高压涡轮导向叶片裂纹原因分析与控制

针对定向凝固过程中高压涡轮导向叶片存在沿柱状晶晶界开裂的现象,分析了高温合金柱状晶凝固收缩机理及材料成分对热裂倾向的影响,并对陶瓷型芯高温形变、陶瓷型芯对金属收缩的阻碍等进行了分析。结果发现,定向凝固柱状晶晶界裂纹与晶界结构、合金收缩受阻、陶瓷型芯的形变与漂移有一定的关系。通过采取调整叶型壁厚、陶瓷型芯定位、调整材料成分等措施来抑制定向凝固叶片沿晶界开裂的倾向。     

晶界状态对定向凝固Al—Cu和Renel25合金热裂倾向的影响

在ＨＲＳ定向凝固设备上进行了合金热裂试验,采用半定量方法评定了定向凝固Ａｌ－Ｃｕ和Ｒｅｎｅｌ２５合金热裂倾向。观察了合金的晶界,并分析讨论了其对合金热裂的影响。用晶界状态分析的结果与试验结果完全一致。证明了晶界状态对热裂纹的形成有重要影响,其影响包括对晶间结合力的破坏作用和对晶界凝固收缩的补偿作用。晶界状态对热裂影响的综合作用取决于晶界低熔点相的分布和数量。     

微量溶质元素在金属晶界的偏聚

溶质元素在金属晶界的偏聚可以分为两类，即平衡偏聚和非平衡偏聚。本文回顾了这两类偏聚现象及其机理，着重讨论分析了有重要工程用途的三类典型的晶界偏聚：硼在奥氏体晶界的两类偏聚的实验规律及对硼钢淬透性影响；磷在奥氏体晶界的平衡偏聚及对钢回火脆性的作用，钢中的其他合金元素对磷的偏聚的影响；硼在多种金属间化合物的偏聚及对这些金属间化合物塑性的影响及其机理。     

高Zn含量Al-Zn-Mg-Cu系铝合金的凝固态显微组织

利用OM、SEM、XRD及TEM等分析方法,对几种高Zn含量Al-Zn-Mg-Cu系合金的凝固态组织进行研究,通过比较不同合金中一次凝固析出相的种类、形貌结构及合金元素在各相中的显微分布,揭示了不同凝固析出相的形成过程与机理。结果表明:法系7449、7056合金晶界处粗大析出相为T(Mg(Zn,Cu,Al)2)四元相共晶组织,且大部分共晶组织网层状结构发达,共晶组织特征明显;美系7136与7095合金晶界处粗大的网状结构第二相数目大大减少,主要以棒条状结构存在,且部分粗大第二相是以两相(T(Al Zn Mg Cu)与θ(Al2Cu))伴生的结构形态存在;不同合金凝固态显微组织的差异是由合金成分的不同而导致的凝固进程的差异造成的;其中,Cu元素含量对凝固态组织中一次凝固析出相的种类及结构形貌有较大影响。     

晶界状态对合金热裂倾向的影响

进行了定向凝固Ａｌ－Ｃｕ合金和Ｒｅｎｅ１２５合金晶界状态分析，并与合金热裂倾向性试验结果对比，揭示了晶界状态对合金热裂倾向的影响。     

凝固过程对热裂纹形成的影响

回顾了热裂纹研究的进展，从合金在凝固过程中的力学行为、晶界状态的影响和合金自身的凝固过程等三个方面对热裂纹的形成机制进行了分析和综述。     

磷含量对IN718合金持久和蠕变性能的影响

研究了不同含量的磷在ＩＮ７１８合金的作用。结果表明,磷对持久和蠕变性能有显著的影响,可提高ＩＮ７１８合金晶界抗蠕变形裂的能力,将磷含帅０．００３％提高至０．０３％,持久寿命先是增加而后降低,并在含磷０．０２５％年达到持久寿命峰值。磷对应力指数影响不大,但对表观蠕变激活能影响显著。磷的有益作用主要来自于抑制晶界扩散和改善晶界δ相。     

磷对GH761合金力学性能的影响

采用金相显微镜、扫描电镜、透射电镜及能谱分析等手段，研究了磷含量对GH761合金力学性能的影响．结果表明：磷含量低于0．040％时，对合金室温和650℃拉伸性能无明显影响．适量磷显著延长合金的650℃，637MPa持久寿命，最佳含量位于0．023％附近，寿命高于970h，比磷含量为0．0007％时的寿命长3倍以上．磷含量升至0．040％时，持久寿命又降至约220h．磷通过阻碍位错运动、促进晶界析出、阻碍环境氧的沿晶侵入等机制，提高GH761合金的持久寿命．过高的磷含量使晶界析出过量，并导致η-NiaTi相析出，弱化晶界，降低合金的持久寿命．     

