## 3 Results and Analysis
### Infiltration Mechanism Analysis  
AgW (70 wt%)-85 materials were prepared using the infiltration method, and three stages of the infiltration process were identified through optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy, as shown in Figure 16.  
Figure 16: Schematic of the infiltration mechanism. (**a**) Prepenetration; (**b**) Silver fusion; (**c**) Infiltration; (**d**) Solidify.  
Solid-phase sintering:  
Ag powder was pressed onto the W skeleton, and the sample was placed in an H\({}_{2}\) atmosphere tube furnace for infiltration. No liquid phase was observed in the temperature range from room temperature up to 960 \({}^{\circ}\)C. However, under Ni activation, secondary sintering of the W skeleton occurred. According to the W-Ni phase diagram, solid-phase diffusion and mutual solubility were present between the W and Ni elements. Additionally, a small amount of Ag existed in the W skeleton. Its atomic diffusion in the W skeleton followed Equations (7) and (8), which describe the diffusion of Ni in Ag and W [32].  
\[D_{Ni\to Ag}=21.9\exp\left(\frac{-54.8\times 10^{3}}{RT}\right) \tag{7}\]  
\[D_{W\to Ni}=2.0\exp\left(\frac{-71.5}{RT}\right) \tag{8}\]  
According to the magnitude of the frequency factor, it can be inferred that diffusion of Ni in Ag was the dominant mechanism during the solid-phase sintering at this stage. As the temperature increased to 960 \({}^{\circ}\)C, the solid-state Ag gradually softened and liquified, reducing the wetting angle.  
Liquid-phase flow infiltration:  
Within this temperature range, both the small amount of Ag in the W skeleton and the infiltrating Ag were in a liquid phase. Owing to the fluidity of Ag, the liquid Ag coalesced into a continuous structure, and the small amount of Ag in W functioned as a conductive agent, facilitating conduction. The addition of Ag during the pre-sintering process significantly enhanced the flowability of the infiltrating Ag, promoting densification [14]. The skeleton formed between W particles creates a network of capillaries. Under the capillary forces, the infiltrating Ag flows through/along the channels formed by Ag in the W skeleton, gradually filling the pores, which densifies the material. This process is classified as liquid-phase infiltration. Meanwhile, the Ni-encapsulated Ag particles in the W skeleton remain in the solid phase because the conditions are inadequate for alloy formation. The diffusion of Ni in Ag continues, and its rate increases with temperature. As the temperature increases, the wettability of Ag to W improves, reducing the wetting angle. The soaking begins at 1050 \({}^{\circ}\)C. Ag infiltrates the W skeleton, filling the pores. At the end of this stage, the W skeleton is densified. The combined effects of liquid-phase flow and solid-phase diffusion improve the interfacial condition between particles, increasing the bonding strength of the W skeleton.  
Liquid-phase solidification and pore filling:  
This stage is known as the furnace cooling stage. After the second stage, the Ag in the W and the infiltrating Ag liquefy and fill the pores in the W skeleton, connecting to form a continuous structure. The liquid Ag solidifies, whereas Ni improves the wettability of Ag to W throughout the infiltration process and facilitates the formation of sintered necks between W particles. Consequently, the material achieves a relative density close to 100%.