A method of directional solidification with localised cooling of liquid metal for single crystal castings

Abstract

The present application belongs to the field of single crystal casting, and particularly relates to a directional solidification method for local cooling of liquid metal for single crystal casting. The method comprises the following steps: designing a liquid metal cooling module which can move synchronously with a casting group; cooling the liquid metal with a water-cooled ring; combining the casting group with a seed crystal at the lower end of the casting group; preparing a full-coated mold shell; synchronously lowering the mold shell system and the liquid metal cooling module away from a heating area; and obtaining a directional solidification casting. The method realizes pollution isolation which may occur during the liquid metal cooling process, ensures that the mold shell is not contaminated by reducing contact, and effectively improves the qualification rate of the liquid metal cooling method.

Description

Technical Field

[0001] This invention belongs to the field of crystal casting, specifically relating to a directional solidification method for local cooling of liquid metal in single-crystal castings. Background Technology

[0002] Single-crystal superalloy castings, as materials capable of withstanding temperatures above 1000℃, possess the ability to withstand high-temperature loads, especially their strong resistance to high-temperature creep, and are widely used in aerospace, aviation, and energy fields. Liquid metal cooling (LMC) is currently the method that can provide the largest temperature gradient, enabling the refinement of the primary dendrite orientation in single-crystal castings. It is one of the mainstream methods for casting high-performance single-crystal castings. Its biggest limitation is that conventional LMC requires the mold shell to be gradually and completely immersed in liquid metal, which can lead to mold shell cracking and casting contamination, thus affecting the yield rate. Furthermore, the high requirements for the mold shell and the process also limit its widespread use. Summary of the Invention

[0003] To address the problems in existing technologies, this invention provides a directional solidification method for localized cooling of liquid metal in single-crystal castings. This effectively solves the practical defects of liquid metal cooling methods, such as mold shell rupture and cracking leading to casting contamination or even fire, while also ensuring a good temperature gradient.

[0004] The technical solution of this invention is: A directional solidification method for localized cooling of liquid metal in single-crystal castings, the method using an apparatus comprising a hot zone module and a liquid metal cooling module, the hot zone module comprising a furnace body, a pouring gate, a heating zone, and a heat insulation baffle, the liquid metal cooling module comprising liquid metal, cooling water channels, and a pull-out system, the method specifically comprising the following steps: Step (1) Use the seed crystal-guided composite casting gating system and prepare the shell, wherein the seed crystal part of the shell is prepared with an additional 5 to 8 layers on the basis of the original shell to ensure the local shell strength. The shell is a fully enclosed shell. Step (2) Immerse the portion of the prepared shell covering the seed crystal below 1 / 2 in liquid metal for fixation; Step (3) is to perform directional solidification casting in the order of vacuuming the equipment, preheating, alloy refining, melting and casting, and pulling the shell downwards. The shell moves downwards along with the liquid metal cooling module, away from the heating zone, to complete the directional solidification forming of the single crystal casting.

[0005] Furthermore, in the aforementioned method for directional solidification of liquid metal for localized cooling of single-crystal castings, the seed crystal used is prepared from the same alloy as the casting.

[0006] Furthermore, in the aforementioned method for directional solidification of liquid metal for localized cooling of single-crystal castings, the liquid metal used is a gallium-indium alloy or a tin alloy.

[0007] Furthermore, in the aforementioned directional solidification method for local cooling of liquid metal in single-crystal castings, the shell moves downwards simultaneously with the liquid metal cooling module at a speed of 4~6 mm / min.

[0008] Advantages and beneficial effects of the present invention: This invention reduces the erosion of the mold shell by liquid metal cooling method, and isolates the possible contamination during the liquid metal cooling process while ensuring the temperature gradient. By reducing contact, it ensures that the mold shell is not contaminated, and effectively improves the yield rate of liquid metal cooling method. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the liquid metal cooling module and the hot zone module of the present invention. Detailed Implementation

[0010] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be used to limit the scope of the present invention. Example 1

[0011] This embodiment describes a directional solidification method for localized cooling of liquid metal in single-crystal castings, using a first-generation nickel-based single-crystal superalloy. The method specifically includes the following steps: Step (1) Use seed crystals to combine 8 test rods to form a casting system and prepare a shell. The basic shell has 6 layers, and the seed crystal shell has an additional 6 layers on the basis of the original 6-layer shell. The seed crystal material is a certain first-generation nickel-based single crystal high-temperature alloy. Step (2) as follows Figure 1 As shown, the apparatus includes a liquid metal cooling module and a hot zone module. The liquid metal cooling module includes liquid metal, cooling water channels, and a pulling system. The apparatus also includes a hot zone module, which includes a furnace body, a pouring port, a heating zone, and a heat insulation baffle. The portion of the prepared shell covering the seed crystal, below 1 / 2, is immersed in the liquid metal and fixed. The liquid metal is a gallium-indium alloy. Step (3) is to perform directional solidification casting in the order of vacuuming the equipment, preheating, alloy refining, melting and casting, and pulling the shell downward. The shell moves downward at a speed of 4 mm / min along with the liquid metal cooling module, away from the heating zone, and finally completes the directional solidification of the single crystal casting.

[0012] In this embodiment, no cracks occurred in the mold shell during the casting process, the test rod was well formed, and the single crystal integrity was good.

Claims

1. A method for directional solidification of liquid metal for localized cooling of single-crystal castings, characterized in that, The apparatus used in the method includes a hot zone module and a liquid metal cooling module. The hot zone module includes a furnace body, a pouring port, a heating zone, and a heat insulation baffle. The liquid metal cooling module includes liquid metal, a cooling water circuit, and a pull-out system. The method specifically includes the following steps: Step (1) Use the seed crystal-guided composite casting gating system and prepare the shell, wherein the seed crystal part of the shell is prepared with an additional 5 to 8 layers on the basis of the original shell to ensure the local shell strength. The shell is a fully enclosed shell. Step (2) Immerse the portion of the prepared shell covering the seed crystal below 1 / 2 in liquid metal for fixation; Step (3) Directional solidification and pouring are carried out in the order of equipment vacuuming-preheating-alloy refining-melting and casting-molding shell pulling down. The shell moves down with the liquid metal cooling module and away from the heating zone to complete the directional solidification and molding of the single crystal casting. The liquid metal used is a gallium-indium alloy or a tin alloy; The seed crystals used are made from the same alloy as the castings; The shell moves downwards at a speed of 4~6 mm / min along with the liquid metal cooling module.

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