查看完整版本: Mechanical properties of nanocrystalline materials

nano 2006-12-11 01:31

Mechanical properties of nanocrystalline materials

[b]M.A. Meyers[/b][b], A. Mishra and D.J. Benson
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o*|A T%a2Q [/b]Department of Mechanical and Aerospace Engineering, Materials Science and Engineering Program, Mail Code 0411, University of California, San Diego La Jolla, CA 92093, United States wP0fE;W

3N,K#W-NLMqL [font=Verdana][size=2][/size][/font][url=http://www.sciencedirect.com.login.ezproxy.library.ualberta.ca/science?_ob=PublicationURL&_cdi=5577&_pubType=J&_auth=y&_acct=C000051251&_version=1&_urlVersion=0&_userid=1067472&md5=e91856533d55895eb0cfa3f6a51abc9a][size=2][color=#0000ff][font=Verdana][b]Progress in Materials Science[/b] [/font][/color][/size][/url], [font=Verdana][url=http://www.sciencedirect.com.login.ezproxy.library.ualberta.ca/science?_ob=PublicationURL&_tockey=%23TOC%235577%232006%23999489995%23616438%23FLA%23&_cdi=5577&_pubType=J&view=c&_auth=y&_acct=C000051251&_version=1&_urlVersion=0&_userid=1067472&md5=e48484f51ab57773000a24a1bc4cda71][size=2][color=#0000ff]Volume 51, Issue 4[/color][/size][/url][size=2] , May 2006, Pages 427-556: [url=http://dx.doi.org.login.ezproxy.library.ualberta.ca/10.1016/j.pmatsci.2005.08.003][size=1][color=#0000ff]doi:10.1016/j.pmatsci.2005.08.003[/color][/size][/url] [/size][/font]o,X| tGk
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[b]Abstract[/b]
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&W2y9y#No ll?Yvj The mechanical properties of nanocrystalline materials are reviewed, with emphasis on their constitutive response and on the fundamental physical mechanisms. In a brief introduction, the most important synthesis methods are presented. A number of aspects of mechanical behavior are discussed, including the deviation from the Hall–Petch slope and possible negative slope, the effect of porosity, the difference between tensile and compressive strength, the limited ductility, the tendency for shear localization, the fatigue and creep responses. The strain-rate sensitivity of FCC metals is increased due to the decrease in activation volume in the nanocrystalline regime; for BCC metals this trend is not observed, since the activation volume is already low in the conventional polycrystalline regime. In fatigue, it seems that the S–N curves show improvement due to the increase in strength, whereas the da/dN curve shows increased growth velocity (possibly due to the smoother fracture requiring less energy to propagate). The creep results are conflicting: while some results indicate a decreased creep resistance consistent with the small grain size, other experimental results show that the creep resistance is not negatively affected. Several mechanisms that quantitatively predict the strength of nanocrystalline metals in terms of basic defects (dislocations, stacking faults, etc.) are discussed: break-up of dislocation pile-ups, core-and-mantle, grain-boundary sliding, grain-boundary dislocation emission and annihilation, grain coalescence, and gradient approach. Although this classification is broad, it incorporates the major mechanisms proposed to this date. The increased tendency for twinning, a direct consequence of the increased separation between partial dislocations, is discussed. The fracture of nanocrystalline metals consists of a mixture of ductile dimples and shear regions; the dimple size, while much smaller than that of conventional polycrystalline metals, is several times larger than the grain size. The shear regions are a direct consequence of the increased tendency of the nanocrystalline metals to undergo shear localization.L%b%y4\N
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The major computational approaches to the modeling of the mechanical processes in nanocrystalline metals are reviewed with emphasis on molecular dynamics simulations, which are revealing the emission of partial dislocations at grain boundaries and their annihilation after crossing them.
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[b]Article Outline[/b]
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{T$E [1? k%e 1. Introduction%E|g*v.\FA)^
2. History;P\i#Uap Z y m
3. ClassificationL0H"Ia5tJy a{
4. Synthesis
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4.1. Inert gas condensation [1]4@$c&N%z d1cP;@ Z6V
4.2. Mechanical alloying
4i M8]V{h(f@? 4.3. Electrodepositionp?[G R,N7YO)B
4.4. Crystallization from amorphous solids/Q8i4ba(ca*l5g
4.5. Severe plastic deformation
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5. Mechanical properties of nanocrystalline metals and alloys2H&q5Cak Bd

%iApD$q0t:@ 5.1. Yield strengthcY? j0b
5.2. Ductility
Em2}a1T9{-L!JID*m^ 5.3. Inverse Hall Petch effect: fact or fiction gx#E1[ y'A-p"h:[
5.4. Strain hardeningx/K'e d;F ne
5.5. Strain-rate sensitivity
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fJ8JGBfE 5.5.1. Strain-rate sensitivity of ultrafine grained and nanostructured HCP metals6az9W0e,j
5.5.2. Mechanical behavior of iron as a representative BCC metal1h:o8L h `&H.U)^A0T

:}@l%z;Nh 5.6. Creep of nanocrystalline materials
sm;f,CFP} 5.7. Fatigue of nanocrystalline materials
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*\#A`u(pbt8P 6. Nanocrystalline ceramics and composites
ghKG.zB 7. Deformation mechanisms in nanostructured materialsAK!E0m#V n$Y7f8fa

~!H!S5Y/je$U 7.1. Pile-up breakdown|$j1x:epY2q*P2d_
7.2. Grain-boundary sliding
6t P6g_2{0Ftl 7.3. Core and mantle models
/t"Cb^;\b 7.4. Grain-boundary rotation/grain coalescence,LH)^u8J[%~5I uS
7.5. Shear-band formation
"k-v1oi&cU7_ 7.6. Gradient models
}5X-I]s z&v;_$nxn 7.7. Twinning,g0D5@ R"?Y$V

(S-I Z+p-HF z~ 7.7.1. Mechanical twins
R7wnZ#C3O 7.7.2. Growth twins0SJhYN
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7.8. Grain-boundary dislocation creation and annihilation
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8. Fracture
$L PC%\ ^!@j&}Dm 9. Numerical modeling
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9.1. Finite element simulationsw4Yq7^,Z!V1`3N
9.2. Molecular dynamics simulations
1x,e;r%m4v(_@ 9.3. The quasicontinuum methodW#}wf/S^bKlO
9.4. Shock wave propagation in nanocrystalline metals
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10. Summary and conclusionsk.dh|r q(hr7L?
Acknowledgements
R?3aR9z1e"s References~@!Vn+@ Hd+j\
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