Oxidation of Titanium Aluminide and Its XD Composite.
Abstract
Martin Marietta Lab. recently developed a unique technology, whereby reinforcement dispersoids can be introduced exothermically into a metal matrix. This special alloying approach, known as Exothermic Dispersion (XD) processing, produces a metal matrix composite with a fine dispersion of a high-modulus, high-strength compound, such as titanium boride, in titanium aluminide. This study was undertaken to characterize the oxidation behavior of a Ti-45 at % Al alloy and its XD composite with TiB2 reinforcement particles. These materials were found to oxidize in air at temperatures ranging from 400 to 1500 C. Oxidation was evidenced by surface discoloration, formation of an oxide scale and an interfacial zone, internal oxide precipitation, internal cracking, and weight gain. The oxide scale consisted of two layers; an inner TiO2 and Al2O3 mixture; and an outer TiO2 and Al2TiO5 mixture. A narrow zone along the oxide scale/base metal interface was depleted in Al, but enriched with O. In the Ti-45 at % Al alloy, an Al-rich oxide, presumably Al2O3, was precipitated in the TiAl plate and a Ti-rich oxide, presumably TiO2, was precipitated in the Ti3Al plate. In the XD composite, an Al-rich oxide was precipitated along the lamellar structure colony boundary, and a Ti-rich oxide was precipitated in the interior of the colony. During oxidation, internal cracking occurred along the boundary and in the interior of the TiAl and Ti3Al plates. In addition, voids were formed at the lamellar structure boundary of the XD composite. The specimen gained weight with increasing oxidation temperature. Activation energies for oxidation were determined to be 63 kcal/mol for the Ti-45 at % Al alloy, and 67 kcal/mol for the XD composites.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 20, 1990
- Accession Number
- ADA240401
Entities
People
- Eun U. Lee
- Jeffrey Waldman
- Thomas Kircher
Organizations
- Naval Air Warfare Center Warminster