TiAl基合金在汽车发动机上的应用

以金属间化合物TiAl为基的合金密度只有铁基或镍基高温合金的一半，且高温比强度高，作为轻质耐热材料非常引人注目。在飞机和汽车发动机中都期待着TiAl基合金的实用化，以降低燃料费，减少排放量。但是，实际上，由于TiAl基合金室温塑性低，高温强度、抗氧化性不足，制造困难等，使实用化相当困难。日本大同特殊钢公司自1985年开展TiAl基合金的实用化研究以来，开发了TiAl基合金近净形加工的精密铸造和接合等相关技术，于1998年实现了TiAl基合金的赛车发动机增压器涡轮的实用化。 1 合金开发 要进行TiAl基合金的实用化，必须要改…     

全层状TiAl合金室温拉伸性能的影响因素

研究了显微组织和应变速率对全层状Ti-47Al-2Cr(at%)合金室温拉伸性能的影响，结果表明，全层状TiAl基合金的室温拉伸强度和室温延伸率随晶团尺寸和层片间距的减小而提高；其室温拉伸强度随应变速率的加快而提高；而应变速率对其室温延伸率的影响与显微组织相关，低延性全层状TiAl基合金的室温延伸率对应变速率不敏感，而高延性全层状TiAl基合金的室温延伸率对应变速率敏感，并随应变速率的加快而提高。     

双相层片型TiAl基合金的室温变形及断裂

TEM原位拉伸研究表明，尽管双相层片型TiAl基合金中与α2相共存的γ层片相的（1／2）＜110]位错具有良好的可滑移性，并在一些γ层片中（1／6）＜112]形变孪生也较为活跃，但对变形有贡献的滑移系统及孪生系统数目少是室温塑性差的重要原因提高多晶体双相TiAl基合金室温塑性的关键在于促使（1／2）＜110]{111）以外的滑移系开动.     

近片层γ-TiAl基合金宏观塑性行为的尺度效应

将近片层-γTiAl基合金视为由等轴γ颗粒和多孪晶PST(polysynthetically twinned crystal)单晶颗粒组成的两相复合材料。基于非均质微极介质塑性理论,构建-γTiAl基合金整体有效微极柔度张量,将传统塑性割线模量法推广到微极材料,建立分析和预测-γTiAl基合金的塑性行为尺度效应的细观力学模型。结果表明:-γTiAl基合金的微结构尺度对其宏观塑性硬化行为存在显著的影响;近片层组织-γTiAl基合金中PST晶体颗粒的尺寸越小,合金中硬相夹杂PST颗粒的体积分数越大,合金材料相应的塑性硬化越明显;微极基体的塑性特征尺度与等轴γ晶粒的平均尺寸大小在同一数量级。     

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.     

TiAl基合金定向凝固中领先相的确定及影响因素

TiAl基合金因其优异的高温性能及较低的密度成为近年的研究热点,室温塑性是其走向工程化应用最主要的障碍。通过定向凝固技术控制TiAl基合金片层取向与生长方向平行时,可有效提高其综合力学性能,领先相的选择及生长取向的控制是TiAl基合金片层取向控制的关键因素。本文综述了定向凝固TiAl合金领先相的类型及生长取向的几种确定方法,及其生长取向的影响因素,最后总结了领先相生长取向控制的研究方向,对制备定向凝固TiAl基合金叶片具有重要的指导意义。     

TiAl基合金定向凝固中领先相的确定及影响因素研究进展

TiAl基合金因其优异的高温性能及较低的密度成为近年的研究热点,室温塑性是其走向工程化应用最主要的障碍。通过定向凝固技术控制TiAl基合金片层取向与生长方向平行时,可有效提高其综合力学性能,领先相的选择及生长取向的控制是TiAl基合金片层取向控制的关键因素。本文综述了定向凝固TiAl合金领先相的类型及生长取向的几种确定方法,及其生长取向的影响因素,最后总结了领先相生长取向控制的研究方向,对制备定向凝固TiAl基合金叶片具有重要的指导意义。     

