增材制造TiAl合金的研究进展

采用等离子电弧双丝增材制造技术成功制备了Ti-48Al合金(at.%),并对其沉积态和热处理后的组织特征进行了系统地研究. 结果表明,沉积态Ti-48Al合金主要由α₂相和γ相组成,沿着沉积方向,沉积态组织呈现由树枝晶区和片层晶团区交替分布的不均匀性特征,并且在树枝晶区存在严重的枝晶间Al元素偏析现象. 在1340 ℃/10 h/炉冷热处理后,不均匀的沉积态组织转变为晶粒尺寸细小的双态组织,Ti-48Al合金的微观组织的不均匀性获得明显改善,并且α₂相含量显著增加,组织的择优取向减弱.

     

粉末冶金制备TiAl合金研究进展

轻质高强耐高温的TiAl合金一直是备受瞩目的先进结构材料,在航空航天、汽车等领域应用潜力巨大。但TiAl合金热加工性差,采用传统方法热成形难度大。而粉末冶金由于近净成形的特点,在制备复杂TiAl合金零部件上具有显著优势。近年来,科研工作者在TiAl合金粉末烧结技术上展开了大量工作,并取得一定进步。本文结合TiAl合金粉末成形技术的国内外发展现状,综述了放电等离子烧结(SPS)、热等静压、热压烧结、喷射成形、金属注射成形等方法制备TiAl合金的工艺、显微组织、力学性能和零部件,论述了上述制备方法的特点以及目前存在的不足,并提出了粉末冶金成形TiAl合金零部件的建议与未来发展方向。     

难熔金属高熵合金研究进展

高熵合金以全新的设计理念及优异的性能引起广泛关注。难熔高熵合金（RHEAs）作为高熵合金的一类,主要由BCC晶体结构构成,具有高强高硬的特点,同时具有抗高温软化能力。本文针对难熔高熵合金制备方法、相结构、组织形貌、力学性能、应用领域等方面进行阐述,并对难熔高熵合金的发展方向进行了展望。     

Effects of high niobium addition on the mechanical properties and high-temperature deformability of gamma TiAl alloy

The effects of Nb on the mechanical properties, high-temperature deformability and some other basic properties of TiAl–Nb alloys were investigated over a wide compositional range, and an appropriate composition for high-temperature applications was investigated for both wrought and cast materials. The lattice parameter of Ti–50Al–xNb alloy, which is a γ single phase alloy, shows an anisotropic variation with Nb content. This lattice distortion is assumed to be responsible for the strengthening and embrittlement of high-Nb ternary alloys. In the case of wrought materials, no appropriate composition exists in the high-Nb content region since wrought materials require good forgeability and high-temperature strength which are properties of antithesis. In the case of cast materials, however, an appropriate composition exists in the vicinity of Ti–46Al–7.5Nb (at.%).     

Dynamic measurements of the load on castings and the contraction of castings during cooling in sand molds

The load on flange castings in sand molds was gradually increased beginning from the end of the solidification process until the final cooling stage. The maximum tensile load on the flange castings in furan sand molds was larger than that of the flange castings in green sand molds. With the furan sand mold, permanent deformation in the flange castings occurred beginning from the end of the solidification process until reaching a temperature of approximately 250 °C. The mechanical interaction between the casting and the sand mold should be considered for more accurate stress calculations, particularly in furan sand molds.     

Simulation on extrusion process of TiAl alloy

The rigid-plastic finite element Deform-3D software was employed to describe the plastic deformation behavior of TiAl billet (Ti-46.5Al-2.5V-1.0Cr-0.3Ni alloy) during its axisymmetric extrusion through a conical die. Under various extrusion conditions, the present numerical analysis investigated the strain distribution, the damage factor distributions and the die load during the extrusion process. The relative influences of the die semi-angle and the extrusion ratio were examined. The results show that the extrusion force was enhanced from 1.54 × 10⁶ N to 2.81 × 10⁶ N with a certain slop coefficient (about 0.04) when die semi-angle increased in the range 40°≤ α ≤ 70°. The uniform effective strain and the lower propensity for fracture could be obtained at the 60° die semi-angle. The 60° die semi-angle will be an appropriate choice for the extrusion of TiAl alloy. With the raising of extrusion ratio, the effective strain, extrusion load and the damage factor in billet would also be increased.     

Research on investment casting of TiAl alloy agitator treated by HIP and HT

Using TiAl alloy to substitute superalloy is a hot topic in aeroengine industry because of its low density, high elevated temperature strength, and anti-oxidization ability. In this research, Ti-47.5AL-2Cr-2Nb-0.2B alloy was used as the test material. By applying a combination process of ceramic shell mold and core making, vacuum arc melting and centrifugal pouring, and heat isostatic pressing (HIP) and heat treatment (HT) etc., the TiAl vortex agitator casting for aeroengine was successfully made. This paper introduced key techniques in making the TiAl vortex agitator with investment casting process, provided some experimental results including mechanical properties and machinability, and explained some concerns that could affect applications of TiAl castings.     

Microstructure and mechanical properties of TiAl castings produced by zirconia ceramic mould

Owing to their low density and attractive high-temperature properties, gamma titanium aluminide alloys (TiAl alloys, hereafter) have significant potential application in the aerospace and automobile industries, in which these materials may replace the heavier nickel-based superalloys at service temperatures of 600-900℃. Investment casting of TiAl alloys has become the most promising cost-effective technique for the manufacturing of TiAl components. Ceramic moulds are fundamental to fabricating the TiAl casting components. In the present work, ceramic mould with a zirconia primary coat was designed and fabricated successfully. Investment casting of TiAl blades and tensile test of specimens was carried out to verify the correctness and feasibility of the proposed method. The tensile test results indicate that, at room temperature, the tensile strength and the elongation are about 450 MPa and 0.8%, respectively. At 700℃, the tensile strength decreases to about 410 MPa and the elongation increases to 2.7%. Microstructure and mechanical properties of investment cast TiAl alloy are discussed.     

