DISCONTINUOUS YIELDING BEHAVIOR OF β PHASE CONTAINING TiAl ALLOY DURING HIGH TEMPERATURE DEFORMATION PROCESS

49 11 Vol.49 No.11 213 Ò 11 Æ 1339 1346 ACTA METALLURGICA SINICA Nov. 213 pp.1339 1346 Ó β TiAl ÕÚÐÅ Æ ß Đ ³ ( Ú ² ÆÀ  ÀĐ² À«, Ú 151) ÐÉË ½ ÆÄ Ë, Ç À β Ti 42Al 9V.3Y Æ, À ¹. Ç, β Ti 42Al 9V.3Y Í β ÐÑ γ ÐÑ, Æ β ÐÑ γ ½Å (Burgers b=1/2 112 ) º». ß Orowan Ý ÅÂÐ Á º Æ ¹, ² ºÐÅÂ Ò ½ Ò Å ÒÒ m ÝÝ TiAl. ÆÒ (11 115 ) Ò Ê (1 s 1 ) ¹ Ð ßÅ ÂË Ì ÈÏÖ. ÑØ TiAl,, ÐÑ Í, ½ÅÂ, Orowan ÝÔ TG146.2 «A «Ô 412 1961(213)11 1339 8 DISCONTINUOUS YIELDING BEHAVIOR OF β PHASE CONTAINING TiAl ALLOY DURING HIGH TEMPERATURE DEFORMATION PROCESS XU Wenchen, SHAN Debin, ZHANG Hao School of Materials Science and Engineering, Harbin Institute of Technogloy, Harbin 151 Correspondent: XU Wenchen, associate professor, Tel: 1864544122, E-mail: xuwc 76@hit.edu.cn Supported by Youth Science and Technology Project of Harbin City (No.28RFQXG4) Manuscript received 213 8 2, in revised form 213 8 24 ABSTRACT γ TiAl base alloys are promising high temperature materials for aviation and aerospace applications due to their low density, exceptional high temperature strength and good oxidation resistance. However, low ductility and poor hot workability limit the use of such alloys. The introduction of β phase appears to be effective to improve the hot workability of TiAl alloys, while the influence of β phase on hot deformation behavior of TiAl alloy has been rarely investigated until now. In this work, high temperature compression experiments of β phase containing TiAl alloy (Ti 42Al 9V.3Y) were conducted on a Gleeble 15 thermal simulation machine at 1 12 and strain rates of.1 1. s 1. The hot deformation behavior of the TiAl alloy was investigated and the discontinuous yielding mechanism was analyzed. The results show that the main deformation softening mechanism was the dynamic recovery(drv) of β phase and dynamic recrystallization(drx) of γ phase. The discontinuous yielding behavior was closely related to the DRV in β phase and the multiplication of the