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.

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.

Structural and Mechanical Properties of Multilayer TiN/CrN Coatings

2007 ◽  
Author(s):  
Manohar S. Konchady ◽  
Sergey Yarmolenko ◽  
Devdas M. Pai ◽  
Jag Sankar
Keyword(s):  
Mechanical Properties ◽  
Layer Thickness ◽  
Single Layer ◽  
Preferred Orientation ◽  
X Ray Diffraction ◽  
Unbalanced Magnetron Sputtering ◽  
Deposition Parameters ◽  
Unbalanced Magnetron ◽  
Crn Coatings ◽  
Modulation Wavelength

Multilayer and superlattice coatings of TiN/CrN coating are deposited on Si(100) substrate at different modulation wavelength by reactive unbalanced magnetron sputtering and characterized using X-ray diffraction, nanoindentation, AFM. Nano-roughness of films is in good correlation with hardness and modulus and this effect has been used for optimization of deposition parameters. Preliminary results have shown slightly better mechanical properties for multilayered TiN/CrN coatings compared to single layer TiN and CrN coatings. The XRD results have shown a preferred orientation in &lt;100&gt; direction for TiN/CrN multilayer coatings at modulation wavelengths below 80 nm. At 100 nm layer thickness, TiN revealed small amount of crystals with &lt;111&gt; orientation and their content significantly increases with increase in layer thickness while CrN layers only show preferred orientation of &lt;100&gt;. Multilayered coatings exhibit better mechanical properties due to presence of large number of interfaces which act as barrier to dislocations. Fracture toughness and tribological properties of these coatings are also expected to show significant improvement and the investigation in this area is under progress.

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.

Synthesis of nanostructured metal (Fe, Al)-C60 composites

2010 ◽  
Vol 1276 ◽  
Author(s):  
I. I. Santana García ◽  
V. Garibay Febles ◽  
H. A. Calderon
Keyword(s):  
Raman Spectroscopy ◽  
Mechanical Milling ◽  
Volume Fraction ◽  
High Volume ◽  
X Ray Diffraction ◽  
Nanostructured Composite ◽  
Plasma Sintering ◽  
Transmission Electron ◽  
Show Evidence ◽  
Spark Plasma

AbstractComposites of M-2.5 mol. % Fullerene C60 composites (where M= Fe or Al) are prepared by mechanical milling and Spark Plasma Sintering (SPS). The SPS technique has been used to consolidate the resulting powders and preserve the massive nanostructure. Results of X-Ray Diffraction and Raman Spectroscopy show that larger milling balls (9.6 mm in diameter) produce transformation of the fullerene phase during mechanical milling. Alternatively smaller milling balls (4.9 mm in diameter) allow retention of the fullerene phase. SEM shows homogeneous powders with different particle sizes depending on milling times. Sintering produces nanostructured composite materials with different reinforcing phases including C60 fullerenes, diamonds and metal carbides. The presence of each phase depends characteristically on the energy input during milling. Transmission Electron Microscopy (TEM) and Raman Spectroscopy show evidence of the spatial distribution and nature of phases. Diamonds and carbides can be identified for the sintered Fe containing composites with a relatively high volume fraction.

Research on Microstructure and Wear Resistance of (Fe,Cr)7C3/Fe Surface Gradient Composite

2015 ◽  
Vol 1120-1121 ◽  
pp. 559-563
Author(s):  
Chong Wang ◽  
Fang Xia Ye ◽  
Li Sheng Zhong ◽  
Ying Lin Yan ◽  
Yu Jun Lai ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Wear Resistance ◽  
Volume Fraction ◽  
Subsurface Layer ◽  
Composite Layer ◽  
High Volume ◽  
Synthesis Process ◽  
X Ray Diffraction ◽  
Surface Gradient

In this study, the (Fe,Cr)7C3 particles strengthened gradient composite was produced by in situ synthesis process with subsequent heat treatment from gray cast iron (HT300) and high purity chrome plate. The microstructure, phase composition and wear resistance of the composite were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and scratch tester. The results showed that the thickness of the gradient layer was about 758 μm after heat treatment at 900 °Cfor 4 h. And it can be divided into three areas depending on microstructure. The outermost layer which was ~60 μm of thickness, was the dense ceramic layer with high volume fraction of (Fe,Cr)7C3 ~90%. No obvious grain boundaries were observed. The subsurface layer was the particles dispersed layer, which was ~525 μm of thickness, with the volume fraction of (Fe,Cr)7C3 decreased to 70%. The lowermost layer was ferrite, with about 173 μm thickness. A good metallurgical bond generated between the composite layer and matrix. The depth and the width of surface scratch increased with the raising loads from 0 to 100 N, and the cracks mainly included micro-crack, tiny dens crack, mixture crack and through-wall crack. The (Fe,Cr)7C3 particles were broken and scraped when the load exceeded 80 N.

