METHOD FOR PREPARING SINGLE CRYSTAL SUPERALLOY TEST BARS BY USING NI-W HETEROGENEOUS SEED CRYSTAL

Abstract

In the method for preparing single crystal superalloy test bars by using a Ni—W heterogeneous seed crystal, on the premise of ensuring that the single crystal superalloy has the required orientation, by reusing the seed crystal, it is achieved that the trouble caused by the need of preparing a new seed crystal when a single crystal superalloy is produced by the seed crystal method every time is avoided, and the production cost is significantly reduced. In the present disclosure, the formation of the stray grains in mushy zone could be avoided by using a Ni—W heterogeneous seed crystal without mushy zone and a built-in corundum tube.

Claims

1. A method for preparing single crystal superalloys by using a Ni—W heterogeneous seed crystal, comprising: step 1, preparing a shell mould; step 2, preparing a seed crystal for preparing Ni—W heterogeneous single crystal test bars: preparing a single crystal test bar by a grain selection method; step 3, preparing a first Ni—W heterogeneous single crystal test bar with a [001] orientation which deviates from the axial direction by 0-12°: preparing a Ni—W heterogeneous single test bar with a [001] orientation which deviates from the axial direction by 0-12° by using the seed crystal obtained in step 2; step 4, preparing a first single crystal superalloy test bar: cutting the obtained first Ni—W heterogeneous single crystal test bar to obtain a Ni—W heterogeneous seed crystal that can be put into the shell mould; preparing a single crystal superalloy test bar by using the cut Ni—W heterogeneous seed crystal, specifically comprising: putting the obtained Ni—W heterogeneous seed crystal into the corundum tube in the shell mould; placing the shell mould filled with the Ni—W heterogeneous seed crystal in a directional solidification furnace; putting a purchased superalloy master alloy block into an electromagnetic melting crucible at the upper part of the furnace; heating the directional solidification furnace to a temperature of 1550° C. at a rate of 10° C./min, so as to melt the upper surface of the Ni—W heterogeneous seed crystal near the heater of the directional solidification furnace; increasing the power of the electromagnetic melting crucible to 7.5 kW, so as to completely melt the superalloy master alloy block in the crucible to obtain a superalloy liquid; casting the superalloy liquid into the shell mould, and full filling the shell mould with the superalloy liquid; generating a mushy zone with a length of 2-3 mm on the upper part of the Ni—W heterogeneous seed crystal by the cast superalloy liquid and holding for 10 min-30 min, wherein the mushy zone is a solid-liquid two-phase region generated at the joint of the superalloy liquid and the Ni—W heterogeneous seed crystal; after the holding is completed, subjecting the obtained system to a crystal pulling by pulling down at a rate of 40 μm/s-100 μm/s; after the crystal pulling is completed, taking out the product after the heating furnace is cooled to 300° C., to obtain a first single crystal superalloy test bar with a [001] orientation which deviates from the axial direction by 0-12°; step 5, recovering the seed crystal for reuse: recovering the Ni—W heterogeneous seed crystal for reuse from the obtained first single crystal superalloy test bar with a [001] orientation which deviates from the axial direction by 0-12°, specifically comprising: removing the shell mould on the obtained first single crystal superalloy test bar with a [001] orientation which deviates from the axial direction by 0-12°; cutting the Ni—W heterogeneous seed crystal from the first single crystal superalloy test bar with a [001] orientation which deviates from the axial direction by 0-12° after the shell mould is removed, and recovering it for reuse; and step 6, preparing other single crystal superalloy test bars: preparing other single crystal superalloy test bars by using the obtained recovered seed crystal, wherein the other single crystal superalloy test bars have a [001] orientation which deviates from the axial direction by 0-12°, and the specific process comprises: putting the recovered seed crystal into the corundum tube in the shell mould; placing the shell mould in a directional solidification furnace, and repeating step 4 to obtain a second superalloy test bar; repeating step 5 to re-obtain the recovered seed crystal; repeating the process of preparing the second superalloy test bar to obtain a third superalloy test bar; repeating the processes of recovering seed crystal and preparing superalloy test bar until the required number of superalloy test bars are obtained.

2. The method as claimed in claim 1, wherein the superalloy master alloy block comprises a DD3 superalloy master alloy block, wherein the DD3 superalloy is the first generation superalloy developed by Beijing Institute of Aeronautical Materials.

3. The method as claimed in claim 1, wherein the shell mould comprises a casting segment and a seed crystal segment with a corundum tube; the seed crystal segment has a length equal to that of the corundum tube, and before preparing a seed crystal, the corundum tube is put into the seed crystal segment; the corundum tube has an inner diameter of 6.98-11.98 mm and a length of 40 mm.

