Luyan Ju

Interfacial microstructure and mechanical properties of Cf/AZ91D composites with TiO2 and PyC fiber coatings

In spite of the effectiveness of the fiber coatings on interface modification of carbon fiber reinforced magnesium matrix composites, the cost and exclusive equipment for the coatings preparation are usually ignored during research work. In this paper, pyrolytic carbon (PyC) and TiO2 were coated on carbon fiber surface to study the effects of fiber coatings on interfacial microstructure and mechanical properties of carbon fiber reinforced AZ91D composites (Cf/AZ91D composites). It was indicated that both the two coatings could modify the interface and improve the mechanical properties of the composites. The ultimate tensile strength of the TiO2-Cf/AZ91D and the PyC-Cf/AZ91D composite were 333MPa and 400MPa, which were improved by 41.7% and 70.2% respectively, compared with the untreated-Cf/AZ91D composite. The microstructure observation revealed that the strengthening of the composites relied on fiber integrity and moderate interfacial bonding. MgO nano-particles were generated at the interface due to the reaction of TiO2 with Mg in the TiO2-Cf/AZ91D composite. The volume expansion resulting from the reaction let to disordered intergranular films and crystal defects at the interface. The fibers were protected and the interfacial reaction was restrained by PyC coating in the PyC-Cf/AZ91D composite. The principle to select the coating of fiber was proposed by comparing the effectiveness and cost of the coatings.

Influence of Notch on Mechanical Properties of Cf/Mg Composite Fabricated by LSEVI

Cf/Mg composite was fabricated by liquid-solid extrusion following vacuum infiltration technique and uniaxial tensile tests were conducted on the notched and unnotched specimens to investigate the mechanical properties of Cf/Mg composite. The effects of circular notch on the notched strength, net tensile strength, tensile modulus, and fracture strain of Cf/Mg composite were investigated. The notch sensitivity of Cf/Mg composite was elucidated through the notch strength ratio (NSR), fracture surface, and fracture mechanism. By comparing the experimental and theoretical NSR, the influences of notch size and stress concentration factor on notch sensitivity of Cf/Mg composite were investigated. The results showed that the fracture strain of the notched specimens increased with increasing the notch size. Meanwhile, net tensile strength, notched strength, and tensile moduli had opposite trends. The NSR had a functional relationship with the notch size and stress concentration factor caused by the notch had no influence on the NSR.

Effect of PyC coating on mechanical properties of Cf/AZ91D composites

ABSTRACT The microstructure of high strength PAN-based T700 carbon fibre (Cf) with pyrolytic carbon (PyC) coating was characterised. Effects of PyC coating on the surface of carbon fibres, interface characteristics, and mechanical properties of Cf/AZ91D composites were evaluated. The results showed that the carbon fibres with PyC coating had higher surface roughness and higher graphitisation which were beneficial to ease hazardous interface reaction. Cf-PyC/AZ91D composites with an optimal PyC coating that is about 150 nm thick and has low texture exhibited ultimate tensile strength of 416 MPa, which demonstrated 35% improvement compared with the Cf/AZ91D composites. The increase of mechanical properties of Cf-PyC/AZ91D composites could be ascribed to a synergistic effect of the rough Cf surface interlocking, an optimum interfacial bonding between fibres and matrix, and protection of fibres from a corrosive attack of the aluminium element in the matrix.

Effect of holding pressure on densification and mechanical properties of Cf/Mg composites

Carbon fibre reinforced magnesium alloy matrix composites were fabricated by using liquid–solid extrusion directly following vacuum infiltration technique. The experimental results showed that the microstructures of Cf/Mg composites depended on the holding pressure. The porosity was reduced gradually, and the densification was improved obviously, respectively, with the increase of the holding pressure. The densification, hardness and Ultimate tensile strength of Cf/Mg composites were significantly improved as the holding pressure increased in the range of 0.1–15 MPa. The densification was not obvious, but the UTS of the Cf/Mg composites decreased gradually as the holding pressure increased in the range of 25–45 MPa. The Cf/Mg composites presented a good performance when the holding pressure was about 15 MPa.