Tungsten Copper Electrode Infiltration

Infiltration is kind of process that uses the metal or alloy which has lower melting point than the product to fill in the pores of products in molten state. For tungsten copper electrode, copper solution has lower melting point and it fill in the porous tungsten skeleton, which has excellent density and strength so that tungsten copper material has better properties, such as thermal conductivity, electric conductivity and high hardness.

 The process is: Tungsten powder (W) + shaping agent (or adds Cu-induced powder) → tungsten skeleton (suppressing + degreasing + sintering) → copper infiltration (Cu) → after treatment. And the most research focus on:

1. Powder granularity

2. Tungsten skeleton

3. Infiltration process

4. After treatment.

Powder granularity: It stresses that tungsten powder granularity has an effect on tungsten copper electrode and other properties. Generally, the higher sintering temperature, the larger average granularity and the better strength of tungsten skeleton. However, if the granularity of tungsten powder exceeds a certain degree, the contact area among tungsten powder will be reduced and the tungsten powder can not be necking, which decreases the strength and hardness of tungsten skeleton and material.Some scientists do some researches about tungsten powder granularity and volume fraction effects on density of tungsten copper electrode, they thought it depends on original grain size of tungsten powder and this effect will decrease by the increasing temperature of sintering temperature.

Other experiment uses three different granularity of tungsten powder (8.7μm, 23.2μm and 65.2μm) for W-15Cu tungsten copper electrode. They thought different process parameters and tungsten powder granularity accounts for obturator or the changing of W-W adjacency rate, which has an effect on the density and resistivity. Nowadays, tungsten copper contacts made of 4-8μm (tungsten powder) granularity is widely used worldwide, which has good molding, contraction, low coefficient of thermal expansion and it is easily to be controlled in size or the porosity of tungsten blank.In order to achieve that corrosion ratio and the efficiency of machining in electrical discharge machining (EDM) with tungsten copper electrode by diverse granularity of tungsten powder, researchers use 1.0-3.0μm five kinds of tungsten powder as tungsten copper electrode. It demonstrates that 2.0 μm average granularity of tungsten copper has better properties in 80WC-20Co tungsten carbide machining.

Besides, mixed with light of Cu-induced powder will improve the corrosion ratio and the efficiency. Chinese scholars use 0.8-3.0μm tungsten powder for mixing, the result shows that despite small average granularity of tungsten powder, the density of sintering blank is still lower and the micro-structure is maldistributed.Viewed from tungsten skeleton, it is a key of high density tungsten copper electrode manufacturing by infiltration. Due to tungsten (W) has high melting point, high hardness and low contraction, it is difficult to be machining and densifying, which becomes the major part of scholars study. The study of tungsten skeleton can be divided into two types, one is the shaping properties of tungsten skeleton, and the other is the sintering properties of tungsten skeleton.

Tungsten Copper Sheet

Due to tungsten copper material is composed of two kinds of metals with a great difference in melting point, which copper evaporates and takes off part of heat for equipments working well at high temperature. Especially in some electronic components with high power and easily heated, tungsten copper as heat sink has wide applications. However, with the rapid development of electronic science and technology, electronic components have become smaller and more precise, which places a greater demand on tungsten copper sheet and heat sine materials. Conventional process of tungsten copper sheet has some defects in thickness and density, so it is difficult to meet the requirements of the properties of heat sink materials. In order to fabricate tungsten copper sheet with uniform thickness and high density, the researchers study on three levels, which include continuous liquid phase sintering, cold rolling and re-sintering.

In the process of continuous liquid phase sintering, the preparation of raw material is also crucial. It should be noticed that the content of elements and granularity, the additives, the stirring time, the granulation process, drying temperature, forming pressure, blank density detection and many parameters controlling. Continuous liquid phase is conducted in molybdenum wire furnace under the protection of hydrogen. It puts tungsten copper sheet in the high temperature zone and holds a period of time, and then push to end cooled rapidly cooled to obtain the sintered sample. Afterwards, The sintered samples in the two-roll cold rolling mill and cold rolling deformation measurements, observed by optical microscopy that is rolling a longitudinal section (parallel to the rolling direction), the evolution of the cross-section (perpendicular to the rolling direction) of the microstructure. Finally, re-sinter tungsten copper sheet after cold rolling in the molybdenum wire furnace under the protection of hydrogen, and temperature should be controlled 1300℃ (above the melting point of Cu), in the high temperature zone without holding time in case of grain growth.

