The Effect of Layer Thickness on Polycrystalline Zirconia Growth in Zirconia-Alumina Multilayer Nanolaminates

1994 ◽  
Vol 343 ◽  
Author(s):  
C. M. Scanlan ◽  
M. D. Wiggins ◽  
M. Gajdardziska-Josifovska ◽  
C. R. Aita
Keyword(s):  
Phase Composition ◽  
Layer Thickness ◽  
Volume Fraction ◽  
Tetragonal Zirconia ◽  
High Resolution Electron Microscopy ◽  
Fused Silica ◽  
Transformation Toughening ◽  
Reactive Sputter Deposition ◽  
Resolution Electron ◽  
Zirconia Films

ABSTRACTThe mechanical properties of zirconia are known to be a function of phase composition. We show here that a nanolaminate geometry can be used to control the phase composition of zirconia films. The experiment consisted of growth of nanoscale multilayer films (nanolaminates) of polycrystalline zirconia and amorphous alumina by reactive sputter deposition on Si (111) and fused silica substrates. The films were characterized using x-ray diffraction and high resolution electron microscopy. The results show that both monoclinic (m) and tetragonal (t) zirconia polymorphs were formed in the zirconia layers. Most crystallites are oriented with either close-packed {111}-t or {111}-m planes parallel to the substrate. The volume fraction of tetragonal zirconia, the desired phase for transformation-toughening behavior, increases with decreasing zirconia layer thickness. Nanolaminates with a volume fraction of tetragonal zirconia exceeding 0.8 were produced without the addition of a stabilizing dopant, and independent of the kinetic factors that limit tetragonal zirconia growth in pure zirconia films.

Martensitic transformation in zirconia-alumina nanolaminates

1995 ◽  
Vol 53 ◽  
pp. 198-199
Author(s):  
M. Gajdardziska-Josifovska ◽  
C. R. Aita
Keyword(s):  
Volume Fraction ◽  
Parent Phase ◽  
Tetragonal Zirconia ◽  
High Volume ◽  
High Resolution Electron Microscopy ◽  
Ceramic Coatings ◽  
Transformation Toughening ◽  
Transformation Mechanism ◽  
Layer Spacing ◽  
Reactive Sputter Deposition

With an eye towards developing transformation-toughening ceramic coatings, we grew multilayers of polycrystalline zirconia and amorphous alumina in which the layer spacing was scaled to insure nanosize zirconia crystallites. In this manner, nanolaminates with a high volume fraction of tetragonal zirconia (t-ZrO2) were produced, independent of the deposition parameters and without the use of dopants.For a coating to be of practical use, not only must it contain a significant amount of t-ZrO2, but this phase must also transform locally to the monoclinic phase (m-ZrO2) m response to stress. In bulk zirconia-alumina composites, with dopant stabilized tetragonal zirconia, the martensitic t → m transition is auto-catalytic, resulting in widespread transformation of the parent phase. Twinning and slip are the recognized transformation mechanisms. In this work, we study the transformation mechanism in zirconia-alumina nanolaminates using high resolution electron microscopy (HREM).The multilayers were grown by reactive sputter deposition in a multiple target if diode system.1 Si (111) wafers were used as substrates for the multilayers studied by microscopy.

High Resolution Electron Microscopy of Sputter-Deposited Zirconia-Alumina Nanolaminates

1995 ◽  
Vol 403 ◽  
Author(s):  
M. A. Schofield ◽  
R. Whig ◽  
C. R. Aita ◽  
M. Gajdardziska-Josifovska
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Volume Fraction ◽  
Void Formation ◽  
Tetragonal Zirconia ◽  
High Resolution Electron Microscopy ◽  
Critical Dimension ◽  
Monoclinic Zirconia ◽  
Growth Interface ◽  
Resolution Electron

AbstractHigh resolution electron microscopy is employed to study the crystallography and morphology of zirconia nanocrystallites in zirconia-alumina nanolaminates and zirconia films. Unity volume fraction of tetragonal zirconia formed when the zirconia layer thickness was less than 6.2 nm, a theoretically predicted critical size for tetragonal-to-monoclinic zirconia (t -> m-ZrO2) transformation. In thicker layers, monoclinic zirconia formed, accompanied by renucleation and void formation which caused roughness to the zirconia nanolayers. The average position of the voids in the layers was 6.3 nm from the growth interface, coinciding with the critical dimension for t -> m-ZrO2 transformation.

