RELATIONSHIP BETWEEN MECHANICAL PROPERTIES AND LAMELLAR ORIENTATION OF PST CRYSTALS IN Ti 45Al 8Nb ALLOY

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1 49 11 Vol.49 No È 11 Ç ² ACTA METALLURGICA SINICA Nov pp Ti 45Al 8Nb ± PST ² ¾ Á ¼ Í Æ Ç È Ì Ï Ç É (À Å ³ Í Å ÑĐ, À ) Â ± ³ÛØ ÉØ Ø À Ò Ti 45Al 8Nb (À µ, %) ºÔÙ Ýº½ (PST) Ý Ú, ± Å, ±Õ ÂÕ Ü À¼, Nb Ú ±. PST Ý ³ÛØ Ø, Ð ³ Ø Ú; ÛÍ ³ÛØ º ØÈ Ì 45, Ð ³ Ø Ú. 0 ÛØ PST Ý Ø ÒÅÆ, Ã 1296 MPa; 45 ÛØ PST Ý ¾ Å, ¾ ÅÌ 1.1%, ËØ Ò Å ØÌ 847 MPa. Nb ³, ÆÏÁÉ Ð ³ÁÅ, Ø Ò Ü Æ. TiAl Ô³Î º, PST Ý, ³ÛØ, Å Ä TG146.2 º A Ã (2013) RELATIONSHIP BETWEEN MECHANICAL PROPERTIES AND LAMELLAR ORIENTATION OF PST CRYSTALS IN Ti 45Al 8Nb ALLOY PENG Yingbo, CHEN Feng, WANG Minzhi, SU Xiang, CHEN Guang Engineering Research Center of Materials Behavior and Design, Ministry of Education, Nanjing University of Science and Technology, Nanjing Correspondent: CHEN Guang, professor, Tel: (025) , gchen@njust.edu.cn Supported by National Basic Research Program of China (No.2011CB605504) and 2012 State Key Laboratory for Advanced Metals and Materials Open Fund Project (No.2012 ZD01) Manuscript received , in revised form ABSTRACT Room temperature compression performance of polysynthetic twinned crystal (PST crystal) in Ti 45Al 8Nb (atomic fraction, %) alloys with different angles between lamellar orientation and uniaxial stress direction was studied. The causes of the fracture failure were investigated by the fracture surface and the effects of the Nb element on strengthening were also studied. It was found that when the lamellar orientation in the PST crystal was paralleled or vertical to the stress direction, shear deformation was vertical to lamellar interface, and when the angle of lamellar orientation to the stress direction was 45, the shear deformation was paralleled to lamellar interface. The yield strength of the 0 PST crystal was the maximum which was up to 1296 MPa. The PST crystal of 45 had the best compression plastic strain of approximately 1.1%, but its yield strength was the minimum of only 847 MPa. Nb element could refine lamellar structure and improve the room temperature yield strength significantly through increasing shear stress of dislocation motion and reducing the stacking fault energy. KEY WORDS TiAl intermetallics, polysynthetic twinned crystal (PST crystal), lamellar orientation, mechanical property TiAl Õ Ï» ³Õ ÓÐ µ, Ê»Õ 50%, * ËÖ Þ Æ Ö 2011CB ÉÒ ÐÔ³ ËÖ «ÔÖ 2012 ZD01 ß Ï : , Ï «: Ñ :, Á, 1985 É, DOI: /SP.J Ã» Æ Æ, Æ ÈÊ»Õ Ô µ [1 5]. ß TiAl»Õ Æ ÜÙ Đ Ñ. Ú Þ»¾Þ [6] (polysynthetic twinned crystal, PST crystal) Ù»Ü Ê³ÜÙ ß Þ, Æ γ Þ α 2 ¾, ³ Ç ¾, ÞÐ Ì, ß ÍÃ «Ê µ.