4. The method as claimed in claim 1, wherein the process for preparing a seed crystal for preparing the Ni—W heterogeneous single crystal test bar comprises: directionally cutting a single crystal cylinder with a [001] orientation which deviates from the axial direction by 0-12° from the single crystal test bar and acting as a seed crystal, wherein the directionally cut seed crystal has a [001] orientation which deviates from the axial direction by 0-12°.

5. The method as claimed in claim 4, wherein the Ni—W heterogeneous seed crystal has a diameter of 6.96-11.94 mm, a length of 35 mm and a gap of 0.02-0.06 mm with the corundum tube.

6. The method as claimed in claim 1, wherein the specific process for preparing a first Ni—W heterogeneous single test bar with a [001] orientation which deviates from the axial direction by 0-12° comprises: taking another corundum tube as a container for preparing Ni—W heterogeneous single crystal test bars, wherein the corundum tube has an inner diameter of 6.97-11.98 mm and a length of 115 mm; using a Ni—W alloy as the master alloy, putting the obtained seed crystal and the Ni—W master alloy into the corundum tube in the order of the seed crystal at the bottom and the Ni—W master alloy on the top; installing the corundum tube filled with the seed crystal and the master alloy on the bottom platform of a LMC directional solidification furnace; and heating the directional solidification furnace to 1550° C. at a rate of 10° C./min and holding for 40-50 min, so as to melt the master alloy in the corundum tube and form a mushy zone with a length of 2-3 mm on the seed crystal; after the holding is completed, subjecting the obtained system to a crystal pulling by pulling down at a rate of 10 μm/s-100 μm/s; after the crystal pulling is completed, taking out the corundum tube after the directional solidification furnace is cooled to 100° C., to obtain the first Ni—W heterogeneous single crystal test bar with a [001] orientation which deviates from the axial direction by 0-12°, wherein the first Ni—W heterogeneous single crystal test bar has a diameter of 6.96-11.94 mm, a length of 35 mm, and a gap of 0.02-0.06 mm with the corundum tube.

7. The method as claimed in claim 1, wherein the Ni—W heterogeneous seed crystal which is cut from the obtained first single crystal supperalloy test bar with a [001] orientation which deviates from the axial direction by 0-12° has a length equal to that of the raw Ni—W heterogeneous seed crystal and a diameter of 6.94-11.90 mm, so as to ensure the gap between the recovered seed crystal and the inner wall of the corundum tube fall within a range of 0.04-0.15 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 shows the structure of the shell mould used in the “seed crystal” method for preparing a single crystal superalloy in the prior art.

[0044] FIG. 2 shows the structure of the shell mould that pre-embedded a corundum tube in the seed crystal segment in the prior art.

[0045] FIG. 3 shows the structure of the cross-section of the single crystal superalloy test bar prepared according to the present disclosure.

[0046] FIG. 4 shows the structure of the longitudinal section of a mushy zone of the seed crystal after the first use of the seed crystal to prepare a single crystal superalloy according to the present disclosure.

[0047] FIG. 5 shows the structure of the longitudinal section of a mushy zone of the seed crystal after the third use of the seed crystal to prepare a single crystal superalloy according to the present disclosure.

[0048] FIG. 6 shows the flow chart of the method according to the present disclosure.

[0049] In the drawings: 1 represents a casting segment; 2 represents a seed crystal segment; 3 represents a corundum tube.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] The present disclosure is to provide a method for preparing single crystal superalloy test bars with a [001] orientation which deviates from the axial direction by a angle by reusing a Ni—W heterogeneous seed crystal. With this method, multiple single crystal superalloy test bars is prepared. The [001] orientation of the seed crystal deviates from the axial direction by 0-12°. In each example of the present disclosure, two superalloy test bars were prepared, the [001] orientation of the seed crystal deviates from the axial direction by 0°, and the superalloy master alloy block is a DD3 superalloy master alloy block, wherein the DD3 superalloy is the first generation superalloy developed by Beijing Institute of Aeronautical Materials.

[0051] The method according to the present disclosure specifically comprises the following steps:

[0052] Step 1: preparing a shell mould.

[0053] The shell mould comprises a casting segment 1 and a seed crystal segment 2 with a corundum tube. The seed crystal segment has a length equal to that of the corundum tube, and before preparing a seed crystal, the corundum tube is put into the seed crystal segment 2. The corundum tube has an inner diameter of 6.98-11.98 mm and a length of 40 mm.

[0054] The process for preparing a shell mould comprises:

[0055] A melted wax material is poured into a mold and solidified to obtain a wax mold base and a cylindrical wax bar respectively, wherein both the wax mold base and the cylindrical wax bar have the same structure as in the prior art.

