热-机械训练对Fe-20Mn-5Si-5Cr-3Ni形状记忆合金性能的影响

研究了热-机械训练对Fe-20Mn-5Si-5Cr-3Ni合金形状记忆效应(SME)的影响,对合金在HCI、NaOH和NaC1溶液中的耐腐蚀性进行了实验研究.结果表明,热-机械训练能够有效提高合金的形状回复率,在600℃进行中间退火,形状回复率较好;热-机械训练次数为3次时,形状回复率达到最大值(98%).Fe-20Mn-5Si-5Cr-3Ni合金的耐腐蚀性在NaOH溶液中较好,在NaC1溶液中次之,在HC1溶液中较差.     

预变形的Fe-15Mn-5Si-9Cr-5Ni-（0．5～1．5）NbC合金

自从Fe-Mn-Si基形状记忆合金被开发成功以来，人们一直致力于改进其形状记忆性能，其中被称做“训练处理”的形状热处理能够有效地改善其形状记忆效应，但这种处理技术的能耗很大，难以推广应用。因此，开发了室温轧制预变形技术，此次则研究了室温拉伸的效果，研究了预拉伸Fe-15Mn-5Si-9Cr-5Ni-（0．5～1．5）NbC合金的形状记忆效应和马氏体转变特性。     

热处理工艺对Fe-15Mn-4.5Si-10Cr-5Ni系形状记忆合金析出相及形状记忆性能的影响

为了进一步提高Fe-15Mn-4.5Si-10Cr-5Ni系形状记忆合金的形状记忆效应,利用OM、TEM及物理相分析等试验方法,研究了直接时效及固溶+时效热处理工艺对试验合金微观组织、第二相析出及形状记忆效应的影响。结果表明,试验合金经固溶处理后,因第二相粒子大幅度回溶,导致试验合金形状记忆性能下降较为明显;同时,因直接时效处理较固溶+时效处理显著提高了试验合金中Cr碳化物第二相析出量,使试验合金形状记忆性能大幅度提升。其中,试验合金在800 ℃直接时效可获得最佳形状回复率。     

热机械"训练"工艺对Fe-20Mn-5Si-8Cr-5Ni-0.05N合金组织及形状记忆效应的影响

利用透射电镜、扫描电镜等设备研究了Fe-20Mn-5Si-8Cr-5Ni-0．05N合金在不同“训练”工艺下的组织，得到结论如下：“训练”2次时，试验合金的形状记忆效应最佳，此时可恢复的ε马氏体含量最大，并呈单一切变模式生长；“训练”3次时试验合金的母相中产生位错缠结，抑制了ε马氏体的逆转变，合金的形状记忆效应开始下降。     

热机械“训练”工艺对Fe-20Mn-5Si-8Cr-5Ni-0．05N合金组织及形状记忆效应的影响

利用透射电镜、扫描电镜等设备研究了Fe-20Mn-5Si-8Cr-5Ni-0．05N合金在不同“训练”工艺下的组织,得到结论如下:“训练”2次时,试验合金的形状记忆效应最佳,此时可恢复的ε马氏体含量最大,并呈单一切变模式生长:“训练”3次时试验合金的母相中产生位错缠结,抑制了ε马氏体的逆转变,合金的形状记忆效应开始下降。     

热-机械循环训练对Fe-15Mn-4Si-8Cr-4Ni形状记忆合金耐腐蚀性能和低温应力松弛的影响

研究了热-机械循环训练对Fe-15Mn-4Si-8Cr-4Ni形状记忆合金耐腐蚀性能以及低温松弛的影响,结果表明,随着循环次数的增加,合金在5%NaOH溶液中的耐腐蚀性能呈下降的趋势,这是因为热-机械循环处理导致了碳化物的大量析出,从而降低合金的耐腐蚀性能;经过热-机械循环处理后合金的低温应力松弛率高于未经循环处理的合金,约提高3%左右.导致合金低温应力松弛率提高的原因是回复应力的提高为应力诱发ε马氏体相变提供了大的机械驱动力以及应力诱发ε马氏体的临界应力的降低.     

Ti-50.8Ni-0.5V形状记忆合金的相变、组织与性能

利用XRD、示差扫描热分析仪(DSC)、光学显微镜和拉伸试验研究退火态Ti-50.8Ni-0.5V(摩尔分数,％)形状记忆合金的相变行为、组织特征和力学性能.结果表明:400～700℃退火态Ti-50.8Ni-0.5V合金室温组成相为母相B2和马氏体B19′.随退火温度升高,该合金冷却/加热时的相变类型由B2→R/R→...     

