Abstract：Directionally solidified specimens of Nb-Ti-Si based ultrahigh temperature alloy with the withdrawing rates of 2.5μm/s and 50μm/s were homogenized at 1250, 1350℃ and 1400℃ for 50h, respectively. The constituent phases were Nbss, β(Nb,X)5Si3 and γ(Nb,X)5Si3. The needle-like precipitates of Cr2(Nb,Ti) appeared in the specimens directionally solidified at the withdrawing rate of 2.5μm/s after homogenizing treatments, and its amount increased with the homogenizing temperatures. After homogenizing treatments, the straight boundaries and sharp edges of the primary hexagonal silicides became smooth, the fine silicides in the center of the eutectic cells became spheroidzed, and some silicide blocks in the eutectic cells broke into small ones. The transformation from β(Nb,X)5Si3 to α(Nb,X)5Si3 did not occur during the homogenizing treatments. After homogenizing treatments, the microhardness of the alloy increased remarkably, and its value first increased and then decreased with the increasing of the homogenizing temperatures. The maximum value of microhardness of the constitute phases occurred in the specimens homogenized at 1350℃ for 50h.
胡永强, 郭喜平, 郭海生. 热处理对定向凝固Nb-Ti-Si基超高温合金组织及显微硬度的影响[J]. 材料工程, 2013, 0(6): 5-11.
HU Yong-qiang, GUO Xi-ping, GUO Hai-sheng. Effects of Heat Treatments on the Microstructure and Microhardness of Directionally Solidified Nb-Ti-Si Based Ultrahigh Temperature Alloy. Journal of Materials Engineering, 2013, 0(6): 5-11.
GUO X P, GAO L M, GUAN P. Microstructure and mechanical properties of an advanced niobium based ultrahigh temperature alloy [J]. Materials Science Forum,2007,539-543:3690-3695.
GUO H S, GUO X P. Microstructure evolution and room temperature fracture toughness of an integrally directionally solidified Nb-Ti-Si based ultrahigh temperature alloy [J]. Scripta Materialia, 2011, 64(7): 637-640.
CHAN K S, DAVIDSON D L. Improving the fracture toughness of constituent phases and Nb-based in-situ composites by a computational alloy design approach [J]. Metallurgical and Materials Transactions A, 2003, 34(9): 1833-1849.
TEWARI R, SONG H, DEY G K, et al. Microstructural evolution in niobium based alloys [J]. Metallurgical and Materials Transactions A, 2008, 39(7): 1506-1518.
BEWLAY B P, JACKSON M R, ZHAO J C, et al. A review of very-high temperature Nb-silicide-based composites [J]. Metallurgical and Materials Transactions A, 2003, 34(10): 2043-2052.
BEWLAY B P, JACKSON M R, LIPSITT H A. The balance of mechanical and environmental properties of a multielement niobium-niobium silicide-based in situ composite [J]. Metallurgical and Materials Transactions A, 1996, 27(12): 3801-3808.
SHA J B, HIRAI H, TABARU T, et al. Mechanical properties of as-cast and directionally solidified Nb-Mo-W-Ti-Si in-situ composites at high temperatures [J]. Metallurgical and Materials Transactions A, 2003, 34(1): 85-94.
贾丽娜, 郭喜平. 合金化和热处理对难熔金属硅化物基合金组织和性能影响的研究现状[J].稀有金属材料与工程, 2007, 36(7): 1304-1308.JIA Li-na, GUO Xi-ping. Effects of alloying elements and heat treatments on the microstructure and mechanical properties of refractory metal silicide-based alloys [J]. Rare Metal Materials and Engineering, 2007, 36(7): 1304-1308.
GUO H S, GUO X P. Microstructure and microhardness of directionally solidified and heat-treated Nb-Ti-Si based ultrahigh temperature alloy [J]. Transactions of Nonferrous Metals Society of China, 2011, 21(6): 1283-1290.
MENDIRATTA M G, DIMIDUK D M. Phase relations and transformation kinetics in the high Nb region of the Nb-Si system [J]. Scripta Metallurgica, 1991, 25(1): 237-242.
王勇, 郭喜平, 张超峰,等. 电弧熔炼Nb-Ti-Si合金的组织和室温力学性能[J].特种铸造及有色合金, 2010, 30(6): 556-561. WANG Yong, GUO Xi-ping, ZHANG Chao-feng, et al. Microstructure and ambient mechanical properties of Nb-Ti-Si based alloy prepared by consumable arc melting [J]. Special Casting and Nonferrous Alloys, 2010, 30(6): 556-561.
ZELENITSAS K, TSAKIROPOULOS P. Study of the role of Al and Cr additions in the microstructure of Nb-Ti-Si in situ compositions [J]. Intermetallics, 2005, 13(10): 1079-1095.
ZELENITSAS K, TSAKIROPOULOS P. Effect of Al, Cr and Ta additions on the oxidation behaviour of Nb-Ti-Si in situ composites at 800℃ [J]. Materials Science and Engineering A, 2006, 416(1-2): 269-280.
TEWARI R, SONG H K, VASUDEVAN V K, et al. Microstructural characterization of multicomponent Nb-Ti-Si-Cr-Al-X alloys [J]. Metallurgical and Materials Transactions A, 2006, 37(9): 2669-2682.
MURRAY J L. The Cr-Ti (chromium-titanium) system [J]. Journal of Phase Equilibria, 1981, 2(2): 174-181.
VENKATRAMAN M, NEUMANN J P. The Cr-Nb (chromium-niobium) system [J]. Journal of Phase Equilibria, 1986, 7(5): 462-466.
OKAMOTO H. Cr-Si (chromium-silicon) [J]. Journal of Phase Equilibria, 1997, 18(2): 222.