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Several typical zirconia toughened ceramics and their uses

Several typical zirconia toughened ceramics and their uses

Common zirconia toughened ceramics are: zirconia-Mg0, zirconia-alumina, zirconia-Yz 03, zirconia-Ca0. Now developed zirconia-Ce02, Y2 03-zirconia-Hf02 and so on. In addition, there are whisker (fiber)-zirconia composite toughened ceramics. Its toughness is shown in Table 2-1-10. Table 2-1-10 KI c value of several toughened ceramic materials Material Kic (MN . m-3/2) ZrOl-Y203 (pseudotetragonal) 6~9 Zirconia-Ca0 (precipitation strengthening) 9.6 Oxidation Zirconium-Mg0 (precipitation strengthening) 5.7 Zirconia (partially stabilized-stable phase) 1.1 Zirconia-A12 0a 9.8 Sia N4 4.8~5.8 SiC 3.4 B4C 6.0 Alz Oa 4.5 Spinel single crystal 1.3 It can be seen from the above table that the toughened ceramic material has much higher mechanical properties than the previous structural materials such as Sia N4 and SiC. The following are the main types of toughened ceramics:

1. Zirconia toughened alumina ceramics (ZTA)

Among the ceramic materials toughened with zirconia, the effect of zirconia toughening alumina ceramics is the best. As shown in Figure 2-1-23. Regarding the toughening mechanism of zirconia, it has been discussed above, and now the process of zirconia toughening A12 03 is discussed.

A good process is the key to obtain the remarkable effect of zirconia toughening and strengthening A12 0u ceramics. Of course, with the development and progress of modern science and technology, with the continuous improvement of technology, its toughening effect is also continuously improved. In the process, the first is to obtain high-quality powder, of course, the preparation of powder can have different methods. Regardless of the method used, the particle size of the zirconia should be small, not larger than Dn (critical phase transition diameter at room temperature), and the particle size distribution should be narrow. The purpose is to obtain two mechanisms of stress-induced transformation toughening and micro-crack toughening simultaneously in ZTA ceramics.

The following introduces several ways to obtain d-AIz Oj, zirconia, and Yz0. Process method for homogeneous ultrafine powder. The preparation of 口-A12 03 powder is NH4 HCO, and NH4 Al(S04) 2.12HzO to synthesize NH4 AI(OH):CO. , and then calcined at 1260 °C to convert to -Al20. The process flow is as follows:

Zirconium oxide (Yz 03) powder was prepared by co-precipitation method. Dissolve Y2 03 in hydrochloric acid and mix it with an aqueous solution of ZrOC12 – 8H20 to make a concentration of 1. 0% (mol) salt solution was added to dilute ammonia water (pH=9) at a constant temperature of 40 °C by spraying. And fast stirring to improve the nucleation rate during precipitation, so that the flocculation during precipitation is small and the precipitated particles are fine. The precipitate is filtered under reduced pressure, and the Cl ion (can be tested by AgN03) is washed away. Wash with absolute ethanol several times (to prevent agglomeration). After drying and grinding, it is calcined at 840°C to obtain zirconia (YZ 03) powder. The preparation technology of zirconia (Yz 03 )-A1203 powder includes mixing method, co-precipitation method and precipitation encapsulation method. Its technological process is as follows:

  • (1) Mixed method
  • (2) Co-precipitation method
  • (3) Precipitation wrapping method

