Effect of Rare Earth Yttrium on Microstructure of Rapidly Solidified Titanium Aluminum Based Alloys

Effect of Rare Earth Yttrium on Microstructure of Rapidly Solidified Titanium Aluminum Based Alloys
　　TiAl-based alloys are one kind of attractive materials for high temperature structural applications because their outstanding mechanical properties such as high specific strength, good creep strength and acceptable oxidation resistance. But their ductility at room temperature is very low, which is the main obstacle to TiAl-based alloys for their applications in aerospace and aircraft. The present paper adopted rapid solidification technique, -melt spinning, to prepare Ti-46Al-2Cr-2Nb based alloys with various Y contents (0, 0.5, 1.0, 1.5, 2.0 at.%). The influence of Y Special shape NdFeB magnets addition and rapid solidification technique on the microstructure and mechanical properties of the alloys was investigated intensively, in order to explore a novel approach of ductility improvement of TiAl based alloys.OM, SEM, EPMA and TEM observations of as ingots and rapidly solidified alloys are performed to show the solidification microstructure.
　　And XRD technique is employed to analyze the phase configuration.It was found that, the microstructure of as cast alloys which addition of 0.5 to 1.0at.% Y are lamellar, Al2Y phase distribute on the grain boundaries as discontinuous reticulation,but 1.5 and 2.0 at.% Y added alloys are spatulate microstructure, Al2Y phase distributes on the grain boundaries as continuous reticulation. With the increasing Y content, the secondary dendritic arm spacing (SDAS) is gradually reducing. Microhardness tests showed a monotonic increase with the increasing of Y content. This is attributed to the strengthening effect stemming from the refined microstructure.For the rapidly solidified alloys, it was found that the microstructure was refined evidently and the SDAS decreases Special shape NdFeB magnets comparing with the as cast counterpart. The Y-rich phase was found to distribute homogeneously on the matrix as very fine precipitates (with a particle size of several tens of nanometer). XRD results showed that B2 phase (a=0.314nm) appears in the alloys containing more than 1.5 at.% Y, rapid solidification extends theβphase region, and retains it to low temperature, leading to a transformation from high temperatureβphase to ordered B2 phase during cooling. Nano-Indentation tests of the rapidly solidified alloy ribbons indicate that, with increasing of Y content the hardness of ribbons does