Electron Theory Research in Mg-Y Alloy

Adding yttrium to magnesium can improve the mechanical properties, especially the mechanical behavior at high temperature. The valence electron structures of Mg-Y alloy were analyzed with the empirical electron theory of solids and molecules (EET). Calculation shows that yttrium is on the fifth hybrid level and magnesium is on the third one in pure metal crystals. By comparing with aluminum in Mg-Al alloy, it is shown that the reason why the solution strengthening effect of yttrium is better than that of aluminum in Mg-Al alloy is the enhanced bond energy according to EET. And it is concluded from EET analysis that intermetallies Mg24Y5 can significantly improve the properties of magnesium alloys because yttrium atoms oceupy the centers of the oetahedron and Mg-Y bonds efficiently strengthen the alloy matrix.     

Synthesis and Characterization of Spark Plasma Sintered FeAl and In situ FeAl–Al2O3 Composite

In the present work, nanocrystalline FeAl and FeAl–Al₂O₃ composite were synthesized by high energy ball milling and subsequent compaction by spark plasma sintering. Microstructural changes during all stages of processing are studied using X-ray analysis. After 20 h of milling, the disordered FeAl and some amount of Fe rich solid solution was obtained in both of these compositions. Subsequent heat treatment results in formation of ordered FeAl. However, disordering of FeAl was observed in both compositions after spark plasma sintering. Nanocrystallinity is retained in both the compositions even after sintering at high temperature of 1,000 °C. Very high hardness of ~575 HV₁ and ~600 HV₁ was exhibited by FeAl and FeAl–Al₂O₃ composite.     

Transient liquid phase sintering of high density Fe3Al using Fe and Fe2Al5–FeAl2 powders Part 2 – Densification mechanism analysis

Abstract

The use of Fe₂Al₅–FeAl₂ prealloyed powders and heating rates >150 K min^?1 overcomes the formation of density restricting Kirkendall porosity in the Fe–Al system. X-ray diffraction, electron probe micro analysis and differential thermal analysis suggest that the absence of a persistent liquid, experienced when liquid phase sintering with elemental powders, is overcome. Homogenisation is greater during heating at a rate of 20 K min^?1 than for 150, 250 or 400 K min^?1 and homogenous Fe₃Al forms across the compact at temperatures below the melting point of the liquid forming constituent, indicating that a liquid will not form under such processing conditions. The maximum density achieved under the processing conditions in the present study is 92% of theoretical density. The presence of large pores shortly after liquid formation suggests that the remaining porosity is largely due to powder agglomeration during mixing.     

Study of the Structure and Properties of Cermets Based on the NiAl–Al2O3 System

Russian Journal of Non-Ferrous Metals - The powder metallurgy method, including the mechanical activation of powders in a planetary mill and spark plasma sintering at 1470°C in an inert...     

Interdiffusion Study in the Fe–Nb System

The diffusion characteristics of the Fe–Nb system were investigated using the diffusion couple technique. The average interdiffusion coefficient was calculated for the Fe₂Nb Laves and the FeNb μ phases. The possible diffusion mechanism was predicted by using the calculated values of the activation energy for diffusion. Kirkendall marker experiments were conducted to determine the relative mobilities of the species. Fe was found to have a faster diffusion rate than Nb in both phases.     

The order-disorder transformation in Ni3Al and Ni3AlFe alloys—II. Phase transformations and microstructures

From a combination of dilatometric and micrographie evidence, the precipitation of the β′ phase at temperatures above the metastable ordering transition, T_tm, is demonstrated for those NiAlFe alloys containing at least 19 at.% Al. Ni-AlFe alloys which have been heated above T_tm and then slow-cooled are found to contain a network of disordered γ phase which outlines the boundaries of antiphase domains in the ordered γ′ phase. The implication of these observations is that the formation of equilibrium γ phase from off-stoichiometric γ′ requires antiphase domain boundaries as nucleation sites: the T_tm determined by dilatometry represents an upper absolute instability limit at which the ordered phase is converted into disordered phase of the same composition, whereas the equilibrium disordered phase would have a different composition. The microstructure of a series of binary Ni-Al alloys are examined: at 22–23 at.%Al, the γ′ phase consists of grains which partly contain fine antiphase domains (with γ at the APD boundaries) and partly very coarse APD's; microanalysis established that this is due to microségregation, and that the coarse APD's are in regions with excess Al so that T_tm is locally above the freezing temperature. The structural distinction between directly and sequentially ordered alloys is thereby made clear: fine APD's form only in alloys which freeze in disordered form.     

