POLYCRYSTALLINE MATERIALS COMPRISING YTTRIUM ALUMINUM PEROVSKITE AND METHODS OF MAKING THE SAME

Abstract

New polycrystalline materials having yttrium aluminum perovskite (YAP) and yttrium zirconate (YZ) are described. In one aspect, a polycrystalline material (e.g., a bulk or monolithic polycrystalline material) may comprise (a) at least 50 wt. % yttrium aluminum perovskite (YAP) phase, and (b) at least 0.1 wt. % yttrium zirconate (YZ) phase. Such polycrystalline materials may realize an improved combination of properties, such as an improved combination of two or more of density, modulus of rupture (MOR), fracture toughness, dielectric strength, loss tangent, and plasma etch resistance, among others.

Claims

1. A polycrystalline material comprising: (a) at least 50 wt. % yttrium aluminum perovskite (YAP) phase; and (b) at least 0.1 wt. % yttrium zirconate (YZ) phase.

2. The polycrystalline material of claim 1 comprising from 0.2 wt. % to 10 wt. % YZ phase.

3. The polycrystalline material of claim 1, comprising at least 95 wt. % YAP phase.

4. The polycrystalline material of claim 1, comprising 0.1-49.9 wt. % yttrium aluminum garnet (YAG) phase.

5. The polycrystalline material of claim 1, comprising not greater than 10 wt. % yttria phase.

6. The polycrystalline material of claim 1, comprising not greater than 10 wt. % alumina phase.

7. The polycrystalline material of claim 1, wherein the polycrystalline material realizes a density of at least 4.5 g/cm.sup.3.

8. The polycrystalline material of claim 1, wherein the polycrystalline material realizes an average grain size of not greater than 30 micrometers and a maximum grain size of not greater than 80 micrometers.

9. The polycrystalline material of claim 1, wherein the polycrystalline material is in the form of a semiconductor component.

10. The polycrystalline material of claim 9, wherein the semiconductor component is in the form of a nozzle blank or a nozzle.

11. A method for producing the polycrystalline material, comprising: (a) producing a green body from a first powder comprising yttrium aluminum perovskite (YAlO.sub.3) and yttrium zirconate (YZ) phases; (b) sintering the green body at a temperature of from 1200 to 1900 C., thereby forming a final product, wherein the final product comprises: (a) at least 50 wt. % of the yttrium aluminum perovskite (YAP) phase; and (b) at least 0.1 wt. % the yttrium zirconate (YZ) phase.

12. The method of claim 11, comprising: prior to the producing a green body step, preparing a precursor powder, wherein the preparing the precursor powder step comprises: (i) blending yttria and alumina to prepare a powder blend, wherein the powder blend comprises from 45-50 mol. % yttria and 50-55 mol. % alumina; (ii) heating the powder blend at a temperature and for a time sufficient to produce the precursor powder, wherein the precursor powder comprises at least 50 wt. % YAP phase, not greater than 10 wt. % yttria phase, and not greater than 10 wt. % alumina phase; and producing the first powder from the precursor powder.

13. The method of claim 12, wherein the precursor powder comprises not greater than 9 wt. % yttria phase.

14. The method of claim 12, wherein the precursor powder comprises not greater than 9 wt. % alumina phase.

15. The method of claim 12, wherein the precursor powder comprises at least 90 wt. % YAP phase.

16. The method of claim 12, wherein the precursor powder comprises not greater than 20 wt. % YAM phase (Y.sub.4Al.sub.2O.sub.9) and not greater than 50 wt. % YAG phase (Y.sub.4Al.sub.2O.sub.9).

17. The method of claim 16, wherein the precursor powder comprises at least 0.5 wt. % YAG (Y.sub.3Al.sub.5O.sub.12) phase, or at least 1 wt. % YAG phase, or both.

18. The method of claim 11, wherein the sintering comprises pressureless sintering.

19. The method of claim 11, wherein the step of producing the first powder from the precursor powder comprises: introducing zirconium into the precursor powder.

20. The method of claim 19, wherein the introducing step comprises adding a zirconium-containing powder to the precursor powder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1 illustrates one embodiment of a method for producing polycrystalline materials having tailored amounts of YAP and YZ phases.

[0066] FIG. 2 illustrates one embodiment of a method for producing a precursor powder.

[0067] FIG. 3 illustrates embodiments for introducing zirconium into the precursor powder to facilitate production of a final powder having YZ phase.

[0068] FIGS. 4-6 are graphs illustrating crystalline phases as a function of temperature for various Example 1 materials.

[0069] FIG. 7 is an SEM micrograph of a YAP/YAG final product of Example 2.

[0070] FIG. 8 is an SEM micrograph of a YAP/YAG/YZ final product of Example 2.

