【作者】 李明；

【导师】 刘洁；

【作者基本信息】 华中科技大学 ， 材料工程， 2018， 硕士

【摘要】 钛铝基合金具有密度低、耐热性好、比强度高、良好的抗氧化性和高温蠕变性等优异的高温性能,被认为是未来应用于航空航天和汽车工业领域制造轻质结构零部件的理想材料。但是,TiAl合金较脆且热加工性较差,利用传统工艺制造零部件的过程中易开裂,无法整体成形结构复杂且性能优异的零部件。激光选区熔化（Selective Laser Melting,SLM）在高能激光束的作用下可以直接熔化TiAl合金粉末成形具有复杂结构的零件,无需刀具和模具,成形速度快,缩短了产品的开发周期,适合航空航天领域结构复杂零部件的整体成形。与传统制造过程相比,SLM成形过程中金属粉末快速熔化、快速冷却,导致SLM成形件的微观组织和力学性能与传统件相比存在较大的差异。本文以Ti-48Al-2Cr-2Nb为基体粉末配制TiAl基金属粉末材料,研究SLM成形TiAl基合金粉末的工艺、微观组织与力学性能。主要内容如下:（1）研究了激光扫描线间距对SLM成形TiAl基合金过程中晶粒的大小与取向、织构、相位关系和力学性能的演变关系。研究发现SLM成形的Ti-48Al-2Cr-2Nb/RGO合金中,随着激光扫描线间距的增加,晶粒尺寸逐渐减小,但是晶粒的取向保持（0001）、（101?1）和（112?1）的混合取向不变;高角度晶界的含量逐渐降低;SLM成形件主要由α₂,γ和B₂相组成,且随着激光扫面线间距的增大,α₂相的含量逐渐降低而γ和B₂相的含量逐渐升高;成形合金试样的纳米硬度和杨氏模量分别由8.13±0.392 GPa和155.62±7.78 GPa增加至9.85±0.458 GPa和179.02±8.90 GPa。（2）研究了B元素的含量对SLM成形TiAl基合金粉末微观组织与力学性能的影响。研究结果表明在SLM成形的TiAl/B合金试样中,随着B元素的质量分数从0%增至2%,晶粒的平均尺寸从16.64μm降至5.66μm,同时晶粒的取向从很强的（101?1）和（112?1）取向转变为以（0001）取向为主;合金试样中{0001}取向的织构指数从10.78增加至22.69,高角度晶界的含量从87.9%升高到94.4%;SLM成形合金试样的抗压强度和应变分别从1083.16 MPa和3.43%增至1610.53 MPa和5.17%,其失效形式呈典型的脆性断裂模式。本文对SLM成形TiAl基复合材料的微观组织和力学性能的研究结果为SLM成形工艺提供理论基础,有利于SLM技术的推广和应用。更多还原

【Abstract】 Titanium aluminum（TiAl）-based alloys has excellent high temperature performance,such as low density,good heat resistance,high specific strength,good oxidation resistance and high temperature creep property.It is considered to be an ideal material for future applications of light structural components in aerospace and automotive industry.However,due to the brittleness and poor thermal deformability of TiAl alloy,the parts manufactured by traditional technology are easy to crack,and cannot form the complex structure parts with excellent performance.Without the using of tools and dies,Selective Laser Melting（SLM）can directly melting the TiAl alloy powder to process the parts with complex structure under the action of high energy laser beam,and the manufacturing speed is fast,so short the product development cycle,it is suitable for forming the complex components in the field of Aeronautics and Astronautics.Compared with the traditional manufacturing process,the rapid melting of metal powders and rapid cooling of molten pool in SLM forming process,so the parts processed by SLM are quiet different from the parts fabricated by the traditional methods in microstructure and mechanical properties.In this paper,TiAl-based metal powder materials were prepared with Ti-48Al-2Cr-2Nb as matrix powder,and the process,microstructure and mechanical properties of TiAl-based alloys formed by SLM were studied.The paper research the forming process,microstructure and mechanical properties of TiAl-based metal powder processed by SLM.The main contents are as follows:（1）TiAl-based metal composite powder had been processed by SLM,and the influence of the laser scan line spacing on grains characteristic,crystallographic texture,phase transition and nanohardness of the SLM-processed samples had been systematic investigated.The study found that in the Ti-48Al-2Cr-2Nb/RGO alloy formed by SLM,with the increase of the laser scan line spacing,the grains of the SLM-processed samples gradually refined,while their grains orientations with a combination of（0001）,（101?1）and（112?1）directions basically remain unchanged.The content of high-angle grain boundaries（HAGBs）decreased with the increase of the laser scan line spacing.The parts fabricated by SLM mainly consist ofα₂,γand B₂ phases.With increasing the laser scan line spacing,the content ofα₂ phase decreased while the contents ofγand B₂ increased.The nanohardness and Young’s modulus respectively increased from 8.13±0.392 GPa and 155.62±7.78 GPa to 9.85±0.458 GPa and 179.02±8.90 GPa when increasing the laser scan line spacing.（2）The microstructure evolution and mechanical properties of SLM-processed TiAl/B parts with varied B content were systematically discussed.And found that the average grain size of SLM-processed TiAl/B parts significant refined from 16.64μm to 5.66μm when the content of B element increased from 0 to 2 wt%,in addition,the crystallographic orientations transformed from a strong（101?1）and（112?1）orientations to a dominated（0001）orientation.With increasing the content of B element from 0 to 1 wt%,the{0001}texture index of SLM-processed TiAl/B parts increased from 10.78 to 22.69,and the HAGBs increased from 87.9%to 94.4%.The compressive strength and strain respectively increased from 1083.16 MPa and 3.43%to 1610.53 MPa and 5.17%when the content of B element increased from 0 to 2 wt%.And the failure mode is typical brittleness fracture.In this paper,the research results of microstructure and mechanical properties of the TiAl matrix composites parts processed by SLM provide a basis theoretical for SLM forming process,which is conducive to the popularization and application of SLM technology.更多还原