Zirconium oxide-based composite material

Abstract

A ceramic composite material and a method for producing same. The ceramic composite material has a ceramic matrix comprising zirconium oxide and at least one secondary phase dispersed therein. The matrix is composed of zirconium oxide as at least 51 vol.-% of composite material, and the secondary phase is in a proportion of 1 to 49 vol.-% of composite material, wherein 90 to 99% of the zirconium oxide is present in the tetragonal phase based on the total zirconium oxide portion. The tetragonal phase of the zirconium oxide is stabilized by at least one member selected from the group consisting of chemical stabilization and mechanical stabilization. The ceramic composite is damage-tolerant.

Claims

1. A composite material comprising: a ceramic matrix, said ceramic matrix comprising zirconium oxide and at least one secondary phase dispersed therein, wherein the matrix composed of zirconium oxide has a proportion of at least 51 vol.-% of composite material, and wherein the secondary phase has a proportion of from 4 to 6 vol.-% of composite material, wherein 95 to 99% of the zirconium oxide is present in the tetragonal phase based on the total zirconium oxide portion; wherein the tetragonal phase of the zirconium oxide is stabilized by at least one member selected from the group consisting of chemical stabilization and mechanical stabilization; wherein the secondary phase comprises at least one member selected from the group consisting of: strontium hexaaluminate, lanthanum aluminate, hydroxyapatite, fluorapatite, tricalcium phosphate, spinel, aluminum oxide, yttrium aluminum garnet, mullite, zircon, quartz, talc, kaolinite, pyrophyllite, potassium feldspar, leucite and lithium metasilicate, and wherein the chemical stabilization is via addition of a chemical stabilizer selected from the group consisting of Y.sub.2O.sub.3, CeO.sub.2, Gd.sub.2O.sub.3, Sm.sub.2O.sub.3, and Er.sub.2O.sub.3; wherein a total content of chemical stabilizer is <12 mol-% based on a zirconium oxide content.

2. A composite material according to claim 1, wherein the matrix composed of zirconium oxide has an average grain size of 0.1 to 2.0 μm.

3. A composite material according to claim 1, wherein the chemical stabilizer is Y.sub.2O.sub.3.

4. A composite material according to claim 3, wherein a content of Y.sub.2O.sub.3 is ≦3 mol, based on the zirconium oxide content.

5. A composite material according to claim 1, wherein at least one of the zirconium oxide or the secondary phase contain a soluble substituent.

6. A composite material according to claim 5, wherein the soluble substituent is selected from the group consisting of Cr, Fe, Mg, Ca, Ti, Y, Ce, a lanthanide and V.

7. A composite material according to claim 6, wherein the soluble substituent is an oxide.

8. A composite material according to claim 1, wherein the secondary phase includes a dispersoid which, due to crystal structure of the dispersoid, allows at least one of shear deformation on the microscopic level or reduces the hardness of the composite material.

9. A composite material according to claim 1, wherein particles of the secondary phase have a particle size of less than or equal to a grain size of the zirconium oxide.

10. A composite material according to claim 1, wherein the particles of the secondary phase have a particle size of from 0.2 to 2.0 μm.

11. A composite material comprising: a ceramic matrix, said ceramic matrix comprising zirconium oxide and at least one secondary phase dispersed therein, wherein the matrix composed of zirconium oxide has a proportion of at least 51 vol.-% of composite material, and wherein the secondary phase has a proportion of 1 vol.-% of composite material, wherein 90 to 99% of the zirconium oxide is present in the tetragonal phase based on the total zirconium oxide portion; and wherein the tetragonal phase of the zirconium oxide is stabilized by at least one member selected from the group consisting of chemical stabilization and mechanical stabilization.

12. A composite material according to claim 1, wherein the secondary phase comprises said aluminum oxide.

13. A composite material according to claim 1, wherein the composite material has a hardness<1350.

14. A composite material according to claim 13, wherein the composite material has a hardness of <1200.

15. A composite material according to claim 1, wherein the composite material has a hardness of <1000.

16. A composite material according to claim 1, wherein the composite material has a breaking strength≧800 MPa.

17. A composite material according to claim 1, wherein the damage tolerance or residual strength following an HV50 indentation is >400 MPa.

