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Mo2FeB2 coatings were fabricated by laser cladding with different pre-placed powder sizes. In the present research, a coaxial nozzle head coupled with a continuous fiber laser with a maximum power of 3 kW was used. The influence of powder size (~ 6 μm, ~ 13 μm, ~ 65 μm) on the morphology, microstructure, microhardness, wear resistance, and fracture toughness of the coating were discussed in this research. The morphology showed that coating obtained with ~ 6-μm powder size had excellent wettability and avoided obvious defects; microstructure revealed that the coating appeared particle agglomeration phenomenon with the increase of powder size. The coating obtained with ~ 6 μm had herringbone and feature structures to improve the density, and the bonding zone had typical columnar crystal and no cracks. The microhardness, wear resistance, and fracture toughness decreased as the increase of powder size. The optimal microhardness, COF, and fracture toughness of coating reached 1138.56 HV0.5, 0.59, 14.65 MPa·m1/2, respectively, when powder size was ~ 6 μm. The wear form of coatings was typical abrasive wear and adhesive wear; the fracture mechanism was transgranular fracture. The research can provide a reference for the preparation of Mo2FeB2 ternary boride coating. [ABSTRACT FROM AUTHOR]

WCoB-TiC composite coatings with in-situ formation of NbC were fabricated on the surface of an AISI 1045 substrate by laser cladding. The geometric characteristics, microstructure, microhardness, and fracture toughness of coatings were investigated by means of an optical microscope (OM), a scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), an electron probe microanalyzer (EPMA), and a microhardness tester. In addition, the elastic constants and bulk property of the reinforced phases were investigated by first principles calculation. The results showed that a reliable metallurgical bonding was formed between the coating and the substrate and in-situ synthesized reinforcement phases of the coating consisted of WCoB, W2CoB2, TiC, NbC, (Nb,Ti,W)C, and traces of Nb2C. The dilution rate and porosity had a negative effect with the addition of Nb. According to the results of SEM, EDS, and EPMA, Nb was diffused uniformly in the TiC structure. The NbC phase had the highest hardness among all in-situ synthesized reinforcement phases, which reached 24.525 GPa, while Nb2C reflected the strongest metallicity. The microhardness and fracture toughness of the coating were increased firstly and then decreased following the increase of Nb content, and when the Nb addition was 4 wt%, the coating had the highest average microhardness and fracture toughness (1755.42 HV0.5, 8.23 MPa·m1/2, respectively). The microhardness and fracture toughness was 24% and 30% higher than that of the coating without Nb addition, respectively. From the crack propagation morphology of coatings, all coatings had fine transgranular fracture. [ABSTRACT FROM AUTHOR]

In this research, the TiC–Ni35A composite coating was fabricated on the AISI 1045 steel substrate by laser cladding process. The cross-sectional morphology, microstructure, microhardness, and wear resistance of coatings obtained under different laser energy densities (E) and TiC powder ratios (PR) were analyzed. According to the results, all the coating had a reliable metallurgical bonding with the AISI 1045 steel substrate. The X-ray diffraction (XRD) analysis revealed that the coating phases were Ni and TiC. The average microhardness of the Ni35A-80wt.% TiC coating reached up to 75.1 HRC. The minimum coefficient of friction of the composite coating was only about 30% of the AISI 1045 steel substrate. The wear form was mainly adhesive wear when altering the TiC powder ratios, while the wear form also contained abrasion wear under different energy densities. The ability of decomposition and re-nucleation of TiC was significantly improved with the increase of laser energy densities and the decrease of TiC powder ratios. The microhardness, wear resistance, and coefficient of friction of the composite coating were improved because of the TiC strengthening phase particles. Compared with the AISI 1045 steel substrate, the microhardness and wear resistance of the composite coating were increased by 5.3 times and 6.3 times, respectively. [ABSTRACT FROM AUTHOR]

This research investigated the influence of different processing parameters in curved surface multi-track laser cladding with curve paths. Mathematical models of flatness ratio, incomplete fusion, and pore area in the clad were developed by central composite design with altering the input laser power, scanning speed, gas flow, and overlapping rate. Response surface methodology was used to analyze the correlation of different processing parameters affecting the selected responses. A clad with better flatness ratio was achieved by properly increasing the laser power and gas flow while reducing the overlapping rate. Appropriately increasing the laser power and overlapping rate while reducing the scanning speed and gas flow effectively diminished the incomplete fusion. Less pore area in the clad was obtained by appropriately increasing the laser power and overlapping rate while reducing the scanning speed and gas flow. Afterwards, desired processing parameters set was obtained by the optimization with the target of maximizing the flatness ratio and also minimizing the incomplete fusion and pore area. Experimental validation with this processing parameter setup provided satisfactory clad, and the error rate for the flatness ratio, incomplete fusion, and pore area was 1.708%, 5.714%, and 6.522%, respectively. This paper provides the theoretical guidance for the prediction and control of the flatness ratio, incomplete fusion, and pore area in curved surface multi-track laser cladding with curve paths. [ABSTRACT FROM AUTHOR]

The work prepared in situ synthesis VC particle-reinforced Ni-based coating using laser cladding. A 3-kW fiber laser was applied with a coupled coaxial nozzle head. The response surface methodology was applied to establish mathematical models of coating hardnesses, aspect ratios, and cladding areas at the laser power of 1200–2000 W, a scanning speed of 3–5 mm/s, and a powder ratio of 30–70% as input variables. The influences of process parameters on coating performance and geometries were explored hereafter. The feasibility of in situ synthesis of VC was analyzed by thermodynamics. The XRD test showed that coatings consisted of FeNi3, VC, V8C7, and Cr23C6 phases, with internal VC compounds of round and petal shapes. The response surface analysis showed that coating hardness increased with increased LP and PRs and decreased with increased SSs. The aspect ratio of coatings increased with increased LP and decreased with the increased SSs and PRs. Besides, the cladding area increased with increased LP and decreased with increased SSs and PRs. Sensitivity analysis indicated that the PR was included in the sensitive items of coating hardness, aspect ratios, and cladding area models. Coating hardness, aspect ratios, and cladding areas were not sensitive to LP. The accuracy of the sensitivity analysis was verified with 7 mm/s SS, while adjusting one factor between LP and PR. This research results provide a theoretical reference and basis for controlling coating properties and geometries in the industrial application of laser cladding. [ABSTRACT FROM AUTHOR]