【作者】 王宇；

【导师】 江树勇；

【作者基本信息】 哈尔滨工程大学 ， 材料科学与工程， 2019， 博士

【摘要】 形状记忆合金作为一种具有形状记忆效应的材料,在工程领域已经得到了广泛的应用。镍钛基形状记忆合金和铁基形状记忆合金是目前发展最为成熟的两种形状记忆合金。形状记忆合金管接头是形状记忆合金工程应用最为成功的范例,主要应用于航空航天、石油化工和核工业的管路连接。目前应用最为成熟的管接头是镍钛基形状记忆合金管接头,因为镍钛基形状记忆合金强度高、可恢复应变大、恢复力大、耐蚀性高,但镍钛基形状记忆合金管接头相变滞后窄,加工制造困难。铁基形状记忆合金管接头虽然具有强度高、成本低、热加工性能好、相变滞后宽等优势,但可恢复应变和恢复力也较小,耐蚀性也不高。针对二种管接头的各自优缺点,本论文创新性地提出了异种形状记忆合金复合管的新概念,即将镍钛基形状记忆合金管和铁基形状记忆合金管挤压成形,制备内层为镍钛基形状记忆合金管、外层为铁基形状记忆合金管的复合管。综合了形状记忆合金各自的优点,弥补了各自的不足,有助于拓宽形状记忆合金管接头的工程应用范围。本论文以FeMnSiCrNi和NiTiNb形状记忆合金为研究载体,将金属力学性能实验、显微组织表征实验、有限元数值模拟和元胞自动机组织模拟相结合,构建了两种形状记忆合金的本构方程和热加工图,阐明了其高温塑性变形流动行为,优化了其热加工工艺参数,揭示了其微观组织演变规律,研究了异种形状记忆合金复合管挤压成形性,为实现异种形状记忆合金复合管挤压成形提供科学的理论基础。本论文的主要研究结果如下:获得了 FeMnSiCrNi形状记忆合金在温度为850～1000℃、应变速率为0.0005～0.5s-1条件下的应力应变曲线。基于Arrhenius本构模型,构建了 FeMnSiCrNi形状记忆合金基于应变补偿的高温塑性变形本构方程。该本构方程能够精确预测FeMnSiCrNi形状记忆合金高温塑性变形流动行为。基于动态模型建立了 FeMnSiCrNi形状记忆合金热加工图,研究了 FeMnSiCrNi形状记忆合金的热加工性。确定了 FeMnSiCrNi形状记忆合金热加工时的稳定区域,即当应变速率小于0.0008s-1时,变形温度范围为850～925℃;在应变速率为0.001～0.03s-1区间时,变形温度范围为925～1000℃。FeMnSiCrNi形状记忆合金的高温塑性变形对其微观组织具有重要的影响。在所有经历高温塑性变形的FeMnSiCrNi形状记忆合金样品中,可以观察到γ奥氏体、ε马氏体、奥氏体孪晶和堆垛层错共存,而且ε马氏体存在变体,与γ奥氏体存在[110]γ//[2110]ε的取向关系,且其含量随着变形温度的增加而增加。堆垛层错对ε马氏体和奥氏体孪晶的形成具有重要的影响。基于Shockley不全位错滑移以及内禀层错和外禀层错的形成机制,揭示了ε马氏体和奥氏体孪晶的形成机制,并基于层错能和淬火应力探讨了ε马氏体和奥氏体孪晶形成的相关性,发现了ε马氏体和奥氏体孪晶形成过程中相互抑制的现象。获得了 NiTiNb形状记忆合金在温度为700～1000℃、应变速率为0.0005～0.5s-1条件下的应力应变曲线。基于Arrhenius本构模型,同样构建了 NiTiNb形状记忆合金基于应变补偿的高温塑性变形本构方程。该本构方程能够精确预测NiTiNb形状记忆合金高温塑性变形流动行为。NiTiNb形状记忆合金在高温塑性变形时主要表现为动态回复和动态再结晶,随着变形温度的增加,亚晶界和位错密度减少。基于动态模型建立了 NiTiNb形状记忆合金热加工图,研究了 NiTiNb形状记忆合金的热加工性,确定了 NiTiNb形状记忆合金热加工时的稳定区域,即当应变速率为0.0003～0.001s-1范围时,变形温度范围为750～840℃;当应变速率为0.016～0.1s-1范围时,变形温度范围为930～1000℃。基于构建的FeMnSiCrNi和NiTiNb形状记忆合金的Arrhenius本构模型,采用刚粘塑性有限元法,对异种形状记忆合金复合管的等温挤压成形进行模拟。研究了不同变形温度(800℃、900℃、1000℃)、不同摩擦系数(0.1、0.15、0.2)、不同减薄量(0.2mm、0.4mm、0.6mm)和不同凹模入口角(60°、90°、120°)对异种形状记忆合金复合管挤压成形性的影响。发现异种形状记忆合金复合管在挤压成形时,变形区始终处于三向压力状态,而且内管的变形量明显高于外管。随着减薄量、摩擦系数和凹模入口角的增加,内外管的协调性变差,这将不利于内外管的界面结合。构建了 FeMnSiCrNi形状记忆合金的元胞自动机模型,自行开发了元胞自动机模拟程序,采用元胞自动机法对FeMnSiCrNi形状记忆合金的高温压缩塑性变形动态再结晶进行了组织模拟,揭示了 FeMnSiCrNi形状记忆合金高温塑性变形动态再结晶时的流动应力、晶粒尺寸和位错密度随着变形温度和变形速率的演化规律。将有限元模拟和元胞自动机组织模拟相耦合,建立了 FeMnSiCrNi形状记忆合金高温塑性变形宏观工艺变量和微观组织变量之间的联系,模拟了异种形状记忆合金复合管等温挤压时FeMnSiCrNi形状记忆合金不同变形区的微观组织演变规律。发现随着变形区塑性应变的增加,动态再结晶晶粒尺寸不断得到细化。更多还原

【Abstract】 As a functional material with shape memory effect(SME),shape memory alloy(SMA)has been widely used in engineering field.NiTi-based shape memory alloy and Fe-based shape memory alloy are the two most mature shape memory alloys at present.Shape memory alloy pipe coupling is the most successful example of shape memory alloy for engineering applications,which are mainly used in pipeline joints in aerospace,petrochemical and nuclear industries.Because of the high strength,large recovery strain,high resilience and high corrosion resistance,NiTi-based shape memory alloy pipe coupling becomes the most mature one.However,the NiTi-based shape memory alloy pipe coupling has a narrow phase transformation hysteresis and it is difficult to manufacture.Although the Fe-based shape memory alloy pipe coupling has the advantages of high strength,low cost,good hot workability and wide phase transformation hysteresis.However,the recoverable strain and