TY - JOUR

T1 - Superior fatigue crack growth resistance, irreversibility, and fatigue crack growth-microstructure relationship of nanocrystalline alloys

AU - Sangid, Michael D.

AU - Pataky, Garrett J.

AU - Sehitoglu, Huseyin

AU - Rateick, Richard G.

AU - Niendorf, Thomas

AU - Maier, Hans J.

N1 - Funding information: Support for this work was provided primarily by Honeywell Aerospace Corporation and partially by the National Science Foundation (DMR 08-03270). The authors would like to thank Josh Kacher for his assistance with filtering the EBSD data and John Oyelakin for his assistance with the initial testing.

PY - 2011/9/23

Y1 - 2011/9/23

N2 - While previous studies have reported that nanocrystalline materials exhibit poor resistance to fatigue crack growth (FCG), the electro-deposited nanocrystalline Ni-Co alloys tested in this paper show superior resistance to FCG. The high damage tolerance of our alloy is attributed to the following: alloying with Co, low internal stresses resulting in stability of the microstructure, and a combination of high strength and ductility. The high density of grain boundaries interact with the dislocations emitted from the crack tip, which impedes FCG, as predicted by the present model and measured experimentally by digital image correlation. Further, the addition of Co increases the strength of the material by refining the grain size, reducing the fraction of low angle grain boundaries, and reducing the stacking fault energy of the material, thereby increasing the prevalence of twinning. The microstructure is stabilized by minimizing the internal stress during a stress relief heat treatment following the electro-deposition process. As a result grain growth does not occur during deformation, leaving dislocation-mediated plasticity as the primary deformation mechanism. The low internal stresses and nanoscale twins preserve the ductility of the material, thereby reaching a balance between strength and ductility, which results in a superior resistance to FCG.

AB - While previous studies have reported that nanocrystalline materials exhibit poor resistance to fatigue crack growth (FCG), the electro-deposited nanocrystalline Ni-Co alloys tested in this paper show superior resistance to FCG. The high damage tolerance of our alloy is attributed to the following: alloying with Co, low internal stresses resulting in stability of the microstructure, and a combination of high strength and ductility. The high density of grain boundaries interact with the dislocations emitted from the crack tip, which impedes FCG, as predicted by the present model and measured experimentally by digital image correlation. Further, the addition of Co increases the strength of the material by refining the grain size, reducing the fraction of low angle grain boundaries, and reducing the stacking fault energy of the material, thereby increasing the prevalence of twinning. The microstructure is stabilized by minimizing the internal stress during a stress relief heat treatment following the electro-deposition process. As a result grain growth does not occur during deformation, leaving dislocation-mediated plasticity as the primary deformation mechanism. The low internal stresses and nanoscale twins preserve the ductility of the material, thereby reaching a balance between strength and ductility, which results in a superior resistance to FCG.

KW - Crack propagation

KW - Fatigue

KW - Grain boundaries

KW - Irreversibility

KW - Nanocrystalline alloys

UR - http://www.scopus.com/inward/record.url?scp=80053174046&partnerID=8YFLogxK

U2 - 10.1016/j.actamat.2011.07.058

DO - 10.1016/j.actamat.2011.07.058

M3 - Article

AN - SCOPUS:80053174046

VL - 59

SP - 7340

EP - 7355

JO - Acta materialia

JF - Acta materialia

SN - 1359-6454

IS - 19

ER -