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To improve the wear resistance of Fe-based cladding, NbC particles with different morphology are generated in situ by adding Nb, Cr 3 C 2 and C with different content. The composition of samples and the morphology of NbC particles generated in situ are revealed by XRD, SEM and EDS. The wear resistance is studied by a reciprocating friction and wear testing machine. The wear mode and the wear mechanism of each sample are investigated. The results show that although NbC particles are generated in situ in samples with different Nb, Cr 3 C 2 and C content, the morphology of NbC particles is varied. The wear resistance of samples containing cross-shaped NbC particles is more outstanding than that of samples containing only rectangular NbC particles. In addition, changing Nb, Cr 3 C 2 and C content does not result in a change in wear mode, but leads to the formation of continuous lattice structure of Cr 0.19 Fe 0.7 Ni 0.11 and Cr 23 C 6 compounds at grain boundaries and a change in the wear resistance. When the additions of Nb, Cr 3 C 2 and C are 11.2 wt%, 8.6 wt% and 0.2 wt% respectively, the coefficient of friction of the sample is the lowest, and the wear resistance is the most outstanding. [ABSTRACT FROM AUTHOR]

Purpose: Laser cladding has been used in the field of repairing damaged parts of machine tools due to its advantages of less processing restrictions and easy formation of a good metallurgical bond with the base material. However, the mechanical properties of the coating sometimes cannot meet the process requirements. Therefore, the purpose of this paper is to prepare coatings with high microhardness and flexural strength. Design/methodology/approach: The YCF102 alloy powder was mixed with different contents of Co and tested for laser cladding on AISI 1045 substrate under the same process parameters. The main phase composition of the coating was revealed by the XRD results. The main chemical composition of the coating was determined by the SEM and EDS results. In addition, the effect of Co content on the microstructure, microhardness and flexural strength of the coatings was investigated. Findings: The results show that when the Co content is 2 wt% and 4 wt%, Co does not form compounds with other elements, but is uniformly distributed in the coating. And when the Co content is 6 wt% and 8 wt%, the Co reacts with Fe in the coating and generates Co3Fe7 in situ. The increase in Co did not result in a monotonic change in microhardness, but significantly improved the flexural strength and the flatness of the microstructure of the coating. When the Co content of the mixed powder is 8 wt%, the coating has high microhardness and flexural strength. Originality/value: Co/YCF102 composite coating with high microhardness and flexural strength was prepared. This paper provides a theoretical and practical basis for research in the area of repairing damaged parts of machine tools by laser cladding. [ABSTRACT FROM AUTHOR]

• Geometric characteristic parameters increase with the increase of tracks and layers. • When depositing the sixth layer, geometric characteristic parameters still increase. • The model of YCF102 cladding layers with multi-track and multi-layer is established. • The maximum prediction error of the theoretical model is 5.69%. This paper proposes a prediction method of the geometric characteristic parameters of cladding layers with multi-track and multi-layer. YCF102 cladding layers with different number of tracks and layers were laser cladded on the AISI 1045 steel substrate. The changing trend of the geometric characteristic parameters was analyzed by a laser microscope, and the prediction method of clad height, clad width and melt pool depth with the different number of tracks and layers under various processing parameters were proposed respectively. The results show that the increase of the number of tracks and layers lead to the increase of clad height, clad width and melt pool depth. When cladding the sixth layer, the clad width and melt pool depth still show an increasing trend, but the increase rate of melt pool depth slows down. The average residual values between the calculated and measured values of clad height, clad width and melt pool depth are 280.01 μm, 158.90 μm and 8.00 μm respectively, which are only 5.69%, 4.01% and 1.72% of the corresponding measured values. It is indicated that the prediction method is reasonable. The proposed prediction method can be used to predict the geometric characteristic parameters of multi-track and multi-layer cladding layers. The application of the method can effectively save the processing time and cost of the laser cladding repair of machine parts. [ABSTRACT FROM AUTHOR]

