Jian Bin Zhang

Microstructure and Hardness of the Laser Surface Treated Titanium

Surface modification is a promising technique to improve wear properties of titanium and titanium alloys by modifying either the surface composition or microstructure. Laser remelting and laser nitriding of commercial purity titanium were carried out under pure argon and pure nitrogen ambient, respectively. Characterization of the laser treated surface was done by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester. During laser irradiation heating, Ti exhibits a height activity and combines with N in the atmosphere of pure nitrogen forming TiN and TiN0.3, whereas Ti only transform into martensitic Ti in pure argon. The Vickers microhardnesses are greatly improved by laser remelting and laser nitriding.

Effect of Cr Additives on the Microstructures and Properties of Laser Cladded Ni3Si

Three compositions, (Ni75Si25)-5Cr, (Ni75Si25)-10Cr and (Ni75Si25)-15Cr, have been cladded onto Ni-based suaperalloy substrate by pre-placing laser cladding process with a 5 kW continuous wave CO2 laser. Ni75Si25 was also cladded with the same method for comparison. The process parameters have been optimized to obtain defect free claddings. The microstructure and the hardness of the cladded layers were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction and microhardness measurement. The corrosion resistance of the cladded layers was measured in a sulfuric acid solution.

Effect of Ceria Additive on Microstructure and Properties of Laser-Cladded Bioceramic Coating

The calcium phosphate bioceramic coating was fabricated on titanium alloy (Ti-6Al-4V) substrate by a 5kW continuous transverse flow CO2 laser. Due to the peculiar role of rare earth oxide in laser cladding, the effect of ceria additive on the microstructure and properties of laser-cladded bioceramic coating was investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), microhardness and corrosion resistance testing. The results indicate that the appearance of rare earth oxide ceria in the precursor powders has an impact on the microstructure and properties of the laser-cladded bioceramic coating. Calcium phosphate bioceramic such as hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) are synthesized on the top surface of laser-cladded specimens. And the addition of rare earth oxide ceria in pre-placed powders has an influence on the formation of calcium phosphate bioceramic phases. Furthermore, it reveals that the laser-cladded bioceramic coating of ceria additive in pre-placed powders has more favorable microhardness and corrosion resistance compared with the coating without rare earth oxide.

Characterization of Laser Cladding WC-Ti Composite Coatings

The applications of titanium and titanium alloys under severe wear conditions are highly restricted due to their low hardness and poor tribological properties. To improve the hardness and wear resistance, laser cladding of commercial purity titanium was carried out with a 5 kW continuous wave CO2 laser. WC powders and Ti powders were mixed for cladding in different proportions. The phases of clad layer were characterized by scanning electron microscopy, X-ray diffractometer and energydispersive X-ray spectroscopy. The mechanism of the reaction between melted WC and Ti is discussed.

Fabrication and Biocompatibility of Gradient Bioceramic Coatings on Titanium Alloy Substrate by Laser Cladding

Based on a high power CO2 laser beam passing by pyramid polygon mirror, the bioceramic coatings of gradient composition were fabricated on titanium alloy substrate (Ti-6Al-4V). The relations among laser processing parameters, microstructure and biocompatibility of the gradient bioceramic coatings were investigated. The results indicated that the contents of rare earth oxide additions had an immediate effect on the formation of bioactive phases. The gradient bioceramic coatings showed favorable biocompatibility in vivo after they were implanted into canine femur for 45, 90, and 180 days, respectively. The bioceramic coatings of Ca/P=1.4 and 0.6wt.% Y2O3 totally combined with new bones merely implanted for 45 days. Furthermore, the MTT (Methyl Thiazolyl Tetrazolium) colorimetry results of cell proliferation demonstrated that the cell growth distinctly increased on the gradient bioceramic coatings by laser cladding compared with the un-treated titanium alloy substrate.