合金化对TiAl合金高温变形行为的影响

TiAl合金的热加工（锻造、热挤压、板材轧制等）窗口窄,高温变形能力差,室温脆性大等成为限制其应用的关键因素,本文主要综述了合金成分对TiAl合金热变形加工以及超塑性成形影响等方面的研究现状,从TiAl合金的晶体结构、β相含量、显微组织细化、热变形激活能四个方面探讨了合金成分对TiAl合金热变形加工的影响,并指出合金化方式提高TiAl合金热变形加工能力应该遵循的几点原则,以及TiAl合金热变形加工的未来发展趋势。     

铝合金无沉淀析出带的研究进展

综述了过去50年来铝合金中无沉淀析出带(PFZ)的研究,重点论述了PFZ的主要形成机理、影响因素及其对合金性能(主要为力学性能和耐腐蚀性能)的影响,系统介绍了PFZ在形成机理及对合金性能上所持的不同观点及其相关理论。最后,提出了对铝合金中PFZ方面存在的难点以及重点研究方向。     

TiAl基合金及其连接技术的研究进展

综述了TiAl基合金熔焊和固态连接的研究状况,主要包括弧焊、激光焊、电子束焊、钎焊、扩散焊、自蔓延高温合成和摩擦焊等连接方法,分析了各种方法用于TiAl基合金连接时的优缺点.由于TiAl基合金室温塑性差,采用熔焊方法连接时焊后冷却速度块,接头组织淬硬倾向大,易形成固态裂纹.固态连接方法大多可控制焊接热循环,焊接过程中加热峰值温度相对较低,对母材组织影响小,可避免裂纹等缺陷,因而采用固态连接方法具有优势.如果能进一步降低冷却速度,则将熔焊方法用于TiAl基合金的连接有很好的应用前景.     

核燃料包壳锆合金表面涂层研究进展

锆合金表面涂层是提高核燃料包壳事故容错能力的重要途径之一。本文综述了锆合金表面涂层的研究进展,包括涂层种类、制备工艺、微观组织以及抗水蒸气氧化性能、耐腐蚀性能等,介绍了锆合金表面涂层种类选择的依据,探讨了涂层的制备工艺、微观组织与性能之间的关系,分析了当前研究中存在的若干问题及未来涂层的发展方向,为进一步促进核燃料包壳锆合金表面涂层的研究提供了有价值的参考。     

TiAl基合金钎焊技术研究现状及展望

TiAl基合金具有质量轻、耐高温等优点,在航空航天、军用战车和民用汽车的高温部件中具有广阔的应用前景。TiAl基合金实用化要求解决其连接问题,而其本质脆性使得钎焊技术成为实现TiAl基合金连接,特别是与其他材料连接的重要方法,综述了TiAl基合金钎焊技术研究现状,指出了目前存在的问题,进而对钎焊研究方向进行了展望。     

Improving hot deformability of TiAl alloys by minor additions of Ni and Mg

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高熵合金涂层的研究进展

高熵合金涂层在工程实际应用中较传统合金具有良好的前景,对近年来高熵合金涂层的研究进展进行了概述.首先对制备高熵合金涂层的表面熔覆技术进行详细的介绍,其中包括激光熔覆技术、等离子熔覆技术、氩弧熔覆技术,分析了各表面熔覆技术的优缺点;然后总结了高熵合金涂层的组织及性能特征,涂层中相的组成包括:固溶体相、金属间化合物、纳米析...     

铒微合金化铝合金的研究进展

微合金化是提高铝合金性能的重要途径,控制微量元素的种类和含量,充分发挥微量元素的作用是当前铝合金研究的主要方向之一。大量研究表明:廉价的Er能够起到有效的微合金化作用,Er元素在铝合金中可形成纳米级Al3Er强化相,并可通过与Zr复合作用形成Al3(ZrxEr1-x)复合相,比Al3Sc相具有更好的热稳定性,从而可以改善铝合金组织,大幅度提高铝合金的强度或塑性、明显抑制铝合金的再结晶以提高其耐热性,改善其综合性能。本文作者针对微合金化元素Er在铝合金中析出Al3Er相及Al3(ZrxEr1-x)复合相的过程及其对合金组织和性能的影响机理,以及Er微合金化在几类工业合金体系中的作用,介绍含铒铝合金的最新研究进展。     

TiAl合金与异种材料的摩擦焊接

TiAl合金与42CrMo直接摩擦焊接性较差,为此分别引入高温合金GH3039、K418、N80A和纯镍N6作为中间材料,对TiAl-GH3039/K418/N80A/N6-42CrMo异种材料的摩擦焊接工艺进行了研究。采用硬度计、扫描电镜和电子万能试验机对焊后接头区域的硬度、组织和焊合区成分变化以及接头力学性能进行了分析。研究表明,TiAl合金与异种材料焊后接头中形成了复杂的多层状金属间化合物;TiAl合金与GH3039、N80A的摩擦焊接性较好,与K418、N6的摩擦焊接性较差;根据不同材料线膨胀系数随温度的变化规律、与TiAl合金摩擦焊接后接头的性能及其与42CrMo的摩擦焊接性,最终选择GH3039作为中间材料。通过引入中间材料,摩擦焊制备了TiAl合金涡轮-42CrMo转轴的异种材料整体转子,使得TiAl合金在涡轮增压器领域的应用成为可能。