Phase selection and mechanical properties of a directionally solidified Cr-20Nb-40Ti alloy

By combining the techniques of directional solidification and coating Y2O3, a Cr-20Nb-40Ti alloy was manufactured successfully with various growth rates. The revolution of microstructures and corresponding mechanical properties was discussed to develop the Cr2Nb based alloys with good combination of mechanical properties. The results show that the favorable growth dynamics of plane (220) of Laves phase Cr2Nb was observed with the increase of growth rate. Phase selection took place in microstructures evolved from the primary Cr2Nb, via the dendrite-like eutectic Cr2Nb/β-Ti, and finally to the primary β-Ti, with increasing the growth rate from 5 to 200 μm/s. Based on the coupled zone of eutectic, the competitive growth of solidified phases in the directionally solidified Cr-20Nb-40Ti alloy was elucidated. In addition, the mechanical properties of alloy depended on the growth rate, and the fracture toughness of the alloy reached 16.50 MPa m^1/2 at 200 μm/s, much larger than 1.40 MPa m^1/2 for single-phase Cr2Nb.