Microstructural Response of DS Nb-Silicide In-Situ Composites During High-Temperature Creep Testing

2000 ◽  
Vol 6 (S2) ◽  
pp. 376-377
Author(s):  
B.P. Bewlay ◽  
S.D. Sitzman
Keyword(s):  
High Temperature ◽  
Electron Backscatter Diffraction ◽  
Czochralski Method ◽  
Longitudinal Section ◽  
Creep Testing ◽  
Directionally Solidified ◽  
Creep Tests ◽  
In Situ Composites ◽  
Structural Applications

Directionally solidified (DS) in-situ composites based on (Nb) and Nb silicides, such as Nb5Si3 and Nb3Si, are being investigated for high-temperature structural applications. The use of alloying additions, such as Hf, Ti and Mo, to these silicides is required to enhance their properties. The present paper describes the microstructural response of a DS Nb-silicide based composite to creep testing.The composites investigated were directionally solidified from a molten alloy using the Czochralski method as described previously. Creep tests were conducted at 1200°C to strains of up 50%. Microstructure and microtexture characterizations were performed using scanning electron microscopy, electron microprobe analysis (EMPA), and electron backscatter diffraction pattern analysis (EBSP).Microstructures of the longitudinal section of a DS composite generated from a Nb-12.5Hf-33Ti- 16Si alloy are shown in Figure 1 in the as-DS (left hand side) and the DS+creep tested conditions (right hand side).

Creep Deformation Microstructures in DS Nb-Hf-Ti-Si In-Situ Composites

1999 ◽  
Vol 5 (S2) ◽  
pp. 258-259
Author(s):  
S.D. Sitzman ◽  
B.P. Bewlay
Keyword(s):  
Creep Deformation ◽  
Microprobe Analysis ◽  
Electron Backscatter Diffraction ◽  
Czochralski Method ◽  
Directionally Solidified ◽  
Creep Tests ◽  
In Situ Composites ◽  
Before And After ◽  
Backscatter Diffraction

Directionally solidified (DS) in-situ composites based on (Nb) and (Nb) silicides, such as Nb5Si3 and Nb3Si, are presently under investigation as high-temperature structural materials [1, 2]. Alloying additions of elements such as Hf, Ti and Mo to these silicides are also being explored. The present paper describes the microstructure of a DS Nb-silicide based composite before and after creep deformation.Alloys were prepared from high purity elements (>99.9%) using induction levitation melting in a segmented water-cooled copper crucible. The alloys were directionally solidified using the Czochralski method [2]. Creep tests were conducted at 1200°C to 50% deformation. Characterization was performed using scanning electron microscopy, electron microprobe analysis (EMPA), and electron backscatter diffraction pattern analysis (EBSP).

Analyses of The Eutectoid Phase Transformation in Complex Ds Nb-Silicide In-Situ Composites

2001 ◽  
Vol 7 (S2) ◽  
pp. 1244-1245
Author(s):  
S.D. Sitzman ◽  
B.P. Bewlay
Keyword(s):  
Crystal Structure ◽  
Pattern Analysis ◽  
Electron Backscatter Diffraction ◽  
Czochralski Method ◽  
Directionally Solidified ◽  
Two Phase ◽  
In Situ Composites ◽  
Structural Applications ◽  
Backscatter Diffraction

In-situ composites based on (Nb) and Nb silicides, such as Nb5Si3 (tI32 crystal structure) and Nb3Si (tP32 crystal structure), are being investigated for revolutionary high-temperature structural applications [1,2]. The use of Hf and Ti alloying additions to these silicides has also been examined; in these systems Nb5Si3 has also been observed with the hP16 structure. The present paper describes EBSD analyses of a directionally solidified (DS) Nb-silicide based composite that experienced a eutectoid transformation. The composites were directionally solidified using the Czochralski method as described previously [1]. The composites were creep tested at 1200°C for 24 hours. Microstructure and microtexture characterization were performed using scanning electron microscopy, and electron backscatter diffraction pattern analysis (EBSD).The microstructure of a composite directionally solidified from a Nb-12.5Hf-33Ti-16Si alloy is shown in Figure 1. in the as-DS condition the microstructure consisted of primary (Nb)3Si dendrites and coarse (Nb)3Si-(Nb) two-phase cells.

Microstructure and Microtexture in Nb-Silicide Based Composites

1998 ◽  
Vol 4 (S2) ◽  
pp. 278-279
Author(s):  
B.P. Bewlay ◽  
J.A. Sutliff
Keyword(s):  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Czochralski Method ◽  
Phase Identification ◽  
Directionally Solidified ◽  
In Situ Composites ◽  
Back Scattering ◽  
Niobium Silicides ◽  
Microstructure And Microtexture

Directionally solidified in-situ composites based on niobium and niobium silicides, such as Nb5Si3 and Nb3Si, are presently under investigation as structural materials [1, 2], Alloying additions of elements such as Hf, Ti and Mo to these silicides are also being explored in order to increase strength and oxidation resistance. The present paper describes the effect of Hf, Mo and Ti additions on microstructure and microtexture of high temperature silcide-based in-situ composites.Alloys were prepared from high purity elements (>99.9%) using induction levitation melting in a segmented water-cooled copper crucible. The alloys were directionally solidified using the Czochralski method [2], Phase identification was performed using scanning electron microscopy, electron microprobe analysis (EMPA), and automated electron back scattering pattern (EBSP) analysis. Using EBSP, positive phase identification was accomplished by direct comparison of the location and character of the diffraction bands in the experimental pattern with those calculated from simulated patterns generated using the possible structure types.

