Grain boundary sliding during ambient-temperature creep in hexagonal close-packed metals

Abstract

Even at ambient temperature or less, below their 0.2% proof stresses all hexagonal close-packed metals and alloys show creep behaviour because they have dislocation arrays lying on a single slip system with no tangled dislocation inside each grain. In this case, lattice dislocations move without obstacles and pile-up in front of a grain boundary. Then these dislocations must be accommodated at the grain boundary to continue creep deformation. Atomic force microscopy revealed the occurrence of grain boundary sliding (GBS) in the ambient-temperature creep region. Lattice rotation of 5° was observed near grain boundaries by electron backscatter diffraction pattern analyses. Because of an extra low apparent activation energy of 20 kJ/mol, conventional diffusion processes are not activated. To accommodate these piled-up dislocations without diffusion processes, lattice dislocations must be absorbed by grain boundaries through a slip-induced GBS mechanism.

Keywords:

• grain boundary sliding
• ambient temperature creep
• hexagonal close-packed structure

Acknowledgements

The authors sincerely appreciate Prof. Takeshi Ogawa, Aoyama Gakuin University for AFM observations. The authors also appreciate funding and support from a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion (JSPS) of Science and a JSPS Fellowship (00020141).