时效Ti-Ni-Cu-Pd窄滞后记忆合金的马氏体相变与应变恢复特性

发布时间：2018-05-02 00:55

本文选题：Ti-Ni-Cu-Pd合金 + 窄滞后形状记忆合金　；参考：《哈尔滨工业大学》2017年博士论文

【摘要】：Ti-Ni合金具有大恢复应变和应力,但相变滞后宽,作为驱动器材料时响应速度慢、灵敏度低,不能满足驱动材料对灵敏度、响应速度日益增长的要求。本文提出制备非化学计量比Ti-Ni-Cu-Pd窄滞后形状记忆合金,通过调整Pd含量来减小相变滞后,并利用时效处理改善形状记忆效应的新思路。采用X射线衍射分析、透射电子显微分析、示差扫描热分析、扫描电镜分析、硬度试验、拉伸试验等方法系统研究了Ti-Ni-Cu-Pd合金的显微组织、马氏体相变、时效析出行为及应变恢复特性。研究表明,随着Pd含量增加,Ti_(50.5)Ni_(38-x)Cu_(11.5)Pd_x和Ti_(49.5)Ni_(39-x)Cu_(11.5)Pd_x合金中马氏体均为正交结构(B19)马氏体。添加适量Pd,使Ti-Ni-Cu-Pd合金λ2值接近1,获得了窄相变滞后和高热循环稳定性。Ti_(50.5)Ni_(33.5)Cu_(11.5)Pd_(4.5)合金仅有4.8oC的相变滞后,相变温度在5000次热循环后变化小于1oC。TEM观察表明,在热循环过程中位错极难引入,这是Ti-Ni-Cu-Pd合金呈现高相变温度稳定性的主要原因。示差扫描量热分析表明,Ti_(49.5)Ni_(34.5)Cu_(11.5)Pd_(4.5)合金经不完整热循环后呈现出明显的温度记忆效应,即在DSC曲线上逆相变峰存在分峰现象。随不完整热循环次数的增加,分峰现象变得明显。在随后的完整热循环过程中Ti_(49.5)Ni_(34.5)Cu_(11.5)Pd_(4.5)合金的温度记忆效应呈现出可重复性。当经过1000次完整热循环后,合金的温度记忆效应仍不消失,这与传统的记忆合金完全不同。这种可重复温度记忆效应的机制在于不完整热循环过程中引入少量位错导致马氏体内位错分布不均匀,而完整热循环过程中引入的位错数量极少,因而不完整热循环过程中形成的不均匀位错组态难于被完整热循环破坏。研究表明,Ti_(50.5)Ni_(33.5)Cu_(11.5)Pd_(4.5)合金时效析出Ti2Cu型第二相,时效初期为细小颗粒状,随时效时间的延长或时效温度的升高,逐渐长大呈片状。时效后,该合金发生两步马氏体相变。Ti_(49.5)Ni_(33.5)Cu_(11.5)Pd_(5.5)合金时效析出(Ni,Cu)2Ti型第二相,在时效温度较低时,析出相为弥散方片状;时效温度较高时,析出相尺寸长大,呈片状及球状。当时效温度为600oC和650oC时,该合金分别发生两步和三步相变。Ti2Cu和(Ni,Cu)2Ti型相析出引起成分变化和产生应力场的综合作用导致多步相变现象出现。硬度和拉伸试验表明,Ti-Ni-Cu-Pd合金的硬度和可恢复应变随时效温度的升高或时效时间的延长呈现峰值效应。在500oC时效1小时,大量细小弥散第二相析出,对基体的强化效果最强,改善了形状记忆效应。拉伸变形5%时,500oC/1h时效Ti_(50.5)Ni_(33.5)Cu_(11.5)Pd_(4.5)合金的应变恢复率达97.8%,较固溶态合金提高了21%。
[Abstract]:Ti-Ni alloy has large recovery strain and stress, but the hysteresis of phase transition is wide, the response speed is slow and the sensitivity is low, which can not meet the requirements of the driving material for the sensitivity and the increasing response speed. In this paper, a new idea of preparing non-stoichiometric Ti-Ni-Cu-Pd narrow-hysteresis shape memory alloys is proposed, which can reduce phase transition hysteresis by adjusting PD content, and improve shape memory effect by aging treatment. The microstructure and martensite transformation of Ti-Ni-Cu-Pd alloy were systematically studied by means of X-ray diffraction, transmission electron microscopy, differential scanning thermal analysis, scanning electron microscopy, hardness test and tensile test. Aging precipitation behavior and strain recovery characteristics. The results show that with the increase of PD content, the martensite in the titix 50.5 / Niac (38-xCZ) and the Ti_(49.5)Ni_(39-x)Cu_(11.5)Pd_x alloy are both orthonormal structure (B19) martensite. The results show that the martensite in the Pdx alloy and the Ti_(49.5)Ni_(39-x)Cu_(11.5)Pd_x alloy are of orthogonal structure. By adding proper amount of PD, the 位 _ 2 value of Ti-Ni-Cu-Pd alloy is close to 1, and the narrow phase transformation hysteresis and high thermal cycle stability. The results show that the phase transition hysteresis of Ti-Ni-Cu-Pd alloy is only the same as that of 4.8oC, and the change of phase transition temperature after 5000 thermal cycles is smaller than that of 1oC.TEM. The results show that the dislocation is difficult to be introduced