Ultrahigh-pressure hot isostatic pressing method based on press machine and using liquid metal as medium

Abstract

The invention belongs to the technical field of surface strengthening, and particularly relates to an ultrahigh-pressure hot isostatic pressing method taking liquid metal as a medium based on a press machine. A to-be-treated workpiece and molten liquid metal are put into a liquid metal container, the whole container is filled with the liquid metal container, and then an upper cover is covered; applying pressure to the liquid metal container by using a press machine, and keeping the displacement unchanged; heating the liquid metal container by using a high-temperature furnace and preserving heat until the upper value of the force sensor is relatively stable; the steps are repeated without liquid metal in the liquid metal container, and the pressure intensity generated in the container is calculated according to the difference value of the two forces and the area of the container; and according to the obtained pressure intensity and temperature, the workpiece to be treated and the molten liquid metal are put into a liquid metal container, and after hot isostatic pressing treatment is conducted, the workpiece is directly taken out of the liquid metal to be rapidly cooled. Compared with traditional hot isostatic pressing achieved through gas and a supercharger, the method has the advantages of being simple in principle, convenient to operate and high in safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface strengthening, and particularly relates to a super-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, which is applicable to the densification treatment of metal structural materials such as titanium alloys and superalloys. Background Art

[0002] At present, commonly used hot isostatic pressing (HIP) equipment generally uses inert gas as the medium, and the gas has problems such as poor thermal conductivity, difficult sealing, and small bulk modulus. Limited by the current technical level, the maximum pressure of current HIP equipment is generally less than 200 MPa, which is very limited compared with the strength of common materials. This leads to the need for high-temperature treatment to achieve micropore healing for metal structural materials such as titanium alloys, superalloys, and steels. In addition, limited by the pressure relief speed, traditional HIP is difficult to balance the pressure to open the furnace and take out the parts in a short time, so the workpiece can only be cooled naturally in the furnace, greatly limiting the room for controlling the material structure during the cooling process. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention aims to provide a super-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, which solves the problems of low pressure, slow cooling, and difficult sealing of traditional HIP technology through the synergistic effect of liquid metal medium, press sealing structure, and rapid cooling technology.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A super-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, comprising the following steps:

[0006] (1) Place the workpiece to be processed and the melted liquid metal into a liquid metal container, heat and keep it warm with a high-temperature furnace to ensure that the liquid metal in the container is completely melted, fill the entire container, and then cover the upper cover;

[0007] (2) Apply pressure to the liquid metal container with a press and keep the displacement unchanged;

[0008] (3) Heat and keep the liquid metal container warm with a high-temperature furnace until the value on the force sensor is relatively stable;

[0009] (4) Repeat steps (1), (2), and (3) without putting liquid metal in the liquid metal container, and calculate the pressure generated in the container according to the difference between the two forces and the cross-sectional area of the inner cavity of the container;

[0010] (5) According to the pressure and temperature obtained in step (4), place the workpiece to be processed and the melted liquid metal into the liquid metal container, after hot isostatic pressing treatment, directly take out the workpiece from the liquid metal and perform rapid cooling.

[0011] In the described ultra-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, in step (1), liquid metal is selected as the medium, and the liquid metal is selected from gallium, indium, tin metals with low melting points and high boiling points or alloys of two or more of them.

[0012] In the described ultra-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, in step (1), in order to prevent the liquid metal from permeating the workpiece to be processed, a layer of high-temperature protective paint is coated on the surface of the workpiece to be processed.

[0013] In the described ultra-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, in step (1), the liquid metal container material is selected from tungsten metal or molybdenum metal with a small coefficient of thermal expansion at high temperatures.

[0014] In the described ultra-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, in step (1), after covering the upper cover, asbestos is used to wipe off the excess liquid metal.

[0015] In the described ultra-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, the hot isostatic pressing device used in this method includes a high-temperature furnace, liquid metal, a liquid metal container, a press, a displacement sensor, and a force sensor. The specific structure is as follows: The liquid metal container containing the liquid metal and the workpiece to be processed is placed in the high-temperature furnace. A force sensor is provided at the upper end of the ram of the press, and a pressurizing ball head corresponding to the upper port of the liquid metal container is provided at the center of the lower end of the ram. An upper cover that matches the pressurizing ball head through a spherical surface is provided at the upper port of the liquid metal container. The ram contacts the upper cover of the liquid metal container through a spherical surface fit, and a displacement sensor is also provided on the lower end surface of the ram.

