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.

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.

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.

Llo Phase Formation in CoPt Thin Films

1997 ◽  
Vol 475 ◽  
Author(s):  
R. A. Ristau ◽  
K. Barmak ◽  
K. R. Coffey ◽  
J. K. Howard
Keyword(s):  
Thin Films ◽  
Phase Formation ◽  
Volume Fraction ◽  
Parent Phase ◽  
High Volume ◽  
Nucleation And Growth ◽  
High Coercivity ◽  
Nucleation And Growth Mechanism ◽  
Very High ◽  
Disorder Transition Temperature

ABSTRACTThe high magnetic anisotropy and high coercivity of equiatomic CoPt thin films make them attractive as potential materials for magnetic recording applications. Magnetic coercivity (Hc) over 10 kOe has been measured in films in which the as-deposited fee phase has been partially transformed to the atomically ordered Ll0 phase. Very high Hc has been related to high volume fraction and small size of the Ll0 precipitates. A better understanding of the Ll0 phase formation and quantification of volume fraction is critical to optimizing the magnetic properties of this material.As we have previously reported, an increase in Hc was observed with an increase in Ll0 volume fraction in 10 nm thick, equiatomic CoPt films. In our current investigation we have observed that, at anneal temperatures far from the order/disorder transition temperature, e.g. at T = 0.6 Tc, numerous, very fine Ll0 precipitates are seen, some of which cluster at the parent phase grain boundaries. At T = 0.85 Tc, very few, larger Ll0 regions were seen. As precipitates of the ordered phase grow to impingement, antiphase boundaries (APB) are formed. This is consistent with a heterogeneous nucleation and growth mechanism for the formation of the Ll0 phase throughout the temperature range studies.

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.

Electron-Beam-induced transformations in zirconia-alumina nanolaminates: An In situ high-resolution Electron–Microscopy study

1996 ◽  
Vol 54 ◽  
pp. 690-691
Author(s):  
M.A. Schofield ◽  
M. Gajdardziska-Josifovska ◽  
R. Whig ◽  
C.R. Aita
Keyword(s):  
Electron Microscopy ◽  
Electron Beam ◽  
High Resolution ◽  
Tetragonal Zirconia ◽  
High Resolution Electron Microscopy ◽  
Microscopy Study ◽  
Irradiation Condition ◽  
Transformation Toughening ◽  
Condenser Lens

Composite systems containing zirconia have been used extensively as transformation-toughening materials based on a stress induced martensitic transformation of the metastable tetragonal phase of zirconia to the monoclinic phase. Recently it has been shown that tetragonal zirconia can be stabilized in zirconia-alumina nanolaminates grown by reactive sputter deposition, when the zirconia layer is less than 6 nm thick. Cross-section high resolution transmission electron microscopy (HRTEM) of these nanolaminates revealed localized tetragonal-to-monoclinic transformation caused by sample preparation. In this study, quantitative HRTEM is used to analyze the zirconia nanocrystallite transformation in situ, by controlled exposure of the sample to the electron beam of the microscope.The irradiation conditions used in this study to induce the zirconia transformation are summarized in Table 1. The mildest irradiation condition corresponds to normal imaging illumination used in this study to obtain high resolution images. Under these normal illumination conditions, the first condenser lens (CI) is used to form a 0.1 μm sized probe which is over focused on the sample by the second condenser lens (C2).

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.

Morphology, Distribution and Identification of Micro-Constituents Along Grain Boundaries in Nickel-Base Alloys

1973 ◽  
Vol 31 ◽  
pp. 176-177
Author(s):  
D. E. Fornwalt ◽  
A. R. Geary ◽  
B. H. Kear
Keyword(s):  
Electron Microscope ◽  
Grain Boundaries ◽  
Volume Fraction ◽  
Rupture Life ◽  
Stress Rupture ◽  
High Volume ◽  
Precipitate Morphology ◽  
Stress Rupture Life ◽  
Nickel Base ◽  
Scanning Electron

A systematic study has been made of the effects of various heat treatments on the microstructures of several experimental high volume fraction γ’ precipitation hardened nickel-base alloys, after doping with ∼2 w/o Hf so as to improve the stress rupture life and ductility. The most significant microstructural chan§e brought about by prolonged aging at temperatures in the range 1600°-1900°F was the decoration of grain boundaries with precipitate particles.Precipitation along the grain boundaries was first detected by optical microscopy, but it was necessary to use the scanning electron microscope to reveal the details of the precipitate morphology. Figure 1(a) shows the grain boundary precipitates in relief, after partial dissolution of the surrounding γ + γ’ matrix.

