Formation of magnesium aluminate (spinel) in cast SiC particulate-reinforced Al(A356) metal matrix composites
- PDF / 2,461,239 Bytes
- 8 Pages / 613 x 788.28 pts Page_size
- 11 Downloads / 231 Views
I.
INTRODUCTION
T H E mechanical properties of metal matrix composites (MMCs) are controlled to a large extent by the structures and properties of the reinforcement/metal interface. It is believed that a strong interface permits transfer and distribution of the load from the matrix to the reinforcement, resulting in an increased elastic modulus and strength. From a metallurgical point of view, the desired interfacial region in a composite relies on several factors. For instance, (1) an intimate contact between the reinforcement and the matrix needs to be established through satisfactory wetting of the reinforcement by the matrix to ensure adequate adhesion and (2) the rate of chemical reaction at the interface should be very low and extensive interdiffusion between the component phases should be avoided so that the reinforcement will not be degraded. The choice of the reinforcing and matrix materials for a composite system often cannot satisfy these requirements at the same time. One of the ways of achieving such a desired interface while not having to sacrifice the performance of the composite is to apply a thin coating or coatings on the reinforcement, t~'2~ which is chemically compatible with both the reinforcement and the .matrix. Selective addition of alloying elements has also proved to he effective in improving wettability and reducing interdiffusion, t31 From a mechanical point of view, on the other hand, the behavior of the interface plays a significant role in controlling the strength of composites. The normal component of interfacial stresses would tend to cause interface debonding, while the shear component could be the cause of splitting of phase boundaries. This effect becomes more pronounced as the difference in the elastic constants between the two constituent phases increases. The following are some important factors in considering the interface properties: (1) a strong interface, as mentioned above, would NING WANG, Graduate Student, and ZHIRUI WANG, Assistant Professor, are with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, ON M5S 1A4, Canada. GEORGE C. WEATHERLY, Professor, is with the Department of Materials Science and Engineering, McMaster University, Hamilton, ON L8S 4L7, Canada. Manuscript submitted June 3, 1991. METALLURGICAL TRANSACTIONS A
ensure transfer of load from matrix to the reinforcement, (2) the mechanical compatibility requirement at the interface would result in stress discontinuity or a steep stress gradient at the interface because of the differences in the elastic and/or thermal coefficients between the reinforcement and matrix, and (3) a moderate coating phase between the reinforcement and matrix may decrease the stress gradient at the interface. Therefore, an ideal interface should be a mechanics continuum, involving coherency of the bond at the atomic level, t41 Because of these metallurgical and mechanical considerations, it is important to characterize the interfacial microstructure to understand the mechanical behavior of a comp
Data Loading...
