Abstract
The effusion of hydrogen from deformed iron wires has been studied by combining low temperature internal friction measurement of the cold-work peak with a thermal cycling procedure. Diffusion constants have been calculated by a modification of the technique developed by Armstrong, for conditions where diffusion takes place over a range of temperatures. The activation energy for effusion between 200 and 300°K. is 7-8 Kcals. /gm. mole, in good agreement with previous work based on other methods. A linear variation of the cold-work peak height with hydrogen content suggests that dislocations act as the major trapping sites when the deformation level (16% R.A.) is insufficient to produce internal voids and when the hydrogen content is low (~ 1 ppm.). A binding energy of 5-6 Kcals. /gm. mole can be derived by taking into account current values for the basic lattice diffusion of hydrogen. This is consistent with a basic elastic interaction energy model based on a partial molar volume for hydrogen of ~ 2ccs./gm.mole, and supports the location of lattice hydrogen in octahedral interstices. The similarity between the dislocation binding energy and the energy of adsorption at free surfaces may account for the conflict which exists regarding the predominant location of hydrogen in ferrite containg both internal voids and a high dislocation density. These implications are considered in connection with current theories on the mechanism of hydrogen embrittlement. The damping properties of the dislocation array were studied in a magnetic field of 100 oersteds in order to remove the magnetic damping contribution. Subsidiary tests at intermediate field strengths show that the magnetic damping can be represented by a vector diagram model and that there is a magneto-mechanical analogy to Rayleigh's Law. The response of Bloch walls to mechanical stimuli indicates that it may be possible to calculate the force required to initiate the movement of unit area of domain wall in ferrite after various degrees of deformation.