Observations on the ductile-to-brittle transition in ultrafine-grained tungsten of commercial purity

Rods of commercial-purity tungsten were subjected to severe plastic deformation by means of equal-channel angular pressing (ECAP). An ultrafine-grained (UFG) equiaxed microstructure with an average grain size of about 0.9 μm was developed. Microhardness measurements in a wide range of temperatures suggest a ductile-to-brittle transition at temperatures below 350 °C in the UFG samples after ECAP. In contrast, the results on the as-received material suggest a ductile-to-brittle transition temperature above 483 °C.