the restoring force of Fe-based shape memory alloy pipe coupling are small,and the corrosion resistance is low.In view of the advantages and disadvantages of the two kinds of pipe coupling,a new concept of composite pipe with dissimilar shape memory alloys is proposed innovatively in this paper.The NiTi-based shape memory alloy pipe and the Fe-based shape memory alloy pipe are combined to form a composite pipe with the inner layer of NiTi-based shape memory alloy pipe and the outer layer of Fe-based shape memory alloy pipe by means of extrusion.It combines the advantages of shape memory alloy and makes up for their shortcomings.It is helpful to widen the engineering application scope of shape memory alloy pipe joint.In this paper,FeMnSiCrNi and NiTiNb shape memory alloys are used as research carriers.The constitutive equations and processing maps of two kinds of shape memory alloys are constructed by combining mechanical property experiments,microstructure characterization experiments,finite element numerical simulation and cellular automata simulation.In this paper,it provides a scientific theoretical basis for the industrialization of extrusion forming of dissimilar shape memory alloy composite pipe to clarify the flow behavior of plastic deformation at high temperatures,to optimize the processing parameters,to reveal the evolution law of microstructure and to study the extrusion formability of dissimilar shape memory alloy composite pipe.The main research results in the paper are as follows:The stress-strain curves of FeMnSiCrNi shape memory alloy at 850～1000℃ and strain rate of 0.0005～0.5s-1 were obtained.Based on the Arrhhenius constitutive model,the constitutive equation of high-temperature plastic deformation of FeMnSiCrNi shape memory alloy based on strain compensation is constructed.The constitutive equation can accurately predict the flow behavior of FeMnSiCrNi shape memory alloy subjected to plastic deformation at high temperature.The hot workability of FeMnSiCrNi shape memory alloy was studied.The stable region of FeMnSiCrNi shape memory alloy during hot working is determined as follows.When the strain rate is less than 0.0008s-1,the deformation temperature range is 850～925℃.When the strain rate range is 0.001～0.03s-1,the deformatin temperature range is 925～1000℃.The high-temperature plastic deformation of FeMnSiCrNi shape memory alloy has an important influence on its microstructure.In all the FeMnSiCrNi shape memory alloy samples subjected to high-temperature plastic deformation,γ austenite,ε martensite,austenite twin and stacking faults can be observed.There are variants of ε martensite,which has an orientation relationship of[110]γ//[2110]with y austenite,and the content of ε martensite increases with the increase of deformation temperature.Stacking faults play an important role in the formation of ε martensite and austenite twin.Based on the mechanism of Shockley partial dislocations slip,intrinsic stacking faults and extrinsic stacking faults,the formation mechanism of ε martensite and austenite twin is revealed.Based on the stacking fault energy and quenching stress,the formation correlation of ε martensite