Fabrication And Mechanical Properties Of Ti₅Si₃/Tial Composite Sheet Based On Ti-（Al-Si） System

As the first choice of high temperature structural materials, TiAl-based alloy platecan be used in the aerospace engines and low-pressure turbine blades. However, thereare difficulties in fabricating TiAl-based alloy sheets because of intrinsic brittleness. Inthis paper, Al-Si alloy foils and pure Ti foils were used as raw materials to synthesizeTi5Si3/TiAl matrix composite sheets by hot pressing and reaction annealing. Themicrostructure and phase composition of the reaction layer during heat treatment wereanalyzed. Meanwhile, mecahnical properties were evaluated at elevated temperatures.In this paper, TiAl3layers were formed by reaction annealing of multi-laminatedTi-(Al-Si) composite sheets during low temperature heat treatment. The reaction ratewas accelerated because of liquid-solid reaction. It was found that Si elementcontinuously dissolved in TiAl3layers. The content of Si in reaction layer Ti(Al,Si)3presented a decreasing trend from the direction of Al-Si/Ti(Al,Si)3interface to theTi/Ti(Al,Si)3interface.Ti5Si3particles precipitated in TiAl layers and TiAl2layers during high temperatureheat treatment. EDS/TEM results showed that a certain amount of Al dissolved intoTi5Si3. TiAl matrix composite sheets consisted of stability intermetallic compounds TiAland Ti3Al by heat treatment at1200oC for8h.A type of Ti5Si3particles reinforced TiAl matrix composite sheets were obtainedby lamellar treatment at1400oC for25min, with an overlapping layered structure of(α2+γ) lamination layer and equiaxed γ-TiAl layer. In detail, the equiaxed γ-TiAl layersformed at initial Al-Si alloy layers, while the (α2+γ) lamination layers formed at initialTi layers.Most of in situ Ti5Si3particles dispersed in equiaxed γ-TiAl layer,while thenumber of in situ Ti5Si3particles in (α2+γ) lamination layer was relatively less. A smallpart of the Ti5Si3particles are distributed around the lamellar tissue, showing thecharacteristics of quasi-continuous network distribution. The bond betweenreinforcement Ti5Si3particles and the substrate was very good and without voids.Tensile tests at elevated temperature showed that with the increase of temperature,the tensile strength and yield strength of Ti5Si3/TiAl composite sheets increase firstlyand then declines. The tensile strength reaches the highest value of531MPa at800oC.The tensile fracture surface of Ti5Si3/TiAl composite sheets has obviously characteristicof intergranular fracture happen in equiaxed γ-TiAl layer, while translamellar mainlyhappens in (α2+γ) lamination layer.