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Tetragonal Zirconia Polycrystals

Tetragonal Zirconia Polycrystals. Structure and properties. MSc Eng Marta Gajewska. Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim. Zirconia - introduction. 950°C. . . . Tetragonal t. Cubic c. Monoclinic m. Melt.

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Tetragonal Zirconia Polycrystals

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  1. Tetragonal Zirconia Polycrystals Structure and properties MScEng Marta Gajewska Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  2. Zirconia - introduction 950°C    Tetragonal t Cubic c Monoclinic m Melt 2680°C 2370°C 1150°C Engineering applications tetragonal phases (mechanical properties) cubic phases (electric properties) Doping with oxides (Y2O3, CaO, Mg2O, CeO2 and others) allows to stabilize the high-temperature phases at room temperature Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  3. t - zirconiastructure Tetragonal zirconia unit cell in both the body-centered tetragonal and pseudofluorite description Space group: P42/nmc Coordination number:8 Z:2 Lattice parameters: a= b = 5,1023 Å c = 5,1817 Å α=β=γ=90° Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  4. TZP - introduction Tetragonal Zirconia Polycrystals with metastable tetragonal structure of very fine zirconia grains sintered at low temperature (e.g. with 2-4 mol% Y2O3) 950°C  Tetragonal t Monoclinic m 1150°C Stabilization of the high-temperature tetragonal (t) form as metastable at room temperature technique oftransformation-toughening Metastable condition:surrounding structure opposes the expansive transition from t- to m-forms t-crystals transform intostable but less densem-ZrO2 concentrated stress field at the crack tip Propagating crack   Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  5. Y-TZP structure Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  6. Properties of TZP ceramics High density – up to 6,1*10³ kg/m³ Low thermal conductivity – 20% of that of alumina ceramics High fracture toughness Very high flexural strength and hardness (11 GPa for 1.5 mol% yttria) Coefficient of thermal expansion similar to that of cast iron Modulus of elasticity similar to steel (150–200 GPa) High chemical resistance Good wear resistance Low coefficient of friction Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  7. References • P. Boch, J.-C. Niepce„Ceramic Materials: Processes, Properties and Applications”, Hermes 2001, 219-228 • J. F. Shackelford, R. H. Doremus“Ceramic and Glass Materials: Structure, Properties and Processing”, Springer 2008, 169-197 • R. E. Smallman, R. J. Bishop, “Modern Physical Metallurgy and Materials Engineering”, Elsevier 1999, 330-331 • http://www.azom.com Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  8. Tetragonal Zirconia Polycrystals Why do we addyttriaorotheroxides to TZP? MScEng Honorata Kazimierczak Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  9. Introduction Zirconia (ZrO2) is an important ceramic material having a wide range of applications in engineering: -catalysis, -sensors, -gas turbines, -magnetic hydrodynamics process of power generation, -thermal barrier coatings, -high temperature nozzles in air engines, etc. • Zirconiaexist in three different crystalline forms: • cubic (c) (stable at 2680 -2370°C) • tetragonal (t) (stable at 2370 -1170°C) • monoclinic (m) Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  10. Zirconiaexistinthreedifferentcrystallineforms: • cubic (c) (stableat 2680 -2370°C) • tetragonal (t) (stableat 2370 -1170°C) • monoclinic (m) • t-m transformation: • 3-5% volume increase => extensive cracking in the material. To stabilizethe high temperauret-phaseatroomtemperature , CeO2, CaO, Y2O3orMgO areusuallyadded to zirconiainappropriateproportions. Ca-TZP 3Y-TZP Mg-TZP Ce-TZP Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  11. t-m transformation: • 3-5% volume increase Itisknownthatthemetastabletetragonalzirconiainclusionsin a ceramicmatrixtransform to thestablemonoclinicmodification on application of externaltensilestressaround a crack tip. Thismartensitictransformationis associated with a volumeexpansionfromthetetragonal to a largermonocliniclatticewhichreduces and eventuallystopsthepropagation of cracks, thusimprovetheresistance to mechanicalfailure. rys.1 Representation of stress-induced transformation toughening process. Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  12. Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  13. In order to retain the tetragonal phase at room temperature the grain size must be kept below a critical value. Rys.2. Retention of tetragonal phase. Critical grain size against oxide content in tetragonal zirconia. Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  14. Rys.3. Fracture toughness vs. yttria content. Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  15. References: • C.Piconi, G.Maccauro „Zirconia as a ceramicbiomaterial”, Biomaterials20 (1999) 1-25 • M.M.R.Boutz, A.J.A. Winnubst, A.J. Burggraaf „Yttria-CeriaStabilizedTetragonalZirconiaPolycrystals: Sintering, Grain Growth and GrainBoundarySegregation”, Journalof EuropeanCeramicSociety 13 (1994) 89-102 • Marek Faryna „Analiza zależności krystalograficznych faz składowych w kompozytach z osnową ceramiczną”, IMIM PAN, Kraków 2003 • 4) H. El Attaoui, M. Saadaoui , J. Chevalier , G. Fantozzi„Static and cyclic crackpropagation in Ce-TZP ceramics with differentamountsof transformationtoughening”,Journal of the European Ceramic Society 27 (2007) 483–486 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  16. Tetragonal Zirconia Polycrystals Mechanicalproperties of Y-TZP MScEng Katarzyna Stan Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  17. Why Y2O3? Strength v. toughness curves for four types of transformation-toughened zirconia. Dashed line represents the critical stress for the tm transformation. Stabilized zirconia as a structural ceramic: An overview J. Robert Kellya, Isabelle Denryb Dental materials 24 ( 2008 ) 289–298 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  18. TZP materials with 2-3% molY2O3 Completely constituted by tetragonal grainswith sizes of the order of hundreds of nanometers Amount of the T-phase fraction retained at room temperature Retention of tertagonal phase. Critical grain size against Yttria content in tetragonal zirconia Influence on mechanical properties of TZP ceramics C. Piconi, G. Maccauro; Zirconia as a ceramic biomaterial; Biomaterials 20 (1999) 1 -25 J Mater Sci 1982;17:240-6 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  19. Properties Aplications Industry • • High strength • • High fracture toughness • • High hardness • • Wear resistance • • Good frictional behavior • • Non-magnetic • • Electrical insulation • • Low thermal conductivity(20% that of alumina) • •Corrosion resistance in acids and alkalis • •Modulus of elasticity similar to steel • • Coefficient of thermal expansion similar to iron • Chemical inertness • Use temperatures up to 2400°C http://www.azom.com/article.aspx?ArticleID=3299#_Mechanical_and_Physical_Properties http://accuratus.com/zirc.html Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  20. Good chemical and dimensionalstability, mechanical strength and toughness, coupledwith a Young’s modulus in the same order of magnitudeof stainless steel alloys was the origin of the interest in using zirconia as a ceramic biomaterial P. F. Manicone, P. R. Iommetti, L. Raffaelli; An overview of zirconia ceramics: Basicpropertiesand clinical applications; Journal of Dentistry 35 (2007) 819 – 826 C. Piconi, G. Maccauro; Zirconia as a ceramic biomaterial; Biomaterials 20 (1999) 1 -25 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  21. Good mechanical properties due to refined grain sizes Y-TZP with small grainsize 0.3–0.4 μm, High flexural strength 1000–1500MPa and High fracture toughness 8–10 MPa Effects of material properties and testing parameters on wear properties of fine-grain zirconia TZP/ Chih-Chung T. Yang, Wen-Cheng J. Wei; Wear 242 2000. 97–104 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  22. Concerning industrial applications – there is a need to investigate wear resistance of such material . Mechanical property degradation in zirconia, known as „ageing”,due to the progressive spontaneous transformationof the metastable tetragonal phase into the monoclinic phase. This behavior is well known in the temperature range above 200°C in the presence of water vapor Without the occurrence of monoclinic phase, a better wear resistance of the Y-TZP with a high fracture toughness is expected The wear resistance and amount of m-phase of Y-TZP as a function of grain size Effects of material properties and testing parameters on wear properties of fine-grain zirconia TZP/ Chih-Chung T. Yang, Wen-Cheng J. Wei; Wear 242 2000. 97–104 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  23. Parameters of the ceramic material are strongly effected by the density of the material. Correlation between Microstructure, Phase Transformation during Fracture and the Mechanical Properties of Y-TZP Ceramics; J. L. Shi, B. S. Li, Z. L.Lu and X. X. Huang Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  24. Tetragonal Zirconia Polycrystals Y-TZPcomposites Reactionsinmaterial MScEng Piotr Bobrowski Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  25. Y-TZP composites • composites with Y-TZP as matrix: • carbides: WC, TiC, SiC, NbC, CrxCy • oxides: Al2O3, TiO2 • nitrides: TiN • other: TiB2,LiNbO3, LiTaO3 • Y-TZP properties: • good bending strength • good fracture toughness • median hardness • poor wear resistance Y-TZP composites are investigated in purpose of improving hardness and wear resistance of pure ZrO2. Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  26. Ti ceramics: • excellent hardness • poor bending strenght • poor fracture toughness Y-TZP/TiB2, TiN and TiC composites Exerimental: - powders diameter: 0.2-2µm Vleugels , van der Biest: J.Am.Ceram.Soc. 82 (1999) 2717-2720 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  27. WC properties: • boiling temperature: 6000OC • excellent hardness • excellent wear resistance • Y-TZP/WC preparation: • - hot pressing needed to obtain dense ceramics • - oxygen free atmosphere Tensile strength Y-TZP/WC composites bending strength [MPa] Solid state reactions in 1400-1500OC: ZrO2 + 3C → ZrC + 2CO – leads to stabilization of high symmetry phases ZrO2 + 6WC → ZrC + 3W2C + 2CO – porous structure WC mol% amount Stresses caused by thermal expansion coefficient mismatch during cooling: αWC=5.2*10-6 K-1, αTZP=11.0*10-6 K-1favours t→m transformation Pędzich, Haberko: Inżynieria Materiałowa 2 (1996) 40-45 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  28. SiC properties: • excellent hardness (Mohs: 9,5) • excellent wear resistance • very brittle • SiC inclusions shapes: • whiskers • platelets • particles Composite properties Y-TZP/SiC composites • stresses caused by thermal expansion coefficient mismatch during cooling (αWC=4.9*10-6 K-1, αTZP=11.0*10-6 K-1 play secondary role. • - other toughening mechanisms appear: • - crack deflection • - crack branching • - microcracking Solid state reactions above 1400OC: ZrO2 + 3/2SiC → ZrC + 3/2SiO + 1/2CO – gaseous CO generates pores SiC + CO → SiO + 2C – decomposition of carbide Ding, Oberacker, Thuemmler: Journal of the European Ceramic Society 12 (1993) 377-385 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  29. Al2O3 properties: • twice as stiff as ZrO2 • chemically compatible with ZrO2, can be mixed in a wide range of concentrations Y-TZP/Al2O3 composites Langa: Journal of Materials Science 17 (1982) 247-254 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  30. Tetragonal Zirconia Polycrystals Thermal etching, hot pressing, pressureless sintering MScEng Grażyna Kulesza Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  31. Thermal etching The thermal etching is performed in a furnace or kiln under a controlledatmospherechosen to the character of etched phase (phases), sometimes it may be vacuum(but also in specific cases) and comprises the following successive stages:rapid rise in the temperature of the furnace to a temperature plateau,maintaining the temperature at theplateau for fewminutes,lowering the temperature to the final temperature. After this treatment the grain boundaries, pores and other microstructures become distinct due to reconstruction by surface diffusion which tends to minimize the total surface energy of the crystals. Thermally etched 99.9% alumina 93.1% Al2O3, 2.9% ZrO2 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  32. Hot pressing • In the ceramic industry  many methods of forming are used e.x.: • pressing • forming at elevated temperatures • slip casting • thermoplastic forming • vibrating • To choose proper forming method is determined by: • shape • size • the required dimensional accuracy • Hot pressing requires moisture powder to a few percent Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  33. Hot pressing • Hot pressing has many advantages: • possibility to obtain high density compacts • forming of non-plastic materials • high strength • dimensional accuracy • sharp edges • high efficiency, low waste • introducing of automation and mechanization • but also disadvantages: • forming limited shapes • cutouts and holes in the same direction like the pressing direction • inhomogeneous densification along the direction of the applied pressure Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  34. Hot pressing Pressing is carried out in dense, rigid metal or graphite molds with smooth walls. It is high-pressure compression mostly 30 MPa (sometimes even till 100 MPa) pc H pc ρ ρ – relative density κ – pressing coefficient p – pressing pressure κ Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  35. Hot pressing The decisive point is size and shape of grains. Very hard to form is fine powder, this situation leads to the inhomogenity of the texture* Use of thicker grains (granules) reduces the risk of cracks. For this purpose, the granulation is needed. *Texture - the spatial distribution of elements of the structure Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  36. Hot pressing An important parameter characterizing if the element is properly pressed is bulk density. Bulk density is defined as weight ratio to the volume of powder poured into the form. where: ρ – bulk density m – weight ratio V – volume of poured powder a) regular loose, b) single chessboard, c) double chessboard, d) pyramidal, e) tetraedrical Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  37. Hot pressing Hot pressing is a high-pressure, low-strain-rate  dense polycrystals synthesis process for forming of a powder or powder compact at a temperature high enough to induce sintering and creepprocesses. This is achieved by the simultaneous application of heat and pressure. gas radiator sample 400 MPa Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  38. Hot pressing • Hot pressing vs. free sintering: • intensification and acceleration of the process leads to denser samples at lower temperatures and limits the growth of grains • elimination of porosity • better mechanical properties • Range of applied pressure depends on the matrix material and temperature Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  39. Pressurelesssintering • Mass transport mechanism: • volume diffusion (Nabarro-Herring) • diffusion along grain boundaries (Coble) • diffusion on the surface of grains • vapor pressure 4 3 2 1 2 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  40. Pressurelesssintering F R2 2 R1 