Effect of Boron Content on Mechanical Properties of Monocrystalline Ni3Al

ABSTRACTThe microstructure and the mechanical properties at room and high temperatures of monocrystalline Ni3Al containing 0, 0.52, 1.37, 2.22 and 3.00 at%B have been studied. The results show that the ultimate and yield strengths at 20°C and 800° C of monocrystalline Ni3Al obviously increase with the increase of B content, and reach maxima when B content is 1.37 and 0.52 at% respectively. With further increasing the B content to 2.22 at%, they slowly drop. The tensile ductilities at 20°C and 800°C of monocrystalline Ni3Al when the B content is 0 and 0.52 at% respectively are the best in five kinds of Ni3Al studied, then they continuously decrease with the increase of B content due to the precipitation of boride eutectic. The rupture life and elongation at 850°C and 100 MPa markedly drop as the B content is raised in the monocrystalline Ni3Al, but they are still higher by 1 to 2 orders of magnitude as compared with those of polycrystalline Ni3Al with the same compositions. When B content exceeds 1.37 at%, the eutectic structure of Ni20Al3B6 and Ni3Al is formed, which is enhanced by the B content and is harmful to the strength and the ductility.