Papers by Author: Qi Lin Deng

Abstract: The experiment is to gain laser cladding complex Ni-based coating with excellent wear resistance and without defects, by adding 5wt.% Ta into laser cladding Ni45 coating. This paper researches the influence of Ta on microstructure and wear resistance of laser cladding Ni45 coating. The results of the experiment show that strong carbide forming element Ta preferentially react with element C to generate the TaC hard phase, which restrains the growth of coarse primary carbide M7C3 and the eutectic structure of γ-Ni+M23C6, refines microstructure of the coating, reduces the cracking susceptibility and then gain the laser cladding coating without defects. The mircrohardness of Ni45+5%Ta complex laser cladding coating improves by about 18% compared to Ni45 coating; and its abrasive wear resistance improves by about 20% in dry friction environment. The solid solution strengthening formed by Ta improves the resistance to plastic deformation of Ni matrix. The refined crystalline grains restrain the nucleation and expansion of micro cracks on grain boundary, which prevents materials from falling off in form of grain. In addition, the primary generated TaC has higher mircrohardness than M7C3 and it disperses in matrix, which in some extent impedes the cutting motion of abrasive, consequently, being conductive to improve the mircrohardness and wear resistance of laser cladding coating.

Abstract: There is large use of directionally solidified superalloy blades in aerospace, but the repair of these blades is a real problem. The laser cladding technology is able to implement the repair. The experiments in this paper study the microstructure of laser cladding, analyze the formation mechanism and control method, implement the directional growth of microstructure in multilevel laser cladding layer, and provide a theoretical and experimental basis of laser cladding repair on directionally solidified superalloy blades.

Abstract: During the laser cladding process, temperature field is an issue worth thorough research. An optimized temperature field can not only ensure the high metallurgical bonding strength between the cladding layer and the substrate, but also can produce relatively mild thermal deformation for the parts to be repaired. This work theoretically analyzes the temperature field during the cladding process and validate the analysis through the microstructure of the cladding layer.

Abstract: The in situ synthesized NbC particles reinforced Ni-based alloy composite coating has been successfully prepared on 1045 steel substrate by laser cladding a precursor mixture of Ni-based alloy, graphite and niobium powders. The microstructure, phase composition and wear property of the composite coating are investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and dry sliding wear test. The experiment results show that the coating is uniform, continuous and free of pores and cracks with excellent bonding between the coating and the substrate. The microstructure of the coating is mainly composed of γ-Ni dendrite, a large amount of interdendritic eutectics of M₂₃(CB)₆, N₃B with γ-Ni, M₂₃(CB)₆ type carbides and dispersed NbC particles. The growth mechanism of the NbC particles with cores is nucleation-growth and the un-melted niobium may act as the nucleation core for NbC, Compared to the pure Ni-based alloy coating, the hardness of the composite coating is increased about 36 %, giving a high average hardness of approximate HV_0.2750. Moreover, the wear volume and wear rate of the composite coating are decreased about 50 % and 42 %, respectively. This is attributed to the presence of in situ synthesized NbC particles and their well distribution in the coating.

Abstract: Laser cladding forming (LCF) is one of the new developed advanced manufacturing technologies. It integrates the advantages of rapid prototyping manufacturing and laser cladding surface modification, and three dimensional near-net-shape metal components can be directly manufactured without dies. Due to the dramatic heating and cooling characteristics of laser cladding forming process, the cladding layers is liable to crack, which greatly impedes the further and wider application of this technology. In this paper, numerical simulation on the three-dimensional transient temperature field and stress field of powder-delivery LCF has been carried out with parametric programming methods. The temperature field, temperature gradient and cooling rate of the laser cladding layer have been obtained. The influences of laser power and scanning speed on the temperature gradient and cooling rate of the cladding layers, especially the cooling rate of solid-liquid interface of the melt pool have been studied, which is tightly correlated with the cracking generation of the deposited layers. According to the simulation, process parameters were optimized to minimize the cracking possibility; LCF experiments have also been conducted to verify the simulation results.

Abstract: Laser rapid forming is a kind of new developed technology combining laser surface modification and rapid prototyping technology. It provides a powerful tool for the manufacturing and repairing of metal components. Laser rapid forming repairing experiments of 45 and 2Cr12 steel have been carried out with 316L stainless steel powder. Microstructure and properties of the repaired components are analyzed and tested with optical microscopy (OM), scanning electron microscopy (SEM) and electronic tensile experimental machine etc. Repaired components of different materials have been metallurgically bonded with the deposited layers, with fine microstructure, better mechanical properties and free of defects.

Abstract: Laser cladding rapid manufacturing technology is a kind of new developed advanced manufacturing technology integrating the advantages of rapid prototyping manufacturing and laser cladding surface modification. Due to the complex thermo-physical and metallurgical factors in the deposition process, the cladding layer is liable to crack, which seriously impedes the industrial application of this technology. Experiments of laser cladding rapid manufacturing 316L stainless steel were carried out. The cracking behavior and phenomena has been observed, cracking mechanism of 316L stainless steel was investigated by means of microstructure characterization and phase analysis with optical microscopy (OM), X-Ray diffraction (XRD), scan electronic microscopy (SEM) and phase diagram analysis. Factors influencing the cracking susceptibility has also been studied. Results show that the cracks of 316L stainless steel were hot solidification cracks caused by the high residual stress and separating of the liquid films among dendrites. Through the optimization of process parameters, adding protective atmosphere, etc. cracking sensitivity has been effectively reduced and crack free 316L stainless steel components have been obtained.

Abstract: Undesirable phase and microstructure formation, and poor HAP/metal bonding strength restrict the fabrication technique to obtain HAP and other calcium phosphate ceramic coatings. In this paper a bioceramic composite coating, which includes HAP andβ-Ca2P2O7, was obtained by laser cladding with pre-depositing mixed powders of CaHPO4·2H2O and CaCO3 directly on the 316L stainless steel metal substrate. The phases, microstructure and bonding feature of the bioceramic composite coating are characterized by X-ray diffraction(XRD), scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS). The microstructure of the coating consists of minute granular HAP that is distributed among the overlapped club-shapedβ-Ca2P2O7. Uniform presences of Ca, P and O in bioceramic composite coating supplie necessary elements for the synthesis of HAP andβ-Ca2P2O7. Diffusions inwards of P and O into alloying layer help form the chemical metallurgical bonding and composition gradient distributions are present. a chemical metallurgical bonding was formed between the bioceramic composite coating and metal substrate.

Abstract: Rapid prototyping full compacted metal parts has becoming the focus of attention in the domain of rapid prototyping. In this paper, the method of forming full compacted metal parts by selective laser melting has been put out and the experimental researches on it have been carried out. The surface quality and the inner microstructure of the parts formed by selective laser melting were analyzed. The full compacted metal parts without any micro-cracks have been attained. The test results show that the tensile strengthen of 316L stainless steel parts formed by selective laser melting is greater than that of casting 316L stainless steel parts.

Abstract: Experimental study on the laser direct fabrication (LDF) of stainless steel powder is carried out. Microstructure and properties of the deposited components are analyzed and tested with optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) etc. Cracking generation mechanisms of this material are investigated, corresponding cracking control strategies have been proposed. Finally, fully dense stainless steel components free of defects and with perfect comprehensive mechanical properties have been produced.