Preparation method of pollution-free eutectic Nb-Si directionally solidified alloy

Abstract

A preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy, which relates to a preparation method of a directionally solidified alloy. The present invention aims to solve the problem that the melt is polluted during the existing directional solidification preparation process, ultimately deteriorating the room temperature fracture toughness. The steps of the present invention are as follows: Step 1: Weigh alloy raw materials; Step 2: Melting and casting ingots; Step 3: Wire-cut the ingots cast in Step 2 into metal rods, clean and polish them to obtain metal rods without machining marks; Step 4: Prepare pure Nb ingots; Step 5: Prepare pure Nb tubes; Step 6: Place the metal rods in Step 3 into the pure Nb tubes in Step 5, and then place them in a vacuum directional solidification furnace for preparation. The prepared directionally solidified Nb-Si alloy ingots are cooled in Ga-In coolant to obtain eutectic Nb-Si directionally solidified alloys. The present invention is used for the melting and preparation of high melting point reactive alloy materials.

Description

Technical Field

[0001] The invention relates to a method for preparing a directional solidification alloy, in particular to a method for preparing a pollution-free eutectic Nb-Si directional solidification alloy, and belongs to the technical field of smelting and preparing high-melting-point active alloy materials. Background Art

[0002] Improving the efficiency of aircraft engines can reduce the emission of nitrogen oxides and non-volatile particulate matter, and achieve the goal of "green aviation" as soon as possible. Nb-Si alloy has become one of the candidate materials for the next generation of aircraft engine blades due to its higher service temperature and density. However, its low room temperature fracture toughness and difficulty in meeting the requirements of processing equipment have hindered its development. Directional solidification can achieve the growth of ingots in a specific direction, thereby greatly improving its axial mechanical properties. Therefore, directional solidification technology is widely used in the preparation of aircraft turbine engine blades.

[0003] Nb-Si alloy consists of room temperature toughened Nbss phase and high temperature strengthened silicide phase. The melting point of this in-situ self-generated composite material exceeds 1950℃. The alumina and yttria ceramic tubes widely used in the directional solidification preparation process react with Nb-Si based alloys, thereby contaminating the melt and eventually deteriorating the room temperature fracture toughness. Therefore, it is necessary to prepare a pollution-free eutectic Nb-Si directional solidification alloy to provide higher performance materials for the field of aircraft engine turbine blades in the future and promote the practical application and development of Nb-Si alloys.

[0004] In summary, in the existing directional solidification preparation process, since both alumina and yttria ceramic tubes react with Nb-Si based alloys, the melt is contaminated, which eventually worsens the room temperature fracture toughness. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that in the existing directional solidification preparation process, both alumina and yttria ceramic tubes react with Nb-Si based alloys, resulting in contamination of the melt and ultimately deterioration of room temperature fracture toughness. Further, a method for preparing a pollution-free eutectic Nb-Si directional solidification alloy is provided.

[0006] The technical solution of the present invention is: a method for preparing a pollution-free eutectic Nb-Si directionally solidified alloy comprises the following preparation steps:

[0007] Step 1: Weigh the alloy raw materials;

[0008] Weigh the elemental Si, Ti, ZrC and Nb in the ratio of 16% Si, 20% Ti, 2% ZrC and 62% Nb in atomic percentage, the total atomic percentage being 100%;

[0009] Step 2: Melting ingot;

[0010] Weigh the raw materials Nb, Si, Ti, and ZrC and sequentially place them into a non-consumable water-cooled copper crucible from top to bottom according to the order of particle size. Pre-vacuum the melting chamber to 5 Pa - 10 Pa, introduce argon for 20 - 30 seconds, and repeat this 3 - 6 times. Then, vacuum the melting chamber to 4×10 -3 Pa - 5×10 -3 Pa, and introduce protective argon to 300 Pa - 500 Pa, and then perform melting to obtain an ingot;

[0011] Step 3: Use wire cutting to cut the ingot cast in Step 2 into metal rods, and clean and polish them to obtain metal rods without machining marks;

[0012] Step 4: Prepare a pure Nb ingot;

[0013] Weigh the elemental raw material Nb and place it into a water-cooled copper crucible. Pre-vacuum the melting chamber to 5 Pa - 10 Pa, introduce argon for 20 - 30 seconds, and repeat this 3 - 5 times. Then, vacuum the melting chamber to 4×10 -3 Pa - 5×10 -3 Pa, introduce protective argon to 300 - 500 Pa, perform melting for ten minutes, and pour it into a graphite mold for casting to obtain a pure Nb ingot;

