Cu-Zn-Al系合金的马氏体稳定化

本文以电阻法和圆弧压弯法研究了ＣｕＺｎＡｌ系合金热弹性马氏体的稳定化过程，用ＤＴＡ法测定了母相Ｂ２→ＤＯ３有序转变温度，分析了合金元素Ｍｎ对ＣｕＺｎＡｌ系合金马氏体稳定化的影响，实验结果表明：热弹性马氏体的稳定化倾向与Ｂ２→ＤＯ３转变温度的高低有关。由此解释了Ｍｎ对改善ＣｕＺｎＡｌ系合金马氏体稳定化的作用。     

Cu-Zn-Al-Mn合金贝氏体相变的位向关系

本文利用两相合成的选区电子衍射谱，介绍了确定平行晶面晶向指数的方法，借助于这一方法，本文测定了Ｃｕ－Ｚｎ－Ａｌ－Ｍｎ合金贝氏体与母相之间的位向关系     

Cu—Zn—Al—Mn合金贝氏体相变的位向关系

本文利用两相合成的选区电子衍射谱，介绍了确定平行晶面晶向指数的方法，借助于这一方法，本文测定了Ｃｕ－Ｚｎ－Ａｌ－Ｍｎ合金贝氏体与母相之间的位向关系。     

快速凝固Al—Li—Cu—Mg—Zr合金中H相的Z相的TEM研究

用ＨＲＴＥＭ、ＴＥＭ及ＥＤＡＸ分析研究了Ａｌ－Ｌｉ－Ｃｕ－Ｚｒ合金中的一种新相（暂名Ｈ相）和六角Ｚ相的结构，确定Ｈ相具有四方点阵，点阵参数为ａ＝２．８ｎｍ，ｃ＝２．４ｎｍ，ＥＤＡＸ分析表明Ｈ明和Ｚ相均含有Ａｌ，Ｍｇ，Ｃｕ。发现Ｈ相与Ｚ相的共存取向关系为［１００］ｈ｜｜［１１２０］ｚ，［０１０］｜｜［０００１］Ｚ。还观察到Ｚ相中一种特有有的旋转畴结构。     

Cu－Zn－Al－Mn合金高温时效时相变机制的研究

用示差扫描量热法（ＤＳＣ）、电阻测量和透射电子显微镜对Ｃｕ－Ｚｎ－Ａｌ－Ｍｎ合金高温时效的贝氏体相变进行了研究。结果表明，合金经高温时效，溶质原子首先析出，有利于降低层错能，随后由于切变引起在（１１１）面上形成大量层错，从而促进了贝氏体相变。     

快速凝固高阻尼Al－Zn－Mg－Cu系合会的研究

本文研究了利用快速凝固粉末冶金工艺制备高阻尼Ａｌ－Ｚｎ－Ｍｇ－Ｃｕ系合金。通过拉伸性能与阻尼性能的测试，以及显微组织分析，探讨了纯铝及石墨对合金拉伸性能及阻尼性能的影响。结果表明：Ａｌ－Ｚｎ－Ｍｇ－Ｃｕ／１５ｗｔ％Ａｌ合金的室温拉伸性能已达到ＬＣ９ＣＧＳＩ的水平，阻尼性能为Ｑ＝６．０×１０￣３；在室温至３００℃温度范围内，随着温度的升高，合金的阻尼能力提高；合金的阻尼机制属复合型机制。     

快速凝固Al—Li─Cu—Mg—Zr合金中H相和Z相的TEM研究

用ＨＲＴＥＭ、ＴＥＭ及ＥＤＡＸ分析研究了Ａｌ─Ｌｉ—Ｃｕ—Ｍｇ—Ｚｒ合金中的一种新相（暂名Ｈ相）和六角Ｚ相的结构，确定Ｈ相具有四方点阵，点阵参数为α＝２．８ｎｍ，ｃ＝２．４ｎｍ，ＥＤＡＸ分析表明Ｈ相和Ｚ相均含Ａｌ、Ｍｇ、Ｃｕ发现Ｈ相与Ｚ相的共存取向关系为［１００］‖［１１２０］Ｚ，［１０１０］Ｈ‖［０００１］Ｚ。还观察到Ｚ相中一种特有的旋转畴结构     

