Search Results (48)

In the present work, the optimization of ceramic-based composite WC(Co,Ni) welds by laser cladding was carried out using response surface methodology based on finite element analysis. The heat distribution and temperature field of laser-melted WC(Co,Ni) ceramic coatings were simulated using ANSYS software, which allowed the computation of the distribution of residual stresses. The results show that the isotherms in the simulation of the temperature field are elliptical in shape, and that the isotherms in front of the moving heat source are dense with a larger temperature gradient, while the isotherms behind the heat source are sparse with a smaller temperature gradient. In addition, the observed microstructural evolution shows that the melting zone domains of WC(Co,Ni) are mainly composed of unmelted carbides. These carbides are dendritic, rod-like, leaf-like, or net-like, and are agglomerated into smaller groups. The W content of these unmelted carbides exceeds 80%, while the C content is around 1.5–3.0%. The grey areas are composed of WC, Co and Ni compounds. Based on the regression model, a quadratic model was successfully constructed. A three-dimensional profile model of the residual stress behaviour was further explored. The estimated values of the RSM-based FEA model for residual stress are very similar to the actual results, which shows that the model is effective in reducing residual stress by laser cladding. Full article

In this research project a large linear electromagnetic actuator (LLEA) was designed and manufactured. The electromagnetic performance was published in previous works, but in this paper we focus on the technological challenges related to the manufacturing in particular. This LLEA was based on the magnet-free switched-reluctance principle, having six effective energised stator “teeth” and four passive mover parts (4:6 ratio). Various aspects and challenges encountered during the manufacturing, transport, and assembly are discussed. Thermal expansion of steel contributed to the decision of the modular design, with each module having 1.3 m in length, with a 2 mm longitudinal dilatation gap. The initial prototype was tested with a 10.6 m length, with plans to extend the test track to 60 m, which was fully achievable due to the modular design and required 29 tons of electrical steel to be built. The stator laminations were cut by a bespoke progressive tool with stamping, and other parts by a CO₂ laser. Mounting was based on welding (back of the stator) and clamping plates (through insulated bolts). The linear longitudinal force was on the order of 8 kN, with the main air gap of 7.5–10 mm on either side of the mover. The lateral forces could exceed 40 kN and were supported by appropriate construction steel members bolted to the concrete floor. The overall mechanical tolerances after installation remained below 0.5 mm. The technology used for constructing this prototype demonstrated the cost-effective way for a semi-industrial manufacturing scale. Full article

Excessive spatter formation in conventional CO₂ arc welding significantly diminishes welding quality and efficiency, posing a critical challenge for industrial applications. To address this issue, this study investigated the mechanisms of metal transfer behavior and spatter formation under the influence of a longitudinal magnetic field (LMF) using a shadow-graph technique with high-speed imaging and back-laser illumination, also coupled with Computational Fluid Dynamics (CFD)-based arc-droplet numerical simulations. The results show that increasing the magnetic flux density (MFD) from 0 to 2 mT shifted the transfer mode from the repelled transfer to the globular transfer, while higher MFDs (3–4 mT) induced rotating repelled transfer. The globular transfer at 2 mT was considered to be primarily produced by the centrifugal effect due to the rotational motion of the molten metal inside the droplet, which was caused by the Lorentz force affected by LMF. The higher droplet temperature in this condition also contributed to forming this transfer mode, preventing the formation of repelled transfer through a decrease in the arc pressure. On the contrary, in the higher MFDs, the droplet temperature decreased to increase the arc pressure, lifting the droplet up. Furthermore, the very strong centrifugal effect rotated the molten metal column around the wire axis to induce the rotating repelled transfer. The spatter formation was found to occur with the two-stage motion of the curved long tail without LMF and at 4 mT, and also with the exploding molten metal column at 4 mT, due to an imbalance of the Lorentz force acting on the molten metal. On the other hand, the neck formation facilitated smooth droplet detachment without forming the curved long tail at 2 mT, reducing spatter significantly. These findings offer valuable insights for optimizing welding quality and efficiency by stabilizing globular transfer under an optimal LMF. Full article

