Formation and modelling of aluminide coatings on iron by a fluidised bed CVD process

Abstract Aluminide coatings have been deposited on ARMCO iron and an iron–chromium alloy (15 at.% Cr) by a fluidised-bed chemical vapour deposition (FBCVD) process at 1000 °C with the use of FeAl donor powder and an NH 4 Cl activator. Examination of the coated samples by means of optical microscopy, SEM and microanalysis has shown the formation of dense and homogeneous coatings consisting of an FeAl outer phase and an α-solid solution inner phase. A simplified process model based on the diffusion equations of aluminium in pure iron, considering the intermetallic compounds according to the FeAl phase diagram, has been derived. The model yields the aluminium composition profiles as a function of time for particular process conditions and can be used for evaluation of the coating growth rate and morphology during aluminisation.

[1]  A. Hishinuma,et al.  Interdiffusion in α-Solid Solution of the Fe-Al System , 1968 .

[2]  D. Tsipas,et al.  Modifying Cr-Al Coatings by Reactive Element Additions: Eiperimental and Theoretical Considerations , 2000 .

[3]  B. Nciri,et al.  Étude de la diffusion dans un système multiphasé appliqué à l'aluminisation du fer et des aciers , 1985 .

[4]  J. Stringer,et al.  Surface Al composition as a result of the pack aluminizing of iron , 1988 .

[5]  A. J. Hickl,et al.  Kinetics of phase layer growth during aluminide coating of nickel , 1974 .

[6]  P. Schaaf,et al.  Controlled formation of surface layers by pack aluminization , 1998 .

[7]  R. Rapp,et al.  Kinetic Study of Aluminization of Iron by Using the Pack Cementation Technique , 1988 .

[8]  B. Wood,et al.  Coating particles by chemical vapor deposition in fluidized bed reactors , 1991 .

[9]  G. Angelopoulos,et al.  Formation of TiC coatings on steels by a fluidized bed chemical vapour deposition process , 1994 .

[10]  G. Angelopoulos,et al.  Feasibility of fluidized bed CVD for the formation of protective coatings , 1995 .

[11]  G. Angelopoulos,et al.  Formation of aluminide coatings on nickel by a fluidised bed CVD process , 2001 .

[12]  A. Sanjurjo,et al.  Chemical vapor deposition coatings in fluidized bed reactors , 1989 .

[13]  R. Rapp,et al.  Fundamental kinetic study of aluminization of iron by pack cementation at 900 °C , 1987 .

[14]  R. Sivakumar,et al.  On the kinetics of the pack—aluminization Process , 1976 .

[15]  T. Wang,et al.  The kinetics of pack aluminization of iron from AlFe alloy packs , 1989 .