Shell treatment process for inhibiting formation of mixed crystals on single crystal test bar by adding dynamic baffle

Abstract

The invention relates to the field of high-temperature alloy test bar casting, and particularly provides a shell treatment process for inhibiting a large-size single crystal test bar from forming mixed crystals by adding a dynamic baffle, which is characterized in that according to the shell treatment process for inhibiting the large-size single crystal test bar from forming the mixed crystals by adding the dynamic baffle, the test bars with the diameter of 32mm and the height of 220mm are combined by adopting a bottom pouring-spiral crystal selection method; the test bars are longitudinally and uniformly distributed on the water-cooling base plate and are connected with the pouring cup and the like to form a complete wax tree; 320 # electro-fused mullite powder and silica sol are mixed to prepare slurry, electro-fused mullite sand with different particle sizes is hung on the surface of the slurry, dewaxing and roasting are carried out after natural drying, and the precision casting single crystal test bar shell is obtained. The method has the advantages that on the premise that the optimal growth mode of the test bar is adopted, the graphite dynamic baffle is additionally arranged, so that the temperature gradient of a local area is improved, the internal temperature field is improved, formation of mixed crystals is inhibited, and the production qualification rate and the performance of the test bar are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of casting of superalloy test bars, and particularly relates to a shell treatment process for increasing a dynamic baffle to suppress the formation of polycrystals in large-size single-crystal test bars. Background Art

[0002] During the grain growth process of single-crystal blades, transverse grain boundaries can be eliminated, and they have better abilities in high-temperature creep resistance, thermal fatigue resistance, oxidation resistance, hot corrosion resistance, etc., enabling single-crystal blades to be applicable to more severe working environments compared to other blades. Therefore, they are widely used in national defense, people's livelihood, and other aspects.

[0003] However, the production process of single-crystal blades is complex, the qualified rate is low, and the cost is high. Therefore, during the blade manufacturing process, single-crystal test bars under the same process conditions are generally used to replace the blades for performance testing. Although the cost of single-crystal test bars is lower than that of single-crystal blades, their requirements during the directional solidification process are basically the same as those of single-crystal blades, and the production difficulty is also very close. Especially as the size of the single-crystal test bar increases, the grain growth becomes more difficult, and the probability of forming polycrystals increases significantly, resulting in most single-crystal test bars not meeting their inspection requirements. Therefore, there is an urgent need to invent a process method for suppressing the formation of polycrystals in large-size single-crystal test bars. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the existing process, the present invention aims to provide a method of increasing multi-layer dynamic baffles at different height positions around the shell of a single-crystal test bar to increase the temperature gradient in a local area. This process can improve problems such as complex temperature field distribution and large supercooling degree differences in the internal and external regions and upper and lower regions of the single-crystal test bar, and greatly reduce the probability of polycrystal defect occurrence.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A shell treatment process for increasing a dynamic baffle to suppress the formation of polycrystals in a single-crystal test bar, using a bottom-pouring - spiral grain selection method to combine test bars with a diameter of 32 mm and a height of 220 mm. The test bars are longitudinally and evenly distributed on a water-cooled chassis, and a pouring cup, etc. are connected to form a complete wax tree. A slurry is made by mixing 320# fused mullite powder and silica sol, and then fused mullite sand with different particle sizes is hung on its surface. After natural drying, dewaxing and roasting are carried out to obtain a precision casting single-crystal test bar shell.

[0007] At a height of every 30 mm from the chassis of the test bar shell, multi-layer dynamic baffles made of graphite are added to completely block the area where the cross-section is located. A high-efficiency solidification furnace (HRS) is used to prepare the single-crystal test bar, with a pulling rate of 3 mm / min, a pouring temperature of 1550 - 1600 °C, the upper and lower zone temperatures of the holding furnace both being 1520 °C, and a pulling height of 270 mm.

[0008] The dynamic baffle is made of graphite and has a thickness of 1.0 - 1.5 mm.