This article presents research on advanced surface preparation methods for sintered carbides (WC-Co, grade B2) commonly used in the tool industry, particularly in the context of bonding these materials with C45 steel using adhesives. Sintered carbides are widely used due to their high hardness, wear resistance, and good ductility, making them ideal for manufacturing tools operating in harsh conditions. Traditional bonding methods, such as brazing and welding, often result in stresses and cracks. Adhesive bonding has therefore emerged as an effective alternative to mitigate these challenges. The research focuses on comparing the results obtained through modern surface treatment techniques, such as laser micro-texturing and plasma treatment, with traditional methods like grinding, abrasive blasting, and electrolytic etching. The influence of these methods on adhesion properties and the strength of adhesive bonds was evaluated through mechanical tests, including static shear and pull-off tests. An approximately 50% increase in the mechanical strength of adhesive joints was observed for surfaces treated with low-temperature plasma (operating voltage: 18 kV, flow of gasses: 20 l/min., treatment time: 60 s) and laser micro-texturing (infrared fiber laser, wavelength: 1064 nm (±5 nm), power: 20 W), as compared to mechanical grinding. The shear strength of the adhesive joints was equal to 32 MPa and 30 MPa on average in the case of treatment with low-temperature plasma made of helium and argon, respectively. The highest strength of an adhesive joint was equal to 34.5 MPa on average in the case of laser micro-texturing. Full article

This study used statistical tools to optimise WC/Co/Ni welds and model construction to improve the mechanical properties of coatings by laser cladding. The effect of the parameters on the wear performance of the weld was determined by analysis of variance. In addition, a polynomial model was constructed using the response surface method based on the experimental data of the orthogonal array designed by Taguchi. The experimental results show that there are white initial precipitation carbides and grey areas of WC mixed with Co and Ni compounds, while less wear and less plastic deformation are observed with WC/Co/Ni alloys. By adding Co/Ni alloys, the composite coating extension is seen to have good anti-wear performance. Based on the regression model, a pairwise interaction model was successfully constructed and further modelling of the 3D contour of the wear behaviour was explored. Comparing all the experiments, the predictions of the interaction model were found to be reliable, with an average error of 8.75%. The findings show that there is a very close match between the predicted values of RSM for wear performance and the experimental data, which proves the effectiveness of the Taguchi design-based RSM in improving the mechanical properties of laser cladding. Full article

The Co-Cr-Fe-Ni high-entropy alloy (HEA) is particularly suitable for preparing coatings due to its excellent comprehensive properties. In this study, we use the laser cladding method to prepare Co-Cr-Fe-Ni HEA coatings with Co-Cr-Fe-Ni cable-type welding wire (CTWW) as the filling material and investigated the dilution rates of the coatings by experimental studies and first-principles calculations. The dilution rate is reduced to about 50% by changing the wire feeding speed, and a Co-Cr-Fe-Ni HEA coating with near nominal composition was prepared by multi-layer cladding. The HEA coating with near nominal composition is successfully prepared in the fourth layer of cladding. The coating is dense and uniform, with good metallurgical bonding. The mechanical properties of the coating were explored using first-principles calculations. All four coatings exhibit a single face-centered cubic (FCC) phase with good mechanical stability in the ground state. The bulk modulus B, shear modulus G, and Young’s modulus E of the four layers of coatings are gradually decreasing from B = 202 GPa, G = 136 GPa, and E = 334 GPa to B = 239 GPa, G = 154 GPa, and E = 380 GPa. The brittleness of the coating shows a trend of first decreasing and then increasing, and the coating closest to the nominal composition has the highest brittleness. Full article

Reducing hot cracking is essential for ensuring seamless production of nickel superalloys, which are extensively used in welded structures for aircraft engines. The prevalence of hot cracking in precipitation-strengthened alloy 718 is primarily governed by two factors: firstly, the chemical composition and the coarse microstructure formed during solidification, and secondly, the activation of hot cracking mechanisms, which is particularly critical in mushroom-shaped welding morphologies. In this study, different nickel-based superalloys welded using laser beam welding (LBW), more specifically bead on plate welding (BoP), specimens are compared. The cracking susceptibility of both wrought and two investment casting 718 alloys with tailored chemical compositions is examined through the application of both continuous and pulsed LBW. Additionally, various pre-weld treatments, including with and without Pre-HIP (hot isostatic pressing), are analyzed. The influences of chemical composition, LBW parameters and pre- and post-welding treatments on both internal and external cracks determined by conventional and advanced non-destructive tests are studied. A clear reduction of hot cracking susceptibility and overall welding quality improvement was observed in a tailored 718 alloy with relatively high Ni (55.6% wt) and Co (1.11% wt) contents. Full article