[0016] The design concept of the present invention is:

[0017] Based on the advantages of good thermal conductivity and large bulk modulus of liquid metal itself, the present invention combines the mechanical pressing of the press with the thermal expansion characteristics of liquid metal for the first time, and realizes the ultra-high pressure (300 - 1000 MPa) hot isostatic pressing technology through the "displacement holding - temperature increase - temperature difference pressurization" mechanism. Sealing is achieved through the press, with convenient operation and high repeatability. Due to the characteristics of low melting point and high boiling point of liquid metal, a larger pressure is achieved through a larger temperature difference. In addition, the two-experiment force difference method proposed by the present invention uses the bulk modulus and coefficient of thermal expansion of liquid metal to accurately calculate the pressure, solving the technical problem of direct measurement in an ultra-high pressure environment.

[0018] The present invention has the following advantages and beneficial effects:

[0019] 1. The present invention realizes the ultra-high pressure hot isostatic pressing technology based on a press and liquid metal medium, with advantages such as simple principle, convenient operation, and high safety.

[0020] 2. Medium Selection and Performance Optimization: The present invention uses liquid metal (such as gallium-indium-tin and its alloys) to replace traditional gas media. Utilizing its high thermal conductivity, high bulk modulus, and easy sealing characteristics, mechanical pressure is applied by a press and displacement is maintained. Combining with the thermal expansion characteristics of liquid metal, the pressure limit of gas media is broken through.

[0021] 3. Press Sealing Structure: The present invention proposes to use a press to seal through spherical mating and apply pressure, replacing traditional thread sealing, to solve the leakage problem caused by material deformation under ultra-high pressure and high temperature, and improve repeatability.

[0022] 4. Dynamic Calculation of Pressure and Quick Cooling Technology: The present invention calculates the actual pressure through the difference between two experiments (with / without liquid metal), and combines with quickly cooling the workpiece directly taken out from the liquid metal to achieve coordinated control of microstructure-defects and improve the fatigue performance of materials. Brief Description of the Drawings

[0023] Figure 1 is the technical schematic diagram of the present invention.

[0024] Figure 2 is a schematic diagram of the liquid metal container.

[0025] Figure 1 - Figure 2 The reference numerals in the figure: 1 high-temperature furnace, 2 liquid metal, 3 liquid metal container, 4 press, 5 displacement sensor, 6 force sensor, 7 indenter, 8 pressurizing ball head, 9 upper cover, 10 spherical surface.

[0026] Figure 3 is the graph of the change of force inside the container when heating from 300°C to 500°C in Example 1. In the figure, the abscissa is time (S), and the ordinate is force (KN). Detailed Embodiment

[0027] As Figure 1 - Figure 2 shown, the hot isostatic pressing device of the present invention includes a high-temperature furnace 1, liquid metal 2, a liquid metal container 3, a press 4, a displacement sensor 5, and a force sensor 6. The specific structure is as follows:

[0028] The liquid metal container 3 containing liquid metal 2 and the workpiece to be processed is placed in the high-temperature furnace 1. A force sensor 6 is provided at the upper end of the indenter 7 of the press 4, and a pressurizing ball head 8 corresponding to the upper port of the liquid metal container 3 is provided at the center of the lower end of the indenter 7. An upper cover 9 that mates with the pressurizing ball head 8 through a spherical surface 10 is provided at the upper port of the liquid metal container 3. The indenter 7 and the upper cover 9 of the liquid metal container 3 are in contact through spherical surface 10 mating, and a displacement sensor 5 is also provided on the lower end surface of the indenter 7. Among them, the high-temperature furnace 1 realizes a high-temperature environment, and the press 4 cooperates with the sensors (displacement sensor 5, force sensor 6) to achieve displacement holding and pressure measurement.

