Development of a scientific basis for design of intermetallic alloys for high-temperature structural uses

Intermetallic compounds have the valuable properties of good oxidation and creep resistance and high strain-hardening rate. They have been ignored as potential materials for high temperature services because they are brittle at room temperature and they are difficult to procss. Interest in utilizing ordered alloys for structural applications was renewed after the discovery that ductility and strength could be simultanously improved using a combination of powder metallurgy and alloying technique as well as rapid solidification processing. In this work the plastic deformation of four L1(sub.)2 compounds with and without boron as a third element have been studied systematically by transmission electron microscopy (TEM), in order to find out more about the relationship between mechanical properties and microstructure. TEM observations show that the deformation microstructures of Ni3Al and Zr3Al and Ni3Ga exhibit a profusion of stacking faults and many single and dipole dislocations, while Ni3Ge did not exhibit any stacking faults. Also the addition of a small amount of boron was shown to have a beneficial effect on the ductility of Ni3Al and Ni3Ga but not for Zr3 Al and Ni3Ge. Boron additions also show a significant effect in removing the stacking faults from Ni3Ga and Ni3Al. The weak beam technique and anisotropic elasticity theory have used to measure the anti phase boundary (APB) and intrinsic stacking faults (ISF) energies of all examined alloys. It seems that the addition of boron changes the stacking fault energy whereas the APB energies seem little changed. (author)