[0071] FIG. 9 is a backscattered SEM micrograph of a YAP/YAG/YZ final product of Example 2.

[0072] FIG. 10a is a photograph illustrating the bulk (monolithic) final parts of Example 2.

[0073] FIG. 10b is a photograph illustrating a white, translucent final part of Example 2 having YZ phase.

[0074] FIGS. 11a-11f are graphs illustrating various properties of the Example 1 alloys.

DETAILED DESCRIPTION

Example 1Formulation and Calcination of Starting Materials

[0075] High purity yttria (Y.sub.2O.sub.3) and alumina (Al.sub.2O.sub.3) were blended to produce a series of powders having from 45-50 mol. % yttria and 50-55 mol. % alumina. The formulated powders were subsequently calcined at various temperatures for 6 hours. The crystalline phases of the calcined samples were then determined using X-ray diffraction (XRD) as a function of composition and calcination time. (Material characterization methods are defined in Section vi of the Summary of the Disclosure of this patent application.) The results are shown in Tables 1-3, below, and in FIGS. 4-6.

TABLE-US-00002 TABLE 1 XRD Analysis of Sample 1 Materials (in weight percent) Calcination YAP YAM YAG Yttria Alumina Temp ( C.) (YAlO.sub.3) (Y.sub.4Al.sub.2O.sub.9) (Y.sub.3Al.sub.5O.sub.12) (Y.sub.2O.sub.3) (Al.sub.2O.sub.3) 1050 10.5 43 0 29.5 17 1150 77.5 7.5 0 10.5 4.5 1250 96.5 1 1.5 0.5 0.5

TABLE-US-00003 TABLE 2 XRD Analysis of Sample 2 Materials (in weight percent) Calcination YAP YAM YAG Yttria Alumina Temp ( C.) (YAlO.sub.3) (Y.sub.4Al.sub.2O.sub.9) (Y.sub.3Al.sub.5O.sub.12) (Y.sub.2O.sub.3) (Al.sub.2O.sub.3) 1050 13.5 36 0 28 22.5 1150 76.5 3.5 0 9.5 10.5 1250 60 0.5 37.5 0.5 1.5

TABLE-US-00004 TABLE 3 XRD Analysis of Sample 3 Materials (in weight percent) Calcination YAP YAM YAG Yttria Alumina Temp ( C.) (YAlO.sub.3) (Y.sub.4Al.sub.2O.sub.9) (Y.sub.3Al.sub.5O.sub.12) (Y.sub.2O.sub.3) (Al.sub.2O.sub.3) 1050 12.5 39 0 22 26.5 1150 71.5 4.5 0 8 16 1250 43 0.5 51 0.5 5

[0076] As shown, tailored amounts of YAP (YAlO.sub.3), YAM (Y.sub.4Al.sub.2O.sub.9), YAG (Y.sub.3Al.sub.5O.sub.12), yttria and alumina phases may be produced using predetermined amounts of yttria and alumina and preselected calcining conditions. Accordingly, materials having preselected crystalline phase structures may be produced. For example, as shown in Table 1, to produce a material having a high weight fraction of YAP phase (e.g., 95 wt. % YAP), about a 50:50 molar ratio of yttria:alumina may be preselected and then calcined a temperature of 1250 C. As another example, about a 45:50 molar ratio of yttria:alumina may be preselected and then calcined at a temperature of 1250 C. to produce a bulk material having about 60 wt. % YAP phase or about 38% YAG phase. Many other combinations may be preselected and achieved, as the data shows.

Example 2Post-Calcination Processing and Firing of Starting Materials

[0077] Several powders were produced as per Example 1. Those powers were selected to have a high weight fraction of YAG phase. Several powders (batches 1.1-1.4) were attrition milled using alumina as the milling media while several other powders (batches 2.1-2.6) were attrition milled using zirconia (ZrO.sub.2) as the milling media. For batch number 2.4, additional zirconia particles (approximately 0.5 wt. %) were added during milling to achieve the target zirconium content. The powders were then screened at 500 mesh, blended with an appropriate organic binder and then spray dried. The powders were then made into bulk parts by filling molds, then dry pressing to form a solid compact, and then sintering at about 1650 C. for 4-6 hours. After sintering, various properties of the bulk parts were measured/characterized, the results of which are shown in Tables 4-5, below. (Material characterization methods are defined in Section vi of the Summary of the Disclosure of this patent application.) Photographs of representative bulk parts are shown in FIGS. 10a-10b. Various graphs illustrating the properties of the Example 1 materials are provided in FIGS. 11a-11f.