母相区时效和热循环对Cu—Zn—Al合金形状记忆特性的影响

采用一种精确测量形状记忆效应（ＳＭＥ）的方法研究了Ｃｕ－２６％Ｚｎ－４％Ａｌ合金８００℃淬火后在母相区１３０，１５０和１７０℃时效以及相变热循环过程ＳＭＥ变化的规律。淬火马氏体进入母相区时效初期回复率迅速升高，达到一个最大值以后随时间开始下降，显示出时效过程中马氏体稳定化效应的消除和贝氏体相变发展这两种机制所引起的相反效果。拘束条件下热循环引起回复率的衰减比起自由状态下要缓慢。这可能是应力的存在有     

Cu—Zn—Al—Mn合金高温时效时相变机制的研究

用示差扫描量热法、电阻测量和透射电子显微镜对Ｃｕ－Ｚｎ－Ａｌ－Ｍｎ合金高温时效的贝氏体相变进行了研究。结果表明，合金经高温时效，溶质原子首先析出，有利于降低层错能，随后由于切变引起在（１１１）面上形成大量层错，从而促进了贝氏体相变。     

母相区时效和热循环对Cu－Zn－Al合金形状记忆特性的影响

采用一种精确测量形状记忆效应（ＳＭＥ）的方法研究了Ｃｕ－２６％Ｚｎ－４％Ａｌ合金８００℃淬火后在母相区１３０，１５０和１７０℃时效以及相变热循环过程ＳＭＥ变化的规律。淬火马氏体进入母相区时效初期回复率迅速升高，达到一个最大值以后随时间开始下降，显示出时效过程中马氏体稳定化效应的消除和贝氏体相变发展这两种机制所引起的相反效果。拘束条件下热循环引起回复率的衰减比起自由状态下要缓慢。这可能是应力的存在有利于诱发马氏体相变，使马氏体回复率显著提高所致。     

Diffraction and Morphology Study of Surface Structures Accomponying with the Formation of α''''Plate(Bainite)in a Cu-Zn-AI Alloy

In the present paper the morphologies of sur-face structures and the anomalous contrast of β_1phase accompanying with the formation of bainiteplate in the Cu-Zn-Al shape memory alloy havebeen investigated in detail by the transmission elec-tron microscopy and diffraction.The experimentalresults have proved that the extra diffraction andanomalous contrast results from the surfacemartensite formed on the β_1 phase.However,thecrystal structure and morphology of the surfacemartensite are varied at different stage of bainiteformation.The observation of interfacial disloca-tion structure of bainite/β_1 matrix reveals thatthere is a large strain in the bainite transformationof β CuZnAl alloy.Based on the experiment resultsthe formation of surface martensite and bainitictransformation were discussed.     

Internal friction behaviour of Ni–Mn–Ga

The internal friction (IF) behaviour of shape memory alloys (SMA) is characterised by an IF peak and a minimum of the elastic modulus during the martensitic transformation (MT), and a higher IF value in the martensitic state than in parent phase. The IF peak is considered to be built of three contributions, the most important of them being the so-called “transient” one, existing only at non-zero temperature rate. On the other hand, the ferromagnetic Ni–Mn–Ga system alloys undergoes a MT from the L2₁ ordered parent phase to martensite, the characteristics of the transformation depending largely on the e/a ratio of the alloys. Indeed, a variety of transformation sequences, including intermediate phases between parent and martensite and intermartensitic transformations, have been observed for a wide set of studied alloys. Furthermore, the IF and modulus behaviour during cooling and heating these alloys show specific characteristics, such as modulus anomalies, strong temperature dependence of the elastic modulus, temperature dependent internal friction in martensite, and, as a general trend, a low transient contribution to the IF. In the present work, the IF and modulus behaviour of several Ni–Mn–Ga alloys will be reviewed and compared to that observed for “classical” systems like Cu- or NiTi-based shape memory alloys.     

Magnetic structure of the modulated martensite phase in Ni-Mn-Ga ferromagnetic shape memory alloys

The magnetic structure of the seven layered (7 M) modulated martensite phases in Mn-rich Ni-Mn-Ga alloys was studied using Mössbauer spectroscopy. The Mössbauer results clearly demonstrate that in contrast to the non-modulated tetragonal structure two new magnetic sublattices exists for the 7 M orthorhombic martensite phase. Based on the unit cell symmetry and atomic coordination, the additional magnetic sublattices have been assigned to the Ni site. The variation in the magnetic properties of the martensite phases has been related to the underlying magnetic structure.     

