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.

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).

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.

Creep Studies of Monolithic Phases in Nb-Silicide Based In-Situ Composites

2000 ◽  
Vol 646 ◽  
Author(s):  
B.P. Bewlay ◽  
C.L. Briant ◽  
E.T. Sylven ◽  
M.R. Jackson ◽  
G. Xiao
Keyword(s):  
Solid Solution ◽  
Creep Rate ◽  
Creep Resistance ◽  
High Strength ◽  
Aircraft Engine ◽  
Great Promise ◽  
In Situ Composites ◽  
Monolithic Phases ◽  
The Individual

ABSTRACTNb-silicide composites combine a ductile Nb-based solid solution with high-strength silicides, and they show great promise for aircraft engine applications. Previous work has shown that the silicide composition has an important effect on the creep rate. If the Nb:(Hf+Ti) ratio is reduced below ∼1.5, the creep rate increases significantly. This observation could be related to the type of silicide present in the material. To understand the effect of each phase on the composite creep resistance, the creep rates of selected monolithic phases were determined. To pursue this goal, monolithic alloys with compositions similar to the Nb-based solid solution and to the silicide phases, Laves, and T2 phases, were prepared. The creep rates were measured under compression at 1100 and 1200°C. The stress sensitivities of the creep rates of the monolithic phases were also determined. These results allow quantification of the load bearing capability of the individual phases in the Nb-silicide based in-situ composites.

The Effects of Substitutional Additions on Tensile Behavior of Nb-Silicide Based Composites

2004 ◽  
Vol 842 ◽  
Author(s):  
Laurent Cretegny ◽  
Bernard P. Bewlay ◽  
Ann M. Ritter ◽  
Melvin R. Jackson
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Room Temperature ◽  
High Strength ◽  
Aircraft Engine ◽  
Tensile Behavior ◽  
Strengthening Mechanisms ◽  
Temperature Capability ◽  
High Temperature Tensile

ABSTRACTNb-silicide based in-situ composites consist of a ductile Nb-based solid solution with high-strength silicides, and they show excellent promise for aircraft engine applications. The Nb-silicide controls the high-temperature tensile behavior of the composite, and the Nb solid solution controls the low and intermediate temperature capability. The aim of the present study was to understand the effects of substitutional elements on the room temperature tensile behavior and identify the principal microstructural features contributing to strengthening mechanisms.

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.

High-Temperature Instability of A Cr2Nb-Nb(Cr) Microlaminate Composite

1996 ◽  
Vol 54 ◽  
pp. 374-375
Author(s):  
M. Larsen ◽  
R.G. Rowe ◽  
D.W. Skelly
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
High Temperature ◽  
Elevated Temperatures ◽  
Aircraft Engine ◽  
Lattice Parameter ◽  
Microstructural Stability ◽  
Elevated Temperature Strength ◽  
Cross Sectional ◽  
Bcc Structure

Microlaminate composites consisting of alternating layers of a high temperature intermetallic compound for elevated temperature strength and a ductile refractory metal for toughening may have uses in aircraft engine turbines. Microstructural stability at elevated temperatures is a crucial requirement for these composites. A microlaminate composite consisting of alternating layers of Cr2Nb and Nb(Cr) was produced by vapor phase deposition. The stability of the layers at elevated temperatures was investigated by cross-sectional TEM.The as-deposited composite consists of layers of a Nb(Cr) solid solution with a composition in atomic percent of 91% Nb and 9% Cr. It has a bcc structure with highly elongated grains. Alternating with this Nb(Cr) layer is the Cr2Nb layer. However, this layer has deposited as a fine grain Cr(Nb) solid solution with a metastable bcc structure and a lattice parameter about half way between that of pure Nb and pure Cr. The atomic composition of this layer is 60% Cr and 40% Nb. The interface between the layers in the as-deposited condition appears very flat (figure 1). After a two hour, 1200 °C heat treatment, the metastable Cr(Nb) layer transforms to the Cr2Nb phase with the C15 cubic structure. Grain coarsening occurs in the Nb(Cr) layer and the interface between the layers roughen. The roughening of the interface is a prelude to an instability of the interface at higher heat treatment temperatures with perturbations of the Cr2Nb grains penetrating into the Nb(Cr) layer.

TIMETAL 829

Alloy Digest ◽  
2001 ◽  
Vol 50 (8) ◽  
Keyword(s):  
Fracture Toughness ◽  
Titanium Alloy ◽  
High Temperature ◽  
High Strength ◽  
Heat Treating ◽  
High Temperature Alloy ◽  
Turbine Engine ◽  
Major Application ◽  
Alpha Titanium ◽  
Engine Components

Abstract TIMETAL 829 is a Ti-5.5Al-3.5Sn-3Zr-1Nb-0.25Mo-0.3Si near-alpha titanium alloy that is weldable and has high strength and is a creep resistant high temperature alloy. The major application is as gas turbine engine components. This datasheet provides information on composition, physical properties, elasticity, and tensile properties as well as fracture toughness, creep, and fatigue. It also includes information on forming and heat treating. Filing Code: TI-118. Producer or source: Timet.

Processing high-temperature refractory-metal silicide in-situ composites

JOM ◽  
1999 ◽  
Vol 51 (4) ◽  
pp. 32-36 ◽  
Author(s):  
B. P. Bewlay ◽  
M. R. Jackson ◽  
P. R. Subramanian
Keyword(s):  
High Temperature ◽  
Refractory Metal ◽  
Metal Silicide ◽  
In Situ Composites
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