| Phase transformations, microstructures, deformation mechanisms and mechanical behavior of Nb-15Al-25Ti alloy has been studied using compression test, tensile test, bend test, optical, scanning and transmission electron microscopy. Yield strengths of as-cast and heat treated Nb-15Al-25Ti have been obtained using compression tests conducted at various temperatures. Crack initiation in the as-cast Nb-15Al-25Ti alloy has been studied using bend tests.;For as-cast Nb-15Al-25Ti deformed at room temperature, 500;In addition to dislocation slip, pseudo-twins have also been observed in Nb-15Al-25Ti alloys deformed at various temperatures. An ordered structure is created by pseudo-twinning mechanism in the B2 matrix. This new structure has been identified to be ordered orthorhombic. This process resembles stress-induced martensitic transformation therefore pseudo-twins observed in deformed Nb-15Al-25Ti alloy are regarded as stress-induced martensites. Martensites induced by quenching experiments also have the same ordered orthorhombic structure.;The stress-induced martensite has been found responsible for crack initiation in Nb-15Al-25Ti B2 alloy when deformed in tension at room temperature. Results of bend tests have shown that cracks were likely initiated by intersection of the stress-induced martensites. TEM analyses of the bent sample evidenced that two variants of the stress-induced martensite with various twinning dislocations have intersected to form cracks before yielding. |