The welded joints of high/medium entropy alloys (H/MEAs) have shown sound mechanical properties, indicating high promise for the industrial application of this new type of metal alloy. However, these joints possess either relatively low strength or low ductility. In this paper, we used ultrasonic-assisted laser welding to weld CrCoNi MEA with the nitrogen as shielding gas. The results showed that the tensile strength of the joint at room and cryogenic temperature is 686 MPa and 1071 MPa, respectively. The elongation at room and cryogenic temperature is 26.8% and 27.7%, respectively. The combination of the strength and ductility in our joints exceeds that of other welded H/MEA joints. We attributed this excellent combination to the refined dendrite, the solution of nitrogen into the matrix, and the low stacking fault energy of the CrCoNi MEA. The findings in this paper not only provide a novel way to weld H/MEAs with high strength and ductility, also are useful for additively manufacturing the high-performance component of H/MEAs. Full article

Traditional resistance spot welding (RSW) has been unsuccessful in forming quality composite joints between steel– or aluminum–polymer-based composites. This has led to the development of spot welding variants such as friction stir spot welding (FFSW), ultrasonic spot welding (USW), and laser spot welding (LSW). The paper reviewed the differences in the bonding mechanisms, spot weld characteristics, and challenges involved in using these spot welding variants. Variants of RSW use series electrode arrangement, co-axial electrodes, metallic inserts, interlayers, or external energy to produce composite joints. FFSW and USW use nanoparticles, interlayers, or energy directors to create composite spot welds. Mechanical interlocking is the common composite joint mechanism for all variants. Each spot welding variant has different sets of weld parameters and distinct spot weld morphologies. FFSW is the most expensive variant but is commonly used for composite spot weld joints. USW has a shorter welding cycle compared to RSW and FFSW but can only be used for small components. LSW is faster than the other variants, but limited work was found on its use in composite spot weld joining. The use of interlayers in FFSW and USW to form composite joints is a potential research area recommended in this review. Full article

In order to enhance the quality of diamond composite materials, this work employs a Cu-Co-Fe and Ni-Cr-Cu pre-alloyed powder mixture as a transition layer, and utilizes laser-welding technology for saw blade fabrication. By adjusting the laser-welding process parameters, including welding speed and welding power, well-formed welded joints were achieved, and the microstructure and mechanical properties of the welded joints were investigated. The results demonstrate that the best welding performance was achieved at a laser power of 1600 W and a welding speed of 1400 mm/min, with a remarkable tooth engagement strength of up to 819 MPa. The fusion zone can be divided into rich Cu phase and rich Fe phase regions, characterized by coarse grains without apparent preferred orientation. The microstructure of the heat-affected zone primarily consists of high-hardness brittle quenched needle-like martensite, exhibiting a sharp increase in microhardness up to 550 HV. Fracture occurred at the boundary between the fusion zone and the heat-affected zone of the base material, where stress concentration was observed. By adjusting the welding parameters and transition layer materials, the mechanical properties of the joints were improved, thereby achieving a reliable connection between diamond composite materials and the metal substrate. Full article

High-entropy alloys (HEAs) are a class of metal alloys consisting of four or more molar equal or near-equal elements. HEA nanomaterials have garnered significant interest due to their wide range of applications, such as electrocatalysis, welding, and brazing. Their unique multi-principle high-entropy effect allows for the tailoring of the alloy composition to facilitate specific electrochemical reactions. This study focuses on the synthesis of high-purity HEA nanoparticles using the method of femtosecond laser ablation synthesis in liquid. The use of ultrashort energy pulses in femtosecond lasers enables uniform ablation of materials at significantly lower power levels compared to longer pulse or continuous pulse lasers. We investigate how various femtosecond laser parameters affect the morphology, phase, and other characteristics of the synthesized nanoparticles. An innovative aspect of our solution is its ability to rapidly generate multi-component nanoparticles with a high fidelity as the input multi-component target material at a significant yielding rate. Our research thus focuses on a novel synthesis of high-entropy alloying CuCoMn_1.75NiFe_0.25 nanoparticles. We explore the characterization and unique properties of the nanoparticles and consider their electrocatalytic applications, including high power density aluminum air batteries, as well as their efficacy in the oxygen reduction reaction (ORR). Additionally, we report a unique nanowire fabrication phenomenon achieved through nanojoining. The findings from this study shed light on the potential of femtosecond laser ablation synthesis in liquid (FLASiL) as a promising technique for producing high-purity HEA nanoparticles. Full article

