Directional solidification equipment for single-crystal high-temperature alloy casting and preparation method of single-crystal high-temperature alloy casting

Abstract

The invention provides directional solidification equipment for a single-crystal high-temperature alloy casting, and relates to the technical field of single-crystal high-temperature alloys. A smelting chamber, a cooling chamber, a cooling structure and a heat insulation device are arranged in the furnace body; the smelting chamber and the cooling chamber are thermally isolated from each other, and the smelting chamber is located at the top of the cooling chamber; the smelting chamber is used for heating the shell; the cooling chamber is used for solidifying alloy liquid in the shell; the cooling structure is used for fixing the shell; the shell can upwards move into the smelting chamber along with the cooling structure and downwards move into the cooling chamber; the heat insulation device comprises a liftable heat insulation plate; the heat insulation plate is located on the upper side of the cooling structure. And when the shell runs, the heat insulation plate is used for blocking heat transfer between the smelting chamber and the cooling chamber. It needs to be explained that in the drawing (shell operation) process, a smelting chamber and a cooling chamber are isolated through a heat insulation plate so as to reduce heat exchange, and therefore temperature gradient reduction of the front edge of a solid-liquid interface is avoided, and dendritic crystal orientation deviation is avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of single crystal superalloy, and particularly relates to a directional solidification equipment for single crystal superalloy castings and a preparation method thereof. BACKGROUND

[0002] With the development of the aviation industry, higher requirements are put forward for the temperature resistance and high-temperature mechanical properties of engine hot-end components, which makes single crystal superalloy gradually occupy the core position of aviation industry materials. With the development of technology and process, the size specification and quantity demand of single crystal superalloy components are continuously improved, and the conventional casting method is difficult to meet the requirements. Large mold group casting technology has become an effective way to improve production and reduce cost, and is also an inevitable trend. At present, the large mold group casting technology commonly uses the high-rate solidification (HRS) method with water-cooled copper disc cooling for casting. This method is simple to operate and does not pollute the alloy composition, and is widely used in industrial production in China.

[0003] However, compared with the conventional mold group HRS process, the large mold group HRS process has the following problems: (1) The large mold group ceramic shell has a large size, and a large volume of hollow area exists in the interior, which is easy to produce heat leakage. When the ceramic shell is pulled from the melting chamber into the cooling chamber, the temperature near the heat baffle area in the melting chamber will decrease, and the temperature near the heat baffle area in the cooling chamber will increase, which will also cause the temperature gradient of the solid-liquid interface front to decrease; (2) During the directional solidification process, as the solid-liquid interface gradually rises away from the water-cooled copper disc, the main heat dissipation mechanism of the entire mold group gradually changes from heat conduction inside the shell to radiation heat dissipation outside the shell, which will cause the temperature gradient of the solid-liquid interface front to rapidly decrease; (3) The conventional HRS method single crystal furnace (directional solidification furnace) mainly realizes the heating and cooling of the entire single crystal superalloy mold group through the radial radiation of the heating components installed on the furnace wall and the water-cooled ring to the furnace, which will cause the area near the furnace body side of the mold group to have a faster heating and cooling speed and thus have a higher temperature gradient, and the area away from the furnace body side to have a slower heating and cooling speed and thus have a lower temperature gradient, that is, there is a significant shadow effect.

[0004] The above-mentioned decrease in the temperature gradient of the solid-liquid interface front and the shadow effect are easy to cause the crystal orientation to deviate, thereby causing the single crystal superalloy blade to form casting defects. Therefore, it is necessary to provide a directional solidification equipment for single crystal superalloy castings and a preparation method thereof. SUMMARY

[0005] Therefore, the present application provides a directional solidification equipment for single crystal superalloy castings and a preparation method thereof, which can solve the problem of easy generation of shadow effect and thus causing the crystal orientation to deviate in the prior art.

[0006] In order to solve the above problems, the application provides a directional solidification device for single crystal superalloy castings, which comprises a furnace body; wherein the furnace body is internally provided with a smelting chamber, a cooling chamber, a cooling structure and a heat insulation device;

[0007] The smelting chamber and the cooling chamber are thermally isolated from each other, and the smelting chamber is located at the top of the cooling chamber; the smelting chamber is used for heating a mold shell; and the cooling chamber is used for solidifying alloy liquid in the mold shell.

[0008] The cooling structure is used for fixing the mold shell; and the mold shell can run upwards into the smelting chamber and downwards into the cooling chamber along the cooling structure.

[0009] The heat insulation device comprises a heat insulation plate which can be lifted; wherein the heat insulation plate is located at the upper side of the cooling structure; when the mold shell runs downwards, the heat insulation plate runs away from the cooling structure; when the mold shell runs upwards, the heat insulation plate runs towards the cooling structure; and the heat insulation plate is used for blocking heat transfer between the smelting chamber and the cooling chamber during the running of the mold shell.

[0010] Further, the heat insulation plate is made of graphite material.

[0011] Further, the furnace body is further provided with a lifting device; the lifting device is used for driving the cooling structure and the mold shell to run upwards or downwards; and / or

[0012] A channel for the running of the cooling structure and the mold shell is arranged between the smelting chamber and the cooling chamber.

[0013] Further, the smelting chamber is internally provided with a heating device;

[0014] The heating device comprises a heating assembly and a central heating column; the heating assembly is arranged around the inner cavity wall of the smelting chamber and around the central heating column.

