Fabrication And Properties Of C/C-SiC-Cu₅Si Composites

Abstract:C/C-SiC-Cu5Si composites were fabricated by RMI (Reactive Melton Infiltration) method.Microstructure,mechanical properties, failure mechanism and tribological properties were investigated. Main research contents and results are as follows.(1) Using non-woven web as perform, C/C-SiC-Cu5Si composites fabricated by RMI were composed of19.87wt%carbon,11.91wt%β-SiC,14.99wt%TiC and53.23wt%Cu5Si. TiC, whose section shape is rectangle, is next to pyrocarbon, and its growth is controlled by Ti diffusion. Outside TiC is Cu5Si matrix, in whichp-SiC distributes equally.(2) Flexural strength, compression strength and impact toughness of C/C-SiC-Cu5Si composites under vertical load are110.4Mpa,354.8MPa and7.9kJ·m-2respectively, which are2.3times,1.2times,2.8times of that of C/C-SiC composites. Flexural strength, compression strength and impact toughness under parallel load are respectively89%,59%and141%of that under vertical load. Three different kinds of interfaces including interface between TiC and Pyrocarbon, pyrocarbon and pyrocarbon, pyrocarbon and carbon fiber existed in the composites, which have a great effect on mechanical properties.Fracture of Cu5Si phase, a typical toughness phase, appears to be dimple.(3) C/C-SiC-Cu5Si composites show pseudoplastic behavior under bend load: crack propagation along three kinds of interfaces leads to parallel failure, while crack pssing through thickness leads to vertical failure. Compressive failure in parallel direction manifests crack propogation along three kinds of interfaces and a small number of transcrystalline fracture of Cu5Si phase, except the mentioned above, c ompressive failure in vertical direction also manifests a mass of intercrystalline fracture of Cu5Si phase. Under impact,rapid loading leads to no propagation of cracks along interfaces, and carbon fiber is fractured along radial direction, which leads to lower toughness value under parallel load than that under vertical load.(4) The effects of braking speed on tribological properties of friction couple, consisted of C/C-SiC composites and30CrMnSiVA are discussed. Friction coefficient of this couple changes between0.16and0.23, which is lower than0.23～0.37, the coefficient of friction couple consisted of C/C-SiC composites and30CrMnSiVA. Linear wear rate of30CrMnSiVA of the former changes between0.17and1.113μm·side-1·cycle-1, which is nearly one fifth of that of the latter. (5) Tribological mechanism of C/C-SiC-Cu5Si and30CrMnSiVA couple is revealed.Friction force comes in two ways ploughing and adhesive effect. Wear mechanism shows in four different forms:abrasive wear, adhesive wear, oxidative wear and fatigue wear, and one form is often accompanied by others.