superdislocation with Burgers vector b=1/2 112 in γ phase. The established dislocation dynamics model based on the Orowan equation in the present work could reasonably explain the causes for the discontinuous yielding phenomenon, indicating that the rapid increase of mobile dislocation density and small dislocation motion velocity sensitivity m could induce the discontinuous yielding of the TiAl alloy. In addition, the fluctuating yielding behavior was attributed to the interaction effect of dislocation slip and twin at lower temperatures of 11 115 and higher strain rate of 1 s 1. KEY WORDS TiAl alloy, discontinuous yielding, dynamic softening, superdislocation, Orowan equation * Û ÈÅÓ¹Á Ç ³ 28RFQXG4 ËÏ Đ : 213 8 2, ËÏ Đ : 213 8 24 Ï Ö«:,, 1976 Ó, Í DOI: 1.3724/SP.J.137.213.47

134 Î 49 TiAl À ÛØ Ó ± ÎÎ Ê, Ù Ó Ì, ¼ Å Ç Þ, Ë Ó Ó Ü [1 3]. г β ±Å ¼ TiAl À Ó Û»ÌÕ, Ë Ì Þ, Ô² ±Ã Í., Ó β ± TiAl À Û Â Ô¼ [4 7]. TiAl À µî ÅÑÒ ÑÒ, Æ Ï» Þ Ú À ÉÑÓÄ ¼ Ç Ð Ð, [8 13]., ¼ º Á 2 Ï, Ò Ï ÑÒ Ï. Ò Ï «Ã Cottrel Đ, Í Ó Ä «Ã Đ, º ȻѫÃ, Î ÓÐÐ. ÑÒ Ï À»Ñ«ÃȻۼ. Jonas [14] ÌÈ Û Á Ò Ï, Ð Þ Zr Nb À Óº Ó Õß Õ ÓÐÅ., É¼Ó ÕÏ Î Ó. [15, 16] È ÑÒ Ï, È Ti V Ti Mn À Þ, Ì Ó Ó», ± Ó ² º. Ni 3 Fe, Ni 3 Mn Û ÎÀ, Besag Smallman [17], ٠ѱà Á Ê «Ã ÑÇ º ¾«Ã«Ã Æ Ø Burgers «ÃÌ, ÙÎ Ó ÐÐ. Ù, ¼ TiAl À Ï ÛÈ, º. β ± Ti 42Al 9V.3Y À Å Á ³È, Á β ± г TiAl À Ô², Û «ÃÑ TiAl À ÁÀ Ç, β ± TiAl À Ó Ó Õµ ϽÎ. 1 À Ti 42Al 9V.3Y ( È, %), ³ Cu ¼ Ó ß ¹ 13 mm, ¼Ó 25 mm Á, Ç 125, 17 MPa Ar Å (HIP) 4 h. ÅÁ ¾ Đß ¹ 8 mm, ¼Ó 12mm ÊÏ, Gleeble 15D ÑÊÌ ¾ Å Ì. Ó 1 12, Ó Ë.1 1 s 1, ÊÏÅ Ç ÀÅÈ Ì. Çß Å ÊÏÊ Þ, Û» Å ¾Õ¾Ç ³ Kroll (5%HNO 3 +3%HF+92%H 2 O, Ö ) Ì, JSM 67F ¹ (SEM) ¾³ (BSE) Á Ì ½. ³ Philips CM12 ß (TEM) ½ ÏÚ Ì, ÊÏ ¾ Ø.1 mm Ç ÖØ, Ö 6%HClO 4 +35%C 4 H 9 OH+59%CH 3 OH (Ö ). 2 ÙÒ Ð 2.1 Û 1 Å ÁÒ Ti 42Al 9V.3Y À XRD Ð. Ù»µ, À Á γ ±, Ï ÛÈ β(b2) ±, Å È Ó³ V Õ Á β ±. 2a ÁÒ Ti 42Al 9V.3Y À Ì,»µ, Ì Ù γ β ±Ì, β ± V (22.31%, È ) Å Û²., Ì ÏÁ Æ YAl 2 ±. 2b  TEM µ, γ ± ÛÈ Ã, Å V ӳРÁ γ ± Ã, ±Ã γ ± ± Þ Í, Ù±Ã È Ã Û» Í Õµ., β ± Æ Ô «Ã ( 2c), ÅÇÁÒ Ì µðó ÁÇ. 2.2 ÖÞ 3 Ti 42Al 9V.3Y À 1 12 Å Ó Ó. Ù»Ù, Ti 42Al 9V.3Y À Å±Ó Ë Ó ±Ã, ±Ý Ó, Ó ÆÓ Ë ÈÙ Ó; Ã Ó Ë, Ó Æ Ó Ùغ. ÓÄ ¼ Çà Ð, Ç ÐÆÄÜÛ, ³ ÒÉ Õ, Ó ÕÎ ÑÒµÎÆ ÛÂ. 4 Ti 42Al 9V.3Y À Ý Ó Ó Ë Å Ç Ì.»µ, Intensity, a.u. 3 4 5 6 7 8 9 2, deg 1 ÀÑ Ti 42Al 9V.3Y XRD Fig.1 XRD spectrum of as cast Ti 42Al 9V.3Y alloy

