The Study Of Fabricating Mullite Matrix Composites Toughed By Three Demension Fiber Through PIP Process

Fiber reinforced mullite matrix composites have excellent mechanical properties and oxidization resistance at high temperature, and are considered to be one candidate materials for turbine-engine components. In this paper, 3D Nextel720/Mullite composites have been fabricated by precursor infiltration pyrolysis process (PIP process) using the mixture precursor of TEOS (Si(OC2H5)4) and AIP (A1(OC3H7)3). The controlling of the matrix composition, the temperature of mullite formation and the densification of the composite as well as the interface layer in the composites have been studied. The results indicated as follows:1. The Al/Si ratio of hydrolysate is affected by pH value and hydrolysis time. In the acid condition, the Al/Si increases with increasing hydrolysis time, and in the alkaline condition, the Al/Si decreases with increasing hydrolysis time.2. The mullite formation temperature is lower than 1200℃ using AIP and TEOS as precursor, which reduces damage to fiber in fabrication process of composites, and thus makes it possible to fabricate the mullite matrix composite.3. A theoretical infiltration value is obtained under pressure of 2MPa from one cycle to fourteen cycles. When the infiltration time exceeds fourteen cycles, it needs higher pressure to enhance infiltration efficiency.4. There is a density gradient of the composites fabricated by PIP process, the exterior is dense, and interior is loose. The reason is that during fabricatingVcomposites, the precursor is cued by hydrolysis, and the densification process is conducted from the exterior to the interior step by step. This density gradient causes infiltration difficulty in the last processing stage5. The carbon interface is oxidized when Nextel720/mullite composites are pyrolyzed at 800℃ in Ar atmosphere. In the subsequent heat treatment, it has formed strong interfacial bonding which causes brittle rupture of the composites. However, no oxidation occurs in interface when the composites are pyrolyzed at 400℃. Thecomposite rupture is of toughness but the strength is only 108MPa. When composites with C-SiC multi-interface is pydrolyzed at 800℃, the composite rupture is toughness with a strength is 244MPa.6. The Nextel720/mulite composites with the C-SiC interface is oxidized in air condition at 1000℃ for 20 hours to form an oxidization resistant fugitive interface. The rupture displacement of the composites is much higher than that of the composites as fabricated. However, the stress and elastic module of the former is much lower than that of later.