TiAl合金热加工性能及其影响因素

TiAl合金以其轻质、耐高温等特点成为替代镍基高温合金的重要高温结构材料。具有优异热加工性能的beta−gamma TiAl合金是变形合金的主要研究方向。总结了TiAl合金的热加工性能研究现状,分析了高温无序α相对热加工性能的作用,对β相稳定元素进行了分类,并归纳了β相稳定元素对热加工性能及力学性能的影响规律,提出了变形TiAl合金的未来研究方向。     

高推重比航空发动机用新型高温钛合金研究进展

综述了我国航空发动机用高温钛合金材料体系的发展状况。针对未来高推重比航空发动机对新型轻质耐高温结构材料的需求,重点介绍了TiAl合金和SiC纤维增强钛基复合材料2种关键的新型高温钛合金国外研究进展和应用情况。目前我国航空发动机主要应用的是α+β型钛合金,工作温度均在500℃以下,在更高温度使用的近α型钛合金(如600℃高温钛合金)尚处于研发阶段。国外对TiAl合金的研究已近20年,在航空发动机领域已公开报导了10多种TiAl零部件,并且完成了地面装机试验,试验结果非常理想。SiCf/Ti复合材料在航空发动机上的典型应用是叶环类和轴类零件,美、英等国均研制出了多个零部件,并进行了发动机考核试验。TiAl和SiCf/Ti复合材料将是新一代高推重比航空发动机用的2种关键结构材料。     

TiAl合金热加工研究进展

TiAl合金作为新一代轻质高温结构材料,具有优异的高温性能,在航空发动机等领域具有重要应用前景。但是TiAl合金具有本征脆性,热加工窗口窄,热变形易开裂,限制了其广泛应用。回顾了TiAl合金的发展历程,综述了其热变形行为以及高温锻造、高温轧制和热挤压等热加工技术,并指出了TiAl合金热加工未来发展方向。     

TiAl基合金的高温氧化及其保护

TiAl基金属间化合物由于其密度低、高温性能好,越来越受到人们的重视.简单介绍了TiAl基合金研究的重点以及研究现状,对TiAl系合金高温氧化机理进行了分析,重点讨论了高温防护涂层发展过程,并简要评述了涂层今后的研究方向     

定向凝固TiAl合金成分−组织−性能研究进展

TiAl合金由于其低密度和高比强度,在航空材料中展现出良好的应用前景。通过定向凝固控制TiAl合金晶体取向,有助于大幅提升合金高温性能和服役温度,促进TiAl合金在新一代航空发动机上的应用。综述了近年来TiAl合金定向凝固的研究方法和成分?组织?性能关系的研究进展,总结了国内外定向凝固TiAl合金的主要研究单位及研究主题,简要介绍了定向凝固方法与模壳材料的应用情况。从合金成分角度,分析并总结了α、β相稳定元素和其他常见元素对定向凝固组织和性能的作用;从力学性能角度,介绍了定向凝固高Nb?TiAl合金在高温拉伸、蠕变、高周疲劳性能上的优势及相关机理;从定向凝固工艺角度,归纳了生长速率和温度梯度对合金凝固路径、片层取向及宏观、微观偏析的影响。展望了定向凝固TiAl合金的未来发展方向。     

TiAl合金片层形成及其稳定性研究现状

TiAl合金具有低密度和优异的高温性能,是650~850 ℃温度区间内替代镍基高温合金的重要候选材料。具有片层组织的TiAl合金高温综合性能优异,但片层组织形成机理、高温服役条件下片层稳定性仍是关注的重点。综述了近年来片层形成和组织稳定性的研究成果,主要分析片层形成机制和γ变体选择机制,以及片层特征对组织稳定性的影响,并对未来的研究方向进行了展望。     

TiAl合金增压器涡轮研究进展

采用轻质TiAl合金代替较重的镍基高温合金制作内燃机增压器涡轮,是改善内燃机加速响应性、实现轻量化的有效技术途径之一.围绕TiAl合金增压器涡轮的工程化应用,分析了TiAl合金增压器涡轮的合金及组织设计、涡轮制备技术、涡轮连接技术、母合金制备技术、应用考核试验等方面的国内外研究现状和研究进展.认为我国铸造技术和连接技术...     

