A high-strength composite ceramic based on matching high-temperature thermal expansion coefficient

Abstract

This invention relates to the field of special ceramic composite materials technology, and in particular to a high-strength composite ceramic based on matching high-temperature thermal expansion coefficients. This composite ceramic consists of two ceramic phases, A and W, wherein phase A is α-Al₂O₃, and the chemical formula of phase W is (W... 1‑ x Me x C, where 0.05 ≤ x ≤ 0.2; Me is Ti or Zr. The W phase is the phase with a thermal expansion coefficient matching that of the A phase at high temperatures. Within the temperature range of 600℃ to 1600℃, the difference Δ between the thermal expansion coefficients of the W and A phases remains within ±10%. This invention features a simple process and is easily scalable for large-scale industrial production. The composite ceramics prepared using this method exhibit high room temperature strength and high temperature strength retention; suitable for applications under high temperature, high pressure, and other extreme conditions, such as CNC cutting tools for machining high-temperature alloys.

Description

Technical Field

[0001] This invention relates to the field of special ceramic composite materials technology, and in particular to a high-strength composite ceramic based on matching high-temperature thermal expansion coefficients. Background Technology

[0002] The machining principle of high-temperature alloys mainly involves the shearing and friction of the cutting tool against the alloy, generating a large amount of heat. This heat locally softens the alloy, allowing for efficient machining. During this process, the tool surface is subjected to high temperature and high pressure. However, traditional special ceramic composite materials often exhibit internal stress due to a mismatch in their coefficients of thermal expansion under high temperature conditions. Under high pressure, the stress concentration causes cracks to propagate rapidly, leading to chipping and ultimately tool failure. Summary of the Invention

[0003] Based on the above, this invention provides a high-strength composite ceramic (hereinafter referred to as "composite ceramic") based on matching high-temperature thermal expansion coefficients. This composite ceramic consists of two ceramic phases, A and W. Phase A is α-Al₂O₃, and phase W is a phase whose thermal expansion coefficient matches that of phase A at high temperatures. Within the temperature range of 600℃ to 1600℃, the difference Δ between the thermal expansion coefficients of phase W and phase A remains within ±10% (-10% to +10%). The composite ceramic retains over 80% of its three-point bending strength, meeting the requirements of demanding applications such as machining high-temperature alloy cutting tools.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] One of the technical solutions of this invention is a W phase with the chemical formula (W 1-x Me x C, where 0.05≤x≤0.2; Me is Ti or Zr.

[0006] The second technical solution of the present invention is a method for preparing the above-mentioned W phase, comprising the following steps:

[0007] WC and MeC were mixed, ball-milled, dried, and heat-treated to obtain the W phase;

[0008] In the MeC, Me represents Ti or Zr.

[0009] The third technical solution of this invention is the application of the aforementioned W phase in the preparation of composite ceramics.

[0010] The fourth technical solution of the present invention is a composite ceramic, the raw materials of which include phase A and the aforementioned phase W; the phase A is α-Al2O3.

[0011] In a preferred embodiment of the present invention, the A phase comprises 40-75% by mass percentage, with the W phase as the remainder.

[0012] The fifth technical solution of the present invention is a method for preparing the above-mentioned composite ceramic, comprising the following steps:

[0013] The A phase and W phase are mixed, ball-milled, dried, pressed into a green body, and sintered to obtain the composite ceramic.

[0014] The sixth technical solution of the present invention is the application of the above-mentioned composite ceramics in the preparation of high-temperature alloy cutting tools.

[0015] The seventh technical solution of the present invention is a cutting tool for processing high-temperature alloys, the raw materials of which include the above-mentioned composite ceramics.

[0016] Invention concept:

[0017] Within a high operating temperature range, the matching thermal expansion coefficients of the phases in the composite ceramic are beneficial for alleviating internal stress concentration under high-temperature conditions and for improving the room temperature strength and high-temperature strength retention rate of the composite ceramic material.

