The Role of Glassy Grain Boundary Phases in the Microwave Joining of Alumina

1994 ◽  
Vol 347 ◽  
Author(s):  
Pamela Davis ◽  
Jon Binner ◽  
Tom Cross ◽  
John Fernie
Keyword(s):  
Dielectric Loss ◽  
Grain Boundary ◽  
Resonant Cavity ◽  
Single Mode ◽  
Alumina Ceramic ◽  
Boundary Phase ◽  
Alumina Ceramics ◽  
Axial Pressure ◽  
Individual Grains

ABSTRACTThe role of intergranular glassy phases in the microwave joining of alumina ceramic rods has been investigated. Alumina ceramics of different purities have been examined using a TE102 single mode rectangular resonant cavity operating at 2.45 GHz. Temperature and axial pressure were varied and the resultant join microstructures analyzed. The presence of a glassy grain boundary phase has been shown to improve the ability to microwave join alumina ceramics by increasing the dielectric loss of the ceramic and, when softened, by enabling the alumina grains to flow under the imposed load. Evidence has also been found for the sintering of individual grains where they have come into contact across the join line.

Electrical Conductivity and Structure of Nanocrystalline CeO2 Thin Films

1996 ◽  
Vol 453 ◽  
Author(s):  
Igor Kosacki ◽  
Harlan U. Anderson
Keyword(s):  
Thin Films ◽  
Electrical Conductivity ◽  
Electrical Properties ◽  
Grain Boundary ◽  
Dominant Role ◽  
Boundary Phase ◽  
Electrical Measurements

AbstractThe results of structural and electrical measurements of nanocrystalline CeO2 thin films are presented. A correlation between the electrical conductivity and microstructure has been observed and discussed. The electrical properties of nanocrystalline CeO2 thin films are attributed to a dominant role of grain boundary phase.

scholarly journals The Effect of Grain Boundary Carbides on Dynamic Recrystallization During Hot Compression of Ni-Based Superalloy Haynes $$282^{\mathrm{TM}}$$

2021 ◽  
Author(s):  
Emil Eriksson ◽  
Joel Andersson ◽  
Magnus Hörnqvist Colliander
Keyword(s):  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Hot Compression ◽  
Boundary Phase ◽  
Stress Evolution ◽  
Critical Limit ◽  
Final Microstructure ◽  
Thermomechanical Processes ◽  
Base Superalloy

AbstractIn alloys where carbides are the main grain boundary phase, the role of carbides during hot working is not known. Here, we address the effect of grain boundary carbides on the dynamic recrystallization during hot compression of Ni-base superalloy Haynes 282. When excluding variations from experimental factors neither stress evolution nor final microstructure indicated that carbides exerted a significant influence on the dynamic recrystallization. The carbide solvus temperature is not a critical limit during thermomechanical processes.

The role of interfaces in the creep-deformation of a Sic whisker-reinforced Si3N4 composite

1990 ◽  
Vol 48 (4) ◽  
pp. 382-383
Author(s):  
K.L. More ◽  
D.A. Koester ◽  
R.F. Davis
Keyword(s):  
Grain Boundary ◽  
Nitrogen Atmosphere ◽  
Boundary Phase ◽  
Sintering Aids ◽  
X Ray Diffraction ◽  
High Temperature Mechanical Properties ◽  
Reinforced Composite ◽  
Linear Behavior ◽  
Transmission Electron

The high temperature mechanical properties of a SiC whisker-reinforced composite are currently being investigated. The deformation characteristics of the composite are controlled not only by the distribution of the constituent phases, but also by the interfaces between phases. The material is a hot pressed 30 vol.% SiC whisker-reinforced Si3N4 containing sintering aids of 1.5 wt.% A12O3 and 6.0 wt.% Y2O3. Constant compressive stress creep experiments were conducted in a continuously purified 0.11 MPa nitrogen atmosphere in a system described elsewhere. This work focussed on two creep experiments conducted at temperatures of 1470 K and 1620 K, both in the stress range 50-350 MPa. Figure 1 shows the stress exponent, n, for creep of the composite at both 1470 K and 1620 K. At 1620 K, n exhibited a bi-linear behavior. However, this behavior was not observed for creep at 1470 K.In the as-hot pressed state, the composite had an amorphous grain boundary phase containing N, O, Al, Si, and Y as determined by energy dispersive spectroscopy. Prior to loading, the specimens were annealed for 4 hr at the creep temperature. During the anneal, the grain boundary phase crystallized and underwent a change in composition as determined by X-ray diffraction and transmission electron microscopy (TEM).

