Analyses of Eutectoid Phase Transformations in Nb–SilicideIn SituComposites

2004 ◽  
Vol 10 (4) ◽  
pp. 470-480 ◽  
Author(s):  
B.P. Bewlay ◽  
S.D. Sitzman ◽  
L.N. Brewer ◽  
M.R. Jackson
Keyword(s):  
Crystal Structure ◽  
Phase Transformation ◽  
High Temperature ◽  
Room Temperature ◽  
Bulk Composition ◽  
High Strength ◽  
Eutectoid Decomposition ◽  
Quaternary Alloys ◽  
Temperature Fracture

Nb–silicide in situ composites have great potential for high-temperature turbine applications. Nb–silicide composites consist of a ductile Nb-based solid solution together with high-strength silicides, such as Nb5Si3and Nb3Si. With the appropriate addition of alloying elements, such as Ti, Hf, Cr, and Al, it is possible to achieve a promising balance of room-temperature fracture toughness, high-temperature creep performance, and oxidation resistance. In Nb–silicide composites generated from metal-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. At high Ti concentrations, Nb3Si is stabilized to room temperature, and the eutectoid decomposition is suppressed. However, the effect of both Ti and Hf additions in quaternary alloys has not been investigated previously. The present article describes the discovery of a low-temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3possesses the hP16 crystal structure, as opposed to the tI32 crystal structure observed in binary Nb5Si3. The Ti and Hf concentrations were adjusted over the ranges of 21 to 33 (at.%) and 7.5 to 33 (at.%) to understand the effect of bulk composition on the phases present and the eutectoid phase transformation.

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.

Phase transformation in nanocrystalline Sm2Co17permanent magnet material

2009 ◽  
Vol 42 (4) ◽  
pp. 691-696 ◽  
Author(s):  
Xiaoyan Song ◽  
Nianduan Lu ◽  
Wenwu Xu ◽  
Zhexu Zhang ◽  
Jiuxing Zhang
Keyword(s):  
Crystal Structure ◽  
Phase Transformation ◽  
Room Temperature ◽  
Permanent Magnets ◽  
Temperature Phase ◽  
The Relationship ◽  
Magnetization Behavior ◽  
Annealing Experiments

Single-phase ultrafine nanocrystalline Sm2Co17, a candidate material for permanent magnets, was prepared by a novel simple route based on a home-built `oxygen-free'in situfabrication system. The as-prepared nanocrystalline Sm2Co17has the stable hexagonal Th2Ni17-type (2:17 H) crystal structure at room temperature, which is distinctly different from the conventional polycrystalline Sm2Co17having the rhombohedral Th2Zn17-type (2:17 R) crystal structure at room temperature. Phase transformations in the nanocrystalline Sm2Co17alloy were investigated systematically by a series of annealing experiments. It was found that, along with the nanograin growth in the heat-treatment process, the crystal structure of the room-temperature phase transforms from 2:17 H to 2:17 R. The magnetization behavior of Sm2Co17alloys in different structural states was characterized. The relationship between the magnetic performance and the structure characteristics was analyzed. Understanding the phase transformation of Sm2Co17nanocrystals facilitates the development of nanocrystalline Sm2Co17-type magnets for high-temperature applications.

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.

Effect of Mo Addition on Microstructure and Properties of Nb/Nb5Si3 In-Situ Composite

2004 ◽  
Vol 449-452 ◽  
pp. 753-756 ◽  
Author(s):  
Wei Li ◽  
Hai Bo Yang ◽  
Ai Dang Shan ◽  
Jian Sheng Wu
Keyword(s):  
Fracture Toughness ◽  
Room Temperature ◽  
Metastable Phase ◽  
High Strength ◽  
High Fracture Toughness ◽  
High Fracture ◽  
Ductile Phase ◽  
Temperature Fracture ◽  
The Stability

Nb/Nb5Si3 in-situ composites are very attractive structural materials for these materials perform a good balance in mechanical properties, including a high strength at high temperature (>1373K) and reasonably high fracture toughness at room temperature. Metastable phase Nb3Si plays an important role in the properties of Nb/Nb5Si3 composites by affecting microstructure and volume fracture of ductile phase. In this paper, Nb-10Si-xMo and Nb-18Si-xMo (x=0,5,15) are prepared by arc melting and annealed at 1473K for 100h. Single edge-notched bending (SENB) test was used to study the fracture toughness of Nb-Si-Mo alloys. The stability of metastable phase is analyzed by XRD. The room temperature fracture toughness of Nb-10Si is 10.47MPa(m)1/2 and higher than that of binary Nb-18Si alloys at near-eutectic compositions. The addition of Mo improves the fracture toughness of as cast Nb-Si alloys from 4.1 MPa(m)1/2 to 9.9MPa(m)1/2 at near-eutectic compositions and decreases it from 10.47 MPa(m)1/2 to 8.8MPa(m)1/2 at hypoeutectic compositions.

