Abstract
Tungsten has many attractive properties, but its brittleness limits its application. Our team has found that the brittleness of tungsten can be greatly improved by combining the brittle tungsten with tantalum. Furthermore, we found that if a suitable transition layer is added between tungsten and tantalum, the properties of the composite will be further improved. In this paper, we studied the effect of different transition layers on the properties of W-Ta laminated composite to explore a suitable transition layer, which can effectively improve the toughness of the composite and solve the problem of tungsten application. We have prepared four kinds of W-Ta laminated composites with Ni, Ti, Nb, and Mo as transition layers. Ta-W laminated composites were prepared by stacking layers with Ta, transition layer, W alternately and sintered by spark plasma sintering (SPS). The tensile and three-point bending tests were carried to compare the mechanical properties. The tensile fracture morphology and three-point bending crack distribution were observed by SEM. In addition, the diffusion of elements in the transition layer and the influence of element diffusion on the tungsten structure were also studied to clarify the toughening mechanism. The results show that Nb is a satisfying transition layer, which not only improves the strength of W-Ta laminated composite, but also improves the toughness. The tensile test of W/Nb/Ta laminated composite shows a typical plastic fracture mode with an elongation of 13%. Three-point bending test also shows high strength and good toughness. In addition, Voigt model was used to predict the elastic modulus of W-Ta laminated composites and compared with the experimental results.
Highlights
Tungsten has many excellent properties, e.g., a high melting point (3422 ◦ C), high thermal conductivity, good mechanical properties in high temperature and low thermal expansion coefficient, which make it very suitable for high heat flux components and extreme environment applications including plasma facing materials (PFMs) in fusion reactors or rocket nozzles in space applications [1,2,3,4].pure tungsten and tungsten alloys are known to be brittle at room temperature and have high ductile-to-brittle transition temperatures (DBTT) which extremely restrict its application
Pure tungsten and tungsten alloys are known to be brittle at room temperature and have high ductile-to-brittle transition temperatures (DBTT) which extremely restrict its application
The results showed that the good interface between the fiber and matrix could improve the fracture toughness and shear strength significantly, but the interface optimization and thermal stability of the system needed further study
Summary
Tungsten has many excellent properties, e.g., a high melting point (3422 ◦ C), high thermal conductivity, good mechanical properties in high temperature and low thermal expansion coefficient, which make it very suitable for high heat flux components and extreme environment applications including plasma facing materials (PFMs) in fusion reactors or rocket nozzles in space applications [1,2,3,4]. J et al [20] reported that severely deformed tungsten foil is ductile at room temperature in the as-deformed state Both texture and dislocations generated by rolling at low temperature or other methods will gradually disappear during high temperature annealing, resulting in an increase in DBTT [21,22]. The test results showed that the DBTT of the material was significantly lower than that of pure tungsten and has better toughness This shows that the laminar composite forming is a viable way of tungsten toughening. Many reports have shown that forming tungsten composites such as W-Ta, W-Ti, W-V, W-Cu can obviously improve toughness of tungsten in both high and low temperature It brings another problem of strong inter-diffusion in the long-term high temperature environment [22], which will weaken the interface and decrease the strength of laminate composites. It is expected to clarify the toughening mechanism of the transition layer and find a suitable transition layer to prepare a tungsten laminated composite with high strength and good plasticity
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