Effects of Preheating Temperature on Microstructure and Properties of Continuous C_f/Al Composites
|School||Nanchang University of Aeronautics and|
|Course||Aviation Aerospace Manufacturing Engineering|
|Keywords||C_f/Al composites vacuum assisted low pressure infiltration microstructure mechanical properties interface structure|
Owning to their combined advantages of high specific strength, high specific modulus, high-temperature strength and low thermal expansion coefficient, continuous carbon fiber reinforced aluminum matrix composites (Cf/Al composites) are important material with great potential in aerospace and advanced weapons’ equipment. To ensure the large-scale application of high-performance Cf/Al composites as complex components, it is important to develop its near net forming technology. Vacuum assisted low pressure infiltration technique combines the preparation of composites and its components forming, and is a new near net shape technology of continuous Cf/Al composites. However, the serious interfacial reaction during liquid infiltration is not conductive to improve the performance of composite material. To solve this problem, a new vacuum assisted low pressure infiltration device was developed to precisely control preheating temperature and time of fiber. Vol.35%Cf/Al composites including T300/Al, Ni-T300/Al and M40/Al were successfully prepared. Microstructures of the composites were examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Properties of the composites were studied by x-ray diffract meter, analytical balance, universal electronic tensile testing machine. Composites density and mechanical properties were tested and analyzed with respect to related factors. The effects of preheating temperature, ranging from400℃to600℃, on microstructure and properties of continuous Cf/Al composites were researched.By transforming the low pressure infiltration device, the preheating temperature of fiber preform was accurately controlled; the preparation cycle and the preparation cost of composites were reduced. Comparative study of the intensity in the fiber before and after preheating showed that the tensile strength of T300, Ni-T300and M40decreased with increasing preheating temperature. When the preheating temperature exceeds550℃, those fiber strength decreased dramatically. Nevertheless, it is difficult to fabricate the composites as preheating temperature of fiber lower than400℃. The integrity of the composite and its microstructures was improved significantly with preheating temperature of fiber increased. The relative densities of composites first increased and then decreased with the rise of the preheating temperature. At preheating temperature of450℃, T300/Al and M40/Al composites have uneven fiber distribution even segregation phenomenon, while Ni-T300/Al composites infiltrated completely, no defect in the tissue was found. At high preheating temperature, Ni coating will peel off from the surface of the fiber. Fibers have obvious fracture phenomena in the direction of the fibers parallel. Fracture of fiber was more obvious with preheating temperature increased.At preheating temperature of450℃, the interface in M40/Al composite was moderate. The fracture surface was uneven, a large number of fiber pulled out and matrix necked were observed, which exhibits a characteristic of ductile fracture. The bending strength of this composite was about1078MPa, which is up to50.1%of ROM value. However, the interface in T300/Al and Ni-T300/Al was over strong. The fracture surface was smooth and the pulling out of fiber and interfacial debonding was not obvious, which indicates a brittle fracture. Tensile strength of the Cf/Al composites decreased significantly with increasing preheating temperature. At the same preparation condition, the size and the amount of Al4C3in Cf/Al composite followed a descending order:T300/Al, Ni-T300/Al and M40/Al. The content of Al4C3in these composites have a continuous linear increase with preheating temperature increased, the rate of increase presented soon after the first slowed down. Nickel coating of fiber can significantly improve the wettability between C/Al. However, it can hardly to block the carbon diffusion and interfacial reaction. As a result, the mechanical properties of the composite can not be improved effectively.