# Graphene-Enhanced CuW Composites for High-Voltage Circuit Breaker Electrical Contacts
## 2 Materials and Methods
### Preparation Process of CuW/Graphene-Enhanced CuW Composites and Electrical Contacts  
Existing processes for the preparation of copper-based contact materials include: induced copper powder fusion infiltration, pre-sintered tungsten skeleton fusion infiltration, activation sintering, high-temperature liquid-phase sintering, vacuum sintering, and injection molding sintering. The microstructures of CuW composites produced under different process conditions are very different, and their comprehensive properties are therefore significantly different [4; 5; 6; 7].  
Tungsten possesses a high melting point of 3410 \({}^{\circ}\)C, and its sintering performance is inadequate below 1700 \({}^{\circ}\)C. Additionally, due to its low density and high hardness, the molding performance of tungsten is subpar, making it challenging to directly mold CuW composites with the desired high tungsten content and density of the tungsten skeleton. Consequently, the incorporation of induced copper powder remains the most widely utilized method for the preparation of CuW composites.  
The induced copper powder fusion infiltration method is to add a certain proportion of induced copper powder during the preparation of tungsten skeleton blanks. Due to the good plasticity of copper, porous CuW skeleton blanks with desired strength and density can be fabricated. During the melting sintering process, the capillary phenomenon facilitates the infiltration of molten liquid copper into the porous tungsten skeleton. The copper then flows through the pores, gradually filling the tungsten skeleton, ultimately yielding CuW composites with superior overall performance.  
In this study, the graphene-enhanced CuW composites were prepared by integrated vacuum infiltration technology, as shown in Figure 1. The raw materials used include tungsten powder, induced copper powder, copper alloy ingots for infiltration, and reduced graphene oxide nanosheets. The preparation process proceeded as follows: tungsten powder, inducing copper powder, and reducing graphene oxide powder were weighted in the appropriate proportions. Subsequently, paraffin and forming agent were added, and the mixture was thoroughly stirred and blended. Following this, the mixture was vacuum-dried at 80 \({}^{\circ}\)C. After sieving, the powder blend was loaded into a rubber sleeve and uniformly compacted. The porous skeleton blanks were obtained through isostatic pressing. Tungsten skeleton blanks and copper alloy ingots were stacked within a specially designed graphite mold. Subsequently, vacuum infiltration sintering was conducted at a temperature exceeding the melting point of copper (1350 \({}^{\circ}\)C) under a vacuum of 10\({}^{-2}\) Pa. This allowed the liquid copper to fully infiltrate the porous tungsten skeleton, resulting in the production of a uniform and dense graphene-enhanced CuW composite. Liquid copper can fully infiltrate into the tungsten porous skeleton, and a uniform and dense graphene-enhanced CuW composite was obtained. The composite composition consisted of 20 wt.% copper and 0.02 wt.% graphene, with the remainder being tungsten. Finally, the electrical contact products were machined precisely in accordance with designated drawings and tailored to meet the specific design requirements of various circuit breakers.  
The preparation process utilized for the CuW composites and the electrical contact products compared in this study followed the same aforementioned methodology, with the exception that the initial powder mixing stage, did not involve the addition of graphene. As a result, CuW composites with a copper content of 20 wt.% were ultimately obtained.