Thermomechanical modelling of polysynthetically twinned TiAl crystals

Butzke, J.E.; Bargmann, Swantje

doi:10.1080/14786435.2015.1070968

Cited by 9 publications

(12 citation statements)

References 49 publications

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“…In this section, the thermomechanically coupled crystal plasticity model from [ 18 ] is revisited and extended in order to capture above mentioned microhardening as well as colony boundary strengthening.…”

Section: Modelingmentioning

confidence: 99%

“…In polysynthetically twinned crystals, however,

and

may be determined from measured

and

values using the Schmid factors of selectively activated slip/twinning systems in certain orientations of the lamella plane with respect to load (cf. e.g., [ 18 ]). The last terms in Equations ( 21 ) and ( 22 ) are obviously only meaningful when modeling polycolony microstructures and thus have to be set to zero for simulations of polysynthetically twinned crystals.…”

Section: Modelingmentioning

confidence: 99%

“…The Hall–Petch slopes

and

for lamella and domain boundary strengthening can be separately determined from experiments with polysynthetically twinned crystals (i.e., specimens that only contain parallel lamellae of one specific orientation) [ 8 , 11 , 18 , 19 ] or by micromechanical testing [ 20 , 21 ]. Colony boundary strengthening, however, can exclusively be investigated in specimens in which naturally all three strengthening mechanisms act simultaneously.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the model parameters in these formulations are generally found for one specific combination of temperature and microstructural lengths, necessitating recalibration of the model whenever the mechanical behavior shall be analyzed at different temperatures or for a different set of microstructural parameters. Therefore, we set up a thermomechanically coupled crystal plasticity model of a polysynthetically twinned crystal that incorporates lamella and domain boundary strenghtening as well as the typical yield stress temperature anomaly to enable yield stress prediction between room temperature and 900

C [ 18 ].…”

Section: Introductionmentioning

confidence: 99%

“…Since a pronounced microyield has been observed in weakly oriented colonies prior to macroscopic yield (cf. digital image correlation (DIC) analyses in [ 40 ]), the hardening relations of the constitutive model [ 18 ] are revised to capture hardening of single colonies/polysynthetically twinned crystals up to several percent of plastic strain. The revised hardening model is subsequently calibrated against the uniaxial compression experiments with polysynthetically twinned crystals reported in [ 9 ].…”

Section: Introductionmentioning

confidence: 99%

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Accessing Colony Boundary Strengthening of Fully Lamellar TiAl Alloys via Micromechanical Modeling

Schnabel

Bargmann

2017

Materials

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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 KC experimentally requires a sufficient number of specimens with different colony sizes λC but constant lamella thickness λL and domain size λD, difficult to produce even with sophisticated alloying techniques. The here presented crystal plasticity model enables identification of the colony boundary strengthening coefficient KC as a function of lamella thickness λL. 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%.

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Section: Modelingmentioning

confidence: 99%

“…In polysynthetically twinned crystals, however,

and

may be determined from measured

and

Section: Modelingmentioning

confidence: 99%

“…The Hall–Petch slopes

and

Section: Introductionmentioning

confidence: 99%

C [ 18 ].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Accessing Colony Boundary Strengthening of Fully Lamellar TiAl Alloys via Micromechanical Modeling

Schnabel

Bargmann

2017

Materials

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Crystal plasticity analysis of deformation anisotropy of lamellar TiAl alloy: 3D microstructure-based modelling and in-situ micro-compression

Chen

Edwards

Gioacchino

et al. 2019

International Journal of Plasticity

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Detailed microstructure characterisation and in-situ micropillar compression were coupled with crystal plasticity-based finite element modelling (CP-FEM) to study the micromechanisms of plastic anisotropy in lamellar TiAl alloys. The consideration of microstructure in both simulation and in-situ experiments enables in-depth understanding of micromechanisms responsible for the highly anisotropic deformation response of TiAl on the intralamella and inter-lamella scales. This study focuses on two specific configurations of / 2 lamellar microstructure with the / 2 interfaces being aligned 25 and 55 to the loading direction. Microstructure-based CP-FEM shows that longituginal slip of super and ordinary dislocations are most responsible for the plastic anisotropy in the 25 micropillar while the anisotropy of the 55 micropillar is due to longitudinal superdislocations and longitudinal twins. In addition, transversal superdislocations were more active, making the deformation in the 25 micropillar less localised than that in the 55 micropillar. Moreover, the CP-FEM 2 / 42 model successfully predicted substantial build-up of internal stresses at / 2 interfaces, which is believed to be detrimental to the ductility in TiAl. However, as evidenced by the model, the detrimental internal stresses can be significantly relieved by the activation of transverse deformation twinning, suggesting that the ductility of TiAl can be improved by promoting transverse twins. IntroductionTitanium aluminide (TiAl) alloys have a density approximately half that of nickel-based superalloys [1] and specific strength that is comparable with nickel-based alloys up to temperatures as high as 700 o C [2], resulting in a potentially wide application of the alloys in aero-engines [3,4]. However, the application of TiAl alloys is limited by their low ductility, which is mainly due to the anisotropy of constituent microstructure in TiAl, and insufficient understanding of the microstructure-property relationships. In-depth understanding of the relationships would lead to wider applications of these lightweight alloys in aerospace, leading to the weight reduction, thereby, increase in the fuel efficiency and decrease in the CO2 emissions. Although there have been significant efforts in understanding the relationships between chemical composition, microstructure and mechanical properties of TiAl alloys, in particular regarding the TiAl lamellar microstructure [1, 5-7], there have been no detailed studies in which both in-situ mechanical testing and microstructure-based modelling are carried out to provide more insights into the direct relationships between constituent microstructures and mechanical properties. This present study aims to integrate modelling and in-situ tests to seek possible solutions to the low ductility of TiAl. The poor ductility of lamellar TiAl alloys is partly due to its strong plastic anisotropy because of the respective anisotropy of constituent phases. Lamellar TiAl alloys consist of two phases: -face centred tetragonal (f.c.t.) and ...

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