[0029] In the specific implementation process, the present invention adopts an ultra-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, including the following steps:

[0030] (1) Place the workpiece to be processed and the melted liquid metal into the liquid metal container, heat it to a certain temperature with a high-temperature furnace and keep it warm for a period of time to ensure that the liquid metal in the container is completely melted, fill the entire container, and then cover the upper cover;

[0031] In step (1), liquid metal is selected as the medium, which has the advantages of good thermal conductivity, high safety, easy sealing, and large bulk modulus compared with gas media. The liquid metal is selected as a metal with a low melting point and a high boiling point, such as gallium, indium, tin metal or an alloy of two or more of them, and the boiling point can reach above 2000 °C. If the liquid metal penetrates the workpiece to be processed, a layer of high-temperature paint or other medium can be coated on the surface of the component to be processed to avoid interface penetration and contamination. The material of the liquid metal container should be selected as a material with a small coefficient of thermal expansion at high temperatures, such as metals like tungsten or molybdenum. After covering the upper cover, wipe off the excess liquid metal with asbestos or the like to observe whether there is any leakage of liquid metal during the entire experiment.

[0032] (2) Apply a certain pressure to the liquid metal container with a press and keep the displacement unchanged.

[0033] In step (2), sealing is achieved by using a spherical fit with a press, which is convenient to operate and has high repeatability, because traditional thread seals do not have suitable materials at ultra-high pressure and high temperature and are also difficult to be reused.

[0034] Among them, "displacement unchanged" means that the indenter 7 or the pressing component of the press 4 is fixed in position after applying pressure, and there is no axial relative movement between the indenter 7 and the liquid metal container 3. That is to say, the total volume of the liquid metal container 3 is forcibly constrained to form an approximately airtight and volume-fixed space. When the liquid metal 2 expands due to heat, it cannot release stress by increasing the volume, but can only balance the external mechanical constraint by increasing the internal pressure.

[0035] The displacement control mechanism of the press of the present invention is as follows:

[0036] 1) Rigid mechanical constraint

[0037] After the press (such as a hydraulic or servo press) applies an initial pressure to the upper cover at the top of the liquid metal container through the punch, the position of the punch is locked to prevent axial displacement during subsequent heating. This fixed displacement ensures that the overall volume of the liquid metal container remains constant. When the liquid metal expands due to heat, it cannot release stress by increasing its volume and can only be converted into an increase in internal pressure. For example, the punch and the upper cover of the liquid metal container are in spherical contact. After applying pressure, the position of the punch is fixed by the servo system or mechanical locking mechanism of the press, forming a rigid displacement constraint.

[0038] 2) Force-displacement closed-loop control

[0039] The press is equipped with a force sensor to monitor the applied force value in real time. When the internal pressure of the liquid metal increases due to temperature rise, the press maintains the position of the punch unchanged through the feedback system to ensure that the external mechanical constraint does not change with the internal pressure.

[0040] (3) Heat the liquid metal container with a high-temperature furnace to a specified temperature and keep it warm for a certain period until the value on the force sensor is relatively stable.

[0041] (4) Without putting liquid metal in the liquid metal container, repeat steps (1), (2), and (3), and calculate the pressure generated inside the container based on the difference in force between the two times and the cross-sectional area of the container cavity.

[0042] (5) According to the pressure and temperature obtained in step (4), place the workpiece to be processed and the melted liquid metal into the liquid metal container. After processing for a certain period of time, directly take out the workpiece from the liquid metal to achieve its rapid cooling technology.

[0043] In step (5), opening the container to remove the workpiece while balancing the pressure in a short time can achieve coordinated control of microstructure and defects through rapid cooling, thereby significantly improving the fatigue performance of the workpiece.

[0044] Next, the present invention will be further elaborated in detail through embodiments.

[0045] Embodiment 1

[0046] As Figure 1 - Figure 2 shown, in this embodiment, the material of the liquid metal 2 is tin (melting point is about 231.9 °C, boiling point is about 2270 °C), and the material of the workpiece to be processed is an additive manufacturing titanium alloy. Based on the ultra-high pressure hot isostatic pressing method with liquid metal as the medium by the press, it includes the following steps:

[0047] (1) Place the workpiece to be processed and the melted liquid metal 2 into the liquid metal container 3 (such as a tungsten crucible), heat it to 300 °C with a high-temperature furnace 1 and keep it warm for 1 h to ensure that the liquid metal 2 in the liquid metal container 3 is completely melted and fills the entire liquid metal container 3, and then cover the upper cover 9;

[0048] (2) Apply a pressure of 63 KN to the liquid metal container 3 with a press 4 and keep the displacement unchanged.

[0049] (3) Heat the liquid metal container 3 with a high-temperature furnace 1 to 500 °C and keep it warm for 1 h until the value of the force sensor reaches 72 KN and the value on the force sensor is relatively stable.

