Lixin Guo

Laser cladding of Ti-6Al-4V alloy with TiC and TiC + NiCrBSi powders

Abstract Laser cladding of Ti-6Al-4V alloy with TiC and TiC+NiCrBSi powders was carried out, and microstructure, as well as microhardness profile, in the clad layers was examined. The results showed that, in the TiC clad layer, TiC was melted and solidified to form dendrites in the clad zone, and dissolved into the melted Ti-alloy substrate and precipitated to form well-developed dendrites in the dilution zone. With increasing specific laser energy, the dilution effect of the Ti-alloy substrate was enhanced, and the microhardness decreased in both the clad and the dilution zones. In the TiC+NiCrBSi laser clad layers, TiC particles dissolved into the melted Ni-based alloy (binder material) in the clad zone. With increasing specific laser energy, the degree of solution of TiC particles was increased. During cooling, fine spherical particles and dendrites of TiC precipitated from the Ni-based alloy. When the TiC volume fraction increased to more than 50%, clustering of TiC particles was observed in the clad zone. The clustering of TiC particles resulted in a decrease in the homogeneity of the microstructure and microhardness distribution in the clad zone. The dilution zone of the TiC+NiCrBSi clad layers is a mutually melted region of the Ni-based alloy and titanium-alloy substrate and presents a microstructure of dendrites.

Microstructure and wear resistance of NiCrBSi laser clad layer on titanium alloy substrate

Abstract Laser cladding of NiCrBSi powders on Ti-6Al-4V alloy substrate was performed, and microstructure, microhardness and wear resistance of the clad layers were evaluated. Results show that the laser clad layer is divided into three regions: the clad, the dilution and the heat-affected zones. In the clad zone, fine particles of TiB2, TiC and M23(CB)6 are distributed in the matrix of the primary γ-Ni and the multi-phase eutectics consisting of γ-Ni, Ni3B and silicides. Microhardness of the clad zone is very high, being approximately HV 1000. The dilution zone is a mixture of melted Ni-base and Ti-base alloys, and possesses a characteristic of directional crystallization. The heat-affected zone has an acicular martensitic structure, and the microhardness is HV 360–380. Compared to titanium alloy, the wear resistance of clad layer is improved. The mechanism of wearing of clad layer is a mixed type of slight peeling-off and abrasion.

Metal organic framework-derived CoZn alloy/N-doped porous carbon nanocomposites: tunable surface area and electromagnetic wave absorption properties

N-Doped porous carbon with uniformly dispersed CoZn alloy nanoparticles has been synthesized through the pyrolysis of a bimetallic zeolitic imidazolate framework containing Zn and Co elements. The surface area, pore size distribution and graphitization of the composites can be modulated easily through changing the molar ratio of Zn to Co in the zeolitic imidazolate framework. Upon increasing the Zn content, the level of graphitization drops gradually and the surface area first increases and then decreases. The increased surface area results in the enhancement of dielectric loss and impedance matching. The sample with a Zn to Co molar ratio of 0.2 in its precursor has the most prominent electromagnetic wave absorption properties, due to appropriate surface area and graphitization properties. The minimum reflection loss reaches −59.7 dB and the widest bandwidth is up to 5.3 GHz. The composites can be good candidates for electromagnetic wave absorption and shielding applications, considering their outstanding performance and simple synthesis route. This study not only offers a simple and facile method for improving dielectric loss and impedance matching of carbon materials, but also sheds light on a new strategy for constructing porous structures, especially porous carbon.