Ti al alloy valve stem and method of making the same

Abstract

The application discloses a TiAl alloy valve stem and a preparation method thereof, and belongs to the technical field of alloy materials. The method comprises the following steps: preparing a W alloyed TiAl alloy ingot by melting; rolling the TiAl alloy ingot to obtain a rolled bar; performing heat treatment on the rolled bar to obtain a sample; and performing surface machining on the sample to obtain the TiAl alloy valve stem. The TiAl alloy is W alloyed, so that the technical effect of improving the friction and wear performance between the TiAl alloy valve stem and a guide pipe is achieved.

Description

Technical Field

[0001] This invention relates to the field of alloy materials technology, and in particular to a TiAl alloy valve stem and its preparation method. Background Technology

[0002] γ-TiAl alloys have low density (3.8-4.2 g / cm³). 3 With high specific strength and specific modulus, as well as good wear resistance, creep resistance, and oxidation resistance, γ-TiAl is a lightweight, high-temperature resistant structural material with great application prospects. In the past two decades, some research and application work on γ-TiAl alloy valves has been carried out internationally. For example, General Motors, Ford, Honda, and Volvo have all conducted research and testing on engine valves made of TiAl-based alloys.

[0003] In recent years, a new class of β-solidified γ-TiAl alloys has emerged. These alloys undergo solidification through the β single-phase region (L+β→β), eliminating peritectic transformation reactions, resulting in fewer metallurgical defects. They can also be machined into various shapes, and the chamber and high-temperature strength of deformed parts is significantly superior to traditional γ-TiAl alloys. This provides strong support for the selection of materials for manufacturing high-performance TiAl valves. However, under uncoated conditions, the wear of TiAl valve stems and guides is higher than that of existing nitrided and chrome-plated valves under the same wear conditions. Therefore, the friction and wear performance between TiAl alloy valve stems and guides still needs improvement. Summary of the Invention

[0004] The main objective of this invention is to provide a TiAl alloy valve stem and its preparation method, aiming to solve the problem of insufficient friction and wear performance between the TiAl alloy valve stem and the guide tube.

[0005] To achieve the above objectives, the present invention provides a method for preparing a TiAl alloy valve stem, the method comprising:

[0006] Smelting to prepare W-alloyed TiAl alloy ingots;

[0007] The TiAl alloy ingot is rolled to obtain a rolled bar;

[0008] The rolled bar is heat-treated to obtain a sample;

[0009] The sample was surface-machined to prepare a TiAl alloy valve stem.

[0010] Optionally, the alloying main system in the TiAl alloy ingot is Ti-(40-45)Al-(1-5)Mn-(0-1.0)Mo by atomic percentage, and the W content in the TiAl alloy ingot is 0.1%-1.0%.

[0011] Optionally, the method of smelting to prepare W-alloyed TiAl alloy ingots includes vacuum induction, a combination of vacuum induction and vacuum self-consumption processes, and plasma arc.

[0012] Optionally, the step of rolling the TiAl alloy ingot to obtain a rolled bar includes:

[0013] The TiAl alloy ingot is heated to 1320-1380℃ and held at that temperature for 0.5-1 hour.

[0014] TiAl alloy ingots that have undergone heat preservation treatment are rolled in an atmospheric environment to obtain rolled bars.

[0015] Optionally, during the rolling process, the initial rolling temperature is 1250-1350℃ and the final rolling temperature is 1100-1150℃.

[0016] Optionally, the rolling process is a three-roll Y-type rolling process.

[0017] Optionally, the diameter of the rolled bar is 8-12 mm.

[0018] Optionally, the step of heat-treating the rolled bar to obtain the sample includes:

[0019] The rolled bar is solution treated at 1230-1280℃ for 0.5-1 hour, and then cooled.

[0020] The cooled rolled bar was subjected to an aging treatment at 760-850℃ for 3 hours to obtain the sample.

[0021] Optionally, after surface machining of the sample, the surface roughness of the TiAl alloy rod is Ra0.8.

[0022] In addition, to achieve the above objectives, the present invention also provides a TiAl alloy valve stem, which is prepared using the TiAl alloy valve stem preparation method described above.

