Papers by Keyword: Zirconia Ceramics

Abstract: A comparative analysis of the efficiency of zirconia ceramics high-energy electron beam sintering by one-step mode and two-step mode sintering was performed for compacts prepared from commercial TZ-3Y-E grade and plasmo-chemical powders. The electron energy was 1.4 MeV. The samples were sintered in the temperature range of 1100–1300°C. The extent of influence of one-step and two-step sintering mode on the characteristics of sintered ceramics depends on the initial powders. Сorrectly chosen the temperature mode of two-step sintering (T_s1=1300°C t = 15 min, T_s2=1200°C t=1 h) leads to an increase of the density and microhardness values of ceramics relatively considered of results at one-step and two-step mode of sintering.

Abstract: Technological features of pulsed laser machining of yttriastabilized tetragonal zirconia polycrystal (Y-TZP) were studied. The connection between the laser power, scanning speed, laser beam steps and surface state of zirconia ceramic was established. The results of the research showed that pulsed laser machining of this material is an effective tool to control surface modification process and presents an attractive alternative to conventional techniques.

Abstract: This article presents some results of laser processing of materials, used for the construction of microsystems and micro-sensors, e.g. Si, Al₂O₃ and zirconia ceramics. The necessity of faithful reproducing the geometry and dimensions in the micro-scale puts specific requirements for laser machining process. Laser micro-technologies must be conducted under conditions which ensure the perfect guidance of a well-focused laser beam, scanning at a suitable speed, and the laser pulse duration with proper repetition frequency. The amount of absorbed energy depends on wavelength of laser radiation and kind of material, which also influence on this process. All these conditions should take into account the need to maintain a small heat affected zone (HAZ). This guarantees keeping the true reproduction of micro-shapes and cutting edges with a different angle of lines even in micro-scale details. The present work confirms the possibility of using laser technology for such applications.

Abstract: The work demonstrated the sintering of zirconium dioxide ceramics by means of an electron beam produced by a plasma-cathode e-beam source operating at fore-vacuum pressure. The sintered ceramics consist of tetragonal-modified zirconium dioxide with grain size from 0.7 to 10 micrometers, depending on the sintering conditions. At constant sintering temperature, the density of the material and its grain size depend on the integrated energy injected into the sintered material by the electron beam.

Abstract: Porous ceramics incorporates pores to improve several properties including thermal insulation, maintaining inherent ceramic properties such as corrosion resistance and large mechanical strength. Conventional porous ceramics is usually fabricated through an insufficient sintering, leading to degraded strength and durability. Contrary to this, we have innovated superplastically foaming method to make ceramic foam only in the solid state. In this method, the previously inserted foam agent evaporates after the full densification of matrix at around the sintering temperature. Closed pores expand utilizing the superplastic deformation driven by the evolved gas pressure. Based on this concept we fabricated 8mol% yttria stabirized zirconia based porous ceramics and examined the properties concerning the high temperature structural material with thermal insulation.

Abstract: Taguchi optimization methodology is used to optimize Rotary Ultrasonic Machining (RUM) parameters for the milling of zirconia ceramic. The influence of the RUM parameters such as vibration frequency, vibration amplitude, spindle speed, feed rate, and depth of cut on the surface roughness is studied. A three-level orthogonal array table is used to determine the signal-to-noise (S/N) ratios based on Taguchi’s design of experiments. Furthermore, analysis of variance (ANOVA) has been performed to study the relative significance of the different factors on the surface roughness of zirconia ceramic. Finally, verification tests were carried out to compare the predicted values of the surface roughness with their experimental values in order to confirm the effectiveness of the Taguchi Optimization.

Abstract: To investigate the bond strength of different adhesive luting materials bond to zirconia ceramics. 40 (30mm×5mm×5mm) Cercon Smart Ceramics samples were divided into groups: (1) glass-ionomer bonded (control group), (2) Clearfil™ Repair bonded, (3) Panavia F bonded, (4) Variolink N bonded. Tensile bond strength and shear bond strength were evaluated after 24h storage at 37°C in distilled water. Each group had 10 samples for different test. Data were evaluated using ANOVA analysis (α=0.05). The experiment groups are statistically significant differences with control group (P<0.05). The shear bond strength of the Glass ionomer FX Ι, the Clearfil™ Repair, Panavia F and Variolink N groups were 14.23±4.48 MPa, 21.95±1.32 MPa, 31.16±1.50 MPa and 43.54±1.97 MPa, separately. Comparisons among groups were significant differences (P<0.001). Variolink N bonded ceramics achieved highest tensile and shear bond strength. Different adhesive materials significantly influence the bond strength of zirconia ceramics.

Abstract: A two-step, biomimetic approach was applied for the rapid deposition of octacalcium phosphate (OCP) coatings on zirconia ceramics (Y-TZP). In the first step, sintered zirconia discs were immersed into a supersaturated Ca-P solution with pH=7.4 (CPS1). In the second step, the substrates were transferred from the CPS1 to another Ca-P solution with a lower pH (CPS2). After 6 hours of immersion in the CPS2, a thick coating consisting of large OCP crystals was obtained. Afterwards, the coated substrates were subjected to a thermal treatment in order to improve the attachment of the coating to the substrate.

Abstract: An investigation was undertaken to explore the grinding energy and removal mechanisms in grinding zirconia by using brazed diamond wheels. The grinding forces were measured and the morphological features of ground workpiece surfaces were examined. The results indicate that material removal mechanisms are dominated by the combined removal modes of brittle and ductile. The prevailing removal mechanism for the ground surface of zirconia changes from brittle to ductile when the maximum chip thickness change from large to small.

Abstract: Considering the SD effect, the parabolic-type yield criterion is obtained by using a new parameter. And by analogy with associated plastic flow rule, the ceramic phase transformation constitutive model is established. Under plane strain condition, the theoretical toughening expressions of mixed-mode I-II stationary cracks and steady-state growing cracks are developed by applying the weight function method. And the toughening effect is discussed under the influence of Poisson ratio, parameter and . The simulation results show that these phase transformation toughening effects are in good agreement with experimental results. And comparing with other yield criterions, it is more in line with actual characteristics of zirconia ceramic materials, when the expression of mixed I-II crack is reduced to mode I crack. And it also could provide theoretical support and reference for the further research of ceramic phase transformation toughening.