with austenite twin is discussed.In addition,it can be concluded that the formation of ε martensite and austenite twin is mutually inhibited.The stress-strain curves of NiTiNb shape memory alloy at 850～1000℃ and strain rate of 0.0005～0.5s-1 were obtained.Based on the Arrhhenius constitutive model,the constitutive equation of high-temperature plastic deformation of NiTiNb shape memory alloy based on strain compensation is constructed.The constitutive equation can accurately predict the flow behavior of NiTiNb shape memory alloy subjected to plastic deformation at high temperatures.NiTiNb shape memory alloy is characterized by dynamic recovery and dynamic recrystallization during plastic deformation at high temperatures.With the increase of deformation temperature,subgrain boundary and dislocation density decrease.The hot workability of NiTiNb shape memory alloy was studied.The stable region of NiTiNb shape memory alloy during hot working is determined as follows.When the strain rate range is 0.0003～0.01s-1,the deformation temperature range is 750～840℃.When the strain rate is 0.016～0.1s-1,the deformation temperature range is 930～1000℃.Based on the Arrhenius constitutive model of FeMnSiCrNi and NiTiNb shape memory alloys,the isothermal extrusion of dissimilar shape memory alloy composite pipe is simulated by rigid viscoplastic finite element method.The effects of different deformation temperatures(800℃,900℃,1000℃),different friction coefficients(0.1,0.15,0.2),different thickness reductions(0.2mm,0.4mm,0.6mm)and different cone angles of bottom die(60,90,120 degrees)on extrusion formability of dissimilar shape memory alloy composite pipes are studied.It can be found that the deformation zone of the dissimilar shape memory alloy composite pipe is always in a three-dimensional compressive stress state during extrusion forming,and the deformation of the inner pipe is obviously higher than that of the outer pipe With the increase of thickness reduction,friction coefficient and bottom die angle,the coordination of inner and outer pipe becomes worse.The cellular automata model of FeMnSiCrNi shape memory alloy is constructed,and the simulation program of cellular automata is developed.The dynamic recrystallization of FeMnSiCrNi shape memory alloy during compression deformation at high temperature is simulated by cellular automaton method.The evolution of flow stress,grain size and dislocation density with deformation temperature and deformation rate during dynamic recrystallization of FeMnSiCrNi shape memory alloy subjected to compression deformation at high temperatures is revealed.The relationship between macroscopic process variables and microscopic variables during plastic deformation of FeMnSiCrNi shape memory alloy at high temperatures is established by coupling finite element simulation and cellular automata simulation.The microstructural evolution of FeMnSiCrNi shape memory alloy in different deformation zones during isothermal extrusion of dissimilar shape memory alloy composite pipe is simulated.It can be found that the grain size of dynamic recrystallization is refined with the increase of plastic strain in the deformation zone.更多还原