A Study on the Dissolving Loss of Nd in the NdCl_3-Containing Systems

The Dissolving loss of Nd in the systems NdCl_3-MCl_n(M=Li,Na,K,Ca,Sr,Ba;n=1 or 2)and the NdCl_3-rich NdCl_3-LiF motlen salts,and in the system of NdCl_3-(90 wt% KCl,10 wt%MCl_n) wasdetermined.It was found that the dissolving loss of Nd (B_(Nd)) in the NdCl_3-KCl,NdCl_3-CaCl_2 andNdCl_3-(90 wt%KCl,10 wt%CaCl_2) melts is rather insignificant.The dissolving loss of Nd in theNdCl_3-KCl system increases with temperature,yet it is only 1/3 of that in pure NdCl_3 when the content ofNdCl_3 was less than 50 wt% in the mixture.Addition of LiF to NdCl_3 can diminish the dissolving loss ofNd.The nature of interaction between metallic Nd and its salts was also discussed.     

Study on the Interaction between Rare Earth and Carbon in High Carbon Steel

ＳｔｕｄｙｏｎｔｈｅＩｎｔｅｒａｃｔｉｏｎｂｅｔｗｅｅｎＲａｒｅＥａｒｔｈａｎｄＣａｒｂｏｎｉｎＨｉｇｈＣａｒｂｏｎＳｔｅｅｌ￥ＬｉｎＱｉｎ（林勤），ＦｕＴｉｎｇｌｉｎｇ（付廷灵），ＹｕＺｏｎｇｓｅｎ（余宗森），ＹｅＷｅｎ（叶文）（Ｕｎｉｖｅｒｓｉｔ...     

添加元素对Fe3Al金属间化合物高温性能的影响

本文对Ｆｅ３Ａｌ金属间化合物的高温力学性能和氧化性能进行了研究。硼、钛、铬等元素对改善Ｆｅ３Ａｌ的高温强度是非常有效的。但元素铬的加入稍许降低了６００℃以上时的抗氧化性。     

热处理工艺对Fe3Al室温力学性能的影响

本文比较了添加Ｃｒ合金元素的Ｆｅ_３Ａｌ金属间化合物在不同热处理工艺条件下的室温力学性能。通过轧制后的二次７００℃／ｌｈ油冷处理，合金的室温塑性有较大的改善。     

铌对Ti_3Al价电子结构及其脆性的影响

应用固体与分子经验电子理论计算了Ｔｉ３Ａｌ 及加入铌后各相的价电子结构， 并从均匀变形因子α、解理能Ｇｃ 及位错行为等方面分析了铌对Ｔｉ３Ａｌ 脆性的影响。铌使Ｔｉ３Ａｌ 合金的α及Ｇｃ 提高； 同时铌也减弱了ＴｉＴｉ 共价键， 增加了基面滑移， 从而导致Ｔｉ３Ａｌ 脆性有本质改善。     

铌对Ti3Al价电子结构及其脆性的影响

应用固体与分子经验电子理论计算了Ｔｉ３Ａｌ及加入铌后各相的价电子结构,并从均匀变形因子α,解理能Ｇｃ及位错行为等方面分析了铌对Ｔｉ３Ａｌ脆性的影响,铌使Ｔｉ３Ａｌ合金的α及Ｇｃ提高;同时氟也减弱了Ｔｉ－Ｔｉ共价键,增加了基面滑移,从而导致Ｔｉ３Ａｌ脆性有本质改善。     