循环热处理工艺对于双态复相γ—TiAl基合金室温拉伸性能的影响

采用循环热处理工艺，获得了复相双态γ－TiAl基合金。研究了循环热处理过程中的显微组织演化，测试了室温拉伸性能，对断口进行了分析。结果表明：经过循环热处理，可以获得晶粒尺度在20μm的均匀复相双态组织，室温拉伸塑性可达2.6%；随着循环次数的增加，材料的均匀性和等轴性有较大的改观，室温拉伸塑性、屈服强度和断裂强度也随之增加。     

稀土Y在γ-TiAl基合金及其精密热成形中应用的研究进展

TiAl合金作为新型轻质高温结构材料,其熔炼及制备技术难度大、铸态组织较粗大、室温塑性较低和高温抗氧化能力的不足成为限制其应用的关键。从材料制备成形和合金成分两个角度综述稀土元素Y在TiAl基合金中应用的研究进展,总结国内外对Y_2O_3陶瓷坩埚和型壳面层在TiAl合金熔炼和精密铸造及制备成形过程中的研究进展;阐述稀土元素Y在合金中的形态与分布及其对合金铸态组织的细化及作用机理,并分析Y对合金室温力学性能和抗氧化性能的影响,对Y在TiAl基合金中的进一步研究应用提出建议。     

TiAl基合金组织对拉伸性能的影响

本文研究了典型TiAl基合金显微组织在热处理过程中的变化规律及组织与室温拉伸性能间的对应关系结果表明,合金经γ+α双相区处理并控制冷却速度,可获得细小的层片状晶粒和等轴γ晶粒组成的复相组织,此组织室温塑性最佳对显微组织的分析表明,高塑性来自于组织的细化和较大的片层体积分量     

Recent developments in engineering γ—TiAl intermetallics

γ-TiAl based alloys are rapidly being developed for elevated temperature applications,due to their high strength,light mass and good oxidation resistance.However,th disadvantages of TiAl based alloys are low ductility and toughness at room temperature,and poor workability.Grain refinement is one of the most effective ways for improving room temperature tensile properties and hot workability of ordered TiAl based alloys.At present,the majority of research works have focused on alloy modifications through compositional controls,alloying additions,thermo-mechanical processing and production techniques.This article discusses the research status of TiAl based alloys in the aras of microstructure,alloying,processing and applications.     

Study of microstructure and mechanical properties of Ti-45Al-(Fe,Nb) (at. %) alloys

In the present work, the microstructure and compression properties of two novel γ(TiAl) based alloys, Ti-45Al-5Fe and Ti-45Al-5Fe-5Nb, have been investigated. Both alloys had a relatively fine as-cast structure generally consisting of the γ(TiAl) and τ₂(Al₂FeTi) phases with a minor amount of the α₂(Ti₃Al) and β(B2) phase. The compression properties of the novel alloys were measured at room and elevated temperatures. The Ti-45Al-5Fe-5Nb alloy showed higher room temperature ductility and similar strength at room and elevated temperatures as well as improved workability at elevated temperatures as compared to β-solidifying γ(TiAl) alloys of last generation (TNM 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。     

钛加工技术—接合篇8

本文简要地介绍了TiAl有序合金的发展历史,较为系统地概述了国内外在制备TiAl合金、克服其室温脆性及难加工成形性方面所开展的研究工作以及TiAl有序合金研究今后的发展趋势。     

The effect of Ruthenium addition on the microstructure and mechanical properties of TiAl alloys

