An extended hardness limit in bulk nanoceramics

Wollmershauser, James A.; Feigelson, Boris N.; Gorzkowski, Edward P.; Ellis, Chase T.; Goswami, R.; Qadri, S. B.; Tischler, Joseph G.; Kub, Fritz J.; Everett, R.K.

doi:10.1016/j.actamat.2014.01.030

Cited by 173 publications

(106 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is clearly seen that the hardness increases by ∼30% with reducing grain size, from Hk=11.3±0.5 GPa with d >200 nm to ∼14.5 GPa at d =30–50 nm, showing that the Hall–Petch effect181920 known for metals is also applied to some ceramics in the nano-crystalline regime. This is consistent with the recent results on polycrystalline MgAl 2 O 4 spinel11 that concluded the Hall–Petch effect is valid down to the grain size of 30 nm, although there is controversy on the applicable grain size for this effect in ceramics21. The latter result on MgO periclase may be due to insufficient sintering of nano-crystals, and our results on pore-free samples clearly demonstrate the Hall–Petch effect is applied to the nano-ceramics.…”

Section: Resultssupporting

confidence: 93%

“…Although highly transparent ceramics have been developed24 and successfully applied to some lasers and optical devices25, those with single-phase crystals in the nano-crystalline regime have never been produced by either sintering techniques3456724 or crystallization from glass or amorphous phases82627 under the ambient pressure and at relatively low pressures. On the other hand, the transparent nano-ceramics produced by these techniques have substantially low transparency relative to the single crystals in the visible light region1127 mainly due to the presence of a number of residual pores and/or defective regions along grain boundaries. To remove these scattering sources, higher-temperature or longer-duration heating is required, which inevitably leads to grain growth at the low pressures and fails to produce nano-crystalline ceramics.…”

Section: Discussionmentioning

confidence: 99%

“…However, it is predicted that the optical transparency will be significantly improved for the ceramics even with non-cubic crystals, if those made of nano-crystals are available910. Moreover, the hardness of such ceramics is suggested to be also enhanced in the nano-crystalline regime711.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Pressure-induced nano-crystallization of silicate garnets from glass

Irifune¹,

Kawakami²,

Arimoto³

et al. 2016

Nat Commun

View full text Add to dashboard Cite

Transparent ceramics are important for scientific and industrial applications because of the superior optical and mechanical properties. It has been suggested that optical transparency and mechanical strength are substantially enhanced if transparent ceramics with nano-crystals are available. However, synthesis of the highly transparent nano-crystalline ceramics has been difficult using conventional sintering techniques at relatively low pressures. Here we show direct conversion from bulk glass starting material in mutianvil high-pressure apparatus leads to pore-free nano-polycrystalline silicate garnet at pressures above ∼10 GPa in a limited temperature range around 1,400 °C. The synthesized nano-polycrystalline garnet is optically as transparent as the single crystal for almost the entire visible light range and harder than the single crystal by ∼30%. The ultrahigh-pressure conversion technique should provide novel functional ceramics having various crystal structures, including those of high-pressure phases, as well as ideal specimens for some mineral physics applications.

show abstract

Section: Resultssupporting

confidence: 93%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Pressure-induced nano-crystallization of silicate garnets from glass

Irifune¹,

Kawakami²,

Arimoto³

et al. 2016

Nat Commun

View full text Add to dashboard Cite

show abstract

“…2 Wollmershauser et al recently showed this relation still applies for nanocrystalline materials, showing hardness increase from about 13.5 GPa for a microcrystalline magnesium aluminate to roughly 20.2 GPa for a sample with grain size 28 nm. 3 The results contradict reports describing a low grain size limit below which transitions to diffusion controlled strain accommodation would be expected, similarly to nanocrystalline metals 4 and reported for MgO, 5 and gives new breath for the development of new super-hard nanoceramics with ultrafine grains.…”

Section: Introductioncontrasting

confidence: 61%

Grain growth resistant nanocrystalline zirconia by targeting zero grain boundary energies

et al. 2015

View full text Add to dashboard Cite

Nanocrystalline ceramics offer interesting and useful physical properties attributed to their inherent large volume fraction of grain boundaries. At the same time, these materials are highly unstable, being subjected to severe coarsening when exposed at moderate to high temperatures, limiting operating temperatures and disabling processing conditions. In this work, we designed highly stable nanocrystalline yttria stabilized zirconia (YSZ) by targeting a decrease of average grain boundary (GB) energy, affecting both driving force for growth and mobility of the boundaries. The design was based on fundamental equations governing thermodynamics of nanocrystals, and enabled the selection of lanthanum as an effective dopant which segregates to grain boundaries and lowers the average energy of YSZ boundaries to half. While this would be already responsible for significant coarsening reduction, we further experimentally demonstrate that the GB energy decreases continuously during grain growth caused by the enrichment of boundaries with dopant, enhancing further the stability of the boundaries. The designed composition showed impressive resistance to grain growth at 1100°C as compared to the undoped YSZ and opens the perspective for similar design in other ceramics.

show abstract

“…and 25GPa for the layers obtained from the nano-structured feedstock in these same coatings. Therefore, the worst values of nano-mechanical properties measured on layers obtained from the nano-structured feedstock indicate that the heterogeneous microstructure made up of pores and above all partially melted areas associated with these layers prevails over the hardening effect expected from a nano-structured ceramic material [19]. The role of porosity and, particularly the amount of partially melted or unmelted areas on the mechanical properties of APS coatings obtained from nano-structured feedstocks has been previously reported for YSZ and other oxide coatings such as alumina and titania [17,20].…”

Section: Microstructure Dependence Of Mechanical Propertiesmentioning

confidence: 99%

Mechanical Properties of Double-Layer and Graded Composite Coatings of YSZ Obtained by Atmospheric Plasma Spraying

et al. 2016

View full text Add to dashboard Cite

Double-layer and graded composite coatings of yttria stabilised zirconia (YSZ) were sprayed on metallic substrates by atmospheric plasma spray (APS). The coatings architecture was built up by combining two different feedstocks: one micro-and one nano-structured. Microstructural features and mechanical properties (hardness and elastic modulus) of the coatings were determined by FE-SEM microscopy and nanoindentation technique respectively. Additional adherence and scratch tests were carried out in order to assess the failure mechanisms occurring between the layers comprising the composites.Microstructural inspection of the coatings confirms the two-zones microstructure. This bi-modal microstructure which is exclusive of the layer obtained from the nano-structured feedstock negatively affects the mechanical properties of the whole composite. Nanoindentation tests suitably reproduce the evolution of mechanical properties through coatings thickness on the basis of the position and/or amount of nano-structured feedstock used in the depositing layer.Adhesion and scratch tests show the negative effect on the coating adhesion of layer obtained from the nano-structured feedstock when this layer is deposited on the bond coat. Thus the poor integrity of this layer results in lower normal stresses required to delaminate the coating in the adhesion test as well as minor critical load registered by using the scratch test.

show abstract

An extended hardness limit in bulk nanoceramics

Cited by 173 publications

References 38 publications

Pressure-induced nano-crystallization of silicate garnets from glass

Pressure-induced nano-crystallization of silicate garnets from glass

Grain growth resistant nanocrystalline zirconia by targeting zero grain boundary energies

Mechanical Properties of Double-Layer and Graded Composite Coatings of YSZ Obtained by Atmospheric Plasma Spraying

Contact Info

Product

Resources

About