[0015] The cooling device comprises a cooling assembly and a central water cooling column; the cooling assembly is arranged around the inner cavity wall of the cooling chamber and around the central water cooling column.

[0016] Further, the cooling structure is a water cooling disc; and the water cooling disc is annular.

[0017] The heat insulation plate is arranged at the top of the central water cooling column; and the central water cooling column is telescopic to drive the heat insulation plate to run away from or towards the water cooling disc.

[0018] Further, the mold shell comprises a sprue cup and a top pouring disc, a single crystal sample cavity, a spiral selector and a seeding section.

[0019] The pouring cup is in communication with the top of the top mold plate; the bottom of the top mold plate is in communication with the top end of the single crystal sample cavity; the bottom end of the single crystal sample cavity is in communication with the first end of the screw selector, and the second end of the screw selector is in communication with the first end of the seeding section;

[0020] The second end of the seeding section is fixed on the top surface of the water-cooling plate.

[0021] Further, the top mold plate is annular, and the central heating column can be retracted and extended in the hollow part of the top mold plate and the mold shell.

[0022] Further, the diameter of the water-cooling plate is φ500 mm; and / or

[0023] The outer diameter of the mold shell is φ400-500 mm, and the inner diameter is φ200-250 mm; and / or

[0024] The distance between the single crystal sample cavity and the center of the mold shell is 200-225 mm; and / or

[0025] The size of the heat insulation plate is φ300-400 mm, and the thickness is 20±5 mm.

[0026] In another aspect, the present application provides a preparation method for preparing a single crystal superalloy casting by using the directional solidification equipment for preparing a single crystal superalloy casting according to any one of the above, comprising the following steps:

[0027] Step 1): the mother alloy raw material is subjected to melting treatment to obtain an alloy liquid, and the mold shell in the melting chamber is subjected to preheating treatment;

[0028] Step 2): the alloy liquid is poured into the mold shell, and heat preservation is performed;

[0029] Step 3): the mold shell is pulled out from the melting chamber into the cooling chamber, and after cooling, the mold shell is removed to obtain a single crystal superalloy test rod.

[0030] Further, in the step 2), the melting treatment is performed in a vacuum melting furnace; wherein the air pressure in the vacuum melting furnace is lower than 5 Pa; and / or

[0031] The temperature of the melting treatment is 1520℃±50℃; and / or

[0032] After the mother alloy raw material is melted, the standing time is 2-5 min; and / or

[0033] The heat preservation time after the alloy liquid is poured is 5-7 min; and / or

[0034] The pulling rate is 3-7 mm / min.

[0035] Compared with the prior art, the present application has at least the following beneficial effects:

[0036] 1. The present application provides a directional solidification device for single crystal superalloy castings, the directional solidification device comprising a furnace body; wherein the furnace body is provided with a melting chamber, a cooling chamber, a cooling structure and a heat insulation device; wherein the melting chamber and the cooling chamber are thermally isolated from each other, and the melting chamber is located at the top of the cooling chamber; the melting chamber is used for heating the shell; the cooling chamber is used for solidifying the alloy liquid in the shell; the cooling structure is used for fixing the shell; the shell can run upwards into the melting chamber and downwards into the cooling chamber along the cooling structure; the heat insulation device comprises a heat insulation plate which can be lifted; wherein the heat insulation plate is located on the upper side of the cooling structure; when the shell runs downwards, the heat insulation plate runs away from the cooling structure; when the shell runs upwards, the heat insulation plate runs towards the cooling structure; and the heat insulation plate is used for blocking the heat transfer between the melting chamber and the cooling chamber during the running of the shell. It should be noted that, during the pulling (running of the shell), the melting chamber and the cooling chamber are isolated by the heat insulation plate to reduce heat exchange, so as to avoid the decrease of the temperature gradient of the solid-liquid interface front and the deviation of the dendrite orientation.

[0037] 2. Further, during the pulling, the heat insulation plate is relatively stationary with the furnace body, and due to the excellent heat insulation performance of the graphite material, the melting chamber and the cooling chamber are only connected through the gap between the heat insulation baffle on the furnace wall and the heat insulation plate where the single crystal sample cavity is located, which greatly reduces the contact area between the melting chamber and the cooling chamber, reduces the occurrence of heat leakage, and reduces the temperature fluctuation at the junction of the melting chamber and the cooling chamber during the pulling of the large mold shell, so that the solid-liquid interface front has a stable high temperature gradient; at the same time, the heat insulation plate has high thermal conductivity, and the heat insulation plate connected with the central water-cooled column can maintain a relatively low temperature, which can be used for cooling the alloy liquid and solid in the shell, avoiding the shadow effect caused by the faster cooling speed on the side close to the furnace body and the slower cooling speed on the side away from the furnace body in the cooling chamber, thereby avoiding the deviation of the dendrite orientation.

[0038] 3. Further, the pulling rate is 3-7 mm / min, and a too fast pulling rate will cause the isotherm to tilt and increase the risk of defects caused by the deviation of the dendrite orientation; a too slow pulling rate will cause the dendrite spacing to increase and damage the performance and life of the casting, so the pulling rate is limited to 3-7 mm / min. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed in the following description of the embodiments or the prior art will be briefly introduced. The drawings in the following description are only exemplary, and for those skilled in the art, other embodiments can be derived from the provided drawings without creative labor.

[0040] Figure 1 Fig. 1 is a schematic diagram of a ceramic mold for a large module single crystal alloy test bar; wherein (a) without heat insulation plate, (b) with heat insulation plate, (c) relative position of heat insulation plate and mold at a certain moment during pulling process.