[0056] The corundum tube is full filled with the melted wax material, and the wax material is cooled and solidified to obtain a corundum tube with an inner wax mold. One end of the inner wax mold in the corundum tube is bonded with the plane of the wax mold base, and the other end is connected with the cylindrical wax bar. The joint of the cylindrical wax bar and the inner wax mold in the corundum tube is trimmed to be smooth to obtain a shell-making wax mold.

[0057] In the shell-making wax mold, the joint of the inner wax mold in the corundum tube and the wax mold base is a right-angle transition, and the joint of the inner wax mold in the corundum tube and the cylindrical wax bar is a rounded transition.

[0058] The shell-making wax mold is subjected to an investment casting by the prior art; that is, the surface of the shell-making wax mold is smeared coating and stuccoed, and then calcined to obtain a shell mould for casting.

[0059] The shell mould for casting is washed with water and placed indoors for 24 h to dry it naturally.

[0060] Before use, the shell mould for casting is dried in a drying furnace for later use.

[0061] Step 2: preparing a seed crystal for preparing Ni—W heterogeneous single crystal test bars:

[0062] A single crystal test bar is prepared by a grain selection method.

[0063] A single crystal cylinder with a [001] orientation which deviates from the axial direction by 0-12° is directionally cut from the single crystal test bar with a wire-cut electric discharge machine and used as a seed crystal. The directionally cut seed crystal is cylindrical in shape and has a [001] orientation which deviates from the axial direction by 0-12°; the seed crystal has a diameter of 6.93-11.94 mm and a length of 25 mm. The seed crystal is sanded down to be smooth with a 1200 # sandpaper.

[0064] A single crystal cylinder with a [001] orientation which deviates from the axial direction by 0° is directionally cut from the single crystal test bar with a wire-cut electric discharge machine and used as a seed crystal. The directionally cut seed crystal is cylindrical in shape and has a [001] orientation which deviates from the axial direction by 0°; the seed crystal has a diameter of 6.93 mm and a length of 25 mm. The seed crystal is sanded down to be smooth with a 1200 # sandpaper.

[0065] Step 3: preparing a first Ni—W heterogeneous single crystal test bar with a [001] orientation which deviates from the axial direction by 0-12°:

[0066] A Ni—W heterogeneous single test bar with a [001] orientation which deviates from the axial direction by 0-12° is prepared by using the seed crystal obtained in step 2. The specific process comprises:

[0067] Another corundum tube is taken as a container for preparing Ni—W heterogeneous single crystal test bars, wherein the corundum tube has an inner diameter of 6.97-11.98 mm and a length of 115 mm.

[0068] A Ni—W alloy is used as a master alloy, the obtained seed crystal and the Ni—W master alloy are put into the corundum tube in the order of the former at the bottom and the latter on the top. The corundum tube filled with the seed crystal and the master alloy is installed on the bottom platform of a LMC directional solidification furnace.

[0069] The directional solidification furnace is heated to 1550° C. at a rate of 10° C./min and held for 40-50 min, so as to melt the master alloy in the corundum tube and form a mushy zone with a length of 2-3 mm on the seed crystal. After the holding is completed, the obtained system is subjected to a crystal pulling by pulling down at a rate of 10 μm/s-100 μm/s. After the crystal pulling is completed, the corundum tube is taken out after the directional solidification furnace is cooled to 100° C., to obtain a first Ni—W heterogeneous single crystal test bar with a [001] orientation which deviates from the axial direction by 0-12°.

[0070] The first Ni—W heterogeneous single crystal test bar has a diameter of 6.96-11.94 mm, a length of 35 mm, and a gap of 0.02-0.06 mm with the corundum tube.

[0071] Step 4: preparing a first single crystal superalloy test bar.

[0072] The obtained first Ni—W heterogeneous single crystal test bar is cut to obtain a Ni—W heterogeneous seed crystal that can be put into the shell mould. A single crystal superalloy test bar is prepared by using the obtained Ni—W heterogeneous seed crystal.

[0073] The specific process comprises:

[0074] The obtained Ni—W heterogeneous seed crystal is put into the corundum tube in the shell mould. The shell mould filled with the Ni—W heterogeneous seed crystal is placed in a directional solidification furnace. A purchased superalloy master alloy block is put into an electromagnetic melting crucible at the upper part of the furnace.

[0075] The superalloy is the first generation superalloy developed by Beijing Institute of Aeronautical Materials.

[0076] The directional solidification furnace is heated to a temperature of 1550° C. at a rate of 10° C./min, so as to melt the upper surface of the Ni—W heterogeneous seed crystal near the heater of the directional solidification furnace.

