On the aluminium diffusion coating of iron

As one of the studies on the interdiffusion between iron and aluminium, pure iron samples diffusion-coated with aluminium at the temperature range of 900-1100℃ were studied by usual methods including microscopic observations, and microhardness tests. The heat resistant property of aluminium-coated samples heated in air at high temperature was also studied by measuring weight gains by oxidation, surface appearances, and microscopic observations. The results were as follows: 1) The greater part of a diffused layer consisted of a α-solidsolution layer, and a adhesion layer of Fe-Al alloy powder. At above 1050℃, needle-shaped particuls were formed in outer part of a α-layer. Voids were formed in a α-layer. 2) Hardness drop was founded at the same position where voids were formed. 3) The diffused layer, and the movement of a iron-diffused layer interface were increased exponentially with increasing the diffusion temperature, parabolically with increasing the diffusion time. Activation energy for these were 58 Kcal/mol, and 50 Kcal/mol. 4) A Al2O3 was formed on the surface of a sample heated in air at high temperature, it peeled off during oxidation, and a new oxide film was formed there. 5) Oxidation of iron was started locally, maybe at cracks by heat repetition