Titanium aluminide coating capable of improving high-temperature oxidation resistance of titanium alloy and preparation method thereof

Abstract

A titanium aluminide (TiAl) coating capable of improving high-temperature oxidation resistance of titanium alloys and a preparation method thereof are provided. The TiAl coating includes α-AlF.sub.3 nanoparticles, and a content of the α-AlF.sub.3 nanoparticles is 5-30 vol. % of the TiAl coating. The preparation method of the TiAl coating includes: using a TiAl alloy target and an α-AlF.sub.3 target as raw materials, and performing magnetron sputtering on a substrate surface to prepare a coating; the magnetron sputtering is double-target co-sputtering, and a substrate temperature during the magnetron sputtering is 150° C., the TiAl alloy target is performed direct current sputtering with a power of 0.5-2 kW, and the α-AlF.sub.3 target is performed radio frequency sputtering with a power of 0.07-0.2 kW. After the coating is obtained by the double-target co-sputtering, the obtained coating is heat-treated at 600-800° C. for 5-20 h to obtain a final coating.

Claims

1. A titanium aluminide (TiAl) coating capable of improving a high-temperature oxidation resistance of titanium alloys, wherein the TiAl coating comprises alpha-aluminum fluoride (α-AlF.sub.3) nanoparticles, and a content of the α-AlF.sub.3 nanoparticles is 5-30 volume percent (vol. %) of the TiAl coating; and wherein the TiAl coating is prepared by using a TiAl alloy target and an α-AlF.sub.3 target as raw materials, and a content of Al in the TiAl alloy target is 35-45 atomic percent (at. %) of a total amount of the TiAl alloy target.

2. The TiAl coating according to claim 1, wherein a thickness of the TiAl coating is in a range of 2-15 micrometres (μm).

3. A preparation method for the TiAl coating according to claim 1, comprising: performing magnetron sputtering on a substrate surface by using the TiAl alloy target and the α-AlF.sub.3 target as the raw materials to prepare a coating.

4. The preparation method according to claim 3, wherein a preparation method of the TiAl alloy target comprises: uniformly mixing a Ti powder and an Al powder to obtain a mixture powder, and performing hot isostatic pressing on the mixture powder to obtain the TiAl alloy target; and wherein a preparation method of the α-AlF.sub.3 target comprises: performing hot isostatic pressing on an α-AlF.sub.3 ceramic powder to obtain the α-AlF.sub.3 target.

5. The preparation method according to claim 4, wherein each of particle sizes of the Ti powder and the Al powder is in a range of 1-50 μm, an amount of the Al powder is 35-45 atomic percent (at. %) of a total amount of the Ti powder and the Al powder, and a purity of the α-AlF.sub.3 ceramic powder is greater than 99.99 percent (%).

6. The preparation method according to claim 4, wherein the uniformly mixing a Ti powder and an Al powder comprises: mixing the Ti powder and the Al powder at a rotating speed of 80-150 revolutions per minute (r/min) for 4-10 hours (h); and wherein a holding pressure temperature of the hot isostatic pressing of the mixture power is in a range of 1100-1300 celsius degrees (° C.), an isostatic pressure of the hot isostatic pressing of the mixture power is in a range of 130-190 megapascals (MPa), and a holding temperature and pressure time of the hot isostatic pressing of the mixture power is in a range of 2-6 h.

7. The preparation method according to claim 4, wherein a holding pressure temperature of the hot isostatic pressing of the α-AlF.sub.3 ceramic powder is in a range of 1700-1800° C., an isostatic pressure of the hot isostatic pressing of the α-AlF.sub.3 ceramic powder is in a range of 130-190 MPa, and a holding temperature and pressure time of the hot isostatic pressing of the α-AlF.sub.3 ceramic powder is in a range of 1-5 h.

8. The preparation method according to claim 3, wherein the magnetron sputtering is double-target co-sputtering, a substrate temperature during the magnetron sputtering is 150° C., the TiAl alloy target is performed direct current (DC) sputtering with a power of 0.5-2 kW, and the α-AlF.sub.3 target is performed radio frequency (RF) sputtering with a power of 0.07-0.2 kW.

9. The preparation method according to claim 8, wherein a sputtering time of the double-target co-sputtering is in a range of 8-20 h, and the double-target co-sputtering is performed under an environment of an Argon (Ar) gas pressure of 0.5-3 Pa.

