average tensile strength values of joints with LBO = +0.3, LBO = 0, and LBO = −0.3 are separately 318.8 ± 20.6, 315.4 ± 19.7, and 317.9 ± 23.9 MPa. All tensile specimens are fractured on the side of Ti, which suggests the superior tensile performance of the welded joints.

A five-element medium-entropy filler alloy with composition of Ti-(18 ~ 24)Mn-(12 ~ 18)Fe-(3 ~ 8)Ni-(3 ~ 8)Zr (wt.%) was proposed for vacuum brazing of TiAl-based alloy. The filler alloy was mainly composed of Ti-based solid solution and Ti-(Fe, Mn) compound dissolved with elements of Ni and Zr. The filler alloy ingot was ground into powder and then the filler powder was preset into the V-shaped groove butt joint with a gap of 50 μm. The Ti-Mn-Fe-Ni-Zr brazing alloy showed the liquidus temperature of 1060.1 °C, and also presented excellent wettability on TiAl substrate at 1110 °C for 10 min. The brazed joint mainly consisted of γ-TiAl, α₂-Ti₃Al, and residual brazing filler reaction phase. The brazing condition of 1210 °C/45 min exhibited the maximum joint thickness of 308 μm and the maximum area percentage of γ-TiAl phase of 33.77%, with almost elimination of residual brazing filler reaction phase within the joint, and meanwhile offered the maximum room-temperature tensile strength of 418 MPa, 70.85% of the base alloy. The joint fracture showed a mixed mode of intergranular and transgranular fracture.