[0050] (4) Without putting liquid metal in the liquid metal container 3, repeat steps (1), (2), and (3), and calculate the pressure generated in the liquid metal container according to the difference between the two forces and the cross-sectional area of the inner cavity of the liquid metal container.

[0051] In this embodiment, the calculation process of the pressure generated in the liquid metal container is as follows: the difference between the two forces is 72 - 63 = 9 KN, the cross-sectional diameter of the inner cavity of the liquid metal container is 10 mm, and the pressure generated in the liquid metal container is P = F / S = 9000 N / (3.14×5×5) = 114.6 MPa.

[0052] As Figure 3 shown, it can be seen from the force change diagram of the container heated from 300 °C to 500 °C in Example 1 that after a certain period of time, the difference between the force sensors in the two experiments (with / without liquid metal) is constant and there is no need to keep warm for a long time.

[0053] (5) According to the pressure and temperature obtained in step (4), place the workpiece to be processed and the melted liquid metal 2 into the liquid metal container 3, heat it to 500 °C by hot isostatic pressing and keep it warm for 1 h to achieve hot isostatic pressing treatment at 114.6 MPa, and directly take out the workpiece from the liquid metal and perform rapid cooling (oil quenching or water quenching).

[0054] The implementation results show that the hot isostatic pressing technology of the present invention utilizes the advantages of good thermal conductivity, high safety, easy sealing, and large body modulus of liquid metal itself, and can achieve ultra-high pressure hot isostatic pressing above 300 MPa according to actual production needs. Compared with the traditional hot isostatic pressing achieved by gas and a booster, it has the advantages of simple principle, convenient operation, and high safety.

Claims

1. A super-high pressure hot isostatic pressing method based on a press with liquid metal as the medium, characterized in that, It includes the following steps: (1) Place the workpiece to be processed and the molten liquid metal into the liquid metal container, heat and keep it warm with a high-temperature furnace to ensure that the liquid metal in the container is completely melted, fill the entire container, and then cover the upper cover; (2) Apply pressure to the liquid metal container with a press and keep the displacement unchanged; (3) Heat and keep the liquid metal container warm with a high-temperature furnace until the value on the force sensor is relatively stable; (4) Repeat steps (1), (2), and (3) without putting liquid metal in the liquid metal container, and calculate the pressure generated in the container according to the difference between the two forces and the cross-sectional area of the inner cavity of the container; (5) According to the pressure and temperature obtained in step (4), place the workpiece to be processed and the molten liquid metal into the liquid metal container, after hot isostatic pressing treatment, directly take out the workpiece from the liquid metal and perform rapid cooling.

2. The ultra-high pressure hot isostatic pressing method based on a press with liquid metal as the medium according to claim 1, wherein In step (1), a liquid metal is selected as the medium, and the liquid metal is selected from low-melting-point and high-boiling-point gallium, indium, tin metals or alloys of two or more of them.

3. A super-high pressure hot isostatic pressing method based on a press with liquid metal as the medium according to claim 1, characterized in that, In step (1), in order to prevent the liquid metal from permeating the workpiece to be processed, a layer of high-temperature protective paint is coated on the surface of the workpiece to be processed.

4. A method for ultra-high pressure hot isostatic pressing based on a press with liquid metal as a medium according to claim 1, characterized in that In step (1), the material of the liquid metal container is selected from tungsten metal or molybdenum metal with a small coefficient of thermal expansion at high temperatures.

5. A super-high pressure hot isostatic pressing method based on a press with liquid metal as the medium according to claim 1, characterized in that, In step (1), after covering the upper cover, wipe the excess liquid metal with asbestos.

6. A method for ultra-high pressure hot isostatic pressing based on a press with liquid metal as a medium according to claim 1, characterized in that, The hot isostatic pressing device used in this method includes a high-temperature furnace, liquid metal, a liquid metal container, a press, a displacement sensor, and a force sensor. The specific structure is as follows: The liquid metal container containing the liquid metal and the workpiece to be processed is placed in the high-temperature furnace. The upper end of the ram of the press is provided with a force sensor, and the center of the lower end of the ram is provided with a pressurizing ball head corresponding to the upper port of the liquid metal container. At the upper port of the liquid metal container, there is an upper cover that matches the pressurizing ball head through a spherical surface. The ram contacts the upper cover of the liquid metal container through a spherical surface fit, and a displacement sensor is also provided on the lower end surface of the ram.

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