10. The preparation method according to claim 3, further comprising: a coating post-treatment comprising: performing a heat treatment on the coating prepared by the magnetron sputtering at 600-800° C. for 5-20 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to more clearly explain the embodiments of the present disclosure or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and for those skilled in the art, other drawings could be obtained according to these drawings without paying creative efforts.

(2) FIG. 1 illustrates a process flow diagram for the preparation method of a TiAl coating to improve the high-temperature oxidation resistance of titanium alloys.

(3) FIG. 2 illustrates a standard Gibbs reaction free energy curve of AlF.sub.3 with Al atoms in the coating.

(4) FIG. 3 illustrates a standard Gibbs reaction free energy curve of AlF.sub.3 with Ti atoms in the coating.

(5) FIG. 4 illustrates a scanning transmission electron microscope analysis diagram of the coating prepared in Embodiment 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) Now various exemplary embodiments of the present disclosure will be described in detail. This detailed description should not be considered as a limitation of the present disclosure, but should be understood as a more detailed description of some aspects, characteristics and embodiments of the present disclosure.

(7) It should be understood that the terms used in this disclosure are only for describing specific embodiments, and are not used to limit the disclosure. In addition, for the numerical range in the present disclosure, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Any stated value or intermediate value within the stated range and any other stated value or every smaller range between intermediate values within the stated range are also included in the present disclosure. The upper and lower limits of these smaller ranges could be independently included or excluded from the range.

(8) Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by the those skilled in the art of this disclosure. Although the present disclosure only describes the preferred methods and materials, any methods and materials similar or equivalent to those described herein could also be used in the practice or testing of the present disclosure. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and/or materials related to the documents. In case of conflict with any incorporated documents, the contents of this specification shall prevail.

(9) Without departing from the scope or spirit of the present disclosure, it is obvious to those skilled in the art that modifications and changes could be made to the specific embodiments of the present disclosure. Other embodiments obtained from the description of the present disclosure will be obvious to those skilled in the art. The description and embodiments of the present disclosure are exemplary only.

(10) The terms “including”, “comprising”, “having”, “containing” and so on used in this description are all open-ended terms, which mean including but not limited to.

Embodiment 1

(11) (1) Preparation of the target material:

(12) The alloy is prepared according to the following components: Al: 40 at. %; Ti: the balance (the particle size is 44 μm), the above powders are mixed in a ball milling tank at a speed of 110 r/min for 6 h, and then pressed into the TiAl target of ϕ20×3 mm.sup.3 by the hot isostatic pressing machine, with the pressure holding temperature of 1250° C., the isostatic pressure of 160 MPa and the holding pressure and temperature time of 3 h. Drying and pressing high purity α-AlF.sub.3 ceramic powder (particle size 37 μm) into α-AlF.sub.3 target with ϕ20×3 mm.sup.3 by the hot isostatic pressing machine, with the pressure holding temperature of 1750° C., the hot isostatic pressing pressure of 160 MPa, and the holding pressure and temperature time of 2 h.

(13) (2) Coating Preparation:

(14) Installing the TiAl target and the α-AlF.sub.3 target on the magnetron coater, installing the Ti60 titanium alloy substrate after the surface pre-treatment (sanding with 800# and 1500# sandpaper in sequence, followed by ultrasonic cleaning with acetone and alcohol and then drying), adjusting the target-base distance to 12 centimetres (cm); using the mechanical pump and diffusion pump to pump the background vacuum to 1×10.sup.−4 Pa; heating the substrate to 150° C.; turning on the flow meter and introducing argon gas to achieve a working pressure of 0.7 Pa; turning on the direct current (DC) and radio frequency (RF) power supplies corresponding to the TiAl and α-AlF.sub.3 targets respectively, with powers of 1.0 kW and 0.12 kW respectively, and sputtering for 10 h; keeping the vacuum chamber under vacuum until cooling down to a room temperature and taking out the sample.

(15) (3) Coating Post-Treatment:

(16) Putting the sample in a high-temperature vacuum furnace, vacuumizing until the air pressure is 0.05 Pa, raising the temperature to 650° C., keeping the temperature for 15 h, and then cooling to the room temperature with the furnace to obtain a new TiAl coating.

(17) The thickness of the TiAl coating is measured to be 12.3 μm.

