Reaction mechanism in an Al-TiO2-C system for producing in situ Al/(TiC + Al2O3) composite

In the last decade, production of particulate reinforced metal matrix composites (MMCs) through in situ reaction has attracted much attention due to its many advantages, e.g., low production costs, clean particle-matrix interfaces, over conventional methods [1–4]. Particulates used for reinforcement mainly include TiC [2–4], Al2O3 [1], TiB2 [1], etc. In a typical in situ reaction, one or more particles is formed through direct chemical reaction in the melt of the metallic matrix. The preparation of Al2O3/TiC ceramic composites through SHS (self-propagating high-temperature reaction) in the TiO2-C-Al system has been extensively studied recently [5–7], but little work has been conducted to prepare TiC and Al2O3 particle reinforced Al matrix composites through in situ reaction of the three starting materials. Aiming to providing a basis for the production of Al/(TiC + Al2O3) composites, this letter mainly deals with the reaction process in an Al-TiO2-C system by using DSC, XRD and TEM. A mixture of 15 g Al, 5 g TiO2, and 0.75 g C powders (99.0% purity or better), i.e., 72.3 wt%Al-14.1 wt% TiO2-3.6 wt% C, was sealed in a vacuum stainless steel vial together with steel balls ten times the weight of the powder mixture, and then ball milled for 9 h using a QM-1SP2 planetary-type ball mill with a planetary rotation speed of 450 rev min−1. About 0.35 g of ballmilled powders were heated under argon in a Netzsch 404 differential scanning calorimeter (DSC) at a rate of 20 ◦C/min, from 25 ◦C to the desired temperatures and then cooled to the ambient temperature. The heated powders were analyzed using a Rigaku D/max-rB Xray diffractometer (XRD) with Cu Kα radiation or a H800 transmission electron microscope (TEM) to detect phases formed during heating. Fig. 1 presents the DSC traces of the powder mixture heated to 1300 ◦C and cooled to ambient temperature, both at a rate of 20 ◦C/min. An endothermic peak during heating, with peak temperature at 667.8 ◦C, and an exothermic peak during cooling are visible. They are obviously caused by the melting and solidification of Al, respectively. No other thermal effects could be observed during cooling besides the solidification of Al, indicating that phases formed during heating are thermodynamically stable. In the heating curve, another endothermic peak with peak temperature at 886 ◦C and