[0009] Medium-temperature die wax is selected for the wax tree, and all test bars are connected by welding.

[0010] In the slurry, the powder-liquid mass ratio is 4.0:1, the pH value of the silica sol is 10, the shell mold is dried naturally, the drying duration is 8 hours, and the weight of the shell mold is 2.7 - 3.0 Kg.

[0011] For the dewaxing process, the dewaxing temperature is 165 - 175 °C, the dewaxing pressure is 0.6 - 0.7 MPa, and the dewaxing time is 13 - 16 min.

[0012] For the roasting process, the shell roasting temperature is 900 - 1000 °C, and the shell roasting duration is 2 - 3 h.

[0013] The advantages of the present invention are as follows:

[0014] On the premise of already adopting the optimal growth mode of the test bar, the present invention increases the temperature gradient in the local area by adding a graphite dynamic baffle, improves its internal temperature field, inhibits the formation of heterocrystals, and greatly improves the production qualification rate and performance of the test bar. Specific Embodiments

[0015] To make the purpose, technical solution and advantages of the present invention clearer, the following examples are listed to further elaborate on this optimized process plan.

[0016] Example 1

[0017] First, a test bar with a diameter of 32 mm and a height of 220 mm and the corresponding runner are combined by the bottom-pouring crystal selection method. Medium-temperature wax is selected for the wax material, the height of the wax tree is 310 mm, and there are 4 test bars in each group. The entire mold is subjected to the precision casting shell-making process. The slurry is prepared by mixing 320-mesh fused mullite powder and silica sol of PICP-AN specification, the powder-liquid mass ratio is 4.0:1, the pH value of the silica sol is 10, and fused mullite sand with particle sizes of 80 - 60 - 60 - 46 - 24 - 24 is used respectively, and the drying duration for each layer is 8 h. After the mold shell is prepared, dewaxing is carried out. The dewaxing temperature is 170 °C, the dewaxing pressure is 0.65 MPa, the roasting temperature is 900 °C, and the duration is 3 h.

[0018] The shell mold after roasting is cleaned with tap water. After natural drying for 48 h, a layer of graphite baffle is added at a height of every 30 mm from the chassis for all the test bars, and the graphite baffle completely covers the area where the corresponding cross-section is located. The shell mold is placed in a high-speed solidification furnace (HRS), and the shell is lifted to the specified position at a uniform speed of 200 mm / min, and then lifted to the target position at a uniform speed of 30 mm / min. The refining temperature of the alloy liquid is 1600 °C, the pouring temperature is 1550 - 1560 °C, the temperatures of the upper and lower zones of the holding furnace are both 1520 °C, and the vacuum degree before pouring the alloy liquid into the shell mold should be below 3 Pa. It is pulled downwards at a uniform speed of 3 mm / min, with a height of 270 mm. After the directional solidification process is completed, shell cleaning, cutting, and macroscopic corrosion are carried out. The corrosion liquid ratio is hydrochloric acid: hydrogen peroxide = 5:1. After cleaning, grain inspection is carried out and it is found that all the test bars prepared by this process are complete single crystals.

[0019] Example 2

[0020] First, test bars with a diameter of 40 mm and a height of 190 mm and the corresponding runners are combined by the bottom-gating and seed selection method. Medium-temperature wax is selected as the wax material, the height of the wax tree is 280 mm, there are 4 test bars in each group, and the whole module undergoes the precision casting shell-making process. The slurry is prepared by mixing fused mullite powder with 320 mesh and silica sol of PICP-AN specification, the powder-liquid mass ratio is 4.0:1, the pH value of the silica sol is 10, and fused mullite sand with 80 - 60 - 60 - 46 - 24 - 24 is used respectively, and the drying time for each layer is 8 h. After the mold shell is prepared, dewaxing is carried out. The dewaxing temperature is 170 °C, the dewaxing pressure is 0.65 MPa, the roasting temperature is 900 °C, and the duration is 3 h.

