アルミニウム拡散被覆現象について

Abstract

The authors studied the effects of treating conditions on the surface concentration of aluminum of 18 Cr/10 Ni/Ti stainless steel aluminized by powder pack process with HCl gas.The results of experiments were as follows:(1) In the specimens diffusion coated with aluminum, the surface positions shifted in proportion to the amount of diffusion coating.(2) Based on Fick's Law, apporoximate solutions of aluminum concentration curves on the formation of aluminum diffusion coated layers were calculated by considering the boundary condition that the position of specimen surface shifted with the lapse of time.The results obtained were as follows:(2-1) Possible explanations were offered for the change in surface aluminum concentration of the diffusion coated specimens by the results of above calculation.(2-2) The main factors controlling the formation of diffusion coated layer were the interdiffusion coefficient, aluminum deposition rate, and coating time.(2-3) The surface aluminum concentration increased with the increase in diffusion coating time and aluminum deposition rate. While, the surface concentration decreased with the increase in interdiffusion coefficient.(2-4) When the both values of surface aluminum concentrations of a specimen treated under the following two conditions were equal, (A) (B)aluminum deposition rate V1 V2interdiffusion coefficient D1 D2diffusion coating time t1 t2there would be a following relationship:t1/t2=(V2/V1)2(D1/D2)(3) The results of X. M. A. analysis were as follows:(3-1) The surface aluminum concentration was slightly lower with the rise of treating temperature.(3-2) The surface aluminum concentration was slightly lower with the increase of treating time.(3-3) The surface aluminum concentration of the specimen treated with concentrated HCl gas (in which aluminum deposition rate was higher than that in dilute HCl gas) was higher than that treated with dilute HCl gas.As described above, the results of calculation correspended well with the experimental results by X. M. A. analysis.