Zn对Mg-9Al合金凝固行为的影响

研究了Zn元素对Mg-9Akl合金的凝固行为，尤其是对热裂倾向性的影响。通过热分析手段考察合金的凝固特征。用热裂环法评价合金的热裂倾向性，引入了热裂倾向性（HSC）因子的概念。并通过金相观察、扫描电镜和电子探针对合金的凝固、热裂行为进行了研究。研究发现，在凝固过程中An,Al元素由于晶间偏析而在晶界富集。Zn元素的加入，增加了晶界低熔点相的量，并降低了其熔点，从而明显增加了合金的热裂倾向性。Mg-9Al-xZn合金的热凝产生于凝固后期，呈沿晶断裂。加入Zn元素对Mg-9Al合金的晶粒有细化作用。     

恒定磁场作用下Al-Pb偏晶合金凝固过程研究

以Al-Pb偏晶合金在恒定磁场下的凝固过程为研究对象,实验分析了不同强度恒定磁场、不同定向凝固速度条件下,磁场强度、凝固速度和合金成分对弥散相液滴形核率及平均尺寸的影响,并模拟了凝固组织演变过程,得到了恒定磁场对偏晶合金凝固的影响机理。     

Cu-P基非晶态钎料基础性研究

研究了四元Cu87.6-x Ni8.3 Sn4.1Px钎料的非晶形成区,发现当x=11.9～16.5at%时,为非晶态合金。该非晶形成区比我们关于三元Cu90-x Nil0 Px钎料的研究结果要宽一些。还测定了四元CuNiSnP非晶态钎料的熔点、润湿性、钎焊接头机械强度、电阻以及显微组织随P含量的变化关系,发现随着P含量增加润湿性增加。而机械强度降低,讨论了其原因。综合所测定的性能指出,四元CuNiSnP非晶态钎料代替Ag-Cu基钎料的可行性。     

黑磷的力学及摩擦学性能研究进展

归纳了黑磷在力学和摩擦学方面的理论计算和实验研究进展,重点总结了黑磷因其独特的褶皱结构而导致的负泊松比及力学性质的各向异性,关注了厚度、缺陷、预应变以及环境降解等因素对其力学性能的影响。黑磷优异的力学性能为运动传感器、柔性器件、安全装备以及微机电系统等的设计与开发提供了新的选择。应变以及缺陷对其力学性能的调控可以为黑磷的应用推广提供新的思路。大气环境条件下,黑磷的表面降解是阻碍其应用的一大瓶颈,但其化学活性可以在摩擦学领域中加以利用,实现超润滑。同时重点概述了近年来对黑磷的微观摩擦学研究,主要集中在黑磷摩擦性能的各向异性、厚度和载荷的影响,以及表面降解对润滑的贡献。黑磷纳米片、黑磷量子点等纳米材料在油基润滑、水基润滑以及聚合物复合材料方面的摩擦学研究表明,高载下黑磷的润滑性能优异,有望推动工程领域超润滑的实现。最后,对二维纳米材料黑磷未来的研究与发展做了进一步的展望。     

Effects of Phosphorus and Iron on Microstructures and Mechanical Properties in NiCrFe-Based Alloys

The microstructures and mechanical properties, especially creep properties, of the NiCrFe-based alloys with various contents of phosphorus and iron were investigated. The results showed that the tensile yield strength decreased with increasing iron contents while had no obvious change with the addition of phosphorus. For creep properties, the alloy with 15.8 wt% iron and 0.09 wt% phosphorus possessed the longest creep life (679 h) among all alloys. Only M₂₃C₆was formed in the alloys with low phosphorus contents, while both intergranular M₃P and M₂₃C₆ precipitated with the increment of phosphorus, which enhanced the strength of grain boundary by hindering the movements of dislocations during creep tests. The reasons for the enhancement of creep life were mainly related to the solid solution strengthening effect of phosphorus and optimization of grain boundary precipitations by phosphorus.     

Effect of semi-solid forming on the microstructure and mechanical properties of the iron containing Al-Si alloys

Iron is the most common impurity in aluminum casting alloys. The iron-bearing intermetallic compounds have the detrimental effects on the mechanical properties of the alloys. The aim of this research is to study the effects of plastic deformation and semi-solid forming on the morphology and distribution of the iron-bearing intermetallics and the microstructure and mechanical properties of the Al-Si alloys. Different amounts of iron and manganese were introduced into the A380 aluminum casting alloys. The alloys were processed through plastic deformation, recrystallisation and partial melting (RAP), and thixoforming. The microstructure and mechanical properties of the thixoformed alloys were investigated. The results showed that the RAP and thixoforming processes promote the formation of the very fine and well-distributed α-Al₁₅(FeMn)₃Si₂ compounds in the aluminum matrix. The yield and tensile strength as well as elongation of the alloys have been increased considerably by semi-solid forming compared with the as-cast condition.     

