【作者】 陈智超；

【导师】 王廷；

【作者基本信息】 哈尔滨工业大学 ， 材料与化工（专业学位）， 2022， 硕士

【摘要】 TiAl合金因其良好的高温性能可在760～850℃高温下持续稳定工作,在航空发动机零部件制造中有很好的应用前景,但该合金室温塑性差,采用传统的热加工方式进行制造较为困难。随着材料制备工艺的改进,电弧增材制造技术（WAAM）逐渐成熟,采用该工艺制造TiAl合金具有效率高,成本低,材料利用率高等优点。本文将采用TIG电弧进行TiAl合金电弧熔丝增材制造,从粉芯焊丝的制作、TIG电弧增材制造TiAl合金工艺参数、增材制造过程中裂纹的抑制、合金元素V及热处理工艺对TiAl合金增材件的影响等方面进行研究。本文首先制备出能用于试验的TiAl合金粉芯焊丝,通过对焊丝成分的计算,设计出TiAl合金粉芯焊丝与纯Ti丝组成的同侧同速双送丝系统,并在此基础上研究TiAl合金电弧增材工艺参数。以单道熔覆层宏观成形和微观组织作为衡量标准,确定最优工艺参数为:电流105 A、送丝速度65 cm/min、焊接速度150 mm/min、丝极间距5 mm。此外,经过试验发现采用基板预热500℃和控制层间温度在500℃的方式能够抑制TiAl合金电弧增材制造中裂纹的产生。采用最优工艺参数制备出无裂纹的Ti-50Al合金增材件,该增材件内部存在很大的组织不均匀性,顶部区域以树枝晶构成,中部区域以层片组织和树枝晶交替构成,底部区域以层片状组织为基体上面析出不规则胞状组织。三个区域均以γ相为主,Al元素含量均在50%（at.%）左右。该成分的合金凝固路线是从液相中首先析出αTi,随着温度的下降,αTi中析出γ,其组织转变过程为L→L+αTi→αTi+γ→γ。铝含量超过50%时,γ相会互相连接成大尺寸的片状,使得合金的拉伸性能不超过250MPa。为优化TiAl合金增材件的性能,以合金化和热处理工艺来研究其对TiAl合金增材件的影响。V的引入使α₂相的含量提高,对大尺寸γ相片层组织起到钉扎作用,晶粒细化,性能得到改善。添加V元素的TiAl合金以层片状的（α₂+γ）组织为基体,显微硬度和室温拉伸强度都得到改善,尤其是顶部区域室温抗拉强度达到386 MPa;采用1320℃保温10 min,50℃纯水淬火、1250℃下回火120 min的淬火-回火工艺对添加V和未添加V的两种TiAl合金增材件进行热处理,未添加V的TiAl合金在热处理结束后表面出现了裂纹,内部晶粒粗大,性能下降;添加V的TiAl合金在热处理之后近层片组织转变为细小的双态组织,室温抗拉强度可以达到400 MPa以上,接近500 MPa,能够满足生产应用的要求。更多还原

【Abstract】 Because of its good high temperature performance,TiAl alloy can work stably at 760～850°C,which has a good application prospect in the manufacturing of aero engine parts.However,the plasticity of TiAl alloy at room temperature is poor,and it is difficult to manufacture by traditional hot processing method.With the improvement of the material preparation process,the arc additive manufacturing technology（WAAM）has gradually matured.The use of this technology to manufacture TiAl alloys has the advantages of high efficiency,low cost and high material utilization.In this paper,TIG arc was used to manufacture TiAl alloy arc wire additive.The effects of powder cored wire production,TIG arc additive manufacturing process parameters,crack suppression during additive manufacturing,alloying element V and heat treatment process on microstructure and properties of TiAl alloy additive were studied.In this paper,TiAl alloy powder cored wire that can be used for test was prepared firstly.Through the calculation of the composition of the wire,the double wire feeding system with the same side and same speed composed of TiAl alloy powder cored wire and pure Ti wire was designed,and on this basis,the process parameters of TiAl alloy arc additive were studied.Taking the macroscopic forming and microstructure of single channel cladding as the measurement standard,the optimal process parameters were determined as follows:current 105 A,wire feeding speed 65 cm/min,welding speed 150 mm/min,and wire electrode spacing 5 mm.In addition,it is found that the crack generation in the manufacturing of TiAl alloy arc additive can be inhibited by preheating the substrate at500°C and controlling the interlayer temperature at 500°C.The crack-free Ti-50 Al alloy additive was prepared by using the optimal process parameters.There is a large microstructure inhomogeneity in the additive.The top area is composed of dendrites,the middle area is composed of lamellar structure and dendrite alternately,and the bottom area is composed of irregular cellular structure above the lamellar structure.The three regions are dominated byγphase,Al element content is about 50%（at.%）.The solidification route of the alloy is the first precipitation ofαTi from the liquid phase.With the decrease of temperature,γprecipitates inαTi,and the microstructure transformation process is L→L+αTi→αTi+γ→γ.When the aluminum content exceeds 50%,theγphase will connect to each other to form large-size flakes,which makes the tensile properties of the alloy not exceed 250 MPa.In order to optimize the properties of TiAl alloy additive,the effects of alloying and heat treatment processes on TiAl alloy additive were studied.The introduction of V increased the content ofα₂ phase,pinned the structure of large sizeγphase lamellar,refined the grain and improved the performance.TiAl alloy with V element was based on lamellar（α₂+γ）structure,and the microhardness and room temperature tensile strength were improved,especially the room temperature tensile strength of the top region reached386 MPa.Two kinds of TiAl alloy additives with and without V were heat treated by quenching-tempering process at 1320°C for 10 min,pure water quenching at 50°C and tempering at 1250°C for 120 min.After the end of heat treatment,cracks appeared on the surface of TiAl alloy without V,and the internal grains were coarse and the performance decreased.After heat treatment,the near lamellar microstructure of TiAl alloy with V addition transforms into fine duplex microstructure,and the tensile strength at room temperature can reach more than 400 MPa,or even close to 500 MPa,which can meet the requirements of production and application.更多还原