(18) The standard Gibbs reaction free energies between AlF.sub.3 and Al atoms and Ti atoms in the coating are calculated, and drawing the curve. The specific method is as follows:

(19) Determining the chemical reaction equations of AlF.sub.3 with Al and Ti atoms as AlF.sub.3(s)+2Al(s)=3AlF(g) and 4AlF.sub.3(s)+3Ti(s)=3TiF.sub.4(g)+4A1(s) respectively. Then finding the specific heat capacity, phase transition heat capacity and enthalpy and entropy of formation at 298K of each reactant and product in Practical Inorganic Thermodynamic Data Manual. Then calculating the reaction enthalpy and entropy at 298K according to the chemical reaction equation, and the functional relations between specific heat capacity and temperature of phase transition is considered. Finally, the Gibbs free energy changing with temperature is obtained according to the relationship between Gibbs free energy and specific heat capacity, temperature, enthalpy and entropy at 298 K.

(20) The obtained standard Gibbs reaction free energy curve of AlF.sub.3 and Al atoms in the coating is shown in FIG. 2, and the standard Gibbs reaction free energy curve of AlF.sub.3 and Ti atoms in the coating is shown in FIG. 3.

(21) Thermodynamic results show that α-AlF.sub.3 will be transformed into β-AlF.sub.3 when heated above 454° C., and the latter could combine with Al atoms to form gaseous AlF aluminum source carrier, which significantly improves the activity of Al (see FIG. 2). And both α-AlF.sub.3 and β-AlF.sub.3 do not react with Ti (see FIG. 3), so that F could exert the maximum activation effect on Al, thus significantly improving the oxidation resistance of the coating. Therefore, using stable α-AlF.sub.3 nanoparticles instead of solid solution F atoms as fluorine source is an effective measure to overcome the limited activation degree of Al in F-modified TiAl coating and improve the oxidation resistance.

(22) Analyzing the distribution of AlF.sub.3 in the coating using scanning-transmission electron microscopy as shown in FIG. 4. The results of the EDS analysis of the locations marked in FIG. 4 are shown in TBL 1.

(23) TABLE-US-00001 TABLE 1 Composition/at.% Position Al Ti F 1 23.61 5.32 71.07 2 22.69 6.07 71.24 3 23.97 5.09 70.94 4 24.03 5.54 70.43 5 22.54 4.93 72.53

(24) As can be seen from the table above, F is mainly present in the form of AlF.sub.3 compounds (with an atomic ratio of Al to F of approximately 1:3), distributed at the TiAl grain boundaries. The Al content of the matrix phase in the coating is about 38.6 at. %. The AlF.sub.3 nanoparticle content is calculated to be approximately 18.0 vol. % according to image processing techniques (the conversion gives an F atomic content of 8.3 at. % in the coating, the conversion formula is as follows:

(25) $F\left(\mathrm{at}.\%\right)=\frac{3n_{A{\mathrm{lF}}_3}}{4n_{A{\mathrm{lF}}_3}+2n_{\mathrm{TiA}1}}=\frac{\frac{3{\rho }_{A{\mathrm{lF}}_3}{V}_{A{\mathrm{lF}}_3}}{M_{A{\mathrm{lF}}_3}}}{\frac{4{\rho }_{A{\mathrm{lF}}_3}{V}_{A{\mathrm{lF}}_3}}{M_{A{\mathrm{lF}}_3}}+\frac{2{\rho }_{\mathrm{TiA}}{V}_{\mathrm{TiA}}}{M_{\mathrm{TiA}}}}=\frac{0.051x}{0.12-0.052x},$$x\mathrm{is}\mathrm{the}$
volume content of AlF.sub.3 particles). Coating the surface of the sample except the coating with anti-high temperature oxidation coating, drying and weighing the sample, then putting the sample in a high temperature tube furnace, keeping the temperature at 670° C. for 500 h, and then air-cooling to the room temperature. Observing that the surface of the sample is intact without peeling off, and the weight gain per unit area of the coating obtained by weighing is 0.08 mg/cm.sup.2.

Embodiment 2

(26) Embodiment 2 is the same as Embodiment 1, except that the power supply power of the α-AlF.sub.3 target is 0.18 kW.

(27) The measured thickness of the coating is 12.4 μm, and the content of the matrix phase Al in the coating is about 38.7 at. %, and the content of AlF.sub.3 nanoparticles is about 25.4 vol. % (the converted F atom content is 12.1 at. %). Coating the surface of the sample except the coating with anti-high temperature oxidation coating, drying, weighing the sample, and putting the sample in a high temperature tube furnace, keeping the temperature at 670° C. for 500 h, and then air-cooling to the room temperature. Observing the sample, the coating does not peel off, and the weight gain per unit area of the coating is 0.05 mg/cm.sup.2.