The cladding layer formed by laser cladding is formed by solidification of the molten pool. The quality of the cladding layer is directly determined by the evolution of the molten pool. The numerical simulation of the evolution of the molten pool is carried out, revealing the relationship between different powers and the evolution of the molten pool. The results show that the volume of the molten pool exhibits a nonlinear expansion of "expansion-shrinkage-re-expansion" before reaching the steady state, and the volume and expansion rate of the molten pool are determined by the laser power. In addition, the degree of shrinkage of the molten pool and the speed of convection can also be controlled by the laser power. When the laser power reaches a certain level, evaporation occurs on the surface of the molten pool. The convection pattern of the molten pool can be changed by evaporation. However, due to the impact of shielding gas and Marangoni movement, the effect of evaporation on the geometry of the cladding layer is limited. [ABSTRACT FROM AUTHOR]

Dilution rate is an important factor affecting the properties of laser cladding. However, the exact estimate of dilution rate in direct laser fabrication is still not fully developed. In this study, high-strength and wear-resistant YCF102 alloy powder is used to laser clad on the steel substrate. The area of the cladding layer is replaced by a part of the circle, and the relationship among the deposition angle, the clad width, and the area of the cladding layer is established. The geometry of the fusion zone is replaced by polynomial function of the fourth degree, and the relationship among the thermal tension angle, the clad width, the melting pool depth, and the area of the fusion zone is established. The value of the dilution rate is obtained by the area of the cladding layer and the fusion zone. The correlation coefficient of the area of cladding layer, the area of the fusion zone, and the dilution rate is also obtained. The estimate results coincident with the measurement results very well. The proposed theoretical model offers a basis for estimate of dilution rate in laser cladding. [ABSTRACT FROM AUTHOR]

Because the convection pattern inside the laser cladding transient molten pool is difficult to measure by experimental means, the numerical analysis model of the inside of the laser cladding molten pool was constructed, and the forming mechanism of the cladding layer was simultaneously analyzed. The internal convection pattern of the single-track, multi-track and multi-layer laser cladding molten pool was analyzed. The results show that the convection inside the laser cladding molten pool in different types is mainly annular convection. The fluid at the bottom of the molten pool flows to the surface of the molten pool, and the fluid on the surface of the molten pool flows along the sides to the bottom of the molten pool. Therefore, the cladding layer is mainly solidified by the fluid flowing from the bottom of the molten pool to the surface of the molten pool. [ABSTRACT FROM AUTHOR]

• Laser remelting tests were conducted on the Fe-based clad layer under different remelting time and remelting power conditions. • The morphological characteristics of the Fe-based clad layer after remelting under different remelting time and remelting power conditions were investigated. • The microhardness of the Fe-based clad layer after remelting under different remelting time and remelting power conditions was investigated. • The wear resistance, wear rate and wear mechanism of the Fe-based clad layer after remelting under different remelting time and remelting power conditions were investigated. • When the remelting time is 1 and the remelting power is 650 W, the clad layer has high microhardness and outstanding wear resistance. Laser remelting is a processing technique to improve the quality of forming. The remelting power and the remelting time are the key factors affecting its processing quality. Laser remelting tests were conducted on Fe-based clad layers with different remelting power and remelting time, and the morphological characteristics of each clad layer was investigated by laser microscopy. The microhardness, wear resistance and wear mechanism of each clad layer were investigated by Vickers microhardness tester and reciprocating friction and wear tester, respectively. The results show that an increase in remelting power or remelting time leads to a decrease in clad height and an increase in melting pool depth, clad width and dilution rate. When the remelting time is 1 and the remelting power is 650 W, the clad height is higher than that of YCF102 clad layer, although the melting pool depth, clad width and dilution rate of the clad layer are greater than that of YCF102 clad layer. In addition, an increase in remelting power or remelting times leads to a decrease in the microhardness of the clad layer and a deterioration in the wear resistance, which leads to an increase in the wear rate, but does not change the trend of microhardness, wear resistance and wear rate. Neither the increase in remelting power nor the remelting time leads to a change in the wear form, but causes the wear between the clad layer and the grinding ball to become more intense. The clad layer with 1 remelting time and 650 W remelting power has higher average microhardness and more outstanding wear resistance than the YCF102 clad layer. [ABSTRACT FROM AUTHOR]