Deformation Behavior of Bulk Amorphous Zr-Base Alloys

1998 ◽  
Vol 554 ◽  
Author(s):  
A. Leonhard ◽  
M. Heilmaier ◽  
J. Eckert ◽  
L. Schultz
Keyword(s):  
Room Temperature ◽  
Small Volume ◽  
Volume Fraction ◽  
High Volume ◽  
X Ray Diffraction ◽  
Crystalline Phases ◽  
Ni Alloys ◽  
Young’S Moduli ◽  
Transmission Electron ◽  
Complex Parts

AbstractBulk Zr-Al-Cu-Ni alloys were produced by die casting into a copper mold under Aratmosphere. The microstructure of fully amorphous as well as partially crystalline samples was analyzed by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), and chemical analysis with special emphasis on the size and composition of the crystallites. The mechanical behavior of the different samples was investigated by constant compression rate tests. At room temperature the samples show inhomogeneous deformation and, independent of the chosen composition, relatively low Young's moduli of about 70 GPa, flow stresses around 2 GPa and elastic strains of up to 3 %. Fully amorphous samples show microplasticity of up to 2 % strain without significant work hardening while specimens with a fairly high volume fraction of crystalline phases are extremely brittle. In contrast, at high temperatures around the glass transition temperature T8 both amorphous and partially crystalline specimens exhibit at low strain rates homogeneous deformation with an initial stress overshoot followed by an extended region of plastic flow. As compared to room temperature, the peak stresses are much lower and are hardly influenced by the presence of small volume fractions of crystalline phases. The observed thermal stability against crystallization provides a promising possibility for easy shaping of complex parts at temperatures around Tg.

scholarly journals The Characterization Of Cast Fe-Cr-C Alloy

2015 ◽  
Vol 60 (2) ◽  
pp. 779-782 ◽  
Author(s):  
K. Wieczerzak ◽  
P. Bała ◽  
M. Stępień ◽  
G. Cios ◽  
T. Kozieł
Keyword(s):  
Volume Fraction ◽  
Microstructural Characterization ◽  
High Volume ◽  
Phase Identification ◽  
Arc Furnace ◽  
X Ray Diffraction ◽  
Cast State ◽  
X Ray ◽  
Average Hardness

AbstractThe paper presents the results of the characterization of alloy from Fe-Cr-C (carbon content 0.79 wt.%) system including the microstructure, phase analysis, morphology and hardness in as cast state. The chemical composition was designed to create chromium-rich ferritic matrix with high volume fraction of carbides in form of interdendritic eutectics. The research was carried out on the cross section of the ingot, synthesized in an arc furnace under high purity argon atmosphere and crystallized on water-cooled copper mould. Microstructural characterization was carried out by light microscopy and scanning electron microscopy (SEM). Phase identification was performed by X-Ray diffraction (XRD). The microstructure of the investigated alloy is composed of primary and secondary dendrites Fe-Cr solid solution and complex M23C6and M7C3carbides in interdendritic areas. Segregation of Cr and C during crystallization causes precipitation of M7C3carbides. The average hardness of the alloy is 205±12 HV10.

