Sintered composite materials on the basis of Fe/FePO4-coated powders

Abstract

Composite materials with a network microstructure of α-Fe areas surrounded by continuous layer of iron phosphate compounds were prepared on the basis of Fe/FePO4 precipitation coated powder. Spherically shaped particles of this powder were compacted and sintered at 912, 930, 980, 1075 and 1130 °C for 3 min in air. Sufficiently fast heating rate, rapid formation of a liquid phase and fast cooling suppress the development of diffusion processes and consequently the formation of Fe-Fe metallic connections. Microscopic observations showed that, after appropriate processing conditions, an even and continuous layer, comprising amixture of ferrous orthophosphate and iron oxide compounds, was achieved. Sintering at 1130 °C and fast cooling at ∼25 000 °C/min resulted in the formation of a phosphate layer consisting of very fine lamellar structure - graftonite. The phase composition of the phosphate layer was correlated with processing conditions. Corrosion resistance of the sintered composites was measured and related to microstructure and processing technique variants.