Structural,electronic, elastic,mechanical and thermal behavior of RESn3(RE = Y,La and Ce) compounds: A first principles study

The structural, electronic, elastic, mechanical and thermal properties of the isostructural and isoelectronic nonmagnetic RESn₃ (RE = Y, La and Ce) compounds, which crystallize in AuCu₃-type structure, are studied using first principles density functional theory based on full potential linearized augmented plane wave (FP-LAPW) method. The calculations are carried out within PBE-GGA, WC-GGA and PBE-sol GGA for the exchange correlation potential. Our calculated ground state properties such as lattice constant (a₀), bulk modulus (B) and its pressure derivative (B′) are in good agreement with the experimental and other available theoretical results. We first time predict the elastic constants for these compounds using different approximations of GGA. All these RESn₃ compounds are found to be ductile in nature in accordance with Pugh's criteria. The computed electronic band structures and density of states show metallic character of these compounds. The elastic properties including Poisson's ratio (σ), Young's modulus (E), shear modulus (G_H) and anisotropy factor (A) are also determined using the Voigt–Reuss–Hill (VRH) averaging scheme. The average sound velocities (v_m), density (ρ) and Debye temperature (θ_D) of these RESn₃ compounds are also estimated from the elastic constants. We first time report the variation of elastic constants, elastic moduli, Cauchy's pressure, sound velocities and Debye temperatures of these compounds as a function of pressure.     

AuCuI（A8AuA4Cu）化合物无序化路径跟踪的原子移动新机制

以由AAu8和ACu4干基因组成的AuCuI（AAu Cu8 A4）化合物的无序化实验路径为例,介绍了3个发现和1个方法。发现AuCuI（AAuCu8A4）化合物抗拒温度变化保持结构稳定性的能力归因于AAu8和ACu4基因的势阱深度远超过其振动能,这导致其无序化实验路径是亚平衡的;发现AuCuI（AAu Cu8 A4）适应温度变化改变结构的原子移动新机制是合金基因的＂共振激活-同步交换＂机制,这导致无序化是非均匀性和递次性的亚平衡转变;发现无序化过程中存在跳变有序度,导致存在跳变温度和升温速度增加跳变温度降低的＂逆反效应＂,即所谓的＂Retro效应＂。采用实验混合焓路径法,建立了一整套亚平衡全息网络路径图。     

钛表面改性Al/NiCu组合涂层反应机理及抗氧化性能

采用等离子结合电弧喷涂的工艺方法在工业纯钛表面制备了Al/Ni Cu组合涂层,在700℃的大气环境下对Al/Ni Cu/Ti试件进行加热处理,使得Al、Ni Cu复合涂层之间发生扩散反应并原位生成具有一定抗高温氧化性能的Ni-Al金属间化合物涂层。对加热改性处理前后涂层的微观组织及Ni-Al金属间化合物的形成机理进行了研究,并对经加热和打磨处理后的Al/Ni Cu/Ti试件及无防护涂层的Ti块进行了800℃/100 h的高温氧化试验。研究结果显示,Ti基体表面Al/Ni Cu涂层经700℃炉中加热改性处理后,Al、Ni Cu涂层间可发生扩散反应并原位生成Ni Al3、Cu Al2、Ni2Al3及含有一定Cu元素的Ni Al金属间化合物,但只有高熔点的Ni Al金属间化合物能够始终稳定地存在,且此金属间化合物对Ti基体起到了较好的高温防护作用。     

Mg-3Al合金中Mn对碳化铝异质形核的影响机制

采用光学显微镜、扫描电镜、EDS能谱和差热分析研究了Mg-3Al合金中AlMn中间相的形貌特征,以及Mn含量对碳质变质剂异质形核作用的影响机制。结果表明:加碳变质处理产生的碳化铝可成为a-Mg的有效形核核心;当合金中的Mn含量小于0.32%(质量分数)时,加碳变质处理能使a-Mg晶粒明显细化,最小平均晶粒尺寸达到66μm,此时形成大量细小的球状和杆状Al Mn中间相,有助于晶粒细化;但当Mn含量增加到0.56%时,形成更多粗大的十字花瓣状AlMn中间相。过量的溶质Mn易与A1_4C_3粒子结合形成不利于形核的Al-Mn-C-O复杂化合物,并导致a-Mg晶粒粗化。     