2 1458 Ò ² Å 49 Ø PST Þ [6 9] ßÑ, ÜÙ Đ Ù Á Ó (0 90 ), Ó Ñ Ð Ù». Î ÜÙ ĐÙ, PST Þ Ñ Ó, Ì «; Î ÜÙ Đ Ù, PST Þ Ó Ä ½µ, Ì Ó Á, Æ¾ Æ 5% 10%; Î ÜÙ ĐÙÉ Ì ËÃ, PST Þ Ù Ó, Ü PST Þ, ÕÕ Ä ½, ÎË ĐÙ ÜÙ, Ù Ó Æ¾Ä «Ê». Matsuo [10,11], Ti 48Al»ÕÊÞß ÜÙ ÌËĐÙ ÜÙ ÌËĐÙ¾ 45 Æ 3. Nb ³ TiAl»Õ Í ³È TiAl»Õ, Nb Ð¾Í² γ TiAl»ÕÓ³ ½»Õ ¼, Ti 48Al 2Cr 2Nb (Á, %, Á)»Õ [12] Ð ¾ 787, ÜÑ ĐÙ Ð Nb Ì Ti Al (5 10)Nb»Õ«. [13 17] ß Ñ,»Õ ¼ Nb Ì Ù Å TiAl»Õ Ã Ó, ÐÝ TiAl»Õ Æ Æ, Ò Nb ÌØ TiAl»Õ ²³. Ì Nb ³ TiAl»Õ PST Þ ÆĐ. ²Ø ÜÙ Ë ĐÙ Á Ó Ti 45Al 8Nb» Õ PST Þ Û Æ, ² Á ÜÙ Ö, Ã Æ Ã Nb Ø» Õ Æ Õ. 1 Ü ÓÅÍ % Ti, Al, Nb Õ Á µ,»õ¾ Û Î, Ì ÓÛ 10 3 Pa Æ ¼Ó»Õ, ¾ 4mm 100mm, ± Ö ¼ Á ÜÙ PST Þ. PST Þ ² ¾ Ð ÜÙ, SANSI cmt5504 ÊÆ (5 t), ÃÞ ÙË Ô PST ÊÞ ÑÜ, ÀÍ 2 mm 4 mm, ÐÍ s 1 ½¾Ø µû. Ó Ë ĐÙÅ ÙË»ĐÙ. ± PHLIPS XL30 ESEM Đ (SEM) Á Ö. ± SEM Ç Æµ (EDS) Ò¾ Ã Ç ¾ Í: Ti 44.26Al 8.65Nb. Æ 1 Í PST Þ ºÆ, ϕ Í PST Þ 1 Ù Ýº½ (PST) Ý ³ÛØ ØÈ ¹Å Fig.1 Sketch of geometry of polysynthetic twinned crystal (PST crystal) compression specimen (ϕ angle between the lamellar orientation and loading axis) ÜÙ ÙĐÙ É, Ì Ó ϕ Ü 0, À ¹ 2.1 PST ³ ½ Ø Á ÜÙ PST Þ Û, 1. Î ÜÙ ÌËĐÙ,»Õ Ö Ó Ù ÓÄ «, Í MPa, Ö Ó ÜÙÍ MPa, ÚÞß, Á Í 0.58%, 90 ÜÙ ß ÙÞ Ò ³. Î ÜÙ»ĐÙÉ Í 45, Í 1.1%, 0 ÜÙÏÌÆ 50%, Ì Ó«, Ù ÓÙÍ 847MPa. 90 ÜÙ Ö ÓÍ 1175MPa, Ä 0 ÜÙ, 45 ÜÙ, Ì ß ÙÞ ³ ÅÍ Ö,. Á ÜÙ PST Þ Æ Ì Æ Á Á ½, Î ±ÊÙ, Á ÜÙ PST Þ Ì». PST Þ ÅÍ Ñ, Î ÜÙ»ĐÙ, Ñ Ð ĐÙ Û; ÜÎ ÜÙ»ĐÙÉ Í 45, Ñ Ð ĐÙ Û., Î Ð ÈÌË, γ {111} Ñ ² Ð, ½, Ñ «² Þ Ð α 2 /γ Ð Ã α 2, ½Ü Æ; ÜÌ 45, γ {111} Ñ Ð, ½,

