热等静压处理ZTC4钛合金低温热处理过程中组织演变

研究了低温热处理后热等静压处理的ZTC4的组织演变规律。利用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)分析了不同尺度的组织特征。研究结果表明:原始组织由粗大的β晶粒和不同取向的α、β片层组成;温度由100℃升高到300℃,组织形态基本没有变化;当热处理温度在400℃时,α、β片层的形态由均匀变为不均匀。元素的微区扩散是造成这种现象的主要原因。     

粉料的粒度分布对TiAl合金熔模精密铸造用氧化锆陶瓷型壳性能的影响(英文)

研究粉料的粒度分布对TiAl合金熔模精密铸造用氧化锆陶瓷性能的影响。对粉料粒度分布、粉末形貌、浆料黏度、型壳抗弯强度和断裂形貌之间的关系进行研究;通过测量氧化锆粉末和粘结剂构成的浆料的黏度来考察粉末粒度分布对浆料黏的影响;对不同粒度分布氧化锆陶瓷型壳断口形貌进行观察。结果表明:粉料粒度分布对未焙烧和焙烧后氧化锆陶瓷型壳的强度影响行为相似;粉料粒度分布对氧化锆陶瓷型壳的质量能产生很大的影响并进而影响到熔模精密铸造制备TiAl合金构件的质量。     

Improvement in collapsibility of ZrO2 ceramic mould for investment casting of TiAl alloys

Investment casting has been widely recognized as the best option in producing TiAl components with key benefits of accuracy,versatility and integrity.The collapsibility of ceramic moulds for investment casting is critical in the manufacturing process of TiAl components due to TiAl’s intrinsic brittleness at room temperature.The aim of the present research is to provide a method for production of TiAl components by investment casting in ZrO2 ceramic moulds with improved collapsibility.Slurries prepared with high polymer additions were utilized during the preparation of ceramic moulds.The stress/strain curves obtained from green and baked ceramic moulds demonstrate that the green strength was increased with the application of high polymer,while baked strength decreased,thus the collapsibility of ceramic moulds was improved.It is suggested that this result is related to the burn-out of high polymer which left a lot of cavities.The experimental findings were also verified by the investment casting of "I"-shaped TiAl components.     

Microstructure and interface reaction of investment casting TiAl alloys

In order to research the microstructure of TiAI alloy and TiAl-mould reaction between TiAI and ceramic mould shells prepared with the low cost binder in investment casting, the ceramic mould shells were prepared with low cost binder and refractory materials. Using two kinds of casting methods （gravity casting and centrifugal casting）, the titanium aluminum alloys with rare earth element （Ti-47.5Al-2Cr-2Nb-0.3Y and Ti-45Al-5Nb-0.3Y） were cast into the mould shells. The microstructures of investment casting titanium aluminum alloys were observed by optical microscope （OM）. The distributions of elements of topping investment on the surfaces of titanium aluminum alloys castings were analyzed by the means of electron probe micro-analysis （EPMA）, and the mechanical properties were studied. The results show that the microstructures of two kinds of titanium aluminum alloys are both lamella shape, and lamella is thin. The thickness of reaction and diffusing layer of Ti-47.5Al-2Cr-2Nb-0.3Y alloy is about 80 μm, and that of Ti-45Al-5Nb-0.3Y is less than 30 μm.     

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.

     

热处理对吸铸TiAl基合金铸件组织的影响

利用金属型底浇式真空吸铸技术和添加合金元素获得TiAl基合金薄板,观察并研究薄板热处理前后的组织。结果表明,在金属型强制冷却和添加合金元素的共同作用下,利用金属型底浇式真空吸铸技术获得的TiAl基合金薄板件铸态组织细小、致密。其中Ti-47Al-5Nb-0.5Si和Ti-47Al-2W-0.5Si合金的铸态平均晶粒多在20μm左右,但是,铸态组织的片层组织不均匀,且在组织内部存在较大的偏析。将试样加热到1300℃,保温5 h,随炉冷却热处理后,TiAl基合金薄板的铸态组织有所长大,但是片层更加平整稳定,偏析也明显得到改善。     

一种钛基钎料钎焊TiAl合金接头的高温力学性能分析

采用自主研发的一种Ti-Zr-Cu-Ni-Co-Mo非晶钎料对TiAl合金进行钎焊连接,钎焊温度为1 000 ℃,时间为5 min,对所得的钎焊接头进行了高温抗剪强度和抗拉强度研究,并与母材强度进行了对比. 结果表明,钎焊接头在700 ℃高温下可长期服役,但剪切试验温度高于700 ℃后由于氧化物的生成和钎焊中心区显微组织发生变化导致剪切性能急剧下降,钎焊接头跟母材在不同拉伸试验温度下的抗拉强度随试验温度上升呈下降趋势,两者差距先减小后增大,分别在不高于600和800 ℃条件下仍能保持室温性能的80%以上.     

