DEVELOPMENT OF LIGHT WEIGHT Ll_2-Al_3Ti ALLOYS AND FORMATION OF GRADED OXIDATION-RESISTANT LAYER FOR TiAl ALLOYS.

轻质Ll_2-Al_3Ti合金的研制及TiAl合金梯度抗氧化层的形成。

• 批准号: 12450285
• 负责人: MABUCHI Hiroshi
• 金额: $ 6.14万
• 依托单位: OSAKA PREFECTURE UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450285/
• 关键词: light-weight high-temperature material; titanium aluminide; oxidation resistance; functionally graded material; crystal structure control; pack cementation; Ll_2^type intermetallic compound; slurry method; 耐熱化特性; 延性改善; L12型金属間化合物

Gamma titanium aluminides (γ-TiAl alloys), having an Ll_0-type structure, are candidate materials for use in future gas turbine aero-engines and automotive engines because of their low density, high specific strength and high stiffness. In air, however, it is well known that titanium aluminide oxidizes at a more rapid rate at temperatures above 1123 K; therefore, the oxidation resistance becomes a critical factor for TiAl alloys to be used at high temperatures (perhaps above 1073 K). Coatings for the TiAl alloy are essential to high temperature oxidation resistance. The recent approaches toward oxidation resistant coatings for titanium aluminides include the aluminide pack coatings, pack coatings with Cr_2_3, SiO_2 and Cr powders, MCrAlY(M=Ni, Fe, Co) alloy coatings, silicides/ceramics coatings, physical vapor deposition coatings, and coatings used a fluidized bed with WO_3 powder. Among the coating processes to improve oxidation resistance, pack cementation is a very simple process an … More d remains a widely used technique for gas turbine components. Especially aluminide coatings are the best documented pack processes used to produce high-temperature protective coatings for nickel-based superalloys.On the other hand, the oxidation resistance of Al_3Ti, having a D0_<22>-type structure, appears to be superior owing to its high aluminum content. Oxidation resistant coatings based on the Al_3Ti phase have been successfully produced on TiAl alloys by diffusion pack aluminizing. But the Al_3Ti is extremely brittle at ambient temperature because of its low-symmetry crystal structure and tetragonal D0_<22> structure; therefore, its application as a coating material for TiAl alloys has been limited. To improve its ductility, recently, much work on the (Al,X)_3 Ti (X=Ni, Fe, Cu, Mn, Cr, Ag and Pd etc.) alloys has been focused on the formation of the cubic Ll_2 crystal structure, with the hope that the Ll_2 structure is highly symmetrical and may have a sufficient number of slip systems for homogeneous deformation. The present authors recently reported that Ti-67Al-8Cr (in mol %) alloy with the Ll_2 structure does possess some intrinsic bend ductility at ambient temperature, and that Ll_2- Ti-61Al-14Cr alloy (with higher chromium content) was more ductile in bending, with a plastic strain of up to 0.9% being recorded.To improve the oxidation resistance of γ-TiAl alloys, Ti-43Al-5Cr(Ll_0) alloy substrates were coated with the Ll_2-(Al,Cr)_3Ti layer by pack cementation or slurry method. Coatings were formed by immersing the substrate in a mixture consisting typically of 90% Ti-61Al-14Cr(Ll_2) alloy powders without activators, or slurry with Ti, Al, And Cr powders, and then heating in an alumina boat under a vacuum of 〜10^<-4> Pa for 1 〜 96 h at 1423 K. The coating layer for γ-TiAl alloys was effectively formed by surface diffusion and bulk diffusion of aluminum, titanium and chromium from pack alloy powders. The coating consisted of the two diffusion layers, an outer Ll_2-phase layer and an inner Ll_0-phase layer. In these layers, the graded alloy composition and microstructures for the oxidation resistant coating was successfully established. The coated alloy showed a remarkable improvement in the oxidation resistance over the uncoated TiAl alloys. Less

γ-TiAl合金具有L1_0型结构，具有低密度、高比强度和高刚度的特点，是未来燃气涡轮机和汽车发动机的候选材料。然而，在空气中，众所周知的是，铝化钛在高于1123 K的温度下以更快的速率氧化;因此，抗氧化性成为TiAl合金在高温（可能高于1073 K）下使用的关键因素。TiAl合金的涂层对于高温抗氧化性是必不可少的。近年来，钛铝化合物抗氧化涂层的研究主要有铝化物包埋涂层、Cr_2_3、SiO_2和Cr粉包埋涂层、MCrAlY（M=Ni，Fe，Co）合金涂层、硅化物/陶瓷涂层、物理气相沉积涂层和WO_3粉流化床涂层等。在提高抗氧化性的涂层工艺中，包埋渗法是一种非常简单的工艺， ...更多信息 D仍然是用于燃气涡轮机部件的广泛使用的技术。铝化物涂层是镍基高温合金高温防护涂层中最有文献记载的一种，而Al_3Ti具有D_0<22>_型结构，由于其高铝含量，其抗氧化性能上级。采用扩散包渗法在TiAl合金表面成功地制备了以Al_3Ti相为主的抗氧化涂层。但由于Al_3Ti晶体结构的低对称性和四方D0_1结构，在室温下极易脆化<22>，限制了其作为TiAl合金涂层材料的应用。为了改善其塑性，近年来，人们对（Al，X）_3Ti（X=Ni，Fe，Cu，Mn，Cr，Ag，Pd等）进行了大量的研究。Ll_2合金的研究一直集中在立方Ll_2晶体结构的形成上，希望Ll_2结构是高度对称的，并且可能具有足够数量的滑移系以实现均匀变形。本文作者最近报道了Ti-67 Al-8 Cr Ll_2- Ti-61 Al-14 Cr合金在室温下具有一定的本征弯曲塑性，（含铬量较高）的γ-TiAl合金在弯曲时塑性更好，塑性应变高达0.9%。采用粉末包埋法或料浆法在Ti-43 Al-5Cr（Ll_0）合金表面涂覆Ll_2-（Al，Cr）_3Ti涂层。通过将基底浸入通常由90%Ti-61 Al-14 Cr（Ll_2）合金粉末组成的混合物中（不含活化剂）或与Ti、Al和Cr粉末组成的浆料中，然后在1423 K下在真空度为100 μ Pa的氧化铝舟中加热<-4>1 × 96 h来形成涂层。γ-TiAl合金的涂层是通过粉末中Al、Ti、Cr的表面扩散和体扩散形成的。涂层由两层扩散层组成，外层为L1_2相，内层为L1_0相。在这些涂层中，成功地建立了用于抗氧化涂层的梯度合金成分和显微组织。涂层合金的抗氧化性能比未涂层的TiAl合金有显著的提高。少