Insight into the Formation of Ultrafine Nanostructures in Bulk Amorphous Zr54.5 Ti7.5Al10Cu20Ni8

2001 ◽  
Vol 703 ◽  
Author(s):  
André Heinemann ◽  
Helmut Hermann ◽  
Albrecht Wiedenmann ◽  
Norbert Mattern ◽  
Uta Kühn ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Volume Fraction ◽  
High Volume ◽  
High Resolution Electron Microscopy ◽  
Scattering Data ◽  
Scanning Calorimetry ◽  
Enhanced Diffusion ◽  
Resolution Electron ◽  
The Mean ◽  
Interparticle Interference

ABSTRACTBulk amorphous Zr54.5 Ti7.5Al10Cu20Ni8 is investigated by means of smal-angle neutron scattering (SANS), differential-scanning calorimetry (DSC), high-resolution electron microscopy (HREM) and other methods. The formation of ultrafine nanostructures in the glassy phase is observed and explained by a new model. Structura fluctuations of randomly distributed partialy ordered domains grow during annealing just below the glass transition temperature by local re-ordering. During anneaing the DSC gives evidence for a increasing volume fraction of the localy ordered domains. At high volume fractions of impinging domains a percolation threshold on the interconnected domain boundaries occurs and enhanced diffusion becomes possible. At that stage SANS measurements lead to satistically significant scattering data. The SANS signals are anayzed in terms of a model taking into account spherica particles surrounded by diffusion zones and interparticle interference effects. The mean radius of the nanocrystaline particles is determined to 1 nm and the mean thickness of the depletion zone is 2 nm. The upper limit for the volume fraction after annealing at 653 K for 4hours is about 20 %. Electron microscopy confirms the size and shows that the particle are crystaline.

The syntheses of SiCp/Al nanocomposites under high pressure

1997 ◽  
Vol 12 (5) ◽  
pp. 1187-1190 ◽  
Author(s):  
Haozhe Liu ◽  
Aimin Wang ◽  
Luhong Wang ◽  
Bingzhe Ding ◽  
Zhuangqi Hu ◽  
...  
Keyword(s):  
High Pressure ◽  
Pressure Range ◽  
Vickers Microhardness ◽  
Volume Fraction ◽  
High Resolution Electron Microscopy ◽  
Synthesis Temperature ◽  
Reaction Behavior ◽  
Sic Particles ◽  
Resolution Electron ◽  
Al Matrix

The SiCp/Al nanocomposites were synthesized under high pressure. The reaction behavior between SiC particles and Al matrix within 2–6 GPa pressure range was determined. The high resolution electron microscopy (HREM) observation and the Vickers microhardness measurement show that the reaction is slight and that the adhesion of SiC particles to the Al matrix is good whether the reaction between them occurred or not. This offers an opportunity to tailor the nanocomposite mechanical properties by adjusting the synthesis temperature, pressure, and volume fraction of SiC particles.

HREM of Rapidly Solidified Al-Li-Zr Based Alloys

1990 ◽  
Vol 48 (1) ◽  
pp. 54-55
Author(s):  
V. Radmilovic ◽  
G. Thomas ◽  
R. Kilaas ◽  
N. J. Kim
Keyword(s):  
Volume Fraction ◽  
Solution Treatment ◽  
Aging Treatment ◽  
High Resolution Electron Microscopy ◽  
Image Simulation ◽  
Large Volume Fraction ◽  
Heat Treated ◽  
Resolution Electron ◽  
Rapidly Solidified

During aging of Al-Li-Zr based alloys δ'(Al3Li) precipitates heterogeneously around β'(Al3Zr), forming so-called composite precipitate[l-4], that has important effects on the mechanical behavior of these alloys. As has been observed in several investigations, the addition of small amount of Zr results in a fairly large volume fraction of β' in the microstructure, and this suggests that there may be a partitioning of Li in the β'. In the present investigation, high resolution electron microscopy (HREM) and image simulation have been used to perform detailed characterization of the chemistry and structure of β' precipitate.The alloy Al-3Li-1Cu-0.5Mg-0.5Zr (wt.%) has been heat treated as follows: a) solution treatment at 550°C for 2 hours and water quenching, b) aging treatment at 150°C for 4 hours or at 200°C for 8 hours and c) 10% cold working followed by aging at 175°C for 64 hours. HREM images were taken on a JEOL ARM electron microscope operating at 400 and 800kV. Simulated HREM images of the composite δ'/β' precipitate were calculated using CEMPAS multislice program described by Kilaas[5].

HREM study of tetragonal zirconia in Al2O3/ZrO2 multilayers

1994 ◽  
Vol 52 ◽  
pp. 754-755
Author(s):  
M. Gajdardziska-Josifovska ◽  
M. R. McCartney ◽  
W. J. de Ruijter ◽  
C. M. Scanlan ◽  
C. R. Aita
Keyword(s):  
Layer Thickness ◽  
Volume Fraction ◽  
Tetragonal Zirconia ◽  
High Volume ◽  
X Ray Diffraction ◽  
Monoclinic Form ◽  
Deposition Parameters ◽  
Metastable Tetragonal Zirconia ◽  
Elastic Constraint ◽  
Crucial Parameter

The bulk zirconia-alumina system is a model ceramic composite whose fracture toughness is increased via martensitic transformation: i.e. metastable tetragonal zirconia (t-ZrO2) transforms to its stable monoclinic form (m-ZrO2) upon application of stress. To achieve this desirable property it is important to retain a high volume fraction of t-ZrO2 at room temperature. In bulk synthesis this is accomplished by adding dopants, such as yttrium. Recently we have demonstrated that multilayer sputter deposition enables stabilization of tetragonal zirconia without the use of dopants.Amorphous alumina layers were used as termination and restart surfaces for the polycrystalline zirconia layers, as well as an elastic constraint for the t → m transition which involves an anisotropic volume expansion. Double angle X-ray diffraction (XRD) was used to explore the deposition parameters under which t-ZrO2 is retained in the nanolaminate. The zirconia layer thickness was found to be the crucial parameter. The tetragonal phase was detected in all multilayers with ZrO2 layer thickness <20nm.

