Research On Casting And Microstructures And Properties Of TiAl/Ti₅Si₃Matrix Composites Toughened By Nb Wires

In this article, Nb wires were chosen as the reinforcements, Ti-40A1-5Si alloy was chosen as matrix alloy. Ti-40A1-5Si alloy has been smelted by water-cooled copper crucible induction melting furnace. The TiAl/TisSi3matrix composite toughened by Nb wires has been produced by using centrifugal casting and investment casting techniques. The microstructures, interface, Vickers hardness, impact properties and bending properties of the composite have been studied by scanning electron microscopy, X-ray energy dispersive spectroscopy, Vickers hardness tester, impact testing machine and universal testing machine.The results show that Nb wires and the matrix alloy have formed a good compound during the forming process of the composite. Nb wires array regularly in the matrix alloy. An interactive diffusion reaction has been happened between Nb wires and the matrix that formed a uniform interface layer.The thickness of the interfacial reaction layer close to Nb wires is about1μm which mainly formed by the elements Ti and Al diffusing from the matrix to Nb wires during the solidification and cooling of the matrix alloy. The thickness of the interfacial reaction layer close to the matrix is about10μm which mainly formed by the Nb element diffusing from Nb wires to the matrix. The results of EDS show that the distribution of the chemical elements in the interfacial layer of the as-cast composite is wide. After950℃×2h annealing treatment, the chemical elements in the interfacial layer distributes moderately. The Vickers hardness of the interfacial layer is514.9HV at as-cast condition and increases to555.1HV after annealed.In the as-cast condition, the impact toughness of Ti-40A1-5Si alloy is3.44J/cm2. The impact toughness of the composite is higher than the matrix alloy. The impact toughness of the composites in which the volume fraction of Nb wires is12%,15%and20%is5.04J/cm2,5.64J/cm2and6.69J/cm2. The heat treatment has a significant influence on the properties of the composite. After950℃×2h annealing treatment, the impact toughness of the matrix alloy and the composites in which the volume fraction of Nb wires is12%,15%and20%is2.72J/cm2,5.85J/cm2,6.80J/cm2and8.22J/cm2.The bending strength of the annealed matrix alloy is654.88MPa, the deflection is0.55mm and the modulus of elasticity is88.86GPa. The bending strength of the annealed composite is550.54MPa, the deflection is0.45mm and the modulus of elasticity is101.31GPa. The bending strength of the composite decrease because there exists some shrink holes in the composite.Because the brittle phases exist in the interfacial layer, Nb wires detach from the matrix when the crack expands. It plays a major role on the toughening of the composite. The main toughening mechanism of the composite is weak interface toughening.