添加Ti对FeMnSiCrNi形状记忆合金性能的影响

研究了添加Ti对铁基形状记忆合金性能的影响.研究结果发现,添加Ti元素不仅使铁基形状记忆合金的力学性能得到改善,而且形状记忆效应也有较大幅度的提高.采用钨极氩弧焊(TIG)后,含Ti合金焊接后的抗拉强度达到706.9 MPa,是母材强度的98%,达到未加Ti合金母材的强度,远高于未加Ti合金焊接试样的强度(625.3 MPa).添加Ti的铁基合金在800℃退火后,在4%弯曲变形下形状记忆效应达到92%,比未添加Ti合金在700℃退火处理后形状回复率高31%.SEM分析表明,添加Ti试样晶粒细小,而且在晶界观察到大量第二相粒子,因此焊接后未出现异常粗大的晶粒,焊接后表现为韧性断口.细晶强化和第二相强化是添加Ti合金提高形状记忆效应的主要原因.     

Fe-30Mn-5Si-1Al形状记忆合金的原子力显微镜组织观察

自从日本开发了价廉且加工性好的Fe—Mn—Si系形状记忆合金以来,在考察其各种应用领域应用情况的同时,又开发了适合实用化的合金组成。相关的研究报告中,最具有代表性的合金组成是Fe-30Mn-6Si,其形状记忆效果是起因于fcc结构的γ奥氏体母相应力诱发了hcp结构的ε马氏体相,在加热时发生了逆相变。另外,Fe-30Mn-6Si合金中用Al置换部分Si的Fe-3Mn-3Si-3Al合金,具有缘于双晶变形的高延性,即显示了双晶诱发塑性的效应,该合金的强度与延伸率的积Rm-A值超过50000MPa％,作为强度、延性匹配优良的结构用钢而倍受关注。     

Fe-15Mn-4.5Si-10Cr-5Ni系形状记忆合金中Cr23C6的析出行为

第二相粒子Cr₂₃C₆作为Fe-15Mn-4.5Si-10Cr-5Ni系形状记忆合金中奥氏体主要强化相,对形状记忆性能起到重要影响。根据经典晶界形核长大动力学理论,分析解决包括Cr₂₃C₆相变化学自由能、界面能等一系列相关参量的理论计算及关键参数选择原则等问题。提出了Cr₂₃C₆在Fe-15Mn-4.5Si-10Cr-5Ni系形状记合金奥氏体基体中沉淀析出的相对定量理论计算方法,计算结果和试验结果吻合较好。计算出的PTT曲线(沉淀量-温度-时间曲线)可以作为Fe-15Mn-4.5Si-10Cr-5Ni系形状记忆合金时效处理参数选择的理论依据。     

The corrosion behaviour of Fe-15Mn-7Si-9Cr-5Ni shape memory alloy

The corrosion behaviour of Fe-15Mn-7Si-9Cr-5Ni (mass%) shape memory alloy at 25 °C in 0.5 M H₂SO₄ and 3.5% NaCl solutions has been studied using potentiodynamic polarization and electrochemical impedance techniques. Three different microstructures viz., single-phase γ, γ-δ and γ-Fe₅Ni₃Si₂, were produced by heat-treating the alloy in different equilibrium phase fields. The corrosion behaviour in 0.5 M H₂SO₄ solution is almost same for all three microstructures, barring a slight difference in the passivation range. Although, the passivation current in 0.5 M H₂SO₄, is in the same range as that of SS 304, the critical current required for onset of passivation is almost three orders higher and the passivation range is much shorter. In 3.5% NaCl solution the corrosion behaviour of all three microstructures of the Fe-15Mn-7Si-9Cr-5Ni shape memory alloy was that of general dissolution without passivity or localized attack (pitting). The best corrosion resistance in both H₂SO₄ and NaCl solutions is shown by the single-phase γ microstructure.     

Inherent oxidation protection of Fe-5Cr-15Ni-2Si-4.5Mo

The oxidation mechanism of Fe-5Cr-15Ni-2Si-4.5Mo alloy was investigated in order to determine the role of Si and Mo in providing oxidation resistance. It was determined that the oxidation protection in the temperature range 750–950°C resulted from formation of a continuous oxide sublayer of SiO ₂ (or possibly Fe ₂ SiO ₄).Molybdenum formed an intermetallic Fe ₂ Mo _1–x Si _x that eventually diffused out into the grain boundaries and formed a protective barrier to the oxidation process. The mechanism behind the improved oxidation is the formation of a SiO ₂ layer at the metal-oxide interface that retards the outward diffusion of Fe. It was also established that the oxidation mechanism was controlled by an activation energy equal to that of Fe ³⁺ ions diffusing through SiO ₂.     