[0041] Figure 2 Fig. 2 is a dendritic morphology of single crystal alloy test bars under different experimental conditions; wherein (a) φ400mm heat insulation plate test bar, (b) φ350mm heat insulation plate test bar, (c) φ300mm heat insulation plate test bar, (d) without heat insulation plate test bar, (e) φ430mm heat insulation plate test bar.

[0042] Figure 3 Fig. 3 is a crystal orientation deviation defect statistics of single crystal alloy test bars poured by mold with different sizes of heat insulation plate and without heat insulation plate.

[0043] Figure 4 Fig. 4 is a schematic diagram of a large module directional solidification equipment in the embodiment.

[0044] Fig. 5 is a schematic diagram of a large module directional solidification equipment in the embodiment. DETAILED DESCRIPTION

[0045] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the description of the embodiments or the prior art. The drawings in the following description are only exemplary, and for those skilled in the art, other drawings can be derived from the provided drawings without creative labor.

[0046] The present application provides a directional solidification equipment for single crystal high-temperature alloy castings, which comprises a furnace body (melting furnace 17), wherein the furnace body is provided with a melting chamber 15, a cooling chamber 16, a mold, a water-cooled disc 7 (cooling structure), a lifting device and a heat insulation device;

[0047] The melting chamber 15 and the cooling chamber 16 are thermally isolated from each other, and the melting chamber 15 is located at the top of the cooling chamber 16; the melting chamber 15 is provided with a heating device for heating the mold; the cooling chamber is provided with a cooling device for solidifying the alloy liquid in the mold;

[0048] The mold is fixed on the top surface of the water-cooled disc; the lifting device is used to drive the mold and the water-cooled disc to move up and down, i.e. to move up into the melting chamber 15 and to move down into the cooling chamber 16;

[0049] The heat insulation device comprises a heat insulation plate 6 which can be lifted; the heat insulation plate 6 is located on the upper side of the cooling structure; when the mold shell runs downward, the heat insulation plate 6 runs away from the cooling structure; when the mold shell runs upward, the heat insulation plate 6 runs toward the cooling structure; the heat insulation plate 6 is used to block the heat transfer between the smelting chamber 15 and the cooling chamber 16 when the mold shell runs.

[0050] Based on the above method, during the pulling (mold shell running) process, the smelting chamber and the cooling chamber are isolated by the heat insulation plate to reduce heat exchange, so as to avoid the temperature gradient of the solid-liquid interface front being reduced and the dendrite orientation being deviated.

[0051] In some embodiments, the mold shell comprises a sprue cup 1 and a top pouring plate 2, a single crystal sample cavity 3, a spiral selector 4 and a seeding section 5.

[0052] The bottom of the sprue cup 1 is in communication with the top of the top pouring plate 2; the bottom of the top pouring plate 2 is in communication with the top end of the single crystal sample cavity 3; the bottom end of the single crystal sample cavity 3 is in communication with the first end of the spiral selector 4, and the second end of the spiral selector 4 is in communication with the first end of the seeding section 5; the second end of the seeding section 5 is fixed on the top surface of the water-cooled plate 7.

[0053] In some embodiments, the heat insulation plate has a low point position and a high point position on the mold shell; when the heat insulation plate is at the low point position, the bottom surface of the heat insulation plate is in contact with the top surface of the water-cooled plate; when the heat insulation plate is at the high point position, the top surface of the heat insulation plate is in contact with the bottom surface of the top pouring plate; the heat insulation plate can be driven to lift to switch between the low point position and the high point position.

[0054] A passage for the water-cooled plate 7 and the mold shell to run is arranged between the smelting chamber 15 and the cooling chamber 16; a heat insulation baffle 13 is further arranged between the smelting chamber 15 and the cooling chamber 16, and the heat insulation baffle is a hollow structure, so that the water-cooled plate 7 and the mold shell can run upward to the smelting chamber or run downward to the cooling chamber.

[0055] Further, the heating device comprises a heating assembly and a central heating column 9; the heating assembly surrounds the inner cavity wall of the smelting chamber and is arranged around the central heating column; a first annular gap is formed between the heating assembly and the central heating column 9; the cooling device comprises a cooling assembly and a central water-cooled column 8; the cooling assembly surrounds the inner cavity wall of the cooling chamber and is arranged around the central water-cooled column 8; a second annular gap is formed between the heating assembly and the central water-cooled column; the mold shell can be driven to lift between the first annular gap and the second annular gap. The heating assembly comprises an upper heating assembly 10 and a lower heating assembly 11; the cooling assembly is a water-cooled ring cooling assembly 12.

[0056] Further, the water cooling disc is annular; the heat insulation plate is arranged on the top of the central water cooling column; the central water cooling column is telescopic to drive the heat insulation plate to ascend and descend in the mold shell.

[0057] Further, the top pouring disc is annular, and the central heating column is telescopic in the hollow part of the top pouring disc and the mold shell to install the mold shell.

[0058] Further, the diameter of the water cooling disc is φ500 mm.

[0059] The outer diameter of the mold shell is φ400-500 mm, and the inner diameter is φ200-250 mm.

[0060] The distance between the single crystal sample cavity and the center of the mold shell is 175-225 mm.

[0061] Further, the size of the heat insulation plate is φ300-400 mm, and the thickness is 20±5 mm.