3 11 Ï : Ti 45Al 8Nb ¹Ó PST Ü ²Ú Ä 1459 Ð Ã α 2 Ø Ñ Ü Ñ, Û. È, 45 ÜÙ, ½ Í γ Ò ½µ Æ. ½, 0 90 ÜÙ Ù Ó, 45 ÜÙ Ù Ó«Ì µ. Õ ÜÙ PST Þ Æ, 90 ÜÙ PST Þ Ó, Ò. 45 ÜÙ PST Þ ÜÙ, Ì Ó½. ÜÙ»ĐÙ PST Þ ³ Á ² Ó, Ó»Æ½, ĐÍ Ü Ù»ĐÙ PST Þ «Ê Æ. 2.2 µ» Æ2a c Í ÜÙ ÌËĐÙÉ Í 0, Ö., Ö Ó Ñ² 2 Õ Ö Đ, Í Ö Ö. Æ 2a c Ó Ð, Ì Ú Æº, ÌË ß Ö, γ Æ, «ÔÆÑÖ, Ö ÎÖ Ï ß Ð Ð. Ñ ²² γ Ã α 2, Æ, Ù Ó. Æ 2b, Ö Í, Ñ ³, Ì ÆÚ ; ÌË Ì Ð ¾ ÁÓ,» Ð ½, Í¾Ö. Ð», Ù Ó. Æ 2d Íß ÙÞ Ö., Ö 4 Þ ¾, Ñ 2 Õ Ö Đ. Ó ³ Þ Ãß Ö, 3 Þ Ã Îß ² Ö. ²Å Þ ÌÒ¹ ÞÐ ± ¾ ÁÓ, ĐË ÏÌ, ÌÞÐ ß Þ Ö. Ú Þ ÌË Ò ß, Æ ÁÓ, ¾ ± ÞÐ ½Â, Å Æ Ò¹ Þ ß Þ Ö, ß ÙÞ ± µ Ù Ó. 1 Â µýú Ti 45Al 8Nb (Â, %) ¼Ö PST ß Ç Table 1 Room temperature compression properties of PST crystal with different lamellar orientations of Ti 45Al 8Nb (atomic fraction, %) alloys ϕ Ultimate stress, MPa Yield stress, MPa Strain, % Full lamellar equiaxed crystal ³ÛØ Ø À Ò PST Ý ÂÞ ³ ØÝ Õ Fig.2 SEM fractographs of PST crystals and full lamellar equiaxed crystal with different lamellar orientations (a) ϕ=0 (b) ϕ=45 (c) ϕ=90 (d) full lamellar equiaxed crystal

1460 Ò ² Å 49 Ì 0 90 ÜÙÖ Ó, Ñ Ñ² B2 Ò, Æ 3 Ó Ä. Ì²Æ β Ò ¼ Nb, ÌË Ó Đ Ó, ß β α, Ò ² Ó Nb Ã ÅÈ Ü ¾ β Ò, ºÌÞ Ã ¾ β, Í β ÒÓ Nb Ü Al, 2. B2 ÒÍ Ò [18], Æ 3a Ó, B2 Ò, ÌË B2 Ò ß, ÜÙß, Ó. 2.3 Nb ½ ± Ti 45Al 8Nb»Õ Á Ü Ù PST Þ Ù Ó«Í 847 MPa, «Î Ä 1296 MPa, Æ 4.

$3 Partial SEM fractographs of PST crystals (a) ϕ=0 (b) ϕ=90 2 EDS β (B2 Ó) Table 2 Compositions of β segregation (B2 phase) by EDS analysis Element Mass fraction, % Atomic fraction, % Al 13.56 24.$

