Effects of Dy on the Microstructure and Hardness of NiAl Alloys

Abstract:

Intermetallic compound NiAl is considered as a potential candidate material for bond coat in thermal barrier coating (TBC) system due to its capability of forming a continuous and uniform alumina scale at temperatures even high than 1200 °C, but its cyclic oxidation is rather poor. Previous study has found that cyclic oxidation resistance of NiAl alloys and coatings can be drastically improved by minor Dy doping as reactive element. In this paper, NiAlDy alloys were produced by vacuum arc-melting and the effects of various Dy contents on the microstructure and hardness of NiAl alloys were investigated. The results suggest that Dy tends to segregate at grain boundaries and precipitate within grains as brittle DyNi₂Al₃ phase with little DyNiAl needles in it. The addition of minor Dy resulted in grain refinement. The grain size of NiAl alloy were reduced from ~1 mm to ~300 µm, with increasing the content of Dy to 0.5 at.%. The addition of ~0.1 at.% Dy caused a 10 % improvement in both the microhardness and macrohardness due to Dy solid-solution and grain-boundary segregation, but the alloy revealed decreased microhardness and macrohardness with further increasing the content of Dy to 0.5 at.% as the formation of Dy-rich phase.

• Periodical: Materials Science Forum (Volumes 747-748)
• Pages: 788-796
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.747-748.788
• Online since: February 2013
• Authors: Zhi Yang Zhang, Hong Bo Guo, Hui Peng, Sheng Kai Gong, Hui Bin Xu
• Keywords: Dysprosium (Dy), Macrohardness, Microhardness, NiAl, Reactive Elements, Strengthening

References

[1] R. Sivakumar, B.L. Mordike, High temperature coatings for gas turbine blades: a review, Surf. Coat. Technol. 37 (1989) 139–160.

DOI: 10.1016/0257-8972(89)90099-6

[2] I. Baker, A review of the mechanical properties of B2 compounds, Mater. Sci. Eng. A 192/193 (1995) 1–13.

[3] D.B. Miracle, The physics and mechanical properties of NiAl, Acta Metall. Mater. 41 (1993) 649–684.

[4] Zhiming Bai, Dongqing Li, Hui Peng, Juan Wang, Hongbo Guo, Shengkai Gong, Suppressing the formation of SRZ in a Ni-based single crystal superalloy by RuNiAl diffusion barrier, Progress in Natural Science: Materials International, 22 (2012).

DOI: 10.1016/j.pnsc.2012.03.007

[5] Jing Wu, Hongbo Guo, Musharaf Abbas, Shengkai Gong, Evaluation of plasma sprayed YSZ thermal barrier coatings with the CMAS deposits infiltration using impedance spectroscopy, Progress in Natural Science: Materials International, 22 (2012) 40-47.

DOI: 10.1016/j.pnsc.2011.12.007

[6] H.B. Guo, X.Y. Wang, J. Li, S.X. Wang, S.K. Gong, Effects of Dy on cyclic oxidation resistance of NiAl alloy, Trans. Nonferrous Met. Soc. China 19 (5) (2009) 925–930.

DOI: 10.1016/s1003-6326(08)60426-4

[7] H.B. Guo, S.X. Wang, X.Y. Wang, S.K. Gong, Cyclic oxidation behaviour of EB-PVD Dy doped β-NiAl coatings at 1100℃, Int. J. Mod. Phys. B 24 (2010) 3143–3148.

DOI: 10.1142/s0217979210066227

[8] H.B. Guo, L.D. Sun, H.F. Li, S.K. Gong, High-temperature oxidation behaviour of hafnium modified NiAl bond coat in EB-PVD thermal barrier coating system, Thin Solid Films 516 (2008) 5732–5735.

DOI: 10.1016/j.tsf.2007.07.031

[9] Noebe RD, Bowman PR, Nathal MV. Physical and mechanical properties of the B2 compound NiAl, International Materials Reviews 38 (1993) 193-232.

DOI: 10.1179/imr.1993.38.4.193

[10] Miracle DB, The physical and mechanical properties of NiAl, Acta Metall. Mater. 41 (1993) 649-684.

[11] Rablbauer R, Fischer R, Frommeyer G, Mechanical properties of NiAl-Cr alloys in relation to microstructure and atomic defects, Z. Metallkd 95 (2004) 525-534.

DOI: 10.1515/ijmr-2004-0103

[12] Frommeyer G, Fischer R, Deges J, Rablbaur R, Schneider A, APFIM investigations on site occupancies of the ternary alloying elements Cr, Fe, and Re in NiAl, Ultramicroscopy 101 (2004) 139-148.

DOI: 10.1016/j.ultramic.2004.05.006

[13] J.T. Guo, K.W. Huai, Q. Gao, W.L. Ren, G.S. Li, Effects of rare earth elements on the microstructure and mechanical properties of NiAl-based eutectic alloy, Intermetallics 15 (2007) 727-733.

DOI: 10.1016/j.intermet.2006.10.020

[14] Hongbo Guo, Dongqing Li, Hui Peng, Yongjing Cui, Shengkai Gong. High-temperature oxidation and hot-corrosion behavior of EB-PVD β-NiAlDy coatings, Corrosion Science 53 (2011) 1050–1059.

DOI: 10.1016/j.corsci.2010.11.041

[15] Dongqing Li, Hui Peng, Xiaoyu Zhao, Hongbo Guo, Shengkai Gong, Cyclic Oxidation Behavior of β-NiAlDy Alloys Containing Varying Aluminum Content at 1200 °C, Progress in Natural Science: Materials International, in press.

DOI: 10.1016/j.pnsc.2012.06.003

[16] George EP, Liu CT, Brittle fracture and grain boundary chemistry of microalloyed NiAl, J Mater Res 5 (1990) 754-762.

DOI: 10.1557/jmr.1990.0754

[17] Guo JT, Ordered intermetallic compound NiAl alloy, Beijing: Science Press, (2003).

[18] C.L. Briant. On the chemistry of grain boundary segregation and grain boundary fracture. Metall Trans. A 21 (1990) 2339-2354.

DOI: 10.1007/bf02646981

[19] Fox A G, Tabbernor M A, The bonding charge density of NiAl, Acta Metal. Mater. 39 (1991) 669-678.

DOI: 10.1016/0956-7151(91)90135-n

[20] Hirth J P, Rice J R, On the thermodynamics of adsorption at interfaces as it influence decohesion, Metall Trans. 295 (1980) 139-149.

[21] White C L, Padagett R A, Liu C T, Surface and grain boundary segregation in relation to intergranular fracture: Born and sulfur in Ni3Al. Script. Metall. 18 (1984) 1417-1420.

DOI: 10.1016/0036-9748(84)90377-6

[22] Ren WL, Guo JT, Li GS, Zhou JY, Effect of Nd on microstructure and mechanical properties of NiAl-based intermetallic alloy, Materials Letters 57 (8) (2003) 1374-1379.

DOI: 10.1016/s0167-577x(02)00990-4