Domestic carbon/carbon composites
Chinese research and development of carbon/carbon composite began in the late 1970s, after decades of development, gaining rich results, advanced to catch up with developed countries. At present, the C919's brake discs are made of carbon/carbon composite materials made in China. Its supplier, Boyun Xinai, also supplies brake discs for Boeing 757 and Airbus 320 aircraft.
As the brake disc belongs to consumables, about one or two thousand takeoff and landing must be replaced, the cost of using imported brake disc is higher. Driven by market demand, domestic material manufacturers have begun to develop civil aircraft carbon brake discs.
Carbon/carbon composite coating has been the focus of research at home and abroad. Since carbon/carbon composites begin to oxidize at around 370 degrees, the material properties decline. Therefore, it is necessary to prepare anti-oxidation coating on the surface when it is used in aerobic environment. In addition to good oxidation resistance and ablative resistance, the coating should have good chemical and physical compatibility and similar expansion coefficient with carbon/carbon composites.
The non-friction surface of the C919 brake disc is coated with boron and phosphorus, which can effectively delay the diffusion of oxygen inside the material and prolong the service life of the material under high temperature working environment. While a typical brake disc may have to be replaced after more than 1,000 takeoffs and landings, the C919's brake disc has been proven capable of 2,000 takeoffs and landings through fatigue tests.
In addition to coating, carbon fiber prefabrication and densification processes also have an important impact on the properties of carbon/carbon composites. In foreign countries, preoxidized wire is commonly used to braid carbon fiber prefabricated, which has the advantages of good fiber flexibility, easy to form, but low strength. The C919 brake discs use organic fibers woven into carbon fiber preforms, which are more difficult to weave, but the resulting preforms are much stronger. At the same time, chemical vapor penetration and liquid impregnation were used to increase the density of the material, and the high-energy brake friction coefficient of the material was greatly increased.
