Papers by Author: Zhi Hao Jin

Abstract: Biomorphic hydroxyapatite (Bio-HA) was fabricated using extracted beech wood that was impregnated with HA sol followed by sintering at 600~1300 °C for 2 hours. The extraction using boiling 5% ammonia solution was helpful to bring more pores to benefit to impregnation of the HA sol into wood templates. The weight changes of the exacted wood sample with HA gel, phase formation and microstructures evolution of resulting products were investigated by TGA, XRD and SEM. The main weight loss occurred below 600 °C. The biomorphic HA sintered at 1100~1300 °C were three dimensions and connective pores structure, in which the main tracheid pores with diameter of 60~80 μm derived from beech wood template and the small pores with 1~8 μm in the strut walls resulted from the sintering process. Bio-HA faithfully retained the woods porous structure. The method provided a novel candidate for fabricating a porous scaffold suitable for bone tissue engineering applications.

Abstract: Porous SiC/SiAlON ceramics were fabricated by carbothermal reduction method from raw materials of fly ash and semi coke in nitrogen atmosphere. The results showed that composites were composed by multi-structure of SiC, Ca-SiAlON and AlN phases. With the increase of semi coke contents, the contents of Ca-Sialon increased. The fracture mode of this material was intergranular. The results also showed that micro area hereditary of semi coke particles was observed in the morphology of this material. The morphology of this material was composed by nanosized SiC and plate like Ca-SiAlON. The median pore diameter was affected by the contents of semi coke and increased with the increase of semi coke content.

Abstract: SiC/0~20% graphite (volume fraction) composites were successfully fabricated by pressureless sintering at 1700 °C for 2 h in nitrogen atmosphere. The impregnating and heat treatment process for the samples with silica sol/phenolic impregnant was carried out at 1450 °C for 2 h in nitrogen atmosphere. The Vickers hardness, oxidation resistance and thermal shock property of the composites before and after treatment were tested, and the microstructure and phase composition were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results shown that the Vickers hardness of SiC/20% graphite was increased from 3.35 GPa to 4.90 GPa by heat treatment, and the oxidation resistance and thermal shock property of the heat treated samples were also improved significantly. The SEM and XRD results revealed that the formation of new SiC particles by the reaction of silica sol and phenolic was the main reason for the mechanical properties improvements.

Abstract: Flower-like AlN microstructure with many cone-like petals was prepared by combustion synthesis assisted with a mechanical activation (MA) method using NH₄Cl as a reacting additive. The products were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrum (EDS) and transmission electron microscopy (TEM). A possible mechanism for the growth of AlN microflowers was proposed base on several parallel experiments and discussion. It was found that both the MA time and NH₄Cl content play crucial roles for the growth of the flower-like microstructure.

Abstract: The three kind of oxides such as 3Y-ZrO₂, Fe₂O₃ and MgO were used as catalyst in reaction bonded silicon nitride (RBSN) with low-purity silicon powder as raw materials. The oxides can strongly promoted the nitridation ratio of RBSN, and the catalysis effects of these oxides for RBSN were investigated. After 4h nitridation, the degree of nitridation increased from 43% to 96% by adding 10wt% of 3Y-ZrO₂ additive comparing with the sample without additive, and the catalystic effects of Fe₂O₃ and MgO were slightly less than 3Y-ZrO₂ additive. XRD patterns revealed that the main phases of the reaction products were α-Si₃N₄, β-Si₃N₄ and Si-N-O intermediation. SEM micrographs show that the hexagonal columnar β-Si₃N₄ separated from acicular α-Si₃N₄.

Abstract: The paper reports on an investigation of the fracture mechanism of both tensile and impact fracture in three types of casing-drilling steels. The results show that the tensile fracture surface of N80 steel includes fibrous zone, radiation area and shear lip zone, and those of both K55 and P110 steels include two zones; all the tensile fracture surfaces of three types of casing drilling steels show the ductile fracture mode, the ductile fracture mode indicated with dimples is observed on all zones; the impact fracture surface of the N80 steel possesses a combined quasi-cleavage and ductile fracture modes, a single fracture mode is observed on the fracture surface of both K55 and P110 steels, the K55 steel impact sample is fractured in a cleavage brittle manner, whereas the P110 steel impact sample is fractured in a dimpled ductile manner.

Abstract: An investigation into the fatigue crack growth behavior of N80 steel was carried out for casing-drilling technology. The results show that the effect of stress ratio on the △K corresponding to access of the tensile overload region is remarkable, and increasing the stress ratio is found to increase the FCGR at the same △K and reduce △K of access of the tensile overload region; the transgranular failure machanism is dominant for the N80 steel in the all crack growth stage; the fracture surface roughness decreases as the cracks propagate through threshold region and into Paris region, whereas it increases as the cracks propagate through Paris region and into the tensile overload region; the typical ductile-dimpled fracture mechanism observed on the tensile overload region is similar to the tensile fracture mode, although the orientation of the dimples significantly inclines to fatigue crack growth direction.

Abstract: C/C-SiC composites were rapidly fabricated by a two-steps processing. Firstly a short-cut carbon fiber felt (SC) and a 2D carbon fiber felt (2D) were densified to C/C composites by a thermal gradient chemical vapor infiltration (CVI) method with vaporized kerosene as a precursor in 2h, 3h, 4h and 5h, respectively. Then the C/C composites were infiltrated and reacted with melting silicon to obtain C/C-SiC composites. The results show that, with increase of the CVI time, the densities of the two types of C/C-SiC composites decrease in the range of 2.28g/cm3 to 2.00g/cm3; their porosities increase ranging from 1.3% to 7.5%; the contents of the β-SiC and the unreacted Si phases in the composites decline. The flexural strength of the 2D_C/C-SiC composite is much higher than that of the SC_C/C-SiC composite when prepared in the same condition.

Abstract: SiC/C (graphite) composite ceramics with 20vol% flake graphite were fabricated by Plasma Activated Sintering (PAS) firstly; the composites treated by silicon infiltration in surface were oxidized from 800oC to 1500oC. Effect of silicon infiltration on the oxidation resistance of SiC/C (graphite) composites was characterized by TG/DTA, SEM and XRD. The results show that the graphite in surface of composites reacted with silicon to form a dense SiC film about 30μm-in-thickness. The oxidation resistance temperature was increased from 600oC to 1300oC. Below 1300oC, the surface of composites by silicon filtration was oxidized to form a dense continuous oxide film to hider the oxidation of graphite in matrix. At 1500oC, the surface oxide film was heavy damaged, and many micropores were produced; inner graphite was oxidized above 1300oC again.

Abstract: The AlN/Ti laminated composites were fabrication by plasma activated sintering. In the composites, the AlN layers were matrix layers and the Ti layers were as the toughening layers. The microstructure and mechanical properties were studied. XRD and SEM results showed that a new phase (TiN, Al5Ti2) in the layer interface was generated by reaction of AlN and Ti. The AlN/Ti interface bonding was strengthened by existing of the new phase, plastic deformation and bridging of ductile Ti phase. The crack propagation path would be extended by the flexuous pattern. Therefore, the fracture toughness of composites was improved obviously comparing with the monolithic AlN and the bending strength decreased a little.