[0018] The composite ceramic is composed of two ceramic phases, A and W. Phase A is α-Al2O3, and phase W is a phase whose thermal expansion coefficient matches that of phase A at high temperatures. Within the temperature range of 600℃ to 1600℃, the difference Δ between the thermal expansion coefficient of phase W and phase A is always kept within ±10%. The composite ceramic retains more than 80% of its three-point bending strength to meet the requirements of high-demand applications such as machining high-temperature alloy cutting tools.

[0019] To ensure that the difference Δ between the thermal expansion coefficients of the W phase and the A phase remains within ±10% in the temperature range of 600℃ to 1600℃, typical ceramic materials that might be used as the W phase, such as TiC, WC, ZrC, TiB2, and ZrO2, cannot meet this requirement. Figure 1 As shown.

[0020] This invention provides a W phase that maintains the difference Δ between the thermal expansion coefficient of the W phase and that of the A phase within ±10% (-10% to +10%) in the temperature range of 600℃ to 1600℃. This W phase is a solid solution carbide of tungsten and another transition metal, Me, with the chemical formula (W...). 1-x Me x C, where 0.05≤x≤0.2; Me is Ti or Zr. Using this W phase and A phase as raw materials to prepare composite ceramics, high room temperature strength and high temperature strength retention rates can be achieved.

[0021] The present invention discloses the following technical effects:

[0022] This invention provides a W phase whose thermal expansion coefficient matches that of the A phase α-Al2O3 of ceramics. In the range of 600℃ to 1600℃, the difference Δ between the thermal expansion coefficient of the W phase and that of the A phase is always kept within ±10% (-10% to +10%), thereby improving the room temperature strength and high temperature strength retention rate of composite ceramics prepared using the A phase and W phase as raw materials.

[0023] The process of this invention is simple and easy to prepare on a large industrial scale.

[0024] This invention is based on a high-strength composite ceramic with a high temperature thermal expansion coefficient matching, which has high room temperature strength and high temperature strength retention rate; it is suitable for applications under high temperature, high pressure and other extreme conditions, such as CNC cutting tools for machining high temperature alloys. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The coefficient of thermal expansion of phase A (α-Al2O3) and typical ceramic materials varies with temperature.

[0027] Figure 2 The thermal expansion coefficients of phase A and phase W1 prepared in Example 1 vary with temperature.

[0028] Figure 3 The thermal expansion coefficients of phase A and phase W2 prepared in Example 2 vary with temperature.

[0029] Figure 4 The three-point bending strength retention rate of the A / W1 sample prepared in Example 3.

[0030] Figure 5 The three-point bending strength retention rate of the A / W2 sample prepared in Example 4.

[0031] Figure 6 Backscattered scanning electron image of the A / W2 sample prepared in Example 4.

[0032] Figure 7 The image shows the XRD pattern of the A / W2 sample prepared in Example 4.

[0033] Figure 8 The wear morphology of the A / W2 sample prepared in Example 4 after processing.

[0034] Figure 9The wear morphology of the A / W2-R sample prepared for Comparative Example 2 after processing. Detailed Implementation

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0036] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0038] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0039] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0040] The first aspect of this invention provides a W phase with the chemical formula (W 1-x Me x C, where 0.05≤x≤0.2; Me is Ti or Zr.

[0041] The W phase is the phase with a thermal expansion coefficient that matches that of the A phase (α-Al₂O₃) in ceramics at high temperatures. Within the temperature range of 600℃ to 1600℃, the difference Δ between the thermal expansion coefficients of the W phase and the A phase remains within ±10% (-10% to +10%). The difference Δ = ((thermal expansion coefficient of W phase - thermal expansion coefficient of A phase) / thermal expansion coefficient of A phase) × 100%.

[0042] This invention also tried using other transition metal elements such as Ta, Nb, Hf, and Cr for Me. The results showed that the thermal expansion coefficient of the prepared W phase was significantly different from that of the A phase, and the effect was not as good as using Ti or Zr for Me.

