Key Engineering Materials Vols. 368-372

Abstract: TZP/SUS304 functionally graded material (FGM) was developed by slip casting. Microscopic observations demonstrated that the chemical composition and microstructure of TZP/SUS FGM distributed gradually in stepwise way, eliminating the macroscopic ceramic/metal interface occurred in traditional ceramic/metal joint. Each interface of layers connected well without evident defects, and the mechanical properties of TZP/SUS system strongly depended on constitutional variation.

Abstract: Electrophoretic deposition (EPD) has been widely studied in preparing clay-modified electrodes (CMEs) and in assembly of nano-laminated composite that mimics nacre. In this paper, the hydrothermal intercalation and EPD were combined to prepare CMEs with a uniform and continuous polymer/clay composite film of brick-and-mortar nano-laminated structure. X-ray diffraction, scanning electronic microscopy and thermal gravimetric analysis were employed to characterize the structure and composition of the films. Stability of aqueous suspension, temperature for hydrothermal intercalation and deposition time, etc. were systematically studied and discussed.

Abstract: A novel rapid prototyping manufacturing technology for glass-alumina functionally gradient materials (G-A FGMs) based on the quick solidification of wax was proposed. The feature of the technology came from its layer-by-layer fabrication of the wax-glass/alumina composite layer carved in accordance with the shape of each layer of the computer designed model and in situ casting of wax into the carved area. Removal of the wax in the G-A FGMs green body was investigated based on differential scanning calorimetry (DSC) analysis. Sintering properties of the G-A FGMs were discussed. Bending strength of the G-A FGMs was measured by a three-point flexural test. Microstructures of the prepared G-A FGMs were observed using environmental scanning electron microscope (ESEM) and the compositional distribution was determined according to energy dispersive spectrum (EDS). Samples were preliminarily and respectively held at 200°C and 300°C for a long time based on the DSC analysis. The range of the optimal sintering temperature is determined to be from 710°C to 720°C and the holding time is 30min. With the increasing alumina content, the bending strength increases and the maximum bending strength is 67.5MPa. There is no delamination of the G-A FGMs via ESEM. Homogeneous distribution of the ingredient materials is confirmed through EDS.

Abstract: In this research, the metal and ceramic laminates Ti/Al2O3, Ni/Al2O3 were prepared by PAS. The bonding interfaces of Ti/Al2O3, Ni/Al2O3 were observed and analyzed. The microstructures of laminates were observed by SEM. It was shown that the joints of the samples were tight and had not visible flaws. Moreover, the comparison of Ti/Al2O3 and Ni/Al2O3 laminates showed that the join mechanisms of them were different. Ni/Al2O3 laminates that had not apparent conversion zone were joined by diffusion and had lower bond strength. Ti/Al2O3 laminates have obvious conversion zone because Ti and oxygen have strong combining power. Three-point bending test indicated that the fracture of laminates was correlated to the bond strength of the interface.

Abstract: TiN/Al2O3 functionally graded composite was fabricated by in-situ aluminothermic reduction of TiO2 in coke bed from mixtures of TiO2 powder and metal Al powder. The reaction process, phase composition, and microstructure of sample treated at 1500°C for 3h were analyzed by XRD, SEM and EPMA. The results indicated that the thermite reduction of TiO2 involves several transitional stages and its initial reaction temperature is lowered by prior reaction between Al and TiO2. EPMA analysis showed that the TiN/Al2O3 ratio in TiN/Al2O3 functionally graded material products changes gradually across the samples without distinct interface between the different layers. The microstructure of the composite changes gradually, and the size of TiN grains increases from the verge region of samples to the centre of samples. These results above were in agreement with thermodynamic analysis.

Abstract: ZrO2-CeO2 thin film was successfully prepared on 316L stainless steel by sol-gel process and the corrosion characteristics of the substrate coated with ZrO2-CeO2 thin film were evaluated through potentiodynamic polarization curve obtained in deaerated 15% H2SO4. The results show that, with the increase of CeO2 content, the corrosion rate of 316L stainless steel substrates coated with ZrO2-CeO2 thin film decreases. The surface morphology of the coating was observed by field scanning electron microscopy and the elements in the surface of coated substrate analyzed by FEM-EDX.

Abstract: In order to obtain dense-porous laminated structure in green bodies of SiC ceramics, rapid aqueous electrophoretic deposition (EPD) was introduced. The suspension for the electrophoretic deposition was prepared using silicon carbide, silicon and carbon powders as the starting materials. During the electrophoretic deposition process, the intending dense and porous layers were deposited alternately to form the green body. After drying, the green bodies were reaction-bonded at 1550°C in vacuum atmosphere. Pore fraction of the porous layers could be adjusted by changing process preferences of EPD and suspension composition. Pore size and size distribution could be controlled by using different sized starting powders. Using this process, no additional substance is necessary to generate the pores via burnt-off, and the dense/porous laminated structure can be obtained by one-step sintering process.

Abstract: The influence of the fiber/matrix interlayers on the mechanical properties of T800-HB fiber (a kind of carbon fiber) (the fibrous is three-dimensional four-directional braided) reinforced silicon carbide (SiC) matrix composites has been evaluated in this paper. The composites were fabricated through PIP process, and SiC layers were deposited as fiber/matrix interlayers by the isothermal CVD process. Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces. The mechanical properties were investigated using three-point bending test and single-edge notched beam test. The T800-HB/SiC composites exhibited high mechanical strength, and the flexural strength and fracture toughness were 511.5MPa and 20.8MPa•m1/2, respectively.

Abstract: The dynamic process of crack initiation and propagation in a SiC/BN-Al2O3 laminated composite was observed in situ by scanning electron microscopy. During a bending test with a single-edge notched-beam specimen, an interfacial crack first initiated in the interlayer near the notch tip, after which a through-thickness crack formed in the matrix layer at the notch tip. After the through-thickness crack had grown across the first matrix layer, it was deflected by the next interlayer and again became an interfacial crack. Interfacial cracks and through-thickness cracks were generated alternately until the composite failed. The load-displacement plot of the laminated composite exhibited several peaks, each caused by one propagation of a through-thickness crack. The toughening mechanisms of the laminated composite included crack deflection, interfacial cracking, and through-thickness branch cracking.

Abstract: Ternary-layered Ti3SiC2 ceramic was prepared by self-propagation high temperature combustion synthesis with pseudo hot isostatic pressing (SHS/PHIP). The effect of Ti/C mol ratio, Si content and Al content on the phase composition of the products was investigated. Experimental results showed that the phase composition of SHS/PHIPed products was influenced greatly by Ti/C mol ratio and Si content in the raw material. When Ti/C mol ratio is 1.5, the main phase was TiC with only a little Ti3SiC2; the content of Ti3SiC2 increased greatly with increase of Si content. The main phase turned to Ti3SiC2 while TiC became the main impurity when the Ti/C mol ratio arrived at 2. With addition of aluminum, the content of Ti3SiC2 increased obviously and the distortion of lattice was caused in Ti3SiC2 crystals.