11 : β TiAl Æ «1341 True stess, MPa 5 4 3 2 1 (a) 12 o C 115 o C..1.2.3.4.5.6.7 True strain 5 (b) True stress, MPa 4 3 2 1 12 o 115 C o C..1.2.3.4.5.6.7 True strain 35 (c) 3 2 ÀÑ Ti 42Al 9V.3Y Ë Fig.2 Microstructures of as cast Ti 42Al 9V.3Y alloy (a) BSE microstructure (b) stacking faults in γ phase (c) dislocations in β phase Å ÇÀ Ì Î, ÀÁÒÌ Å YAl 2 ±Ý º À Ö Ì. Æ Ó, β ±Û ØÆÄ, Ó Ë Ð β ±Ü Ó. DSC, B2+γ β+γ Ã Ó 11 ÎÜ, Í Ó ¾ 11, γ ±Ü β ±Ã, Ë Ç β ± «Al ßØÅ γ ± Á ( 4d). 5 Ti 42Al 9V.3Y À Ý Ó Ó Ë Å Ç TEM µ., À Ó Ó Ë γ ± Í «ÃÌ ( 5a), Ù β ± È Æ «Ã ( 5b), ÑÒ Ô. Æ Ó Ë Ð, γ ± ÁÈ «Ã True stress, MPa True stress, MPa 25 2 15 1 5 115 o C 12 o C..1.2.3.4.5.6.7 True strain 15 1 (d) 5 115 o C 12 o C..1.2.3.4.5.6.7 True strain 3 Ti 42Al 9V.3Y ÜÒ Ê ÆÒ Ò Ò Fig.3 True stress strain curves of Ti 42Al 9V.3Y alloy with different strain rates ε at different temperatures (a) ε = 1 s 1 (c) ε =.1 s 1 (b) ε =.1 s 1 (d) ε =.1 s 1

V G 1342 G xæncn arlhn\ 49 ( 4 Ti 42Al 9V.3Y SEM Fig.4 SEM images of Ti 42Al 9V.3Y alloy after hot compression at different temperatures T and strain rates (b) 115,.1 s 1 (c, d) 115,.1 s 1 (a) 15,.1 s 1 $ (~ 5c), a 11 K T a C Y 7 b7, # <, # 3 W? fn o 2< o }} P z ;I γ % (~ 5d), u β % m n 3, ah C E + i IA s K h Z C (~ 5e), m nz N w P ÆL. D, n;w6 O. 11,.1 s uw M i9 9 :W/ ) X β ~ 7 Ti 42Al 9V.3Y M iuw o % \* γ %*?, a γ %% β %(A, V5 β 11, o bs.1 s, o.5 uw TEM % x t (~ 5f). ). u~ 7a /), D H z; C E, β % 2.3 a krz : b 7 6 I N (~ 3b), a&7{ o }}4 k Z J g M, Ti 42Al 9V.3Y H _ j β % : K 2b /M H;, k N 7 n a β o D o bs qj o "? / a C E %b 9I K 2b / 7 q. %}, β % mn :, o fn o G o u 2b o, Z t4 β % B K +, G o )V, 8_ I a o GO LX, fo hb }. ULXd [H 7 β %l o }}. y _ 7 1 #,*O z? Io( q V,. ;I xe. uw γ % : K 7 n&~ 7b D c kj, * K U o bs u o a, 94. ;I te, i " a K%B TaD / q, Z{sH o m +. S M, U o m E } a, C E }}.;p&. D m + y, =. < C E +, γ % < 7 w /z ; {111} T a \2, w 1 2 }?, u 1 `, 9 Burgers FG b = 1/2h11i {w K T a ^ =. D, o bs (11 115, o bs 1/6h112i U;6 :, Zw /kw9 b = 1/2h112i 1. s ) W/ ) X C E O? m + D h11i 2 K 6 :. 