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Study on Transformation and Deformation Characteristics of Ti-Ni-Cr Superelastic Alloy

Author: WangQi
Tutor: HeZhiRong
School: Shaanxi Institute of
Course: Materials Processing Engineering
Keywords: Ti-50.8Ni-0.3Cr alloy A shape memory alloy Hyperelastic Phase change Deformation
CLC: TG139.6
Type: Master's thesis
Year: 2011
Downloads: 18
Quote: 0
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Abstract


This article as the research object Ti-50.8Ni-0.3Cr (atomic%) shape memory alloys (SMAs), X-ray diffraction, differential scanning calorimetry, tensile test, optical microscopy and electron microscopy to study the annealing The aging process of the phase transformation, deformation behavior and microstructure. The results show that: the annealing temperature T an significant influence on the phase transition behavior of Ti-50.8Ni-0.3Cr alloy. T an = 350 ~ 450 ℃, the alloy A → R / R → A-type reversible phase transition; T an = 500 ° C, the alloy A → R → M / M → R → A-type phase transition; T an = 550 ~ 600 ℃, the alloy A → R → M / M → A-type phase transition; T an = 650 ~ 800 ℃, the alloy phase transition occurs. Aging time t ag extension of 300 ℃ aged alloy phase change type A → R / R → A 400 ° C aging alloys A → R / R → A to A → R → M / M → R → A transition to 500 ° C - aged alloy A → R → M / M → R → A A → R → M / M → A transformation. With elevated T an alloy R-phase transition temperature T R increased at first and then decreased to M phase transition temperature T M increased the M phase change thermal hysteresis ΔT M reduced. Alloy after aging at 300 ~ 500 ℃ the T R 400 gt; the T R 300 gt; T R 500 . With the extension of t ag , T R , T M first rapid increase stabilized, ΔT M first reduced quickly stabilized. In addition, annealing and aging alloys R phase change thermal hysteresis ΔT R in about 4 ℃. In the annealing process, due to the supply of Ti-50.8Ni-0.3Cr alloy state of cold-worked state, the annealing will occur recovery and recrystallization. T an = 350 ~ 500 ℃, the alloy for the recovery phase, continued to show a fibrous microstructure; T the an = 550 to 580 ° C, and alloy recrystallization fibrous tissue gradually becomes undistorted equiaxed grain; T an = 590 ~ 800 ℃, phase, grew up as the grain microstructure is coarse and uneven size of the grain; with T increased an alloy of stress-induced martensite critical stress σ M first and then decreased, and subsequently stabilized; residual strain εR T an < / sub> = 350 ~ 590 ℃ little change, and always maintained at a lower level, when T AN GT; sharp rise in ° C of 590. Also can be drawn, the recrystallization temperature of the start of the alloy at about 570 ℃, for the alloy to obtain a good super-elastic, the annealing temperature should be lower than the recrystallization temperature. Solution and aging process, 800 ℃ solid solution quenched alloy plastic, suitable for cold forming. Aging time t ag extension of 300 ° C and 400 ℃ aged tensile strength σ the 300 and σ b < / sub> 400 stabilized after the first increases rapidly, and σ b 300 lt; σ b < sup> 400 , elongation δ k 300 and δ k 400 first decreases sharply stabilized stabilized; aging at 500 ℃ the σ b 500 first decreases sharply the δ k , 500 first increases rapidly stabilized. With t ag extend alloys aged at 300 ° C and 400 ℃ stress-induced martensite critical stress σ the M the 300 σ M 400 are gradually decreases, and σ M 500 at first decreases and then increase again reduce greatly the value t ag = 10h get. In addition, with the t ag Extension 300 ℃ aging the alloys Ti3Ni4 precipitation phase dispersed fine granular; 400 ℃ aging the alloys Ti3Ni4 precipitation phase granular evolved into the lenticular; 500 ℃ aging The alloys Ti3Ni4 precipitation occurred the lenticular to acicular further coarse flake evolution. The effect of aging temperature on Ti3Ni4 precipitation phase morphology than the aging time significantly. Td increased with test temperature annealing and aging state Ti-50.8Ni-0.3Cr alloy spring of stress-induced martensitic transformation critical shear stress τ M increased gradually; which, with T elevated an , τ M first and then decreased; With the extension of t ag 300 ℃ aging state alloy spring τ M gradually reduced. N increases with the number of cycles, alloy spring strain to restore the lead to rapid attenuation, after stabilizing; Precycling can enhance the stability of the spring element SE.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Other special nature of the alloy > Shape Memory Alloys
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