Study On Wriction Properties Of SiC Foam/Cu Bi-continuous Phase Composites

With the improvement of the transport speed and carrying capacity, excellent properties of friction material are needed. Copper-based materials of brake pads made by powder metallurgy have been applied extensively for the mature technology and good performance so far. However, owing to their high wear rate and poor high temperature resistance, the development of the materials is hampered to a great degree. Recently, SiC foam/metal bi-continuous phase composites have attracted much attention. As a new kind of friction material, SiC foam/Cu bi-continuous phase composites have an integral reinforcing mechanism that SiC foam and the metal matrix are interconnected mutually to form a network structure. The composites perform an excellent property for the combination of SiC ceramics (high hardness, high wear resistance and high temperature resistance) and the metal matrix (high ductility, high strength and good thermal conductivity), which enables the composite to possess the properties of high temperature resistance, stable friction coefficient, lower wear rate, quick response and so on.In this paper, SiC foam/Cu bi-continuous phase composites were successfully prepared using squeeze casting method. Thereafter, the thermophysical properties, mechanical properties, friction and wear properties and wear mechanism were studied systemically.SiC foam/Cu bi-continuous phase composites exhibit excellent thermophysical properties for the function of SiC foam that limiting the deformation of the metal matrix. The coefficient of linear expansion of the composite is about (8.69～13.7)×10-6/℃(20～100℃). The specific heat of the composite is about455～563J·kg-1g·℃-1(20～100℃). The thermal conductivity of the composite is about59.9～63.5W·m-1·℃-1(20～100℃).SiC foam/Cu bi-continuous phase composites exhibit excellent mechanical properties for the rigid load-bearing role of SiC foam and its function of limiting the slip of Cu. The maximum values of impact toughness, flexural strength and compressive strength are3.69J/cm2,267.0MPa and568.9MPa with the SiC volume fraction of20%,30%and70%, respectively. The composites are damaged in a mixed fracture mode that cracks originate from SiC foam skeleton, while the metal phase bridges cracks and makes cracks deflected.The friction and wear experiments are carried out, in which the SiC foam/Cu bi-continuous phase composites is used as the stationary block and the forged steel28CrMoV is used as the rotating ring. It was shown from the results that the friction coefficient and wear rate of the composites are all reduced with the increase of the volume of SiC, however the friction coefficient (and its stability) and wear rate of the composites with friction-component are all increased. Compared with SiC/Cu composites made by powder metallurgy, SiC ceramic foam/Cu bi-continuous phase composites have more stable friction coefficient and lower wear rate. The wear rate of SiC foam/Cu bi-continuous phase composites is one-fifth to one-forth of that of the composites made by powder metallurgy.The simulated experiment of high-speed braking is carried out, in which the SiC foam/Cu bi-continuous phase composites is used as the stationary block and the forged steel28CrMoV is used as the rotating ring. It was shown from the results that with the increasing of braking speed, the high-speed braking time is increased and the friction coefficient of the composites is reduced, but the friction coefficient stability coefficient is high. With the increasing of braking pressure, the high-speed braking time and the friction coefficient of the composites are both reduced, but the friction coefficient stability coefficient is high. Compared with SiC/Cu composites made by powder metallurgy, SiC foam/Cu bi-continuous phase composites have shorter braking time and quicker response to the high-speed braking tests.The wear mechanism of SiC foam/Cu bi-continuous phase composites is mainly adhesive wear that the material transport from the forged steel28CrMoV to the composites during the friction wear. The phenomenon of "transferred Fe" is obvious, at the same time, oxidation wear occurs. The wear mechanism of SiC foam/Cu bi-continuous phase composites filled with friction-component is mainly adhesive wear and abrasive wear with the oxidation wear accompanying..