[0023] The TiAl alloy valve stem and its preparation method provided by this invention utilize W alloy ingots to prepare TiAl alloy valve stems. Under uncoated conditions, the performance of TiAl alloy is enhanced by the addition of W element, improving the reciprocating sliding friction and wear performance between TiAl alloy valve stem and guide. The processing technology is relatively simple, and it can simultaneously improve alloy oxidation resistance and microstructure stability. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of the preparation method of the TiAl alloy valve stem according to an embodiment of the present invention;

[0025] Figure 2The image shows a physical photograph of the TiAl alloy valve stem according to an embodiment of the present invention.

[0026] Figure 3 The image shown is a physical representation of the TiAl alloy valve stem and guide assembly involved in the embodiments of the present invention.

[0027] Figure 4 This is a schematic diagram illustrating the working principle of the TiAl alloy valve stem according to an embodiment of the present invention.

[0028] Figure 5 The figures show the valve stem wear results of wear tests conducted on the embodiments and comparative examples of the present invention with PMF10E and 5520 guides, respectively.

[0029] Figure 6 The figures show the wear results of wear tests conducted on PMF10E and 5520 catheters in the embodiments and comparative examples of the present invention.

[0030] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0031] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0032] γ-TiAl alloys have low density (3.8-4.2 g / cm³). 3 γ-TiAl alloy is a lightweight, high-temperature resistant structural material with high specific strength and specific modulus, good wear resistance, creep resistance and oxidation resistance. In the past two decades, some research and application work on γ-TiAl alloy valves has been carried out internationally. For example, General Motors, Ford, Honda, and Volvo have all conducted research and testing on engine valves made of TiAl-based alloys. Practice has proved that engine intake and exhaust valves made of TiAl alloys can achieve the following: (1) significant reduction in spring force and inertial force; (2) 25% reduction in rocker arm force and 45% reduction in exhaust valve rod force; (3) 30% reduction in camshaft drive torque, which can further reduce the weight of rocker arms and camshafts; (4) improved durability; (5) 1% reduction in fuel consumption under fixed operating conditions, comprehensive energy saving of more than 5%, significant reduction in noise and emissions, and significant improvement in the overall performance of the engine. It can be seen that using TiAl as a valve material will have a very promising application prospect.

[0033] It is worth noting that currently, the alloys used in the manufacture of TiAl valves abroad are still mainly traditional γ-TiAl alloys with (α2 / γ) two phases. These alloys have a high Al content (45-48 at.%), and a peritectic reaction (L+β→α) occurs during solidification, resulting in significant alloy composition segregation and a very narrow hot working window. Even during casting and machining, they are prone to cracking, and valve manufacturing is generally based on casting processes. Furthermore, the alloys have low high-temperature strength and service temperatures are generally below 650℃, making them unsuitable for higher-temperature applications. In recent years, a new type of β-solidified γ-TiAl alloy has emerged. This type of alloy undergoes solidification through the β single-phase region (L+β→β), eliminating the peritectic transformation reaction. It has fewer metallurgical defects and can be machined into various shapes. The chamber and high-temperature strength of deformed parts are significantly better than traditional γ-TiAl alloys, providing strong support for the selection of materials for high-performance TiAl valve manufacturing.

[0034] Studies have shown that deformed TiAl valves, manufactured through processes such as rolling, electric upsetting, die forging, heat treatment, and machining, exhibit significantly less overall valve wear and valve cone wear compared to surface-hardened Ni30 valves and uncoated In-751 valves under uncoated conditions and impact wear with existing seat ring materials, demonstrating excellent resistance to reciprocating impact wear of the seat ring. However, tests on the resistance to reciprocating sliding friction and wear between the deformed TiAl valve stem and guide revealed that, under uncoated conditions, the wear of both the TiAl valve stem and guide is higher than that of existing nitrided and chrome-plated valves under the same wear conditions.

[0035] Therefore, to improve the reciprocating sliding friction and wear performance between TiAl valve stems and guides, it is necessary to explore effective methods for improving the wear resistance of TiAl valves and guides from both the alloy itself and surface treatment perspectives, thereby promoting the mass commercial application of deformed TiAl valves. Compared with surface treatment methods, improving the wear resistance of the alloy itself not only takes into account the improvement of the alloy's own wear resistance and other mechanical properties, but also, on this basis, surface treatment will be more beneficial to improving the alloy's wear resistance. Therefore, exploring suitable methods for improving the wear resistance of TiAl alloys themselves, such as alloying methods, is particularly necessary.

[0036] This invention provides a method for preparing a TiAl alloy valve stem, referring to... Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of a method for preparing a TiAl alloy valve stem according to the present invention.