• A numerical model of laser cladding for V-grooves was constructed. • The volumetric evolution of the oscillatory expansion of the melt pool, different from that in the planar, V-shaped trough, was revealed. • The heat transfer characteristics of the melt pool with different angles of the V-groove were revealed with Marangoni convection patterns at different viewing angles. • The mechanism of cavitation generation in V-grooves with small pinch angles and its avoidance measures were predicted. In comparison to planar-oriented laser cladding, non-planar laser cladding also deserves to be discussed. A numerical model of non-planar laser cladding was constructed for V-grooves with different tension angles. The simulation results show that the melt pool generated at the bottom of the V-groove undergoes an oscillatory expansion phase similar to that of planar laser cladding and ends up in a periodic steady state. As the tension angle θ of the V-groove decreases, the absorption of laser energy by the bevels on both sides becomes more and more, and the melt pool volume starts to decrease. However, after θ is reduced to a certain threshold, the melt pool volume starts to become larger instead, and this change brings about a complex melt pool convection pattern. Finally, the mechanism of cavitation generation at the bottom of the V-groove when θ is less than 60° and the possible avoidance measures are also analyzed. [ABSTRACT FROM AUTHOR]

Due to the increasing necessity for a global reaction to climate change, there is a worldwide emphasis on achieving carbon peaks and carbon neutrality. In particular, optimizing carbon emissions in directed energy deposition manufacturing has gained significant attention. In this study, we analyze the carbon emission characteristics of each system used in directed energy deposition processes. In addition, we formulate an optimization model for the directed energy deposition manufacturing process, focusing on carbon emission reduction, powder utilization rate improvement, and aspect ratio enhancement. A new iteration of the Generalized Differential Evolution 3 algorithm is presented in this study. The enhanced algorithm makes use of chaotic memory weight factors to promote diversity. This approach effectively avoids premature convergence of the algorithm while also increasing the speed of convergence and accuracy of the solution. Experiments are carried out on the platform of LDM4030 directed energy deposition equipment. The results indicate that implementing the proposed model and algorithm in this study resulted in a 25% decrease in carbon emissions during printing of components, a 19% enhancement in powder utilization rate, and a 6% improvement in aspect ratio. The study investigates the influence of the variable on the optimization target through S/N ratio analysis and contour plots. Furthermore, the investigation examines the modifications of a single factor's regulations for the objective, presenting a promising approach for the directed energy deposition manufacturing equipment industry to achieve carbon peak and neutralization. [ABSTRACT FROM AUTHOR]

The assembly of remanufactured machine tools is crucial for ensuring their accuracy. Poor assembly accuracy, low remanufacturing resource utilization, and inefficient assembly have become common issues in remanufacturing processes. This limitation is addressed in the study, wherein Taguchi's mass loss function (QLF) and a cost function for the remaining parts are employed. Both assembly accuracy and minimum cost are ensured through the establishment of a comprehensive matching model with closed-loop dimensional chains as constraints. The solution process of the PSO-GA model is outlined, effectively reducing uncertainty and resource waste associated with impractical matching schemes. Practical results from the CAK6163 headstock demonstrate that not only is the low success rate issue in matching remanufactured parts resolved by the proposed method, but resource utilization is also significantly enhanced, and costs are reduced. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the effect of laser re-melting on the morphology and mechanical properties of cladding layer under different laser power conditions. In this study, the laser re-melting tests were performed on YCF102 cladding layer with different laser power, and the morphology and microstructure of each cladding layer were researched by optical microscopy. Meanwhile, the microhardness and wear resistance of YCF102 cladding layer after laser re-melting with different laser power were studied. The results show that laser re-melting can not only improve the morphology of cladding layer, but also improve the microhardness and wear resistance of cladding layer. However, the excessive re-melting laser power leads to the increase of the number of defects in the cladding layer and the deterioration of the mircrohardness and wear resistance of cladding layer. When the re-melting laser power is 650 W, the cladding layer not only has a small surface roughness and no defects, but also has good mechanical properties. • Laser re-melting can reduce the number of defects in the cladding layer. • Laser re-melting can improve the surface morphology and mechanical properties. • Excessive re-melting laser power causes degradation of the mechanical properties. • Re-melting laser power is related to surface morphology and mechanical properties. [ABSTRACT FROM AUTHOR]

