The brittle-ductile transition of tungsten single crystals at the micro-scale

Abstract

The loading rate effect on the brittle-ductile transition temperatures of tungsten single crystals at the micro-scale was investigated by microcantilevers with a (100)[001] crack system. Specimens with a length to width to height of 15 µm / 4 µm / 6 µm were fabricated by focused ion beam milling. At low temperatures (-90 to -25 °C) the samples failed by brittle cleavage fracture, irrespective of the applied loading rate at a fracture toughness of 3.2 MPa•m 1/2 . With increasing temperatures up to 500 °C and depending on the applied loading rate, the fracture toughness increased and significant crack tip plasticity and dislocation-controlled microcleavage were observed by means of high resolution electron backscatter diffraction measurements performed after testing. With respect to macroscopic specimens, a shift of the brittle-ductile transition to lower temperatures and a significantly lower activation energy of the brittle-ductile transition of 0.36 eV were found. We explain this by the increase in flow stresses due to sample size effects.

Temperature-dependent mechanical behavior of three-dimensionally ordered macroporous tungsten

“…However, it is evident that a BDT begins somewhere below 125°C, where in bulk W, plasticity begins to be enhanced. This is in relative agreement with the literature regarding the BDTT of bulk single crystals of tungsten; Gumbsch et al [31] found the BDTT of tungsten single crystals to depend on both crack plane and crack front direction, ranging from 370-470 K. The BDT also is not a sharp transition, as shown by both Gumbsch for macroscale crystal fracture and Ast et al [39] for fracture of microcantilevers oriented for fracture along the {100}<010> crack system. In addition, 3DOM W is polycrystalline; some averaging of the BDTT across crack systems is to be expected.…”

Наноиндентирование И Механические Свойства Материалов В Субмикро- И Наношкале. Недавние Результаты И Достижения (О Б З О Р)

“…Описанные методы и приемы опробованы и использовались на макрооднородных монокристаллических, аморфных, композитных материалах, высокоэнтропийных и интерметаллических сплавах [119,163,164], пленочных керамических покрытиях (как для определения их собственных свойств, так и энергии адгезии к подложке) [193][194][195]. В [196][197][198] этими методами определяли условия перехода от вязкого к хрупкому разрушению (в частности, температуру и размеры пластической зоны в вершине трещины), а в [199] -закономерности водородного охрупчивания.…”

The brittle-to-ductile transition in cold-rolled tungsten sheets: the rate-limiting mechanism of plasticity controlling the BDT in ultrafine-grained tungsten

“…[18,20]: filled square: single-crystalline; open square: polycrystalline hot-deformed; crossed square: polycrystalline assintered; Ref. [19]: half-filled square (bottom filled): singlecrystalline; Refs. [17,82]: half-filled square (top filled): singlecrystalline; Ref.…”

“…Experiments using the model material tungsten (W) [16] have suggested that the glide of dislocations controls the BDT [17]. For W this has been validated and specified to the glide of h111i screw dislocations by studies performed on single crystals on the macroscale [18] and microscale [19], on a hot-deformed fine-grained [20], on coarsegrained recrystallized microstructures [21], and on hot-deformed materials that have undergone at least partial recrystallization [20,22].…”