The effect of grain boundary phase on contact damage resistance of alumina ceramics

2004 ◽  
Vol 39 (23) ◽  
pp. 7023-7030 ◽  
Author(s):  
Jae Hun Kim ◽  
Shiwoo Lee ◽  
Kee Sung Lee ◽  
Do Kyung Kim
Keyword(s):  
Grain Boundary ◽  
Boundary Phase ◽  
Alumina Ceramics ◽  
Contact Damage ◽  
Damage Resistance

Strain-induced martensite effects on transgranular carbide precipitation in type 304 stainless steels

1991 ◽  
Vol 49 ◽  
pp. 604-605
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D. Matlock
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Stress Corrosion Cracking ◽  
Stainless Steels ◽  
Deformation Twin ◽  
Austenitic Stainless Steels ◽  
Carbide Precipitation ◽  
Strain Induced Martensite ◽  
Type 304

Thermomechanically induced strain is a key variable producing accelerated carbide precipitation, sensitization and stress corrosion cracking in austenitic stainless steels (SS). Recent work has indicated that higher levels of strain (above 20%) also produce transgranular (TG) carbide precipitation and corrosion simultaneous with the grain boundary phenomenon in 316 SS. Transgranular precipitates were noted to form primarily on deformation twin-fault planes and their intersections in 316 SS.Briant has indicated that TG precipitation in 316 SS is significantly different from 304 SS due to the formation of strain-induced martensite on 304 SS, though an understanding of the role of martensite on the process has not been developed. This study is concerned with evaluating the effects of strain and strain-induced martensite on TG carbide precipitation in 304 SS. The study was performed on samples of a 0.051%C-304 SS deformed to 33% followed by heat treatment at 670°C for 1 h.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

Characterization of intergranular cuprous oxide in polycrystalline YBa2Cu3O7-x

1988 ◽  
Vol 46 ◽  
pp. 880-881
Author(s):  
Bradley L. Thiel ◽  
Chan Han R. P. ◽  
Kurosky L. C. Hutter ◽  
I. A. Aksay ◽  
Mehmet Sarikaya
Keyword(s):  
Grain Boundary ◽  
Cuprous Oxide ◽  
Room Temperature ◽  
Boundary Phase ◽  
Spectroscopic Techniques ◽  
Transition Width ◽  
Practical Applications ◽  
Thin Foils ◽  
Superconducting Oxides

The identification of extraneous phases is important in understanding of high Tc superconducting oxides. The spectroscopic techniques commonly used in determining the origin of superconductivity (such as RAMAN, XPS, AES, and EXAFS) are surface-sensitive. Hence a grain boundary phase several nanometers thick could produce irrelevant spectroscopic results and cause erroneous conclusions. The intergranular phases present a major technological consideration for practical applications. In this communication we report the identification of a Cu2O grain boundary phase which forms during the sintering of YBa2Cu3O7-x (1:2:3 compound).Samples are prepared using a mixture of Y2O3. CuO, and BaO2 powders dispersed in ethanol for complete mixing. The pellets pressed at 20,000 psi are heated to 950°C at a rate of 5°C per min, held for 1 hr, and cooled at 1°C per min to room temperature. The samples show a Tc of 91K with a transition width of 2K. In order to prevent damage, a low temperature stage is used in milling to prepare thin foils which are then observed, using a liquid nitrogen holder, in a Philips 430T at 300 kV.

On the role of tin underlays for the prevention of thermal grooving in thin gold films

1986 ◽  
Vol 44 ◽  
pp. 732-733
Author(s):  
Jin Young Kim ◽  
R. E. Hummel ◽  
R. T. DeHoff
Keyword(s):  
Thin Film ◽  
Free Surface ◽  
Grain Boundary ◽  
Beneficial Effect ◽  
Failure Mechanism ◽  
Failure Mechanisms ◽  
Distinct Advantage ◽  
Gold Films ◽  
Gold Thin Film

Gold thin film metallizations in microelectronic circuits have a distinct advantage over those consisting of aluminum because they are less susceptible to electromigration. When electromigration is no longer the principal failure mechanism, other failure mechanisms caused by d.c. stressing might become important. In gold thin-film metallizations, grain boundary grooving is the principal failure mechanism.Previous studies have shown that grain boundary grooving in gold films can be prevented by an indium underlay between the substrate and gold. The beneficial effect of the In/Au composite film is mainly due to roughening of the surface of the gold films, redistribution of indium on the gold films and formation of In2O3 on the free surface and along the grain boundaries of the gold films during air annealing.

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