Microstructure and High-Temperature Oxidation Behavior of Dy-Doped Nb-Si-Based Alloys

doi:10.1007/s40195-018-0701-0

Abstract

Abstract:

Microstructures and oxidation behaviors of four Dy-doped Nb-Si-based alloys at 1250 °C were investigated. The nominal compositions of the four alloys are Nb-15Si-24Ti-4Cr-2Al-2Hf-xDy (at.%), where x = 0, 0.05, 0.10 and 0.15, respectively. Results showed that the four alloys all consisted of Nbss, αNb₅Si₃ and γNb₅Si₃, and the addition of Dy produced no obvious effect on the phase constitution and the microstructures of Nb-Si-based alloys. After oxidation at 1250 °C for 58 h, it was found that the addition of Dy accelerated the oxidation rate of Nb-Si-based alloys and caused a larger weight gain, accompanied by the formation of a more porous and less protective oxide scale. The oxides of Nb₂O₅, Ti₂Nb₁₀O₂₉, TiNb₂O₇, Ti_0.4Cr_0.3Nb_0.3O₂ and glassy SiO₂ were formed on Dy-doped Nb-Si-based alloys. The high-temperature oxidation mechanism of Dy-doped Nb-Si-based alloys was discussed.

Key words: Nb-Si alloy, Intermetallics, Directional solidification, Oxidation, Microstructure

Yue-Ling Guo, Li-Na Jia, Hua-Rui Zhang, Bin Kong, Yong-Lin Huang, Hu Zhang. Microstructure and High-Temperature Oxidation Behavior of Dy-Doped Nb-Si-Based Alloys[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(7): 742-752.

Figures/Tables 12

Fig. 1 XRD patterns of Dy-doped Nb-Si-based alloys

Fig. 2 Microstructures of Dy-doped Nb-Si-based alloys: base alloy (a, b); 0.05Dy alloy (c, d); 0.10Dy alloy (e, f); 0.15Dy alloy (g, h). (a, c, e, g) are the vertical microstructures parallel to DS direction. (b, d, f, h) are the transversal microstructures perpendicular to DS direction

Table 1 Compositions of the main phases in the base alloy and the 0.15Dy alloy (at.%)

Specimen	Nb	Si	Ti	Cr	Al	Hf	Dy
Base alloy
Nbss	60.34	0.78	28.42	6.15	3.01	1.30	-
αNb₅Si₃	42.53	38.57	15.79	0.28	0.66	2.17	-
γNb₅Si₃	28.35	37.38	27.94	0.72	1.43	4.18	-
0.15Dy alloy
Nbss	60.28	0.49	28.52	6.48	2.96	1.27	-
αNb₅Si₃	42.77	38.67	15.50	0.22	0.66	2.18	0.01
γNb₅Si₃	26.93	37.92	28.91	0.74	1.26	4.24	0.03

Fig. 3 Weight gain versus time a and the square root of time b for Dy-doped Nb-Si-based alloys during oxidation at 1250 °C

Fig. 4 XRD patterns of the oxides grown on Dy-doped Nb-Si-based alloys after oxidation at 1250 °C for 58 h

Fig. 5 SEM morphologies of oxide scales grown on Dy-doped Nb-Si-based alloys after oxidation at 1250 °C for 58 h: a base alloy; b 0.05Dy alloy; c 0.10Dy alloy; d 0.15Dy alloy

Fig. 6 TEM images of the oxide scale grown on 0.15Dy-doped Nb-Si-based alloy after oxidation at 1250 °C for 58 h a, b and the typical selected-area diffraction of Ti0.4Cr0.3Nb0.3O2 c, Nb2O5 d, TiNb2O7 e and Ti2Nb10O29 f. The inset in b shows the typical selected-area diffraction pattern of SiO2

Table 2 Compositions of the oxides grown on 0.15Dy after oxidation at 1250 °C for 58 h (at.%)

	Crystal structure	Composition
	Crystal structure	O	Nb	Si	Ti	Cr	Al
SiO₂	Amorphous	66.76	-	33.24	-	-	-
Nb₂O₅	Monoclinic	62.44	29.21	-	8.35	-	-
TiNb₂O₇	Monoclinic	72.45	18.94	-	8.61	-	-
Ti₂Nb₁₀O₂₅	Monoclinic	57.76	31.45	-	10.79	-	-
Ti_0.4Cr_0.3Nb_0.3O₂	Tetragonal	49.93	14.90	-	24.71	10.46	-

Fig. 7 a Cross sections of the layer-structured oxide scale formed on 0.15Dy-doped Nb-Si-based alloy after oxidation at 1250 °C for 58 h. b The microstructure of the oxide scale at a high magnification

Fig. 8 Sectional microstructures of Dy-doped Nb-Si-based alloys after oxidation at 1250 °C for 58 h: a base alloy; b 0.05Dy alloy; c 0.10Dy alloy; d 0.15Dy alloy. a Displays the vertical microstructure parallel to DS direction. b, c, d show the transversal microstructures perpendicular to DS direction

Fig. 9 Elemental X-ray mapping of 0.15Dy-doped Nb-Si-based alloy after oxidation at 1250 °C for 58 h obtained using WDS attached with EPMA

Fig. 10 Ellingham-Richardson diagram illustrating the thermodynamic stability of selected oxides (plotted with HSC Chemistry 6.0)

