Deformation behaviour of a newer tungsten heavy alloy

The present study attempts to investigate room temperature and high temperature flow behaviour of a tungsten heavy alloy (W-7.10Ni-1.65Fe-0.5Co-0.25Mo alloy). The alloy was deformed under compression at room temperature and elevated temperatures (400-700 degrees C) at different strain rates (1-0.0001 s(-1)) to observe plasticity under compression loading at these temperatures and strain rates. The alloy showed higher plasticity and positive strain rate sensitivity at room temperature. Samples hardness after 70% deformation at room temperature increased from 3.20 +/- 0.14 to 5.08 +/- 0.03 GPa. Barreling was observed in room temperature compression tested samples. Microstructure of the alloy after heavy compressive deformation at room temperature showed that severe deformation of W grains took place along a direction at 45 degrees to the direction of applied stress. The alloy showed varying (positive and negative) strain rate sensitivity at elevated temperatures. Samples hardness after 70% deformation at elevated temperatures increased from 3.20 +/- 0.14 to 4.60 +/- 0.23 GPa. At 600 and 700 degrees C, the specimens failed by shear along the direction which is at an angle 45 degrees to the direction of applied stress. Microstructural evidences indicate that the failure at these elevated temperatures seems to be triggered by the excessive void generation in the matrix and their coalescence under the influence of the applied stress. Room temperature deformation mechanism of tungsten heavy alloy was also studied by carrying out tensile testing at room temperature in strain rates ranging from 0.1 to 0.0001 s(-1). The values of strain rate sensitivity, and apparent activation volume with respect to different level of strain suggest that the deformation mechanism of the alloy is similar to that of bcc metals such as tungsten and molybdenum, i.e. Peierls mechanism controls the dislocation motion. (C) 2011 Elsevier B.V. All rights reserved.