新型的金属间化合物基复合材料

以金属间化合物为基体的复合材料是目前正在研究的一种新型高温结构材料。本文综述了这种新型复合材料的发展现状及其制造方法。初步研究表明:纤维增强的Ni_3Al,Ti_3Al,FeAl等铝化物金属间化合物基复合材料性能优子基体材料和目前广泛使用的镍基高温合金,展现出了诱人的前景。将来的研究方向将主要集中于增强剂与基体的化学相容性,热膨胀系数的匹配,力学模型和断裂模式的建立,制备工艺的开发与优化等方面。     

TiAl基金属间化合物表面涂层研究进展

TiAl合金具有优异的高温力学性能,可以作为Ni基高温合金的轻量化替代材料,但氧化和磨损等行为限制了TiAl合金的高温服役时间,不利于工业化应用。通过在TiAl合金表面沉积涂层,可以使材料兼具基体的力学性能和涂层材料的表面性能,以提高TiAl合金适应不同服役环境的能力,进而拓展其应用范围。列举了TiAl合金使用的涂层材料应具有的性质;介绍了常见涂层的制备方法;以涂层成分分类,分别总结了不同涂层体系的研究现状,并展望了制备工艺和涂层性能的发展趋势。     

铸造用TiAl母合金制备技术研究进展

目前,新型轻质高温结构材料TiAl合金铸造部件已经进入工业化生产阶段,急需工业级铸造用TiAl母合金的制造技术和评估体系作为支撑。结合了钢铁研究总院铸造TiAl合金工程化研究和应用成果,概述了国内外铸造TiAl合金材料和部件的工程化应用现状,在此基础上,提出了铸造TiAl母合金的化学成分、规格等技术要求,并进一步对比分析了2次自耗熔炼、自耗熔炼+凝壳熔炼、自耗熔炼+凝壳熔炼+自耗熔炼等母合金制备工艺的优缺点,最后提出了工业级铸造TiAl母合金的技术发展方向。     

Reaction-sintered hot-pressed TiAl

Titanium aluminide intermetallic alloys and composites were formed from elemental titanium and aluminium powders by self propagating, high-temperature synthesis in an induction-heated hot-press. The crystal phases, density, transverse rupture stress, and hardness of the reaction-sintered compacts, were observed to be controlled by hot-pressing conditions. The principal phase formed was TiAl together with a significant second-phase concentration of Ti₃AI. The transverse rupture strength (TRS) of the intermetallic composites was observed to vary directly with compact density. Under selected high-temperature synthesis hot-pressing conditions, TRS values were comparable to those obtained for fully dense TiAl. Titanium aluminide composites were formed by adding boron, carbon, silicon and Al₂O₃, and SiC powders and whiskers to the Ti-Al powders before reaction sintering. Changing the alloying additions did not have as strong an effect on properties of the composite compacts as did varying hot-pressing conditions.     

Twinning in TiAl

The results of this investigation are in agreement with the findings of Richards and Cahn which show that the formation of twin-related TiAl regions, TiAl_T, and the Ti₃Al phase, rather than TiAl deformation twins, will be favored energetically in a two-phase titanium aluminide alloy. Due to the formation of Ti₃Al at the TiAl_T interface, all possible {111}<112> TiAl_T, as opposed to only {111}[112] deformation twins, can be formed within TiAl lamellae without the destruction of the symmetry of L1₀ structure.     

Preparation of TiAl/Mo and TiAl/NiAl composites by powder processing

Processes for preparing TiAl/Mo and TiAl/NiAl composites are described and results of the investigation are reported. It was found that the hardness of the TiAl/NiAl composites was largely influenced by the amount of hard ternary phases formed through reactions between TiAl and NiAl. The possibility of ductilizing and toughening TiAl by introducing molybdenum as a ductile reinforcement has also been shown. For both composites, optimal process parameters still remain to be determined by further experiments to suppress the formation of hard ternary phases, which are believed to be detrimental to ductility and fracture toughness. This revised version was published online in November 2006 with corrections to the Cover Date.     