[0043] A second aspect of the present invention provides a method for preparing the above-mentioned W phase, comprising the following steps:

[0044] WC and MeC were mixed, ball-milled, dried, and heat-treated to obtain the W phase;

[0045] In the MeC, Me represents Ti or Zr.

[0046] In a preferred embodiment of the present invention, the heat treatment temperature is 1700-1900℃ and the time is 1h-3h.

[0047] When the heat treatment temperature is below 1700℃ or the time is less than 1 hour, the Me element cannot overcome the diffusion activation energy to enter the WC lattice and form a uniform solid solution. When the heat treatment temperature is above 1900℃, the solid solution grain size will grow, which is not conducive to the subsequent preparation of fine-grained composite ceramics. When the heat treatment temperature is greater than 3 hours, the long-term heat treatment will not only cause the solid solution grain size to grow, but also cause the Me element to desorb and segregate on the grain surface.

[0048] The third aspect of this invention provides the application of the above-described W phase in the preparation of composite ceramics.

[0049] A fourth aspect of the present invention provides a composite ceramic, the raw materials of which include an A phase and the aforementioned W phase; wherein the A phase is α-Al2O3.

[0050] In a preferred embodiment of the present invention, the A phase comprises 40-75% by mass percentage, with the W phase as the remainder.

[0051] If the amount of phase A is lower or higher than the parameter range described above (and similarly, if the amount of phase W is higher than the range described above), the difference Δ between the thermal expansion coefficients of phase W and phase A will exceed ±10% (-10% to +10%), thereby affecting the high-temperature strength retention rate of the composite ceramic.

[0052] A fifth aspect of the present invention provides a method for preparing the above-mentioned composite ceramic, comprising the following steps:

[0053] The A phase and W phase are mixed, ball-milled, dried, pressed into a green body, and sintered to obtain the composite ceramic.

[0054] In a preferred embodiment of the present invention, the sintering is pressureless sintering or hot pressing sintering;

[0055] The pressureless sintering process specifically involves: first pressing the material into a green body, and then sintering it at 1550℃-1650℃ for 0.5h-2h;

[0056] The hot-pressing sintering specifically involves sintering at 1550℃-1650℃ for 0.5-2 hours under a pressure of 0.5-50 MPa.

[0057] The pressing process involves applying a pressure of 150 MPa to the blank and holding it for 15 seconds.

[0058] In pressureless sintering, when the pressing pressure is below 150 MPa, the green body has low density, resulting in insufficient density of the sintered composite ceramic. When the pressing pressure is above 150 MPa, delamination or cracking of the green body is likely to occur. When the holding time is less than 15 seconds, the elastic aftereffect of the ceramic green body cannot be adequately mitigated, and delamination or cracking of the green body is likely to occur during the depressurization process. Holding time more than 15 seconds has a negative impact on production efficiency.

[0059] In hot pressing sintering, the hot pressing sintering pressure is below 0.5MPa and cannot play an auxiliary sintering role. When it is above 50MPa, the mold life is significantly reduced and the cost is greatly increased.

[0060] In pressureless sintering and hot pressing, composite ceramics with low density and poor mechanical properties result in sintering temperatures below 1550℃. Sintering temperatures above 1650℃ cause abnormal grain growth, further deteriorating mechanical properties. Sintering times less than 0.5 hours cannot yield composite ceramics with high density and well-developed microstructure. Sintering times greater than 2 hours lead to significant grain growth, which is detrimental to mechanical properties.

[0061] The sixth aspect of the present invention provides the application of the above-described composite ceramic in the preparation of high-temperature alloy cutting tools.

[0062] The seventh aspect of the present invention provides a cutting tool for machining high-temperature alloys, the raw materials of which include the above-mentioned composite ceramics.

[0063] Unless otherwise specified, all raw materials used in the embodiments of this invention can be obtained through commercial channels.