18. An article of manufacture comprising the composite material of claim 1, wherein the article of manufacture is a member selected from a dental prostheses, a dental restoration, a dental root pin, a dental implant, an abutment and a spinal implant.

19. A method for producing a sintered molded body made of a composite material according to claim 1, comprising the steps of: a) placing a powder mixture of the ceramic matrix into water, b) homogenizing in a dissolver; c) grinding in an agitator ball mill; d) spray drying to form a granulate; e) moistening the granulate with water; f) axially pressing the granulate to form a block; g) machine cutting a block to form pre-sintered state; h) sintering the pre-sintered state block to form a sintered block; and i) hard machining the sintered block.

20. A composite material according to claim 1, wherein the content of CeO.sub.2 is ≦12 mol-%, based on the zirconium oxide content.

21. A composite material according to claim 1, wherein the content of Gd.sub.2O.sub.3 is ≦3 mol-%, based on the zirconium oxide content.

22. A composite material according to claim 1, wherein the content of Sm.sub.2O.sub.3 is ≦3 mol-%, based on the zirconium oxide content.

23. A composite material according to claim 1, wherein the content of Er.sub.2O.sub.3 is ≦3 mol-%, based on the zirconium oxide content.

24. A composite material comprising: a ceramic matrix, said ceramic matrix comprising zirconium oxide and a secondary phase dispersed therein, wherein the matrix composed of zirconium oxide has a proportion of at least 51 vol.-% of composite material, and that the secondary phase has a proportion of from 4 to 6 vol.-% of composite material, wherein 95 to 99% of the zirconium oxide is present in the tetragonal phase based on the total zirconium oxide portion; and wherein the tetragonal phase of the zirconium oxide is stabilized by at least one member selected from the group consisting of chemical stabilization and mechanical stabilization.

25. A method for producing a sintered molded body made of a composite material according to claim 24, comprising the steps of: a) placing powder mixture of the zirconium oxide and the secondary phase into water to form an aqueous mixture b) homogenizing the aqueous mixture in a dissolver to form a homogenized aqueous mixture; c) grinding the homogenized aqueous mixture in an agitator ball mill to form a ground homogenized aqueous mixture; d) spray drying to form a granulate; e) moistening the granulate with water; f) axially pressing a block; g) machine cutting a block in a green or pre-sintered state; h) sintering; and i) hard machining.

26. A composite material comprising: a ceramic matrix, said ceramic matrix comprising zirconium oxide and at least one secondary phase dispersed therein, wherein the matrix composed of zirconium oxide has a proportion of at least 51 vol.-% of composite material, and wherein the secondary phase has a proportion of 1 to 10 vol.-% of composite material, wherein 90 to 99% of the zirconium oxide is present in the tetragonal phase based on the total zirconium oxide portion; wherein the tetragonal phase of the zirconium oxide is stabilized by at least one member selected from the group consisting of chemical stabilization and mechanical stabilization; and wherein the secondary phase comprises zircon.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the results of a test series with and without dispersoids according to the invention, in each case with different chemical stabilizers.

(2) FIG. 2 shows a test series with different dispersoids in the composite material according to the invention.

(3) FIG. 3 shows a plurality of test series with dispersoids according to the invention and different contents (vol.-%) of dispersoid phases (x axis 31).

(4) FIG. 4 shows a test series which illustrates the influence of the chemical stabilizer on pure zirconium oxide material and on the composite material according to the invention.

(5) FIG. 5 shows a test series with different dispersoids and their influence on the fracture toughness of the composite material according to the invention.

(6) FIG. 6 shows a plurality of test series of the composite material according to the invention with dispersoids and different contents of dispersoid phases.

(7) FIG. 7 shows composite materials according to the invention with Y stabilization and strontium hexaaluminate as the secondary phase.

