ZTA Ceramics Research Articles

Mechanical properties of zirconia toughened alumina with 10–24 vol.% 1Y-TZP reinforcement

Abstract Zirconia toughened alumina ceramics have found broad applications in industrial scale as they can provide high strength, toughness and wear resistance. Processing and compositional parameters have to be properly adjusted to achieve optimum mechanical properties. ZTA ceramics with an yttria content of 1 mol% and zirconia contents ranging from 10 to 24 vol.% were hot-pressed at 1475 °C at 50 MPa axial pressure and different dwell of 1–3 h. Stabilization of the reinforcement phase in ZTA with yttria was performed by a nitrate coating process of monoclinic zirconia nanopowders and subsequent blending with sub-micron size alumina. Microstructure and mechanical properties were investigated. A high ISB toughness of 8.5 MPa √m in combination with a 3-point bending strength of 1198 MPa was determined for the 1 mol% yttria 17 vol.% ZTA overmatching previous studies of coated ZTA ceramics. The interaction between stabilizer and reinforcement phase has a strong influence on the mechanical properties.

Influence of Cr-Fe coating on wettability of aluminum on ZTA ceramics

The influence of Cr-Fe alloy coating on the spreading kinetics and contact angles of aluminum on ZTA ceramics were investigated using a sessile drop method. For this purpose, SEM and EDS were used to investigate the spreading kinetics transition of the reactive wetting system. The results show the contact angle of Al/ZTA is 88° at 1373 K, which is almost equal to that of Al/Al2O3 and Al/ZrO2. Sputtering coated Cr-Fe film on ZTA substrate improves the wettability markedly. The contact angle decreases to 9.2° at the temperature of 1223 K.

Study on the Prediction of Surface Roughness of ZTA Ceramics under Ultrasonic Assisted Grinding

By means of Adaptive Neural-Fuzzy Inference Systems(ANFIS), the prediction model of surface roughness of zirconia toughened alumina ceramics (ZTA ceramics) under ultrasonic assisted grinding is established, and the model may obtain the higher forecast precision (81.25%) by dealing with nonlinear problem among grinding parameters, and fuzzy rule curved face formed by prediction model showed four input factors have different influence on surface roughness Ra, and they are abrasive grain size, grinding method, grinding depth, axial feed and speed of worktable from top to bottom. So the prediction model provides a new and efficient method for intelligent information processing, and it could be applied in modeling and real-time control etc, and it is possible to be widely applied in engineering.

Surface Phase Transformation Analysis of Nanozirconia Toughened Alumina Ceramics under Two-Dimentional Ultrasonic Vibration Grinding

Based on good processing property of two-dimentional ultrasonic vibration assisted grinding (TUVAG), phase transformation in the grinding surface of nanozirconia toughened alumina ceramics (ZTA ceramics) is studied by XRD analysis. Experimental results show different processing method and grinding depth may lead to surface phase transformation of ZTA ceramics. Under the same grinding parameters, phase transformation ratio of grinding surface under TUVAG is higher than that under diamond grinding (DG), and its phase transformation ratio increases with the increasing of grinding depth. Phase transformation ratio can effectively inhibit generation and expansion of microcracks of grinding surface.

Research on the Surface/Subsurface Damages of ZTA Ceramics under Two-Dimensional Ultrasonic Vibration Assisted Grinding

ZTA ceramics is a kind of high performance structural ceramics, and its surface/subsurface damages after machining have great effect on reliability and long-service life of ceramic parts, so it introduces two-dimensional ultrasonic vibration assisted grinding (TUVAG) which is applied in the precision finishing of ZTA ceramic, mathematic motion model of abrasive grain during TUVAG is established, and the special machining path of abrasive grain during TUVAG is analyzed, and the surface/subsurface damages of ZTA ceramics after TUVAG are further discussed. Experimental results prove that TUVAG may make materials removed in a plastic state mostly, the probability of cracks formation and propagation becomes less, and obviously reduce surface damages of ZTA ceramics, and the grinding badness layer of ceramics after TUVAG is shallower than that after diamond grinding at the same grinding parameters.