The high temperature compression behavior of TiAl–Ru alloys was studied at different temperatures and strain rates. Ru was found to have a strong strengthening effect on TiAl alloys. However the Ru addition amount was limited by its low solubility in γ-TiAl and α₂-Ti₃Al, and the detrimental effect of excessive ternary phase precipitation. Furthermore, the melting temperature decreases when Ru ≥0.6 at.% as the alloy composition approaches a ternary eutectic point. The strengthening mechanism is discussed and two separate mechanisms are proposed, viz. solid solution strengthening and refined colony strengthening. Intergranular cracks were found in the alloys with low Ru or no Ru addition, but were barely detected as Ru content increased to above 0.6 at.%. It was suggested that Ru showed a beneficial effect on both strength and ductility of TiAl alloys due to the refined colony size. Three-point bend test results showed that the Ru addition can also improve the room temperature ductility of TiAl alloys. Hot workability was increased according to the compression tests. Thermal-mechanically treated TiAl–Ru had much smaller grain size than the heat-treated samples due to dynamic recrystallization. But it did not show superior strength in the compression test compared to the heat-treated samples. The Zener–Hollomon parameter was calculated from the compression strength of heat-treated TiAl–Ru alloys. Its relationship with dynamic recrystallization and hot work is discussed. The mechanical properties of TiAl–Ru alloys are compared with TiAl–Nb samples and demonstrate a promising combination of strength and ductility.     

粉末冶金TiAl基合金显微组织及力学性能的研究

采用粉末冶金方法制备多种成分的ＴｉＡｌ基合金,并研究其显微组织及室温、高温力学性能,结果表明,采用粉末冶金方法能制备成分均匀、显微组织细小的Ｔｉ－Ａｌ－Ｃｒ－Ｎｂ系列合金。添加合金元素对粉末冶金ＴｉＡｌ基合金的显微组织具有显著影响。粉末冶金ＴｉＡｌ基合金的力学性能与其显微组织有密切的关系,显微组织越细小,其室温强度及延性越高,但在高温下,其屈服强度随晶粒尺寸增加而增加。所制备出的Ｔｉ－４７Ａｌ－３     

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.     

快速凝固TiAl化合物的研究进展

TiAl合金是一种很有希望的航空、航天及汽车用高温结构材料,但是其较低的室温塑性限制了它的应用.快速凝固技术有望使其性能得到改善.综述了近年来快速凝固TiAl合金的研究进展,包括快速凝固工艺、合金的发展以及合金的组织演变及其特征、力学性能及添加合金化元素的作用,亚稳相的产生及稳定性以及快速凝固薄带或粉末的固结等.     

Microstructural control and mechanical properties of dual-phase TiAl alloys

This paper summarizes our recent work on the effects of microstructural features on the mechanical properties of TiAl alloys prepared by powder and ingot metallurgy. TiAl alloys based on Ti-47Al-2Cr-2Nb (at%) were alloyed with small amounts of Ta, W, and B additions for control of alloy phases and microstructure. The alloys were processed by hot extrusion above and below T, followed by short- and long-term heat treatments at temperatures to 1350 °C in vacuum. The microstructural features in the lamellar structures were characterized by metallography, SEM and TEM, and the mechanical properties were determined by tensile tests at temperatures to 1000 °C. The tensile elongation at room temperature is mainly controlled by the colony size, showing an increase in ductility with decreasing colony size. The yield strength, on the other hand, is sensitive to the interlamellar spacing. Hall-Petch relationships hold well for both yield strength and tensile elongation at room and elevated temperatures. TiAl alloys with refined colony size and ultrafine lamellar structures possess excellent mechanical properties for structural applications at elevated temperatures.     

Effect of boron addition on tensile ductility in lamellar TiAl alloys

Various cast or wrought fully lamellar TiAl-based alloys with and without boron addition have been assessed. It has been found that titanium boride precipitates are the predominant factor influencing the room temperature tensile ductility. Large sized titanium boride precipitates often observed in high-alloyed TiAl alloys (such as Ti–44Al–8Nb–1B) cause premature failure in as-cast samples through promoting crack propagation via debonding between boride-matrix interfaces or cracking through boride precipitates themselves, giving rise to a typical tensile ductility of 0.3%. Refinement in titanium boride precipitates, via hot working or fast cooling during casting, will significantly improve the tensile ductility. In low-alloyed alloys (such as Ti–48Al–2Cr–2Nb–1B) the effect of boride precipitates is not as significant as it is in the high-alloyed alloys mainly because of their small sizes.