[0062] It should be noted that the lifting device described above can adopt a servo motor / stepping motor to drive a precision ball screw, and the nut is fixedly connected with the water cooling disc support to realize the lifting (operation) of the water cooling disc; wherein the screw is protected by a heat insulation cover or a water cooling jacket to avoid the influence of the radiation heat of the furnace body; the lifting device can also adopt a motor driven chain wheel and chain or gear and rack system to lift the water cooling disc through the lifting support 14.

[0063] On the other hand, the present application provides a preparation method for preparing a single crystal superalloy casting by using the directional solidification equipment according to any one of the above, comprising the following steps:

[0064] Step 1): fixing a pre-prepared large module single crystal alloy ceramic mold shell on a water cooling copper disc (water cooling disc), and then fixing a specially prepared heat insulation plate on the top end of the central water cooling column of the water cooling copper disc of the large module directional solidification equipment liftable support;

[0065] Step 2): adding a master alloy raw material into a melting furnace at the upper part of the melting chamber of the large module directional solidification equipment, melting the master alloy under the condition that all working areas inside the equipment are kept in airtight vacuum, and at the same time, the large module single crystal alloy ceramic mold shell will be preheated synchronously, and the master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal superalloy.

[0066] Step 3): After the master alloy is melted, the molten alloy is poured into the large module single crystal alloy ceramic mold shell in the smelting furnace, the pouring is completed, and the heat preservation is carried out.

[0067] Step 4): The large module single crystal alloy ceramic mold shell containing the molten alloy is pulled into the cooling chamber under the driving of the transmission device to realize directional solidification. After the directional solidification process is completed, the cooling is completed, the vacuum state in the furnace is released, and the large module single crystal alloy ceramic mold shell is taken out.

[0068] Step 5): The ceramic mold shell is removed, the top pouring disc and the crystal selection device are cut off, and the single crystal high-temperature alloy test rod without orientation deviation defect is obtained.

[0069] Further, the vacuum treatment condition in the smelting process is that the air pressure in the smelting chamber is less than 5 Pa; and / or

[0070] The annular heating assembly and the central heating column are turned on at the same time, the master alloy melting temperature is 1520℃±50℃, and the preheating temperature of the large module single crystal alloy ceramic mold shell is consistent with the master alloy melting temperature; and / or

[0071] In step 3), the master alloy is melted, and the standing time is 2-5 min; and / or

[0072] After the pouring of the molten alloy is completed, the heat preservation time is 5-7 min; and / or

[0073] The pulling rate is 3-7 mm / min.

[0074] The application will be further described below in combination with specific examples and comparative examples.

[0075] Example 1

[0076] The embodiment provides a preparation method of a single crystal high-temperature alloy casting, which comprises the following steps:

[0077] Step 1, a large module single crystal alloy ceramic mold shell with a size of φ500mm is fixed on the water-cooled copper disc of the multi-layer module directional solidification equipment, and then a specially-made heat insulation plate is fixed on the central axis at the top end of the central water-cooled column of the water-cooled copper disc of the lifting support of the large module directional solidification equipment. The size of the heat insulation plate is φ400mm.

[0078] As Figure 1(a) as shown, the large module single crystal alloy test bar ceramic shell is an integrated structure connected in turn from top to bottom by sprue cup 1, top pouring plate 2, single crystal alloy test bar 3, spiral selector 4, seeding section 5, and water-cooled plate 7, the shell is a special ring-shaped shell, the outer diameter size of the shell is φ500mm, the inner diameter size is φ250mm, 16 rod-shaped modules are arranged in the ring-shaped shell, the test bars are spaced 22.5° apart, the distance between the test bars and the center of the shell is 225mm, and each single crystal alloy test bar 3 is connected by the top pouring plate 2 at the upper end, the spiral selector 4 at the lower end, the seeding section 5, and the water-cooled copper plate 7.

[0079] As shown in Figure 4 As shown, the large module directional solidification equipment is a large-size directional solidification furnace with a ring-shaped heating assembly, a water cooling device, a central heating column, and a central water cooling column, the directional solidification furnace includes a smelting furnace 17 placed above a smelting chamber 15, a central heating column 9 extending from the center of the top end of the smelting chamber 15, an upper heating assembly 10 and a lower heating assembly 11 vertically arranged on the inner wall of the smelting chamber 15, a water-cooled copper plate 7, a central water cooling column 8 placed inside the center of the water-cooled copper plate 7, a water-cooled ring cooling assembly 12 located in a cooling chamber 16, a heat insulation baffle 13, and a liftable support 14; wherein the smelting chamber 15 and the cooling chamber 16 correspond to each other, the ceramic shell is placed on the top of the liftable support 14 through the water-cooled copper plate 7, the central heating column 9 and the central water cooling column 8 can control the working length through a numerical control device, the ring-shaped heating assembly (the upper heating assembly 10 and the lower heating assembly 11) and the water-cooled ring cooling assembly 12 are respectively located at the upper part and the lower part of the initial position of the liftable support 14, and are separated by the ring-shaped heat insulation baffle 13, so as to realize the isolation of the smelting chamber 15 (hot zone) and the cooling chamber 16 (cold zone), the water-cooled copper plate 7 and the ceramic shell are driven by the liftable support 14 to pass through the center hole of the heat insulation baffle 13, and reciprocally ascend and descend between the smelting chamber 15 and the solidification cavity 16, the special heat insulation plate 6 is fixed on the top end of the central water cooling column 8 of the water-cooled copper plate 7 of the liftable support 14 of the large module directional solidification equipment through a high-temperature adhesive, and the heat insulation plate 6 is driven in the ceramic shell by the central water cooling column 8 through the numerical control device;