HOT CORROSION OF CERIA-YTTRIA STABILIZED ZIRCONIA PLASMA SPRAYED THERMAL BARRIER COATING BY EUTECTIC VANDIUM PENTAOXIDE-SODIUM SULFATE

2018 ◽  
Vol 18 (1) ◽  
pp. 182-192 ◽  
Author(s):  
Mohammed J Kadhim ◽  
Mohammed H Hafiz ◽  
Maryam A Ali Bash
Keyword(s):  
Thermal Barrier Coating ◽  
Hot Corrosion ◽  
Monoclinic Phase ◽  
Volume Fraction ◽  
High Volume ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Plan View ◽  
Barrier Coating ◽  
Plasma Sprayed

The high temperature corrosion behavior of thermal barrier coating (TBC) systemconsisting of IN-738 LC superalloy substrate, air plasma sprayed Ni24.5Cr6Al0.4Y (wt%)bond coat and air plasma sprayed ZrO2-20 wt% ceria-3.6 wt% yttria (CYSZ) ceramic coatwere characterized. The upper surfaces of CYSZ covered with 30 mg/cm2 , mixed 45 wt%Na2SO4-55 wt% V2O5 salt were exposed at different temperatures from 800 to 1000 oC andinteraction times from 1 up to 8 h. The upper surface plan view of the coatings wereidentified for topography, roughness, chemical composition, phases and reaction productsusing scanning electron microscopy, energy dispersive spectroscopy, talysurf, and X-raydiffraction. XRD analyses of the plasma sprayed coatings after hot corrosion confirmed thephase transformation of nontransformable tetragonal (t') into monoclinic phase, presence ofYVO4 and CeVO4 products. Analysis of the hot corrosion CYSZ coating confirmed theformation of high volume fraction of YVO4, with low volume fractions of CeOV4 and CeO2.The formation of these compounds were combined with formation of monoclinic phase (m)from transformation of nontransformable tetragonal phase (t').

scholarly journals Face Grinding Surface Quality of High Volume Fraction SiCp/Al Composite Materials

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Xu Zhao ◽  
Yadong Gong ◽  
Guiqiang Liang ◽  
Ming Cai ◽  
Bing Han
Keyword(s):  
Friction Coefficient ◽  
Surface Morphology ◽  
Surface Quality ◽  
Volume Fraction ◽  
High Volume ◽  
Spindle Speed ◽  
High Volume Fraction ◽  
Machining Parameters ◽  
Al Composite

AbstractThe existing research on SiCp/Al composite machining mainly focuses on the machining parameters or surface morphology. However, the surface quality of SiCp/Al composites with a high volume fraction has not been extensively studied. In this study, 32 SiCp/Al specimens with a high volume fraction were prepared and their machining parameters measured. The surface quality of the specimens was then tested and the effect of the grinding parameters on the surface quality was analyzed. The grinding quality of the composite specimens was comprehensively analyzed taking the grinding force, friction coefficient, and roughness parameters as the evaluation standards. The best grinding parameters were obtained by analyzing the surface morphology. The results show that, a higher spindle speed should be chosen to obtain a better surface quality. The final surface quality is related to the friction coefficient, surface roughness, and fragmentation degree as well as the quantity and distribution of the defects. Lower feeding amount, lower grinding depth and appropriately higher spindle speed should be chosen to obtain better surface quality. Lower feeding amount, higher grinding depth and spindle speed should be chosen to balance grind efficiently and surface quality. This study proposes a systematic evaluation method, which can be used to guide the machining of SiCp/Al composites with a high volume fraction.

scholarly journals Study on the High-Speed Milling Performance of High-Volume Fraction SiCp/Al Composites

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4143
Author(s):  
Youzheng Cui ◽  
Shenrou Gao ◽  
Fengjuan Wang ◽  
Qingming Hu ◽  
Cheng Xu ◽  
...  
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Volume Fraction ◽  
Simulation Analysis ◽  
Cutting Temperature ◽  
High Volume ◽  
Cutting Parameters ◽  
High Volume Fraction ◽  
High Wear Resistance ◽  
Element Analysis

Compared with other materials, high-volume fraction aluminum-based silicon carbide composites (hereinafter referred to as SiCp/Al) have many advantages, including high strength, small change in the expansion coefficient due to temperature, high wear resistance, high corrosion resistance, high fatigue resistance, low density, good dimensional stability, and thermal conductivity. SiCp/Al composites have been widely used in aerospace, ordnance, transportation service, precision instruments, and in many other fields. In this study, the ABAQUS/explicit large-scale finite element analysis platform was used to simulate the milling process of SiCp/Al composites. By changing the parameters of the tool angle, milling depth, and milling speed, the influence of these parameters on the cutting force, cutting temperature, cutting stress, and cutting chips was studied. Optimization of the parameters was based on the above change rules to obtain the best processing combination of parameters. Then, the causes of surface machining defects, such as deep pits, shallow pits, and bulges, were simulated and discussed. Finally, the best cutting parameters obtained through simulation analysis was the tool rake angle γ0 = 5°, tool clearance angle α0 = 5°, corner radius r = 0.4 mm, milling depth ap = 50 mm, and milling speed vc= 300 m/min. The optimal combination of milling parameters provides a theoretical basis for subsequent cutting.

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