热等静压处理对Ti6242合金铸件的组织和拉伸性能的影响

研究Ti6242合金铸件及经热等静压后的组织和拉伸性能变化,观察分析了熔炼铸坯和重力铸造铸件热等静压处理前后的组织,并测试了其拉伸性能。结果表明,热等静压消除了铸造时产生的缩松、缩孔等缺陷,增加了材料的抗拉强度。经热等静压处理后Ti6242合金铸件的抗拉强度(sm)为852 MPa,较熔炼铸坯的提升了9.2%,较重力铸造铸件的提升了3.3%。热等静压处理后Ti6242合金铸件的伸长率为6.32%,较熔炼铸坯的提升了13%,而较重力铸造铸件的降低了8.9%。     

Elimination of misrun and gas hole defects of investment casting TiAl alloy turbocharger based on numerical simulation and experimental study

Casting technology of thin-wall TiAl alloy turbochargers was studied by investment casting and numerical simulation.Misruns and gas holes were the main defects observed in preliminary work due to the poor fluidity of alloy,and to gas entrapment.In order to eliminate these defects,cast parameters,such as centrifugal rotation rate and mould preheating temperature,were optimized by numerical simulation,meanwhile,the structure of the shell mould was optimized to improve the filling capacity of TiAl alloy.Pouring experiments were carried out by vacuum induction melting furnace equipped with a water-cooled copper crucible based on the above optimization.The quality of the TiAl alloy casting was analyzed by fluorescent penetrant inspection and X-ray detection.The results show that a centrifugal rotation rate of 200 rpm,mould preheating temperature of 600°C,shell preparation through organic fiber addition can dramatically improve the mould filling capacity,and integrated turbochargers were finally prepared.     

A high-Nb TiAl alloy with highly refined microstructure and excellent mechanical properties fabricated by electromagnetic continuous casting

In the present research, microstructure refinement of a high-Nb TiAl alloy(Ti-48Al-8Nb-0.15B) was realized by means of the electromagnetic continuous casting(EMCC) technique. The microstructure of an ingot obtained by EMCC was analyzed using scanning electron microscopy(SEM). As compared with the raw as-cast al oy, the obtained EMCC alloy presented a much finer microstructure with lamellar colonies with a mean size of about 50-70 μm because the electromagnetic stirring broke initial dendrites and enhanced the heterogeneous nucleation. As the grains were refined, the properties of the TiAl alloy were improved significantly. This implies that the EMCC technique could offer the possibility of application for high-Nb TiAl alloys with a refined microstructure and excel ent properties to be used as a structural material.     

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。     

热等静压及后续热处理对铸造铝合金叶片力学性能的影响

本文应用抗拉试验、冲击试验、疲劳试验、无损检验及显微分析等手段 ,对ZL4 0 2、ZL4 0 1合金铸造叶片的热等静压 (HIP)及后处理工艺进行了研究。结果表明 :HIP处理使叶片的气孔、疏松、针孔等缺陷得到了愈合 ,改善了叶片综合力学性能及其分散程度 ,大大提高了材料的抗疲劳性能 ;HIP后进行T6处理 ,将导致叶片严重的变形和开裂 ;HIP后进行一个月的自然时效或 4 0～ 70℃× 4 8h人工时效 ,有利于提高叶片强度。     

Effects of hot isostatic pressing temperature on casting shrinkage densification and microstructure of Ti6Al4V alloy

The Ti6Al4V alloy castings were produced by the investment casting process, and the hot isostatic pressing(HIP) was used to remove shrinkage from castings. The processing pressure and holding time for HIP were 150 MPa and 20 min, respectively. Four different HIP temperatures were tested, including 750 ℃, 850 ℃, 920 ℃ and 950 ℃. To evaluate the effects of temperature on densification and microstructure of Ti6Al4V alloy treated by HIP, non-destructive testing and metallographic observation was performed. The experimental results show that the shrinkage was completely closed at 920 ℃ and 950 ℃. The densification of Ti6Al4V alloy increased as the HIP temperature increased below 920 ℃. The lamel ae were more uniform, the thickness of lamel ae was obviously broadened and the structure was coarsen. Besides, the Norton creep equation was used to simulate the effect of different temperatures on the densification of Ti6Al4V alloy during HIP. The simulation results were in good agreement with the experimental results. It was also found that 920 ℃ is a suitable temperature for HIP for Ti6Al4V alloy.     