Due to the complex transient characteristics, it is difficult to directly measure the formation and development of a molten pool formed by laser cladding. Considering the change of thermophysical properties at high temperatures and the coupling between the heat source and the molten pool surface, a new numerical simulation method was proposed and verified. The thermal history and formation of the molten pool, the convective pattern, and the solidification morphology of the cladding have been analyzed. The results show that the molten pool can reach steady-state in a very short time, and both considerable temperature gradient and fast circular convection exist in the molten pool. The bottom of the molten pool mainly showed columnar growth, while the top was equiaxed. Columnar to equiaxed transition occurred at the center of the molten pool. • Established a multiphysics three-dimensional simulation model for laser cladding. • Two annular Marangoni convections were founded inside the molten pool. • Evaporation hardly affects the shape of the cladding. • CET occurs during solidification. [ABSTRACT FROM AUTHOR]

• Annular convection and longitudinal convection occur in the molten pool. • The Marangoni movement drives the formation of the deposit layer. • Gravity has almost no effect on convection in the molten pool. • Convection mainly drives heat transfer. • CET occurs in the solidification process of the molten pool. Metal Laser Direct Deposition (MLDD) is an additive manufacturing method involving multiple physical processes. Due to the existence of various complicated physical processes inside the molten pool, it is necessary to study the convection mode and solidification morphology in the molten pool. The convection of the molten pool generates heat and rapid solute transfer in the molten pool, which has an important influence on the solidification morphology of the deposited layer. In this study, the constructed MLDD numerical model was used to analyze the internal convection morphology of the molten pool. The convection form in the molten pool was revealed by setting different physical conditions. The results show that the Marangoni movement is the main factor in the formation of cladding layers. The impact force generated by the protective gas has an influence on the convective morphology, while the influence of gravity on the convection is limited. Through the numerical calculation, the relevant solidification parameters of the molten pool were obtained and verified by the MLDD experiment of the iron-based alloy powder. Numerical analysis and experimental results show that the Marangoni motion caused by the temperature gradient is the decisive factor leading to the solidification structure, and the phenomenon of columnar to equiaxed transition (CET) from the bottom to the top of the molten pool occurs. [ABSTRACT FROM AUTHOR]

Grinding process of particle reinforced metal matrix composites (PRMMCs) is extremely challenging due to the addition of hard particles. To reveal the material removal mechanism, a meso-scale numerical model for single grain grinding of TiC–Fe composites was established, considering the random particle distribution model and cohesive zone model. The simulated grinding forces and machined surface topography based on the proposed model show a similar trend and were consistent with the experimental results. The transition stage of ductile-brittle removal of TiC–Fe composites was explored. Results indicated that the grinding forces increase abruptly due to the obstruction of high-strength TiC particles and fluctuate periodically in the Fe matrix. The grinding forces decrease with the elevated grinding speed. Additionally, the material removal processes at different stages were studied and the removal modes mainly include: matrix plastic removal, particles wear, particles debonding, particles fracture, particles pull out. This paper provides significant guidance for the digitization and information construction of PRMMCs machining in enterprises and increases the economic benefits for the manufacturing industry. [ABSTRACT FROM AUTHOR]

• An improved finite element model is developed for the laser cladding process. • The powder temperature-rise and shielding gas pressure are taken into account. • The average error between experiment and simulation is less than 6.05%. • The dynamic growth and solidification mechanism of the coating are revealed. To accurately predict the three-dimensional (3D) characteristics of the coating and dynamic solidification process during coaxial powder-fed laser cladding, an improved 3D multi-physics finite element model including heat transfer, fluid flow, shielding gas pressure, powder temperature-rise, surface tension, and free surface movement is proposed. The input parameters of the model only depend on the thermophysical properties of the deposited material and the process parameters. Therefore, the model has good universality, and can be flexibly applied in other laser cladding systems or deposited materials. The average width and height error for the experimental and simulated is 6.05% and 4.15%, respectively. The numerical model has good abilities to predict the 3D geometry of the coating. The accuracy of the model can be indeed improved by considering the powder temperature-rise and shielding gas pressure during the modeling process. The dynamic growth process of the coating, spatiotemporal variations of the temperature and temperature gradient were discussed in detail to reveal the solidification mechanism. Finally, the relationship between the crystal characteristic (planar, cellular, columnar, and equiaxed grains) and thermal parameters (the temperature, the temperature gradient, and the solidification rate) was established. The results show that the temperature gradient and undercooling at the solidification interface are significantly responsible for the crystal characteristic, while the grain size is mainly governed by the solidification rate. [ABSTRACT FROM AUTHOR]