真空压铸Mg-7Al(-2Sn)合金组织性能研究及第一性原理计算

利用光学显微镜、扫描电子显微镜、能谱分析、X射线衍射、差热分析及拉伸试验比较分析了2%Sn(质量分数)对真空压铸和固溶态Mg-7Al合金的组织与力学性能的影响。结果表明,向Mg-7Al合金中添加2%Sn元素后,能够细化晶粒,抑制Mg17Al12相的生长,在组织中形成新相Mg2Sn,其以颗粒状弥散分布于基体中;固溶处理后Mg-7Al合金中第二相数目明显减少,AT72合金基体中仍存在细小颗粒状Mg2Sn。由于合金组织细化、第二相数量的增加,Mg17Al12相形貌改善以及具有良好热力学性质的Mg2Sn相的析出的综合作用,使得AT72合金表现出比Mg-7Al合金更好的室温及高温拉伸力学性能;固溶处理后的AT72合金表现出更为优异的力学性能,主要强化机制包括:固溶强化和弥散强化。此外,利用第一性原理计算从微观理论角度探讨了Sn合金化Mg-7Al合金力学性能改善的原因。     

Al alloys: The influence of concurrent precipitation on recrystallization behavior,kinetics, and texture

Concurrent precipitation has a profound influence on the recrystallization behavior of aluminum alloys. This paper will highlight its effects on recrystallization kinetics and texture and its subsequent effects on mechanical anisotropy (earing) and general mechanical property behavior of aluminum alloys. For more information, contact J.G. Morris, University of Kentucky, Light Metals Research Laboratories, College of Engineering, 151 Anderson Hall, Lexington, KY 40506; (859) 257-8090; fax (859) 323-1929; e-mail wcliu@engr.uky.edu.     

Intergranular corrosion of iron-phosphorus alloys in nitrate solutions

The corrosion of Fe-P alloys with 0.003–2.5 wt.%P has been studied in hot nitrate solutions. The current-potential curves show an extended active range and increased corrosion currents for high phosphorus alloys. The alloy with 2.5P does not passivate at all. The other alloys have been tested for intergranular corrosion in the passive range at 1,000 mV(SHE). The intergranular attack increases with increasing phosphorus content and can be correlated to its grain boundary concentration. The grain boundary concentrations had been established by equilibrium segregation at temperatures between 400 and 80°C and were determined by Auger electron spectroscopy (AES). The presence of phosphorus in solid solution and segregated to the grain boundaries prevents the formation of a passive layer on iron, if its local concentration is higher than ca. 2–3 at.%.     

To the co-effect of impurity atoms and structure on the dissolution of iron and its low alloys

With the use of tracers, the separate effect of small nickel additions, as well as phosphorus and manganese impurities (including their combinations with sulfur) on the corrosion electrochemical behavior of active iron is studied. Nickel (2.2%) and phosphorus (only 0.07%), which are substantially more corrosion resistant than iron, are found to noticeably suppress the active dissolution of iron from its alloys, whereas the unstable manganese (0.43%) and its sulfides (in an alloy containing 0.43% Mn and 0.06% S) accelerate the dissolution. An effect similar to that of manganese is produced by a simple increase in the defectiveness of the iron crystalline structure. The largest deceleration is observed at a small surface coverage of the dissolving alloy with nickel or phosphorus, whereas the activating effect of manganese and its sulfides is accompanied by their selective transfer to the solution. With an increase in the potential, both effects decrease in magnitude. Generalizing these and other data on the effects of impurities and structural defects on the active dissolution of iron made us reveal the substantial effect of the metal purity and its surface defectiveness (including that induced by a potential increase) on the steady-state kinetics of the process. All the regularities of the effect theoretically follow from the crystal-chemistry concept of dissolution.Translated from Zashchita Metallov, Vol. 41, No. 2, 2005, pp. 141–148.Original Russian Text Copyright © 2005 by Plaskeev.     

Research progress on microstructure evolution of semi-solid aluminum alloys in ultrasonic field and their rheocasting

The effects of ultrasonic vibration（UV）treatment on microstructure of semi-solid aluminum alloys and the application of UV in rheocasting process are reviewed.Good semi-solid slurry can be produced by high-intensity UV process for aluminum alloys.The microstructures of Al-Si,Al-Mg and Al-Cu alloys produced by rheocasting assisted with UV are compact and with fine grains.The mechanical properties of the UV treated alloys are increased by about 20%-30%.Grain refinement of the alloys is generally considered because of cavitation and acoustic streaming caused by UV.Apart from these mechanisms,a hypothesis of the fuse of dendrite root caused by capillary infiltration in the ultrasonic field,as well as a mechanism of crystallites falling off from the mould-wall and crystal multiplication by mechanical vibration effect in indirect ultrasonic vibration are proposed to explain the microstructure evolution of the alloys.     

TiAl基合金的工艺—显微组织—力学性能关系

因密度、比刚度、高温比强度和阻燃性等方面的优势,TiAl基金属间化合物被认为是最有应用潜力的新一代结构材料。室温脆性以及延性、蠕变性能和其它性能的平衡是阻碍TiAl基合金作为高温结构材料实际应用的主要障碍。在分析合金化对组织与性能的影响及机理、加工／热处理 对组织与性能的影响、变形和断裂机制、显微组织与拉伸性能的关系、抗氧化性及改善、蠕变性能与蠕变机制的基础上,论述了TiAl基合金的工艺－显微组织－力学性能关系。