Structural and Phase Transformations in Thin Film Ti-Aluminides and Ti/Al Multilayers

1996 ◽  
Vol 434 ◽  
Author(s):  
R. Banerjee ◽  
S. Swaminathan ◽  
R. Wheeler ◽  
H. L. Fraser
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Layer Thickness ◽  
High Resolution Electron Microscopy ◽  
Silicon Substrates ◽  
Two Phase ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Sputter Deposited

AbstractMultilayered Ti/Al thin films (with nominally equal layer thickness of Ti and Al) have been sputter deposited on oxidized silicon substrates at room temperature. Transmission electron microscopy (TEM) and high resolution electron microscopy have been used to characterize the structure of these multilayers as a function of the layer thickness. Ti changed from an hcp to an fcc and back to an hcp structure on reduction of the layer thickness. Al too changed from an fcc to an hcp structure at a layer thickness of 2.5 nm. The observed structural transitions have been explained on the basis of the Redfield-Zangwill model. Subsequently Ti-aluminide thin films were deposited using a γ-TiAl target. These films were found to be amorphous in the as-deposited condition with crystallites of α-Ti(Al) embedded in the amorphous matrix. On annealing under a protective Ar atmosphere at a temperature of 550 °C, the Ti-aluminide film crystallized into a nanocrystalline two phase microstructure consisting of γ-TiAl and α2-Ti3Al. The crystallization of the aluminide film has been investigated in detail by in-situ annealing experiments on a hot stage in the TEM. The results of this investigation have been discussed in this paper.

Ultrafine nanostructure of partially crystallized bulk amorphous Zr54.5Ti7.5Al10Cu20Ni8

2001 ◽  
Vol 34 (5) ◽  
pp. 666-668 ◽  
Author(s):  
Helmut Hermann ◽  
André Heinemann ◽  
Hans-Dietrich Bauer ◽  
Norbert Mattern ◽  
Uta Kühn ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Small Angle Neutron Scattering ◽  
Volume Fraction ◽  
High Resolution Electron Microscopy ◽  
Scattering Data ◽  
Depletion Zone ◽  
Upper Limit ◽  
Resolution Electron ◽  
The Mean ◽  
Interparticle Interference

Bulk amorphous Zr54.5Ti7.5Al10Cu20Ni8was investigated by means of small-angle neutron scattering and high-resolution electron microscopy. Partially crystallized states were generated by annealing. The scattering data were analyzed in terms of a model taking into account both properties of the particles and interparticle interference. The mean radius of the particles is 1.3 nm. They are surrounded by a depletion zone with mean thickness of 2.6 nm. The volume fraction of the particles is estimated from the interparticle interference effect; its upper limit after annealing at 653 K for 4 h is 12%. Electron microscopy confirms the size determined from the scattering data and shows that the particles are crystalline.

Synthesis of Coatings With Hardness Exceeding 40 GPa by Magnetron Sputtering

1998 ◽  
Vol 120 (2) ◽  
pp. 179-183 ◽  
Author(s):  
Mei-Ling Wu ◽  
Zunde Yang ◽  
Yip-Wah Chung ◽  
Ming-Show Wong ◽  
William D. Sproul
Keyword(s):  
Mechanical Properties ◽  
Magnetron Sputtering ◽  
Volume Fraction ◽  
High Resolution Electron Microscopy ◽  
Substrate Bias ◽  
Cathode Sputtering ◽  
Lattice Match ◽  
Wetting Properties ◽  
Resolution Electron ◽  
Composition Structure

Single- and dual-cathode DC magnetron sputtering was used to produce TiB2 coatings and CNx/ZrN multilayers, respectively, with hardness exceeding 40 GPa. The composition, structure, topography, and mechanical properties were determined by various techniques, including Auger electron spectroscopy, X-ray diffraction, high-resolution electron microscopy, atomic force microscopy, and nanoindentation. An optimum combination of the sputtering pressure and substrate bias results in the production of ultrasmooth TiB2 coatings with hardness up to 50 GPa and excellent wetting properties. The rationale for studying the CNx/ZrN system is that ZrN(111) provides excellent lattice match to the hypothetical β-C3N4(0001) face (β-C3N4 was predicted to have mechanical properties comparable to diamond). Using a dual-cathode sputtering system, we produced crystalline multilayers of CNx/ZrN with bilayer thickness of 1–2 nm. Using various combinations of nitrogen partial pressure, target powers, and substrate bias, we found that the hardness of these coatings correlates very strongly with the occurrence of (111) texture of ZrN, consistent with the lattice-match strategy. Even with a ZrN volume fraction of 70 percent, such multilayer coatings have been synthesized with hardness in the 50 GPa regime.

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