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«STRUCTURE AND PROPERTIES OF ELECTRODEPOSITED NANOCRYSTALLINE NI AND NI-FE ALLOY CONTINUOUS FOILS by Jason Derek Giallonardo A thesis submitted in ...»

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Figure 4.23.

HR-TEM image and indexed FFT pattern (inset) of the faulted regions in the grain interior of sample no. 5 (Ni, 23 nm) having a [011] zone axis.

Figure 4.24.

HR-TEM image and indexed FFT pattern (inset) of the faulted regions in the grain interior of sample no. 7 (Ni-16wt.%Fe, 12 nm) having a [011] zone axis.

Figure 4.25.

HR-TEM image and indexed FFT pattern (inset) of the faulted regions in the grain interior of sample no. 9 (Ni-32wt%Fe, 10 nm) having a [011] zone axis.

Figure 4.26.

XRD pattern (Cu-Kα) for sample no. 5 (Ni, 23 nm).

Figure 4.27.

XRD pattern (Cu-Kα) for sample no. 7 (Ni-16wt.%Fe, 12 nm).

Figure 4.28.

Plot of lattice parameter vs. Fe concentration in the deposit.

Figure 4.29.

Plot of XRD grain size estimations vs. TEM grain size determinations. The reference (dashed) line represents a 1:1 agreement between the two methods.

Figure 4.30.

Plot of growth fault probability vs. Fe concentration in the deposit showing an increasing trend with increasing Fe. The dashed line is a (linear) best fit for the current data.

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Figure 4.32.

Anisothermal anneal (DSC) curve for sample no. 4 (Ni, 37 nm).

Figure 4.33.

Anisothermal anneal (DSC) curve for sample no. 9 (Ni-32wt.%Fe, 10 nm).

Figure 4.34.

Total enthalpy plotted as a function of grain size for the nanocrystalline Ni samples. The dashed line is an approximate trend line.

Figure 4.35.

Total enthalpy plotted as a function of grain size for the nanocrystalline Ni samples. The dashed lines are approximate trend lines.

Figure 4.36.

Plot of interfacial free energy (ΔHic) vs. grain size. The dashed line is a best fit for both sets of data.

Figure 4.37.

Plot of grain boundary energy (  gb ) vs. grain size. The dashed line is a best fit for both sets of data.

Figure 5.1.

Compositional variation of Young’s modulus for the Fe-Ni alloys [Ledbetter and Reed (1973)].

Figure 5.2.

Force-depth graph showing load-unload curves of sample no. 7 (Ni-16wt.%Fe, 12 nm).

Figure 5.3.

Hall-Petch plot for the series of nanocrystalline Ni and Ni-Fe alloys.

Figure 5.4.

Normalized Young’s modulus values as a function of grain size. The horizontal solid line represents Em / E0 = 1, where Em is the measured value and E0 is the respective conventional (randomly oriented) polycrystalline counterpart value. The dashed lines correspond to the values predicted by the upper bound composite model (Eq. 5-1). The solid lines correspond to the values predicted by the lower bound (Eq. 5-2) composite model.

Figure 5.5.

Measured Young’s modulus values for the series of nanocrystalline Ni and Ni-Fe alloys compared with Voigt-Reuss-Hill average values, and Voigt and Reuss bounds.

Figure 6.1.

Plot of microstrain vs. grain size (dashed line) and intercrystal volume fraction vs.

grain size (solid line).

Figure 6.2.

Plot of microstrain vs. Fe concentration in the deposit showing an increasing trend with increasing Fe.

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Figure 6.4.

GADDS software output image of integration along the (311) ring during stress analysis for sample no. 4 (Ni, 37 nm). Embedded within the image is the peak intensity profile as a function of 2 for the example region that is integrated.

Figure 6.5.

Shear stress component,  12, for the nanocrystalline Ni and Ni-Fe alloys as a function of grain size.

Figure 6.6.

Plot of the planar components  11 and  22 for the nanocrystalline Ni and Ni-Fe alloys as a function of grain size.

Figure 6.7.

Plot of the planar components  11 and  22 for the nanocrystalline Ni samples as a function of grain size with the best fit (solid line) curve based on Eq. 6-4.

Figure 6.8.

Lennard-Jones pair potential model: (a) bond-energy curve where a0 is the equilibrium interatomic spacing value, U a is the attractive bond-energy, U r is the repulsive bond-energy, and U t is the total energy, (b) bond-force curve where a0 is the equilibrium interatomic spacing value, Fa is the attractive bond-energy, Fr is the repulsive bond-energy, and Ft is the total energy [Lennard-Jones (1924)].

Figure 6.9.

