Papers by Author: Jian Bin Zhang

Abstract: 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.

Abstract: Based on a high power CO2 laser beam passing by an integral mirror, the bioceramic coatings of gradient composition were designed and fabricated on titanium alloy substrate (Ti-6Al-4V). The relations among laser processing parameters, microstructure and thermal behavior of the gradient bioceramic coatings were investigated. The morphology of the composites was observed by scanning electron microscope (SEM). Phase composition of the coatings was analyzed by X-ray diffraction (XRD). And the thermal behavior of raw powders was evaluated through thermal gravimetry and differential scanning calorimetry (TG-DSC) test. The results demonstrated that the bioceramic coatings were metallurgically bonded to the titanium alloy substrate. The bioceramic coatings contained such bioactive phases as HA and β-TCP, which offered an advantageous condition for osseo-connection. The DSC thermograms showed the endothermic peaks at different temperature, which resulted from the different transitions process, respectively. Furthermore, the DSC results were in accordance with TG data of the powders and showed that with the increasing temperature the weight of sample accordingly decreased.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: Laser cladding technique was used to form Ni3(Si,Ti) intermetallic coating by Nb addition on Ni-based superalloy substrate. The coating was investigated by optical microscopy and X-ray diffraction (XRD). The clad coating was dense, compact and smooth. An excellent bonding between the coating and the substrate was ensured by a strong metallurgical interface. Ni3(Si,Ti) phase was detected in all of the claddings, and NbNi3, Nb3Ni2Si were detected in Nb additional experiments. The peaks intensity of Nb3Ni2Si and NbNi3 increased with the increasing of Nb content. The Ni3Nb and Nb3Ni2Si were formed when Nb was beyond its solubility in the L12 Ni3(Si,Ti). The average microhardness of the coating was improved with the increasing of the Nb content. The microhardness was up to 530Hv when the atom percentage of Nb addition reached 5%, and it was much greater than that of Ni-based superalloy substrate.

Abstract: Carbides reinforced intermetallic matrix composite coatings for elevated temperature environmental resistance were prepared on Ni-based suaperalloy substrate using CO2 laser cladding process. The phases of clad layer were investigated by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and energy-dispersive spectrometer (EDS). The laser cladding of the Ni78Si13Ti9/WC powder shows that the products mainly consist of TiC, WC and Ni3(Si,Ti) phases. A chemical reaction between WC particle and Ti powder occurs during the laser process, therefore TiC is formed. The microhardness of the samples increases with the increase of the content of WC.