Microstructure and High-Temperature Strength of Directionally Solidified Al2O3/YAG/ZrO2 Eutectic Composite

A2O3/YAG/ZrO2 eutectic Melt-Growth-Composites (MGCs) were unidirectionally solidified by the modified-pulling-down method (MPD) and the Bridgman type method, in which a crucible was brought down at different speeds. The microstructures and crystallographic textures were studied by field emission scanning electron microscopy (FE-SEM) and electron backscattered pattern (EBSP) method. The high-temperature strength was investigated by compression tests. All MGC rods show strong preferred growing orientation, although the structural size of eutectic microstructure among MGC rods was different. The high-temperature strength of MGC rods is dependent on orientation, compression temperature and strain rate. The high-temperature strength of MGC rods is controlled by the anisotropic strength of constituent Al2O3, as well as the structural size of eutectic microstructure.

Download Full-text

Microstructure and Properties of Directionally Solidified NbSi2/ Nb5Si3 Composites

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.733 ◽

2005 ◽

Vol 475-479 ◽

pp. 733-736 ◽

Cited By ~ 2

Author(s):

Wei Li ◽

Hai Bo Yang ◽

Ai Dang Shan ◽

Lan Ting Zhang ◽

Jian Sheng Wu

Keyword(s):

High Temperature ◽

High Temperature Strength ◽

Directionally Solidified ◽

Zone Method ◽

Phase Constitution ◽

Good Oxidation Resistance ◽

Transmission Electron ◽

Complex Crystal Structure ◽

Electron Microscopes ◽

Scanning Electron Microscopes

NbSi2 is an attractive material for high temperature applications due to its high melting point, low density and good oxidation resistance. The high-temperature strength of NbSi2 is expected to be further improved by incorporation with Nb5Si3, which performs a high creep resistance and strength at high temperature due to its complex crystal structure. In this paper, directionally solidified NbSi2/ Nb5Si3 in-situ composites have been prepared using an optical floating zone method. Scanning Electron Microscopes (SEM) and X-ray diffraction (XRD) have been used to investigate the phase constitution and microstructure. The orientation relationship between Nb5Si3 and NbSi2 is investigated by transmission electron microscopy (TEM). High-temperature properties of alloys are tested by compression at the strain rate of 1×10-4/s at 1673K and 1773K. It was found that high temperature strength and phase constitution of directionally solidified alloys depended on the addition of Mo.

Download Full-text

Material Evaluation of Large Single Crystal and Directionally Solidified Bucket Castings for Advanced Land-Based Gas Turbines

Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; IGTI Scholar Award ◽

10.1115/95-gt-449 ◽

1995 ◽

Cited By ~ 2

Author(s):

H. Yamamoto ◽

M. Yamamoto ◽

K. Imai ◽

M. Miyazaki ◽

M. Satoh ◽

...

Keyword(s):

High Temperature ◽

Single Crystal ◽

Gas Turbines ◽

Low Cycle Fatigue ◽

Stress Rupture ◽

Inlet Temperature ◽

High Temperature Strength ◽

Directionally Solidified ◽

Large Single Crystal ◽

Molding Process

The development of large single crystal and directionally solidified hollow and solid bucket castings has been carried out for the high performance advanced land-based gas turbine of 1500°c class turbine inlet temperature, using CMSX-2 single crystal and CM247LC directionally solidified alloys*. The castability for large single crystal bucket casting has been established by optimizing the casting parameters and bucket shape in order to prevent the grain defects which tend to be formed more easily for larger casting size and are most harmful for high temperature strength of single crystal. These casting processes were successsfully applied to larger directionally solidified buckets with additional modified molding process. The developed large single crystal hollow and solid bucket castings after solution and optimized aging treatment indicated excellent microstructure and high temperature mechanical properties such as stress rupture and low cycle fatigue strength. Also, long-term phase stability of both alloys at intermediate temperatures has been verified.

