Interface structure and solute segregation behavior in SiC/2124 and SiC/6061 Al composites exhibiting high-strain-rate s
- PDF / 584,170 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 120 Downloads / 142 Views
Dong-Wha Kum Division of Materials, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul, 130-650, Korea
Ha-Guk Jeong Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Received 2 April 2001; accepted 5 June 2001)
Interface structure and solute-segregation behavior in the high-strain-rate superplastic SiCp /2124 and SiCp /6061 Al composites were investigated. Evidence for interfacial reaction between reinforcement and Al matrix, which was evident in the superplastic Si3N4p,w /2124 Al and Si3N4p,w /6061 Al composites, could not be detected in the current SiC-reinforced Al composites. Instead, strong solute segregation was observed at SiC/Al interfaces. Extensive formation of whiskerlike fibers was observed at the fractured surface of tensile samples above the critical temperature where particle weakening began to be seen. These results suggest that partial melting occurs at the solute-enriched region near SiC interfaces and is responsible for the particle weakening. The absence of reaction phase in the SiC-reinforced composite may explain why no endothermic peak for partial melting appears in its differential scanning calorimetry curve and why its optimum temperature for superplasticity is generally higher than that of the Si3N4-reinforced composite.
I. INTRODUCTION
A number of experimental data for high-strain-rate superplastic (HSRS) aluminum matrix composites fabricated through either powder-metallurgy (PM) or mechanical alloying process are now available.1–11 As the HSRS behavior has been often observed near the onset temperature for partial melting, it is believed that a proper amount of liquid phase is needed for superplasticity in aluminum matrix composites.12,13 Microstructures of aluminum composites reinforced with Si3N4 whiskers or particles have been studied by using transmission electron microscopy (TEM) and high-resolution TEM (HRTEM),14–16 and the melting of a reaction phase between Si3N4 and Al matrix was claimed to cause the partial melting. Recently, Kim and co-workers11,17,18 studied HSRS behavior of PM 2124 and PM 6061 alloys and PM SiCp / 2124 and PM SiCp /6061 Al composites (p denotes particulate) and observed that “particle weakening” a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 16, No. 8, Aug 2001
http://journals.cambridge.org
Downloaded: 02 Apr 2015
occurred in the aluminum composites at elevated temperatures where plastic flow is controlled by grain boundary sliding. Particle weakening means that the strength of a reinforced composite is lower than that of the unreinforced matrix alloy. The strength differential between the composite and matrix alloy was large at high temperatures and converged to the same values at about 460 and 480 °C in the 2124 and 6061 Al composites, respectively, when the experimental data were extrapolated to lower temperatures. Besides the particle weakening, the composites exhibited a high activation energy for superplastic flow, which was considerably highe
Data Loading...