Schematic diagram of the sample planar cross-section showing conventional XRD lines from an unstressed lattice with equally spaced atoms and a Bragg angle,  0, corresponding to the interplanar spacing, d 0.

Figure 6.10.

Schematic diagram of the sample planar cross-section showing conventional XRD lines from a lattice in a state of (bi-axial) compressive stress. A contraction of the lattice in the planar direction is accompanied by an expansion that is normal to the plane.





The net result is a lower Bragg angle, , and increased interplanar spacing value, d.

Figure A.1. SEM image (60,000X) of sample no. 1 (Ni, ~255 nm).

Figure A.2. SEM image (60,000X) of sample no. 2 (Ni, 81 nm).

Figure A.3. SEM image (60,000X) of sample no. 5 (Ni, 23 nm).

Figure A.4. SEM image (60,000X) of sample no. 6 (Ni-7.3wt.%Fe, 32 nm).

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Figure A.6. SEM image (60,000X) of sample no. 9 (Ni-32wt.%Fe, 10 nm).

Figure B.1. TEM images of sample no. 1 (Ni, ~255 nm): (a) BF image, (b) DF image, and (c) SAD pattern.

Figure B.2. TEM images of sample no. 2 (Ni, 81 nm): (a) BF image, (b) DF image, (c) SAD pattern, and (d) grain size distribution.

Figure B.3. TEM images of sample no. 3 (Ni, 44 nm): (a) BF image, (b) DF image, (c) SAD pattern, and (d) grain size distribution.

Figure B.4. TEM images of sample no. 4 (Ni, 37 nm): (a) BF image, (b) DF image, (c) SAD pattern, and (d) grain size distribution.

Figure B.5. TEM images of sample no. 5 (Ni, 23 nm): (a) BF image, (b) DF image, (c) SAD pattern, and (d) grain size distribution.

Figure B.6. TEM images of sample no. 6 (Ni-7.3wt.%Fe, 32 nm): (a) BF image, (b) DF image, (c) SAD pattern, and (d) grain size distribution.

Figure B.7. TEM images of sample no. 7 (Ni-16wt.%Fe, 12 nm): (a) BF image, (b) DF image, (c) SAD pattern, and (d) grain size distribution.

Figure B.8. TEM images of sample no. 8 (Ni-23wt.%Fe, 10 nm): (a) BF image, (b) DF image, (c) SAD pattern, and (d) grain size distribution.

Figure B.9. TEM images of sample no. 9 (Ni-32wt.%Fe, 10 nm): (a) BF image, (b) DF image, (c) SAD pattern, and (d) grain size distribution.

Figure C.1. XRD pattern (Cu-Kα) for (calculated) Ni powder standard.

Figure C.2. XRD pattern (Cu-Kα) for sample no. 1 (Ni, ~255 nm).

Figure C.3. XRD pattern (Cu-Kα) for sample no. 2 (Ni, 81 nm).

Figure C.4. XRD pattern (Cu-Kα) for sample no. 3 (Ni, 44 nm).

Figure C.5. XRD pattern (Cu-Kα) for sample no. 4 (Ni, 37 nm).

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Figure C.7. XRD pattern (Cu-Kα) for sample no. 6 (Ni-7.3wt.%Fe, 32 nm).

Figure C.8. XRD pattern (Cu-Kα) for sample no. 7 (Ni-16wt.%Fe, 12 nm).

Figure C.9. XRD pattern (Cu-Kα) for sample no. 8 (Ni-23wt.%Fe, 10 nm).

Figure C.10. XRD pattern (Cu-Kα) for sample no. 9 (Ni-32wt.%Fe, 10 nm).

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a0 Equilibrium interatomic spacing value ahkl Lattice parameter of respective (hkl) Binst Full-width at half-maximum (FWHM) due to the instrument Bm Experimentally measured full-width at half-maximum (FWHM) Bsize Full-width at half-maximum due to grain size Bstrain Full-width at half-maximum due to microstrain cij Elastic stiffnesses

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Ei Young’s modulus for the indenter Er Reduced Young’s modulus Etj Young’s modulus of triple junction Em Measured Young’s modulus EVRH Young’s modulus (Voigt-Reuss-Hill average)

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f Atomic scattering factor; interface stress fg Grain interior volume fraction f gb Grain boundary volume fraction f ic Total intercrystal volume fraction f tj Triple junction volume fraction G Internal (free) energy; shear modulus GR Shear modulus (Reuss bound) GV Shear modulus (Voigt bound)

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Δρ Increment in electrical resistivity C.G. Displacement of the center of gravity d Change in interplanar spacing f ic Change in intercrystal volume fraction G Change in internal (free) energy resulting from cold work H Change in enthalpy (stored energy) H ic Excess interfacial enthalpy H total Change in total enthalpy (stored energy)

