Braking Behaviors And Mechanisms Of C/C-SiC Paired With Cu-based PM Friction Pairs Under Different Service Conditions

The braking behaviors are not solely determined by the properties of friction pair materials,but also affected by multiple aspects such as braking parameters and exposure to open environmental conditions.Carbon-ceramic（C/C-SiC）composites have many advantages such as excellent thermophysical properties,high strength and low density,which are expected to solve the problems of thermal degradation of braking performance of steel-based brake discs.Copper-based powder materials（Cu-PM）have stable friction performance,excellent weather resistance and thermal conductivity.Therefore,combining the advantages of both,C/C-SiC and copper-based powder metallurgy（Cu-PM）materials were prepared by chemical vapor deposition combined with molten silicon infiltration and powder metallurgy respectively,and the braking behaviors of the new friction pairs under different braking parameters and service environments were studied.The main research contents and results are as follows:（1）The braking behaviors of C/C-SiC friction material paired with Cu-PM brake pairs（C/C-SiC–Cu-PM）at various braking parameters were studied.With the increase of braking speed,the worn surface of C/C-SiC material has experienced a stage from non-friction film to gradually forming friction film.The main wear mechanisms of the friction pairs transitions from abrasive wear to adhesive wear,and then change to a combination of adhesive wear,oxidative wear and fatigue wear.With the increase of braking pressure,the worn surface of C/C-SiC friction material undergo a rough to smooth evolution process.And the worn surface changes from the SiC skeleton structure at low braking pressure to an incomplete and unstable tribo-films,and then transitions to a complete tribo-films.（2）The material composition and structure of the C/C-SiC friction surface of the brake pairs were studied.The friction layer consist of a nanostructured transfer layer with a thickness of about 700 nm and a deposition layer.The oxidation and exfoliation of carbon materials lead to voids left in the nanostructured transfer layer,which are filled with transfer materials dominated by Fe₃O₄to prevent further oxidation of carbon materials in the deposition layer.In addition,the transfer substances are deposited in this deposition layer and is dispersed in and tightly bound to the amorphous silicate.（3）The braking behaviors of C/C-SiC–Cu-PM brake pairs in different service environments were studied.Under dry condition,the main wear mechanisms of brake pairs are adhesion,fatigue and oxidation wear.However,abrasive wear and water lubrication play a dominant role under continuous wet,transient wet and freezing conditions.And the corresponding frictional performance degradation rates are 14.1%,5.3%and 5.6%,respectively.The wear mechanisms of the first braking under salt fog condition are abrasive wear and fatigue wear.