Intermetallic compound formation in Fe–Al–Si ternary system: Part I

Abstract

The phase equilibria in the Fe–Al–Si system has been studied in the temperature range 1020–1115 °C using ternary diffusion couple experiments involving pure Fe and Al–Si eutectic alloy prepared with high purity metals. A number of binary and ternary intermetallic compounds have been observed in the diffusion couples cooled at different rates from the annealing temperatures. The microstructure and composition of the intermetallic compounds have been described and compared with the results published earlier. In all, nine ternary intermetallic compounds have been identified. Except for the τ 3 and τ 5 phases, compositions of τ 1, τ 2, τ 4, τ 6, τ 7, τ 9, and τ 10 phases agree quite well with the work of Murav'eva et al. [Second All-Union Conference on the Crystal Chemistry of Intermetallic Compounds, L'vov, October 1974, 35]. The τ 8-phase composition has not been observed in this investigation, which may be due to very high Si in this intermetallic compound. The possible invariant reactions originally proposed by Takeda and Mutuzaki [Tetsu to Hagane 26 (1940) 335] are postulated to be responsible for the observed microstructure. The τ 10 phase has been observed only in diffusion couples rapidly cooled from the annealing temperature and is proposed to be a metastable phase (μ).