[0064] Example 1

[0065] According to (W) 0.85 Ti 0.15 Weigh out the corresponding masses of WC and TiC raw materials according to the chemical formula of C. Add the above raw materials to a ball mill for wet milling, then dry the wet slurry and fill the dried mixture into a graphite boat. Heat treat the mixture in a sintering furnace at 1800℃ (heating rate 5℃ / min, heat treatment time 2h) to obtain the W1 phase. The thermal expansion coefficients of the A phase (α-Al2O3) and the W1 phase are compared as follows: Figure 2As shown, within the temperature range of 600℃ to 1600℃, the difference in thermal expansion coefficients Δ between the two phases remains within ±10%.

[0066] Example 2

[0067] According to (W) 0.95 Zr 0.05 Weigh out the corresponding masses of WC and ZrC raw materials according to the chemical formula of C. Add the above raw materials to a ball mill for wet milling, then dry the wet slurry and fill the dried mixture into a graphite boat. Heat treat the mixture in a sintering furnace at 1800℃ (heating rate 5℃ / min, heat treatment time 3h) to obtain the W2 phase. Compare the thermal expansion coefficients of the A phase (α-Al2O3) and the W2 phase as follows: Figure 3 As shown, within the temperature range of 600℃ to 1600℃, the difference in thermal expansion coefficients Δ between the two phases remains within ±10%.

[0068] Example 3

[0069] A phase A (α-Al₂O₃) with a mass fraction of 40% and a phase W₁ with a mass fraction of 60% were used as raw materials for the A / W₁ sample (composite ceramic). The raw materials were added to a ball mill for wet milling, and then the wet slurry was dried (drying at 70℃ for 2 hours). The dried mixture was filled into a mold and pressed into a green body using a press (pressing speed 15 mm / min, pressing pressure 150 MPa, holding time 15 s). The green body was then sintered without pressure in a sintering furnace at a sintering temperature of 1650℃ for 2 hours to obtain the composite ceramic. The room temperature and high temperature strength of the composite ceramic were tested, and the results are as follows: Figure 4 As shown, the strength retention rate = (high temperature strength / room temperature strength) × 100%. Within the temperature range of 600℃ to 1600℃, the three-point bending strength retention rate of sample A / W1 is over 80%.

[0070] Example 4

[0071] A phase with a mass fraction of 65% and a W2 phase with a mass fraction of 35% were used as raw materials for the A / W2 sample (composite ceramic). The raw materials were added to a ball mill for wet milling, and then the wet slurry was dried (drying at 70℃ for 2 hours). The dried mixture was filled into a mold and pressed into a green body using a press (pressing speed 15 mm / min, pressing pressure 150 MPa, holding time 15 s). The green body was hot-pressed and sintered in a sintering furnace at a sintering temperature of 1550℃, a sintering pressure of 50 MPa, and a sintering time of 1 hour to obtain the composite ceramic. The room temperature and high temperature strength of the composite ceramic were tested, and the results are as follows: Figure 5 As shown, the strength retention rate = (high temperature strength / room temperature strength) × 100%. Within the temperature range of 600℃ to 1600℃, the three-point bending strength retention rate of sample A / W2 is over 80%.

[0072] The backscattered scanning electron microscope was used to observe the microstructure of the A / W2 sample prepared in Example 4, as shown in the figure. Figure 6 As shown. By Figure 6 It can be seen that the microstructure of the composite ceramics does not show obvious pores and has good density; the A and W phases are evenly distributed, the microstructure is fine and dense, the grain size is small, and there is no abnormal grain growth.

[0073] X-ray diffraction (XRD) analysis was performed on the A / W2 sample prepared in Example 4, and its spectrum was plotted on [date missing]. Figure 7 .Depend on Figure 7 It can be seen that the diffraction peaks of the A and W phases in the composite ceramic are sharp, indicating good crystallinity. The phases are stable after sintering, without decomposition or phase separation.

[0074] Preparation of Comparative Example 1 (W3-W5)

[0075] W phase (W) 1-x Me x The raw material composition of C (where Me is Ti, Zr, or Ta, and correspondingly labeled W3, W4, and W5) is shown in Table 1, and the preparation method is the same as in Example 1. The difference Δ between the thermal expansion coefficients of the prepared W3, W4, and W5 and the A phase in the range of 600℃ to 1600℃ is statistically shown in Table 1.

