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Studies consisting of both bulk sample and diffusion couple experiments have been conducted in order to establish an isothermal section of the Ti-Nb-Al system. Bulk samples were prepared by arc-melting and then annealed in a gettered, flowing, argon atmosphere for extended equilibration periods. The results obtained so far have established the existence of two ternary phases with the following approximate compositions, TI (Ti-18 at% Nb-34 at% Al) and T2 (Ti-ll at% Nb-44 at% Al). Moreover, several of the binary phases were found to have extensive solubilities, including the TiAl phase. The phases TiAl3 and NbAl3 form a continuous solid solution. Several heterogeneous equilibria were also determined. Determination of these phase fields was accomplished through the use of electron microprobe analysis (EMPA), x-ray diffraction, microstructural observations and backscatter electron imaging (BEI).

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Unlubricated sliding tests were performed at room temperature and at 400°C on polycrystalline Ni3Al with and without boron and on IC218, an alloy containing nickel plus 8.94 Al, 7.55 Cr, 0.88 Zr, 0.015 B and 0.01 Hf (all in wt. %). A pjn/disk geometry was used with self-mated samples in air and vacuum (1.3×10-3 Pa). Normal load was 1.5 kg (14.7 N), sliding speeds were 15–19 mm/s and sliding distances were 145–175 m.It had been expected that materials with and without boron would behave differently during sliding because of their well-known differences in ductility and fracture resistance. However, sliding behavior was similar for materials with and without boron. Environmental effects were more dramatic. For tests in vacuum, the friction trace was very noisy and the average coefficient of friction varied erratically during most of each test. Wear debris ranged from 100 μm to 1 mm in size. Wear scars were smooth, but with signs of heavy deformation. All test materials exhibited smoother sliding behavior in air than in vacuum, but the wear rate was usually higher in air. Debris particles were finer, most of them were at least partially oxidized, and they included at least one ferromagnetic component, probably arising from selective oxidation. It is suggested that the increased wear rate in air is related to oxygen-enhanced fracture of these nickel aluminides.