[0077] The power of the electromagnetic melting crucible is increased to 7.5 kW, so as to completely melt the superalloy master alloy block in the crucible to obtain a superalloy liquid. The superalloy liquid is cast into the shell mould, and the shell mould is full filled with the superalloy liquid.

[0078] A mushy zone with a length of 2-3 mm is generated on the upper part of the Ni—W heterogeneous seed crystal by the cast superalloy liquid and held for 10 min-30 min. The mushy zone is a solid-liquid two-phase region generated at the joint of superalloy liquid and Ni—W heterogeneous seed crystal.

[0079] After the holding is completed, the obtained system is subjected to a crystal pulling by pulling down at a rate of 40 μm/s-100 μm/s; after the crystal pulling is completed, the product is taken out after the heating furnace is cooled to 300° C., to obtain a first single crystal superalloy test bar with a [001] orientation which deviates from the axial direction by 0-12°.

[0080] Step 5: recovering the seed crystal for reuse.

[0081] The Ni—W heterogeneous seed crystal is recovered for reuse from the obtained first single crystal superalloy test bar with a [001] orientation which deviates from the axial direction by 0-12°. The specific process comprises:

[0082] The shell mould on the obtained first single crystal superalloy test bar with a [001] orientation which deviates from the axial direction by 0-12° is removed. The Ni—W heterogeneous seed crystal in the first single crystal superalloy test bar with a [001] orientation which deviates from the axial direction by 0-12° is cut; the cut Ni—W heterogeneous seed crystal has a length equal to that of the raw Ni—W heterogeneous seed crystal, and it acts as a recovered seed crystal for reuse.

[0083] The recovered seed crystal is sanded with a 1200 # sandpaper, so as to obtain a recovered seed crystal with a diameter of 6.94-11.90 mm and a length of 35 mm, wherein the sanded recovered seed crystal has a gap of 0.04-0.15 mm with the inner wall of the corundum tube.

[0084] Step 6: preparing other single crystal superalloy test bars.

[0085] The obtained recovered seed crystal in step 5 is used to prepare a second single crystal superalloy test bar. The second single crystal superalloy test bar has a [001] orientation which deviates from the axial direction by 0-12°.

[0086] The sanded recovered seed crystal is put into the corundum tube of the shell mould. The shell mould is placed into a directional solidification furnace, and the process in step 4 is repeated to obtain a second superalloy test bar.

[0087] The process in step 5 is repeated to re-obtain the recovered seed crystal; the process of preparing the second superalloy test bar is repeated to obtain a third superalloy test bar.

[0088] The processes of recovering seed crystal and preparing superalloy test bar are repeated until the required number of superalloy test bars are obtained.

[0089] The present disclosure will be specifically illustrated by the following four examples. Each example has the same preparation procedure.

[0090] The parameters in each example are shown in Table 1:

TABLE-US-00001 TABLE 1 Example Step 1 2 3 4 1 The inner diameter of the corundum tube (mm) 6.98 9.04 11.98 11.96 The length of the corundum tube (mm) 40 40 40 40 The number prepared 2 4 8 14 The deviation angle of [001] orientation from the 0 5 9 12 axial direction 2 The diameter of the seed crystal (mm) 6.93 8.97 11.93 11.94 The length of the seed crystal (mm) 25 25 25 25 3 The inner diameter of the corundum tube (mm) 6.97 9.02 11.98 11.97 The length of the corundum tube (mm) 115 115 115 115 Heating rate (° C./min) 10 10 10 10 Heating temperature (° C.) 1550 1550 1550 1550 Holding time (min) 40 43 50 47 The height of the mushy zone (mm) 2 2.3 3 2.5 Pulling rate (μm/s) 10 100 70 30 The diameter of the first Ni—W heterogeneous 6.96 8.98 11.94 11.93 single crystal test bar (mm) The gap between the first Ni—W heterogeneous 0.02 0.06 0.04 0.03 single crystal test bar and the corundum tube (mm) Length 35 35 35 35 4 Heating rate (° C./min) 10 10 10 10 Heating temperature (° C.) 1550 1550 1550 1550 The power of electromagnetic melting crucible 7.5 7.5 7.5 7.5 (kW) Holding time (min) 40 43 50 47 The height of the mushy zone (mm) 2 2.4 3 2.6 Pulling rate (μm/s) 40 100 80 60 5 The diameter of the recovered seed crystal 6.94 8.89 11.90 11.90 (mm) The length of the recovered seed crystal (mm) 35 35 35 35 The gap between the recovered seed crystal and 0.04 0.15 0.08 0.06 the corundum tube (mm)