As an advanced additive manufacturing technology, laser cladding has become a research hotspot in the fields of rapid manufacturing and surface modification in recent years. The quality of the cladding layer directly depends on the choice of process parameters. In order to obtain high quality cladding layer, the effects of laser power, scanning speed, and powder feeding rate on the quality of JG-3 iron-based powder cladding layer were studied by interaction orthogonal experiments. Three-dimensional measurement laser microscopy (3D MLM) and variance analysis were used to analyze the results. It was found that the interaction between laser power and powder feeding rate directly affects the optimum process parameters. Laser power 750 W, scanning speed 420 mm/min, and powder feeding rate 6.96 g/min were selected as the optimum process parameters. Scanning electron microscope (SEM), X-ray diffraction (XRD), and Thermo-Calc software were used to analyze the microstructure, phase composition, and solidification process of the coating, and compared with the experimental results. The results show that under the optimum process parameters, a dense crack-free and non-porous coating was obtained. The coating can be divided into three areas: coating zone (CZ), bonding zone (BZ), and heat affected zone (HAZ). The CZ is composed of α-Fe, Cr2B, Fe2B, and Cr23C6 phases. The calculated results obtained from the Thermo-Calc software are in good agreement with the experimental data. It is beneficial to the coating design for a desirable microstructure and mechanical properties. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to study the influence of the porous structure on the maximum stress and modulus of elasticity of the specimens which are fabricated by rapid prototypes. According to the experimental results, modify the theoretical formula of elastic modulus. Design/methodology/approach: The Objet Eden 250 was used to prepare the Vero White photosensitive resin samples with different porosity (ranges from 25 to 65 per cent) and different pore structures. The mechanical properties of different samples were numerically simulated and the formulas of the modulus of elasticity were established. Through the compression test, the performance of the specimen is compared and analyzed, and the theoretical elastic modulus formula is optimized. Findings: With the increase of porosity, the maximum stress of honeycomb structure specimens decreases. The maximum stress of the honeycomb structure specimen with circular pore shape is higher than the hexagon cross-section while the hexahedron and octahedron structure are the arms (wall thickness between pores) with a square cross-section. The error comparison between the modulus of elasticity before and after the structure models regression analysis shows that after the regression analysis, the error of theoretical value and the actual value is between 0 and 14 per cent which is lower than the value before the regression analysis which was between 5 and 27 per cent. Originality/value: The paper obtains rules of the influence of different porous structures which were fabricated by the Vero White photosensitive resin material on mechanical properties and higher prediction accuracy formula of elastic modulus. The conclusions provide a theoretical basis for Northeastern University, China, to reduce mass and mechanical properties prediction of load-bearing parts. [ABSTRACT FROM AUTHOR]

Properties of vitrified bond with varying Ni doping amounts were extensively investigated. Effects of Ni addition on microstructures and properties of vitrified bond cubic boron nitride (CBN) composites prepared in strong magnetic field were investigated for applications in CBN grinding tools. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction and other methods. The refractoriness, fluidity, and bending strength of vitrified bond were evaluated. Bending strengths, microstructures, and phase compositions of vitrified bond CBN composites achieved using conventional and strong electromagnetic sintering techniques were compared. Results show that the addition of Ni to vitrified bond CBN composites improved the fluidity and bending strength of the vitrified bond. Strong electromagnetic sintering improved the mechanical strength and pore structure of vitrified bond CBN composites. Moreover, the introduction of the strong magnetic field facilitated Ni migration and aggregation in vitrified bond, rotated abrasives, and formed new substances, thus increasing the stability of vitrified bond CBN composite thermal material. Also, strong magnetic field inhibit grain growth of non-magnetic and ferromagnetic materials with fine-grain effect. [ABSTRACT FROM AUTHOR]