[0037] In this embodiment, the method for preparing the TiAl alloy valve stem includes:

[0038] Step S10: Melt and prepare W-alloyed TiAl alloy ingots;

[0039] Smelting refers to the process of melting solid metal into a liquid state, and ingots are the product of smelting. W-alloyed TiAl alloy ingots can be prepared by smelting W-free TiAl alloys and W-containing raw materials. In this embodiment, the main alloy system in the TiAl alloy ingot can be Ti-(40-45)Al-(1-5)Mn-(0-1.0)Mo, and the W content in the TiAl alloy ingot is controlled to be 0.1%-1.0%. This main system is a Ti-Al-Mn or Ti-Al-Mn-Mo β-solidified γ-TiAl alloy. Mn has a strong β-phase stabilizing effect, and Ti-Al-Mn alloys have the advantages of good hot deformability and low cost. Adding Mo to Ti-Al-Mn alloys can improve the stability of the alloy structure. However, valve stems made solely using Ti-Al-Mn or Ti-Al-Mn-Mo alloys still suffer from insufficient friction and wear resistance with the guide tube. Adding W to the above two systems can improve the friction and wear performance between the valve stem and the guide while improving the alloy's oxidation resistance.

[0040] Methods for preparing W-alloyed TiAl alloy ingots through smelting can include vacuum induction, a combination of vacuum induction and vacuum consumable processes, and plasma arc melting. The raw materials for smelting can be Ti-Al-Mn alloys and W raw materials, or Ti-Al-Mn-Mo alloys and W raw materials, proportioned according to atomic percentages. Alternatively, sponge titanium, industrial pure aluminum, purified manganese, aluminum-molybdenum master alloys, and aluminum-tungsten master alloys can also be used, proportioned according to atomic percentages. The smelting process described above should be selected based on actual needs.

[0041] Step S20: Roll the TiAl alloy ingot to obtain a rolled bar;

[0042] Rolling can shape alloy ingots into the required shapes. In this embodiment, valve stems are prepared, so the alloy ingots can be rolled into bars for easy subsequent processing.

[0043] In some feasible implementations, the step of rolling TiAl alloy ingots to obtain rolled bars may include:

[0044] Step S21: Heat the TiAl alloy ingot to 1320-1380℃ and hold for 0.5-1h;

[0045] Heating and heat preservation treatment can control the microstructure of alloy ingots.

[0046] Step S22: Roll the TiAl alloy ingot after heat preservation treatment in an atmospheric environment to obtain a rolled bar.

[0047] Rolling can reduce the cross-section and increase the length of alloy ingots, making it suitable for processing bars. The rolling method used can be three-roll Y-rolling, with an initial rolling temperature in the range of 1250-1350℃ and a final rolling temperature in the range of 1100-1150℃. The diameter of the rolled bar can be 8-12mm. The three-roll Y-rolling process uses three rolls at 120° angles to process the material. The rolls can compress the workpiece simultaneously from three directions, and the roll positions can be changed, thus subjecting the workpiece to forces in all directions and ensuring uniform deformation.

[0048] Step S30: The rolled bar is heat-treated to obtain a sample;

[0049] Heat treatment is a metal hot working process that involves heating, holding, and cooling materials in a solid state to obtain the desired microstructure and properties. Heat treating rolled bars at a specific temperature can yield samples with the desired properties.

[0050] In some feasible implementations, the step of heat-treating the rolled bar to obtain a sample may include:

[0051] Step S31: The rolled bar is solution treated at 1230-1280℃ for 0.5-1 hour and then cooled;

[0052] Step S32: The cooled rolled bar is subjected to aging treatment at 760-850℃ for 3 hours to obtain the sample.

[0053] Within a temperature range of 1230-1280℃, the alloy exists in a single-phase region. Holding at this temperature for 0.5-1 hour can fully dissolve the excess phase into the solid solution, resulting in a supersaturated solid solution upon cooling. Cooling can be achieved through air cooling or furnace cooling. Further aging treatment at a relatively lower temperature range of 760-850℃ is then performed. This is expected to increase the alloy's hardness and strength, while reducing its plasticity and internal stress, thus ensuring the sample's performance meets the desired requirements.

[0054] Step S40: Perform surface machining on the sample to prepare a TiAl alloy valve stem.