[0021] The shell mold after roasting is cleaned with tap water. After natural drying for 48 h, a layer of graphite baffle is added at a height of every 30 mm from the chassis for all the test bars, and the graphite baffle completely covers the area where the corresponding cross-section is located. The shell mold is placed in a high-speed solidification furnace (HRS), and the shell is lifted to the specified position at a uniform speed of 200 mm / min, and then lifted to the target position at a uniform speed of 30 mm / min. The refining temperature of the alloy liquid is 1600 °C, the pouring temperature is 1550 - 1560 °C, the temperatures of the upper and lower zones of the holding furnace are both 1520 °C, and the vacuum degree before pouring the alloy liquid into the shell mold should be below 3 Pa. It is pulled downwards at a uniform speed of 3 mm / min, with a height of 240 mm. After the directional solidification process is completed, shell cleaning, cutting, and macroscopic corrosion are carried out. The corrosion liquid ratio is hydrochloric acid: hydrogen peroxide = 5:1. After cleaning, grain inspection is carried out and it is found that all the test bars prepared by this process are complete single crystals.

[0022] Matters not covered by the present invention are well-known technologies.

[0023] The above embodiments are only used to illustrate the technical concept and features of the present invention. The purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A shell treatment process for adding a dynamic baffle to suppress the formation of stray crystals in a large-sized single crystal test rod, characterized in that: The shell processing process for adding a dynamic baffle to suppress the formation of impurity crystals in a large-sized single crystal test rod adopts a bottom injection-spiral crystal selection method to combine a test rod with a diameter of 32 mm and a height of 220 mm. The test rod is evenly distributed longitudinally on a water-cooled chassis and connected to a pouring cup to form a complete wax tree. 320# fused mullite powder and silica sol are mixed to form a slurry, and fused mullite sand of different particle sizes is hung on the surface of the slurry. After natural drying, it is dewaxed and roasted to obtain a precision casting single crystal test rod shell.

2. The shell treatment process for adding a dynamic baffle to suppress the formation of stray crystals in a large-sized single crystal test rod according to claim 1, characterized in that: At a height of 30mm from the bottom plate of the test rod shell, multi-layer graphite dynamic baffles are added to completely cover the area where the cross section is located. The single crystal test rod is prepared using a high-efficiency solidification furnace, with a pulling rate of 3mm / min, a pouring temperature of 1550-1600℃, a temperature of 1520℃ in the upper and lower zones of the insulation furnace, and a pulling height of 270mm.

3. The shell treatment process for adding a dynamic baffle to suppress the formation of stray crystals in a large-sized single crystal test rod according to claim 1, characterized in that: The dynamic baffle is made of graphite and has a thickness of 1.0-1.5 mm.

4. The shell treatment process for adding a dynamic baffle to suppress the formation of stray crystals in a large-sized single crystal test rod according to claim 1, characterized in that: The wax trees are all made of medium-temperature mold wax, and all test rods are connected by welding.

5. The shell treatment process for adding a dynamic baffle to suppress the formation of stray crystals in a large-sized single crystal test rod according to claim 1, characterized in that: In the slurry, the powder-liquid mass ratio is 4.0:1, the pH value of the silica sol is 10, the shell is dried naturally, the drying time is 8 hours, and the shell weight is 2.7-3.0 kg.

6. The shell treatment process for adding a dynamic baffle to suppress the formation of stray crystals in a large-sized single crystal test rod according to claim 1, characterized in that: The dewaxing process has a dewaxing temperature of 165-175° C., a dewaxing pressure of 0.6-0.7 MPa, and a dewaxing time of 13-16 min.

7. The shell treatment process for adding a dynamic baffle to suppress the formation of stray crystals in a large-sized single crystal test rod according to claim 1, characterized in that: The shell burning temperature of the roasting process is 900-1000° C., and the shell burning time is 2-3 hours.