4 1460 Ò ² Å 49 Ì 0 90 ÜÙÖ Ó, Ñ Ñ² B2 Ò, Æ 3 Ó Ä. Ì²Æ β Ò ¼ Nb, ÌË Ó Đ Ó, ß β α, Ò ² Ó Nb Ã ÅÈ Ü ¾ β Ò, ºÌÞ Ã ¾ β, Í β ÒÓ Nb Ü Al, 2. B2 ÒÍ Ò [18], Æ 3a Ó, B2 Ò, ÌË B2 Ò ß, ÜÙß, Ó. 2.3 Nb ½ ± Ti 45Al 8Nb»Õ Á Ü Ù PST Þ Ù Ó«Í 847 MPa, «Î Ä 1296 MPa, Æ 4., Ý»Õ Ti 49.3Al [6] Ò, ÓÐÝ. ½, Nb ³ TiAl» ÕÒØÃ»Õ ¹½Æ Ó«Å²»Õ Ó. [19,20], Î 5% 10% (Á, Á) Nb Ì TiAl»ÕÓ, ÐÝ Ý, ³ (5% 10%)Nb TiAl»Õ Ù Ó¼ ² 800 MPa, Ð TiAl ß»Õ Ú. 3 PST Ý Õ Fig.3 Partial SEM fractographs of PST crystals (a) ϕ=0 (b) ϕ=90 2 EDS β (B2 Ó) Table 2 Compositions of β segregation (B2 phase) by EDS analysis Element Mass fraction, % Atomic fraction, % Al Ti Nb Yield stress, MPa Ti-45-8Nb alloy Ti-49.3Al alloy [6] Lamellar orientation, deg 4 Ti 45Al 8Nb ºÔ Ti 49.3Al [6] ºÔ PST Ý Ø Ò Fig.4 Room temperature compression yield stress in Ti 45Al 8Nb and Ti 49.3Al [6] alloys PST crystals Nb Ý»Õ. Nb ÌÐ Ý ²»Õ, Ï ¹Û, Ó½.»ÕÓ ÕÐ Ó½, ÞÐ Â, Ø»Õ Ó, Nb ³ TiAl»Õ Ù Ó Á½³. Ì ÂÐ Đ, TiAl»Õ Ì 1/2[110], 1/2[112] [011]3Õ Â, Æ ÂÍÛ, [011] ¼ Â¹ Í 1/2[112] ÂÌÀ, È Þ. Ý TiAl»Õ 1/2[110] Â, Þ Ì ½Âß. Nb ³ TiAl»ÕÓ Nb Ì, Þ ÆÆ ¼ Â Ð, ÜÒ [011] ¼ Â 1/2[112] ÂÌÀ 1/2[112] ÂÒØ 1/2[110] Â Æ (Æ 30%), 1/2[110] ÂÉ ¾ Ð Ñ Ä260MPa, Ü³ Ý»Õ MPa, Nb TiAl»Õ Ó Ì ²»Õ 1/2[110] ÂÊÐ Ñ ² ÂÆ. 3 ¹ (1) PST Þ Æ ÜÙ Đ Ñ : ÜÙ ĐÙ, PST Þ Đ Ó 1296 MPa, Á 0.58%, ÜÙ PST Þ Ò, Ó Ä «Ê». (2) Nb, µ, TiAl»Õ 1/2[110] ÂÊÐ Ñ, ÂÆ,»Õ Ù Ó. (3) Ti 45Al 8Nb ÊÞ PST 2 Õ Ö Đ : Ö Ö. Ó 45 ÜÙ Ö,» Û, Ó ; 0 90 ÜÙÍ Ö, Æ, Ó.

5 11 Ï : Ti 45Al 8Nb ¹Ó PST Ü ²Ú Ä 1461 [1] Kear B H, Thompson E R. Science, 1980; 208: 847 [2] Taub A I, Fleischer R L. Science, 1989; 243: 616 [3] Malinov S, Sha W. Mater Sci Eng, 2004; A365: 202 [4] Cui W F, Liu C M, Bauer V, Christ H J. Intermetallics, 2007; 15: 675 [5] Lapin J. Intermetallics, 2006; 14: 115 [6] Fujiwara T, Nakamura A, Hosomia M, Nishitani S R, Shirai Y, Yamaguchi M. Philos Mag, 1990; 61A: 591 [7] Inui H, Nakamura A, Yamaguchi M. Acta Metall, 1992; 40: 3059 [8] Yokoshima S, Yamaguchi M. Acta Mater, 1996; 44: 873 [9] Fu H Z, Guo J J, Su Y Q, Liu L, Xu D M, Li J S. Chin J Nonferrous Met, 2003; 13: 797 (,,» Ô,», Ã, Ô. Ò Ô ³ «, 2003; 13: 797) [10] Matsuo T, Nozaki T, Asai T, Chang S Y, Takeyama M. Intermetallics, 1998; 6: 695 [11] Matsuo T, Nozaki T, Takeyama M. Mater Sci Eng, 2002; A : 774 [12] Huang H C. US Pat , 1989 [13] Zhang W J, Chen G L, Wang Y D, Sun Z Q. Scr Mater, 1993; 28: 1113 [14] Chen G L, Zhang W J, Liu Z C, Li S J, Kim Y W. In: Kim Y W, Dimiduk D M, Loretto M H eds., Gamma Titanium Aluminides Warrendale, PA: TMS, 1999: 371 [15] Liu Z C, Lin J P, Li S J, Chen G L. Intermetallics, 2002; 10: 653 [16] Zhang W J, Liu Z C, Chen G L, Kim Y W. Mater Sci Eng, 1999; A271: 416 [17] Chen G L, Zhang L C. Mater Sci Eng, 2002; A329: 163 [18] Chen G L, Xu X J, Teng Z K, Wang Y L, Lin J P. Intermetallics, 2007; 15: 625 [19] Paul J H, Appel F, Wagner R. Acta Mater, 1998; 46: 1075 [20] Zhang W J, Deevia S C, Chen G L. Intermetallics, 2002; 10: 403 ( ÎÅË: Ê)

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