Practice has shown that the properties, forming properties, sintering properties and toughening properties of the obtained powders are also different depending on the process method. The performance results of the above three process methods are listed in Table 2-1-11. 2-1-11 Properties of powders and their sintered bodies prepared by different technological processes ━┳━━━━┳━━━━┳━━━━┳━━━━┳━━━━━━━━┓ ┃Process ┃ D ┃ Powder ┃Specific Surface Area ┃Green ┃A12 03 ┃Sintering ┃ Volume ┃ Linear Shrinking ┃ ┃ Retention £Zr(): ┃ ┃ ┃ ┃ ┃ ┃ Density ┃ ┃ Density ┃ ┃ ┃ Dispersity ┃ ┃ ┃ Flow ┃(pLm) ┃ Status ┃(m2/g) ┃ ┃Crystal Form ┃ ┃ Score ┃ (%) ┃ ┃ Volume Fraction ┃ ┃ ┃ ┃ ┃ ┃(g/ems) ┃ ┃(g/cm3) ┃ ┃ ┃ ┃ ┃ ┣━━━╋━━━╋━━━━╋━ ━━━━╋━━━━╋━━━━━━╋━━━━╋━━━━╋━━━━━╋━━━━╋━━━━━━━━┫ ┃ 1 ┃ ┃ spherical ┃ ┃ 2. 86 ┃ a -A12 0a ┃ 5. 19 ┃ high ┃ 18.3 ┃ poor ┃86. 2 Vu ( VoIJ ┃ ┣━━━╋━━━╋━━━━━╋━━━ ━━╋━━━╋━━━━━━╋━━━━╋━━━━╋━━━━━╋━━━╋━━━━━━━━┫ ┃ 2 ┃ 0. 05 ┃ Multilayer Flake ┃ 178 ┃ 1. 89 ┃ y-AIz 03 ┃ 5. 00 ┃ High ┃ 30.2 ┃ Even ┃ 95%(vui) ┃ ┣━━━╋━━━╋━━━━━ ╋━━━━━╋━━━━╋━━━━━╋━━━━╋━━━━╋━━━━╋━━━━╋━━━━━━━━┫ ┃ 3 ┃ 0. 02 ┃ spherical ┃ ┃ 2. 69 ┃ r-AIz 03 ┃ 5. 20 ┃ high ┃ 20.8 ┃ even ┃ 990/ (VoI) ┃ ┗━━━┻━━━━┻━━━━━ For the sake of To further improve the toughening effect, appropriately introduce other substances to form a solid solution, such as the introduction of Mg0, Al. () . ,[:c()andHfozetcWhenthezirconiacontains012%(mol)MgOthefracturetoughness(KIc)ofZTAceramicshasamaximumvalueAsshowninFigure2-1-24TheintroductionofAlzOacaninhibitthegrowthofzirconiagrainsAnotherexampleistheintroductionofHfozbecauseHf07hasasimilarstructureandcharacteristicstozirconiaandbecauseithashigherM(phasetransitiontemperature)andA(reversephasetransitionterminationtemperature)thanzirconiaitalsohasahigherratiothanzirconiaLowthermalexpansioncoefficientofzirconiumandvolumeeffectofphasetransitiont-zirconiatom-zirconiaThereforeHf02hashigherhightemperatureresistanceandthermalshockresistanceOntheotherhandduetothehighYaotemperatureofHfO2thedrivingforceforthephasetransitionoft-zirconiatom-zirconiaislargeandthecriticalparticlesizeofthephasetransitionisalsosmallsoitisdifficulttopreserveenought-zirconiaduringthecoolingprocessZirconiumwhichisbeneficialfortransformationtougheningHoweverwhenasmallamountofY20aisintroducedintotheHf02-zirconiasolidsolutionandspecialtechnologicalmeansareusedtheY20a-Hf02-zirconiasolidsolutioncanobtainhighert-zirconiawhichhasagoodtougheningandstrengtheningeffectandcanimproveZTAceramicshightemperatureperformance

In the range of a certain amount of YZ 03, the fracture toughness and flexural strength of ZTA ceramics vary with Y20. increased by the increase. As shown in Figure 2-1-25. This is because the addition of Y2 03 can effectively inhibit the grain growth of the main crystal phase of ZTA, and also limit the grain growth rate of the dispersed phase (zirconia).

When preparing the raw materials, the key is to disperse the zirconia uniformly, so that the alumina particles wrap the zirconia, so that a good toughening effect is produced during the phase transition.

In terms of molding process, the molding method can be selected according to different requirements. Of course, to obtain good compactness, hot pressing and isostatic pressing can be used. During sintering, a corresponding sintering system can be used to sinter the ZTA ceramics densely and refine their crystals. The sintered products have different heat treatment conditions and different stress and strain states, which have different effects on the martensitic transformation temperature and the precipitation amount of £-zirconia that can be transformed under stress induction, thus affecting the material’s performance. Strength, fracture toughness and thermal shock resistance.

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