References

[1]	T.M. Pollock, Nat. Mater. 15, 809(2016)
[2]	W. Liu, H. Xiong, N. Li, S. Guo, R. Qin, Acta Metall. Sin.(Engl. Lett.) (2018). https://doi.org/10.1007/s40195-017-0619-y
[3]	B.P. Bewlay, M.R. Jackson, P.R. Subramanian, J. Zhao, Metall.Mater. Trans. A 34, 2043 (2003)
[4]	Y.L. Guo, L.N. Jia, B. Kong, Y.L. Huang, H. Zhang, Acta Metall. Sin. (Engl. Lett.) (2018).
[5]	W. Liu, J.B. Sha, Mater. Des. 111, 301(2016)
[6]	B. Kong, L. Jia, L. Su, K. Guan, J. Weng, H. Zhang, Mater. Sci.Eng. A 639, 114 (2015)
[7]	J. Zhao, J.H. Westbrook, MRS Bull. 28, 622(2003)
[8]	S. Majumdar, J. Kishor, B. Paul, R.C. Hubli, J.K. Chakravartty,Corros. Sci. 95, 100(2015)
[9]	S. Mathieu, S. Knittel, P. Berthod, S. Mathieu, M. Vilasi, Corros.Sci. 60, 181(2012)
[10]	D. Yao, R. Cai, C. Zhou, J. Sha, H. Jiang, Corros. Sci. 51, 364(2009)
[11]	J. Zhang, L. Jia, J. Weng, L. Su, B. Kong, H. Zhang, Rare Met.(2016). https://doi.org/10.1007/s12598-016-0788-2
[12]	D. Yao, C. Zhou, J. Yang, H. Chen, Corros. Sci. 51, 2619(2009)
[13]	K.S. Chan, Metall. Mater. Trans. A 35, 589 (2004)
[14]	R.M. Dasary, S.K. Varma, J. Mater. Res. Technol. 3, 25(2014)
[15]	L. Su, L. Jia, J. Weng, Z. Hong, C. Zhou, H. Zhang, Corros. Sci.88, 460(2014)
[16]	W. Wang, C. Zhou, Corros. Sci. 110, 114(2016)
[17]	H. Lan, Z.G. Yang, Z.X. Xia, Y.D. Zhang, C. Zhang, Corros.Sci. 53, 1476(2011)
[18]	H. Guo, T. Zhang, S. Wang, S. Gong, Corros. Sci. 53, 2228(2011)
[19]	B.A. Pint, J. Am. Ceram. Soc. 86, 686(2003)
[20]	G. Zhang, H. Zhang, J. Guo, Surf. Coat. Technol. 201, 2270(2006)
[21]	Y.X. Tian, J.T. Guo, L.Z. Zhou, G.S. Li, H.Q. Ye, Acta Metall.Sin. 44, 589(2008). (in Chinese)
[22]	S. Yuan, L. Jia, L. Ma, R. Cui, L. Su, H. Zhang, Mater. Lett. 84,124(2012)
[23]	N. Birks, G.H. Meier, F.S. Pettit, Introduction to the High Temperature Oxidation of Metals (Cambridge University Press,Cambridge, 2006), pp. 3-5
[24]	X.M. Hou, K.C. Chou, J. Eur. Ceram. Soc. 29, 517(2009)
[25]	J. Zheng, X. Hou, X. Wang, Y. Meng, X. Zheng, L. Zheng,Corros. Sci. 96, 186(2015)
[26]	J. Geng, P. Tsakiropoulos, Intermetallics 15, 382 (2007)
[27]	H. Bakker, H.P. Bonzel, C.M. Bruff, M.A. Dayananda, W. Gust,J. Horvath, I. Kaur, G.V. Kidson, A.D. Berlin, 1990)
[28]	J.A. Dean, N.A. Lange, Michigan, 1992)
[29]	E.J. Felten, J. Less-Common Met. 17, 199(1969)
[30]	A.M. Samarin, Israel Prog. Sci. Trans. 95(1965)
[31]	W. Wang, C. Zhou, Corros. Sci. 74, 345(2013)
[32]	S. Zhang, X. Guo, Intermetallics 70, 33 (2016)
[33]	D.P. Whittle, J. Stringer, Philos. Trans. R. Soc. Lond A 295, 309(1980)
[34]	D. Li, L. Zhou, Y. Xi, L. Liu, Z. Liu, J. Si, K. Zhu, J. Alloys Compd. 692, 427(2017)
[35]	X.L. Li, S.M. He, X.T. Zhou, Y. Zou, Z.J. Li, A.G. Li, X.H. Yu,Mater. Charact. 95, 171(2014)
[36]	X. Wang, X. Peng, X. Tan, F. Wang, Sci. Rep. UK 6, 29593(2016)
[37]	E.J. Felten, J. Electrochem. Soc. 108, 490(1961)
[38]	H. Fujikawa, T. Morimoto, Y. Nishiyama, S.B. Newcomb, Oxid.Met. 59, 23(2003)
[39]	D. Li, H. Guo, D. Wang, T. Zhang, S. Gong, H. Xu, Corros. Sci.66, 125(2013)
[40]	F.A. Golightly, F.H. Stott, G.C. Wood, J. Electrochem. Soc. 126,1035(1979)
[41]	A. Vazquez, S.K. Varma, J. Alloys Compd. 509, 7027(2011)
[42]	V.K. Tolpygo, D.R. Clarke, High Temp. Technol. 17, 59(2014)
[43]	H. Zheng, S. Lu, Z. Jianye, L. Guangming, Int. J. Refract. Met.Hard Mater. 27, 659(2009)