2 K T a / 4i, (~ 3a). {w K DU; %?Y % L o. TEM ~ 6 Ti 42Al 9V.3Y H o }} o a, B T a D / q K 2 K, σ σ (σ o, σ, o ) f o V Burgers FG b = 1/2h112i(~ 7c), a γ % : b = ". u ~/), o }}GD o 2<X w a % 1/2h112i 2 K } / Z { 6 o }}. 1 1 [18,19] [2,21] 1 p v p v

11 3^ : < β # TiAl FÆ 5[ AC 8 ~ 5 Ti 42Al 9V.3Y 1343 G Lh 6\ TEM ( Fig.5 TEM images of Ti 42Al 9V.3Y alloy after hot compression at different temperatures and strain rates (Inset in Fig.5a shows the SAED pattern) (a) twin in γ phase at 15, 1. s 1 (b) subgrains in β phase at 15, 1. s 1 (c) dislocations in γ phase at 11,.1 s 1 (d) recrystallization in γ phase at 11,.1 s 1 (e) subgrains in β phase at 11,.1 s 1 (f) γ phase nibbled by β phase at 11,.1 s 1 M1 < 7M K X s 7, w//s Orowan 9 6 ZM1 o bs ε D 1:/ m K [o ρ g Kam w&bo v *q : [22] m ε = φbρm v (1) I:, φ Q Schmid k P, b M u p j " +DT a %j Burgers FGd, u v / L [23]: v = v ( τeff m ) exp( Q/RT ) τ (2) I:, v M K r:t a e b o; τeff M w/o, i>o o τ j o *q, ; τ MG Z K R bot a k?y o ; m Q Kbo o _ \; Q Md\k; R M r / \; T M o. : [24] : τeff = τ αgbρ1/2 (3) I:, α MjE k P,.2 D 2 *q; G Ms T <

1344 Î 49 12 1 8 1 s -1 1-2 s -1 1-1 s -1 1-3 s -1 p - v, MPa 6 4 2-2 15 11 115 12 Temperature, o C 6 Ti 42Al 9V.3Y Ü Ä ØÚ Ò Ò (σ p σ v) Fig.6 Stress drops (σ p σ v) of Ti 42Al 9V.3Y alloy after hot compression with different conditions (σ p peak stress, σ v valley stress) ; ρ ÅÉ «Ã Ó, τ = σ 2 (σ ÅÉÑÓ). Ù» : σ ( = αgbρ 1/2 ε +τ 2 φbρ m v exp( Q/RT) ) 1/m (4) À Õ, «Ã Ó, : ( αgbρ 1/2 ε τ φbρ m v exp( Q/RT) ) 1/m (5) Á (4) (5),» : ε φbρ pv exp( Q/RT) )1/m σ p τ ( σ ε v τ ( = (ρ v ) 1/m (6) ρ φbρ vv exp( Q/RT) )1/m p Á, ρ p É ¼Ó»Ñ«Ã Ó, ρ v É ¼ ӻѫà Ó. Á (1) λ : ln ε lnσ = lnρ m lnσ + lnv lnσ (7) Ù Ó Ë m = lnσ ln ε, «Ã ÓÓ m = lnv lnσ, : m 1[25]. m 1 = m + lnρ m lnσ (8) ÍÓ Áº,»Ñ«Ã ÓÁ, m 8 Ó ε=.5, Ý Ó m., m ¼ 15 115, Û ²¼.262, 12.319, Ù 1.172. 