Study on the Phase Transition Characteristics in Ultrasonic High Efficiency Lapped Surface of Engineering Ceramics

Surface phase structure has an important effect on the surface machining quality. The surface phase transition characteristics of ZrO2 and ZTA ceramics under different machining methods were tested by X-ray diffraction in the paper. Through the qualitative and quantitative phase analyses, the influences of several different precision machining methods on the phase transitions in the machined surface were studied. Research results show that there are more transitions from tetragonal phase ZrO2 to monoclinic phase ZrO2 in the high speed grinding surface; because of the high-frequency vibration of lapping tool in ultrasonic lapping, the stress condition in the grinding area can be improved and the stable tetragonal phase ZrO2 in the ultrasonic lapped surface is easy to get. The research conclusions have important significance on analyzing the surface residual stress and improving the surface machining quality of engineering ceramics.

Theoretical and Experimental Research on the Material Removal Rate in Ultrasonic Aided Lapping of ZTA Ceramic

Lower machining efficiency of traditional lapping with free abrasive restricts the enhancement of the precision parts’ production efficiency. It is necessary to improve lapping efficiency on the premise of guarantee of lapping quality. In this paper, a new ultrasonic aided lapping technology was developed by combining lapping technology and ultrasonic machining technology and a series of lapping experiments of ZTA engineering ceramic with and without ultrasonic assistance were carried out. The results of theoretical analysis and experimental study show that it is the ultrasonic assistance of the lapping tool that promotes the enhancement of lapping efficiency and the ultrasonic aided lapping technique with fixed abrasive can be regarded as a high efficiency processing method of the precision engineering ceramic part.

Corrosion Behaviour of ATZ and ZTA Ceramic

The aim of this study was to record corrosion behaviour of ZTA and ATZ ceramics under hydrothermal conditions and under influence of boiling acids. Ageing was performed for 30 h and for 100 h in an autoclave at 134 °C and at a pressure of 2 bar. The sample surface was characterised with the help of measurements of surface finish, strength and microhardness, as well as by means of determination of wetting angle of contact. Leaching behaviour was analysed by means of scanning electron micrographs and weightings. The results of all tests with ZTA and ATZ ceramics performed in connection with this survey showed positive results, i.e. neither acid treatment nor hydrothermal ageing resulted in significant changes of properties.

Low temperature ageing in water vapor and mechanical properties of ZTA ceramics

ZTA ceramics were conventionally prepared by mixing Al 2O 3, Y–TZP and sintering aids in water for 2 h, isostatically pressing at 200 MPa and sintering at 1450 °C for 2 h in air. The Y 2O 3 content in Y–TZP was specially designed to be a little high (3 mol%) to obtain good stability of t-ZrO 2. The fraction of t-ZrO 2 up to 93% was retained at room temperature after sintering. The ZTA ceramics were then aged in water vapor at 240 °C for different times to adjust the stability of t-ZrO 2 and furthermore to optimize the zirconia transformation toughening. It was shown that the fraction of t-ZrO 2 gradually decreased to 85% after ageing for 2000 h. In contrast, fracture toughness grew continuously to 7.2 MPa m 1/2. Strength went up to the maximum 680 MPa when aged for short times, and then dropped gradually to 620 MPa, which was still higher than that without ageing. These results showed that this ZTA material is a good candidate for applications in humid environments and at elevated temperatures.

In situ formation of LaAl 11O 18 rodlike particles in ZTA ceramics and effect on the mechanical properties

A small amount of sintering aids, which contain MgO, kaolin and La 2O 3, was introduced into ZTA ceramics to realize densification at low temperature and to obtain a fine-grained microstructure. On the base of this, different amounts of La 2O 3 were added and rodlike LaAl 11O 18 was formed in situ due to its anisotropic growth habit during sintering. The effects of sintering temperature and the amount of rodlike LaAl 11O 18 were investigated. It was shown that the mechanical properties of ZTA ceramics were improved by the LaAl 11O 18, with strength over 500 MPa and fracture toughness 7 MPam 1/2. As the LaAl 11O 18 amount increased, part of the t-ZrO 2 transformed to m-ZrO 2, which is revealed by the decrease in the peak intensity of X-ray diffraction pattern, and which brought about a reduction in hardness and Young's modulus. It is believed that crack bridging and crack deflection were major factors contributing to strengthening and toughening of the materials as revealed through the microstructural observations by SEM and TEM.

