Influence of HPT deformation temperature on microstructures and thermal stability of ultrafine-grained tungsten

In the present work high pressure torsion (HPT) was imposed on commercial purity (CP) tungsten at different temperatures of 450 degrees C and 490 degrees C to achieve different microstructures and grain boundary misorientation spectra (GBMS). After HPT at 450 degrees C, ultrafine grained microstructure with an average grain size of similar to 150 nm was developed in the metal. HPT at 490 degrees C results in an elongated structures with average width of similar to 500nm. EBSD investigations showed that over 92% are HAGB type in microstructure HPT-processed at 450 degrees C, and in contrast, over 50% of grain boundaries are LAGB in sample processed at 490 degrees C. Annealing at 900 degrees C for 1h, of the sample with homogeneous UFG structure resulted from HPT at 450 degrees C, leads to only limited decrease (similar to 20%) in microhardness.