Superstrength through Nanotwinning

An, Qi; Goddard, William A.; Xie, Kelvin Y.; Sim, Gi-Dong; Hemker, Kevin J.; Munhollon, Tyler; Toksoy, Muhammet Fatih; Haber, Richard A.

doi:10.1021/acs.nanolett.6b03414

Cited by 67 publications

(54 citation statements)

References 38 publications

(72 reference statements)

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“…To examine how nanoscale twins affect the mechanical properties of r‐LiB 13 C 2 , we constructed the nanotwinned r‐LiB 13 C 2 , as shown in Figure C. Here we used the (010) plane as the twin plane since the previous study suggests that the {100} rhombohedral plane is the twin plane for B 4 C, B 6 O, and other related icosahedral materials . The DFT optimized lattice constant for nanotwinned r‐LiB 13 C 2 are a = 5.322 Å, b = 18.255 Å, c = 5.322 Å, and β = 115.79°.…”

Section: Resultsmentioning

confidence: 99%

“…Working at extreme conditions of high temperature and high pressure requires that the materials possess high strength and high ductility. Therefore, enhancing materials strength has been a very hot research area . Many approaches have been proposed and tested to enhance the strength of many types of materials such as metals, semiconductors, and superhard materials .…”

Section: Introductionmentioning

confidence: 99%

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Strengthening boron carbide through lithium dopant

Shen

Tang

et al. 2019

J Am Ceram Soc

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The high strength of boron carbide (B4C) is essential in its engineering applications such as wear‐resistance and body armors. Here, by employing density functional theory simulations, we demonstrated that the strength of B4C can be enhanced by doping lithium to boron‐rich boron carbide (B13C2) to form r‐LiB13C2. The bonding analysis on r‐LiB13C2 indicates that the electron counting rule (or Wade's rule) is satisfied in r‐LiB13C2 whose formula can be written as r‐Li+(B12)2‐(CB+C). The shear deformation on r‐LiB13C2 indicates that its ideal shear strength is larger than that of B4C because of the existing of Li dopant. The failure process of r‐LiB13C2 under ideal shear deformation initiates from breaking the icosahedral‐icosahedral B‐B bonds. Then these B atoms react with the middle B in the C‐B‐C chain, resulting in the disintegration of icosahedral clusters and brittle failure. More interesting, the nanotwinned r‐LiB13C2 is even stronger than r‐LiB13C2 because of the directional nature of covalent bonding at the twin boundaries. This suggests that the nanotwinned r‐LiB13C2 has a significant enhanced strength compared to B4C. Our simulation results illustrate the deformation mechanism of Li‐doped boron carbide and its nanotwinned microstructure. We proposed to improve the strength of boron carbide by doping Li into B13C2 and increasing its twin densities.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Strengthening boron carbide through lithium dopant

Shen

Tang

et al. 2019

J Am Ceram Soc

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“…10,29 This suggests that existence of GBs, dramatically decrease the strength of B 4 C. We find that brittle failure of GB structures under pure shear deformation arises 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 from shear-induced icosahedra disintegration in the GB region, while brittle failure under biaxial shear deformation starts from compressing the icosahedral layers in GB region. Doping Fe atoms into the GB-I model leads to a negative enthalpy of formation (referenced to α-Fe and the GB-I model) suggesting that impurities preferred to the GBs regions.…”

