Reaction in the Al-ZrO2-C system

The reaction in ball milled Al-ZrO2-C powders with different ZrO2/C molar ratios was studied by using DSC, XRD and EPMA. During heating fully milled powders, the Al first reacts with ZrO2 and carbon simultaneously to form ZrAl3 and Al4C3 phases, which further react with each other at about 896∘C, causing the formation of Zr2Al3C5. Then at 1140∘C, Zr2Al3C5 reacts with ZrAl3, producing ZrC and ZrAlC2 phases. In the un-fully milled powder, only an exothermic reaction between the three starting phases occurs at a higher temperature of about 956∘C. Heating Al-ZrO2-C powders with different ZrO2/C ratio (r) to 1250∘C produces different phases in the final aluminum matrix: Al-Al2O3-Zr2Al3C5-Al4C3 (r < 2:5), Al-Al2O3-Zr2Al3C5 (r = 2:5), Al-Al2O3-Zr2Al3C5-ZrC-ZrAlC2 (2:5 < r < 3:5), Al-Al2O3-ZrC-ZrAlC2 (3:5 ≤ r ≤ 3:4), Al-ZrAl3-Al2O3-ZrC-ZrAlC2 (r > 3:4). Zr2Al3C5 presents fine platelet morphology, both ZrAlC2 and ZrC have polygonal shape, ZrAl3 exhibits flaky morphology at lower temperature, but blocky form at higher temperatures.