Patent Application
20130052438
1. Field of the Invention
The present invention relates to a MAX phase ceramic with sufficient orientation of the MAX phase, obtained by sufficiently orientating (texture of) the MAX phase, and to a method for producing the same.
2. Description of the Related Art
A Mn+1AXn(M is a transition meta; and A is an A group element (that is often belong to the IIIA group or IVA group, and contains Cd, Al, Ga, In, Ti, Si, Ge, Sn, Pb, P, As, and S, and n=1 to 3)) compound, which are ternary compounds, are also called MAX phases, and these compounds have crystallized multilayer microstructure of hexagonal crystals. In a crystal structure of each of M2AX, M3AX2, M4AX3 phases, respectively, every third, fourth, and fifth layer are a layer of an A group element. A thin layered ceramic containing the MAX phase has combined characteristics of metal and ceramic, such as high strength, high Young's modulus, and excellent electric and thermal conductivity, together with simple machinability, excellent damage resistance, and thermal shock resistance (see U.S. Pat. Nos. 5,882,561, 5,942,455, 6,231,969, 6,461,989, and 7,235,505). To date, more than fifty M2AX phases, five M3AX2 phases (Ti3SiC2, Ti3AlC2, Ti3GeC2, Ti3SnC2, and Ta3AlC2), and seven M4AX3 phases (Ta4AlC3, Ti4AlN3, Ti4SiC3, Ti4GeC3, Nb4AlC3, V4AlC3, and Ti4GaC3) have been found (see Barsoum et al., “The MN+1AXN Phases: a New Class of Solids; Thermodynamically Stable Nanolaminates”, Prog. Solid State Chem. 28: 201-281 (2000), and Hu et al., “In Situ Reaction Synthesis, Electrical and Thermal, and Mechanical Properties of Nb4AlC3”, J. Am. Ceram. Soc. 91: 2258-2263 (2008)). Further, several new MAX phases have been discovered by a solid solution method, such as (Ti,Nb)2AlC, Ti3Si(Al)C2, Ti3Si(Ge)C2, (V,Cr)3AlC2, (V,Cr)4AlC3, and (V,Cr)2GeC (see Hu et al., “In Situ Reaction Synthesis, Electrical and Thermal, and Mechanical Properties of Nb4AlC3”, J. Am. Ceram. Soc. 91: 2258-2263 (2008)). It has been discovered that there are two types of orders of lamination of atoms along the [0001] direction in the crystal structure of the M4AX3. One of the atom arrangements, ABABACBCBC, belong to atom arrangements of Ti4AlN3, Ti4SiC3, Ti4GeC3, α-Ta4AlC3, Nb4AlC3, and V4AlC3, and the other type of the atom arrangements, ABABABABAB, belong to only an atom arrangement of β-Ta4AlC3. It is assumed that the atom arrangement is varied because of variations in positions of atoms in a crystal structure.
It has been found that an oriented microstructure film, which is sufficiently dense, and a basal plane of which is parallel to a surface thereof, can be obtained by tape casting and/or cold pressing fine Ti3SiC2, followed by pressureless sintering in an argon atmosphere, or Si-rich atmosphere (see Barsoum et al., “The MN+1AXN Phases: a New Class of Solids; Thermodynamically Stable Nanolaminates”, Prog. Solid State Chem. 28: 201-281 (2000).). Further, it has been known that ceramic crystals having asymmetric unit cells exhibit crystal magnetic anisotropy. There are reports that control and design of an oriented texture of each of Al2O3 (hexagonal crystal-base), AlN (hexagonal crystal-base), Si3N4 (hexagonal crystal-base), and ZrO2 (monoclinic crystal-base) has been accomplished by forming them in a strong magnetic field (see Sakka et al., “Fabrication of Oriented β-Alumina from Porous Bodies by Slip Casting in a High Magnetic Field”, Solid State Ion. 172: 341-347 (2004)., Sakka et al., “Textured Development of Feeble Magnetic Ceramics by Colloidal Processing under High Magnetic Field”, J. Ceram. Soc, Jpn. 113: 26-36 (2005)., Sakka et al., “Fabrication and Some Properties of Textured Alumina-related Compounds by Colloidal Processing in High-magnetic Field and Sintering”, J. Eur. Ceram. Soc. 28: 935-942 (2008)., Suzuki et al., “Effect of Sintering Additive on Crystallographic Orientation in AlN Prepared by Slip Casting in a Strong Magnetic Field”, J. Eur. Cearm. Soc. 29: 2627-2633 (2009)).
