激光选区熔化TiAl合金成形和组织演变规律及机制

Forming behavior and microstructural evolution mechanisms of TiAl alloys processed by selective laser melting

摘要

TiAl 合金室温塑性不佳，传统铸造和锻压工艺难以满足复杂结构部件的加工需求。激光选区熔化技术（SLM）具有制造周期短、材料利用率高、成形精度优异等特点，被认为适用于航空航天领域复杂零部件的制造。本研究采用 Ti48Al2Cr2Nb 与 4% FeMo60（质量分数）合金粉末混合，制备名义成分为 Ti47Al3.5Cr1Nb1Mo1Fe 的合金。采用棋盘式搭接打印策略，同时优化打印参数，成功实现低缺陷率（仅为 0.49%）TiAl 合金的 SLM 成形。此外，利用 X 射线衍射、扫描电子显微镜等设备探究组织形成原因。进一步通过热处理工艺将打印态合金中大量的 α₂ 相转变为大量的 γ 相，同时将打印过程中未熔化 FeMo60 粉末固溶实现固溶强化，合金抗压强度达 770.3 MPa，提高 30%。本研究为高性能、复杂形状 TiAl 合金的制备提供了重要参考。

Abstract

TiAl alloys exhibit poor room-temperature ductility，which poses a challenge for traditional casting and forging processes to fulfill the manufacturing demands for complex structural components. Selective laser melting (SLM) technology，renowned for its short manufacturing cycle， high material utilization， and exceptional forming accuracy， is deemed well-suited for fabricating complex parts in the aerospace industry. In this research，Ti48Al2Cr2Nb alloy powder is mixed with 4% (mass fraction) FeMo60 alloy powder to formulate an alloy with a nominal composition of Ti47Al3.5Cr1Nb1Mo1Fe. By employing a chessboard overlap scanning strategy (which mitigates thermal stress during processing) and optimizing printing parameters，SLM fabrication of the TiAl alloy with a remarkably low defect rate (only 0.49%) is successfully accomplished. Moreover，the samples are characterized using X-ray diffraction and scanning electron microscopy to explore the underlying reasons for microstructure formation. Additionally，a substantial portion of the α ₂ phase in the as-printed alloy is converted into the γ phase through heat treatment. Simultaneously，the unmelted FeMo60 powder from the printing process is dissolved，achieving solid solution strengthening. This phenomenon leads to a significant 30% enhancement in the compressive strength. This study offers a crucial reference for the preparation of high-performance TiAl alloys with complex geometries.

关键词

TiAl 合金 / 激光选区熔化技术 / 热处理 / 组织演变 / 力学性能

Key words

TiAl alloy / selective laser melting (SLM) / heat treatment / microstructural evolution / mechanical property

参考文献

[1] 陈国良. 金属间化合物结构材料研究现状与发展[J].材料导报，2000，14（9）：1-5.

[2] CHEN G L . R & D status and prospect on the ordered structural intermetallics[J].Materials Review，2000，14（9）：1-5.

[3] DIMIDUK D M . Gamma titanium aluminide alloys：an assessment within the competition of aerospace structural materials[J].Materials Science and Engineering： A，1999，263（2）：281-288.

[4] WU X H . Review of alloy and process development of TiAl alloys[J].Intermetallics，2006，14（10/11）：1114-1122.

[5] APPEL F， BROSSMANN U， CHRISTOPH U， et al. Recent progress in the development of gamma titanium aluminide alloys[J].Advanced Engineering Materials，2000，2（11）：699-720.

[6] CLEMENS H， GLATZ W， EBERHARDT N，et al. Processing， properties and applications of gamma titanium aluminide sheet and foil materials[J].MRS Online Proceedings Library，1996，460（1）：29-43.

[7] TETSUI T . Development of a TiAl turbocharger for passenger vehicles[J].Materials Science and Engineering： A，2002，329：582-588.

[8] ALI H， MA L， GHADBEIGI H， et al. In-situ residual stress reduction，martensitic decomposition and mechanical properties enhancement through high temperature powder bed pre-heating of selective laser melted Ti6Al4V[J].Materials Science and Engineering： A，2017，695：211-220.

[9] PROMOPPATUM P， ROLLETT A D . Physics-based and phenomenological plasticity models for thermomechanical simulation in laser powder bed fusion additive manufacturing： a comprehensive numerical comparison[J].Materials & Design，2021，204：109658.

[10] SOFINOWSKI K A， RAMAN S， WANG X G， et al. Layer-wise engineering of grain orientation (LEGO) in laser powder bed fusion of stainless steel 316L[J].Additive Manufacturing，2021，38：101809.

