Chemical reaction strengthening of Al/TiC metal matrix composites by isothermal heat treatment at 913 K
- PDF / 1,743,884 Bytes
- 10 Pages / 576 x 792 pts Page_size
- 26 Downloads / 240 Views
The effect of solid state heat treatment at 913 K on extruded XD Al/TiC metal matrix composite with 0.7 and 4.0 /nm particle sizes has been investigated. The interfaces between Al and TiC after extrusion were atomically abrupt, as observed by HRTEM. On holding at 913 K, the composite with submicron particle size showed substantial changes in the phases present due to reaction between Al and TiC at 913 K. The stable reaction products are Al3Ti and A14C3. A substantial increase in Young's modulus occurs. The room and elevated temperature strength and hardness of the composite with submicron particles also increase significantly with time of heat treatment, but at the expense of ductility. The effect of heat treatment over the time range investigated is limited to the interfaces for the 4.0 /xm TiC particle size composite due to longer diffusion paths.
I. INTRODUCTION Aluminum based metal matrix composites are of increasing interest because of their stiffness to weight ratios and wear resistance.1 For high temperature applications and because of possible reaction during fabrication, the thermodynamic stability of the reinforcement phase with respect to reaction with the matrix is of great significance. In many cases such as Ti/SiC or Al/SiC composites, formation of reaction products at the interface results in degradation of ductility and fracture toughness.2'3 Recently, theoretical4"8 and experimental9"11 studies on the Al—Ti—C system have been reported. In situ Al/TiC composites have been prepared by several research groups12"14 and the XD processing technique is of particular interest. The Al and TiC phases have been reported to be thermodynamically stable at the processing temperature which is well above that of molten aluminum.15 The interfaces in XD Al/TiC composites are atomically abrupt16; the atom planes of each phase extend to the interface. However, in a theoretical work, Yokokawa et al} predicted that Al and TiC cannot coexist in thermodynamic equilibrium at low temperatures like 973 K. Ternary phase diagrams have been drawn at different temperatures above the melting point of Al,4-5'17 but only one publication has reported appearance of Al3Ti and A14C3 in an Al/TiC composite on isothermal solid state heat treatment (873 K). No explanation of the conditions and no thermodynamic data were given.11 The phases produced and the kinetics of evolution of the more stable phases at 913 K, where Al and TiC do not coexist in thermodynamic equilibrium, were investigated in the present work. Preliminary results of this investiga2370
http://journals.cambridge.org
J. Mater. Res., Vol. 8, No. 9, Sep 1993
Downloaded: 17 Mar 2015
tion were reported previously.17 Substantial increases in Young's modulus and strength properties from the solid state reactions were observed, but there was a decrease in ductility. A component made by forming highly ductile XD Al/TiC composite may be heat-treated to give much higher stiffness, hardness, and strength. This may be a route to developing a useful high modulus aluminum alloy bas
Data Loading...