[0080] Step 2: The master alloy raw material is added to the smelting furnace of the multi-layer module directional solidification equipment, and the master alloy is smelted at 1500℃ under the condition that all the working areas inside the equipment are kept in a sealed vacuum state, at the same time, the multi-layer module single crystal alloy ceramic shell is preheated (the temperature of the two ring-shaped heating assemblies vertically arranged in the smelting chamber is 1450℃ in the upper zone and 1500℃ in the lower zone), the preheating temperature of the multi-layer module single crystal alloy ceramic shell is consistent with the smelting temperature of the master alloy, and the master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high-temperature alloy;

[0081] Step 3, after the mother alloy raw material is completely melted, the alloy liquid is poured into the multi-layer mold set single crystal alloy ceramic mold shell, the pouring and filling are completed, and the heat preservation is performed for 5 min;

[0082] Step 4, the multi-layer mold set single crystal alloy ceramic mold shell containing the alloy liquid is slowly moved into the cooling chamber under the driving of the downward pulling transmission device at a pulling speed of 5 mm / min, when the top surface of the heat insulation plate and the bottom surface of the heat insulation baffle are at the same horizontal line, the central water cooling column is controlled to rise from the surface of the water cooling copper disc at the same rising rate as the pulling rate of the ceramic mold shell, when the top surface of the heat insulation plate rises to the same horizontal line as the bottom surface of the top pouring disc, the central water cooling column is controlled to stop moving. After the directional solidification process is completed, the cooling is waited, the vacuum state in the furnace is released, and the multi-layer mold set single crystal alloy ceramic mold shell is taken out;

[0083] Step 5, the ceramic mold shell is removed, the pouring and sprue and the crystal leading segment are cut off, and the single crystal high-temperature alloy test bar without crystal orientation deviation defect is obtained. The dendritic morphology of the obtained single crystal high-temperature alloy test bar is as shown in Figure 2 (a).

[0084] Example 2

[0085] The embodiment provides a preparation method of a single crystal high-temperature alloy casting, comprising the following steps:

[0086] Step 1, a multi-layer mold set single crystal alloy ceramic mold shell with a size of φ500 mm is fixed on a water cooling copper disc of a multi-layer mold set directional solidification device; the multi-layer mold set single crystal alloy ceramic mold shell is fixed on the water cooling copper disc, and then a specially-made heat insulation plate is fixed at the central axis of the top end of the central water cooling column of the water cooling copper disc of the lifting support of the multi-layer mold set directional solidification device, and the size of the heat insulation plate is φ350 mm.

[0087] Step 2, the mother alloy raw material is added into a smelting furnace of the multi-layer mold set directional solidification device, and the mother alloy smelting is performed at 1500 ℃ under the condition that all working areas in the device are kept in a sealed vacuum state, and at the same time, the multi-layer mold set single crystal alloy ceramic mold shell is preheated (the temperatures of the two annular heating components arranged vertically in the smelting chamber are 1450 ℃ in the upper area and 1500 ℃ in the lower area respectively), the preheating temperature of the multi-layer mold set single crystal alloy ceramic mold shell is consistent with the smelting temperature of the mother alloy, and the mother alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high-temperature alloy;

[0088] Step 3, after the mother alloy raw material is completely melted, the alloy liquid is poured into the multi-layer mold set single crystal alloy ceramic mold shell, the pouring and filling are completed, and the heat preservation is performed for 5 min;

[0089] Step 4, the large module single crystal alloy ceramic shell filled with alloy liquid is slowly moved into the cooling chamber at a pulling speed of 5 mm / min under the driving of the downward pulling transmission device. When the top surface of the heat insulation plate and the bottom surface of the heat insulation baffle are at the same horizontal line, the central water cooling column is controlled to rise from the surface of the water cooling copper disc at the same rising rate as the pulling rate of the ceramic shell. When the top surface of the heat insulation plate rises to the same horizontal line as the bottom surface of the top pouring disc, the central water cooling column is controlled to stop moving. After the directional solidification process is completed, waiting for cooling, releasing the vacuum state in the furnace, and taking out the multi-layer module single crystal alloy ceramic shell;

[0090] Step 5, removing the ceramic shell, cutting off the pouring riser and the seeding section, and obtaining a single crystal high-temperature alloy test bar without crystal orientation deviation defects. The dendritic morphology of the obtained single crystal high-temperature alloy test bar is shown in Figure 2 (b).

[0091] Example 3

[0092] The embodiment provides a preparation method of a single crystal high-temperature alloy casting, comprising the following steps:

[0093] Step 1, fixing a previously prepared large module single crystal alloy ceramic shell with a size of φ500 mm on a water-cooled copper disc of a multi-layer module directional solidification device; fixing the previously prepared large module single crystal alloy ceramic shell on the water-cooled copper disc, and then fixing a specially prepared heat insulation plate on the central axis at the top end of the central water cooling column of the water-cooled copper disc of the liftable support of the large module directional solidification device. The size of the heat insulation plate is φ300 mm.

[0094] Step 2, adding a master alloy raw material into a smelting furnace of the multi-layer module directional solidification device, and smelting the master alloy at 1500 ℃ under the condition that all working areas inside the device are kept in a sealed vacuum state. At the same time, the multi-layer module single crystal alloy ceramic shell is preheated (the temperatures of the two annular heating components arranged vertically in the smelting chamber are 1450 ℃ in the upper area and 1500 ℃ in the lower area, respectively). The preheating temperature of the multi-layer module single crystal alloy ceramic shell is consistent with the smelting temperature of the master alloy. The master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high-temperature alloy.

