Key Engineering Materials Vols. 280-283

Abstract: In order to improve the adhesion between diamond coatings and cemented tungsten carbide (WC-Co) substrates, the diamond coatings were deposited on one kind of cobalt-deficient gradient WC-Co by the microwave plasma chemical vapor deposition (MPCVD). Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were used to characterize the diamond coatings. The results showed dense, well facet diamond coatings. The cobalt content at the surface of substrate was measured by electron probe microanalysis. It was found that Co did not largely move to the surface as usual with deposition time increasing compared with the conventional tungsten carbide; The cobalt content at the surface of substrate after deposition (about 1 wt %) was lower than before (3.42wt%), which improved diamond coating’s adhesion against the tungsten carbide substrate.

Abstract: For practical applications such as artifical joints and dental implants, there is a strong demand for hydroxyapatite coatings with excellent performances to ensure long-term fixation. In the present study, functionally gradient HA-ZrO2-Bioglass coatings were prepared using net-energy controlled plasma spraying technology. The structural characteristics andmechanical performances of the coatings were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and nanoindentation. The results showed that: (1) Pore sizes and compositions of the coatings changed gradually along the vertical substrate, crystal HA with few calcium phosphates was presented in the heat-treated coatings. (2) Surface of the coating was very rough with nano-sized crystalline grains and micropores; (3) Young’s modulus and hardness changed gradually at the range of coating-Ti6Alo4V interface. Compared with HA coatings, the tensile adhesive strength of the functionally graded HA-ZrO2-Bioglass coatings reached 38.6 MPa, much higher than that of single HA coatings.

Abstract: Electrophoretic deposition (EPD) is a promising, simple and cost-effective method for fabrication of piezoelectric ceramic films. In this study, commercial lead zirconate titanate (PZT) powders were deposited onto silicon wafers coated with platinum electrodes by using EPD method in ethanol solution with a few amount of HCl to introduce surface charges to PZT particles. The sintering densification of the EPD-derived green PZT films were attempted with approaches: addition of a low-temperature eutectic sintering aid consists of Cu2O and PbO, infiltration of PZT sol into the green film. Thick PZT films on Si wafers were obtained by sintering at 700oC with sintering aid and sol-infiltration.

Abstract: Epitaxially graded barium strontium titanate (BaxSr1-x)TiO3 (x = 0.75, 0.8, 0.9, 1.0, abbreviated as BST75, BST80, BST90 and BTO respectively) thin films were fabricated by pulsed laser deposition method on the (La0.7Sr0.3)MnO3 (LSMO)/LaAlO3 (LAO) single crystal substrate. Scanning probe microscopy with a contact mode was used to characterize the temperature dependence of polarization from room temperature to 140°C. Results indicated that the piezo-response signal of the BST graded films had an obvious change with temperature, and that the graded structures had a flatter temperaturedependence of permittivity. Furthermore, the contrasts of the SPM images were lower for the ferroelectric – paraelectric (F-P) phase transition temperatures of BST 75, BST 80, and BST90, but higher for the F-P transition temperature of BTO.

Abstract: Compositional graded thin films of (Ba0.8Sr0.2)(Ti1-xZrx)O3 (BSTZ) are grown on MgO by pulsed laser deposition technique with four BSTZ ceramic targets. Gradients of composition are achieved by artificially tailoring composition in multilayered thin films to form compositional graded layers (CGL). In each CGL four individual layers of BSTZ with x = 0.36, 0.18, 0.08 and 0 are grown^in series with equal thickness. Three kinds of CGL samples comprising one, two or four CGLs have been elaborated with the same total thickness by varying the thickness of each CGL. Raman spectra show existence of tetragonal structure in all the multilayered BSTZ thin films. Raman peak at 535 cm-1 shifts to high frequency with increasing of compositional gradient, and the peak at 750 cm-1 also shows a small shift to high frequency. Moreover, other Raman peak is observed at about 830 cm-1, which is associated with phonon mode of cubic phase, and such peak shifts towards lower frequency with increasing of compositional gradient. The shift of Raman peak is related to variation of internal stress in BSTZ thin film due to increasing compositional gradient.

Abstract: Homogeneous PZT/Ag composites and compositionally graded PZT/Ag actuators were fabricated and evaluated in this work. The piezoelectric constant decreases gradually and the dielectric constant increases significantly with an increase in silver content of the PZT/Ag composites. The fracture toughness of the PZT/Ag composites is enhanced with addition of the silver powders. Based on the corresponding piezoelectric properties of the monolithic PZT/Ag composites, a graded material with symmetric silver compositions from 1 to 10 vol % then inversely to 1 vol % was successfully fabricated by conventional sintering. This study indicates that the PZT/Ag composites can be used to acting as bimorph actuator materials.

Abstract: Electrical contact material is a very important material for the electric power industry. An electrical contact material should display good structural characteristics (suitable hardness, high thermal conductivity and stabilization) as well as a good functional characteristic (low electrical resistivity). It is difficult to fabricate such a contact material with all these good performing parameters by common techniques because these physical parameters influence each other. In this paper, we report a novel investigation to design and prepare silver-metal oxide composite materials according to functionally layered and graded material (FLGM) concept and meeting requirement as electrical contact material. The silver-based composite samples characterized by layered component were prepared with conventional solid-phase sintering technique. One kind of sample consists of tin dioxide and silver material, in which SnO2 exhibits a graded distribution. Another consists of two metal oxides, cadmium and zinc oxides, and silver material, in which each layer has different metal oxide. Hardness, thermal conductivity and electrical conductivity, were measured and related problems are discussed. Especially, welding resistance as an important parameter for practical application was tested. SEM analyses before and after electrical erosion were also performed. We conclude that the functionally graded material (FGM) concept as a novel designing and fabricating method has potential for electrical contact composite material.

Abstract: Chip-type PTC thermistors with multilayer stacked structure have been fabricated by bonding sintered ceramic chips with internal electrodes to offer low resistance at room temperature and correspondence to surface mounted technology. The resistance-temperature characteristics of multiplayer stacked PTC thermistors made up of different numbers (N = 1, 3, 5) of layers were experimentally investigated (the typical size of each layer was 10 mm × 7.0 mm × 0.38 mm). The selection and extraction of additives in roll-forming process were also discussed. This resulted in a crack-free multiplayer stacked PTC thermistor.

Abstract: Ceramics metal functionally graded materials (FGM) is applied on the dual friction pair of the green automobiles. The structure and component characteristics of FGM are better, compared with traditional Ceramics. Even with the same components, FGM bears an outstanding mechanical performance and its cracking strength, toughness and fatigue strength are relatively superior. The influence of Ceramics metal functionally graded materials on the performance of automobiles are analyzed via a comparative research and comparison of the external characteristics of automobile is made in terms of mechanism. The results indicate that the power output, fuel consumption and durability are improved considerably on the green automobiles. Improvement is also made on the wearing capability, lubricity and sealing performance as well. Hence comes the reduction of friction loss and leakage loss. The principal abrasion mechanism of FGM is plastic flowing and the secondary are brittle failure and grain abrasion.