Experimental and numerical engineering of novel eutectic high melting Mo-Si-Ti alloys processed by additive manufacturing: microstructure, texture and ensuing properties

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The proposed study aims at a combined experimental and modeling engineering approach for developing novel eutectic alloys within the Molybdenum-Silicon-Titanium system. Multi-phase refractory metal (RM) silicide alloys are considered to be very promising candidates for ultrahigh temperature structural applications beyond currently used Ni-base superalloys. However, because of their rather (i) high melting point and (ii) brittle-to-ductile transition temperature they are difficult to process in complex shaped parts using conventional equipment. Therefore, a still novel bottom-up processing method called additive manufacturing (AM) is applied aiming at understanding the elementary mechanisms for this far from equilibrium process governing microstructural development utilizing texture formation and phase field modeling. Additionally, these alloys usually suffer from a mid-temperature phenomenon called “pesting”, the spontaneous sublimation of RM-based oxides. Specifically, employing selected electron beam melting (SEBM) allows the production of parts in a protective (high vacuum) environment at elevated powder bed temperatures which makes SEBM the best choice for manufacturing of “clean” and crack-free samples of oxidation-sensitive alloy systems. In own preliminary work we could demonstrate that even conventionally processed, i.e. arc-melted, fully eutectic Mo27-Si20-Ti53 (composition given in at.%) possesses attractive creep properties and simultaneously does not show “pesting”, in other words it reveals already satisfying oxidation resistance. It was concluded that both these properties benefit from the rather fine and lamellar microstructure. Since AM is known to be a manufacturing process exhibiting high cooling rates and thermal gradients, we anticipate even finer and likely far from equilibrium microstructures on the one hand and crystallographic texture formation on the other. The properties of such microstructures are hitherto unknown and will be explained based on elementary physical metallurgy mechanism. Thus, this proposal reflects a combined effort by colleagues with mutually supplementing competences in the fields of AM of high temperature structural materials, texture formation and phase field simulation.