[0076] Table 1

[0077] Sample Name Me x Minimum thermal expansion coefficient difference Δ from 600℃ to 1600℃, % W3 Ti 0.25 +14.5％ W4 Zr 0.01 +11.2％ W5 Ta 0.15 +12.7％

[0078] Comparative Example 2

[0079] The raw material composition of the composite ceramics (A / Wy, where y represents 1, 2, 3, 4, 5, and Wy corresponds to the W phases W1, W2, W3, W4, W5 prepared above) is shown in Table 2. In the table, A / W1-R represents composite ceramics with raw material composition of A and W1 but in a different ratio than in Example 3, and A / W2-R represents composite ceramics with raw material composition of A and W2 but in a different ratio than in Example 4. The preparation methods of A / W1-R and A / W3 are the same as in Example 3, and the preparation methods of A / W2-R, A / W4, and A / W5 are the same as in Example 4. The strength retention rate of the prepared composite ceramics at 1600℃ is statistically shown in Table 2.

[0080] Table 2

[0081] Sample Name A, mass % W, mass % Retention rate at 1600℃, % A / W1-R 35 65 68 A / W2-R 80 20 70 A / W3 40 60 45 A / W4 65 35 51 A / W5 65 35 43

[0082] Application Example 1

[0083] The A / W2 sample from Example 4 was machined into an insert, specification model RNGN120700T01020, for high-speed turning testing of a difficult-to-machine annealed high-temperature alloy (grade GH4169). The workpiece dimensions were D65mm*85mm round bar. The cutting parameters were V... c =400m / s, A p =1mm, f n =0.15mm / rev. Total cutting length is 255mm. The rake face wear, flank face wear width, and flank face wear length of sample A / W2 are 176.56μm, 558.58μm, and 1335.63μm, respectively. The insert is not chipped. See Figure 8 .

[0084] Application Comparative Example 1

[0085] The A / W2-R sample from Comparative Example 2 was machined into an insert, specification model RNGN120700T01020, for high-speed turning testing of a difficult-to-machine annealed high-temperature alloy (grade GH4169). The workpiece dimensions were D65mm*85mm round bar. The cutting parameters were V... c =400m / s, A p =1mm, f n =0.15mm / rev. Total cutting length is 255mm. The rake face wear, flank face wear width, and flank face wear length of the A / W2-R sample are 222.71μm, 785.04μm, and 4075.67μm, respectively. Small area defects are observed in the insert. Figure 9 .

[0086] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A composite ceramic, characterized in that, By mass percentage, the raw material comprises 40-75% A phase and the balance of W phase; the A phase is α-Al2O3. The chemical formula of the W phase is (W 1-x Me x C, where 0.05 ≤ x ≤ 0.2; Me is Ti or Zr; The preparation steps of the W phase include: WC and MeC were mixed, ball-milled, dried, and heat-treated to obtain the W phase; In MeC, Me represents Ti or Zr; The heat treatment temperature is 1700℃-1900℃, and the time is 1h-3h.

2. A method for preparing the composite ceramic according to claim 1, characterized in that, Includes the following steps: The A phase and W phase are mixed, ball-milled, dried, and sintered to obtain the composite ceramic.

3. The method for preparing composite ceramics according to claim 2, characterized in that, The sintering is either pressureless sintering or hot-press sintering; The pressureless sintering process specifically involves: first pressing the material into a green body, and then sintering it at 1550℃-1650℃ for 0.5h-2h; The hot pressing sintering specifically refers to sintering at 1550℃-1650℃ for 0.5h-2h under a pressure of 0.5-50MPa.

4. The application of the composite ceramic as described in claim 1 in the preparation of high-temperature alloy cutting tools.

5. A cutting tool for machining high-temperature alloys, characterized in that, The raw materials used in the preparation include the composite ceramic described in claim 1.

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