Download Full-text

Spatial Distribution of Crystallographic Orientational Variants in Yag-Al2O3 Directionally Solidified Eutectic Composite

Microscopy and Microanalysis ◽

10.1017/s1431927600037235 ◽

2000 ◽

Vol 6 (S2) ◽

pp. 948-949

Author(s):

Colleen S. Frazer ◽

Elizabth C. Dickey

Keyword(s):

Spatial Distribution ◽

Incident Angle ◽

Fiber Axis ◽

Chinese Script ◽

Great Promise ◽

High Temperature Strength ◽

Eutectic Composite ◽

Directionally Solidified ◽

Orientation Relationships ◽

Diamond Saw

YAG-A12O3 directionally solidified eutectic composites show great promise in applications requiring high temperature strength and creep resistance.’ The orientation relationships between YAG and Al2O3 have been established within the composite by use of SEM Electron Backscatter Diffraction (EBSD) and x-ray diffraction (XRD). The orientation relationships of were determined. Two related variants of A12O3 were discovered in the sample. EBSD was employed to determine the spatial distribution of the variants within the sample.The microstructure of the eutectic composite, shown in Figure 1, reflects a “chinese script” pattern, neither lamellar nor fibrous. The directionally solidified eutectic fibers, approximately 2.5 mm in diameter, were cut into disks normal to the fiber axis by a diamond saw and polished by with diamond-imbedded paper to reduce chances of phase-preferential wear. Samples used for EBSD were ion milled for 30 minutes at low power and incident angle to improve the patterns.

Download Full-text

Effect of Growth Rate on Microstructure and Mechanical Properties of the Directionally Solidified Nb-Si Eutectic Alloy

MRS Proceedings ◽

10.1557/proc-753-bb5.25 ◽

2002 ◽

Vol 753 ◽

Cited By ~ 1

Author(s):

Nobuaki Sekido ◽

Yoshisato Kimura ◽

Yoshinao Mishima

Keyword(s):

Mechanical Properties ◽

Fracture Toughness ◽

Growth Rate ◽

High Temperature ◽

Eutectic Alloy ◽

Unidirectional Solidification ◽

High Temperature Strength ◽

Directionally Solidified ◽

System A ◽

Superior Mechanical Properties

ABSTRACTThe development of ultra-high temperature structural materials having superior mechanical properties to the nickel based superalloys has been pursued in the niobium silicide based composites. The unidirectional solidification technique was performed on the (Nb)/Nb3Si eutectic alloy in the Nb-Si binary system. A continuity of Nb phases in the eutectic microstructure increases with decreasing a growth rate, which yields the enhancement of fracture toughness as well as high temperature strength. The mechanisms of microstructural formation, toughening, and strengthening are briefly discussed.

Download Full-text

Microstructure and High Temperature Strength Characteristics of Unidirectionally Solidified Al2 O3 /GdAlO3 Eutectic Composite

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.317-318.437 ◽

2006 ◽

Vol 317-318 ◽

pp. 437-440 ◽

Cited By ~ 4

Author(s):

Hideki Ohtsubo ◽

Narihito Nakagawa ◽

Kazutoshi Shimizu ◽

Koji Shibata ◽

Atsuyuki Mitani ◽

...

Keyword(s):

Plastic Deformation ◽

High Temperature ◽

Temperature Gradient ◽

Flexural Strength ◽

Mechanical Strength ◽

Unidirectional Solidification ◽

Strength Characteristics ◽

High Temperature Strength ◽

Flexural Test ◽

Eutectic Composite

Enploying unidirectional solidification, Al2O3/GdAlO3(Gadolinium Aluminum Perovskite:GAP) eutectic composite was fabricated. The Al2O3/GAP eutectic composite obtained has a flexural strength of over 600Mpa above 1500C. The composite also showed plastic deformation above 1550C on the flexural test. The effect of microstructure on mechanical strength at high temperature was investigated. Al2O3/GAP eutectic composites having different microstructure were fabricated by controlling the temperature gradient on unidirectional solidification. It was found that the flexural strength at high temperature of the composite became higher with refining the microstructure.

Download Full-text