Ti-Modified Niobium-Silicide Based Directionally Solidified in-situ Composites

1996 ◽  
Vol 460 ◽  
Author(s):  
B. P. Bewlay ◽  
M. R. Jackson ◽  
H. A. Lipsitt
Keyword(s):  
Solid Solution ◽  
Fracture Toughness ◽  
High Temperature ◽  
Cold Crucible ◽  
Directionally Solidified ◽  
In Situ Composites ◽  
Czochralski Crystal Growth ◽  
Three Phase ◽  
Binary Eutectic

ABSTRACTThis paper examines microstructure-property relationships in high-temperature directionally solidified (DS) in-situ composites based on Nb silicides, such as Nb3Si and Nb5Si3. These in-situ composites are based on the Nb3Si-Nb binary eutectic, and are alloyed with Ti. They were prepared using cold crucible Czochralski crystal growth. Ternary Nb-Ti-Si alloys with Ti concentrations from 9 to 45%, and Si concentrations from 10 to 25%, were directionally solidified to generate aligned two- and three-phase composites containing a Nb solid solution with Nb3Si and Nb5Si3 silicides. Fracture toughness values generally greater than 10 MPa√m were measured in these composites. For a given Si concentration, the fracture toughness of the Ti-containing composites was increased ∼ 6 MPa√m over that of the binary alloy composites. The effects of Si concentration, and a range of Nb:Ti ratios, on microstructure, phase equilibria, and fracture toughness were examined.

Eutectoid Phase Transformations in Nb-Silicide In-Situ Composites

2002 ◽  
Vol 753 ◽  
Author(s):  
B. P. Bewlay ◽  
S. D. Sitzman ◽  
L. N. Brewer ◽  
M. R. Jackson
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Low Temperature ◽  
Phase Transformations ◽  
Oxidation Resistance ◽  
High Strength ◽  
Eutectoid Decomposition ◽  
In Situ Composites ◽  
Structural Applications

ABSTRACTNb-silicide based composites have excellent potential for future high-temperature structural applications. Nb-silicide composites possess Nb together with high-strength silicides, such as Nb5Si3 and Nb3Si. Alloying elements such as Ti and Hf, are added to obtain a balance of properties such as creep performance and oxidation resistance. In Nb-silicide composites generated from Nb-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. The present paper describes a low temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3 possesses the hP16 structure, as opposed to the tI32 structure observed in binary Nb5Si3.

The microstructure and crystallography of the Cr-Cr3Si eutectic

1991 ◽  
Vol 49 ◽  
pp. 598-599
Author(s):  
J.A. Sutlif ◽  
B.P. Bewlay ◽  
K.M. Chang ◽  
M.R. Jackson
Keyword(s):  
High Temperature ◽  
High Strength ◽  
Aircraft Engine ◽  
Microstructural Stability ◽  
Directionally Solidified ◽  
In Situ Composites ◽  
Interface Reactions ◽  
Engine Components ◽  
Directionally Solidified Eutectics

New materials for high temperature aircraft engine components should have a good combination of low density and high strength at temperatures as high as 1300-1500°C. This will probably require the use of composite materials. In-situ composites, or directionally solidified eutectics, are good candidates for this demanding application and have major advantages over alternative synthetic composites, such as MoSi2-SiC or carbon-carbon composites. The fabrication of components from eutectic castings is simpler and eutectic alloys offer some intrinsic microstructural stability with no reinforcement-matrix interface reactions at high temperatures. We are investigating the Cr-Si, Nb-Si and V-Si eutectic systems as potential high temperature in-situ composites. In this paper, we present results on the microstructure and crystallography of the Cr-Cr3Si eutectic which has a eutectic composition of ∼15 at% Si and a melting temperature of ∼1705 °C.

Effect of Cr Addition on the Phase Equilibria of the Nb-Si System

2006 ◽  
Vol 980 ◽  
Author(s):  
B. P. Bewlay ◽  
Y. Yang ◽  
R. L. Casey ◽  
M. R. Jackson ◽  
Y. A. Chang
Keyword(s):  
Experimental Data ◽  
High Temperature ◽  
Phase Equilibria ◽  
Thermodynamic Description ◽  
Directionally Solidified ◽  
Isothermal Sections ◽  
Environmental Properties ◽  
Structural Applications ◽  
Cr Addition

AbstractNb-silicide based in-situ composites are promising materials for future high-temperature structural applications. Nb-silicide composites are typically alloyed with Hf, Ti, Cr, and Al to provide a balance of mechanical and environmental properties. A thermodynamic description of the Nb-Cr-Si system has been developed previously in literature based on reported isothermal sections. According to the previously calculated phase diagrams, selected alloys were directionally solidified. The as-solidified microstructures could not be interpreted using the liquidus projection calculated from the existing thermodynamic descriptions. Therefore, an improved thermodynamic description was developed by incorporating the new experimental data.

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