Microstructural refinement and strengthening of Nd-bearing TiAl alloys

The microstructures and the tensile properties and creep resistance of Ti–47.5Al–0.25Nd and Ti–46.5Al–2Cr–2Nb–0.25Nd alloys were studied. With the addition of Nd, neodymium oxides formed, and a uniform and homogeneous distribution of the neodymium oxides was observed in Ti–46.5Al–2Cr–2Nb–0.25Nd alloy. The cast microstructure of the Ti–46.5Al–2Cr–2Nb–0.25Nd alloy was remarkably refined after conventional heat treatment. The tensile strengths and ductility of the Ti–46.5Al–2Cr–2Nb–0.25Nd alloy at room temperature were increased. The colony refinement of the Ti–46.5Al–2Cr–2Nb–0.25Nd alloy by Nd was attributed to the accelerated recrystallization due to the decrease of the activation energy, and the impediment of the neodymium oxide particle to the grain growth. The strengthening of the Nd-bearing TiAl alloys was the superposition of the second phase strengthening by big neodymium oxide particles, the dispersion strengthening by fine precipitated neodymium oxides and fine colony grain size strengthening.