Effect of Aging Treatment on Shape Memory and Fatigue Properties in Ni-rich Ti-Ni Alloy

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1 [ ] œwz, 20«1y(2007) J. of the Korean Society for Heat Treatment, Vol. 20, No. 1, (2007) pp. 11~16 Ni Ti-Ni w x» p v p e z w ½ *Á x*á ž**á y* * w œw ** w œw Effect of Aging Treatment on Shape Memory and Fatigue Properties in Ni-rich Ti-Ni Alloy J. I. Kim *, J. H. Sung*, S. Miyazaki**, S. H. Lee* *Materials and Science Engineering, Dong-A University, Busan , Korea **Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki , Japan Abstract The fatigue properties of Ti-Ni shape memory alloy wires were investigated. In Ni-rich Ti-Ni shape memory alloys, Ti 3 precipitates formed by aging treatments are believed to vary the shape memory and mechanical properties. In this study, the effect of aging temperature and aging time on shape memory properties and fatigue life were investigated using Ti-50.9Gat% Ni alloy wires. The specimens were solution-treated at 1073 K for 3.6Gks followed by aging at 573GK, 673GK and 773GK for periods between 3.6Gks and 3600Gks. It was found that the fatigue life under a constant stress decreased with increasing aging temperature. When the specimens were aged at 573GK for periods between 36Gks and 360Gks, superior shape memory and fatigue properties were obtained. The fatigue life also decreased when the test temperature and strain amplitude increased. It was concluded that the fatigue life exhibited a linear relationship with the critical stress for slip. (Received November 27, 2006; accepted December 27, 2006) Key words: Aging, Shape memory alloys, Fatigue, Ti 3 precipitate 1. Ti-Ni w w x» p ü, w, ƒœ ù œ s š. w Ti-Ni w x» p e þ ƒœ z [1-4], y z z [1, 2, 5-7], 3 (Fe, Cu, Al ) ƒ[8-10]. z x y w š z w w x» z. Ni Ti-Ni w z TiNi 3 [11] Ti 2 Ni 3 [12-13] Ti 3 [14-16]. TiNi 3 Ti 2 Ni 3» j w e š. ù Ti 3 x» p j w eš, p wš e w x Ti 3 x» p s w k š š [1, 2, 5-7]. Ti-Ni w l k w j p w» v p sƒ w š. p Cu ƒ w k j p w k š [8]. ù, ¾ š Ti-Ni Ti-Ni-Cu w v p w w [17-19]. p z w v p e w w w. z v x»(rotary-bending fatigue test) kimchi@dau.ac.kr

2 12 ½ Á xá žá y w z ƒ Ni- Ti-Ni w v p e w w. 2. x e Ti-50.9at%Ni w š q œ w w w Ingot w z þ w 1 mm. w þ ƒœ 30%. x v x ƒƒ 40 mm 100 mm ¼ w z t yv w» w s s w K 3.6 ks y z þ w š. y 573 K, 673 K, 773 K ¾ z w z þw. w z ƒ óù yv w s ƒ s w z t w» w w w.» p ƒ þƒ w» w g ƒ x» w xw. x 218 K 383 K w. z - v x» Fig. 1 ùkü. p w x (strain amplitude) ƒw» w z ó š w x, x ƒw. w w ƒw x (strain amplitude) w. w x w w. ε α l 0 l = ε l A max 0 (l 0 : ¼, l : z ¼ ) š k lƒ z w x z ƒ v ƒ q. g x ƒ v x 308 K 368 K ww š Fig. 1 4 Fig. 1. Schematic figure of rotary-bending fatigue tester. Ÿ ƒ z d w. š z 400 rpm š w. 3. x š x» p sƒw» w j z x (Maximum recovery strain : ) (Critical stress for slip : σ s ) sƒ w. p σ s p w y w x z ƒ ùkü x» p sƒw ƒ w, Ti-Ni w σ s þ ƒœ y y w w. x w 573 K z w σ s z Fig. 2 ùkü. σ s z ƒ w ƒw z w.