[0055] The surface machining method can be milling or turning to prepare the sample to the required dimensions and surface roughness. The surface roughness of the machined sample can be Ra0.8 to meet the surface roughness requirements of the valve stem.

[0056] In this embodiment, addressing the problem of insufficient friction and wear performance of valve stems and guides made from easily deformable Ti-Al-Mn-Mo β-solidified γ-TiAl alloys, an alloying method is provided to improve the reciprocating sliding friction and wear performance between TiAl alloy valve stems and guides. This method requires the deformed TiAl alloy to undergo W alloying, with the alloying content controlled at 0.1-1.0 at.%. This invention utilizes trace W alloying to significantly improve the reciprocating sliding friction and wear performance between TiAl valve stems and guides without coating. The process is simple and simultaneously improves alloy oxidation resistance and microstructure stability, providing a strong foundation for the integrated manufacturing of high wear-resistant TiAl components.

[0057] This invention also provides a TiAl alloy valve stem, see [link / reference]. Figure 2 , Figure 2 The image shows a physical picture of a TiAl alloy valve stem, which was prepared using the TiAl alloy valve stem preparation method described above. Figure 3 A physical image of a TiAl alloy valve stem and guide assembly, as shown below. Figure 3 As shown, the guide tube is fitted onto the rod-shaped valve stem during use, and the guide tube can reciprocate in the direction of the valve stem.

[0058] Figure 4 A schematic diagram of the working principle of the valve stem and guide, such as... Figure 4 As shown, valve stem 1 and guide 2 are paired. One end of valve stem 1 is connected to transmission component 3. The rotation of camshaft 4 causes transmission component 3 to change position, which in turn causes valve stem 1 to change position. Valve stem 1 and guide 2 generate relative reciprocating motion. During the continuous reciprocating motion, friction and wear occur between valve stem 1 and guide 2.

[0059] Example 1

[0060] The TiAl alloy ingot with W alloying has the following composition: Ti-42Al-5Mn-0.4Mo-0.4W. The alloy valve stem fabrication process is as follows:

[0061] (1) Ti-44Al-3Mn-0.4Mo-0.4W ingots were prepared by vacuum induction melting, i.e., the W content in the Mo-containing ingots was controlled at 0.4 at.%. Two furnaces were smelted, denoted as Example 1-1 and Example 1-2. Each furnace ingot weighed 20 kg and had the following dimensions: The main raw materials for alloy preparation were sponge titanium, industrial aluminum, purified manganese, aluminum-molybdenum master alloy, and aluminum-tungsten master alloy. The O, N, and H contents in the ingots were analyzed using a TCH600 oxygen, nitrogen, and hydrogen analyzer, and the Al, Mn, W, and Mo contents in the ingots were analyzed using inductively coupled plasma atomic emission spectrometry. The chemical composition analysis results for Examples 1-1 and 1-2 are shown in Table 1.

[0062] (2) The ingot is hot rolled and deformed. The hot rolling deformation is carried out by a three-roll Y-type mill in one pass to roll into a bar with a diameter of 12mm. The initial deformation temperature of the rolling is 1380℃.

[0063] (3) The hot-rolled bar is subjected to a high temperature treatment of 1270℃ for 30 minutes and air cooling. Then it is treated at 850℃ for 3 hours and furnace cooling is used.

[0064] (4) The bar is ground and polished to achieve a surface roughness of Ra0.8.

[0065] (5) The wear behavior between the TiAl rod of Example 1 and the conduits of PMF10E and 5520 materials was tested. The test conditions are shown in Table 2.

[0066] (6) Quantitatively measure and record the weight of the valve stem and guide before and after the test, calculate the weight change of the valve stem and guide after wear, and compare the results as follows: Figure 5 and Figure 6 As shown, Figure 5 This is a graph showing the test results for valve stem wear. Figure 6 The graph shows the test results for the wear of the conduit.

[0067] Comparative Example 1

[0068] The TiAl alloy ingot has the composition Ti-42Al-5Mn-0.4Mo. The alloy valve stem fabrication process is as follows:

[0069] (1) Ti-44Al-3Mn-0.4Mo ingots were prepared by vacuum induction melting. Two furnaces were smelted, denoted as Comparative Example 1-1 and Comparative Example 1-2. Each ingot weighed 20 kg and had the following dimensions: The main raw materials for alloy preparation were sponge titanium, industrial aluminum, purified manganese, and aluminum-molybdenum master alloy. The O, N, and H contents in the ingots were analyzed using a TCH600 oxygen, nitrogen, and hydrogen analyzer, and the Al, Mn, and Mo contents in the ingots were analyzed using inductively coupled plasma atomic emission spectrometry. The chemical composition analysis results for Comparative Examples 1-1 and 1-2 are shown in Table 1.

