CN111036914A

CN111036914A - Additive manufacturing method of tungsten-based diffusion cathode

Info

Publication number: CN111036914A
Application number: CN202010006398.5A
Authority: CN
Inventors: 王金淑; 骆凯捷; 杨韵斐; 周帆; 梁轩铭; 刘伟; 陈树群
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2020-01-03
Filing date: 2020-01-03
Publication date: 2020-04-21

Abstract

A material increase manufacturing method of a tungsten-based diffusion cathode belongs to the technical field of preparation of hot cathode electron emission materials, a cathode porous tungsten base is prepared by adopting a Selective Laser Melting (SLM) technology capable of three-dimensional forming, and the relation between laser energy and the density of the porous tungsten base is researched. The research result shows that the cathode matrix with the relative density of 65.7 percent can be obtained by adopting the preparation process with the laser power P of 160W, the scanning speed V of 1600mm/s and the scanning distance D of 0.10mm, the requirements of subsequent preparation and processing of the cathode can be met, and the impregnation amount of the active salt reaches 13 percent. The emission performance of the cathode is tested, and the result shows that the emission performance of the cathode can reach the emission performance of the traditional barium-tungsten cathode material.

Description

Additive manufacturing method of tungsten-based diffusion cathode

Technical Field

The invention belongs to the field of rare earth refractory metals and electron emission materials, and mainly relates to a preparation method of a tungsten-based diffusion cathode.

Background

The cathode is an electron source of an electro-vacuum device and is known as the heart of the device. In recent years, as vacuum electronic devices are developed to high frequency, miniaturization and diversification, the requirements of the devices on the size appearance, precision and emission performance of cathodes are continuously increased. At present, the most widely used cathode in the electro-vacuum device is a barium-tungsten cathode and an improved M-type cathode based on the barium-tungsten cathode, the device has the characteristics of large emission current density and strong environment tolerance, the working mechanism is that barium oxide capable of improving the emission performance of the cathode is stored in a porous tungsten matrix through immersion after being melted at high temperature in an aluminate mode, and then barium in the aluminate is continuously diffused outwards at the working temperature to form an emission active layer on the surface of tungsten, so that the emission performance of the cathode is improved. The porous tungsten substrate is prepared by pressing and high-temperature sintering tungsten copper serving as a raw material in a powder metallurgy mode to prepare an alloy, and then copper is removed to obtain porous tungsten with holes, so that the tungsten can be prevented from being greatly contracted in the holes in the high-temperature impregnation process of the tungsten electrode body after high-temperature sintering, and the purpose of storing active substances is achieved. However, the cathode prepared by the traditional powder metallurgy method has a single shape and a large processing amount, so that a large amount of raw materials are wasted in the preparation process of the cathode, and the cost for preparing the cathode by the traditional powder metallurgy method is relatively high.

The selective laser melting technique is a manufacturing method which is recently developed and mainly utilizes metal powder which is completely melted under the heat action of laser beam and is formed by cooling and solidifying. The method has the advantages of high speed, strong controllability, high precision, less material loss and the like, and particularly has the advantages of direct forming of complex shapes and small later processing amount, so that the method applies the technology to the preparation of the porous tungsten matrix, not only can improve the preparation efficiency of the cathode, but also can directly prepare the cathode with the complex shape, and further reduces the preparation cost of the cathode.

Disclosure of Invention

The invention provides a research method for preparing a tungsten-based cathode by an additive manufacturing technology (3D printing), which adopts tungsten powder as a raw material, obtains a porous tungsten matrix by a selective laser melting technology, and then obtains the tungsten-based diffusion cathode by dipping active barium salt and surface treatment. At present, no research report on the material and the method is found.

The invention prepares a tungsten-based diffusion cathode obtained by a selective laser melting technology, and is characterized by rapidness, strong controllability, high precision and low energy consumption. The shape and microstructure of the formed tungsten piece are controlled by adjusting parameters of laser density, scanning speed and scanning distance. The dipping substance is active salt, and the mass percentage of the active salt is 0.5-25%.