Since a ratio of c and a crystal axes in a unit cell in the MAX phase is large, it is expected that orientation of grains of the MAX phase is controlled in a strong magnetic field. To this end, two main factors need to be addressed. The first one is to prepare a slurry having excellent fluidity, in which each of grains are dispersed, namely preparing a suspension, and the other is to use a strong magnetic field. It is further expected that an extremely hard and strong MAX phase material is obtained by the aforementioned process.
The present invention aims to provide an orientated Max phase ceramic, which is an extremely hard and strong oriented material formed of a MAX phase compound with maintaining desirable characteristics of the MAX phase compound, and to provide a production method thereof.
The present invention is directed to a ceramic in which an Mn+1AXn phase that is a ternary compound has been orientated, and to a production method thereof. Here, M is an early transition metal, A is an A group element, X is C or N, and n is an integer of 1 to 3.
According to another aspect of the present invention, a method for producing an oriented ceramic contains an Mn+1AXn phase that is a ternary compound, the method comprising:
(a) a suspension forming step, containing mixing powder of the Mn+1AXn phase that is the ternary compound, a dispersion medium, and a dispersing agent to form a suspension;
(b) a strong magnetic field applying step, containing applying a strong magnetic field to the suspension with performing solidification forming to thereby obtain a compact;
(c) a pressure applying step, containing applying high pressure to the compact to thereby obtain a pressed compact; and
(d) a sintering step, containing sintering the pressed compact in an inert gas atmosphere or under vacuum, to thereby obtain a sintered compact,
wherein M is an early transition metal, A is an A group element, X is C or N, and n is an integer of 1 to 3.
The present invention can provide an orientated Max phase ceramic, which is an extremely hard and strong oriented material formed of a MAX phase compound with maintaining desirable characteristics of the MAX phase compound, and can provide a production method thereof.
The present invention can provide a layered material having bending strength of greater than 1 GPa, and fracture toughness of 20 MPa·m1/2. Owing to its excellent physical properties in addition to typical characteristics of a MAX phase material (e.g., damage resistance, machinability, and oxidation resistance at high temperature), the oriented MAX phase can be an ideal option in various structural or functional uses.
The present invention is directed to orientation of ceramic of a MAX phase, which is a ternary compound. The ternary compound ceramic is represented by a chemical formula of Mn+1AXn, where M is an early transition metal, A is an A group element, X is C or N, and n=1 to 3. A dispersion medium and a dispersing agent are each appropriately selected. The produced oriented ceramics can be used as structural parts. An amount of the MAX phase in the sample is about 100% by weight relative to the total oriented sample. As for the target for orientation, more than fifty M2AX phases, five M3AX2 phases (Ti3SiC2, Ti3AlC2, Ti3GeC2, Ti3SnC2, and Ta3AlC2), and seven M4AX3 phases (Ta4AlC3, Ti4AlN3, Ti4SiC3, Ti4GeC3, Nb4AlC3, V4AlC3, and Ti4GaC3) can be used. In addition to the foregoing MAX phases, several new MAX phases, such as (Ti,Nb)2AlC, Ti3Si(Al)C2, Ti3Si(Ge)C2, (V,Cr)3AlC2, (V,Cr)4AlC3, and (V,Cr)2GeC, may be selected as the target for orientation by utilizing a solid solution method. Among them, Nb4AlC3 and Ti3SiC2 are preferable as the MAX phase.
A suspension is produced by mixing the dispersion medium, ceramic powder the ternary compound, and the dispersing agent. As for the ternary compound, Nb4AlC3 and Ti3SiC2 are preferable. A volume ratio of the ceramic powder in the dispersion medium is preferably 10% to 60% relative to a total volume of the suspension. An amount of the dispersing agent added is preferably 0.1% by weight to 10% by weight, more preferably 1% by weight to 3% by weight, relative to the ceramic powder.
The suspension is poured into a mold formed of gypsum or porous alumina in a glass tube. A final size of the sample depends on an amount of the suspension charged. Specifically, the larger the amount of the suspension used is the larger sample finally obtained. Of course, the mold is not limited to the glass tube. Next, the suspension is placed in a strong magnetic field. Strength of the magnetic field is appropriately selected depending on the intended purpose without any limitation, but it is preferably 1 T to 12 T. The suspension is then dried in air for 10 minutes to 24 hours. This target material for sintering is taken out, and is subjected to cold isostatic pressing to thereby obtain a compact. The applied pressure is preferably 50 MPa to 400 MPa. The resultant is sintered in a furnace, for example, under desirable conditions, such as at the temperature ranging from 1,000° C. to 1,700° C. for 5 minutes to 4 hours, to thereby obtain a dense sample. The heating rate is preferably 1° C./min. to 400° C./min. The pressure applied during the sintering is preferably in a range of 0 MPa to 700 MPa, and the sintering atmosphere is an inert gas atmosphere, or under vacuum.