Section: Introductionmentioning

confidence: 99%

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Yang

Coleman

LaSalvia

et al. 2018

ACS Appl. Mater. Interfaces

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Abstract:The role that grain boundaries (GB) can play on mechanical properties has been studied extensively for metals and alloys. However, for covalent solids such as boron carbide (B 4 C), the role of GB on the inelastic response to applied stresses is not well established. We consider here the unusual ceramic, boron carbide (B 4 C), which is very hard and lightweight but exhibits brittle impact behavior. We used quantum mechanics (QM) simulations to examine the mechanical response in atomistic structures that model GBs in B 4 C under pure shear and also with biaxial shear deformation that mimics indentation stress conditions. We carried out these studies for two simple GB models including also the effect of adding Fe atoms (possible sintering aid and/or impurity) to the GB. We found that the critical shear stresses of these GB models are much lower than for crystalline and twinned B 4 C. The two GB models lead to different interfacial energies. The higher interfacial energy at the GB only slightly decreases the critical shear stress but dramatically increases the critical failure strain. Doping the GB with Fe decreases the critical shear stress of at the boundary by 14% under pure shear deformation. In all GBs studied here, failure arises from deconstructing the icosahedra within the GB region under shear deformation. We find that Fe dopant interacts with icosahedra at the GB to facilitate this deconstruction of icosahedra. These results provide significant insight for designing polycrystalline B 4 C with improved strength and ductility.

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“…This grain size effect has been widely examined in metal alloys and ceramics [18][19][20], but not in nanocrystalline semiconductors. TBs are expected to have a much lower formation energy than GBs, making TBs more stable than GBs, which can make them more effective in strengthening materials [21]. For example, ultrafine-grained Cu with nanoscale twins embedded in individual grains leads to a superstrength relative to conventional coarsegrained polycrystalline Cu [22].…”

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Superstrengthening Bi2Te3 through Nanotwinning

Aydemir

Morozov

et al. 2017

Phys. Rev. Lett.

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Bismuth telluride (Bi 2 Te 3 ) based thermoelectric (TE) materials have been commercialized successfully as solid-state power generators, but their low mechanical strength suggests that these materials may not be reliable for long-term use in TE devices. Here we use density functional theory to show that the ideal shear strength of Bi 2 Te 3 can be significantly enhanced up to 215% by imposing nanoscale twins. We reveal that the origin of the low strength in single crystalline Bi 2 Te 3 is the weak van der Waals interaction between the Te1 coupling two Te1─Bi─Te2─Bi─Te1 five-layer quint substructures. However, we demonstrate here a surprising result that forming twin boundaries between the Te1 atoms of adjacent quints greatly strengthens the interaction between them, leading to a tripling of the ideal shear strength in nanotwinned Bi 2 Te 3 (0.6 GPa) compared to that in the single crystalline material (0.19 GPa). This grain boundary engineering strategy opens a new pathway for designing robust Bi 2 Te 3 TE semiconductors for high-performance TE devices. DOI: 10.1103/PhysRevLett.119.085501 The continued use of fossil fuels to satisfy escalating global energy requirements is causing severe unacceptable environmental impact. This has generated renewed interest in thermoelectric (TE) conversion technology to convert waste heat directly into electricity, which involves no CO 2 production, is scalable to large power plants, and involves no moving parts (silent) [1]. Over the past two decades, the conversion efficiency (zT) of TE materials has enhanced remarkably, approaching to ∼1.8 [2-4], putting TE materials on the threshold of commercial applications. However, under severe operation conditions, TE materials suffer from unavoidable thermomechanical stresses from cycling of the temperature gradients, leading to rapid deterioration of material performance and accelerated failure of TE devices [5][6][7]. In order for thermoelectrics to play a significant role in engineering applications to alternative energy, the strength and the toughness must be dramatically enhanced.Industrial low temperature waste heat accounts for almost one-third of total energy consumption [8]. The bismuth telluride (Bi 2 Te 3 ) state-of-the-art TE material has been widely used for TE refrigeration in this temperature range (300-550 K) [9], and is now being considered in the automotive industry for recovering waste heat from exhaust systems. Traditional elemental doping strategies have been successful in significantly improving TE properties [10,11], but they have had little effect on enhancing the mechanical properties [12]. Recently, nano-SiC particles dispersed in Bi 2 Te 3 were reported to enhance mechanical strength compared to pure Bi 2 Te 3 , but with concomitant deterioration of the electronic transport properties [13].A well-known mechanism for strengthening metal alloys is to increase the number of such interfacial boundaries as grain boundaries (GBs) and twin boundaries (TBs). These boundaries can strengthen the material by pinning...

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Superstrength through Nanotwinning

Cited by 67 publications

References 38 publications

Strengthening boron carbide through lithium dopant

Strengthening boron carbide through lithium dopant

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Superstrengthening Bi2Te3 through Nanotwinning

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