[0078] For comparison purposes, a bulk part was made from a conventional pure yttria powder in generally the same manner as described above. This bulk material was white, realized a density of 4.95 g/cm.sup.3, an average grain size of 3.0 micrometers, a maximum grain size of about 15 micrometers, a MOR (4-pt, MPa) of 130 MPa, a K.sub.IC fracture toughness of 1.2 MPa m.sup.1/2, a dielectric constant (4 GHz) of 11.5, and a loss tangent (4 GHz) of 2.510.sup.5.

TABLE-US-00005 TABLE 4 XRD Analysis of Example 2 Bulk Materials (in weight percent) Batch No. 1.1 1.2 1.3 1.4 2.1 2.2 2.3 2.4 2.5 2.6 Percent YAP 80 90 88 79.5 91 75 87.0 82.0 88.5 92.5 (YAlO.sub.3) Percent YAG 20 10 12 20.5 8 23.5 11.0 14.5 10.5 6.5 (Y.sub.3Al.sub.5O.sub.12) Percent YZ 0 0 0 0 1 1.5 2.0 3.0 1.0 1 (Y.sub.4Zr.sub.3O.sub.12)

TABLE-US-00006 TABLE 5 Properties of Example 2 Bulk Materials Part No. 1.1 1.2 1.3 1.4 2.1 2.2 2.3 2.4 2.5 2.6 Color Tan Tan Tan Tan White White White White White White Density 5.02 5.24 5.15 5.13 5.29 5.24 5.21 5.22 5.22 5.30 (g/cm.sup.3) Grain Size 1.81 3.46 2.37 1.97 1.98 1.33 1.37 1.25 1.14 1.26 (Avg - m) Grain Size 7 11 8.1 8 7 6 6 5 5 7 (Max. - m) MOR, 4-pt. 335 321 337 367 386 348 319 347 391 (MPa) Toughness, 4.7 4.8 4.5 4.9 5.3 5.2 K.sub.IC (MPa m.sup.1/2) Dielectric 15.1 14.8 15.5 Strength, 1 mm (AC) (KV/mm) Dielectric 14.1 15.4 15.0 15.7 14.8 15.5 15.3 15.6 Constant, 4 GHz Loss 3.0 2.8 4.0 7.6 9.2 9.5 1.4 6.6 Tangent, 10.sup.5 10.sup.5 10.sup.5 10.sup.5 10.sup.5 10.sup.5 10.sup.4 10.sup.5 4 GHz

Phase Differences Between Alumina and Zirconia Milled Powders

[0079] As shown in Table 4, different phases may be achieved by using alumina or zirconia milling media, or by addition of zirconia particles to the powder. Products made from the alumina milled powders resulted in bulk products (1.1-1.4) consisting essentially of YAP and YAG phases. Products made from the zirconia milled powders resulted in bulk products (2.1-2.6) having YAP and YAG phases, but also measurable amounts of Y.sub.4Zr.sub.3O.sub.12 (YZ) phase. The production of the YZ phase is the result of zirconium transferred to the formulation during attrition milling. As shown by batch/part no. 2.4, YZ phase may also be achieved by addition of zirconium-containing materials (e.g., zirconia) to the bulk powders. As described in further detail below, the addition of zirconium may impart beneficial properties. Zirconium may be introduced to produce YZ phase by, for instance, using zirconium-containing milling media and/or by direct addition of zirconium materials (e.g., zirconia) to the powder blend. Organic or aqueous solutions comprising zirconium may also be used to introduce zirconium.

Density

[0080] As Table 5 shows, high densities were achieved. Considering the theoretical densities of YAP and YAG phases have been reported at 5.35 and 4.55 g/cc, respectively, the measured density values are exceptionally high.

Microstructure and Grain Size

[0081] As Table 5 shows, the average grain sizes are small and repeatable. The maximum grain sizes are likewise small.

[0082] FIG. 7 is a micrograph of bulk part no. 1.4 (79.5% YAP and 20.5% YAG phases by weight). As shown, the grain size is uniform and generally homogenous. The absence of porosity is notable, confirming the measured density is near the theoretical maximum. There is also an absence of intragranular porosity. The small amount of porosity that does exist appears to be intergranular-located along the grain boundaries. Enhanced mechanical and/or corrosion resistance properties may, therefore, be realized.

[0083] FIG. 8 is an SEM micrograph of bulk part no. 2.1 (75% YAP, 23.5% YAG and 1.5% YZ phases by weight). The weight ratio of YAP/YAG is similar to that of bulk part no. 1.4 shown in FIG. 7, but with 1.5 wt. % YZ phase. Without being bound by theory, it is believed that the presence of the YZ phase likely contributes to reduced grain size and increased uniformity. At sintering temperatures (e.g., about 1650 C.), the zirconium may be in solid solution with the yttria. Upon cooling, YZ phase precipitates at the grain boundaries, thereby depleting some yttria from the system and shifting the YAP/YAG ratio slightly closer to YAG.

