Shinji Hirai1 and Shigetomo Ueda2
1Graduate Student, Waseda University, Tokyo
Titanium diffusion coating using the powder pack process was applied to commercial iron (SPHC) and plain carbon steel (S45C). The effects of the kind of activator and blending ratio of the activator, and the diluent contained in the pack material on the treated layers were investigated.
The results obtained are as follows:
(1) The optimum composition of the pack material was determined from the mass increase of the specimen after diffusion coating. When the specimen was treated at 1373 K for 21.6 ks using a pack material consisting of 33 mass% titanium, 65 mass% alumina, and 2 mass% calcium chloride, the resulting treated layer had a thickness of 40 μm and a Ti concentration of 65 mass%.
(2) When ammonium chloride was used as an activator, a Ti-H compound is formed on the treated layer, Calcium chloride as an activator proved to be the most suitable for obtaining a thick treated layer with a high Ti concentration.
(3) Alumina used as a diluent was reduced with titanium to produce Al. The resulting Al, together with Ti, diffused into steel. This reducing reaction is considered to result from a reduction of the Al activity, which occurs in accordance with the diffusion of the Al into the steel.
(4) Regarding the Al diffusion mechanism in the case of S45C, the diffusion of Al is suppressed by a TiC layer present in the additive layer. However, as the concentration gradient of Al becomes greater, Al diffuses into the basis metal through the TiC layer to form a diffusion layer while the basis metal is decarburized.
titanium diffusion coating, pack process, pack material, activator, diluent, commercial iron, plain carbon steel, alumina, calcium chloride
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