Qilin Deng

Microstructure and Wear Resistance of in situ NbC Particles Reinforced Ni-based Alloy Composite Coating by Laser Cladding

The in situ synthesized NbC particles reinforced Ni-based alloy composite coating was produced by laser cladding a precursor mixture of Ni-based alloy powder, graphite and niobium powders on a steel substrate. The microstructure, phase composition and wear property of the composite coating were investigated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and dry sliding wear test. The experiment results show that the composite coating is homogeneous and free from cracks, and about 0.8 mm thick. The microstructure of the composite coating is mainly composed of NbC particles, CrB type chromium borides, γ-Ni primary dendrites, and interdendritic eutectics. CrB phases often nucleate and grow on the surface of NbC particles or in their close vicinity. NbC particles are formed via in situ reaction between niobium and graphite in the molten pool during the laser cladding process and they are commonly precipitated in three kinds of morphologies, such as quadrangle, cluster, and flower-like shape. Compared with the pure Ni-based alloy coating, the microhardness of the composite coating is increased about 38%, giving a high average hardness of HV0.21000, and the wear rate of the composite coating is decreased by about 32%, respectively. These are attributed to the presence of in situ synthesized NbC particles and their well distribution in the coating.

Influence of Ta on microstructure and abrasive wear resistance of laser clad NiCrSiB coating

A mixture of NiCrSiB alloy powder and tantalum (Ta) powder was used as laser clad material to improve abrasive wear resistance of the Ni-based coating. The microstructure and wear resistance of the coating were investigated. Addition of Ta element works to suppress the growth of coarse M7C3 carbide in the coating, resulting in a decrease in aspect ratio of coarse carbide. In the abrasive wear test, in situ synthesized TaC particles well bond with Ni-based matrix, and are hardly pull out from wear surface. Grooves on the worn surface of NiCrSiB coating are much deeper and sharper than those in the NiCrSiB+Ta composite coating. Also, a weight loss of the composite coating is much lower than that of the NiCrSiB coating. The wear resistance of the laser clad Ni-based coating is enhanced to a much greater extent through the addition of Ta. This is attributed to the in situ synthesized hard TaC particles of nearly equiaxed shape, the Ni-based matrix strengthened by Ta and the decrease in aspect ratio of the coarse brittle carbides.

Mechanism of Zr in in situ-synthesized particle reinforced composite coatings by laser cladding

By adding mixture of ZrO2 and carbon, a Zr-enhanced composite coating was produced onto an AISI 1045 substrate by laser cladding. The microstructure and phase formation, microhardness and wear resistance of the composite coating were studied. The experimental results indicate that the composite coating with metallurgical bonding to substrate consists of γ-Ni, massive ceramic particles of ZrC, NiZr2, Ni7Zr2, (Fe, Ni)23C6 and Fe3C. The in situ-synthesized ZrC particles are uniformly dispersed in composite coating, which refines the microstructure of composite coating. With different ZrO2 and carbon additions, the properties are improved differently. Finally, the fine in situ ZrC particles improve the microhardness of composite coating to HV0.2 650, which is nearly 2.7 times that of Ni25 coating. Also, the composite coating has an advantage in wear resistance; it offers better wear resistance when more mixture of ZrO2 and carbon was added in nickel alloys.

Modification and fabrication of metal components with CO 2 laser cladding forming

Modification of nickel based alloys was carried out, effects of process parameters and ceramic contents on the microstructure and hardness were investigated. With the addition of WC particles, the microstructure has been refined, hard phase particles bond well with the nickel based matrix, the hardness and wear resistance of the cladding layers has been significantly improved. At a laser power of 1.2 KW, hard phase particles are homogeneously distributed in the cladding layers. Three dimensional metal components free of defects were fabricated with CO2 laser cladding forming technology. Factors influencing the forming quality of components were discussed. The precision and surface quality of the deposited samples has been improved through parameter optimization and close-loop control of melt pool temperatures. Optical microscopy (OM) observation and tensile strength testing show that the microstructure of laser cladding forming components is fine and compact, the mechanical properties has reached or surpassed that of the conventionally processed methods.