The active salt mainly comprises an active salt formed by sintering alkaline earth oxides such as barium oxide, calcium oxide and strontium oxide and one or more of aluminum oxide, zirconium oxide, silicon oxide and tungsten oxide at a high temperature, which is a conventional technology.

The preparation process comprises the following steps:

the method comprises the following steps: printing and molding tungsten powder by a selective laser melting technology to prepare a cathode substrate with pores, wherein the volume of through holes in the cathode substrate is 5-35%, namely the porosity;

step two: dipping the cathode matrix prepared in the step one in an emission active salt at a high temperature;

step three: treating the surface of the cathode according to different cleanliness of the surface of the cathode, wherein the treatment mode is a washing mode such as water washing, acid washing, alkali washing and the like, or a physical treatment method such as machining and the like; and then annealing treatment is carried out.

Further preferred is the step one: selecting 100nm-100um tungsten powder, annealing and reducing the tungsten powder in periodic hydrogen, and screening, for example, keeping the tungsten powder in hydrogen at 800 ℃ for 2 h.

Further preferred is the step one: and respectively adopting a continuous pulse laser device for forming. The tungsten matrix with the porosity of 10-30% is obtained by adjusting laser parameters and the like.

Different laser printing parameters can be adopted to obtain tungsten-based substrates of different models, the laser power P is 150-200W, the scanning distance d is 0.10-0.20mm, and the scanning speed v is 800-1600 mm/s.

It is further preferred that the temperature of the annealing in the third step is 850-1700 ℃ for 1 minute-5 hours.

Further preferably, before the high-temperature dipping of the emission active salt is carried out in the second step, the obtained cathode substrate is annealed at the temperature of 850-1700 ℃ for 1 min-5 h.

The preparation method is simple, strong in operability, material-saving, short in preparation period, high in strength of prepared samples, suitable for large-scale industrial preparation, capable of working at normal temperature in devices, and suitable for high-frequency and high-power electro-vacuum devices and electron beam sources with high requirements on precision.

Drawings

In order to describe the technical solution of the embodiment of the present invention in more detail, the drawings used in the description of the embodiment are briefly introduced below. It is obvious that the drawings in the following description are of some embodiments of the invention only, and that for a person skilled in the art, other drawings can be derived from such drawings without inventive effort.

FIG. 1 is an SEM image of the surface morphology of a tungsten-based porous substrate obtained by a selective laser melting technique;

FIG. 2 is an SEM image of the cathode surface after completion of the impregnation and surface treatment

FIG. 3 is a graph showing the pulse emission current density I-V characteristic of the cathode;

table 1 shows the inflection point current densities of the space charge regions of the cathodes in the respective examples.

Detailed description of the invention

The present invention is further illustrated below with reference to examples, but the present invention is not limited to the following examples.

Example 1: tungsten powder with an average particle size of 15-25 μm is selected. Reducing the precursor powder in a hydrogen atmosphere at the reduction temperature of 800 ℃, and keeping the temperature for 2 h. The print size was designed as a cylinder 2.9mm in diameter and 2mm in height. The tungsten-based matrix with the porosity of 13% is finally obtained by adopting a preparation process that the laser power P is 160W, the scanning speed V is 800mm/s and the scanning distance D is 0.10 mm. And annealing the substrate at 1200 ℃ for 0.5 hour. The matrix is impregnated with barium calcium aluminate 411 salt, the impregnation amount of the active salt is 5%. And cleaning residual salt on the surface of the cathode, and annealing at 1200 ℃ for 1 hour.

Example 2: tungsten powder with an average particle size of 15-25 μm is selected. Reducing the precursor powder in a hydrogen atmosphere at the reduction temperature of 800 ℃, and keeping the temperature for 2 h. The print size was designed as a cylinder 2.9mm in diameter and 2mm in height. The tungsten-based matrix with the porosity of 19% is finally obtained by adopting the preparation process that the laser power P is 160W, the scanning speed V is 1300mm/s and the scanning distance D is 0.10 mm. And annealing the substrate at 1200 ℃ for 0.5 hour. The matrix was impregnated with barium calcium aluminate 411 salt in an active salt impregnation amount of 9%. And cleaning residual salt on the surface of the cathode, and annealing at 1200 ℃ for 1 hour.