Embodiment 3

(28) The same as Embodiment 1, except that the power supply of the TiAl target is 0.6 kW.

(29) The measured thickness of the coating is 7.3 μm, and the content of matrix phase Al in the coating is about 38.4 at. %, and the content of AlF.sub.3 nanoparticles is about 28.4 vol. %. Coating the surface of the sample except the coating with anti-high temperature oxidation coating, drying, weighing the sample, and putting the sample in a high temperature tube furnace, keeping the temperature at 670° C. for 500 h, and then air-cooling to the room temperature. The sample is observed the coating does not peel off, and the weight gain per unit area of the coating is 0.09 mg/cm.sup.2.

Embodiment 4

(30) The same as Embodiment 1, except that the ingredients of the TiAl target are Al: 43 at. % and Ti: the balance.

(31) The measured thickness of the coating is 12.3 μm, and the content of the matrix phase Al in the coating is about 41.2 at. %, and the content of the AlF.sub.3 nanoparticles is about 18.1 vol. %. Coating the surface of the sample except the coating with anti-high temperature oxidation coating, drying, weighing the sample, and putting the sample in a high temperature tube furnace, keeping the temperature at 670° C. for 500 h, and then air-cooling to the room temperature. Observing the sample, the coating does not peel off, and the weight gain per unit area of the coating is 0.06 mg/cm.sup.2.

Comparative Embodiment 1

(32) Comparative embodiment is the same as Embodiment 3, except that both the TiAl target and the α-AlF.sub.3 target use RF power supply.

(33) The measured thickness of the coating is 1.2 μm, and the content of matrix phase Al in the coating is about 38.3 at. %, and the content of the AlF.sub.3 nanoparticles is about 47.5 vol. %. Coating the surface of the sample except the coating with anti-high temperature oxidation coating, drying, weighing the sample, and putting the sample in a high temperature tube furnace, keeping the temperature at 670° C. for 500 h, and then air-cooling to the room temperature. Observing the sample, and finding that there is local cracking inside the coating, and the weight gain per unit area of the coating is 3.1 mg/cm.sup.2.

Comparative Embodiment 2

(34) Comparative embodiment 2 is the same as Embodiment 1, except that the ingredients of the TiAl target are Al: 28 at. % and Ti: the balance.

(35) The measured thickness of the coating is 12.3 μm, and the content of matrix phase Al in the coating is about 27.0 at. %, and the content of AlF.sub.3 nanoparticles is about 18.2 vol. %. Coating the surface of the sample except the coating with high-temperature oxidation resistant coating, drying, weighing, placing the sample in a high-temperature tube furnace, keeping the temperature at 670° C. for 500 h, and then air-cooling to the room temperature. Observing the sample, the oxide skin on the coating surface is obviously peeled off, and the weight gain per unit area of the coating by weighing is 2.1 mg/cm.sup.2.

Comparative Embodiment 3

(36) Depositing a TiAl coating on the Ti60 titanium alloy substrate. The deposition process is the same as in Embodiment 1, except that only a single TiAl target is sputtered, but no AlF.sub.3 target is sputtered. Using plasma immersion to inject the F atoms by a plasma injection machine. The plasma power supply is 500 W, the bias voltage is 10 kV, the gas is Ar/CH.sub.2F.sub.2, the working pressure is 0.5 Pa, the pulse width is 10 μs, and the F atoms are injected continuously for 5 min.

(37) The measured thickness of the coating is 12.3 μm, the content of substrate phase Al in the coating is about 38. 7 at. %, and the content of the F atoms in the coating is about 8 at. % (basically equivalent to the content of the F atoms in Embodiment 1). Coating the surface of the sample except the coating with high-temperature oxidation resistant coating, drying, weighing, placing the sample in a high-temperature tube furnace, keeping the temperature at 670° C. for 500 h, and then air-cooling to the room temperature. Observing the sample, and finding that the oxide skin on the coating surface has obvious peeling off, and the oxidation gain per unit area of the coating 1.7 mg/cm.sup.2 is obtained after weighing.

(38) The foregoing are only preferred embodiments of the disclosure and are not intended to limit the disclosure. Any modifications, equivalent substitutions and improvements etc. made within the spirit and principles of the disclosure shall fall in the scope of protection of the disclosure.