Micro and macro strain-induced damping and dislocation structures in tungsten and molybdenum single crystals

Abstract

The connections between micro-macro strain behaviour, damping spectra and dislocation structures have been examined in four orientations (the three principals and the easy glide orientation) of high purity molybdenum and tungsten single crystals ( R R = 10 +) for molybdenum and R R = 5 × 10 4 for tungsten). The samples were deformed in compression at 300.550 and 600 K in microplastic (ϵ ∼- 10 −4) and plastic (ϵ ∼- 10 −2) ranges prior to internal friction measurements (between 30 and 800 K.) and to transmission electron microscopy examination. Several peaks have been revealed, in particular a peak on the low temperature side of the α peak (α' peak) and a peak around room temperature (γ' peak). A direct connection for molybdenum and tungsten has been established between stress-strain behaviour, dislocation structure and internal friction spectra:screw dislocations controlling plastic flow are directly involved in high temperature peaks mechanisms, nonscrew dislocations induce low temperature peaks. Our observations are very well explained by the double kink generation and kink diffusion models in nonscrew dislocations respectively for the α and α' peak, by the double kink generation and point defect impurity dislocation interaction models in screw dislocations respectively for the γ and β peaks and by the kink diffusion model in screw dislocations for the γ' peak ( RT peak).