In order to explain the present invention, MAX phases of Nb4AlC3 and Ti3SiC2 are used in the following examples. However, it should be understood that the spirit of the present invention is not limited to these specific two ceramics, and is applied to all MAX phases.
The embodiments of the present invention includes, for examples, as follows.
The present invention is directed to a ceramic in which an Mn+1AXn phase that is a ternary compound has been orientated, and to a production method thereof. Here, M is an early transition metal, A is an A group element, X is C or N, and n is an integer of 1 to 3. A dispersion medium may be water, ethanol, or acetone, but it is not limited to the foregoing media. A dispersing agent can be polyethyleneimine (PEI), or a polyacrylic acid material, such as ammonium polyacrylate, but it is not limited to the foregoing materials. The present invention contains the following steps in order to impart orientation to a ceramic material.
Note that, in the present specification, the early transition metal indicates all transition metals belong to A group in a periodic table, such as Ti, V, Cr, Nb, and Ta.
(a) Powder of the MAX phase, the dispersion medium, and the dispersing agent are mixed to form suspension. The rheological behavior of the suspension can be optimized by changing a volume ratio of the powder, and a weight ratio of the dispersing agent, in order to attain preferable characteristics of the oriented ceramic, and moreover, it can be evaluated by measuring viscosity of the suspension.
(b) The suspension is poured into a mold formed of gypsum or porous alumina.
(c) The mold in which the suspension has been poured is placed in a strong magnetic field, and is left to stand for 10 minutes to 24 hours, to thereby perform slip casting.
(d) The compact of the MAX phase is taken out, and the compact is subjected to cold isostatic pressing at pressure of 50 MPa to 400 MPa.
(e) The pressure formed sample is sintered for 5 minutes to 4 hours in a furnace at temperature of 1,000° C. to 1,700° C. Here, a heating rate is 1° C./min. to 400° C./min. Moreover, pressure applied is 0 MPa to 700 MPa, and sintering atmosphere is an inert gas atmosphere, or vacuumed atmosphere.
According to one aspect of the present invention, provided is an oriented ceramics, which contains an Mn+1AXn phase (M is an early transition metal, A is an A group element, X is C or N, and n is an integer of 1 to 3) that is a ternary compound, has a layered microstructure similar to shell layers of pearl, which is formed by laminating a layer of a nano-order to milli-order in a thickness thereof, and is an oriented bulk material a total thickness of which is in milli-order or larger at smallest.
M may be selected from the group consisting of Ti, V, Cr, Nb, Ta, Zr, Hf, Mo and Sc.
A may be selected from the group consisting of Al, Ge, Sn, Pb, P, S, Ga, As, Cd, In, Ti and Si.
The ternary compound may be Nb4AlC3, or Ti3SiC2.
The oriented ceramic may be substantially composed of the ternary compound.
According to another aspect of the present invention, a method for producing an oriented ceramic contains an Mn+1AXn phase that is a ternary compound, the method comprising:
(a) a suspension forming step, containing mixing powder of the Mn+1AXn phase that is the ternary compound, a dispersion medium, and a dispersing agent to form a suspension;
(b) a strong magnetic field applying step, containing applying a strong magnetic field to the suspension with performing solidification forming to thereby obtain a compact;
(c) a pressure applying step, containing applying high pressure to the compact to thereby obtain a pressed compact; and
(d) a sintering step, containing sintering the pressed compact in an inert gas atmosphere or under vacuum, to thereby obtain a sintered compact,
wherein M is an early transition metal, A is an A group element, X is C or N, and n is an integer of 1 to 3.
The dispersion medium may be selected from the group consisting of water, ethanol, and acetone.
The dispersing agent may be polyethyleneimine or ammonium polyacrylate.
The (b) strong magnetic field applying step may be performed after pouring the suspension into a mold.
The mold may be a glass tube.
The (b) strong magnetic field applying step may be performed for 10 minutes to 24 hours.
Strength of the strong magnetic field may be in a range of 1T to 12T.
The strong pressure may be in a range of 50 MPa to 400 MPa.
The (c) pressure applying step may be performed by cold isostatic pressing.