Electron backscattering diffraction study of acicular ferrite,bainite, and martensite steel microstructures

Abstract

This study deals with acicular ferrite, bainite, and martensite microstructures observed in three low alloy steels. Electron backscattering diffraction (EBSD) was used to assess crystallographic features of these microstructures. In each area studied by EBSD mapping, ‘crystallographic packets’ defined as clusters of points sharing the same crystallographic orientation were compared with ‘morphological packets’ observed in the corresponding light micrograph. Microtexture studies suggested that acicular ferrite and upper bainite grow with Nishiyama– Wassermann relationships with the parent austenite phase, whereas lower bainite and martensite consist of highly intricate packets having Kurdjumov–Sachs relationships with the parent phase. In all cases three highly misoriented texture components were found within each former austenite grain. Electron backscattering diffraction also gave information about the cleavage and intergranular reverse temper embrittlement fracture mechanisms of these steels. In conclusion, it is shown that EBSD is a powerful tool for studying phase transformation and fracture mechanisms in steels on a microscopic scale.     

The effect of hydrogen on the bainite transformation

The effect of hydrogen on the upper bainite transformation in two silicon containing steels has been investigated. For comparison, isothermal transformation at the same temperature has also been performed in a helium atmosphere. In both Fe-0.2C-3Mn-2Si and Fe-0.4C-4Ni-2Si (nominal wt %) alloys it was discovered that the bainite reaction proceeds further towards completion when the transformation is carried out in a hydrogen atmosphere. This can result in the reduction or elimination of the martensite phase which forms from residual austenite upon quenching to room temperature. The resultant microstructure of specimens heat treated in hydrogen was a fine aggregate of upper bainitic ferrite and interlath retained austenite. This effect is discussed in terms of hydrogen interactions in the lattice undergoing bainite transformation via a displacive mechanism. Additionally, it is found that the stability of the retained austenite in the final bainitic microstructure is not markedly influenced by hydrogen.     

Ti＋B复合细化对CuZnAl形状记忆合金的影响

ＣｕＺｎＡｌ形状记忆合金中复合加入Ｔｉ＋Ｂ能够显著地细化晶粒，降低了马氏体相变滞后宽度，使马工体不易稳定性，同时合金具有良好的形状记忆效应，合金经过Ｔｉ＋Ｂ复合细化后，提高了合金的综合机械性能，显著地改善了合金的冷加工性能，单独加入Ｔｉ细化的合金马氏体有稳定化的倾向。     

贝氏体相变的三面观

目前，三种不同的贝氏体定义正被广泛采用。第一种是显微组织的定义：贝氏体是非层状共析分解的产物，两种共析相通过扩散形核和长大相互竞争形成。第二是相变动力学定义（ＯＲＫ）：它是用铁碳合金的术语来描术贝氏体。通常用ＴＴＴ图中两个重迭的Ｃ曲线来描述共析温度以下的奥氏体分解。温度，贝氏体相变越加不完全，最后在上限温度消失。第三种是表面浮突定义：贝氏体是在马氏体区域以上（有时也在以下）形成的片状转变产物，相变     

Transformation processes and products for C–Mn steels during continuous cooling

Abstract

The continuous cooling transformation (CCT) diagrams for four C–Mn steels were constructed using dilatometry and metallography. All diagrams involved the formation curves of second phases and the formation curves of matrix structures. Between polygonal ferrite and martensite, acicularferrite and bainite were observed. The formation of acicularferrite was associated with a kinetic change which was an indication of the formation of second phases such as pearlite, pseudopearlite, and martensite. The pseudopearlite wasfound to form by separate precipitation of cementite and ferrite in austenite. It was thought that the transformation of martensite second phases followed a Kurdjumov–Sachs relationship. Three types of carbide, i.e. upper bainitic, lower bainitic, and Widmanstätten, were observed in continuously cooled bainite. An increase of manganese content suppressed the formation of polygonal ferrite, promoted the formation of acicular ferrite and bainite, and changed the second phase from pearlite to pseudopearlite and to martensite.

MST/913     

65Si2MnWA钢下贝氏体碳原子调幅分解及有序化的TEM研究

利用Ｓｉ元素阻碍碳化物析出的作用，对６５ＳｉＭｎＷＡ钢进行适当热处理，获得无碳化物析出的下贝氏体组织，通过透射电镜分析了贝氏体基体衍射花样特征，进而考察其碳含量，结果表明，该钢下贝氏体转变初期存在碳原子调幅分解及有序化过程，其碳原子行为与马氏体回火早期阶段碳原子行为相似，说明该钢下贝氏体基体含碳量是过饱和的。