Hydrogen Embrittlement Processes and AL／AL2O3 Hydrogen Resistance Coatings of NdFeB Magnets

After analyzing the phenomena and processes of hydrogen embrittlement of NdFeB permanent magnets, RF magnetron sputtering was used to fabricate A1 thin films and then oxidized to form the Al/Al2O3 composite films on the magnets as the hydrogen resistance coatings. SEM and EDS were used to examine the morphology and composition respectively. Hy-drogen resistance performance was tested by exposing the magnets in 10 MPa hydrogen gas at room temperature. The results show that the magnets with 8μm Al/Al2O3 coatings can withstand hydrogen of 10 MPa for 65 min without being embrittledinto powd er. The samples with and without hydrogen resistance coatings have almost the same magnetic properties.     

Microstructure and Room Temperature Tensile Properties ofFe_3Al－based Alloys with Cerium Addition

ＭｉｃｒｏｓｔｒｕｃｔｕｒｅａｎｄＲｏｏｍＴｅｍｐｅｒａｔｕｒｅＴｅｎｓｉｌｅＰｒｏｐｅｒｔｉｅｓｏｆＦｅ_３Ａｌ－ｂａｓｅｄＡｌｌｏｙｓｗｉｔｈＣｅｒｉｕｍＡｄｄｉｔｉｏｎＺｈａｎｇＺｈｏｎｇｈｕａ（张忠铧），ＳｕｎＹａｎｇｓｈａｎ（孙扬善），Ｇｕ?..     

非对称Fe_3Al金属间化合物粉末滤芯研究

采用湿法喷涂与真空高温烧结工艺,制备非对称Fe_3Al金属间化合物粉末滤芯。利用扫描电子显微镜、能谱仪及X射线衍射仪等设备,观察与分析了滤芯的微观形貌、成分及物相。研究了不同表面膜层厚度滤芯样品的孔隙特性,分析了黏结剂与固化剂对滤芯力学性能的影响,测试了实验样品表面膜层与基体的结合强度。结果表明:经真空高温烧结之后,滤芯表面膜层颗粒仍为球状形貌,颗粒之间形成了相互连接的烧结颈;粗大的滤芯基体颗粒与细小的膜层颗粒之间也形成了烧结颈,两者发生了冶金结合;表面膜层厚度在200μm时,孔径与渗透性具有较好的匹配关系;黏结剂与固化剂对滤芯力学性能没有明显影响;滤芯表面膜层与基体的结合强度高于25 MPa。     

建筑型材常温封孔后氧化膜陈化过程的研究

Ni-F体系常温封孔的氧化膜曝露在大气中，封孔反应仍在缓慢而持续的进行，氧化膜的结构发生变异，即氧化膜的陈化过程。本文对在常规工艺下生成的氧化膜封孔后陈化历程进行了研究。     

热机械处理对Ti3Al基合金板条组织形貌及室温拉伸性能的影响

研究了热机械处理（ＴＭＰ）对Ｔｉ３Ａｌ基合金Ｔｉ－２４Ａｌ－１４Ｎｂ－３Ｖ（原子分数％）板条组织的形貌及室温拉伸性能的影响，通过ＴＭＰ可获得各种各样的板条组织。Ｔｉ－２４Ａｌ－１４Ｎｂ－３Ｖ板条组织的最高断裂强度可达１２２５ＭＰａ，最大伸长率达８．５％，对板条形貌与室温拉伸性能的关系进行了分析，用ＳＥＭ观察了室温拉伸过程中的裂纹扩展情况，经ＴＥＭ观察发现，在缓冷样品中板用周边存在着一种α２＋Ｏ相的     

铬,锰对Fe3Al合金连续加热中有序转变的影响

本文用电阻法对Ｆｅ３Ａｌ使合金在连续加热过程中的有序转变进行了研究。并探讨了合金化元素Ｃｒ、Ｍｎ及合金加热次数的影响。结果表明，Ｃｒ、Ｍｎ对Ｆｅ３Ａｌ合金的有序化转变有延缓作用，并且这种作用与合金元素分布有关。