Preparation And Properties Research Of Colored Zirconia Ceramics With High Toughness

The ZrO2 ceramic is a kind of new ceramics with low thermal conductivity, thermal-expansion coefficient and friction coefficient,high chemical stability and great corrosion resistance performance, especially the ability of anti-chemical corrosion and the microorganism corrode.This make it not only become the research hotspot at the scientific research domain,but also obtained the widespread application in the industrial production.It is the important raw material of fire-proof material, the high temperature structural material and electronic material. Within all kinds of metal oxide ceramic materials,ZrO2 has the best high temperature thermostability and the heat insulation property,which make it very suitable for ceramic coating and high temperature refractory product, and it was applied widely in high temperature ceramics pigments' research and production. Zirconia's heat conductivity which is the lowest in the common ceramic materials, the thermal-expansion coefficient closer with metallic material,and zirconia phase transition toughening cause it to become the plastic ceramic material. The good mechanical property and thermophysical property enable zirconia to become reinforcing phase with excellent properties in the metal matrix composites. The TZP has very good hardness, wearability and chemistry resistance,and is often used under atrocious environment and harsh loading condition, for instance the drawing die,the bearing,the seal and the human bones substitution, as well as engine piston top,cam in valve train, glass fiber and magnetic tape's cutter,and so on. But ceramic materials'inherent brittleness limit its application.Therefore, improving the ceramic's brittleness, increasing intensity and toughness and enhancing practical application reliability have been the key element of zirconia's widespread application.Scholars worldwide put forward many kinds of plasticizing and reinforcement mechanism of ZrO2 around improving ceramic materials'brittleness and enhancing their intensity. Zirconia ceramics are based on the martensitic transformation to realize toughening effect.According to the action modes to the toughness, the main toughening mechanisms of zirconia ceramic include: the stress-induced transformation toughening, the microcrack toughening, the crack branching and deflection toughenning and superficial strengthening toughening.Making use of zirconia phase-transformation toughening effect, ceramic matrix composites with zirconia as the second phase have been studied deeply, mainly including zirconia/alumina composite ceramics, zirconia/silicon carbide ceramics, the zirconia/silicon nitride ceramic, the zirconia/titanium carbide ceramics, the zirconia/molybdenum dioxide ceramic, the zirconia toughed and reinforced hydroxyapatite bioceramic composite, the zirconia toughed mullite ceramics and so on. However many ceramic composites taking zirconia as the first phase can realize toughening through phase transition, the microcracks increase along with phase transition,and then the microcracks become harm flaw to the intensity.Therefore many scholars studied to enhancing zirconia ceramics'mechanical properties through adding a certain amount of high elasticity module and hardness degree of Al2O3. But the research did not achieve unified results, even achieved opposite conclusions when different person taking different test methods. For the toughening and enhancing of ZrO2 ceramics taking ZrO2 as the first phase, further experimental study is required.The zircoa has another important use.Because of ZrO2's high refractive index, many kinds of decorative gem made of ZrO2 have mohs' scale up to 8.5, and their gloss can scarely be distinguished from natural gem. Besides cubic zirconia gem accessories,there are many other accessories made of zirconia at present market,such as permanently wearable watch case and watch chain.Most of them were prepared by making use of superfine ZrO2 powder sintering at high temperature to obtain raw ceramic and then being fabricated and polished to supply the market. As living standards improve, people's demand for accessories is rising along with the improving living standards.Colored ceramics can be used as metal decorative material substitutions because of its bright color, metallic gloss and brightness in surface,nonallergenic function properties,and so on.Colored zirconia ceramics attract considerable interests from kinds of colored ceramic materials for its outstanding mechanical property,and becomes the new favorite material of the upscale decoration. Because most ceramic pigments decompose under the high temperature condition and can cause color no longer or weaken the color. In the present market, colored zirconia ceramics' color is more monotonous.If the enhancing of zirconia ceramics'mechanical properties can be combined with the color richness to develop colored zirconia ceramics with high toughness,it will be of great theory significance and have a giant potential market. This paper studies the Y-ZTP further strengthens and toughening under this background exactly,and develops colored zirconia ceramics with high toughness which color are stable and diverse.Taking 5.4%Y2O3-stabilized nanometer ZrO2 powder as base material,and Al2O3, SiO2, MgO, CaO as toughening agent respectively to prepare toughed ZrO2 ceramics.The mechanical properties of the ceramic specimens in which Al2O3 with high elasticity module was added as toughening agent were enhanced at first and then decreased along with quantity of Al2O3 increasing. When is less than 10%, it is at 1550℃that the specimens are sintered to abtain the best mechanical properties,and when Al2O3 content more than 10%, it is at 1600℃.Over all,the specimen with 25% of Al2O3 content sintered at 1600℃and held one hour shown the best mechanical properties of bending