Effects of Re Alloying on Mechanical Properties of In-Situ Composites with Base Composition of Nb-18Si-2HfC

2006 ◽  
Vol 306-308 ◽  
pp. 941-946
Author(s):  
Sheng Wu Wang ◽  
Tatsuo Tabaru ◽  
Hisatoshi Hirai ◽  
Hideto Ueno
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
High Temperature ◽  
Base Composition ◽  
Room Temperature ◽  
High Temperature Strength ◽  
Strengthening Effect ◽  
In Situ Composites ◽  
Temperature Fracture

Nb-base in-situ composites with the base composition of Nb-18Si-2HfC were prepared by conventional arc-melting. Their microstructures and mechanical properties, such as high-temperature strength and room temperature fracture toughness, were investigated to elucidate the effects of Re alloying. The in-situ composites predominantly have eutectic microstructures consisting of an Nb solid solution (NbSS) and Nb5Si3. The compressive strength increased with the increasing Re contents at 1470K and not at 1670 K. The strengthening effect observed at 1470 K is higher than that by W and Mo. Re alloying of about 2 % is valuable for improving both the high temperature strength and room temperature fracture toughness of Nb-18Si-2HfC base materials.

Microstructure and Tensile Properties of 1-D Forged (TiB+TiC)/Ti Composite

2013 ◽  
Vol 747-748 ◽  
pp. 926-931 ◽  
Author(s):  
Chang Jiang Zhang ◽  
Fan Tao Kong ◽  
Shu Long Xiao ◽  
Li Juan Xu ◽  
Yuong Chen ◽  
...  
Keyword(s):  
High Temperature ◽  
Aspect Ratio ◽  
Grain Boundaries ◽  
Tensile Properties ◽  
Room Temperature ◽  
Fracture Mechanisms ◽  
Cast Composite ◽  
Temperature Fracture ◽  
Cast Microstructure

In this work, 2.5vol. % (TiB+TiC)/Ti composite was prepared by in situ casting route then 1-D forging. The microstructure and tensile properties were presented and discussed. The results indicate that the as cast microstructure can be significantly modified by 1-D forging. After forging, TiB and TiC segregated at the prior β grain boundaries within the as-cast composite tend to fracture and align perpendicular to forging direction. Reduction in aspect ratio of reinforcements and α lath is also observed. 1-D forging can enhance the strength and elongation of as cast composite significantly. However, the increment in strength is quite limited as strain temperature increases to 700 °C. Additionally, room temperature and high temperature fracture mechanisms are also discussed.

Single Crystal Growth of High-Pressure Phases of Ice and Salt Hydrate Far Below the Original Melting Point by Mixing Alcohol: Crystal Structure Determination of Magnesium Chloride Heptahydrate

2020 ◽  
Author(s):  
Keishiro Yamashita ◽  
Kazuki Komatsu ◽  
Hiroyuki Kagi
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Crystal Growth ◽  
Single Crystal ◽  
Room Temperature ◽  
Growth Technique ◽  
Salt Hydrate ◽  
X Ray

An crystal-growth technique for single crystal x-ray structure analysis of high-pressure forms of hydrogen-bonded crystals is proposed. We used alcohol mixture (methanol: ethanol = 4:1 in volumetric ratio), which is a widely used pressure transmitting medium, inhibiting the nucleation and growth of unwanted crystals. In this paper, two kinds of single crystals which have not been obtained using a conventional experimental technique were obtained using this technique: ice VI at 1.99 GPa and MgCl<sub>2</sub>·7H<sub>2</sub>O at 2.50 GPa at room temperature. Here we first report the crystal structure of MgCl2·7H2O. This technique simultaneously meets the requirement of hydrostaticity for high-pressure experiments and has feasibility for further in-situ measurements.

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