固液反应球磨制备Cu-Sn金属间化合物

研究通过Cu球对液态金属Sn在不同温度及时间内球磨制备Cu-Sn金属间化合物的过程,采用X射线和扫描电镜及透射电镜等分析手段分析产物特征.结果表明,在球料比为10：1,转速为80r/min的条件下,用Cu球对液态Sn进行不同时间及温度的液态球磨后,得到了不同的金属间化合物.在400℃时金属间化合物为Cu6Sn5,500℃及600℃时产物为Cu3Sn.加铜粉可以加快反应速度.采用固液反应球磨技术在高温下可以形成粒度很小,甚至达到纳米级的金属间化合物粉末.与机械合金化相比,固液反应球磨技术生成金属间化合物的速度较快,且成分单一.     

高硼/钇合金化提高FeAl基金属间化合物多孔材料的抗氧化性能（英文）

利用反应合成法制备高铬(Cr)、硼(B)、钇(Y)复合合金化的B2结构FeAl基金属间化合物多孔材料,通过研究FeAl基多孔材料氧化后的孔结构演变、氧化动力学和氧化膜构型,探讨其高温氧化行为。结果显示,添加高含量合金元素Cr、B和Y后,FeAl多孔材料在600～800℃下氧化增质显著降低。富集在氧化膜表面的B和偏聚在氧化膜与基体界面处的Y共同促进多孔材料表面形成薄且具有优异防护性的结节状α-Al₂O₃氧化膜。研究表明,引入较高含量的活性元素如B和Y有利于FeAl金属间化合物在较低氧化温度和无预处理的情况下选择性生长单一的α-Al₂O₃氧化膜。     

Ti-Cu复合中间层在钨/CLAM钢扩散连接中的性能

采用Ti-Cu复合中间层扩散连接钨与CLAM钢,在30 MPa、1h和800～950 ℃的条件下,成功获得了W/Ti-Cu/CLAM钢接头.接头界面连接良好,中间层区域发现有Ti2Cu或TiCu4等金属间化合物产生.TiC脆硬层使得中间层/钢界面处的硬度远高于钢母材,同时造成了接头处钢母材的失C并软化现象.随焊接温度的...     

Welding of unique and advanced ductile intermetallic alloys for high-temperature applications

Intermetallic alloys represent a unique class of materials with atomic arrangements that are different from those of conventional disordered alloys. Among them are alloys based on Ni₃Al, Fe₃Al, and TiAl. Intermetallic alloys have unique properties, such as high melting point, low density, high-temperature strength, and high-temperature corrosion and oxidation resistance. Their only disadvantage is the lack of ductility at room temperature and at elevated temperatures. However, they can be ductilised by micro- and macroalloying. Application of intermetallic alloys for structural use at elevated temperature depends on their ability to be welded using conventional welding procedures. This paper focuses on the development of these alloys, their behaviour when subjected to weld thermal cycles, and their weldability. Most intermetallic alloys are susceptible to cracking during or after welding, but some can be modified to have good weldability. The paper discusses welding and weldability of Ni₃Al-, Fe₃Al-, and TiAl-based intermetallic alloys. In addition, the weldability of other long-range ordered alloys, of the type (Fe, Ni)₃V and (Fe, Co)₃V, are briefly discussed.     

Fe3Al基合金高温变形过程中原位再结晶现象

ＴＥＭ及金相分析发现Ｆｅ３Ａｌ在高温变形过程中伴生原位再结晶。Ｆｅ３Ａｌ合金良好的高温塑性与ＩＳＲ有密切的关系，形变产生的晶格位错通过攀移或交滑移形成位错墙，在进一步的变形中，位错墙通过吸收晶内滑移位错增大两侧晶体的位向差，并逐渐向亚晶界和大角晶界演化。     

High temperature oxidation of Ti−48%Al−2%W intermetallics

Powder metallurgically produced Ti-48% Al-2%W alloys were oxidized between 800 and 1050°C in air. The W-addition was quite effective in providing isothermal and cyclic oxidation resistance. The alloys oxidized parabolically up to 1050°C during isothermal oxidation, with small weight gains. The scales were adherent up to 900°C during cyclic oxidation. Oxide scales consisted primarily of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner (TiO₂+Al₂O₃) mixed layer. Tungsten was present below the intermediate Al₂O₃ layer. and also at the scale-matrix interface as W-enriched compounds. Below the oxide scale, a Ti₃Al zone containing some W and O existed.