Papers by Keyword: Zro₂

Abstract: Zirconia (ZrO2) films were deposited by metal-organic chemical vapor deposition (MOCVD) on {1 0 0} Si single crystal using Zr(thd)4 precursors. The thickness of obtained films is typically of 3.5 μm. The samples have been characterized by Field-Emission-Gun Scanning Electron Microscopy (FEG-SEM) for morphologic and microstructure study, and by X-ray Diffraction (XRD) for crystalline structure. The microstructure analysis showed that unexpected stable single tetragonal phase preferentially grew in low temperature area. According to the literature, the tetragonal phase stabilization is related to the crystalline size and the internal compressive stress. To analyze the effect of grain size and internal stress on the phase transformation, the thermal annealing were carried out in different temperatures and internal stress was measured by XRD method.

Abstract: In this paper, the microstructure of nanostructured zirconia (ZrO₂) based coating fabricated by newly developed process, high efficiency supersonic atmospheric plasma spraying (SAPS), is studied. The velocity and surface temperature of in-flight particles during spraying were monitored by on-line system and the microstructure and phase composition of the as-sprayed coating was characterized with SEM, TEM and XRD. Meanwhile, the bonding strength between the top coating and bond coating was measured. The results showed the average in-flight velocity of YSZ particles in SAPS was about 430m/s, which was much higher than that of conventional atmospheric plasma spraying (APS). The as-sprayed coating was composed of well-adhered fine lamellar structures with thickness of 1-4μm. The desirable structure was attributed to higher impact velocity of in-flight particles during SAPS process, resulting in the improvement of flattening degree of molten particles. Meanwhile, the SAPS-YSZ coating exhibited a bimodal distribution with small grains (30-50nm) and large grains (60-110nm), the latter was the main microstructure of the coating. In addition, it was found that the monoclinic zirconia existing in the original powders transformed into tetragonal phase after plasma spraying and the bonding strength of as-sprayed coating was as high as 46±3MPa. The high efficiency supersonic plasma spray, which offers some unique advantages over the conventional plasma spraying process, is expected to be potentially used to deposit a wide variety of nanostructured coatings at lower cost.

Abstract: Tribological behavior of ZrO2 and Si3N4 based nanocomposites with addition of carbon nanofibres and nanotubes has been studied by the pin-on-disc technique. Friction coefficients were measured and recorded, wear rates were calculated in terms of material volume loss per load and sliding distance. The wear damage was studied using optical and electron microscopy and its mechanisms were identified. In monolithic materials the dominant wear mechanism was abrasion, in composites with CNF and with higher volume fraction of CNTs (5 and 10%) fiber pull-out and lubricating by the carbon phases occurred.

Abstract: A new ZrO2 nano-composite ceramic tool and die material was prepared with vacuum hot pressing technique. The effects of sintering parameters on the nano-composite ceramic tool and die materials were studied. The results indicated that the mechanical properties of ZrO2 nano-composite ceramic tool and die material with the additions of TiB2 and Al2O3 are higher than that of the pure ZrO2 ceramic material. Sintering at 1100 for 120min could improve the density and mechanical properties of ZrO2 nano-composite ceramic material. The flexural strength, fracture toughness and hardness with the optimum sintering parameters can reach 878MPa, 9.54MPa•m1/2 and 13.48GPa, respectively, obviously higher than that with non-optimum sintering parameters.

Abstract: Glass matrix composites based on NextelTM fibre reinforced borosilicate glass were fabricated. Unidirectional fibres were arranged in two directions with a periodic interspacing sandwiched between two glass slides. XRD analysis and SEM observations proved that the selected process parameters were effective in densifying the composites without significant transparency losses. A geometry based equation was derived to evaluate the expected light transmittance of the composites. ZrO2 coating on Nextel™ fibres, developed by a sol-gel method, was investigated in order to provide a weak bonding at the fibre/matrix interface to promote fibre pull-out during fracture. A developed hybrid sol-gel coating method was employed to form a smooth and crack free coating surface on the Nextel™ fibre bundles. The present composites show potential for applications in architecture and special machinery requiring strong transparent windows.