[0084] FIG. 9 is backscattered SEM micrograph of bulk part no. 2.1 (91% YAP, 8% YAG and 1% YZ phases by weight), and illustrates the physical nature of the YZ precipitate phases. The dark phase is YAG, the grey phase is YAP and the small white regions are the YZ precipitates.

MOR (Modulus of Rupture) and Fracture Toughness

[0085] As Table 5 shows, dramatic improvements in mechanical properties were realized for the bulk parts as compared to pure YAG phase and pure yttria phase. The 4-point flexural strength (MOR) of the yttria phase and the YAG phase is approximately 100 to 150 MPa, and both materials generally realize low fracture toughness, typically about 1.2 MPa*m.sup.1/2, as confirmed by the comparative data for the bulk yttria product, provided above.

[0086] Conversely, the inventive materials realize a high MOR (321-386 MPa), which is similar to that of high purity alumina (>300 MPa). The inventive materials also realize exceptionally high fracture toughness (4.5-5.3 MPa*m.sup.1/2). Indeed, bulk part no. 2.1 (91% YAP, 8% YAG, 1% YZ phases by weight) was measured to have a 4-point flexural strength of 386 MPa and a fracture toughness of 5.3 MPa.Math.m.sup.1/2. These mechanical property improvements offer significant advantages in component design and application as well as in processing that requires diamond grinding/machining procedures.

Dielectric Properties

[0087] The inventive materials show very good dielectric performance. Pure yttria has a dielectric constant and loss tangent of approximately 11.5 and 210.sup.5, respectively, as confirmed by the comparative data for the bulk yttria product, provided above. The inventive materials realized dielectric constants in the range of 14 to 16 with loss tangents ranging from 310.sup.5 to 810.sup.5. Pure YAP phase is reported to have a dielectric constant above 15, while pure YAG phase is reported to have a dielectric constant of about 11.7. The dielectric constant variation shown by the compositions of Example 2 is derived from the relative content of YAG and YAP phases.

Color

[0088] Another interesting result was the color of the bulk products made from the zirconia milled powders. As shown in FIG. 10a, products made from the alumina milled powders (materials 1.1-1.4) are tan (light brown) in color. Surprisingly, the YZ-containing materials (2.1-2.6), however, realize a brilliant white color. The YZ-containing materials are also translucent (FIG. 10b). Thus, in addition to potentially providing enhanced physical properties, YZ-containing materials may also provide products with an enhanced visual appearance.

Example 3Evaluation of Plasma Etch Resistance

[0089] An additional coupon was made from the powder of material 2.1 of Example 2. Comparative coupons were made from aluminum oxide (99.5% and 99.8% purity) and yttrium oxide. The samples were then prepared for plasma etch testing by lapping with stages of sequentially smaller diamond abrasives and finally polished on a Sn-composite lapping plate with a diamond slurry. After lapping, surface roughness measurements were taken with a Zeiss LSM 800 scanning laser confocal microscope over 700700 m areas, with the areal surface texture calculations performed following ISO 25178, the results of which are provided in Table 6, below.

[0090] Next, a carbon tetrafluoride (CF4) etch was performed for 10 hours. The gas rate was set at 50 sccm at 5.0 Pa. Upper and lower plate RF power was set at 135 W (13.56 MHz) and 10 W (13.56 MHz) respectively, resulting in an expected ion energy of less than 200 eV. All material samples were etched at the same time, minimizing any possible differences in etch conditions. Etch rates were calculated from differential step height measurements taken via diamond stylus profilometry, between plasma exposed and masked portions of the sample surface. The etch rate results are also shown in Table 6, below.

TABLE-US-00007 TABLE 6 Properties of Example 3 Materials Average Average Bulk Density Grain Size Roughness, Etch Rate Material (g/cm3) (m) Sa (m) (m/hr) Al.sub.2O.sub.3 (99.5%) 3.92 3.12 0.030 0.08 Al.sub.2O.sub.3 (99.8%) 3.97 1.80 0.019 0.08 Y.sub.2O.sub.3 4.96 2.11 0.025 0.01 YAP (Ex. 2, 5.30 1.56 0.025 0.01 Sample 2.1)

[0091] As shown, sample 2.1 from Example 2 realizes lower surface roughness as compared to the comparative materials. Sample 2.1 from Example 2 also realizes higher density and lower grain size as compared to the comparative materials. Sample 2.1 also realizes much better plasma etch resistance as compared to the comparative alumina materials. Sample 2.1 realizes a comparable etch rate to the comparative yttria material, but with much better mechanical properties.

[0092] While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.