Fabrication And Properties Of CNTs And Ti Doped W Alloys

Tungsten (W) and its alloys have been considered as the most attractive armour material in the fields of nuclear energy, aerospace, military, chemical and other fields due to its extremely high melting point, high thermal conductivity, low erosion rate and low tritium retention. Key issues for this refractory metal however are its high fabrication temperature, high ductile-to-brittle transition temperature (DBTT:about 400℃), low recrystallization temperature (RCT:about 1400℃) and poor ductility. Therefore, the improvement of the sintering properties and mechanical performance of W alloys is very important.In view of the brittle fracture nature of W, metal solid solution and fine-grain strengthening methods were used to improve the fracture toughness. In this paper, titanium (Ti) or/and carbon nanotubes (CNTs) are chosen as sintering additives to reduce the sintering temperature and improve fracture toughness due to their excellent physical and chemical properties. So, W-based alloys (W-CNTs,W-Ti,W-Ti-CNTS) were fabricated at 1500℃ by hot pressing under a pressure of 25 MPa. After hot pressing, the bending strength and fracture toughness of sintering sample were measured by three-point bending and single edge-notched beam tests, respectively. The micro structure was characterized by scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS).The results found that CNTs or Ti can effectively enhance the sintering behavior of W alloys. For example, W-0.1 CNTs and W-5Ti have a high relative density of 95.8% and 96.5%, respectively. However, bigger grain size were exhibited by these two W-based alloys, which is detrimental to the mechanical properties. When added CNTs and Ti together into W-based alloys, fine grain size and high relative density were both achieved with improved mechanical properties. For example, W-3Ti-0.1CNTs alloy has the highest fracture toughness of 13.0 MPa·m1/2, and W-5Ti-0.1CNTs alloy showed the excellent overall performance:microhardness (7.32 GPa), bending strength (654.3 MPa), fracture toughness (10.1 MPa·m1/2). The microstructure analysis revealed that the intergranular fracture is the main mode for W-0.1 CNTs and W-5Ti alloys, but W-Ti-CNTs alloys fractured in a mixture mode of intergranular and transgranular fracture. These results demonstrated that both the addition of CNTs and Ti can refine the microstructure and enhance the bending strength and fracture toughness of W-based alloys.