A heating rate in the (d) sintering step may be in a range of 1° C./min. to 400° C./min.
Sintering temperature in the (d) sintering step may be in a range of 1,000° C. to 1,700° C.
The (d) sintering step may be performed for 5 minutes to 4 hours.
The (d) sintering step may be performed under pressure of 0 MPa to 700 MPa.
The (d) sintering step may be performed by pulse electric current sintering.
M may be selected from the group consisting of Ti, V, Cr, Nb, Ta, Zr, Hf, Mo, and Sc.
A may be selected from the group consisting of Al, Ge, Sn, Pb, P, S, Ga, As, Cd, In, Tl, and Si.
The ternary compound may be Nb4AlC3 or Ti3SiC2.
A ratio of the powder to the suspension may be 10% by volume to 60% by volume.
A ratio of the dispersing agent to the powder may be 0.1% by weight to 10% by weight.
The ratio of the dispersing agent to the powder may be preferably 1% by weight to 3% by weight.
A cylindrical sample having a dense laminate structure of layered ceramic grains was produced by dispersing, in 10 mL of water, 17.6 g of Nb4AlC3 ceramic powder, and 2% by weight of a polyethyleneimine dispersing agent relative to the weight of the powder, orientating the ternary compound Nb4AlC3 in a strong magnetic field of 12 T, and sintering. Moreover, the details thereof are as follows.
As for the Nb4AlC3 ceramic powder, used was one obtained by sintering powder of Nb, Al and C at an appropriate equivalent molar ratio to the chemical equivalent by spark plasma sintering, followed by powderizing. The average grain size of the Nb4AlC3 was 0.91 μm, and a surface area of the Nb4AlC3 ceramic powder was 10.18 m2/g.
The suspension obtained by the aforementioned dispersing process was poured into a mold formed of gypsum or porous alumina. Next, the mold with the suspension therein was placed in a strong magnetic field. After drying the suspension for 12 hours, a resulting compact was taken out, and subjected to cold isostatic pressing for 3 minutes under pressure of 350 MPa (
It was understood from the X-ray diffraction analysis and observation under a scanning electron microscope that the oriented Nb4AlC3 ceramic as produced had a layered microstructure as depicted in
On the oriented side surface (textured side surface, TSS), a main diffraction peak was belong to the (110) plane and (10L) plane (the spectrum depicted in the middle of
Accordingly, it was concluded by comparing between the etched top surface (
On the fracture surface, it was clearly observed that the Nb4AlC3 grains indicated cracks within and between layered grains (
Accordingly, in accordance with the orientation technique, the layered MAX phase could be built up to from nano-scale to milli-scale, namely to a layered bulk ceramic.
As depicted in
Specifically, the indentation on the top surface clearly was appeared as the isotropic square shape, and the diagonal lines of the indentation had length of 39.9 μm±0.7 μm and 40.1 μm±0.6 μm, respectively (
In
In
The Vickers hardness tested on the oriented top surface (11.39 GPa±0.26 GPa) was higher than the value measured on the oriented side surface (9.40 GPa±0.47 GPa) (for the measuring method, see Barsoum et al., “The MN+1AXN Phases: a New Class of Solids; Thermodynamically Stable Nanolaminates”, Prog. Solid State Chem. 28: 201-281 (2000)). The fact that these values were higher than the conventional values (3.7 GPa, see Hu et al., “In Situ Reaction Synthesis, Electrical and Thermal, and Mechanical Properties of Nb4AlC3”, J. Am. Ceram. Soc. 91: 2258-2263 (2008)) was owing to that oxides were present (about 15% by volume, calculated by converting the total area ratio in the SEM picture into a volume ratio) in the Nb4AlC3 matrix (
Further, bending strength and fracture toughness thereof were tested at room temperature. Here, the bending strength test was performed in accordance with the three-point bending test (sample size: 1.5 mm×2 mm×18 mm), and, the fracture toughness test was performed in according to the SENB test (sample size: 2 mm×4 mm×18 mm).
When the direction of the load applied was a vertical direction with respect to the basal plane of the Nb4AlC3 sample, bending strength was a high value, which was 1,185 MPa. When the direction of the load applied was a parallel direction with respect to the base plane of the Nb4AlC3 matrix, the measurement value of the bending strength was 1,214 MPa.
When the direction of the load applied was a vertical direction with respect to the basal plane of the Nb4AlC3 sample, moreover, fracture toughness was a high value, which was 20 MPa·m1/2. When the direction of the load applied was a parallel direction with respect to the base plane of the Nb4AlC3 matrix, the measurement value of the fracture toughness was 11 MPa·m1/2.
