Recent results on the development of Ti3AI base materials, including orthorhombic alloys, are reviewed. Included in this discussion are new data and ideas concerning alloy development, phase equilibria, processing for improved toughness and ductility, environmental degradation, oxidation and corrosion resistance, and coating development. Several new families of alloys have been developed in recent years and the microstruc-ture%processing%property relationships in these alloys are reviewed. It is shown that errors in processing this class of alloy can lead to microstructural instabilities under service conditions. Finally, some immediate needs and some directions for further development are suggested.

Polycrystalline NiAl exhibits <001> slip at temperatures below about 450°C. In Fe-Al alloys there is a transition in the Burgers vector from a/2<111> at low temperatures to a<001> at intermediate temperatures. The transition temperature is dependent upon composition.

A transition in the Burgers vector from a/2<111> to a<001> has been found to exist as a function of composition and temperature in the B2 pseudo-binary (Fe,Ni)-40Al (at%) system. At room temperature, this transition occurs at a composition between Fe-40Al-10Ni, which exhibits <111> slip, and Fe-40Al-3ONi, which exhibits <001> slip. At 400°C this transition shifts further toward the iron-rich compositions. Fe-40Al-10Ni exhibits both <111> and <001> slip, whereas Fe-40Al-20Ni exhibits <001> slip.

Recent studies suggested that additions of either Fe or Mn to polycrystalline Ni3Al without boron, result in a ductile alloy. In the present study the effects of Fe and Mn additions on the strength and ductility of Ni3Al were investigated at 25°C, 600°C in air and at 600°C in vacuum. Metallographic examination showed that with 4 at.% solute a single phase structure existed but at higher solute levels the alloys were two phase. Single phase materials tested in bending showed virtually no plastic strain and low bend strengths at all temperatures. The two phase materials tested at 25°C and 600°C in vacuum showed marked ductility. However, the same alloys tested at 600°C in air exhibited brittle failure. These results suggest that Fe and Mn have no effect on the high temperature dynamic environmental embrittlement known to occur in Ni3Al.

This paper presents a review of recent research conducted at the Air Force Wright Aeronautical Laboratories (AFWAL)/Materials Laboratory to develop iron-aluminides as elevated temperature structural materials. The research consisted of investigations on the microstructure, tensile behavior, deformation, and fracture mechanisms of the DO3 and B2 ironaluminides. Binary Fe-Al alloys with a wide range of Al contents, solidsolution ternary alloys and precipitation- and dispersion-strengthened two-phase alloys have been investigated. It is shown that iron-aluminides have a potential to be structural materials at least up to 650°C.

The influence of a number ternary additions in Fe3Al upon the DO3 domain structures and DO3 → B2 transformation temperature, Tc, has been investigated. It was found that additions in (atomic percent) of 5 Ti, 5 Cr, 6 Mn, 12 Mn, 10 Ni, 3 Mo, 6 Mo, 3 Si, and 5 Si raise Tc. In the Fe-20 Al-5 Ti alloy not only is Tc raised significantly (≧ 750°C), but the DO3 antiphase domain boundaries with fault vector become highly crystallographic and are parallel to {100} planes.

The object of this paper is to describe a coordinated research and development program which has been pursued by an Air Force-Industry-University team for more than twelve years. The focus of our attention has been on the development, processing, and engine testing of alloys based on intermetallic compounds, specifically on the aluminides of titanium, iron, and nickel. The titanium aluminides, Ti3Al and TiAl, are the materials with which we have been working the longest and on which development has proceeded the furthest. This Symposium has provided the first opportunity to review the progress of the titanium aluminide development programs sponsored by the Air Force and some of the engine testing efforts undertaken by the engine manufacturers.