(8) FIG. 8 shows the residual strength values following different damage (in the present case, Vickers hardness indentations) to different material systems, to a zirconia toughened alumina (ZTA) 82, a Y-stabilized polycrystalline zirconia (Y-TZP) 83, and a composite material according to the invention (strontium hexaaluminate-toughened zirconia) 84.

DETAILED DESCRIPTION

(9) The advantages of the novel material according to the invention over the prior art are quantitatively determined based on the improved “damage tolerance.” Damage tolerance is a mechanical characteristic value which describes the resistance of a material to an externally applied damage. The damage may occur in practice, for example, due to grinding using diamond tools.

(10) For measuring the damage tolerance in the laboratory, the test piece is subjected to damage using a diamond tip (Vickers) under a defined stress force. Cracks form in the area of the hardness indentation, so that the test piece experiences weakening at this location. The weakening is quantitatively determined by measuring the residual breaking stress, i.e., residual strength, at this location. The higher the residual strength after a defined weakening, the higher the damage tolerance of the material.

(11) For the detailed description of the damage tolerance, a series of test pieces is subjected to damage, using different stress forces. This results in a characteristic curve for the material (residual strength versus stress force). Improved damage tolerance of a material with respect to the prior art is demonstrated by comparing these characteristic curves; see FIGS. 7 and 8.

(12) The invention relates to the production and use of a zirconium oxide-based composite material, in particular for damage-free hard machining in the dense-sintered state. The production of the composite material according to the invention is carried out using conventional ceramic technology which is known per se. The important process steps are, for example: a) Placing powder mixture according to the predefined composition into water, optionally using liquefiers to avoid sedimentation b) Homogenization in a dissolver (high-speed agitator) c) Grinding in an agitator ball mill, thus increasing the specific surface of the powder mixture (comminution and homogenization) d) Optionally adding organic binders e) Spray drying, resulting in a pourable granulate having defined properties f) Moistening the granulate with water and optionally further pressing aids g) Axial pressing of blocks h) Machine cutting of blocks in the green or pre-sintered state, thus largely imparting the final contour, taking the sintering shrinkage into account i) Sintering (This may also take place in a 3-step sintering process: prefiring to a theoretical density of approximately 97%. The remaining residual pores are closed from the outside. Hot isostatic pressing (HIP) under high temperature and high gas pressure, resulting in virtually complete final compaction. So-called white burning, thus compensating for the imbalance of oxygen ions, produced during the hot isostatic pressing, in the ceramic.) j) Hard machining by grinding and polishing with a diamond tool.

(13) The composite material according to the invention may be used, for example, for producing sintered molded bodies, for producing artificial dental prostheses and dental restorations such as bridges, crowns, inlays, and onlays, and for producing dental root pins, implants, and abutments. The application in the area of implant technology is preferred. The application in the spinal area as a spacer or cage is particularly preferred.

(14) The zirconium oxide-based composite material contains zirconium oxide as the ceramic matrix, and at least one secondary phase or dispersoid and optionally further additives dispersed therein. The composite material includes as the first phase a zirconium oxide proportion of at least 51 vol.-% and a secondary phase having a proportion of 1 to 49 vol.-%, and optionally one or more inorganic additives. The predominant portion, preferably 90 to 99%, particularly preferably 95 to 99%, based on the total zirconium oxide portion, of the zirconium oxide is present in the tetragonal phase, wherein the stabilization of the tetragonal phase of the zirconium oxide sometimes takes place not only chemically but also mechanically. The terms “secondary phase” and “dispersoid” are used synonymously within the scope of this text.

(15) The mechanical stabilization of the zirconium oxide, in addition to the chemical stabilization, which is present in the tetragonal phase, advantageously allows the content of chemical stabilizers to be reduced compared to the prior art.

