Effect of TM (TM=Fe, Mn, Cr) alloying on the high temperature properties and strengthening mechanism of Cf/Al composites

In this paper, the C-f/pure Al composite and the C-f/Al-Fe-Mg-Si composite were prepared by pressure infiltration method, and the microstructure and high temperature mechanical properties of these two kinds of composites were studied. The main interface phase of the C-f/pure Al composite is Al4C3, while in the C-f/Al-Fe-Mg-Si composite, a new type of Fe-rich phase containing Al, Fe, Mn, Cr, Si and other elements with a body-centered cubic structure calibrated by TEM diffraction pattens is discovered, whose lattice constant is 1.39 nm. Results of high temperature bending tests and researches of microstructure demonstrated that, the bending strength of the C-f/Al-Fe-Mg-Si composite decreased first at room temperature to 200 degrees C, due to re-dissolution of nano-precipitates. Afterwards, the bending strength increased under the combined action of the stress relaxation mechanism, the crack deflection mechanism and the high temperature strengthening mechanism of the Fe-rich phase at a temperature range in 200 degrees C-400 degrees C, and reached about 880 MPa at 400 degrees C, which demonstrated better high temperature mechanical properties than that of the C-f/pure Al composite. The results indicated that the formation of high-temperature stable precipitates through TM alloying can effectively increase the ultimate service temperature of C-f/Al composites. The work in this paper is of great significance in the design and preparation of C-f/Al composites with excellent high-temperature properties.