No abstract

No abstract

No abstract

A simple diffusion model is proposed to estimate the growth kinetics of Fe 2 B layers created at the surface of pure iron. This model employs the mass balance equation at the Fe 2 B/substrate interface to evaluate the boron diffusion coefficient (D Fe 2 B ) in the boride layer. The Fe 2 B layers were formed using the paste boriding process, at four temperatures with different exposure times. Analysing the results, the evolution of the parabolic growth constant (k) of the Fe 2 B layer is presented as a function of boron concentration and boride incubation time [t 0 (T)]. Furthermore, the instantaneous velocity of the Fe 2 B/substrate interface and the weight gain of borided pure iron were estimated for different boriding temperatures. Finally, to validate the diffusion model, the boride layer thicknesses were predicted and experimentally verified for two boriding temperatures and for different treatment times.

No abstract

No abstract

The general features of the a-c impedance at a metal-electrolyte interface as a function of frequency are depicted, and recently developed measurement techniques are described. It is established that at low and very low frequencies, down to the millihertz domain, relaxation phenomena are found in those cases where the assumptions used in Stern's derivation are not met. Under such conditions polarization resistance techniques can hardly be used owing to experimental and theoretical reasons. Charge transfer resistance, when used instead of polarization resistance in a Stern's type equation, is proved to overcome these difficulties on the basis of a theoretical derivation. Correlation between charge transfer resistance and corrosion rate is illustrated by practical examples of pure iron and anodized aluminum alloys.

In the present study, a new diffusion model based on the integral method was suggested to investigate the boriding kinetics of pack-borided AISI D2 steel. This diffusion model considered the effect of boride incubation time of the total boride layer (FeB + Fe 2 B). Firstly, the diffusion coefficients of boron in the FeB and Fe 2 B layers were estimated using a simple approach derived from the integral method. Secondly, the values of boron activation energies for the FeB and Fe 2 B layers were determined and compared with the literature data. The formulated diffusion model has been validated by using additional boriding conditions. The total boride layer thicknesses, obtained experimentally at 1243 K for 2, 4 and 6 h, were compared to the predicted thicknesses. Finally, a good agreement was observed between the experimental and the predicted results.