Optimization of Fe-15Mn-5Si-9Cr-5Ni Shape Memory Alloy for Pipe and Shaft Couplings

We investigated whether Fe-Mn-Si shape memory alloys could be manufactured into machine parts and devices, in particular pipe and shaft couplings. Accounting for the optimal parameters affecting shape memory properties, i.e., the chemical composition, the amount of processing deformation, the annealing temperature, and the correlation between the reversibility of the martensitic transformation and the conditions of the microstructure (particularly the role of crystal defects), we found that maximum recovery in a Fe-15Mn-5Si-9Cr-5Ni alloy is achieved by rolling at 800 °C followed by annealing at 650 °C. Furthermore, we investigated certain properties that establish technological feasibility limits to industrial production, including alloy weldability and mechanical response. Bending and tensile specimen tests determinate the expected behavior of parts joined by welding. We also developed an original process to produce the couplings. The degree of shape recovery of the couplings manufactured by this method depends on the annealing temperature after welding. The couplings annealed at 800 °C recovered 83% of a 3.6% permanent diametrical expansion.     

(NiTi)_(50-0．5x)Nb_x形状记忆合金的阻尼性能及力学性能

通过加入Nb制备了具有双相组织的(NiTi)50-0.5xNbx(x=5,10,15,20)形状记忆合金,合金兼具高阻尼性能和高屈服强度.随着Nb含量x的增大,合金中(NiTi+β-Nb)共晶组织比例含量增加,合金轧制样品在马氏体状态自协作屈服强度随之升高,在x=15时达到最高(289 MPa);同时,合金轧制样品保持高阻尼性能,本征阻尼性能tan δ＞0.01,并随x增大而升高.根据形状记忆合金阻尼理论以及NiTiNb形状记忆合金的阻尼性能随温度的变化规律,探讨了β-Nb和NiTi相界面阻尼对合金阻尼性能的影响.     

Fe-30Mn-6Si-xN形状记忆合金层错能的热力学计算

利用包含置换原子和间隙原子的层错能热力学模型,计算了不同Ｎ含量下Ｆｅ－３０Ｍｎ－６Ｓｉ－ｘＮ形状记忆合金的层错能。计算结果表明,Ｎ对合金层错能的作用是先境加后降低（存在一个转折点Ｐ,对应Ｎ含量（质量分数）为ｗｐ）：当少量的Ｎ固溶在合金中（ｗＮ〈ｗｐ）时,由于Ｎ和近邻原子间的交互作用,合金的层错能有所增加;在Ｎ含量比较高时（ｗＮ〉ｗｐ）,Ｎ在层错区的偏聚对层错能的降低起了重要作用,Ｎ在合金中不同的间     

铁基合金中马氏体的显微组织力学性能和形状记忆效应

本文简述铁基合金中条状马氏体显微组织的特点和其与力学性能之间的关系;铁基形状记忆合金的现状。     

Fe—28Al—5Cr与Fe—28Al—5Cr—0.5Nb—0.1C合金的超塑性变形能力与特征

研究了 Ｆｅ－２８Ａｌ－５Ｃｒ（原子分数）与 Ｆｅ－２８Ａｌ－５Ｃｒ－０．５Ｎｂ－０．１Ｃ合金的高温变形行为,结果表明,在 ８５０ ℃左右,应变速率为 ８．３×１０－４ ｓ－１时,呈现一定的超塑性变形能力,延伸率分别达到 １４５％和 ２５４％;应变速率敏感指数 ｍ分别为 ０．４与 ０．３５;激活能分别为： ２４３ ｋＪ／ｍｏｌ与 ２１８ ｋＪ／ｍｏｌ．在变形过程中,位错堆积形成小角度晶界,并逐渐转变成大角度晶界,使粗大的原始晶粒细化．     

Improved Shape Memory Characteristics of Fe-14Mn-6Si-9Cr-5Ni Alloy Via Mechanical Alloying

In this work, the aim was to investigate how the deformation by cold rolling affects the microstructure and transformation temperatures of Fe-14Mn-6Si-9Cr-5Ni alloy prepared by powder metallurgy route. The characteristic of the martensitic transformation in the given alloy composition was investigated in terms of the amount of deformation via cold rolling. Mechanical alloying was applied for reaching better chemical homogenization level in powder state and for this purpose the as-blended powder mixture having target composition was mechanical alloyed for 4 h under protective atmosphere. Compacted samples were sintered at 1150 °C for 2 h under Ar atmosphere. After applying different amounts of cold deformation to the sintered samples, the changes in microstructure of the shape memory alloys were characterized by x-ray diffraction and scanning electron microscopy. With increasing amount of cold deformation, shape memory recovery ratios increased remarkably and ε-martensite phase was simultaneously detected during phase analysis.