Internal friction and modulus changes in cold-worked iron containing carbon

Abstract

Experiments are reported on the effect of carbon-dislocation reactions on the damping and modulus defect associated with dislocation motion in iron. Speciments of iron wire containing low concentrations of dissolved carbon were deformed in torsion at low temperature. Transient creep and temperature, frequency, and strain amplitude dependences of the damping and modulus defect were measured by the torsion pendulum method during pulse annealing. The damping introduced by the deformation is independent of temperature T and frequency v at low temperature and approaches the functional dependence [ v exp ( H/ RT)] −0.2as the temperature exceeds that of the previous anneal. The energy H is approximately equal to the observed activation energy for transient creep. These observations suggest that the Köster effect, the viscosity effect, and the transient creep are manifestations of the same phenomenon. When the solute carbon concentration is < 3 wt. p.p.m., the damping and modulus defect at low temperature (85°K) are relatively insensitive to annealing treatments prior to Snoek atmosphere formation, decrease about 15 per cent upon Snoek atmosphere formation, and decrease an order of magnitude when carbon is permitted to diffuse to the dislocations. When the solute carbon concentration is ⩾10 wt. p.p.m., the damping and modulus defect at 85°K partially anneal before carbon is permitted to diffuse. The damping varies linearly with strain amplitude over two orders of magnitude in strain and approaches amplitude independent values both at low and high strains. Present theories are unable to explain the amplitude, frequency and temperature dependences of the dislocation damping in iron.