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  41. Pressurelesssintering 1) and 2) mechanisms that cause contraction of the whole system, close-upofcenters of each grains, leads to loss of porosity 3) and 4) withoutcontraction, only mass transport 3) atlowtemperaturesfrom long time, activated as a first process, preventelimination of porosity, increaseinneck 2) easierthan 1) becausediffusionalonggrainboundaries (as an areawith a lot of defects) 1) athighertemperature, atomsexhaustion 4) atthehighesttemperatures, near meltingtemperature 4 3 2 1 2 Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  42. Pressureless sintering Neck growth mechanism: x – neck radius R – grain radius t – time n, m – powers identifying the mechanism of sintering Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  43. Pressureless sintering Pressureless sintering is the sintering of a powder compact (sometimes at very high temperaturesorrelativelylowtemperatures, depending on the powder) without applied pressure. The powder compact (if ceramic) can be created by slip casting into a plaster mould, then the final green compact can be machined if necessary to final shape before being heated to sinter. Particular advantages of this powder technology include: Very high levels of purity and uniformity in starting materials Preservation of purity, due to the simpler subsequent fabrication process (fewer steps) that it makes possible Stabilization of the details of repetitive operations, by control of grain size during the input stages Absence of binding contact between segregated powder particles – or "inclusions" (called stringering) – as often occurs in melt processes No deformation needed to produce directional elongation of grains Capability to produce materials of controlled, uniform porosity. Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  44. References R. Pampuch, K. Haberko, „Nauka o procesach ceramicznych”, PWN, Warszawa 1982 Wykłady: Prof. dr hab. inż. K. Haberko, Dr. inż. Z. Pędzich, „Procesy i technologie ceramiczne” Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  45. Tetragonal Zirconia Polycrystals Mechanisms inproveing fracture toughness in TZP based composites MScEng Jagoda Poplewska Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  46. Fracture toughness Fracture Toughness is ability of material to resist fracture when a crack is present(The more energy is needed to grow a crack, the higher the toughness of the material). General factors affecting the fracture toughness of material are: temperature, strain rate, presence of structure defects, presence of stress concentration (notch) on the specimen surface. Stress intensity factor: K = σ(πa)1/2f(r,θ) where: σ – normal stress 2a- size of the crack • Three types of stress intensity factors: • the opening mode KI • the sliding mode KII • the tearning mode KIII Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  47. Toughening mechanisms in ceramics Crack-Tip interactions – obstacles in the crack path to impede crack motion (second-phase particles, whiskers, fibers, etc.): • Crack Bowing • Crack Deflection Crack-Tip Shielding – eg. transformation toughening, microcrack toughening; Crack Bridging – frictionally bonded fiber composites. Comparison of crack fully bridged by frictionally bonded fibers with the case where fibers break during matrix cracking forming a bridging zone behind the moving crack front Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  48. Crack Deflection Crack Deflection – tilt and twist out of the crack plane around grains and second-phase additions. SEM image showing crack propagation around a sapphikon (Al2O3) fiber in acalcium aluminosilicate (CAS) glass-ceramic SEM image showing fiber pullout on the fracture surface of AlPO4-coated alumina/mullite fiber /Al2O3 CMC, hot pressed at 1250°C for 1h Ceramic materials: science and engineering, C. Barry Carter,M. Grant Norton Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  49. Crack Bridging • Ligaments can be formed by mechanical interlocking of the grains; • These ligaments will make it more difficult to open the crack at a given applied stress and will increase fracture toughness; • This mechanism is important in frictionally bonded fiber composites; • In these materials the final failure is not the result of propagation of a single crack. Illustration of crack bridging mechanisms with debonding and fiber pullout Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

  50. Transformation Toughening • Some materials can transform from one crystal structure to another; • Commonly this transformation is thermal, but in particular cases it is stress-induced; • One uses the tetragonal to monoclinic phase transformation. The monoclinic structure is less compacted than tetragonal structure, and the theory says that increment of this volume closes the crack tips. This causes the toughening effect. • Zirconia is the most important material due to transformation toughening behavior. Illustration of transformation toughening in a ceramics matrix containing ZrO2 particles Interdyscyplinarne studia doktoranckie z zakresu inżynierii materiałowej z wykładowym językiem angielskim

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