strength being 1016MPa and fracture toughness being as high as 14.2MPa·m1/2. The mechanical properties of the ceramic specimens with SiO2 as toughening agent show the same tendency as whose added Al2O3.The specimens'bending strength value achieved the biggest when the SiO2 content was 20%,but it was still less than those with the same content of Al2O3. SiO2 mixed in increase the ceramics'glass phase for sake of glass plasticity will deactivate ceramics' crack tip to toughen. But the glass phase in ceramics would be too much when the SiO2 content was more than 20% to play the toughening role.Because the glass phase itself would increase the ceramics'brittleness and decrease the intensity.The specimens's mechanical properties decreased gradually along with the toughening agents increasing when mixed with MgO or CaO as toughening agent.That result didn't meet the theoretical enhancing and toughening effect.In the four kind of toughened zirconia ceramics' XRD atlas, m-ZrO2 was absent, the MgO and the CaO diffraction peak not appear, and weakα-Al2O3 peak and the SiO2 peak present. Therefore, we infer that MgO and CaO were dissolved in ZrO2, and that Al2O3 and SiO2 were not melt together with ZrO2 but dispersed in ZrO2 matrix. In the SEM image, Al2O3 toughed ZrO2 ceramic has finer crystal grain than the Y-ZrO2 ceramic, and both of them don't have blowhole.It shows that Al2O3 toughed ZrO2 ceramic has very good compactness,but also shows partial uneven distribution which need to be improved.Toughening mechanism of Al2O3 toughed ZrO2 ceramic:Al2O3 dispersed in the ZrO2 matrix which,for one thing,hindered the Zr4+ diffusive mass transfer,prevented crystal boundary from moving, restrained the growth of ZrO2 crystal grain, thus suppressed ZrO2 transition undercooling on some degree to achieve toughening effect; and for the other thing,would have pinning effect on the cracks,caused the crack deflection, curving and the furcation,inhibited cracks from growing and dissemination.And the cracks'deflection, curving and furcation extension the path wich the crack bypassed in the ceramic composite to consumpt fracture energy. The crack path's extension as well as the ceramic intensity enhancement, increased the quantity of t-ZrO2 transition and realized enhancing transition toughening effect.Taking Y-ZrO2 powder with 25% Al2O3 as basic material to which adding different coloring agent, many kinds of toughened colorful ceramics of bright stable and even color were prepared successfully after experimenting more than 100 coloring formulas. Following are the coloring agents formula and their relative color: Fe2O3—brick red; MnO2—black; Co2O3+Fe2O3 ,with their ratio of 5:5—dark green; Co2O3+SiO2,with their ratio of 9:1—dark blue; NiO—reseda; Cr2O3+SiO2, with their ratio of 9:1—pink; NH4VO3—yellow; NiO+Co2O3, with their ratio of 9.5:0.5—light blue.When specimens with a, b, c, and d formula were sintered in 1450℃, the one with e formula in 1500℃,and those with f, g, h formula in 1550℃, both of them being held for three hours,the colored ceramic specimens'stucture had the best densification level.Their bending strength was about 1000MPa, the compressive strength was above 1250MPa.And all specimens with different coloring formula had very good thermal shock resistance at low temperature and acid and alkali resistance at ambient temperature.Among all coloring agents above,Co2O3 and NH4VO3 have the strongest tinting strength so that the relative specimens assume sharp color when add a little amount of them,and that the color changed little along with increasing coloring agent content. The specimens with other coloring showed gradually deepening color along with the stain to increase. Joining SiO2 was helpful to improve colored ceramics' glossiness when joined to the Co2O3 and the Cr2O3 formula.It is presumed by the colored toughening zirconia ceramics'XRD atlas that the coloring mechanism of different colorant formula is that Fe2O3, MnO2, Co2O3, Cr2O3, NH4VO3 melt into Al2O3 and ZrO2 forming stable solid solution; in the specimens colored by the mixture of Co2O3 and SiO2, Co forms spinel CoAl2O4 with Al and olivine-type Co2SiO4 with Si separately,where Co exists as divalence and causes the specimen to present the very deep blue color; in the specimens colored by NiO, Ni forms spinel NiAl2O4 with Al, and the specimens show stable reseda; in the specimens colored by mixture of NiO and Co2O3 ,Co partially forms forms spinel CoAl2O4 with Al2O3 and the rest forms CoNiO2 with Ni, in both Co exists as divalence and assumes blue which superimposed together with the NiO's green causing the ceramic to present light blue. In the colored zirconia ceramics without Al2O3 to play the toughening role, Fe2O3 was still melted in the ZrO2 crystal lattice and caused the specimen to present deep red, and the XRD had no difference between specimens with and without Al2O3; mixed colorant of Co2O3 and NiO caused the specimen to assume green, when Co2O3 and NiO partially formed the CoNiO2 where Co exists as divalence and the rest formed spinel NiCo2O4 where Co was likely tervalent and present green, finally caused the ceramic to present green. To those coloring formula which couldn't response with Al2O3, Al2O3 weakened the coloring effect, made the specimens'color light.Although in this paper we have done massive research on the toughened colorful zirconia ceramics and prepared satisfying specimens,there are still many problems needed further research on the coloring of the toughened zirconia ceramic. The author thought that mainly includes several aspects as follows: (1) mixed coloring effect and the coloring mechanism of more than two kinds of ionic coloring agent compound mixed with complex proportion;(2) the influence of preparation process on the coloring agents'existing form in ceramics and the consequent coloring effect; (3) how Al2O3 affect the colorants'coloring effect and how to improve.