In Situ Formation of TiC Reinforced Intermetallic-Matrix Composite Layers Produced by Laser Cladding

Laser cladding technique was used to form Ni3(Si,Ti) intermetallic composite coating reinforced by in-situ formation TiC particles on Ni-based superalloy substrate. The experimental results showed that an excellent bonding between the coating and the substrate was ensured by a strong metallurgical interface. The clad coating was very well and free from cracks and pores. By means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), the effect of Ti-C addition to the microstructure and microhardness of the coating was investigated. The microstructure of the coating was mainly composed of Ni(Si), Ni3(Si,Ti) and TiC. The average microhardness of the coating was improved with increasing the Ti-C content. The microhardness was up to 780Hv when Ti-C addition was 20 wt. pct, which was much greater than that of Ni-based superalloy substrate.

The effect of surface dispersants on electrodeposited antimony nanoparticles

Stable antimony nanoparticles with various particle morphologies and particle sizes were fabricated by electrodeposition method with different surface dispersants. The particle phase, morphology and size of resulting antimony particles were analysed. The results show that the surface dispersant has a remarkable effect on particle size, morphology and aggregation of the antimony particles. The coating surface formed from a mixture of Tween-80 and alkyl phenol polyoxyethylene ether can lead to particles aggregation; another kind of coating surface formed from a mixture of sodium dodecyl sulfate and alkyl phenol polyoxyethylene ether cannot prevent particles agglomeration; and such agglomeration occurred when mesitylene was used as surface dispersant. When used independently, alkyl phenol polyoxyethylene ether effectively adsorbed to the surface of antimony particles. The good densification and large space steric effect of this organic coating resulted played an important role in obtaining the well dispersed antimony nanoparticles with an average particle size of 12 nm.

The Preparation of Size-Controlled Antimony Nanoparticles by Electrochemical Method

This paper prepared some antimony nanoparticles with different particle size by electrochemical method. A method of preparing size-controlled antimony nanoparticles was established in the hydrochloric acid solution, which alkyphenol ethoxylates emulsifier was used as surface dispersants by electrochemical technology based on the optimization of the preparation technology. Those obtained antimony nanoparticles was characterized and analyzed by means of transmission electron microscopy (TEM), Fourier transform infrared absorption spectrum (FT-IR), X-ray diffraction (XRD). The experiment results show that alkyphenol ethoxylates emulsifier can effectively coat on the surface of antimony nanoparticles, current density and electrolysis time have an important influence on the particle size of those obtained antimony nanoparticles. When the current density is 25mA/cm2 and electrolysis time is 30minutes, spherical antimony nanoparticles with an average diameter of 12nm and good dispersion can be prepared.

In Situ Formation of NbC Reinforced Ni3Si Intermetallic Compounds by Laser Cladding

Laser cladding technique was used to form Ni3Si intermetallic composite coating reinforced by in-situ formation NbC particles on Ni-based superalloy substrate. The process parameters were optimized to obtain cladding. The effect of Nb-C addition to the microstructure of the coating was investigated. The morphology of reinforcement particles was discussed. The experimental results showed that an excellent bonding between the coating and the substrate was ensured by a strong metallurgical interface. The clad coating was very good and free from cracks and pores. The microstructure of the coating was mainly composed of Ni(Si), Ni3(Si, Nb) and NbC. The NbC particles were formed by in-situ reaction between Nb and C during laser cladding process. NbC particles were homogeneously distributed in the composite material. Moreover, the maximum size of NbC particles was more than 4 μm.

Intermetallic Alloys Ni3Si and Ni3(Si,Ti): Microstructures and Properties

Laser cladding experiment was carried out with a 5 kW continuous wave CO2 laser by preplacing Ni75Si25 and Ni78Si13Ti9 powders onto Ni-based superalloy substrate. The microstructure of the specimens was monitored by using optical and scanning electron microscopy. The chemical compositions of the alloys and their phases were obtained using X-ray diffraction and energy dispersive x-ray spectroscopy. The phase transformation temperatures were determined by non-isothermal differential scanning calorimetry tests. The microhardness of the laser cladded sample was measured.