Search

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]

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]

• 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]

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]

The vitrified bond CBN grinding wheels are characterized by high efficiency, high precision, and low environmental pollution. In recent years, the vitrified bond CBN grinding wheel has been widely used in manufacturing industries such as aerospace, automotive, and machine tools. In this study, a novel vitrified bond formulation containing nano SiO 2 and nano CeO 2 is selected to prepare the grinding wheel. The grinding experiments on 45# steel and YG20 alloy indicate that the grinding performance of the nano vitrified bond grinding wheel is significantly better than that of the conventional vitrified bond grinding wheel. The introduction of nano SiO 2 and nano CeO 2 greatly improves the machining performance of the vitrified bond CBN grinding wheel. [ABSTRACT FROM AUTHOR]

Optical glass BK7 is widely used in optical lenses. It is a kind of hard and brittle material and thus difficult to machine. To solve the problems it has encountered in terms of polishing efficiency and quality, the axial ultrasonic vibration assisted polishing (UVAP) method is adopted in this study. A mathematical-prediction-model, firstly considering the effects of periodically changing pressure caused by ultrasonic vibration, is developed to predict the generated surface-profile. And for the first time, the concept of "Preston-coefficient distribution-function" is proposed to describe the effect of the abrasive-particle distribution on material-removal distribution-function. A series UVAP experiments on optical glass BK7 at different polishing parameters are conducted to validate the polishing efficiency and feasibility of the developed prediction model and proposed concept. The results confirm that UVAP method can realize a higher material removal rate (MRR) and a better surface quality. Compared to conventional method, the predictions are in good agreement with the experiments. The comparison of the obtained surface profiles proves the benefits of ultrasonic vibration as well. Moreover, the research results can be used to guide the adjustment of polishing parameters for deterministic material removal in straight feeding process of UVAP, and provide a valuable basis for trajectory planning of the global polishing of workpiece surfaces. [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]

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]

This paper studies the different lap joint methods of YCF101 alloy powder by direct laser fabrication (DLF) technology and analyzes the structure, porosity, cracks, and surface topography of multichannel forming parts fabricated by DLF to optimize the ideal lap joint mode. The selection basis of lap joint modes is based on the surface adhesion powder of single-layer cladding surface, inner cracks and porosity, and microstructure of the forming parts under different scanning modes. Regardless of any scanning method, there would be obvious sticky powder at the lap joint, and the pore and cracks are mainly present at the lap joint. The uneven energy density of the weld during the fusion process makes a great difference in the microstructure of the molten pool and the lap joint, the structure of molten pool is small isometric crystal, and the structure of lap joint is bulky dendrite. The defects caused by the uneven energy distribution and sticky powder had been improved by different lap joint modes between layers. The uniform distribution of the linear trace poles at the outer contour surface improved the surface quality of the forming part. As the mesh size of the cladding region that is divided by the cladding trajectory becomes smaller, the quality of forming parts has changed. The double decussation and outline mode has the smallest mesh size, the porosity is 0.47%, the microstructure of the lap joint area is no longer just dendrites, there appears isometric crystal and structure refining, the crack reduces, and the compressive strength is improved. To some extent, the problem brought by sticking powder and uneven heat distribution had been worked out. [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 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]