Mechanism of destruction of the Al–Al4C3–Al2O3 alumo-matrix dispersion-hardened composite material with a layered structure on static and shock loading

Abstract

Alumo-matrix dispersion-hardened composite materials are widely used in engineering due to the combination of high strength and low density, allowing the production of lightweight endurable structural elements for various purposes. They are used for manufacturing abrasive, triboengineering products, parts of the internal combustion engine cylinder-piston group, airframe and other special products. The paper is aimed to study the fracture mechanism of a layered dispersion-hardened Al–Al2O3–Al4C3 composite on static loading and impact. Specimens were obtained by liquid phase sintering of PAP-2 powder blanks in a vacuum. The liquid phase was formed due to Al–Al4C3 eutectic melt. The layered structure appeared due to the liquid-phase splicing of PAP-2 scaly particles along the contacting planes. Dispersion hardening of aluminum matrix was achieved due to nanosized lamellar alumocarbide crystals precipitated from the eutectic melt on cooling. The synthesis of alumina crystals – δ-Al2O3 – occurred due to the interaction of aluminum with residual oxygen molecules of the air on sintering at the furnace rarefaction of 10–5 mm Hg. The stable destruction of samples by the «shear stratification» mechanism was found to occur under static loading accompanied by the formation of cavities due to tearing of layered blocks under the action of shear stresses (σb = 430÷500 MPa, K1s = 14.0÷ ÷15.5 MPa·m1/2) At shock loading, a significant amount of material is involved in the fracture accompanied by the formation of cleavage steps between layered blocks and extended regions of ductile fracture dimples. Thanks to this mechanism, a high KCU (1.1·105 J/m2) is achieved comparable with that of the VT-5L titanium alloy. The developed composite can be used for manufacturing lightweight structural elements operated under dynamic loading.