Toughness-curve behaviour of alumina-SiC and ZTA-SiC composites

The fracture behaviour of alumina and ZTA matrix ceramics containing 10–30 wt% SiC particles was investigated during controlled crack growth using three point bending tests of single-edge-notched samples. The crack was initiated and slowly grown by repeated loading and removing of the load. The crack length, c, was measured by in-situ observation using a special video camera. The necessary force, P, responsible for a crack length increase was recorded by computer control of the testing machine. From the crack length, c, and the applied force, P, the stress intensity factor, K I, was calculated. The tests showed that SiC addition strongly decreases the R-curve effect in alumina and ZTA ceramics. This phenomenon was explained by analysis of the residual stress state in the ceramics. An increased resistance to crack initiation as well as to fracture with increase of SiC addition was also found for the studied ceramics.

Effect of SiC Addition on R-Curve Behaviour of Alumina and ZTA Ceramics

Effect of SiC Addition on R-Curve Behaviour of Alumina and ZTA Ceramics

Crack propagation and fatigue in zirconia-based composites

This paper reviews existing published studies on crack propagation behavior of zirconia-based composites. The first part of the paper is concerned with slow crack growth (SCG) under static loading. SCG in zirconia ceramics is shown to be a consequence of stress corrosion by water molecules at the crack tip. The influence of transformation toughening on SCG is discussed in terms of a stress intensity factor acting to reduce the net driving force for propagation. This proposition is in agreement with results obtained on 3Y-TZP and Mg-PSZ ceramics. A master curve is proposed which could be applied roughly to all zirconia ceramics. The influence of zirconia addition to alumina ceramics (ZTA ceramics) is also discussed. The second part of the paper deals with SCG under cyclic loading. A mechanical degradation of all zirconia-based composites is observed by a decrease of crack shielding. This degradation of zirconia-based composites under cyclic loading leads to increased velocities as compared to the static fatigue case. A master curve is also obtained, as in the case of static fatigue. Cyclic fatigue results are interpreted in terms of stress corrosion at the crack tip assisted by a decrease of the reinforcement.

常圧焼結により作製されたジルコニア強化アルミナ焼結体の物理特性と研削性状

Several kinds of zirconia toughened alumina ceramics (ZTA ceramics) with the different amount of monoclinic zirconia were produced by a slip casting and a normal sintering using fine powders. Grinding force was adopted as a criterion of grindarbility, and fracture toughness, bending strength and tetragonal zirconia contents were also measured as properties related to toughened mechanisms. The results are summarized as follows:1) ZTA ceramics with the addition 10vol% of monoclinic zirconia indicated the maximum fracture toughness and tetragonal zirconia content.2) The grinding force was the maximum value at the addition 10vol% of monoclinic zirconia. The grindarbility of ZTA ceramics was dominated by fracture toughness.3) The toughened mechanism of ZTA ceramics in this study was closely connected with tetragonal zirconia contents.

Effects of a second phase on the tribological properties of Al 2O 3 and ZrO 2 ceramics

The tribological properties of four different materials are investigated, tetragonal zirconia (Y-ZTP), Al 2O 3 dispersed in Y-TZP (ADZ), ZrO 2 dispersed in Al 2O 3 (ZTA) and Al 2O 3 (with 300 ppm MgO). These materials are used as a cylinder sliding against a plate of Y-TZP (TZ-3Y)). Compared to Y-TZP, the wear resistance of ADZ composites is increased by a factor of 4–10. At a contact pressure of 230 MPa, a wear transition for Y-TZP is observed from plastic deformation to microchipping and microfracture due to the high interfacial temperature (450°C–550°C) generated by frictional heating. Because of the higher elastic modulus, hardness and fracture toughness at high temperature, ADZ composites show better wear resistance and a higher transition contact pressure (over 400 MPa) under the present conditions. For Al 2O 3, the transition from mild to severe wear occurs when the contact pressure is changed from 250 to 400 MPa. For ZTA ceramics, the wear behaviour does not change because of the presence of a compressive layer due to the zirconia phase transformation during sliding. In water the wear resistance for ADZ and ZY5 is almost two orders of magnitude higher than the results under dry conditions. Reduction of the interfacial temperature by using water and the formation of a hydroxide layer at the contact surface by the tribochemical reaction of water with the ceramic, as observed by XPS, gives a positive effect on wear resistance.

Toughening Fractors in ZTA Ceramics Having Zirconia with Various Y<sub>2</sub>O<sub>3</sub> Contents

Toughening Fractors in ZTA Ceramics Having Zirconia with Various Y<sub>2</sub>O<sub>3</sub> Contents