预热下激光沉积TA15/GH4169梯度结构各梯度层组织及性能研究

在预热400℃的锻态TA15合金基材上,应用激光沉积制造技术制备了具有3层梯度层的TA15/GH4169梯度结构,研究了GH4169含量对各梯度层组织与性能的影响.利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线能量色散谱仪(EDS)、X射线衍射仪(XRD)、显微硬度计、摩擦磨损试验机对沉积样件进行了显微组织观...

Microstructure and Properties of Gradient Layers of Laser Deposited TA15/GH4169 Gradient Composite Structure under Preheating

In the field of aerospace,most of the hot-end parts in engines do not work at constant temperature,and the performance requirements of different positions in the same part are also different.Therefore,if the titanium alloy/superalloy gradient structure can be applied to the engine matrix in practice,the engine weight can be significantly reduced while the thrust is ensured during flight,thereby the flight efficiency of the aircraft could be improved effectively.So,the titanium alloy/superalloy gradient structure is of great potential significance in actual application.Laser deposition manufacturing technology has technical advantages in the preparing of gradient composite structure.The difference of thermal-physical parameters of titanium alloy and superalloy produces severe residual thermal stress during the laser deposition manufacturing process,which leads to the bad forming quality of the transition interface of titanium alloy/superalloy gradient composite structure,and substrate preheating can solve this problem effectively.TA15/GH4169 gradient composite structure with three gradient layers was fabricated by laser deposition manufacturing technology on forged TA15 alloy substrate preheated at 400 ℃ by constant-temperature heating platform.OLYMPUS optical microscope(OM),JSM-6700 scanning electron microscope(SEM)and X-ray diffractometer(XRD)were used to observe the microstructure and phase change of each gradient layer,and the EDS module on the scanning electron microscope was used for surface scanning of element distribution in designated area.The HVS-1000 A microhardness tester and the HT-1000 ball-disk friction and wear tester were used to measure the microhardness and abrasion properties of different positions of the gradient structure along the gradient direction.The effect of GH4169 content on the microstructure and properties of TA15/GH4169 gradient layer was investigated.The results showed that the TA15/GH4169 gradient structure with three gradient layers was successfully fabricated and the deposited samples were fully dense and defect-free.The main elements Ti,Ni,Cr and Fe in TA15 and GH4169 alloys were distributed reasonably along the gradient direction without element mutation,and the gradient transition zone greatly alleviated the difference in composition between the two materials.The macrostructure of as-deposited TA15 side was composed of columnar crystals passing through multiple sedimentary layers,the microstructure was typical basket structure,and in the grains appeared primarily α phase and lamellar phase.Some α phases were obviously coarsened and the length-width ratio was about 6.While the GH4169 side structure presented columnar dendrites growing epitaxially through the deposition layers,with strong orientation,the growing direction tended to be parallel to the laser deposition direction,and irregular Laves phases were precipitated between dendrites.With the increasing of GH4169 content in the gradient transition zone,the phase composition was α→ α+Ti₂Ni → Ti₂Ni+TiNi₃→ Ti₂Ni+TiNi₃+γ→γ.The 75%TA15 gradient layer was mainly composed of Ti₂Ni(the strengthening phase distributed on Ti based solid solution),the microstructure of 50% TA15 gradient layer was mainly composed of Ti₂Ni and TiNi₃,and the microstructure of 25%TA15 layer was composed of a large number of TiNi₃ distributed in Ni matrix.The microhardness of each gradient layer increased obviously with the increasing of GH4169 content,and the hardness of 25%TA15 layer reached the maximum value of HV_0.2537,increasing by 97% compared with that of 100%TA15 gradient layer.The wear scar width and the wear weight loss decreased with the increasing of GH4169 content in each gradient layer.The friction coefficient of 25%TA15 layer decreased to the lowest value of 0.33,which was 72% lower than that of TA15 layer.The substrate preheating effectively alleviated the stress between the different materials of titanium alloy and superalloy during the laser deposition process,reduced the temperature gradient between the cladding material and the base material,and made the temperature field of the forming process more uniform and stable.The TA15/GH4169 gradient structure of good quality was achieved by designing three gradient layers with different proportions.The comprehensive performance of 25%TA15 layer was the best.Because more strengthening phases with high hardness and face-centered cubic crystal structure were precipitated in 25%TA15 layer compared with that of 100%GH4169 layer.This study would provide basic data for the final formation of TA15/GH4169 gradient composite structure.