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2D Two-dimensional 2D-XRD Two-dimensional X-ray diffraction ASTM American Society for Testing and Materials bcc Body-centered cubic

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DSC Differential scanning calorimetry EDS Energy dispersive X-ray spectroscopy fcc Face-centered cubic FFT Fast Fourier transform FPA Fundamental parameter approach FWHM Full-width at half-maximum GADDS General area detector diffraction system GFP Growth fault probability hcp Hexagonal close-packed HR-TEM High-resolution transmission electron microscopy IFFT Inverse fast Fourier transform MDSC Modulated differential scanning calorimetry

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SEM Scanning electron microscopy SFE Stacking fault energy TEM Transmission electron microscopy VHN Vickers hardness number VRH Voigt-Reuss-Hill XRD X-ray diffraction

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1.1. Background and Motivation for Study Nanocrystalline materials are of great interest since they can have enhanced, diminished, or strikingly similar characteristics when compared to their conventional polycrystalline counterparts. When the grain size is reduced sufficiently below 100 nm, certain structurally sensitive characteristics are greatly enhanced, e.g., yield strength, hardness, and wear resistance, while electrical conductivity is diminished [Erb et al. (2007)].

Hardness, in particular, obeys the Hall-Petch relationship down to about 20 nm, however a unique phenomenon occurs at grain sizes less than 20 nm where a deviation from the expected behaviour is observed. This deviation is due primarily to a change in deformation mechanisms [Chokshi et al. (1989), Palumbo et al. (1990), Wang et al. (1997)]. On the other hand, structurally insensitive characteristics tend to remain similar over a wide grain size range, e.g., Young’s modulus, magnetic saturation, heat capacity, and thermal expansion [Erb et al. (2007)]. The Young’s modulus of nanocrystalline materials produced by compaction of inert gas condensed precursor powders was initially reported to have significant reductions (50%), e.g., Nieman et al. (1991). However, this synthesis technique is known to produce materials with a substantial amount of porosity that was eventually considered to be an artifact causing the observed reductions in Young’s modulus [Krstic et al. (1993), Zugic et al.

(1997)]. Thus, it is extremely important that the synthesis method be taken into consideration when studies are performed and conclusions are made. The electrodeposition technique is an example of a process which is known to produce negligible amounts of porosity, e.g., nanocrystalline Ni [Van Petegem et al. (2003)] and Ni-2.5wt.%P [Zhou et al.

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(2009)]. As a result, only small deviations are observed in the Young’s modulus for electrodeposited materials [Zhou et al. (2003a), Zhou et al. (2003b), Zhou et al. (2009)].

In general, electrodeposited nanocrystalline materials are of significant commercial importance [Palumbo et al. (2003), McCrea et al. (2011)]. In particular, the nanocrystalline Ni-Fe alloys have many interesting properties. For example, at approximately 20 wt.%Fe, an alloy commonly known as permalloy possesses unique soft magnetic properties including a high magnetic permeability and a low coercivity. However, certain microstructural defects may affect these properties. In conventional polycrystalline Ni-Fe alloys, plastic deformation introduces internal stresses which can bring about negative effects on certain magnetic properties. Electrodeposited nanocrystalline materials have similar magnetic saturation when compared to their polycrystalline counterparts [Aus et al. (1992), Aus (1999)], but other properties such as coercivity are affected by grain size [Herzer (1995)]. Aus (1999) reported a decreasing coercivity trend with increasing Fe in electrodeposited nanocrystalline Ni-Fe alloys which is similar to that reported for their large grain polycrystalline counterparts [Marsh (1938), Bozorth (1978)]. However, the coercivity values for the nanocrystalline NiFe alloys were noticeably higher, even when no plastic deformation had been imposed on the material. A limited understanding for this observation provokes the need for more study on this subject and related matters, including the influences of processing, microstructure, and internal stresses.

In many respects, electrodeposited nanocrystalline Ni and Ni-Fe alloys have been studied quite extensively [Erb et al. (2007)]. All of these studies have been based on

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materials that have been produced as individual coupons in a batch-wise manner using a standard electroplating set-up, namely with a stationary cathode. A novel technique for producing continuous electrodeposited nanocrystalline metal and metal matrix composite foils for use in various applications has the advantage of being able to yield bulk quantities of material with practically unlimited length [Palumbo et al. (2005)]. This also proves to be a commercially viable method and serves to fulfill demand in an economical and efficient manner. Due to the nature of the continuous deposition process, i.e., a rotating circular cathode which is also referred to as a “drum”, therein lies various questions around the effects of this method on the structure and properties of the materials produced. Therefore, studies are necessary on materials produced using this technique.



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