[0014] Step 5: Prepare a pure Nb tube;

[0015] Use electrical discharge wire cutting to cut the pure Nb ingot into a hollow tube, and clean and polish it to obtain a pure Nb tube without wire cutting marks;

[0016] Step 6: Preparation of a directionally solidified Nb - Si alloy;

[0017] Place the metal rod in Step 3 into the pure Nb tube in Step 5, and then place it in a vacuum directional solidification furnace. Vacuum it to 5×10 -3 Pa, introduce protective argon to 200 Pa, and then heat it. Raise the temperature to 2200 °C and hold it for 15 - 20 minutes. Start the experiment at a pulling rate of 1 μm / s - 20 μm / s. Cool the prepared directionally solidified Nb - Si alloy ingot in Ga - In coolant to obtain a eutectic Nb - Si directionally solidified alloy.

[0018] Furthermore, the expression of the directionally solidified Nb - Si alloy prepared in Step 6 is Nb - 16Si - 20Ti - 2ZrC.

[0019] Preferably, the alloy in Step 2 is melted 6 times.

[0020] Preferably, the metal rod in Step 3 is first polished with sandpaper to remove wire cutting marks, and then cleaned with alcohol.

[0021] Preferably, the pure Nb ingot is prepared by melting three times in step four.

[0022] Preferably, the drawing rate in step six is 1 μm / s.

[0023] Preferably, the drawing rate in step six is 4 μm / s.

[0024] Preferably, the drawing rate in step six is 20 μm / s.

[0025] The present invention has the following effects compared with the prior art:

[0026] The present invention uses reasonable alloying elements to prepare a eutectic Nb-Si-based alloy without primary phase, providing a new preparation method for pollution-free eutectic Nb-Si directional solidification alloy. The hollow tube prepared by the pure Nb ingot eliminates the pollution problem of the melt during the directional solidification process, improves the purity of the directional solidification Nb-Si-based alloy ingot, and effectively improves the room-temperature fracture toughness. Large-sized blades and other structural components can be prepared. Description of the Drawings

[0027] Figure 1 It is the microstructure diagram of the Nb-16Si-20Ti-2ZrC directional solidification Nb-Si alloy with a drawing rate of 1 μm / s in Example 1 of the present invention;

[0028] Figure 2 It is the microstructure diagram of the Nb-16Si-20Ti-2ZrC directional solidification Nb-Si alloy with a drawing rate of 20 μm / s in Example 2 of the present invention;

[0029] Figure 3 It is the XRD comparison schematic diagram of the directional solidification Nb-Si alloy in Example 1 and Example 2 of the present invention;

[0030] Figure 4 It is the schematic diagram of the comparison of the room-temperature fracture toughness values of the directional solidification Nb-Si alloy in Example 1 and Example 2 of the present invention. Detailed Embodiments

[0031] Detailed Embodiment 1: A preparation method for a pollution-free eutectic Nb-Si directional solidification alloy in this embodiment includes the following preparation steps:

[0032] Step 1: Weigh the alloy raw materials;

[0033] Weigh the elemental Si, Ti, ZrC, and Nb according to the atomic percentages of 16% Si, 20% Ti, 2% ZrC, and 62% Nb, and the total atomic percentage is 100%;

[0034] Step 2: Melt the ingot;

[0035] Weigh the raw materials Nb, Si, Ti, and ZrC, and sequentially place them into a non-consumable water-cooled copper crucible from top to bottom according to the order of particle size. Pre-vacuum the melting chamber to 5 Pa - 10 Pa, introduce argon for 20 - 30 seconds, and repeat this process 3 - 6 times. Then, evacuate the melting chamber to 4×10 -3 Pa - 5×10 -3 Pa, and then charge protective argon to 300 Pa - 500 Pa, and then carry out melting to obtain an Nb-Si alloy ingot;

[0036] Step 3: Cut the Nb-Si alloy ingot cast in Step 2 into metal rods using wire cutting, clean and polish them to obtain Nb-Si alloy metal rods without wire cutting processing marks;

[0037] Step 4: Prepare a pure Nb ingot;

[0038] Place the weighed elemental raw material Nb into a water-cooled copper crucible. Pre-vacuum the melting chamber to 5 Pa - 10 Pa, introduce argon for 20 - 30 seconds, and repeat this process 3 - 5 times. Then, evacuate the melting chamber to 4×10 -3 Pa - 5×10 -3 Pa, charge protective argon to 300 - 500 Pa, melt for ten minutes, and pour it into a graphite mold for casting to obtain a pure Nb ingot;

