Mechanism of ceramic-like friction of quasicrystal reinforced Al matrix composites formed by in-situ directed energy deposition

The wear of aluminum alloy may be decreased by its reinforcement with quasicrystals prepared by melt, which in itself has good wear-resisting properties. This research paper considers the part played by a dense Al-Fe-Cr quasicrystal (QC) reinforced Al matrix composite fabricated by the directed energy deposition (DED) in reducing wear between sliding surfaces and discusses briefly some of the factors which, in practice, explain ceramic-like properties of quasicrystal including low friction and wear resistance. The hardness of reinforcement phases, QC Al91Fe4Cr5 and Al13(Fe, Cr)4, was up to ~ 91 and ~ 112 HV respectively, while the Al matrix was just ~ 70 HV. Furthermore, the reinforcement phases contributed to form the mechanical mixing layer (MML) which significantly decreased the coefficient of friction (COF) and improves the wear resistance. With the increase of load from 1N to 5N, the COF dropped from 0.82 to 0.33 because the higher load was beneficial to the formation of harder and denser MML. Through the comprehensive analysis of the wear test and worn surface, the wear behavior and mechanism of this QC reinforced Al matrix composite has been explained in detail. The results indicate that the quasicrystal reinforced Al matrix composites formed by DED is one of the promising wear-resistance materials.

Mechanical Properties of Al Matrix Composite Enhanced by In Situ Formed SiC, MgAl2O4, and MgO via Casting Process

Al matrix composite, reinforced with the in situ synthesized 3C–SiC, MgAl2O4, and MgO grains, was produced via the casting process using phenolic resin pyrolysis products in flash mode. The contents and microstructure of the composites’ fracture characteristics were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Mechanical properties were tested by universal testing machine. Owing to the strong propulsion formed in turbulent flow in the pyrolysis process, nano-ceramic grains were formed in the resin pyrolysis process and simultaneously were homogeneously scattered in the alloy matrix. Thermodynamic calculation supported that the gas products, as carbon and oxygen sources, had a different chemical activity on in situ growth. In addition, ceramic (3C–SiC, MgAl2O4, and MgO) grains have discrepant contents. Resin pyrolysis in the molten alloy decreased oxide slag but increased pores in the alloy matrix. Tensile strength (142.6 ± 3.5 MPa) had no change due to the cooperative action of increased pores and fine grains; the bending and compression strength was increasing under increased contents of ceramic grains; the maximum bending strength was 378.2 MPa in 1.5% resin-added samples; and the maximum compression strength was 299.4 MPa. Lath-shaped Si was the primary effect factor of mechanical properties. The failure mechanism was controlled by transcrystalline rupture mechanism. We explain that the effects of the ceramic grains formed in the hot process at the condition of the resin exist in mold or other accessory materials. Meanwhile, a novel ceramic-reinforced Al matrix was provided. The organic gas was an excellent source of carbon, nitrogen, and oxygen to in situ ceramic grains in Al alloy.

In-Situ Formed Al3Zr Compounds Reinforced Al Composites and Tribological Application

An Al3Zr-reinforced Al matrix composite using metal powders was fabricated via in-situ synthesis in vacuum; these were subjected to a pin-on-disc wear test with a SUS304 disc specimen under oil lubrication. The elemental mixture of Al and ZrH2 particles was sintered in vacuum for the in-situ-formed Al3Zr. ZrH2 particles were thermally decomposed in the reaction with the Al matrix to form hard Al3Zr intermetallic compounds. The friction coefficient and wear volume values of the Al–Al3Zr composites were significantly lower than those of the pure Al specimen. This is attributed to the uniform dispersion of Al3Zr particles in the Al matrix, which prevented the metallurgical bond from falling and blocked the direct contact between the Al matrix and SUS304 disc.