(16) The mechanical stabilization of the zirconium oxide in the tetragonal phase is known from zirconia toughened alumina (ZTA) composite materials. In that context, it has been assumed that the mechanical stabilization is influenced on the one hand by the grain size of the zirconium oxide. In aluminum oxide composite materials, this grain size should not be greater than 0.5 μm, measured according to the linear intercept method. On the other hand, it has been assumed that the embedding of the individual zirconium oxide particles in the aluminum oxide matrix has a significant portion of the mechanical stabilization, wherein minimum contents of aluminum oxide of 65 vol.-%, preferably higher contents, have been considered necessary.

(17) With the present invention, it has been possible to demonstrate that such mechanical stabilization of the zirconium oxide functions not only when zirconium oxide is incorporated into aluminum oxide as the dispersoid phase, but also in a ceramic which is composed substantially of zirconium oxide. The addition according to the invention of the secondary phases/dispersoids compensates for the strain which occurs during the transformation of the tetragonal crystal structure into the monoclinic crystal structure of the zirconium oxide, in that micromotions/microshears on the crystallite level are possible in an otherwise comparatively rigid ceramic structure without macroscopic cracks necessarily arising.

(18) Furthermore, mechanical stabilization is also understood to mean that the tetragonal crystal phase of the zirconium oxide is stabilized by mechanical stresses in the overall structure. Different coefficients of thermal expansion of ZrO.sub.2 and of the secondary phase during cooling after the sintering process may result in such stresses.

(19) The mechanical stabilization is advantageous in particular in that lower proportions of compounds used for the chemical stabilization are thus necessary. The chemical stabilization is based on the partial substitution of zirconium oxide ions with cations which produce oxygen vacancies in the crystal lattice, and which thus have a smaller “space requirement” However, the oxygen vacancies in the lattice may be points of attack for hydrothermal aging. Mechanical stabilization, which at the same time at least reduces the need for chemical stabilization, thus results in improved resistance of the composite material to hydrothermal aging.

(20) According to one preferred embodiment of the invention, the zirconium oxide matrix has an average grain size of 0.1 to 2.0 μm, particularly preferably 0.5 to 2.0 μm on average. According to one refinement of the invention, the proportion of chemical stabilizers in the composite material according to the invention for Y.sub.2O.sub.3 is ≦3 mol-%, preferably ≦2.5 mol-%, for CeO.sub.2 is ≦12 mol-%, for Gd.sub.2O.sub.3 is ≦3 mol-%, for Sm.sub.2O.sub.3 is ≦3 mol-%, and for Er.sub.2O.sub.3 is ≦3 mol-%, the proportion in each case relative to the zirconium oxide content. The chemical stabilizers in the composite material according to the invention include one or more of the mentioned additives, with Y.sub.2O.sub.3 being preferred. The total content of chemical stabilizers is advantageously <12 mol-% relative to the ZrO.sub.2 content.

(21) According to one embodiment, the zirconium oxide and the dispersoid may contain soluble substituents. Soluble substituents may be Cr, Fe, Mg, Ca, Ti, Y, Ce, lanthanides, and/or V, for example. These substituents may function on the one hand as color additives, and on the other hand as sintering aids. The substituents are generally added as oxides.

(22) The particle sizes of the secondary phase or dispersoids are preferably not much greater than the grain sizes of the zirconium oxide matrix. The former are preferably 0.2 to 2.0 μm, particularly preferably 0.2 to 0.5 μm. The volume proportion of the secondary phase or dispersoids is much lower than the proportion of the zirconium oxide, and is up to 49 vol.-%, preferably 1 to 10 vol.-%, particularly preferably 4 to 6 vol.-%, of the total volume. The secondary phase is chemically stable, and does not go into solution in the zirconium oxide during production of the composite material due to sintering at high temperatures.