表面粗糙度对TiAl/AgCu/TiAl钎焊质量的影响

为探究表面粗糙度对钎焊质量的影响,在优选的钎焊温度870 ℃和保温时间5 min条件下,以AgCu合金为钎料,进行TiAl合金的真空钎焊,研究了表面粗糙度与磨痕方向对钎料润湿铺展、钎焊接头界面组织、力学性能的影响.采用扫描电镜、能谱分析、光学显微镜和万能材料试验机等分析测试手段,对钎焊接头的组织与力学性能进行分析.结果表明：AgCu钎料在各向异性的TiAl基板表面润湿铺展时会受表面特征影响,沿着特定的方向优先铺展,当基板表面不具各向异性特征时,钎料润湿铺展近似为圆形;表面粗糙度S_a=0.103 μm的基板,钎焊接头的平均剪切强度最优,达到323 MPa,而表面粗糙度S_a=0.133 μm的基板,接头平均剪切强度为245 MPa,钎焊接头强度均方差最大.     

TiAl及TiC／TiAl合金的XD合成研究

本文研究了用ＸＤ工艺合成ＴｉＡｌ合金及ＴｉＣ／ＴｉＡｌ复合材料，研究结果表明，可在Ａｌ的熔点附近用ＸＤ工艺制备ＴｉＡｌ合金及其ＴｉＣ颗粒增强复合材料。ＴｉＡｌ合金由ＴｉＡｌ＋Ｔｉ３Ａｌ相组成，而ＴｉＣ／ＴｉＡｌ复合材料由ＴｉＣ＋ＴｉＡｌ＋Ｔｉ３Ａｌ相组成。     

Oxidation of TiAl based intermetallics

The high temperature oxidation behaviour of the binary and ternary alloys of the Ti–48Al system was studied at different temperatures. The primary objectives of this work were the establishment of the activation energies, the migration tendencies of the alloy species, mechanism of oxidation and chemistry of the oxide scales. The ternary additions were Cr (1.5 at 19%), V (2.2 at%), W (0.2 at%) and Mn (1.4 at%). The addition of ternary additions did not play a significant role in the oxidation behaviour at 704°C. At 815°C the alloys with Cr and V exhibited linear oxidation behaviour with large weight gains while the base Ti–48Al alloys exhibited the best behaviour. At 982°C the Mn-containing alloy was the worst, exhibiting a linear oxidation behaviour while the alloy with V and W and the base alloy with 400 p.p.m. oxygen exhibited the best oxidation behaviour. At 982°C the outermost oxide layer in contact with air is always near stoichiometric TiO₂. In all the alloys a layer of porosity is created just below the outer TiO₂ layer by the Kirkendall mechanism due to the rapid outward diffusion of Ti atoms. The addition of trivalent atoms like Cr in small amounts appear to be detrimental to the oxidation process as they can generate additional oxygen vacancies while the addition of atoms with valence of 5, such as V, and 6, such as W, appear to have beneficial effect on the oxidation behaviour at 982°C by tying up oxygen vacancies. This revised version was published online in November 2006 with corrections to the Cover Date.     

TiAl基金属间化合物研究进展

与普通超合金相比，TiAl基金属间化合物以其优异的性能在航空和汽车工业中应用越来越广泛，本文总结了TiAl基合金在微观结构控制、微观组织对性能影响、合金化、熔炼技术、加工技术以及应用等方面的研究进展。     

High-temperature internal friction on TiAl intermetallics

In order to study the microscopic mechanisms controlling the plastic deformation at high temperature of two γ-TiAl alloys with nominal compositions: Ti–46.5Al–4(Cr, Nb, Ta, B) and Ti–45Al–(5–10)Nb (in at.%), internal friction (IF) measurements have been performed. A subresonant torsion pendulum has been used working in two different modes; changing the temperature between 300 and 1200 K at a constant frequency, and varying the frequency between 0.001 and 10 Hz at a fixed temperature. The resulting mechanical spectra show an anelastic relaxation peak at about 1060 K at 1 Hz in one of the alloys and a high-temperature background in both of them. Activation parameters of the loss peak have been calculated and an activation enthalpy of about 3.8 eV is obtained. The characteristics and a possible responsible mechanism for this relaxation peak are discussed.