[0095] Step 3, after the master alloy raw material is completely melted, standing for 4 min, pouring the alloy liquid into the multi-layer module single crystal alloy ceramic shell, completing the pouring and filling, and performing heat preservation for 5 min;

[0096] Step 4, the large module single crystal alloy ceramic shell filled with alloy liquid is slowly moved into the cooling chamber at a pulling speed of 5 mm / min under the driving of the downward pulling transmission device. When the top surface of the heat insulation plate and the bottom surface of the heat insulation baffle are at the same horizontal line, the central water cooling column is controlled to rise from the surface of the water-cooled copper disc at the same rising rate as the pulling rate of the ceramic shell. When the top surface of the heat insulation plate rises to the same horizontal line as the bottom surface of the top pouring disc, the central water cooling column is controlled to stop moving. After the directional solidification process is completed, waiting for cooling, the vacuum state in the furnace is released, and the multi-layer module single crystal alloy ceramic shell is taken out;

[0097] Step 5, the ceramic shell is removed, the pouring riser and the crystal growth guide section are cut off, and a single crystal superalloy test bar without crystal orientation deviation defect is obtained. The dendritic morphology of the obtained single crystal superalloy test bar is as shown in Figure 2 (c).

[0098] Comparative Example 1

[0099] The present comparative example provides a preparation method of a single crystal superalloy casting, comprising the following steps:

[0100] Step 1, a large module single crystal alloy ceramic shell with a size of φ500 mm prepared in advance is fixed on the water-cooled copper disc of the multi-layer module directional solidification equipment, and no heat insulation plate is used in the shell;

[0101] Step 2, the master alloy raw material is added into the melting furnace of the multi-layer module directional solidification equipment. The master alloy is melted at 1500°C while keeping all the working areas inside the equipment in a sealed vacuum state. At the same time, the multi-layer module single crystal alloy ceramic shell is preheated (the temperature of the two annular heating components arranged vertically in the melting chamber is 1450°C in the upper area and 1500°C in the lower area respectively). The preheating temperature of the multi-layer module single crystal alloy ceramic shell is consistent with the melting temperature of the master alloy. The master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal superalloy.

[0102] Step 3, after the master alloy raw material is completely melted, it is left for 4 min, the alloy liquid is poured into the multi-layer module single crystal alloy ceramic shell, the pouring and filling are completed, and the heat preservation is carried out for 5 min;

[0103] Step 4, the large module single crystal alloy ceramic shell filled with alloy liquid is slowly moved into the cooling chamber at a pulling speed of 5 mm / min under the driving of the downward pulling transmission device. After the directional solidification process is completed, waiting for cooling, the vacuum state in the furnace is released, and the multi-layer module single crystal alloy ceramic shell is taken out;

[0104] Step 5, the ceramic shell is removed, the pouring riser and the crystal growth guide section are cut off, and a single crystal superalloy test bar without crystal orientation deviation defect is obtained. The dendritic morphology of the obtained single crystal superalloy test bar is as shown in

[0105] The dendritic morphology of the single crystal alloy test bar prepared using the large module single crystal alloy ceramic shell without heat insulation plate is as shown inFigure 2 (d) as shown.

[0106] As Figure 2 shown, under the condition of unchanged directional solidification process, with the setting of the heat insulation plate, the dendrite deviation angle of the prepared single crystal alloy test bar is significantly reduced. The crystal deviation angle of the cross section 70 mm, 140 mm, 210 mm above the spiral selector of the single crystal alloy test bar of example 1, example 2, example 3 and comparative example is measured respectively, and the results are shown in Figure 3 As can be seen from the figure, the crystal deviation angle of the single crystal bar prepared in the comparative example without the heat insulation plate is 32.8°, 24°, 36°, which is too large and cannot be applied. After adding the heat insulation plate, the crystal deviation angle of the single crystal bar prepared in the three groups of examples is reduced to different degrees, and with the increase of the size of the heat insulation plate, the crystal deviation angle gradually decreases from 18.3°, 13.9°, 14.8° to 12.9°, 9.1°, 12.8°, and finally to 3.7°, 5.3°, 4°. Figure 2 It can be seen that with the setting of the heat insulation plate, the number of dendrite patterns in the picture increases significantly, which indicates that the dendrite spacing is also reduced, and the heat leakage in the pulling process is improved. Therefore, by adding the heat insulation plate in the multi-layer mold single crystal alloy ceramic shell, the purpose of controlling the crystal deviation angle and reducing the dendrite spacing can be achieved.

[0107] The above implementation results show that by setting the heat insulation plate in the directional solidification process of the large mold single crystal alloy shell, due to the excellent heat conductivity of graphite, the internal heat dissipation of the annular large mold single crystal alloy shell is improved, the horizontal temperature field distribution in the solidification process is effectively controlled, the cooling rate of the inner and outer sides of the single crystal bar is similar, and the solid-liquid phase line front tends to be horizontal. At the same time, the heat insulation plate in the shell and the heat insulation baffle on the furnace body remain in a relatively static state during the pulling process, effectively isolating the heat exchange between the hot zone (melting chamber) and the cold zone (cooling chamber), reducing the occurrence of heat leakage phenomenon, and improving the temperature gradient of the solid-liquid phase line front of the casting.

