The thermal behavior of atoms in ultrafine-grained Ni processed by severe plastic deformation

Abstract

X-ray diffraction investigations in a temperature range from 85 to 295 K were performed on an ultrafine-grained (UFG) Ni sample processed by severe plastic deformation. A significantly enhanced thermal expansion coefficient of 3.75×10−5 K−1 was observed in the UFG Ni sample, which is three times higher than in the conventional coarse-grained Ni polycrystal. The Debye–Waller parameter and its temperature-dependent and temperature-independent components are revealed to be larger in the UFG Ni sample. The obtained Debye temperature in the UFG Ni sample is decreased by 22%. The altered thermal properties in the UFG Ni sample are attributed to the nonequilibrium dislocations that disturb grain boundaries leading to large atomic displacements near interfaces.