Additive manufacturing of high temperature Mo-Si-B-Ti alloys

With the drive to increase the operating temperature of gas turbine engines beyond the limits of Ni-base superalloys, refractory metal alloys are receiving increased attention. To achieve enhanced performance, an alloy must be designed to satisfy several challenging requirements involving mechanical properties, thermophysical properties, and environmental resistance at 1300 °C. To address these challenges, an effective design has been established based upon additive manufacturing (AM) utilizing a reactive synthesis of component powders of Mo, Si₃N₄, BN, and Ti where a high-throughput synthesis and characterization are employed together with guidance from computational thermodynamics to identify promising alloy compositions. The selected Mo-3.3Si-4.5B-10Ti alloy includes Ti for both density reduction to 9.2 g/cm3 and to reduce the Si content in Mo to 1.3 at.% and the associated embrittlement effect of Si. The alloy design exhibits a high compressive strength of about 1.6 GPa and compressive strain to failure above 20% at room temperature. An effective oxidation resistance is provided by a pack cementation borosilica coating. With AM and optimized processing parameters, turbine blades have been produced at full scale.