Controlling Factors for the Brittle-to-Ductile Transition in Tungsten Single Crystals

Abstract

Materials performance in structural applications is often restricted by a transition from ductile response to brittle fracture with decreasing temperature. This transition is currently viewed as being controlled either by dislocation mobility or by the nucleation of dislocations. Fracture experiments on tungsten single crystals reported here provide evidence for the importance of dislocation nucleation for the fracture toughness in the semibrittle regime. However, it is shown that the transition itself, in general, is controlled by dislocation mobility rather than by nucleation.

Temperature dependence of surface topography and deuterium retention in tungsten exposed to low-energy, high-flux D plasma

“…However, at near-room temperatures the stress relaxation results in plastic deformation and crack formation inside the grains. Thus, the temperature dependence of the structure modification correlates well with the temperature dependence of fracture toughness for W [18,19].…”

“…The stress is may be increased by the gas overpressure inside the cavities. At elevated temperatures exceeding the brittle-to-ductile-transition temperature, the stress can be relaxed by dislocations moving along lattice planes through the whole crystallite leading to the cavities at the grain boundaries [18]. This corresponds to the observed material migration above the surface, i.e., the blister-like surface topography.…”

Surface morphology and deuterium retention in tungsten and tungsten–rhenium alloy exposed to low-energy, high flux D plasma

“…The BDT temperature depends also on the material microstructure and, for W single crystals, on the crystal-lattice orientation [25]. Note that in W materials liable to plastic deformation under D plasma exposure, vacancy-type defects are produced in very high densities which are typically close to those of vacancies in thermal equilibrium at the melting point [20], and the vacancy-type defects are formed in surroundings of D atoms.…”

Effects of high temperature annealing on the dislocation density and electrical properties of upgraded metallurgical grade multicrystalline silicon

“…Generally, the rates of both dissolution and diffusion of metal impurities increase as the temperature is increased [10]. Upon dissolution and diffusion of metal precipitates, grain boundaries and dislocations in Si wafers can move within certain crystallographic glide planes at about 600°C [11]. As the temperature is increased above 1000°C, dislocations can move unconstrained by glide planes and be removed from Si wafers via out-diffusion to surfaces or pairwise annihilation [12].…”