常规铸造定向层片TiAl合金持久加载中的组织退化及改善途径

基于TiAl合金常规铸造定向层片组织与多孪晶合成晶体(polysynthetically twinned crystals,PST)的组织差别,详细讨论这些组织差别对常规铸造定向层片组织TiAl合金持久加载过程中组织退化的影响,并探讨降低这些不利影响的微合金化途径。结果表明:定向层片组织与PST晶体的差别主要包括存在层片团界和小角度取向差、Al元素成分偏析以及α_2相体积分数高于热力学平衡状态,同时,后续热等静压导致等轴γ晶粒析出和层片间距增加也是另外的明显差别。这些组织差别对定向层片组织持久加载过程中的组织退化造成不同程度的加剧作用。其中,Al元素成分偏析和α_2相体积分数过高促进了定向层片组织铸态试样的组织退化,热等静压试样中析出的等轴γ晶粒进一步加剧了其组织退化,这些均对定向层片组织持久寿命造成不利影响。而层片团界对组织退化的影响程度较小。此外,探讨了采用Zr、C、Si微合金化抑制持久加载过程中组织退化进而改善持久性能的可行性。     

带缺口的熔模铸造TiAl合金断裂特性的扫描电镜原位观察(英文)

采用感应凝壳熔炼技术和熔模铸造方法制备TiAl合金。在增量加载情况下,采用扫描电镜原位观察技术观察带缺口的熔模铸造TiAl合金试样的裂纹扩展和断裂特性。在拉伸变形的整个过程中,观察并分析裂纹萌生、扩展直至断裂的全过程。结果表明,TiAl合金的断裂机制不仅对于缺口区域附近的微裂纹敏感,而且与层片方向和加载轴的位向有关。当局部应力大于TiAl合金的断裂韧性时,高的拉伸应力就会导致裂纹萌生、扩展直至断裂失效。因此,TiAl合金的塑性和高的拉伸应力导致带缺口的TiAl合金的断裂失效。     

放电等离子烧结的钛铝合金组织及氧化性能研究

研究了TiH2-45Al-0.2Si-5Nb未球磨和球磨两种粉末的放电等离子烧结组织特征以及经1000℃、100h高温氧化后的氧化性能.结果表明,未经球磨粉末的烧结组织由层片状TiAl和Ti3Al相组成,而经球磨粉末的烧结组织由细小的颗粒状TiAJ和Ti3Al相组成.球磨粉末的烧结组织氧化速度低于未球磨粉末的烧结组织,形成了连续的Al2O3和TiO2混合氧化物层,具有良好的高温抗氧化性.     

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.     

高铌TiAl高温合金的研究现状与展望

高铌TiAl高温合金是一种具有发展前途的新一代高温结构材料,合金化元素铌的添加能够显著提高γ-TiAl合金的工程应用。文章首先综述了高铌TiAl合金的性能特点和应用前景,并简单介绍了该合金的最新基础研究情况,随后介绍了制备高铌TiAl合金的基本工艺。最后论述了国内外高铌TiAl高温合金的发展历史和趋势。     

Deformability and microstructure transformation of PM TiAl alloy prepared by pseudo-HIP technology

Microstructures and deformation properties of Ti-46Al-(Cr,Nb,W,B)alloy consolidated by pseudo-HIP technology were investigated.The results show that the pseudo-HIP temperature has a significant effect on microstructures.When the sintering temperature is 1 100℃,the microstructure of as-pseudo-HIPped alloy is similar to that of the prealloyed powder and the interfaces of these powder particles are still discernible,but a nearγmicrostructure appears in particles.Increasing the pressing temperature to 1 200℃develops successfully a homogeneous and fine-grained duplex microstructure.A typically fully lamellar microstructure with residualβphase is developed at 1 300℃.The compact exhibits excellent deformation properties at elevated temperatures. When the compression temperature is higher than 1 100℃,high quality products without cracks can be obtained even if the engineering compression strain is up to 0.8 at strain rates of 10-2-10-3s-1.It can be established that the mechanical twinning and matrix deformation due to ordinary dislocation slip/climb contribute to the whole hot deformation.