[0070] (2) The ingot is hot rolled and deformed. The hot rolling deformation is carried out by a three-roll Y-type mill in one pass to roll into a bar with a diameter of 12mm. The initial deformation temperature of the rolling is 1380℃.

[0071] (3) The hot-rolled bar is subjected to a high temperature treatment of 1270℃ for 30 minutes and air cooling. Then it is treated at 850℃ for 3 hours and furnace cooling is used.

[0072] (4) The bar is ground and polished to achieve a surface roughness of Ra0.8.

[0073] (5) The wear behavior between the TiAl rod of Comparative Example 1 and the conduits of PMF10E and 5520 materials was tested. The test conditions are shown in Table 2.

[0074] (6) Quantitatively measure and record the weight of the valve stem and guide before and after the test, calculate the weight change of the valve stem and guide after wear, and compare the results as follows: Figure 5 and Figure 6 As shown.

[0075] Test and Result Analysis

[0076] Table 1

[0077]

[0078] Table 2

[0079]

[0080] Figure 5 Table 2 shows the valve stem wear results after testing Comparative Examples 1-1, 1-2, 1-1, and 1-2 with guides made of 5520 and PMF10E materials under the test conditions shown in Table 2. Figure 6 Table 2 shows the wear results of catheters made of Comparative Example 1-1, Comparative Example 1-2, Example 1-1, and Example 1-2 compared to catheters made of 5520 and PMF10E materials, tested under the conditions shown in Table 2. (Comparison) Figure 5 and Figure 6 The wear of the valve stems shows that, under the test conditions shown in Table 2, the Ti-42Al-5Mn-0.4Mo alloyed with W exhibits similar patterns when paired with both 5520 and PMF10E valve stems. Specifically, after W alloying, when paired with the 5520 valve stem, the valve stem wear decreased from 0.0217g to 0.0181g, a reduction of 16.6%; the valve stem wear decreased from 1.06705g to 0.8089g, a reduction of 24%. When paired with the PMF10E valve stem, the valve stem wear decreased from 0.00985g to 0.0048g, a reduction of 51.3%; the valve stem wear decreased from 0.19135g to 0.16295g, a reduction of 14.8%. The above test results show that the W alloying provided by the present invention can significantly improve the resistance to sliding friction of the duct in the deformed TiAl alloy, which will provide strong technical support for the manufacturing and application of high-performance deformed TiAl valves.

[0081] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0082] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0083] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing a TiAl alloy valve stem, characterized in that, The preparation method includes the following steps: A TiAl alloy ingot with W alloying is prepared by melting and smelting, wherein the main alloy system in the TiAl alloy ingot is Ti-(40-45)Al-(1-5)Mn-(0-1.0)Mo by atomic percentage; The TiAl alloy ingot is heated to 1320-1380℃ and held at that temperature for 0.5-1 hour. In an atmospheric environment, a three-roll Y-type rolling mill is used to roll the heat-insulated TiAl alloy ingot in one or more passes; The hot-rolled bar is solution treated at 1230-1280℃ for 0.5-1 hour, and then air-cooled. The air-cooled rolled bar was subjected to an aging treatment at 760–850°C for 3 hours, followed by furnace cooling to obtain the sample. The sample was surface-machined to prepare a TiAl alloy valve stem, wherein the roughness of the TiAl alloy valve stem reached Ra0.

8.

2. The method for preparing the TiAl alloy valve stem as described in claim 1, characterized in that, The methods for preparing W-alloyed TiAl alloy ingots by smelting include vacuum induction, a combination of vacuum induction and vacuum self-consumption processes, and plasma arc.

3. The method for preparing the TiAl alloy valve stem as described in claim 1, characterized in that, During the rolling process, the initial rolling temperature is 1250-1350℃, and the final rolling temperature is 1100-1150℃.

4. The method for preparing the TiAl alloy valve stem as described in claim 1, characterized in that, The diameter of the rolled bar is 8-12 mm.

5. A TiAl alloy valve stem, characterized in that, The TiAl alloy valve stem was prepared using the preparation method described in any one of claims 1-4.

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