Papers by Author: Jie Cai Han

Abstract: The large-sized sapphire (Ø225×205 mm, 27.5 kg) was grown successfully by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at cooled center). The surface quality of the specimens was characterized by micro-Raman spectroscopy, and double crystal X-ray diffractometry (DCD) was utilized to investigate its crystalline perfection. The measurement of rocking curves was performed on various specimens from different region of large sapphire boule. The experimental results showed that CMP (chemo-mechanical polishing) with subsequent suitable chemically etching can develop the best-quality sapphire crystal surface and the values of FWHM obtained by conventional DCD were in the range from 27” to 58”. The infrared spectral transmission (2.0-4.5 5m) of sapphire crystal exceeded 82%. It is confirmed of SAPMAC growth method characteristics with in-situ annealing, small temperature gradient and low residual stress level by numerical simulation analysis.

Abstract: In the present work, a SiCp/Al composite was fabricated by pressureless infiltration of aluminum alloy into loose-packed SiC particles preform, and its microstructure and hardness performance were investigated. The results showed that the composite was fully infiltrated and the particles were distributed uniformly in the composite. Interfacial reactions were found in the as-cast composite and the reaction product was identified as MgAl2O4 by TEM observation and XRD analysis. The interfacial reactions enhanced the wettability and promote the spontaneous infiltration process. The thermal exposure process increased the Brinell hardness of the composite. After the thermal exposure process, the block-like interfacial reaction products were distributed discretely, but the amount of the reaction products was increased.

Abstract: The feasibility of fabricating h-BN-SiC high-temperature ceramics by in-situ combustion synthesis was demonstrated by igniting the mixture of boron carbide and silicon powder under 100MPa nitrogen pressure. The reaction thermodynamics and the adiabatic combustion temperature were calculated theoretically. The phase composition, microstructure and mechanical properties of composite were identified by XRD and SEM. The maximum bending strength and fracture toughness of the composite were 65.2 MPa and 1.4 MPa·m1/2 under room temperature, respectively. The effects of h-BN and SiC dilution contents on the mechanical properties of composite were also discussed.

Abstract: The compressive properties characterized as a function of the true stress-strain response of the ferritic oxide dispersion strengthened (ODS) alloys, fabricated by mechanical alloying, were examined at strain rates ranging from 0.01 to 0.5s-1. Based on the differential scanning calorimeter (DSC) analysis, the solidus temperature of the ferritic ODS alloys is 1446oC. Therefore, the compressive temperatures were chosen to be from 1050oC to 1300oC. Transmission electron microscopy (TEM) observation is indicative of the homogeneous distribution of the nano-yttria particles with the granularity of 100~200nm, which may exert a strong pinning effect on subgrains. The results indicate that flow stress of the ferritic ODS alloys enhances with decreasing compressive temperature and increasing strain rate. Investigation of the strain rate sensitivity exponent and apparent activation energy of the ferritic ODS alloys has been carried out in detail.

Abstract: DSC/TG analysis was used to investigate the change of TiSi2-SiC-N2 system in the temperature range from room temperature to 1400°C. The relationships between $G and T about the reactions possible occurring in TiSi2-N2 system during combustion synthesis were calculated. In order to study the combustion process in detail, the reaction of TiSi2-SiC-N2 system was stopped at different stages by quenching the samples. The composition and microstructure in different reaction zones were analyzed by means of XRD and SEM, accordingly, reaction kinetic model of TiSi2-SiC-N2 combustion system was established. The result showed that TiSi2 firstly reacted with N2 to form TiN and Si, and subsequently Si were nitrified.

Abstract: The sheet metal of a new Ni-based superalloy has been prepared by Electron Beam Physical Vapor Deposition (EB-PVD) technology. The phases, the microstructures and mechanical properties of this alloy before and after heat treatment have been analyzed by X-ray diffractometer, transmission electron microscope, optical microscope, scanning electrical microscope and tensile equipment. Results showed that the size of γ' particles increases gradually and the morphologies of γ' particles changed from spherical shape into cubical shape when temperature increased from low to high. Compared with as-deposited alloy, mechanical properties of heat-treated alloy were improved obviously. It is feasible that superalloy of better properties can be prepared by EB-PVD technology.

Abstract: Two Al-Si alloys (Al-12Si and Al-20Si) and an industrial pure Al were reinforced with 70vol.% dual-sized SiC particles. The composites experienced annealing treatment, to investigate the effect of silicon addition and thermal history on the thermal expansion behavior of high SiC content aluminum matrix composites. The results showed that silicon additions led to a beneficial reduction in the coefficients of thermal expansion (CTEs) of the composites. In the temperature range between 20°C and 400°C, a continuous increase in CTEs with temperature was observed for SiCp/pure Al composite. However, the CTEs of SiCp/Al-12Si and SiCp/Al-20Si showed the maxima at 350°Cand 250°C respectively, then diminished at higher temperatures. This was related to the change of solid solubility of silicon in aluminum at elevated temperatures. The thermal expansion behavior of SiCp/Al composites was also influenced by thermal history. After annealing treatment, the CTEs were reduced when compared with those of as-cast composites. Annealing treatment reduced the original thermal residual stresses, and then altered thermal expansion behavior of the composites.

Abstract: An experimental investigation is carried out to machine SiC ceramic material through method of high speed plane lapping with fixed abrasive. The results show that the material removal mechanism and the surface roughness are chiefly related to the granularity of abrasive and the lapping pressure for the brittle materials such as SiC ceramic. It is easily realized to machine SiC ceramic material in ductile mode with a high efficiency and a low cost using W3.5 grit under a lapping pressure of 0.1MPa and then a smooth surface with surface roughness of Ra 2.4nm can be achieved.

Abstract: The TiB2-40Cu-8Ni composite prepared by combustion synthesis is investigated. Both 2D digital radiography (DR) and 3D computed tomography (CT) are used to test the specimens nondestructively. The result shows that ceramic phase aggregation is the main defect. Then the mechanical properties of samples are assessed by means of three-point-bend test. It appears that mechanical properties are related with the distribution of TiB2 phase and Cu phase. The scanning electron microscope (SEM) is also used to observe the crack growth of the bending test sample.

Abstract: Titanium diboride nanoparticles reinforced copper matrix composite by combustion synthesis technology from titanium, boron and copper powders without other activated methods. Thermodynamics of the system was calculated theoretically. It was found that TiB2 was stable phase in the composite and TiCu interphase compound can convert into stable phase. The phases of the synthesized product were identified using X-ray diffraction and the results showed that only TiB2 and Cu phases, no other phases existed in the product. It is consistent with the calculated result of thermodynamics. SEM microstructural characterization showed that a homogenous distribution of the titanium diboride nanoparticles in the copper matrix.