(23) The following compounds may be used as the secondary phase or dispersoids: Strontium aluminate (SrAl.sub.12O.sub.19), lanthanum aluminate (LaAl.sub.11O.sub.18), hydroxyapatite (Ca.sub.10(PO.sub.4).sub.6(OH).sub.2), fluorapatite.(Ca.sub.10(PO.sub.4).sub.6F.sub.2), tricalcium phosphate (Ca.sub.3(PO.sub.4).sub.2), spinel (MgAl.sub.2O.sub.4), aluminum oxide (Al.sub.2O.sub.3), yttrium aluminum garnet (Y.sub.3Al.sub.5O.sub.12), mullite (Al.sub.6Si.sub.2O.sub.3), zircon (ZrSiO.sub.4), quartz (SiO.sub.2), talc (Mg.sub.3Si.sub.4O.sub.10(OH).sub.2), kaolinite (Al.sub.2Si.sub.2O.sub.5(OH).sub.4), pyrophyllite (Al.sub.2Si.sub.4O.sub.10(OH).sub.2), potassium feldspar (KAlSi.sub.3O.sub.8), leucite (KAlSi.sub.2O.sub.6), and lithium metasilicate (Li.sub.2SiO.sub.3). Strontium aluminate, lanthanum aluminate, hydroxyapatite, fluorapatite, spinel, aluminum oxide, and zircon are preferred, and lanthanum aluminate, fluorapatite, spinel, and aluminum oxide are particularly preferred.

(24) The secondary phase or dispersoids may allow inelastic microdeformations on the microscopic level, and due to their crystal structure may allow shear deformations on the microscopic level.

(25) According to one particularly preferred embodiment of the invention, the secondary phase is not formed during the sintering, but, rather, is part of the starting substances used for producing the ceramic.

(26) The breaking strength of the composite material is preferably 800 MPa.

(27) It has surprisingly been shown that the secondary phase or dispersoids may greatly reduce the hardness of the composite material. Likewise, it has surprisingly been shown that the type of chemical stabilizer has a great influence on the hardness of the composite material.

(28) Furthermore, it has surprisingly been shown that the fracture toughness, the hardness, and the damage tolerance of the composite material are influenced by the type and the quantity of the secondary phase or dispersoids, and by the type of chemical stabilizer.

(29) The present invention is explained below with reference to test series, without being limited thereto:

(30) Test Series 1: Hardness as a Function of the Chemical Stabilizer

(31) FIG. 1 shows the results of a test series with and without dispersoids according to the invention, and in each case with different chemical stabilizers. The quantity and type of the dispersoid phase used, namely, zirconium oxide containing no dispersoids with Y.sub.2O.sub.3 stabilization 13 or CeO.sub.2 stabilization 14, zirconium oxide containing 15 vol.-% strontium hexaaluminate dispersoids and Y.sub.2O.sub.3 stabilization 15 or CeO.sub.2 stabilization 16, and zirconium oxide containing 30 vol.-% Al.sub.2O.sub.3 dispersoids and Y.sub.2O.sub.3 stabilization 17 or CeO.sub.2 stabilization 18, are represented on the x axis 11, and the Vickers hardness HV 10 is represented on the y axis 10.

(32) The chemical stabilizers yttrium oxide (Y.sub.2O.sub.3) and cerium oxide (CeO.sub.2) were tested. It has surprisingly been shown that all variants with Ce stabilization 14, 16, 18 have much lower hardness values compared to variants with Y stabilization 13, 15, 17. The hardness was determined by Vickers indentation (HV10) with a force of 98.07 N.

(33) Pure Ce-stabilized zirconium oxide has the lowest hardness at 800 (HV10). With regard to the application according to the invention in the dental field, lower hardnesses are desired. In the regions of the molar teeth, an artificial dental prosthesis made of frequently used Y-TZP may strike against a natural tooth. The hardness of Y-TZP is approximately 1250 (HV10). The natural tooth or the enamel has a much lower hardness of approximately 400 (HV10) due to the incorporated hydroxyapatite crystals. For stress-related grinding of the teeth (bruxism), for example, this difference in hardness may result in significant abrasion of the natural tooth. For this reason, lower hardnesses of the composite material according to the invention are expedient. In addition, a lower hardness of the composite material could result in damage-free hard machining (for example, during grinding-in of the artificial tooth in an articulator).