[0039] Step 5: Prepare a pure Nb tube;

[0040] Use electrical discharge wire cutting to cut the pure Nb ingot into a hollow metal tube, clean and polish it to obtain a pure Nb metal tube without wire cutting marks;

[0041] Step 6: Preparation of directionally solidified Nb-Si alloy;

[0042] Place the Nb-Si alloy metal rod in Step 3 into the pure Nb metal tube in Step 5, and then place it in a vacuum directional solidification furnace. Evacuate to 5×10 -3 Pa, introduce protective argon to 200 Pa, then heat, raise the temperature to 2200 °C and hold for 15 - 20 min, and start the experiment at a pulling rate of 1 μm / s - 20 μm / s. Cool the prepared directionally solidified Nb-Si alloy ingot in Ga-In coolant to obtain a eutectic Nb-Si directionally solidified alloy.

[0043] In this embodiment, the diameter of the Nb-Si alloy metal rod is similar to the inner diameter of the pure Nb metal tube, ensuring that the metal rod is in contact with the inner wall of the alumina tube.

[0044] In Step 1 of this embodiment, the purity of the elemental Nb sheet is >99.95 wt.%, in the form of a 1×1 cm sheet; the purity of the elemental polycrystalline Si is >99.99 wt.%, in the form of a 1-5 mm block; the purity of the elemental sponge-like Ti is >99.4 wt.%, in the form of 1-3 cm particles; and the purity of the elemental ZrC is >99.98 wt.%, in the form of 400-mesh powder.

[0045] The raw material elemental particles in Step 1 need to be pretreated before melting. The pretreatment process is as follows: pickling treatment, ultrasonic treatment, and drying treatment are carried out in sequence. Among them, the HF content in the pickling treatment is 1%-5%, the HNO3 content is 20-30%, and the H2O content is 65-79%.

[0046] In Step 2 of this embodiment, the argon filling value is 100-800 Pa.

[0047] Specific Embodiment 2: The expression of the directionally solidified Nb-Si alloy prepared in Step 6 of this embodiment is Nb-16Si-20Ti-2ZrC. Other compositions and connection relationships are the same as those in Specific Embodiment 1.

[0048] Specific Embodiment 3: In Step 2 of this embodiment, the alloy is melted 6 times. With this setting, it is convenient to obtain an alloy with more uniform composition and structure. Other compositions and connection relationships are the same as those in Specific Embodiment 1 or 2.

[0049] Specific Embodiment 4: In Step 3 of this embodiment, the metal rod is first polished with sandpaper to remove the wire cutting marks, and then cleaned with alcohol. With this setting, it is convenient to remove the processing marks during the wire cutting process and ensure... Other compositions and connection relationships are the same as those in Specific Embodiments 1, 2, or 3.

[0050] Specific Embodiment 5: In Step 4 of this embodiment, the pure Nb ingot is melted 3 times. With this setting, the occurrence of stirring blind spots is avoided. Other compositions and connection relationships are the same as those in Specific Embodiments 1, 2, 3, or 4.

[0051] Specific Embodiment 6: Combining Figure 1 With reference to this embodiment, the pulling rate in Step 6 of this embodiment is 1 μm / s. With this setting, a relatively large-sized Nbss phase can be obtained, which can increase its continuity, hinder the propagation of cracks, and improve the room-temperature fracture toughness. Other compositions and connection relationships are the same as those in Specific Embodiments 1, 2, 3, 4, or 5.

[0052] Specific Embodiment 7: The pulling rate in Step 6 of this embodiment is 4 μm / s. With this setting, an eutectic structure with moderate size can be obtained, taking into account both room-temperature mechanical properties and oxidation resistance. Other compositions and connection relationships are the same as those in Specific Embodiments 1, 2, 3, 4, 5, or 6.

[0053] Embodiment VIII: In combination with Figure 2 Describe this embodiment. In step six of this embodiment, the drawing rate is 20 μm / s. With such a setting, fine eutectic structures can be obtained, and a large number of phase interfaces can improve the room-temperature fracture toughness. Other compositions and connection relationships are the same as any one of Embodiments I to VII.

[0054] In combination with Figures 1 to 4 Describe the working principle of the present invention:

[0055] Example 1

[0056] A preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy includes the following steps:

[0057] Step 1: Weigh according to the atomic percentages of 16% Si, 20% Ti, 2% ZrC, and 62% Nb to obtain elemental materials. Si is small-sized blocky crystals, Ti is sponge blocks, ZrC is powder, and Nb is small-sized plates.

