Observation of tension/compression asymmetry in an Nb–Al–V alloy

Mechanical tests at room temperature have been performed on a B2 Nb–15Al–20V alloy and transmission electron microscopy (TEM) was used to examine the microstructures. The alloy exhibited a significant difference in deformation behavior between tension and compression. In tension, the alloy was brittle while in compression it exhibited very good ductility. This asymmetry can be explained by examining the dislocation structures after deformation. The Burgers vectors of the dislocations in tension were found to be 12〈1 1 1〉 slipping on {1 1 0}. In compression the slip plane was determined to be {1 1 2}. The dislocations in tension exhibited a very low mobility and piled up dislocation arrays were easily seen. In compression, the dislocations showed good mobility and dislocation clusters also triggered the formation of pseudotwins, which is consistent with the mechanical properties.