3 Ni Ti-Niw x» p v p e z w 13 Fig. 2. Effect of aging time on critical stress for slip in the specimens aged at 573 K. Fig. 3. Effect of aging temperature on critical stress for slip in the specimens aged for 1 hr. û 573 K y» z, Ti 3 y w ù [7]. z ƒ w Ti 3, ƒ ƒw z (pinning point) w» z ƒ σ sƒ ƒw š ƒ [7]. w z 100 yƒ ù w ù σ sƒ w š. w σ s z z Fig. 4. Strain amplitude (ε a ) vs. fatigue life (N f ) curves measured at various temperatures for specimen at 673 K for 1 hr. w 773 K z z ƒw σ sƒ w w z ƒ š yƒ ù». Fig. 3 1 z σ s z š. z ƒ ƒw σ s w. z ƒ ƒw yƒ, w w ù» σ sƒ w š. l 1 z z ƒ ƒw v w. ƒ v p e z z w. Fig. 4 ƒ x 673 K-1 h z x (strain amplitude : ε a ) v (N f ) ùkü. ε aƒ ƒw N f wš, x ƒ ƒw N f w w š. k (superelasticity : SE)» l p k (stress for inducing martensitc transformation : σ M ) ƒw x(slip deformation) ù š. x l w σ M x (Clausius-Clapeyron, Fig. 5(a) ) ƒ ƒw σ M ƒw x ƒ ƒw σ M ƒ ƒw

4 14 ½ Á xá žá y Fig. 5. Schematic diagram showing (a) the relationship between the stress for inducing martensitic transformation (σ M ) and test temperature. (b) Strain amplitude (ε a ) vs. fatigue life (N f ) curves. v š ƒ. v x ƒw j wš. w w ƒw x w x ƒw w» w Fig. 5 w. Fig. 5(a) σ M x (Clausius- Clapeyron )» w ùk ü x ƒ w Ì σ M ƒwš ƒ»». σ M ƒ 400 MPaƒ A, B, C ƒƒ 342 K, 338 K, 353 Kƒ. Fig. 5(b) A Fig. 6. Fatigue life (N f ) as a function of aging time for the specimens aged at 573 K under a test condition with the applied stress of 400 MPa and the strain amplitude of 1.5%. N f -ε a ùkü. A 400 MPaƒ ƒw 342 K N f - ε a v w ý B C 400 MPa ƒw N f -ε a w ƒ ƒ v w w. 400 MPa w ε a ƒ 1.5% 573 K z N f z w v Fig. 6 ùkü. z ƒw σ s ƒ w ùkü z w Fig. 3 ùkü σ s z w š. Fig MPa w ε aƒ 1.5% w N f z v. z ƒ ƒw N f wš w Fig. 4 w š. Fig. 6 Fig. 7 v p σ s j. v p σ s» w z w σ s w w(400 MPa) N f Fig. 8 ùkü. z v ƒ ƒw w v

5 Ni Ti-Niw x» p v p e z w 15 Fig. 7. Fatigue life (N f ) as a function of aging temperature for the specimens aged at 573 K under a test condition with the applied stress of 400 MPa and the strain amplitude of 1.5%. Fig. 8. A linear relationship between N f and σ S for all specimens tested under a test condition with the applied stress of 400 MPa and the strain amplitude of 1.5%. σ s j wš. Ti-Ni w x z 7-8%. w z l p k p (distortion)» w j p w(eg. ) w l p k» k w w w. k w w. z - v x - l p k k w w š q. z w x wš e w sw Ti 3 l p k w p w w w z w. Ti-50.9at%Ni w v p» e z w w» w 573 K-773 K 1 hr-1000 hr z w x z - v x (Rotary-bending fatigue test) ww ; 573K z (σ s ) z ƒ wì ƒw ùkü z w š v p 10hr 100hr z yw. z ƒ ƒw (σ s ) w. v x ƒ w x s (ε a )ƒ ƒw w. 573 K z v z ƒw ƒw z w. (σ s ) z w. z w w w v z (σ s ). z» 2003w w w (œ ) w ww. š x 1. S. Miyazaki, Y. Ohmi, K. Otsuka, and Y. Suzuki : J de Phys 43 (1982) (suppl.12) : C S. Miyazaki, In: T.W. Duerig et al., editors. Engineering Aspects of Shape Memory Alloys.

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