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Item type:Publication, Access status: with files , Studying the effects of Nb on high-temperature deformation in TiAl alloys using atomistic simulationsIntermetallic γ(TiAl)-based alloys find their application as high-temperature materials for aero engine and automotive components. Microstructure optimization and microalloying play key roles in optimizing these alloys. Several pioneering experimental works showed improved mechanical properties of γ(TiAl)-based alloys containing Niobium (Nb). Despite Nb being a key alloying element, its contribution remains debated, if not least understood, due to the TiAl microstructure's complexity with hierarchical interfaces. This work examines the effects of Nb on the high-temperature deformation behavior of TiAl alloys using atomistic simulations. These revealed that Nb alloying retarded the stress-induced phase transformation of γ → α2, favoring a refined microstructure with the dislocation sources from microstructure boundaries and interfaces at high temperature and improving thus the ductility. Our microstructure-informed atomistic models reveal a comprehensive picture of the underlying nanomechanical events.Publicationtype: Journal ArticleScopus© Citations 2 12 118 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Understanding creep in TiAl alloys on the nanosecond scale by molecular dynamics simulationsMolecular dynamics (MD) simulations of creep generally face the problem that the creep most often evolves on time scales hard to capture with MD due to their typically short time step size. Consequently, MD studies of creep often use unrealistically high temperatures and stresses and simplified atomistic models to make creep-like processes happen on computationally accessible time scales. Apparently, this compromises the physical reliability of such studies. To alleviate this problem, we designed an MD model of titanium aluminide (TiAl) with a microstructure matching at least many of the key parameters of experimentally observed microstructures. We applied this MD model with stresses much lower than the ones used in most previous creep studies (well below yield stress) and in the temperature range 0.55TM-0.7TM, with melting temperature TM. Compared to typical previous MD studies, this much more realistic setup produces creep rates more than three orders of magnitude smaller and thus much closer to reality. We identified the driving mechanisms of primary creep on the nanosecond scale that agree very well with recent experimental observations, thus contributing towards the overarching goal of bridging the gap between atomistic creep simulations and continuum-scale creep simulations for engineering applications.Publicationtype: Journal ArticleScopus© Citations 7 118 602 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Quantifying the high-temperature separation behavior of lamellar interfaces in γ-titanium aluminide under tensile loading by molecular dynamicsγ-titanium aluminide (TiAl) alloys with fully lamellar microstructure possess excellent properties for high-temperature applications. Such fully lamellar microstructure has interfaces at different length scales. The separation behavior of the lamellae at these interfaces is crucial for the mechanical properties of the whole material. Unfortunately, quantifying it by experiments is difficult. Therefore, we use molecular dynamics (MD) simulations to this end. Specifically, we study the high-temperature separation behavior under tensile loading of the four different kinds of lamellar interfaces appearing in TiAl, namely, the (Formula presented.), (Formula presented.), (Formula presented.), and (Formula presented.) interfaces. In our simulations, we use two different atomistic interface models, a defect-free (Type-1) model and a model with preexisting voids (Type-2). Clearly, the latter is more physical but studying the former also helps to understand the role of defects. Our simulation results show that among the four interfaces studied, the (Formula presented.) interface possesses the highest yield strength, followed by the (Formula presented.), (Formula presented.), and (Formula presented.) interfaces. For Type-1 models, our simulations reveal failure at the interface for all γ/γ interfaces but not for the (Formula presented.) interface. By contrast, for Type-2 models, we observe for all the four interfaces failure at the interface. Our atomistic simulations provide important data to define the parameters of traction–separation laws and cohesive zone models, which can be used in the framework of continuum mechanical modeling of TiAl. Temperature-dependent model parameters were identified, and the complete traction–separation behavior was established, in which interface elasticity, interface plasticity, and interface damage could be distinguished. By carefully eliminating the contribution of bulk deformation from the interface behavior, we were able to quantify the contribution of interface plasticity and interface damage, which can also be related to the dislocation evolution and void nucleation in the atomistic simulations.Publicationtype: Journal ArticleScopus© Citations 5 162 304