Example 3: tungsten powder with an average particle size of 15-25 μm is selected. Reducing the precursor powder in a hydrogen atmosphere at the reduction temperature of 800 ℃, and keeping the temperature for 2 h. The print size was designed as a cylinder 2.9mm in diameter and 2mm in height. The tungsten-based matrix with the porosity of 27% is finally obtained by adopting a preparation process that the laser power P is 160W, the scanning speed V is 1600mm/s and the scanning distance D is 0.10 mm. And annealing the substrate at 1200 ℃ for 0.5 hour. The matrix was impregnated with barium calcium aluminate 411 salt in an active salt impregnation amount of 13%. Residual salt on the surface of the cathode is cleaned, annealing treatment is carried out, the annealing temperature is 1200 ℃, the annealing time is 1 hour, and the emission performance is shown in figure 3.

Example 4: selecting tungsten powder with the grain diameter of 1-60 mu m. Reducing the precursor powder in a hydrogen atmosphere at the reduction temperature of 800 ℃, and keeping the temperature for 2 h. The print size was designed as a cylinder 2.9mm in diameter and 2mm in height. The tungsten-based matrix with the porosity of 33% is finally obtained by adopting a preparation process that the laser power P is 160W, the scanning speed V is 1600mm/s and the scanning distance D is 0.10 mm. And annealing the substrate at 1200 ℃ for 0.5 hour. The matrix was impregnated with barium calcium aluminate 411 salt in an amount of 15% active salt impregnation. And cleaning residual salt on the surface of the cathode, and annealing at 1200 ℃ for 1 hour.

Example 5: selecting tungsten powder with the grain diameter of 100nm-100 mu m. Reducing the precursor powder in a hydrogen atmosphere at the reduction temperature of 800 ℃, and keeping the temperature for 2 h. The print size was designed as a cylinder 2.9mm in diameter and 2mm in height. The tungsten-based matrix with the porosity of 25% is finally obtained by adopting the preparation process that the laser power P is 160W, the scanning speed V is 1600mm/s and the scanning distance D is 0.10 mm. And annealing the substrate at 1200 ℃ for 0.5 hour. The matrix was impregnated with barium calcium aluminate 411 salt in an active salt impregnation amount of 12%. And cleaning residual salt on the surface of the cathode, and annealing at 1200 ℃ for 1 hour.

TABLE 1

Claims

1. The additive manufacturing preparation method of the tungsten-based diffusion cathode is characterized by comprising the following steps of:

step three: and treating the surface of the cathode according to the cleanliness of the surface of the cathode, and then annealing.

2. The additive manufacturing method of a tungsten-based diffusion cathode according to claim 1, wherein the first step: selecting 100nm-100um tungsten powder.

3. The additive manufacturing method of a tungsten-based diffusion cathode according to claim 1, wherein the tungsten powder obtained in the step one is annealed, reduced and screened in hydrogen, and is kept at 800 ℃ for 2 hours in hydrogen.

4. The additive manufacturing method of a tungsten-based diffusion cathode according to claim 1, wherein the first step: and respectively adopting a continuous pulse laser device for molding, and obtaining the tungsten matrix with the porosity of 10-30% by adjusting laser parameters and the like.

5. The method as claimed in claim 1, wherein different laser printing parameters are used to obtain different tungsten-based substrates, the laser power P is 150-200W, the scanning distance d is 0.10-0.20mm, and the scanning speed v is 800mm/s-1600 mm/s.

6. The method as claimed in claim 1, wherein the annealing temperature in step three is 850-.

7. The method as claimed in claim 1, wherein the annealing treatment is performed on the cathode substrate at 850-1700 ℃ for 1 min-5 h before the high temperature impregnation of the emission active salt is performed in step two.

8. The additive manufacturing method of a tungsten-based diffusion cathode according to claim 1, wherein the treatment in step three is any one or more of washing methods such as water washing, acid washing, alkali washing and the like, or physical treatment methods such as machining and the like.

9. A tungsten-based diffusion cathode prepared according to the method of any one of claims 1 to 8.