Fatigue and Fracture of a Bulk Nanocrystalline NiFe Alloy

Yang, Yong; Imasogie, B. I.; Fan, G. J.; Liaw, Peter K.; Soboyejo, Winston O.

doi:10.1007/s11661-008-9487-4

Cited by 44 publications

(18 citation statements)

References 39 publications

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“…1 though 5, clearly depicts deformation-induced grain growth along the crack path, which asserts Yang's finding [5]. The grown grain morphology is dependent on the stress intensity factor range (…”

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confidence: 67%

Grain Structure at Crack Path in Fatigued Nano-Crystalline Ni

2009

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The generally acceptable mechanisms of fatigued crack growth in nanocrystalline (NC) materials were based on empirical studies and molecular dynamics (MD) simulations of pure Ni films [1,2]. MD simulation suggested that fatigued crack growth is due mainly to crack-tip blunting, nanovoid formation, subsequent decohesion at grain boundaries [2] while Meirom et al. suggested a crack propagation rate dependent and dislocation-slip mechanism [3]. However, these studies were based on two-dimensional thin films. The lack of 3-dimensional constraint and a high volume fraction of the surface, 2-D thin-film samples may not represent the mechanical behavior of bulk polycrystalline materials [4]. Furthermore, the investigations of fatigued crack structures in NC materials have been limited to surface studies using SEM; the lack of knowledge on the inner grain structure at the crack path impedes the further understanding of fatigued crack growth mechanism in NC materials. A crack propagation study of sufficient thick, full condensed 3-dimensional fatigued NC Ni with the emphasis of grain structure at crack path using TEM was thus undertaken.Bulk NC Ni-99.9% sheets (0.5 mm in thickness with average grain size of 29 nm) were fabricated using a pulsed electrodeposition technique (Integran Technologies Inc., Canada). Testing specimens (37.5mm x 3.81mm x 0.5 mm) were machined from the as-deposited sheets by electrical discharged machining (EDM) (Misubishi DWC90C with 0.25 mm brass wire), followed by mechanical polishing along the longitudinal direction to flatten the surface (final thickness = 0.43 mm) and remove transverse scratches that may serve as crack precursors. Tests were conducted with a three-point bend fatigue system under deflection-controlled conditions. After examining the crack/fracture surfaces with a SEM, crack/fracture surfaces were protected by electrodepositing a thick Ni layer to prevent possible artifacts before/during preparing TEM specimens.

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confidence: 67%

Grain Structure at Crack Path in Fatigued Nano-Crystalline Ni

2009

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“…To date, the majority of NC metals used in experiments are produced by electrodeposition, of which Ni is a prime example [7,8,11,14,20,22,24,30,[58][59][60][61][62][63][64][65][66][67][68][69][70][71][72]. A Watts electrochemical bath [73] is often used in this process, in which current is passed between two electrodes submersed in an aqueous bath of metal salts [ Fig.…”

Section: Deposition Techniquesmentioning

confidence: 99%

“…Advantages of cold spray are that (i) theoretically any micron sized metal powder with an appropriate starting microstructure can be deposited in a NC form and (ii) coating thicknesses in excess of 1 cm can be achieved by [63], (b-c) electrodeposition, [14,72] respectively repeated passes of the spray nozzle. Disadvantages to this process include (i) entrapped porosity and (ii) the presence of impurities that enter the powder feedstock as a result of ball milling.…”

Section: Deposition Techniquesmentioning

confidence: 99%

“…Although the term nanocrystalline was initially used to refer to material with a grain size below 10 nm, the consensus in the literature defines three groups by grain size: nanocrystalline (NC) metals (<100 nm), ultra fine grained (UFG) metals (100 nm-1 µm), and microcrystalline metals (MC) (>1 µm), also called coarse grained (CG) metals. During this period of increasing interest in nanocrystalline metals, experimental observations of their properties have included extremely high strength and hardness [3][4][5][6][7][8][9][10], evidence of a breakdown in the Hall-Petch effect [9,11,12], modest ductility [3,13,14] and improved properties over coarse-grained metals in areas of fatigue resistance [8,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], friction and wear [31][32][33][34], and corrosion resistance [35][36][37]. Molecular dynamics simulations have also been used to study mechanisms which may play a role in the deformation of these metals [38][39][40][41][42][43][44][45].…”

