Xia Chang-qing

Effect of temperature on microstructure of molybdenum diffusion coating on titanium substrate

The halide-activated pack cementation process was used to form molybdenum diffusion coating on titanium substrate. The morphology, structure, elements diffusion distribution and microhardness of the coatings formed at different diffusion temperatures were studied. The results indicate that the coating is made up of deposition layer and diffusion layer, and the surface roughness of specimens is increased after diffusion. In the diffusion layer, the major phases are Mo and β-Ti phase with addition of α′-Ti phase and α″-Ti phase. And the phase composition of Mo →β→β″→β′ is formed for different Mo contents in the diffusion layer from outside to inside. The diffusion of Ti element is very obvious as well as Mo element. With increasing the diffusion temperature, the thickness of diffusion layer is increased rapidly, and the microhardness is changed more smoothly with diffusion depth, which shows the same distribution rules as the Mo content.

Stability of aqueous nano-ceramic coatings with two different dispersants

The effects of sodium carboxymethyl cellulose and sodium citrate as dispersants on nano-ceramic aqueous suspension were examined by the measurements of ζ-potential and the sedimentation test. The results show that proper addition of sodium carboxymethyl cellulose or sodium citrate into nano-ceramic coating, exhibits an enhanced dispersion and stability compared with the coating without dispersants. The negative ζ-potential of the particles in the nano-coating increases with the increase of pH value of the coating, and the curve of ζ-pH moves to lower pH range when the dispersants are added into the coating. To ensure that the coating has not only good stability and dispersibility but also no corrosivity to substrate alloy, adding 1.00% sodium citrate into coating with pH value of 7–8 is preferable to adding sodium carboxymethyl cellulose.

Evolution of microstructure and diffusion paths in the molybdenum-steel explosion weld interface during heat treatment

Abstract The carbide layers formed in the bond interface of the explosively welded molybdenum-steel composite after heat treatment between 973 and 1273 K was examined metallgraphically and analyzed using an electron microprobe technique. The diffusion paths at 973, 1023 and 1273 K were constructed and interpreted by means of the FeMoC equilibrium phase diagram assuming that local equilibrium is established at all the phase boundaries.

Effect of nano-size nickel particles on wear resistance and high temperature oxidation resistance of ultrafine ceramic coating

In order to improve the wear resistance and high temperature oxidation resistance of titanium and titanium alloy, the high temperature ultra fine ceramic coating containing nano-size nickel particles was prepared by flow coat method on the surface of industrially pure titanium TB1-0. The effects of nano-size nickel particles on the wear resistance and high temperature oxidation resistance of coating substrate system were investigated through oxidation kinetics experiment and wear resistance test. The morphologies of the specimens were examined by means of optical microscopy, scanning electron microscopy and X-ray diffraction. The results show that the high temperature ultra fine ceramic coating has notable protection effect on industrially pure titanium TB1-0 from oxidation. The oxidation and wear resistance properties of the coating can be effectively improved by adding nano-size nickel particles. The oxidative mass gain of the specimen decreases from 11.33 mg · cm−2 to 5.25 mg · cm−2 and the friction coefficient decreases from 1.1 to 0.6 by adding nano-size nickel particles, and the coating containing 10% (mass fraction) nano-size nickel shows the optimum properties.

Examination of carbon diffusion in niobium clad steel composite

The Nb2 C layer formed in the bonding interface of a niobium clad steel composite at 1023 K for 112 h was examined metallographically and analyzed using the electron microprobe technique. The mechanism of Nb2 C phase diffusion layer formation was discussed using Fick’s law assuming that stationary diffusion of carbon was established in niobium/steel diffusion couples.

Interfacial reaction in the tantalum-steel explosion weld composite at 1053 K

The microstructure of the interface of the explosively welded tantalum-steel composite which had been subjected to heat treatment at 1053 K was investigated by using optical microscopy and electron probe micro-analysis. It was confirmed that a Ta2C layer grew along the tantalum-steel interface. The carbon diffusion path at 1053 K, going through the γ-Fe, α-Fe, Ta2C and α-Ta phase regions was identified and interpreted by means of the Fe-Ta-C equilibrium phase diagram assuming that local equilibrium is established at all the phase boundaries.