(34) Test Series 2: Hardness as a Function of the Type of Dispersoid Phase

(35) FIG. 2 shows a test series with different dispersoids in the composite material according to the invention. In the test series, only variants having the same proportion (5 vol.-%) of the dispersoid phase in the composite material were compared to one another. The Vickers hardness HV 10 is provided on the y axis 20. The x axis 21 shows zirconium oxide in each case with 5 vol.-% dispersoids (SrAl.sub.12O.sub.19 23, 23a, MgAl.sub.2O.sub.4 24, 24a, SiO.sub.2 25, ZrSiO.sub.4 26, Al.sub.6Si.sub.2O.sub.13 27, Al.sub.2Si.sub.2O.sub.5(OH).sub.4 28), and without dispersoids 22, 22a for comparison. Variants with Y.sub.2O.sub.3 stabilization 22, 23, 24, 25, 26, 27 and 28 were tested for all compositions, and in addition, variants with CeO.sub.2 stabilization 22a, 23a were tested for the zirconium oxide composite materials containing strontium hexaaluminate and spinel as dispersoids.

(36) It has surprisingly been shown that the hardness may be influenced by adding dispersoids. It has likewise been shown that the degree of influence is a function of the composition of the dispersoid phase.

(37) Test Series 3: Hardness as a Function of the Content of the Dispersoid Phase

(38) FIG. 3 shows a plurality of test series with dispersoids according to the invention and different contents (vol.-%) of the dispersoid phases (x axis 31). Aluminum oxide (Al.sub.2O.sub.3) 32, hydroxyapatite (Ca.sub.10(PO.sub.4).sub.6(OH).sub.2) 34, and strontium hexaaluminate (SrAl.sub.12O.sub.19) 33 in Y-stabilized zirconium oxide and spinel (MgAl.sub.2O.sub.4) 35 were tested in Ce-stabilized zirconium oxide.

(39) It has surprisingly turned out that the Vickers hardness, plotted on the y axis 30, may be greatly influenced by the content of the dispersoid phase. The hardness of the composite material customarily results from the percentage mix of the individual hardnesses of the components involved. In the test series it has surprisingly been shown that this mixture rule does not always apply. The hardness may be reduced from approximately 1250 to approximately 1050 (HV10) by introducing 15 vol.-% hydroxyapatite 34 into Y-stabilized zirconium oxide. The hardness of Y-stabilized zirconium oxide may be reduced from 1250 to 1210 (HV10) by introducing 5 vol.-% strontium aluminate 33.

(40) Test Series 4: Fracture Toughness as a Function of the Chemical Stabilizer

(41) FIG. 4 shows a test series which illustrates the influence of the chemical stabilizer on the pure zirconium oxide material and the composite material according to the invention. The material containing the particular dispersoid phase is indicated on the x axis, namely, pure zirconium oxide 42, 43, zirconium oxide containing 25 vol.-% strontium hexaaluminate as the dispersoid phase 44, 45, and zirconium oxide containing 30 vol.-% Al.sub.2O.sub.3 as the dispersoid phase 46, 47, in each case with Y.sub.2O.sub.3 42, 44, 46 or CeO.sub.2 43, 45, 47 as chemical stabilizers.

(42) It could surprisingly be shown that the use of cerium oxide (CeO.sub.2) as chemical stabilizer greatly increases the fracture toughness (y axis 40) of the pure material 43 and of the composite material 45, 47. The fracture toughness of the variants according to the invention was determined at the Vickers hardness indentation (HV10). High-strength variants such as pure Ce-stabilized zirconium oxide 43, for example, showed no cracks at the hardness indentation. Therefore, for the high-strength variant a fracture toughness value of 15 MPa*m.sup.0.5 was assumed by extrapolation in FIG. 4.

(43) Test Series 5: Fracture Toughness as a Function of the Dispersoid Phase

(44) FIG. 5 shows a test series with different dispersoids and their influence on the fracture toughness (y axis 50) of the composite material according to the invention. The pure zirconium oxide material 52, 52a, zirconium oxide containing strontium hexaaluminate 53, 53a, zirconium oxide containing spinel 54a, zirconium oxide containing quartz 55, zirconium oxide containing zircon 56, zirconium oxide containing mullite 57, and zirconium oxide containing kaolinite 58 as dispersoid phase, partially with Y.sub.2O.sub.3 stabilization 52, 53, 55, 56, 57, 58 and partially with CeO.sub.2 stabilization 52a, 53a, 54a, are plotted on the x axis 51.

