improvement of Strength and Ductility of Ni_3Al and Challenge to a High Temperature Structural Material

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Attempts have been made to improve the mechanical properties of Ni_3Al' because its yield strength is too low for using as a high temperature structural material. Solid solution hardening is one of the most fundamental and important strengthening methods. Many elements dissolve into Ni_3Al, but it is still uncertain whether Ni_3Al+M compounds are ductilized by microalloying with B.Particularly, it is interesting whether the deviation to the Ni-rich side is essential for ductilization of these alloys. In the present work, the effect of simultaneous alloying of B and the substitutional element M on ductilization of Ni_3Al has been investigated by the bend test and the tensile test. Ni_3Al is ductilized by macroalloying with Zr, Hf, V,NB,Mo, W,Co, Pd, Cu, Cr, Mn and Fe. The Ni_3 (Al, M) compounds, where M substitutes exclusively for the Al atoms, are ductilized by microalloying with B on the Ni-rich side. On the contrary, the (Ni, M)_3Al compounds and the (Ni, Mn)_3 (Al, Mn) compounds are ductilized by microalloying with B on both the Ni-rich and Al-rich sides. The yield strength of Ni_3Al+B increases by alloying with M except for Fe and Ga. The fracture strength of Ni_3Al+B increases by alloying with Pd, Ga, Si and Hf, but decreases with the other elements. Elongation of Ni_3Al+B increases by alloying with Ga, Fe and Pd, but decreases with other elements. Hf and Pd is the effective element for the increase of the yield strength and the fracture strength of Ni_3Al+B,respectively. Alloying with Hf leads to the increases of the yield strength and the fracture strength of Ni_3Al+B,but to the lowering of elongation. On the other hand, alloying with Pd improves all mechanical properties, i. e. the yield strength, the fracture strength and elongation. Alloying with Ti, V and Co leads to the lowering of mechanical properties of Ni_3Al+B.The reason why ductility of Ni_3Al+B is reduced by alloying with some elements M was discussed.