[0108] Comparative example 2

[0109] The present comparative example provides a preparation method of a single crystal superalloy casting, comprising the following steps:

[0110] Step 1, fixing the pre-prepared large mold single crystal alloy ceramic shell with a size of φ500mm on the water-cooled copper disc of the multi-layer mold directional solidification equipment; fixing the pre-prepared large mold single crystal alloy ceramic shell on the water-cooled copper disc, and then fixing the specially prepared heat insulation plate on the center axis at the top of the central water-cooled column of the water-cooled copper disc of the large mold directional solidification equipment, and the size of the heat insulation plate is φ430mm.

[0111] Step 2, the master alloy raw material is added into the melting furnace of the multi-layer mold set directional solidification device, and the master alloy is melted at 1500℃ under the condition that all the working areas inside the device are kept in a sealed vacuum state. At the same time, the multi-layer mold set single crystal alloy ceramic mold shell is preheated (the temperature of the two annular heating components arranged vertically in the melting chamber is 1450℃ in the upper area and 1500℃ in the lower area respectively), and the preheating temperature of the multi-layer mold set single crystal alloy ceramic mold shell is consistent with the melting temperature of the master alloy. The master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal high-temperature alloy;

[0112] Step 3, after the master alloy raw material is completely melted, the alloy liquid is poured into the multi-layer mold set single crystal alloy ceramic mold shell after being placed for 4 minutes, the pouring and filling are completed, and the heat preservation is carried out for 5 minutes;

[0113] Step 4, the multi-layer mold set single crystal alloy ceramic mold shell containing the alloy liquid is slowly moved into the cooling chamber under the driving of the downward pulling transmission device at a pulling speed of 5mm / min. When the top surface of the heat insulation plate and the bottom surface of the heat insulation baffle are at the same horizontal line, the central water cooling column is controlled to rise from the surface of the water cooling copper disc at the same rising rate as the pulling rate of the ceramic mold shell. When the top surface of the heat insulation plate rises to the same horizontal line as the bottom surface of the top pouring disc, the central water cooling column is controlled to stop moving. After the directional solidification process is completed, the cooling is waited, the vacuum state in the furnace is released, and the multi-layer mold set single crystal alloy ceramic mold shell is taken out;

[0114] Step 5, the ceramic mold shell is removed, the pouring and sprue are cut off, and the single crystal high-temperature alloy test bar is obtained.

[0115] The crystal deviation angle of the prepared single crystal test bar is measured, and the result is 9.1°, 12.5°, and 14.8°, which is greater than that of the single crystal test bar obtained in Example 1, and the deviation direction is opposite to that of the test bars obtained in Examples 1, 2, 3 and Comparative Example 1. The reason for this phenomenon is that the heat dissipation speed of the test bar far from the furnace wall is greater than that near the furnace wall due to the too close distance between the heat insulation plate and the single crystal test bar, and because of the pulling process, the top pouring disc of the mold shell gradually approaches the heat insulation plate, blocking the heat radiation of the melting chamber to the heat insulation plate, so that the temperature of the heat insulation plate decreases, the inclination angle of the isotherm in the single crystal test bar increases, and the crystal deviation angle at the top of the single crystal test bar is greater than that at the bottom.

[0116] Comparative Example 3

[0117] The present comparative example provides a preparation method of a single crystal high-temperature alloy casting, comprising the following steps:

[0118] Step 1, fix the pre-prepared large mold module single crystal alloy ceramic shell with a size of φ500mm on the water-cooled copper plate of the multi-layer mold module directional solidification equipment; fix the pre-prepared large mold module single crystal alloy ceramic shell on the water-cooled copper plate, and then fix the specially-made heat insulation plate on the central axis at the top end of the central water-cooled column of the water-cooled copper plate of the liftable support of the multi-layer mold module directional solidification equipment, the heat insulation plate has a size of φ400mm and a thickness of 40mm.

[0119] Step 2, add the master alloy raw material into the smelting furnace of the multi-layer mold module directional solidification equipment, and smelt the master alloy at 1500℃ under the condition that all the working areas inside the equipment are kept in a sealed vacuum state, at the same time, preheat the multi-layer mold module single crystal alloy ceramic shell (the temperature of the two annular heating components arranged vertically in the smelting chamber is 1450℃ in the upper area and 1500℃ in the lower area respectively), the preheating temperature of the multi-layer mold module single crystal alloy ceramic shell is consistent with the smelting temperature of the master alloy, and the master alloy raw material of the single crystal alloy is DD5 nickel-based single crystal superalloy.

[0120] Step 3, after the master alloy raw material is completely melted, stand for 4min, pour the alloy liquid into the multi-layer mold module single crystal alloy ceramic shell, complete the pouring and filling, and keep warm for 5min;

[0121] Step 4, the large mold module single crystal alloy ceramic shell containing the alloy liquid slowly moves downward into the cooling chamber at a pulling speed of 5mm / min under the driving of the downward pulling transmission device, when the top surface of the heat insulation plate and the bottom surface of the heat insulation baffle are at the same horizontal line, control the central water-cooled column to rise from the surface of the water-cooled copper plate at the same rate as the pulling rate of the ceramic shell, when the top surface of the heat insulation plate rises to the same horizontal line as the bottom surface of the top pouring plate, control the central water-cooled column to stop moving. After the directional solidification process is completed, wait for cooling, release the vacuum state in the furnace, and take out the multi-layer mold module single crystal alloy ceramic shell;

[0122] Step 5, remove the ceramic shell, cut off the pouring riser and the seeding section, and obtain a single crystal superalloy test bar.

