Reactions Between Ti2AlC, B4C, and Al and Phase Equilibria at 1000 A°C in the Al-Ti-B-C Quaternary System

As automotive, aerospace and the power industries increasingly look to carbide and boride based aluminum, Al, composites for their high specific strengths and increased thermal stability, it is important to characterize the equilibrium phase relations at temperatures common for processing these composites. Herein, two composites were fabricated starting with Al, Ti2AlC, and B4C. The Ti2AlC/B4C powders were mixed in both 50/50 and 75/25 vol.% ratios and cold pressed into 53% dense preforms. The preforms were pressureless melt infiltrated in the 900-1050 A degrees C temperature range with Al. Ten hour equilibration experiments were also conducted at 1000 A degrees C. X-ray diffraction and scanning electron microscopy confirmed that neither Ti2AlC nor B4C was an equilibrium phase. A number of reaction phases-AlB2, Al3BC, TiB2, TiC, TiAl3 and Al4C3-could be found in the non-equilibrated samples. However, the equilibrium phases were found to be Al, TiB2, Al3BC, and Al4C3 for the more B-rich composite and Al, TiB2, TiC, and Al4C3 for the Ti-rich composite. From these results, the 1000 A degrees C quaternary phase diagram adjacent to the Al-TiB2-Al4C3 triangle and in the Al-rich corner was developed for the first time. This study is a requisite first step for the development and use of advanced composites in the Al-Ti-B-C system.