Evolution of boride layers during a diffusion annealing process

New results about the evolution of the FeB-Fe2B layers during a diffusion annealing process (DAP) are presented in this work. First, the growth of the boride layers over the surface of an AISI 1045 steel was developed by means of the powder-pack boriding process (PPBP) at temperatures of 1173-1273 K with different exposure times for each temperature. The boron diffusion coefficients in the FeB and Fe2B were estimated according to the mass balance equations on the growth interphases, and expressed as a function of the boriding temperatures by the Arrhenius equation. Moreover, the DAP was conducted on borided samples obtained at 1273 K with 4-8 h of exposure using a SiC atmosphere, and considering the theoretical values of annealing times proposed by the extended model. The evolution of the boride layer microstructure was represented by the interphase velocities of the FeB/Fe2B and Fe2B/substrate, and the relationships between the growth of the Fe2B at the expense of the FeB layer for the applied range of annealing times.