Evolution of microstructure and phases in in situ processed Ti–TiB composites containing high volume fractions of TiB whiskers

1999 ◽  
Vol 14 (11) ◽  
pp. 4214-4223 ◽  
Author(s):  
S. S. Sahay ◽  
K. S. Ravichandran ◽  
R. Atri ◽  
B. Chen ◽  
J. Rubin
Keyword(s):  
Volume Fraction ◽  
High Volume ◽  
Comparison Method ◽  
Relative Volume ◽  
X Ray Diffraction ◽  
Volume Fractions ◽  
Structure Factors ◽  
Integrated Intensities ◽  
Evolution Of Microstructure

A series of titanium composites, with varying volume fractions of titanium monoboride (TiB) whiskers, were made by mixing various proportions of titanium (Ti) and titanium diboride (TiB2) powders followed by hot pressing. The phases present were identified by x-ray diffraction. Microstructural examination revealed three different types of TiB whisker morphologies: (i) long and needle-shaped TiB whiskers that are isolated and randomly oriented in the Ti matrix at relatively low volume fractions (0.3), (ii) colonies of refined and densely packed TiB whiskers from intermediatevolume (0.55) to high volume (0.73 and 0.86) fractions, and (iii) coarse and elongated TiB particles with a few needle-shaped whiskers at the highest volume fraction (0.92). In all the composites, TiB was found to be the predominant reinforcement. However, in Ti–TiB composites with 0.86 and 0.92 volume fractions of TiB, a significant amount of TiB2 was also present. The relative volume fractions of Ti, TiB, and TiB2 phases were estimated from the integrated intensities of diffraction peaks by the direct comparison method employing the calculated structure factors and Lorentz polarization factors. The composite microstructure, as well as the evolution of different morphologies, of TiB whiskers is discussed.

scholarly journals Characterization of γ′ Precipitates in Cast Ni-Based Superalloy and Their Behaviour at High-Homologous Temperatures Studied by TEM and in Situ XRD

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2397 ◽  
Author(s):  
Łukasz Rakoczy ◽  
Ondrej Milkovič ◽  
Bogdan Rutkowski ◽  
Rafał Cygan ◽  
Małgorzata Grudzień-Rakoczy ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Matrix Material ◽  
High Volume ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
In Situ Xrd ◽  
Transmission Electron ◽  
The Matrix

In situ X-ray diffraction and transmission electron microscopy has been used to investigate René 108 Ni-based superalloy after short-term annealing at high-homologous temperatures. Current work is focused on characterisation of γ′ precipitates, their volume fraction, evolution of the lattice parameter of γ and γ′ phases and misfit parameter of γ′ in the matrix. Material in the initial condition is characterised by a high-volume fraction (over 63%) of γ′ precipitates. Irregular distribution of alloying elements was observed. Matrix channels were strongly enriched in Cr, Co, W and Mo, whereas precipitates contain large amount of Al, Ti, Ta and Hf. Exposure to high-homologous temperatures in the range 1100–1250 °C led to the dissolution of the precipitates, which influenced the change of lattice parameter of both γ and γ′ phases. The lattice parameter of the matrix continuously grew during holding at high temperatures, which had a dominant influence on the more negative misfit coefficient.

Silica/GO hybrids reinforced NR: Better interface interaction and dynamic behavior

2019 ◽  
Vol 52 (7) ◽  
pp. 575-592
Author(s):  
Kaikai Liu ◽  
Yuanyuan Shang ◽  
Liu Yang ◽  
Aihua Du
Keyword(s):  
Mechanical Performance ◽  
Volume Fraction ◽  
High Volume ◽  
Interfacial Interaction ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Interface Interaction ◽  
Transmission Electron ◽  
Strong Interfacial Interaction ◽  
Filler Dispersion

With silica firstly modified by 3-aminopropyl-triethoxysilane (APES), graphene oxide (GO) was prepared by modified Hummer’s method. APES-silica/GO (AsGO) hybrids were fabricated through hydrogen bond to reduce the polarity of silica and GO and increase the compatibility between natural rubber (NR) and AsGO. Subsequently, AsGO was incorporated into NR latex. The interaction between GO and silica in AsGO was characterized by X-ray diffraction, Raman, and Zeta potential. It was confirmed by transmission electron microscopy that the silica was uniformly dispersed on the surface of the GO. The filler–rubber interfacial interaction was thoroughly investigated. The amount of constrained region was quantified through differential scanning calorimetry results, and it showed that the high volume fraction of constrained region is responsible for the strong interfacial interaction. Besides, the mechanical performance, dynamic property, and electrical and thermal conductivity of NR-AsG x were studied. The results showed that the overall performance of NR-AsG x has an optimum value when the GO loading is 1.5 phr, which is due to the good filler dispersion and strong interface interaction.

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