Comparing to the previously reported values (see Hu et al., “In Situ Reaction Synthesis, Electrical and Thermal, and Mechanical Properties of Nb4AlC3”, J. Am. Ceram. Soc. 91: 2258-2263 (2008)), these values were the highest values of bending strength for ceramics. There is no doubt that this ceramic has remarkable reliability in application.
Accordingly, the present invention has led to significantly remarkable mechanical properties of the oriented MAX phase by the design of the aforementioned microstructure.
After slip casting in a strong magnetic field of 12 T, Ti3SiC2, which is an oriented transition metal ternary compound, was produced successfully by spark plasma sintering.
As a parameter of a suspension optimized for slip casting, it was determined that 20% by volume of Ti3SiC2 powder relative to the suspension, and 1.5% by weight of polyethyleneimine (PEI) serving as a dispersing agent for the powder, relative to the powder were added into ion-exchanged water. This powder was obtained from a commercial route (manufactured by 3-one-2 Corp), and contained about 9.78% by weight of TiC. The average grain size of the Ti3SiC2 was about 0.36 μm. The resulting suspension was poured into a mold formed of gypsum or porous alumina.
In this operation, used were a steady magnetic field, which was vertical to the horizontal plane, and a rotating magnetic field, which was parallel to the horizontal plane. The rotating speed was set to 20 rpm. It was determined that the rotating magnetic field was more suitable for orientating the Ti3SiC2. After drying for 15 hours, this target for sintering was taken out, and subjected to cold isostatic pressing for 10 minutes at pressure of 392 MPa (
It was confirmed from the analysis of XRD and SEM that the preferential direction vertical to the magnetic direction of the Ti3SiC2 grain was along the c-axis of the crystal axis, as depicted in
Specifically, two (101) and (110) planes had clearly the strongest diffraction peaks on the oriented side surface (the spectrum depicted at the top of
It was also found here that the (00L) basal plane of the oriented Ti3SiC2 sample was parallel to the oriented top surface, and a layered microstructure of nano-scale to milli-scale was formed.
The values of the Vickers hardness tested on the oriented top surface and oriented side surface were 8.70 GPa±0.71 GPa, and 7.31 GPa±0.28 GPa, respectively (for a measuring method, see Barsoum et al., “The MN+1AXN Phases: a New Class of Solids; Thermodynamically Stable Nanolaminates”, Prog. Solid State Chem. 28: 201-281 (2000)). The higher hardness than the conventional value (about 4 GPa, see Barsoum et al., “The MN+1AXN Phases: a New Class of Solids; Thermodynamically Stable Nanolaminates”, Prog. Solid State Chem. 28: 201-281 (2000)) was measured probably because TiC was present in the matrix, and the grain size was small.
In any case, an isotopic mechanical response of the oriented Ti3SiC2 ceramic was verified as depicted in
There was no crack present in the body part along the c-axis (
It should be mentioned here that various compositions, preparation methods for a suspension, molding method, and sintering methods be used or performed to attain the oriented MAX phase. Such various process factors are within the spirit and scope of the present invention, and do not adversely affect the effects of the present invention. Therefore, these process factors are incorporated within the technical concept of the present invention.
The bending strength and fracture toughness are dramatically enhanced due to the layered microstructure of the MAX phase, and therefore, the oriented phase can be applied to wider fields compared to a ternary compound without orientation. The oriented MAX phase has, in addition to excellent mechanical characteristics, typical characteristics of MAX, such as oxidization resistance, self-lubricating properties, low friction coefficient, and excellent electric conductivity.
Because of the aforementioned physical properties, the oriented MAX phase is particularly suitable for the following applications.
(1) Use as structural parts of chemical or petrochemical plants, because the oriented MAX phase is low cost as a raw material, easily machined, used at high temperature and is resistant to corrosion.
(2) Use as high-temperature turbine parts, because the oriented MAX phase is acid resistant and creep resistant.
(3) Use as a structural material, because of an unparalleled combination of high bending strength and high fracture toughness, which cannot seen with other materials.
(4) Use as a wear resistant electric conductive material, because of excellent electric conductivity, self-lubricating properties, and low friction coefficient.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-104687 | Apr 2010 | JP | national |
This application is a continuation of PCT/JP2011/059908, filed on Apr. 22, 2011, which claims priority of Japanese application No. 2010-104687, filed on Apr. 30, 2010, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2011/059908 | Apr 2011 | US |
| Child | 13661756 | US |