Abstract: Cr3C2-NiCr type cermets are used in cutting technology for their low sintering temperatures and relatively low densities. Their high corrosion resistance at high cutting speeds and high temperatures increases the interest to these materials. In this study, a powder mixture of 75wt% Cr3C2 and 25wt% NiCr with a Ni-Cr ratio of 4/1 by weight was sintered at 1350°C as the master composite. 3 mol % Y2O3 stabilized tetragonal ZrO2 and 8 mol % Y2O3 stabilized cubic ZrO2 powders were added to study the effect of ZrO2 content on the mechanical and wear properties of Cr3C2-NiCr cermets at the same sintering temperature. SEM and EDX analysis were performed for identifying microstructures. Elastic modulus and microhardness of master and doped cermets were measured by impulse excitation technique and Vickers (HV10), respectively. Wear tests were conducted by ball on reciprocating flat method to characterize the wear properties.

Abstract: Functionally Grated Materials (FGMs) have usually been expected as candidates for a wide variety of industrial applications due to their desirable properties such as high heat resistance capability, good wear resistance, bio-compatibility, chemical stability and so on. Scaling-up and three dimensional (3-D) near-net shape forming technique for FGMs are one of the most important key-factor to produce the industrial engineering components and products in practical use. On the other hand, it is generally well known that the Spark Plasma Sintering (SPS) method is a novel process to produce homogeneous FGMs, nano-structural sintered compact, thermoelectric semiconductors and bio-medical materials in shorter sintering time with finer microstructure. This paper will present development of FGMs fabricated by SPS and future prospects of SPS on research and industrialization activities in Japan. A brief historical review progress of SPS technology is also given and the applicable field is exemplified. Then, the paper is focused on manufacturing processes on FGM by SPS technology.

Abstract: Sliding wear was investigated for ZrO2 ceramics against M50 bearing steel under vacuum condition. The research was studied on the ball-disk machine under different loads and steady sliding velocity. The worn surfaces of tested samples were examined using optical microscope, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The results showed that the friction coefficient of ZrO2 was decided by the applied load, the critical load of ZrO2 was 10N applied load under vacuum condition, the specific wear rate of ZrO2 drop rapidly with exceeded applied critical loads. The ZrO2 ceramics materials have transferred on the M50 bearing steel surface under high vacuum condition. The dominant wear mechanisms of ZrO2 ceramics were mico-adhesion, tribochemical wear, brittle scraps and micro-furrow wear under vacuum condition.

Abstract: The electrolytic codeposition has drawn interest as an alternative method for the preparation of metal matrix composite electrocoatings with improved properties. Moreover, the application of a current periodically varied by time during electrodeposition, i.e. pulse current (p.c.), instead of the commonly used direct current (d.c.), has been proved to lead to the preparation of surfaces with well-defined properties. In this work, Ni/TiO2-ZrO2 composite electrocoatings were produced under direct and pulse current conditions. The synergetic action of both the pulse application and the simultaneous codeposition of the two different types of particles on the structure, the morphological characteristics and the microhardness of the composite electrocoatings, were studied. Concerning their mechanical behaviour, it was found that the Ni/TiO2-ZrO2 deposits prepared by pulse electrolysis are characterized by Vickers microhardness threefold harder than the d.c. ones.

Abstract: The study of composite electroless Ni-P coatings is pursued in order to obtain coatings on a metal substrate with advanced properties i.e. with high wear and corrosion resistance for particular engineering uses. Composite NiP-ZrO2 layers were prepared by simultaneous electroless co-deposition of Ni-P and ZrO2 on steel, from a reducing solution in which ZrO2 particles were kept in suspension by stirring. The particles load in the bath was 0, 0.5, 1.0, 2.0 and 5.0 g/l. The deposits of 30 m in thickness, were characterized for structure, morphology and hardness by scanning electron microscopy and microanalysis as well as X-ray diffraction. It was found that the maximum ZrO2 particle incorporation attained was 7-10% of Zr. Vickers microhardness was measured for the plain deposit and found to be 720 HV and for the maximum zirconia content of 10%, 820 HV. After a vacuum heat treatment for 10 min, the microhardness of the composite is found to be 1500 HV. The electrochemical linear polarization measurements in a corrosive NaCl 3.5% solution shows at 2.0 g/l bath load favourable conditions for the formation of a defects free composite deposit could be created.