during thermal cycling. This is the main reason for the high temperature stability of Ti-Ni-Cu-Pd alloy. The differential scanning calorimetry (DSC) analysis shows that there is an obvious temperature memory effect after incomplete thermal cycling in the titiaphe alloy (49.5 / nil / 34.5 / C), i.e., the phenomenon of peak splitting is found in the inverse phase transition peak on the DSC curve. With the increase of incomplete thermal cycles, the phenomenon of peak splitting becomes obvious. During the subsequent complete thermal cycle, the temperature memory effect of TiStug 49.5NiS / 34.5 / C / C / C / C / C / C / C / C / C / C / C / T / T / T / T / T / T / T / T / T / T / T / T / T / T / T / After 1000 complete thermal cycles, the temperature memory effect of the alloy does not disappear, which is completely different from the traditional memory alloy. The mechanism of this repeatable temperature memory effect lies in the fact that the introduction of a small amount of dislocation in the incomplete thermal cycle leads to the uneven distribution of dislocation in martensite, while the number of dislocations introduced in the complete thermal cycle is very small. Therefore, the nonuniform dislocation configuration formed during incomplete thermal cycling is difficult to be destroyed by complete thermal cycle. The results show that the second phase of Ti2Cu is precipitated from the second phase of the Ti2Cu type after aging, and the prolongation of the aging time or the increase of the aging temperature makes the alloy gradually grow up as a sheet. After aging, the two-step martensite transformation. Tiken 49.5Ni33.5 / CuD _ (5. 5) was precipitated from the alloy, and the precipitated phase was in the form of dispersive flake at a lower aging temperature, and the precipitated phase grew in flake and spherical shape at a higher aging temperature. When the aging temperature is 600oC and 650oC, the two-step and three-step phase transition. Ti _ 2Cu and Ni _ 2O _ Cu _ 2Ti precipitates lead to the composition change and the comprehensive effect of the stress field, which leads to the multi-step phase transition phenomenon. Hardness and tensile tests show that the hardness and recoverable strain of Ti-Ni-Cu-Pd alloy show a peak effect on the increase of temperature at any time or the prolongation of aging time. After 500oC aging for 1 hour, a large number of fine dispersed second phases precipitated, which had the strongest strengthening effect on the matrix and improved the shape memory effect. The strain recovery rate of 500oC / 1 h aging titip 50.5 / Nix / Ni33.5 / CuSP 11.5PdD / 4.5) alloy is 97.8, which is higher than that of the solid solution alloy by 21. 8%. The strain recovery rate of the alloy is 97.8%, which is higher than that of the solid solution alloy, and the strain recovery rate of the alloy is 97.8%, higher than that of the solid solution alloy.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG139.6

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