[0058] Step 2: Put the weighed raw materials into a non-consumable water-cooled copper crucible in order of particle size from top to bottom. Use a mechanical pump to evacuate the melting chamber to 15 Pa, introduce protective argon gas for 20 seconds, repeat three times, and then use a molecular pump to evacuate the melting chamber to 5×10 -3 Pa, fill with protective argon gas to 500 Pa, and then melt to obtain a Nb-Si alloy ingot. Cut the ingot into metal rods by electric discharge machining, use 400 - 800# water sandpaper to eliminate the cutting marks, and finally clean with alcohol. Put the Nb elemental material into a water-cooled crucible, evacuate to 8×10-3 Pa, introduce protective argon gas, melt for ten minutes to generate an ingot, and finally cast with a graphite mold. Cut the pure Nb ingot into a hollow metal tube, clean and polish to obtain a pure Nb metal tube without wire cutting marks; place the Nb-Si alloy metal rod in the pure Nb metal tube, place it in a directional solidification vacuum chamber, evacuate to 5×10 -3 Pa, introduce protective argon gas to 200 Pa, then heat, raise the temperature to 2200 °C and hold for 15 - 20 min, start the experiment at a drawing rate of 1 μm / s, and cool the prepared directionally solidified Nb-Si alloy ingot in Ga-In coolant.

[0059] It can be seen from Figure 1 that the Nb-Si-based directionally solidified alloy is a eutectic structure with a specific direction, and the Nbss / Nb 5 Si 3 dendritic eutectic structure phase sizes vary from 1 to 2 μm. In addition, there is also Nbss / Nb 5 Si 3The divorced eutectic structure has phase sizes ranging from 5 to 8 μm. The Nb-Si-based alloy prepared by the directional solidification of pure Nb tubes is free from the contamination of other impurities. Figure 3 The XRD results in 5 show that only Nbss and Nb 3 Si Figure 4 phases exist in the phase composition. As can be seen from 1 / 2 , the room-temperature fracture toughness of this alloy is 17.4 MPa·m

[0060] . In summary, the eutectic Nb-Si directional solidification alloy prepared in this example is pollution-free and has excellent mechanical properties. Compared with using yttrium oxide ceramic tubes, it has increased by 43%, promoting the application process of Nb-Si-based alloys in structural materials such as aeroengine blades.

[0061] Example 2

[0062] A preparation method of a pollution-free eutectic Nb-Si directional solidification alloy, comprising the following steps:

[0063] Step 1: Weigh according to atomic percentages of 16% Si, 20% Ti, 2% ZrC, and 62% Nb to obtain elemental materials. Si is small-sized blocky crystals, Ti is sponge-like blocks, ZrC is powder, and Nb is small-sized plates.

[0064] Step 2: Put the weighed raw materials into a non-consumable water-cooled copper crucible in order of decreasing particle size from top to bottom. Use a mechanical pump to evacuate the melting chamber to 15 Pa, introduce protective argon gas for 20 seconds, repeat three times, and then use a molecular pump to evacuate the melting chamber to 5×10 -3 Pa, fill with protective argon gas to 500 Pa, and then melt to obtain a Nb-Si alloy ingot. Cut the ingot into metal rods using electrical discharge machining, eliminate the cutting marks using 400 - 800# water sandpaper, and finally clean with alcohol. Put the Nb elemental material into a water-cooled crucible, evacuate to 8×10-3 Pa, introduce protective argon gas, melt for ten minutes to form an ingot, and finally cast using a graphite mold. Cut the pure Nb ingot into a hollow metal tube, clean and polish to obtain a pure Nb metal tube without wire cutting marks; place the Nb-Si alloy metal rod in the pure Nb metal tube, place it in a directional solidification vacuum chamber, evacuate to 5×10 -3Pa, introduce protective argon gas to 200 Pa, then heat up, raise the temperature to 2200 °C and hold for 15 - 20 min, start the experiment at a pulling rate of 1 μm / s, and cool the prepared directionally solidified Nb - Si alloy ingot in Ga - In coolant.

