The behavior and effect of rare earth CeO 2 on in-situ TiC/Al composite
- PDF / 262,299 Bytes
- 5 Pages / 612 x 786 pts Page_size
- 110 Downloads / 189 Views
9/27/04
9:53 PM
Page 2511
The Behavior and Effect of Rare Earth CeO2 on In-Situ TiC/Al Composite YOUMING LIU, WENYI LI, BOFAN XU, XUN CAI, LIUHE LI, and QIULONG CHEN Rare earth CeO2 was investigated as an additive for in-situ preparation of TiC/Al composites using XD (exothermal dispersion) casting technology. Experiment results showed that an optimum CeO2 addition of 0.5 wt pct promotes the generation and refinement of TiC particles, prevents the formation of Al3Ti, increases the wettability between the TiC ceramic particles and the Al matrix, and improves the mechanical properties of composite. A corresponding thermodynamic model was proposed for the mechanism.
I. INTRODUCTION
ALUMINUM matrix composites have undergone rapid developments recently. Among various Al matrix composites, the in-situ TiC/Al[1–6] composite is the highlight of research interest, due to its high hardness, high elastic modulus, and high stability. The low-cost in-situ processing method provides TiC/Al composite with good wettability, high production rate, and a strong possibility of near-net shape forming. There are reports[1,2] that use some active additives in the reinforcements for TiC/Al composite, such as Mg and a mixture of KAlF4 and K3AlF6; however, none has mentioned rare earth as the additive. Inspired by the special behavior (refinement, purification) of rare earths in steel, the authors were interested in using rare earth CeO2 as the active additive to prepare the in-situ TiC/Al composite. The in-situ XD (exothermal dispersion) casting technology method was used: Elements and compounds such as Ti, C, CeO2, and Al, which can react to form the reinforcing phase homogeneously, were well mixed and pressed into preforms. The particle-reinforced Al composite was produced based on reactions by immersing the preforms in molten Al at high temperature. This article established a new thermodynamic model to illustrate the mechanism of how CeO2 prompts the reaction between Ti and C, eliminates the brittle Al3Ti phase, and refines the TiC particles.
in diameter and 30 mm in height under 30 MPa pressure. Pure aluminum (900 g) was melted and superheated to near 960 °C in a 8000 W electric furnace containing a graphite crucible, and the preforms were preheated at 300 °C for 2 hours in a 4000 W electric furnace. The preforms were then inserted into the molten aluminum with a bell. The temperature was held for 10 minutes after the reactions were complete, and the melt was stirred after that for 10 minutes using a graphite stirrer at 800 °C. Finally, the metal was degassed by using C2Cl6 at 750 °C and cast into a steel mold at room temperature. All of these processes were carried out in air. The cast rods were cut into three specimens: upper, middle, and lower part of rods. The specimens were polished and examined by X-ray diffraction (XRD) for phase determination. Their microstructure was observed by Neopht-II optical microscopy (German Democratic Repubic) and JXA-8800R electronic probe (Japan Electronic Corporation, Japan). The hardness
Data Loading...