[0123] Observe the test bar by slicing and metallographic observation, it is found that most of the test bars have the phenomenon of crystal selection failure, and it is found by cutting and observing the crystal selector that the crystal selector near the heat insulation plate cannot directly receive the radiation heating of the central heating column due to the excessive thickness of the heat insulation plate, which causes a large temperature difference between the two sides of the crystal selector, the solid-liquid interface cannot be maintained horizontally, and the crystal selection failure phenomenon occurs. When the thickness of the heat insulation plate is too small, the heat insulation effect is insufficient and the heat leakage phenomenon cannot be effectively suppressed.

[0124] Those skilled in the art can easily understand that the advantageous technical features of the above-mentioned modes can be freely combined and superimposed without conflict.

[0125] The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A directional solidification apparatus for single-crystal superalloy castings, characterized in that, The directional solidification equipment includes a furnace body; wherein, the furnace body is provided with a melting chamber (15), a cooling chamber (16), a cooling structure and a heat insulation device; The melting chamber (15) and the cooling chamber (16) are thermally isolated from each other, and the melting chamber (15) is located on top of the cooling chamber (16); the melting chamber (15) is used to heat the mold shell; the cooling chamber (16) is used to solidify the alloy liquid inside the mold shell; The cooling structure is used to fix the mold shell; the mold shell can move upward with the cooling structure into the melting chamber (15) and downward into the cooling chamber (16); The heat insulation device includes a liftable heat insulation plate (6); wherein the heat insulation plate (6) is located on the upper side of the cooling structure; when the shell moves downward, the heat insulation plate (6) moves away from the cooling structure; when the shell moves upward, the heat insulation plate (6) moves closer to the cooling structure; when the shell is in motion, the heat insulation plate (6) is used to block heat transfer between the melting chamber (15) and the cooling chamber (16).

2. The directional solidification equipment for single-crystal high-temperature alloy castings according to claim 1, characterized in that, The heat insulation board (6) is made of graphite.

3. The directional solidification equipment for single-crystal high-temperature alloy castings according to claim 1, characterized in that, The furnace body is also equipped with a lifting device; the lifting device is used to drive the cooling structure and the mold shell to move upward or downward; and / or A channel for the operation of the cooling structure and the shell is provided between the melting chamber (15) and the cooling chamber (16).

4. The directional solidification equipment for single-crystal high-temperature alloy castings according to claim 1, characterized in that, The smelting chamber is equipped with a heating device; The heating device includes a heating component and a central heating column (9); the heating component surrounds the inner wall of the melting chamber (15) and is arranged around the central heating column (9); The cooling device includes a cooling assembly and a central water-cooled column (8). The cooling assembly surrounds the inner wall of the cooling chamber (16) and is arranged around the central water-cooled column (8).

5. The directional solidification equipment for single-crystal high-temperature alloy castings according to claim 4, characterized in that, The cooling structure is a water-cooled plate (7); the water-cooled plate (7) is annular; The heat insulation plate (6) is located on the top of the central water-cooling column (8); the central water-cooling column (8) is retractable to drive the heat insulation plate (6) to move away from or closer to the water-cooling plate (7).

6. The directional solidification apparatus for single-crystal superalloy castings according to any one of claims 1-5, characterized in that, The shell includes a pouring cup (1) and a top pouring plate (2), a single crystal sample chamber (3), a spiral crystal selector (4) and a crystal guide section (5); The pouring cup (1) is connected to the top of the top pouring plate (2); the bottom of the top pouring plate (2) is connected to the top of the single crystal sample cavity (3); the bottom of the single crystal sample cavity (3) is connected to the first end of the spiral crystal selector (4), and the second end of the spiral crystal selector (4) is connected to the first end of the crystal guide section (5). The second end of the crystal-leading segment (5) is fixed on the top surface of the water-cooling plate (7).

7. The directional solidification equipment for single-crystal high-temperature alloy castings according to claim 6, characterized in that, The top pouring plate (2) is annular, and the central heating column (9) can extend and retract within the hollow part of the top pouring plate (2) and the mold shell.

8. The directional solidification equipment for single-crystal high-temperature alloy castings according to claim 6, characterized in that, The diameter of the water-cooling plate is φ500mm; and / or The outer diameter of the shell is φ400-500mm, and the inner diameter is φ200-250mm; and / or The distance between the single crystal sample cavity (3) and the center of the shell is 200-225 mm; and / or The insulation board has a size of φ300-400mm and a thickness of 20±5mm.

9. A method for preparing single-crystal superalloy castings using the directional solidification equipment for preparing single-crystal superalloy castings as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1): Melt the master alloy raw material to obtain a liquid alloy, and at the same time preheat the mold shell in the melting chamber. Step 2): Inject the molten alloy into the mold shell and keep it at a constant temperature; Step 3): Pull the shell from the melting chamber into the cooling chamber, and remove the shell after cooling to obtain a single crystal high-temperature alloy test bar.

10. The preparation method according to claim 9, characterized in that, In step 2), the smelting process is carried out in a vacuum melting furnace; wherein the gas pressure inside the vacuum melting furnace is below 5 Pa; and / or The melting process is performed at a temperature of 1520℃ ± 50℃; and / or After the master alloy raw materials are melted, the settling time is 2-5 minutes; and / or The holding time after the alloy liquid is poured is 5-7 minutes; and / or The pulling speed is 3-7 mm / min.

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