[0065] It can be seen that the Nb - Si - based directionally solidified alloy is a eutectic structure with a specific direction, Nbss / Nb Figure 2 The dendritic eutectic structure phase sizes vary from 500 to 800 nm. In addition, there is also Nbss / Nb 5 Si 3 The divorced eutectic structure, and the phase sizes are mostly in the range of 3 - 8 μm. The Nb - Si - based alloy prepared by directionally solidifying pure Nb tubes is not contaminated by other impurities. 5 Si 3 The XRD results in [reference] show that only Nbss and Nb Figure 3 Si 5 phases exist in the phase composition. From 3 it can be known that the room - temperature fracture toughness of this alloy is 19.1 MPa·m Figure 4 . In summary, the eutectic Nb - Si directionally solidified alloy in this example and its preparation are pollution - free and have excellent mechanical properties. Compared with the above, it has increased by 56.6% compared with using yttrium oxide ceramic tubes, promoting the application process of Nb - Si - based alloys in structural materials such as aero - engine blades. 1 / 2 .

[0066] The diameter of the Nb - Si - based directionally solidified ingot prepared in this experiment is 16 mm. Due to the use of pure Nb tubes for preparation, it can be pollution - free and a large amount of materials are saved. The melting point of ceramic tubes is low, and they react with high - temperature melts during the directional solidification preparation process, are burned out, and cannot be reused. The ablation products enter the melt, pollute the ingot, and the actual utilization rate of the final ingot is at most 90%.

[0067] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those skilled in the art can also make other changes within the spirit of the present invention and apply them to fields not mentioned in the present invention. Of course, these changes made according to the spirit of the present invention should be included within the scope claimed by the present invention.

Claims

1. A preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy, characterized in that: it includes the following preparation steps: Step 1: Weigh alloy raw materials; Weigh elemental Si, Ti, ZrC and Nb according to the atomic percentage of 16% Si, 20% Ti, 2% ZrC and 62% Nb, and the total atomic percentage is 100%; Step 2: Melting and casting ingots; The weighed raw materials Nb, Si, Ti, and ZrC are sequentially placed into a non-consumable water-cooled copper crucible from top to bottom according to the order of particle size. The melting chamber is pre-evacuated to 5 Pa - 10 Pa, and argon is introduced for 20 - 30 seconds, repeated 3 - 6 times. Then the melting chamber is evacuated to 4×10 -3 Pa - 5×10 -3 Pa, and protective argon is flushed in to 300 Pa - 500 Pa, and then melted to obtain an ingot; Step 3: Cut the ingot cast in Step 2 into metal rods by wire cutting, clean and polish to obtain metal rods without machining marks; Step 4: Prepare a pure Nb ingot; Weigh the elemental raw material Nb and place it in a water-cooled copper crucible. Pre-pump the melting chamber to a vacuum of 5 Pa - 10 Pa, introduce argon for 20 - 30 seconds, and repeat this process 3 - 5 times. Then pump the melting chamber to a vacuum of 4×10 -3 Pa - 5×10 -3 Pa, fill it with protective argon to 300 - 500 Pa, melt for ten minutes, and pour it into a graphite mold for casting to obtain a pure Nb ingot; Step 5: Prepare a pure Nb tube; Cut the pure Nb ingot into a hollow tube by wire electrical discharge machining, clean and polish to obtain a pure Nb tube without wire cutting marks; Step 6: Preparation of the directionally solidified Nb-Si alloy; Place the metal rod in step three into the pure Nb tube in step five, and then place it in a vacuum directional solidification furnace. Evacuate the furnace to 5×10 -3 Pa, introduce protective argon gas to 200 Pa, then heat. Raise the temperature to 2200 °C and hold for 15 - 20 min. Start the experiment at a pulling rate of 1 μm / s - 20 μm / s. Cool the prepared directional solidification Nb-Si alloy ingot in Ga-In coolant to obtain the eutectic Nb-Si directionally solidified alloy.

2. The preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy according to claim 1, characterized in that: The expression of the directionally solidified Nb-Si alloy prepared in Step 6 is Nb-16Si-20Ti-2ZrC.

3. The preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy according to claim 2, characterized in that: The alloy is melted 6 times in Step 2.

4. The preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy according to claim 1 or 3, characterized in that: The metal rod in Step 3 is first polished with sandpaper to remove wire cutting marks, and then cleaned with alcohol.

5. The preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy according to claim 1, characterized in that: The pure Nb ingot in Step 4 is melted 3 times during preparation.

6. The preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy according to claim 1 or 5, characterized in that: The drawing rate in Step 6 is 1 μm / s.

7. The preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy according to claim 1 or 5, characterized in that: The drawing rate in Step 6 is 4 μm / s.

8. The preparation method of a pollution-free eutectic Nb-Si directionally solidified alloy according to claim 1 or 5, characterized in that: The drawing rate in Step 6 is 20 μm / s.

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