Novel Joining Technique for Oxide-Dispersion Strengthened Iron Aluminide Alloys

60754 Oxide-dispersion strengthened (ODS) iron aluminide alloys have been shown to exhibit high creep strength and excellent corrosion resistance. However, it is difficult to join the alloys because the dispersed oxides agglomerate, thus compromising the mechanical properties of the base material. Diffusion bonding, in which two clean surfaces are joined by diffusion under high temperature and pressure, would be a candidate solution, but residual surface oxide contamination can cause lower fracture toughness and ductility of the joint. This project will utilize a pulsed electric field during diffusion bonding to join ODS intermetallic materials at lower pressures and shorter times. In this processing technique, no alloying elements are used in the joined interface, leading to joint strengths near those of the base material at high temperature. In Phase I, MA956 rods that were diffusion-bonded for only 30 minutes at low pressure, using pulsed-electric field conditions, showed substantially higher strength than specimens fabricated without the pulsed electric field. Ultrasonic and x-ray analysis suggested that the pulsed electric field enhanced metal diffusion across the interface. In Phase II, the pulse-bonding technology will be statistically tested using a wider range of experimental conditions, including pressure, variation of temperature, and pulsing conditions. High-temperature tensile testing will be conducted on MA956 and Fe3Al rods and tubes. Sequential creep testing and environmental characterization under oxidizing and sulfidizing atmospheres will also be performed. Commercial Applications and Other Benefits as described by the awardee: The major application of this technology will be in the manufacture of iron aluminide components for high-temperature turbines and coal gasification furnaces. The pulse-bonding technology may be applicable for bonding other types of dissimilar metals and ceramics for automotive and aerospace applications