Creep Mechanisms in Niobium-Silicide Based In-Situ Composites

1998 ◽  
Vol 552 ◽  
Author(s):  
B. P. Bewlay ◽  
P. W. Whiting ◽  
A. W. Davis ◽  
C. L. Briant
Keyword(s):  
Creep Rate ◽  
Creep Behavior ◽  
Detrimental Effect ◽  
Higher Order ◽  
In Situ Composites ◽  
Niobium Silicide ◽  
Creep Mechanisms ◽  
Stress Levels ◽  
The Relationship

ABSTRACTThis paper will discuss the relationship between microstructure and creep behavior in hightemperature niobium-silicide based in-situ composites. The creep behavior of composites generated from binary Nb-Si alloys, and higher order alloys containing Mo, Hf and Ti additions, will be described. In-situ composites were tested in compression at temperatures up to 1200°C and stress levels in the range 70 to 280MPa. It was found that the Hf concentration can be increased to 7.5 with little increase in creep rate, over that for the binary Nb3Si-Nb composite, but at higher concentrations the creep rate is increased at stress levels higher than 21OMPa. At stresses less than 21OMPa the Ti concentration can be increased to 21 without a detrimental effect on creep performance, but at higher concentrations there is a substantial increase in the creep rate.

The Effect of Silicide Volume Fraction on the Creep Behavior of Nb-Silicide Based In-Situ Composites

2000 ◽  
Vol 646 ◽  
Author(s):  
B.P. Bewlay ◽  
C.L. Briant ◽  
A.W. Davis ◽  
M.R. Jackson
Keyword(s):  
High Temperature ◽  
Creep Rate ◽  
Creep Behavior ◽  
Volume Fraction ◽  
Phase Volume ◽  
In Situ Composites ◽  
Volume Fractions ◽  
Stress Levels

ABSTRACTThis paper will describe the creep behavior of high-temperature Nb-silicide in-situ composites based on quaternary Nb-Hf-Ti-Si alloys. The effect of volume fraction of silicide on creep behavior, and the effects of Hf and Ti additions, will be described. The composites were tested in compression at temperatures up to 1200°C and stress levels in the range 70 to 280 MPa. At high (Nb) phase volume fractions the creep behavior is controlled by deformation of the (Nb) and, as the volume fraction of silicide is increased, the creep rate is reduced. However, at large silicide volume fractions (>0.7) damage in the silicide begins to degrade the creep performance. The creep rate has a minimum at a volume fraction of ∼0.6 silicide. The creep performance of the monolithic and silicide phases will also be discussed.

Creep Mechanisms in High-Temperature In-Situ Composites

1999 ◽  
Author(s):  
Bernard P. Bewlay ◽  
Melvin R. Jackson ◽  
Clyde L. Briant
Keyword(s):  
High Temperature ◽  
In Situ Composites ◽  
Creep Mechanisms

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.

Niobium Silicide High Temperature In Situ Composites

2002 ◽  
pp. 541-560 ◽  
Author(s):  
B. P. Bewlay ◽  
M. R. Jackson ◽  
M. F. X. Gigliotti
Keyword(s):  
High Temperature ◽  
In Situ Composites ◽  
Niobium Silicide

Creep Behavior and Microstructures of Nb-26Ti-48Al Alloy and Composite

1994 ◽  
Vol 350 ◽  
Author(s):  
C. R. Feng ◽  
D. J. Michel
Keyword(s):  
Activation Energy ◽  
Creep Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Creep Testing ◽  
Combined Effects ◽  
Creep Mechanisms

AbstractThe creep behavior of Nb-26Ti-48Al alloy and its composite were investigated. After creep testing, precipitates were observed in the composite and mobile dislocations were found to be pinned by these precipitates. The combined effects of the reinforcements and the pinned dislocations were responsible for a reduced creep rate of the composite. The possible creep mechanisms were discussed based on the stress exponent and the activation energy of creep.

The effect of Hf and Ti additions on microstructure and properties of Cr2Nb–Nb in situ composites

1996 ◽  
Vol 11 (8) ◽  
pp. 1917-1922 ◽  
Author(s):  
B.P. Bewlay ◽  
M. R. Jackson
Keyword(s):  
Mechanical Properties ◽  
Tensile Properties ◽  
Laves Phase ◽  
Directionally Solidified ◽  
Two Phase ◽  
In Situ Composites ◽  
Niobium Silicide ◽  
Microstructure And Properties ◽  
Two Phases

The present paper describes the effect of Hf and Ti additions on the microstructures and mechanical properties of two-phase composites based on the Cr2Nb–Nb eutectic. The microstructures of directionally solidified in situ composites containing 50–70% by volume of the Laves phase Cr2Nb which was modified with Hf (7.5–9.2%) and Ti (16.5–26%) are described. Partitioning of Hf and Ti between the two phases is discussed using microprobe and EDS results. The tensile properties at 1100 and 1200 °C are described and compared with those of an analogous niobium silicide-based composite. The Cr2(Nb)–(Nb) composite tensile yield strengths at 1200 °C were increased over that of monolithic Cr2Nb to ∼130 MPa. However, at 1200 °C the yield strengths of the silicide-based composites were approximately twice those of the Cr2(Nb)–(Nb) composites.

Simulations of Creep in Ductile-Phase Toughened Nb5Si3/Nb In-Situ Composites

1994 ◽  
Vol 364 ◽  
Author(s):  
G. A. Henshall ◽  
M. J. Strum ◽  
P. R. Subramanian ◽  
M. G. Mendiratta
Keyword(s):  
Steady State ◽  
Creep Rate ◽  
Creep Behavior ◽  
Bulk Material ◽  
Continuous Phase ◽  
Primary Creep ◽  
Equation Model ◽  
Solid Solution Phase ◽  
Ductile Phase

AbstractThe primary and steady-state creep behavior of ductile-phase toughened Nb5Si3/Nb in-situ composites has been simulated using analytical and finite element (FE) continuum techniques. The microstructure of these composites is complex, consisting of large, elongated primary dendrites of the ductile (Nb) solid-solution phase in a eutectoid matrix with the silicide as the continuous phase. This microstructure has been idealized to facilitate the modeling; the effects of these idealizations on the predicted composite creep rates are discussed. Further, it has been assumed that the intrinsic creep behavior of each phase within the composite is the same as that of the corresponding bulk material. Thus, the experimentally measured creep properties of the bulk Nb5Si3 and (Nb) phases have been analyzed to provide the required material constants in the creep constitutive equation. Model predictions of the steady-state composite creep rate have been compared with the experimental results for a Nb-10 at.% Si alloy. While accurate at low stress, the models underpredict the composite creep rate at large stresses because the composite stress exponent is underpredicted. In the case of primary creep, the models somewhat over-predict the composite creep strain but are reasonably accurate given uncertainties in the primary creep data. Finally, FE predictions of the tensile stress distributions within the composites have been shown to be qualitatively consistent with the cracking observed experimentally during tertiary creep.

scholarly journals Creep behavior using Ti-TiB in situ composites.

2002 ◽  
Vol 14 (1/2) ◽  
pp. 57-58
Author(s):  
Kumi Endo ◽  
Jun-ichi MATSUSHITA ◽  
Kenshi KAWABATA ◽  
Eiichi SATO ◽  
Kazuhiko KURIBAYASHI
Keyword(s):  
Creep Behavior ◽  
In Situ Composites
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