9 Ó Ë m Ó ε Î ÑÀ. Û ÝÓ ÑÀ 7 Ti 42Al 9V.3Y Ä ØÚ T=11, ε=.1 s 1, Ò ε=.5 TEM Fig.7 TEM images of Ti 42Al 9V.3Y alloy after hot compression at the condition of T=11, ε=.1 s 1, strain ε=.5 (b Burgers vector) (a) subgrains in β phase (b, c) dislocations in γ phase ε,»ôö m 15 12 Õ ¼ 3.58 3.831, 1 ¼ 7.937. Á (6)»µ, ¾ Ó»Ñ«Ã Ó m ß Î ÓÐÐ. 11 12 À Õ γ ± «Ã Ð ÑÅ«Ã Ó¾ Ó, Ù m (3.58 3.831) Û Ð Á³. 1, Ù m ± 11 È, Í, Î «Ã», ÓÐÐ, «Ã» ÑÒ Ï ± Ç

11 : β TiAl Æ «1345 ln(, MPa) 7. 6.5 6. 5.5 5. 4.5 4. 3.5 3. 2.5 2. m=.172 m=.26 m=.248 m=.279 m=.319 115 o C 12 o C Fitted -7-6 -5-4 -3-2 -1 1 ln(., s -1 ) 8 Ti 42Al 9V.3Y Ò.5, ÜÆÒ Ò Ê m m Fig.8 Linear regressing results of strain rate sensitivity coefficient m of Ti 42Al 9V.3Y alloy after hot compression at various temperatures with ε=.5 (σ flow stress).4.35.3.25.2.15 115 o C.1 12 o C Fitted.5..1.2.3.4.5 9 Ti 42Al 9V.3Y ÜÆÒ m Ò Í Ð Fig.9 Nonlinear fitting curves of m of Ti 42Al 9V.3Y alloy after hot compression with varying strains at various temperatures β ± TiAl À Å [26]. 1 À 11, ε=1 s 1, ε=.5 Å «Ã Í ĐÉ TEM µ. γ ± Å«Ã Ì Í, Í «Æ Ó Ð Ó Ë Õ Ó. ͱà «ÃÌ Í, «Ã ± Ó² Í Å., À Ñ ( 3a) Ó «Ã Í ĐÉ. ÍÊÏ 11, ε=1 s 1 115, ε=1 s 1, «ÃÌ Í ÝÁ γ. Ç, «ÃÌ Í Å, º «Ã. ¾Û ± Ó Û, «Ã²» Í ÅÑ Ì. ÙÍ«Ã Í ÅÇ, Ñ Ì Ó Ð. Æ Ó, γ ± Í Ì ĐÉ Ù, ¹Ó ÑÙËÜÕ, Ù ÑÅÓ Üغ. Í 1 Ti 42Al 9V.3Y 11, ε=1 s 1, ε=.5 Ä γ Ì Ë ÈÏÖ TEM Fig.1 TEM image of the interaction of slip and twin in γ phase of Ti 42Al 9V.3Y alloy during hot compression at 11, ε = 1 s 1, ε=.5 Ó Ð, Í «Õ, Í Å Ó Ó Ñ Á, ÅÀ 1 Å Ñ. 3 ÙÐ (1) β ± Ti 42Al 9V.3Y À Ó Ó Ë γ ± Í «ÃÌ. Æ Ó ( 11 ) Ë Ð, γ ± «ÃÌ Ã, Ù β ÑÒ γ ± ÑÒ µ Î. (2) À β ± ÑÒ γ ± «Ã»±¼. β ± ÑÒ Ø Á β ± Å «Ã, Û ÉÑÓ Ð, Ù γ ± ¾«Ã (Burgers b = 1/2 112 ) Ѿ«Ã Î ÁÓÐÐ. (3) Û Orowan Đ Þ «ÃÑ» À Ç»Ñ«Ã Ó Î «Ã ÓÓ m TiAl À ÉÑÓÐÐ Ô². 11 ¾ Ó»Ñ«Ã Ó m ß Î ÓÐÐ, Ù 1 m ± 11 È, Í, Î «Ã», ÓÐÐ Ø. (4) Ñ Ó «Ã Í ĐÉ. Í Ó Ð, Í «Õ, Í Å Ó ÉÑÓ Ñغ, À 1 Ñ. Ü«[1] Hu D. Intermetallics, 21; 9: 137 [2] Das G, Kestler H, Clemens H, Bartolotta P A. J Met, 24; 56(11): 42 [3] Xu X J, Lin J P, Wang Y L, Gao J F, Lin Z, Chen G L.

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