Section: Introductionmentioning

confidence: 99%

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A Review of Fatigue Behavior in Nanocrystalline Metals

2009

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Nanocrystalline metals have been shown to exhibit unique mechanical behavior, including break-down in Hall-Petch behavior, suppression of dislocation-mediated plasticity, induction of grain boundary sliding, and induction of mechanical grain coarsening. Early research on the fatigue behavior of nanocrystalline metals shows evidence of improved fatigue resistance compared to traditional microcrystalline metals. In this review, experimental and modeling observations are used to evaluate aspects of cyclic plasticity, microstructural stability, crack initiation processes, and crack propagation processes. In cyclic plasticity studies to date, nanocrystalline metals have exhibited strongly rate-dependent cyclic hardening, suggesting the importance of diffusive deformation mechanisms such as grain-boundary sliding. The cyclic deformation processes have also been shown to cause substantial mechanicallyinduced grain coarsening reminiscent of coarsening observed during large-strain monotonic deformation of nanocrystalline metals. The crack-initiation process in nanocrystalline metals has been associated with both subsurface internal defects and surface extrusions, although it is unclear how these extrusions form when the grain size is below the scale necessary for persistent slip band formation. Finally, as expected, nanocrystalline metals have very little resistance to crack propagation due to limited plasticity and the lack of crack path tortuosity among other factors. Nevertheless, like bulk metallic glasses, nanocrystalline metals exhibit both ductile fatigue striations and metal-like Paris-law behavior. The review provides both a comprehensive critical survey of existing literature and a summary of key areas for further investigation.

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“…[3][4][5][6][7][8][9] Indeed, published literature on the fatigue performance of NC metals clearly demonstrates improvements in fatigue strength over CG metals. [10][11][12][13][14][15] Aside from quantitative improvements in fatigue performance, NC metals also hold the possibility of new insight into the mechanisms responsible for traditional fatigue failure. In the recent past, studies on the monotonic strength of NC metals have not only revealed quantitative details regarding the Hall-Petch strengthening effect, [16][17][18] but also led to the discovery of mechanistic transitions in dislocation behavior.…”

Section: Introductionmentioning

confidence: 99%

Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

Boyce

Padilla

2011

Metall Mater Trans A

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Fatigue failure due to repetitive loading of metallic devices is a pervasive engineering concern. The present work reveals extraordinary fatigue resistance in nanocrystalline (NC) alloys, which appears to be associated with the small (<100 nm) grain size inhibiting traditional cyclic damage processes. In this study, we examine the fatigue performance of three electrodeposited NC Nibased metals: Ni, Ni-0.5Mn, and Ni-22Fe (PERMALLOY). When subjected to fatigue stresses at and above the tensile yield strength where conventional coarse-grained (CG) counterparts undergo low-cycle fatigue failure (<10 4 cycles to failure), these alloys exhibit exceptional fatigue lives (in some cases, >10 7 cycles to failure). Postmortem examinations show that failed samples contain an aggregate of coarsened grains at the crack initiation site. The experimental data and accompanying microscopy suggest that the NC matrix undergoes abnormal grain growth during cyclic loading, allowing dislocation activity to persist over length scales necessary to initiate a fatigue crack by traditional fatigue mechanisms. Thus, the present observations demonstrate anomalous fatigue behavior in two regards: (1) quantitatively anomalous when considering the extremely high stress levels needed to drive fatigue failure and (2) mechanistically anomalous in light of the grain growth process that appears to be a necessary precursor to crack initiation.

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Fatigue and Fracture of a Bulk Nanocrystalline NiFe Alloy

Cited by 44 publications

References 39 publications

Grain Structure at Crack Path in Fatigued Nano-Crystalline Ni

Grain Structure at Crack Path in Fatigued Nano-Crystalline Ni

A Review of Fatigue Behavior in Nanocrystalline Metals

Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

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