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Intermetallic Compounds

Intermetallic Compounds

Ö. N. Dog˘an, X. Song, D. Palacio, M. C. Gao (2014). Coherent precipitation in a high-temperature Cr–Ni–Al–Ti Alloy, J Mater. Sci., 49, 805-810.

$A bright field TEM image from a Cr solid solution grain and selected area diffraction patterns from the matrix and precipitates. The sample was heat treated at 1400 °C for 4 h and at 1200 °C for 4 h followed by furnace cool$

Developing more efficient fossil energy conversion technologies with less environmental impact require high-performance structural materials of long-term reliability that can be used in aggressive environments. Next generation gas turbines combusting hydrogen-rich fuels and oxy-fuels are predicted to have inlet temperatures higher than the current gas turbines. The current gas turbines utilize state-of-the-art nickel-based superalloys in the hottest sections. These materials possess excellent creep strength because they contain high volume fraction of γ’ precipitates coherent with the γ matrix and excellent high-temperature oxidation resistance due to ability to form protective oxide scales on the surface. However, these alloys perform at their temperature capability limit, and there is not much room left for improvement since the application temperatures are already very near their melting points. Chromium alloys present a potential for development of new high-temperature materials. Precipitation characteristics of a Cr–5Ni–5Al–0.5Ti (at.%) alloy were investigated utilizing a series of heat treatments. XRD, SEM, and analytical TEM were used to characterize the microstructure. This study has shown that the small spherical B2-NiAl precipitates forming below 1345 °C are highly coherent and have a well-defined orientation relationship with the Cr-matrix. Also, some evidence has been presented for the formation of L21-Ni2AlTi phase within the B2-NiAl phase.

Ö. N. Doğan, S. Chen, X. Song, J. Sears (2011). Structurally modulated precipitates in a refractory Cr–V alloy , Journal of Alloys and Compounds, 509(23), 6556-6560.

TEM bright field images of intragranular (a) and intergranular (b) precipitates.

$Diffraction pattern indicating the spots that correspond to the first and second level of modulations.$ HRTEM image showing the first and second level modulations as well as the fcc structure in the orthorhombic C20Cr25V55. (a) HRTEM image taken from C–Cr–V phase, (b) Magnified image of the smaller framed area in (a), (c) Fourier transformation of the larger framed area in (a), and (d) Fourier transformation of the imaged area in (b)

HRTEM image showing the first and second level modulations as well as the fcc structure in the orthorhombic C20Cr25V55. (a) HRTEM image taken from C–Cr–V phase, (b) Magnified image of the smaller framed area in (a), (c) Fourier transformation of the larger framed area in (a), and (d) Fourier transformation of the imaged area in (b)

Ö. N. Doğan, X. Song, S. Chen, M. C. Gao (2013). Microstructural study of high-temperature Cr–Ni–Al–Ti alloys supported by first-principles calculations , Intermetallics, 35, 33-40.

$Diffraction contrast images and selected area electron diffraction patterns from the NiTi-rich precipitates (a), and the interface between the matrix and the precipitates (b) in Alloy A$

X. Song, Y. Chen, C. Sequeira, Y. Lei, Q. Wang, Z. Zhang (2003). Microstructure evolution of bcc structure related Ti-Zr-Ni phases in non-stoichiometric Zr-based Zr-Ti-Mn-V-Ni hydride electrode alloys , Journal of Materials Research, 18, 37-44.

$Left figure: Diffraction patterns for the P* phase in the B2-type (TiZr)Ni phase matrix from the [100] and [111] directions. Right figure: Oblate spindle-like P phase, indicated by capital letter B, precipitated in the B2-type (TiZr)Ni phase matrix$

X. Song, Z. Zhang, X. Zhang, Y. Lei, and Q. Wang (1999). Effect of Ti substitution on the microstructure and electrochemical properties of Zr-Mn-V-Ni system alloys , J . Materials Research, 14, 1279-1285.

Composite EDP’s of Ti0.8Zr0.2Ni phase in the alloy Zr0.5Ti0.5(Mn0.1V0.3Ni0.6)2

Y. Chen, C. Sequeira, X. Song, C. Chen (2006). Effect of amorphous transformation on the electrochemical capacity of Rare-earth Mg-based Alloys, Z. Phys. Chem, 220, 631-639.

SEM surface morphology of ball-milled CeMg 11 Ni + x wt.% Ni composites. (a) x = 0, (b) x = 50, (c) x = 100, and (d) x = 200.

Y. Chen, C. Sequeira, X. Song, R. Neto, Q. Wang (2002). Polytypism of La-Ni phases in multicomponent $A B_{5}$ type hydride electrode alloys, International Journal of Hydrogen Energy, 27 (1), 63-68.

Morphology and interface structure of CaCu5 matrix and the polytypes. The matrix is indicated by letter B and the polytypes are indicated by letter A. The dislocations existing at interface is indicated by arrow

X. Song, Y. Chen, Z. Zhang, Y.Q. Lei, X.B. Zhang, Q.D. Wang (2000). Microstructure and electrochemical properties of Ti-containing $A B_{2}$ type hydrogen storage electrode alloy, International Journal of Hydrogen Energy, 25, 649-656.

Morphology and substructure of C14 and C15 Laves phase in Zr(MnVNi)2 alloy: (A) stacking faults of C15 Laves phase; (B) C14 Laves phase

X. Song, X. Zhang, Y. Lei, Z. Zhang, Q. Wang (1999). Effect of microstructure on the electrochemical properties of Zr-Mn-V-Ni system $A B_{2}$ type hydride electrode alloys, International Journal of Hydrogen Energy, 24, 455 - 459.

$Composite electron difraction patterns of <0-109> C14 and <009> C15$

Lu G., Chen L., Hu X., Gu J., Shu K., Song X., Lei Y., Wang Q. (1999). Acta. Metall. Sinica (in Chinese), 35, 453.

X. Zhang, X. Yang, X. Song, Y. Lei, Q. Wang, Z. Zhang (1999). TEM investigation of $Z r O_{2}$ in $Z r (N i_{0.55} V_{x} M n_{0.45 - x})_{2}$ Hydrogen Storage Alloys, Journal of Alloys and Compounds, 293, 101-106.

The typical microstructure of ZrNiVMn hydrogen storage alloys showing C15, C14 Laves phases and Zr9Ni11 coexist as indicated by A, C and B respectively (a), and zirconia particles were found in the alloys (b)

G. Lu, K. Shu, L. Chen, X. Song, X. Yang, Y. Lei, Q. Wang (1999). Structure study on rapidly solidified hydrogen storage alloy $Z r (N i M)_{2.1}$ , Journal of Alloys and Compounds, 293, 107.

TEM images of rapidly solidified alloys showing the presence of two different morphological regions, lamellar and homogeneous

X. Song, X. Zhang, Y. Lei, Z. Zhang and Q. Wang (1998), Correlation between the microstructure and electrochemical properties of Zr-based $A B_{2}$ type hydride electrode alloys, Acta Metallurgica Sinica (in Chinese), 34, 977.