Abstract
In this article, we present a strategy to decouple the relative influences of colony, domain and lamella boundary strengthening in fully lamellar titanium aluminide alloys, using a physics-based crystal plasticity modeling strategy. While lamella and domain boundary strengthening can be isolated in experiments using polysynthetically twinned crystals or mircomechanical testing, colony boundary strengthening can only be investigated in specimens in which all three strengthening mechanisms act simultaneously. Thus, isolating the colony boundary strengthening Hall–Petch coefficient experimentally requires a sufficient number of specimens with different colony sizes but constant lamella thickness and domain size , difficult to produce even with sophisticated alloying techniques. The here presented crystal plasticity model enables identification of the colony boundary strengthening coefficient as a function of lamella thickness . The constitutive description is based on the model of a polysynthetically twinned crystal which is adopted to a representative volume element of a fully lamellar microstructure. In order to capture the micro yield and subsequent micro hardening in weakly oriented colonies prior to macroscopic yield, the hardening relations of the adopted model are revised and calibrated against experiments with polysynthetically twinned crystals for plastic strains up to 15%.
Highlights
After decades of academic and industrial research, γ-based fully lamellar titanium aluminides (TiAl) outperform most competing high-temperature lightweight materials up to temperatures around800 ◦ C [1,2,3]
This assumption seems reasonable evaluating lamella/domain size ratios reported for polysynthetically twinned crystals [8,19]
If no α2 was reported in corresponding reference, it was set to 10 Vol %; the domain sizes λ D are assumed to be 50 λ L
Summary
After decades of academic and industrial research, γ-based fully lamellar titanium aluminides (TiAl) outperform most competing high-temperature lightweight materials up to temperatures around. 800 ◦ C [1,2,3] Their exceptional properties originate from the dense arrangement of three types of microstructural boundaries, namely lamella, domain and colony boundaries [4,5]. Despite advances in understanding the three corresponding Hall–Petch effects, their relative contributions to the strength of fully lamellar TiAl is not yet consistently quantified. Micromechanical modeling helps to separate and quantify these effects as shown in the following. Microstructure and Micromechanics of Fully Lamellar TiAl. 1.1.1.
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