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

提出的研究旨在结合实验和建模工程方法，在钼-硅-钛系统中开发新型共晶合金。多相难熔金属（RM）硅化合金被认为是除目前使用的镍基高温合金外，在超高温结构应用中非常有前途的候选材料。然而，由于它们相当(i)高熔点和（ii）脆性到延性转变温度，它们很难用传统设备加工成复杂形状的零件。因此，一种新的自下而上的加工方法被称为增材制造（AM），旨在利用织构形成和相场建模来理解这种远离平衡过程控制微观结构发展的基本机制。此外，这些合金通常会遭受一种称为“害虫”的中温现象，即rm基氧化物的自发升华。具体来说，采用选定的电子束熔化（SEBM）允许在提高粉末床温度的保护性（高真空）环境中生产零件，这使得SEBM成为制造“干净”和无裂纹氧化敏感合金系统样品的最佳选择。在我们自己的初步工作中，我们可以证明，即使是传统的加工，即电弧熔化，完全共晶的Mo27-Si20-Ti53（成分给出）。%)具有吸引人的蠕变特性，同时不显示“害虫”，换句话说，它显示出已经令人满意的抗氧化性。结果表明，这两种性能都得益于较细的层状组织。由于已知增材制造是一种具有高冷却速率和热梯度的制造工艺，我们预计一方面会有更精细的、可能远离平衡态的微观结构，另一方面会形成晶体织构。这种微观结构的性质迄今为止是未知的，将根据基本的物理冶金机制来解释。因此，该提案反映了在高温结构材料AM，织构形成和相场模拟领域具有互补能力的同事的共同努力。

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.