(45) It has surprisingly been shown that the addition of dispersoid phases to the Ce-stabilized composite material had no effect on the fracture toughness.

(46) In contrast, it has surprisingly been shown that the addition of dispersoid phases to the Y-stabilized composite material sometimes had a considerable influence on the fracture toughness. The fracture toughness could be greatly increased from 5.3 to 12.3 MPa*m.sup.0.5 by adding strontium aluminate (SrAl.sub.12O.sub.19) as dispersoid phase to the composite material 53.

(47) Test Series 6: Fracture Toughness as a Function of the Content of the Dispersoid Phase

(48) FIG. 6 shows a plurality of test series of the composite material according to the invention with dispersoids and different contents of the dispersoid phases. The contents of the dispersoid phase in vol.-% are indicated on the x axis 61. The fracture toughness in MPa*m.sup.0.5 is plotted on the y axis 60.

(49) Aluminum oxide (Al.sub.2O.sub.3) 62 and strontium aluminate (SrAl.sub.12O.sub.19) 63 in Y-stabilized zirconium oxide, and spinel (MgAl.sub.2O.sub.4) 64 in Ce-stabilized zirconium oxide were tested. It has surprisingly been shown that, depending on the dispersoid used, with regard to good fracture toughness there is an optimum for the content of the dispersoid phase in the composite material according to the invention. The optimum for strontium aluminate as dispersoid phase in the composite material according to the invention is between 1 and 15 vol.-%

(50) Test Series 7: Damage Tolerance as a Function of the Content of the Dispersoid phase

(51) FIG. 7 shows composite materials according to the invention with Y stabilization and strontium hexaaluminate as the secondary phase. The various composite materials are characterized based on their secondary phase contents in vol.-% on the x axis 71. The residual strength of the composite materials following HV50 damage is plotted in MPa on the y axis 70. The tested composite materials are provided with reference numeral 72.

(52) It is clearly shown that for composite materials 72 having a hexaaluminate content between 5 and 15 vol.-%, and in particular with a 5 vol.-% secondary phase, the residual strength of the composite material increases by several times in comparison to the other tested materials.

(53) Test Series 8: Damage Tolerance of the Composite Material Compared to Materials of the Prior Art

(54) FIG. 8 shows the residual strength values following different damage (in the present case, Vickers hardness indentations) to different material systems, to a zirconia toughened alumina (ZTA) 82, a Y-stabilized polycrystalline zirconia (Y-TZP) 83, and a composite material according to the invention (strontium hexaaluminate-toughened zirconia) 84. The tested indentation load is logarithmically plotted in N on the x axis 81 versus the residual strength in MPa on the y axis 80.

(55) In comparison to materials from the prior art, it is shown that the novel composite material, with the initial strength constant, shows significantly higher damage tolerances following various damage loads.

(56) The advantages of the composite material according to the invention are once again summarized below: Production of the composite material according to the invention takes place using known, conventional ceramic technology 3-stage sintering (prefiring, HIP, white burning), resulting in greater strength No hydrothermal aging on account of using CeO.sub.2 as chemical stabilization Greatly reduced hydrothermal aging due to smaller proportions of Y.sub.2O.sub.3 as chemical stabilization on account of the mechanical partial stabilization, or the extra addition of other chemical stabilizers which show no negative effect on the aging resistance High damage tolerance Lower-risk hard machining Lesser hardness Use of the composite material according to the invention in the fields of dental technology and dentistry for producing blanks and blocks for CAD/CAM machining in the pre-sintered or dense-sintered state, and for dental prostheses and dental restoration (bridges, crowns, inlays, onlays) Preferably used as dental root pins, implants, abutments, and other applications Particularly preferably used as spinal implants (spacers/cages, for example)