[11] YU Y F， LI Y， LIN F，et al. A multi-grid cellular automaton model for simulating dendrite growth and its application in additive manufacturing[J].Additive Manufacturing，2021，47：102284.

[12] KASTENHUBER M， RASHKOVA B， CLEMENS H，et al. Enhancement of creep properties and microstructural stability of intermetallic β-solidifying γ-TiAl based alloys[J].Intermetallics，2015，63：19-26.

[13] XU W C， HUANG K， WU S F，et al. Influence of Mo content on microstructure and mechanical properties of β-containing TiAl alloy[J].Transactions of Nonferrous Metals Society of China，2017，27（4）：820-828.

[14] CHLUPOVÁ A， HECZKO M， OBRTLÍK K， et al. Mechanical properties of high niobium TiAl alloys doped with Mo and C[J].Materials & Design，2016，99：284-292.

[15] MUGWAGWA L， DIMITROV D， MATOPE S， et al. Evaluation of the impact of scanning strategies on residual stresses in selective laser melting[J].The International Journal of Advanced Manufacturing Technology，2019，102（5）：2441-2450.

[16] MALEKIPOUR E， EL-MOUNAYRI H， MARREY M，et al. An innovative fast layer-wise simulation of temperature distribution using a chessboard strategy (FALSTECHS) in the powder-bed fusion process[J].Additive Manufacturing，2021，46：102065.

[17] LI W， LIU J， ZHOU Y，et al. Texture evolution，phase transformation mechanism and nanohardness of selective laser melted Ti-45Al-2Cr-5Nb alloy during multi-step heat treatment process[J].Intermetallics，2017，85：130-138.

[18] YOUN S J， KIM Y K， KIM S W，et al. Elevated temperature compressive deformation behaviors of γ-TiAl-based Ti-48Al-2Cr-2Nb alloy additively manufactured by electron beam melting[J].Intermetallics，2020，124：106859.

[19] PARK S H， GOKCEKAYA O， OH M H，et al. Effects of hatch spacing on densification， microstructural and mechanical properties of β-solidifying γ-TiAl alloy fabricated by laser powder bed fusion[J].Materials Characterization，2024，214：114077.

[20] 骆伟航. 选区激光熔化 TiAl 基复合材料工艺及性能研究[D]. 无锡：江南大学，2023：71-74.

[21] LUO W H . Study on the properties of TiAl composites manufactured by selective laser melting[D]. Wuxi： Jiangnan University，2023：71-74.

[22] SCHUSTER J C， PALM M . Reassessment of the binary aluminum-titanium phase diagram[J].Journal of Phase Equilibria and Diffusion，2006，27（3）：255-277.

[23] CHO K， KAWABATA H， HAYASHI T，et al. Peculiar microstructural evolution and tensile properties of β-containing γ-TiAl alloys fabricated by electron beam melting[J].Additive Manufacturing，2021，46：102091.

[24] MISHIN Y， HERZIG C . Diffusion in the Ti-Al system[J].Acta Materialia，2000，48（3）：589-623.

[25] VUJIC D， LI Z X， WHANG S H . Effect of rapid solidification and alloying addition on lattice distortion and atomic ordering in L10 TiAl alloys and their ternary alloys[J].Metallurgical Transactions A，1988，19（10）：2445-2455.

[26] GAO P， WANG Z M . Tailored microstructure and enhanced comprehensive mechanical properties of selective laser melted Ti-40Al-9V-0.5Y alloy after aging treatment[J]. Materials Science and Engineering： A，2020，780：139183.

[27] LI W， LIU J， WEN S F，et al. Crystal orientation，crystallographic texture and phase evolution in the Ti-45Al-2Cr-5Nb alloy processed by selective laser melting[J].Materials Characterization，2016，113：125-133.

[28] YANG G， KOU H C， YANG J R，et al. Microstructure control of Ti45Al8.5Nb(W，B，Y) alloy during the solidification process[J].Acta Materialia，2016，112：121-131.

[29] LI W， YIN Y J， XU Q，et al. Tensile behavior of γ/α₂ interface system in lamellar TiAl alloy via molecular dynamics[J].Computational Materials Science， 2019，159：397-402.

[30] ZHENG M， HAN J F， QU D F，et al. Compression and fretting wear studies of γ/α₂ duplex TiAl alloys at the nanoscale[J].Physica Scripta，2024，99（6）：065001.

基金资助

国家自然科学基金面上项目(52474377)