Crystallographic Orientation Evolution in NbSS-Nb5Si3 Eutectic Alloys by EBSD Analyses

2013 ◽  
Author(s):  
Y. L. Li ◽  
C. L. Ma ◽  
H. Zhang
Keyword(s):  
Growth Rate ◽  
Grain Size ◽  
Crystallographic Orientation ◽  
Intermetallic Phase ◽  
Eutectic Alloys ◽  
Directionally Solidified ◽  
Solidification Condition ◽  
In Situ Composites ◽  
Nb5si3 Phase

The progresses in high temperature materials encourage the development of turbine engine in terms of thrust and efficiency. Ni-based superalloys, which are predominant in elevated temperature application, have limited potential to raise serving temperature. In-situ composites, such as Cr-Cr3Si, NiAl-Cr and Nb-Nb5Si3 eutectic alloys, consisting of a ductile metallic phase and a hard intermetallic phase, are attractive candidates to replace Ni-based superalloys. The microstructure and mechanical properties of these in-situ composites are widely investigated. However, little work is focused on crystallography of in-situ composites, except for preferred growth direction and crystallographic orientation relationship. In this paper, Nb-Si-Mo-based alloys were fabricated by non-consumable arc melting, and then were directionally solidified in an optical floating zone (OFZ) melting furnace. The crystallographic orientation evolutions in Nb-Nb5Si3 eutectic alloy are studied by electron back-scattered diffraction (EBSD) analyses. First, the effect of solidification condition on crystallographic orientation is examined. The as-cast alloy displays cellular microstructure. The Nb phase shows different crystallographic orientations in different cells, while the Nb5Si3 phase shows similar crystallographic orientation in a number of cells. In directionally solidified alloys, when growth rate is 5mm/h without seed rod rotation, the grain sizes of Nb and Nb5Si3 are both several millimeter. As growth rate rises or seed rod rotates, the grain size of Nb decreases much more drastically than that of Nb5Si3. Thus, solidification condition is supposed to influence nucleation of the Nb phase rather than the Nb5Si3 phase. Second, the effect of annealing on crystallographic orientation is studied. The Nb5Si3 has three allotropic phases. The allotropic phase transformations occur through annealing, during which the Nb5Si3 grain size decreases.

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.

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).

Microstructure Evolution and Compression Properties of a Directionally Solidified Ni-24.8%Nb Hypereutectic Alloy

2010 ◽  
Vol 654-656 ◽  
pp. 1351-1354
Author(s):  
Shuang Ming Li ◽  
Bing Lun Jiang ◽  
Heng Zhi Fu
Keyword(s):  
Mechanical Properties ◽  
Microstructure Evolution ◽  
Growth Velocity ◽  
Thermal Gradient ◽  
Hypereutectic Alloy ◽  
Directionally Solidified ◽  
In Situ Composites ◽  
Compression Properties ◽  
Deformation Behaviors

At normal solidification conditions, in-situ composites of a Ni-24.8%Nb hypereutectic alloy can be produced at growth velocities below 5μm/s, with a thermal gradient of 180K/cm, and this low productivity remarkably restricts the application of this kind of in-situ composites. In this paper, we proposed an approach that employs an abrupt growth velocity to make the in-situ composites grow stably out of the coupled zone. In-situ composites of the Ni-24.8%Nb hypereutectic alloy were obtained at a growth velocity of 100μm/s and the productivity was greatly improved. This value is in the same order magnitude imposed on the single-crystal superalloys. The compression strengths were investigated on different microstructures involving the coupled eutectics and non-coupled eutectics. The results showed that the crack distribution and extension were mainly localized in primary Ni3Nb dendrites in the non-coupled eutectics, and that in-situ composites with the entirely coupled eutectics have improved mechanical properties and different deformation behaviors.

Effect of growth rate on microstructure and microstructure evolution of directionally solidified Nb-Si alloys

2008 ◽  
Vol 1128 ◽  
Author(s):  
Yoshihito Sekito ◽  
Seiji Miura ◽  
Kenji Ohkubo ◽  
Tetsuo Mohri ◽  
Norihito Sakaguchi ◽  
...  
Keyword(s):  
Growth Rate ◽  
Orientation Relationship ◽  
Microstructure Evolution ◽  
Crystallographic Orientation ◽  
Floating Zone ◽  
Directionally Solidified ◽  
Solidification Direction ◽  
Arc Melting ◽  
Heat Treated ◽  
Crystallographic Orientation Relationship

AbstractIn the present work, Nb-18.1Si-1.5Zr alloy rods are produced with a growth rate ranging from 1.5 to about 1500 mm/h using the optical floating zone (OFZ) furnace. A part of each specimen is heat-treated at 1650 oC for 100 h. The microstructure was observed using SEM and TEM and analyzed using EPMA and EBSD.Eutectic-cells are observed in as-grown specimens with a growth rate of 150 mm/h or higher. It is found by EBSD analysis that the solidification direction of Nb is along <113> and that of Nb3Si is along <001], and {112} of Nb and {110) of Nb3Si are parallel. The present crystallographic orientation relationship between Nb and Nb3Si is different from that found in previous reports by several researchers. It was also confirmed that the heat-treated microstructure in the specimen grown by OFZ with a growth rate of 150 mm/h is similar to that in the heattreated specimen prepared by arc-melting.

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).

Well-aligned in situ composites in directionally solidified Fe–Ni peritectic system

2006 ◽  
Vol 89 (23) ◽  
pp. 231918 ◽  
Author(s):  
Yanqing Su ◽  
Liangshun Luo ◽  
Xinzhong Li ◽  
Jingjie Guo ◽  
Huimin Yang ◽  
...  
Keyword(s):  
Directionally Solidified ◽  
In Situ Composites
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