Tungsten Copper Electrode Manufacturing

Except liquid-phase sintering, infiltration and direct sintering, there are some new technologies of tungsten copper come out recently, which make the structure and micro-structure of tungsten copper more stable.

1. Rapid directional solidification

Based on good thermal and electric conductivity, rapid solidification remarkably improves the strength and erosion resistance of tungsten copper electrode at high temperature. However, the cooling rate of rapid solidification is still lower so that solidification structure has sufficient time to grow up and coarsening, which may cause severe support segregation and decrease the properties of tungsten copper.

Given concern such situation, it need to improve the cooling rate by increasing the gradient temperature of the solid-liquid interface in the process of solidification. There are many kinds of rapid directional solidifications, such as SDS (Supercooling Directional Solidification), laser rapid directional solidification with ultra-high temperature gradient and electromagnetic shaping directional solidification.

2. In-situ reactions

Tungsten copper electrode always adopts passive pressure infiltration casting, but it has an unavoidable disadvantage that tungsten skeleton will be oxidized, which decreases the associativity of matrix and the properties of product. In the process of in-situ reactions, enhanced phase is forming in metal liquid and do not expose in the air so that it is isolated from outside and the properties will be improved. The process is that mix tungsten and copper powder (WO3 and CuO), and sinter in the air after forming (CuWO₄), then reduce in H₂. Finally, put the blank into copper solution. The relative density of tungsten copper composite material can reach 99% in such this way.

3. FGM (Functional Gradient Material)

W-Cu composite material is kind of new material that tungsten copper composite layer is between Cu and W. It can apparently relax the heat stress by mismatch between tungsten and copper properties. There are two techniques for FGM, one is that discontinuous gradient layer, such as traditional powder piling, which has faults among each layer, the other is that continuous gradient layer, such as slip casting, settle casting, centrifugal casting, which takes advantage of natural transfer to forming continuous contents.

 To some extent, FGM sintering is similar to traditional PM (Powder Metallurgy) process, which can be specifically divided into solid-phase sintering, liquid-phase sintering and dipping sintering. In addition, some processes adopt non-sintering method, such as plasma coating, laser-cladding, electrophoresis deposition and centrifugal casting.

Tungsten Copper Rod

Tungsten copper (copper-tungsten, CuW, or WCu) rod is a pseudo-alloy of copper and tungsten. As copper and tungsten are not mutually soluble, the material is composed of distinct particles of one metal dispersed in a matrix of the other one. The microstructure is therefore rather a metal matrix composite instead of a true alloy. The material combines the properties of both metals, resulting in a material that is heat-resistant, ablation-resistant, highly thermally and electrically conductive, and easy to machine. Parts are made from the CuW alloy by pressing the tungsten particles into a desired shape, sintering the compacted part, then infiltrating with molten copper. Sheets, rods and bars of the alloy are available as well.
Tungsten copper rod is consisting of pure tungsten (W) powder suspended in a matrix of copper (Cu), these alloys are known for good thermal and electrical conductivity, low thermal expansion, and resistance to erosion from arcing. Thus, they are often used as electrical contacts, particularly in high voltage applications. Most sizes and shapes can be supplied with short lead times. We can also manufacture parts from these materials to your specifications.
Tungsten copper rod combines the advantages of tungsten and copper, with a high melting point of tungsten (tungsten melting point of 3410 ℃, copper melting point 1080 ℃), high density (tungsten density of 19.25g / cm, copper density of 8.92 / cm3); excellent thermal conductivity properties of copper, tungsten copper alloy (composition generally ranges WCu7 ~ WCu50) have uniform microstructure, high temperature, high strength, resistance to arc erosion, high density; moderate conductivity, thermal conductivity, high temperature materials are widely used in military, high-voltage switch with electrical alloy, EDM electrode, microelectronic materials, parts and components as widely used in aerospace, aviation, electronics, electricity, metallurgy, machinery, sports equipment and other industries.