Due to the notable disparities in the physical and chemical characteristics between titanium and steel, the direct fusion of titanium/steel bimetallic sheets results in a considerable formation of fragile intermetallic compounds, making it difficult to achieve excellent metallurgical welded joints. In this study, a multi-principal powder of CoCrNiMn was designed and utilized as a filler material in the welding of the TA1/Q345 bimetallic sheet. It was expected that the in situ formation of Fe_x(CoCrNiMn)Ti_y high-entropy alloys would be achieved using the filler powders, combined with the Ti and Fe elements from the melting of the TA1 and Q345 so as to restrain the generation of Fe-Ti IMCs and obtain the promising welded joints of the TA1/Q345 bimetallic sheet. An interesting finding is that high-entropy alloys were successfully obtained in the weld metal. The Fe-Ti intermetallic compounds at the welding interface were significantly reduced. The tensile strength was ~293 MPa, accounting for 60% of the strength of the base metal. Dimples were observed at the fracture of the welded joint. Full article

A few components used in the aerospace and petrochemical industries serve in corrosive environments at high temperatures. Corrosion-resistant metals or unique processes, such as coating and fusion welding, are required to improve the performance of the parts. We have used laser powder bed fusion (LPBF) technology to deposit a 5 mm thick corrosion-resistant CoCrMo layer on a high-strength IN625 substrate to improve the corrosion resistance of the core parts of a valve. This study found that when the laser volumetric energy density (E_V) ≤ 20, the tensile strength increases linearly with the increase in E_V, and the slope of the curve is approximately 85°. The larger the slope, the greater the impact of E_V on the intensity. When E_V > 20, the sample strength reaches the maximum tensile strength. When the E_V increases from 0 to 20, the fracture position of the sample shifts from CoCrMo to IN625. When E_V ≤ 38, the strain increases linearly with the increase in E_V, and the slope of the curve is approximately 67.5°. The sample strain rate reaches the maximum when E_V > 38. Therefore, for an optimal sample strength and strain, E_V should be greater than 38. This study provides theoretical and technical support for the manufacturing of corrosion-resistant dissimilar metal parts using LPBF technology. Full article

An innovative non-homogeneous dynamic model is presented for the recovery of temperature during the industrial laser welding process of Al-Si $5\%$ alloy plates. It considers that, metallurgically, during welding, the alloy melts with the presence of solid/liquid phases until total melt is achieved, and afterwards it resolidifies with the reverse process. Further, a polynomial substitute thermal capacity of the alloy is chosen based on experimental evidence so that the volumetric solid-state fraction is identifiable. Moreover, to the usual radiative/convective boundary conditions, the contribution due to the positioning of the plates on the workbench is considered (endowing the model with Cauchy–Stefan–Boltzmann boundary conditions). Having verified the well-posedness of the problem, a Galerkin-FEM approach is implemented to recover the temperature maps, obtained by modeling the laser heat sources with formulations depending on the laser sliding speed. The results achieved show good adherence to the experimental evidence, opening up interesting future scenarios for technology transfer. Full article

In order to improve the hold and function of dentures for the patient, various prostheses made of metal, mostly metal alloys, are used every day in dental practise. Cobalt-chromium alloys are usually the first choice because they have very good mechanical properties and satisfactory clinical conditions. Nowadays, laser welding is increasingly used in dental practise due to its numerous advantages over other technologies. In this work, therefore, six commercially available Co-Cr alloys were investigated. Three of them are used for metal-ceramic work, two for denture frameworks and one is suitable for both applications. They were joined by laser welding and subsequently analysed microscopically. Their mechanical properties were determined and statistically evaluated. The microhardness of the laser-welded alloys is in the range of 282–465 MPa in the weld zone and between 283 and 435 MPa in the heat-affected zone. The flexural strength of the laser-welded alloys is lower than the control group, but an alloy for the metal-ceramic work (I-BOND NF) shows very similar value. Furthermore, this alloy, together with two other metal-ceramic alloys, survived a maximum of cycles in dynamic tests. It was found that the laser method can be used for joining Co-Cr alloys while ensuring appropriate parameters that guarantee the quality of the dental work. Full article