热处理对电子束粉末床熔融TiAl-4822合金组织和高温力学性能的影响

Influence of Heat Treatment on the Microstructural Evolution and High-Temperature Mechanical Behavior of TiAl-4822 Alloy Produced by Electron Beam Powder Bed Fusion

摘要:

为探究不同热处理所形成的微观组织对Ti–48Al–2Cr–2Nb(TiAl-4822, at.%)合金750℃高温力学性能的影响,本研究采用电子束粉末床熔融(Electron Beam Powder Bed Fusion,EB-PBF)技术制备了TiAl-4822合金,并通过热处理获得了不同组织类型的试样。结果表明,沉积态试样呈现由粗大的γ相条带与细晶双态组织共同组成的非均匀组织特征。经1330 ℃/0.5 h-FC热处理后,合金获得了晶粒均匀、尺寸增大的双态组织；而经1380 ℃/0.5 h-FC热处理后,晶粒显著长大,组织转变为全片层结构。随着热处理温度的升高,α?相在层间或界面处富集,并与γ相形成典型的Blackburn取向关系。力学性能测试结果表明,试样的室温硬度随热处理温度升高而提高,但其在750 ℃下的抗拉强度和延伸率均较沉积态有所下降。沉积态样品表现出优异的高温综合力学性能(抗拉强度654.67 ± 17.01 MPa,断后伸长率42.5 ± 2.29%),这主要归因于快速凝固形成的细小γ晶粒及晶内细密片层组织。热处理过程中α?与γ两相通过择优取向生长以降低界面能,促进片层化和粗化,粗大的片层组织及在晶界/片间富集的脆性α?相成为裂纹萌生与扩展的优先通道,从而导致塑性降低。本研究揭示了EB-PBF成形TiAl-4822合金中热处理-组织-性能的内在关联,为通过热处理调控γ-TiAl合金的组织结构及其高温性能提供了重要参考。

Abstract:

To investigate the influence of heat treatment–induced microstructural evolution on the high-temperature mechanical behavior of Ti–48Al–2Cr–2Nb (TiAl-4822, at.%) alloy at 750 °C, specimens were fabricated via electron beam powder bed fusion (EB-PBF) and subsequently subjected to various heat treatment conditions to obtain distinct microstructures. The as-fabricated sample exhibited a heterogeneous bimodal structure composed of coarse γ bands and fine-grained duplex regions. After heat treatment at 1330 °C for 0.5 h followed by furnace cooling (FC), the alloy developed a homogeneous duplex microstructure with slightly coarsened grains. Increasing the heat treatment temperature to 1380 °C resulted in pronounced grain growth and the formation of a fully lamellar structure. With rising temperature, α? phases tended to segregate along interlamellar or intergranular regions, establishing the typical Blackburn orientation relationship with the γ phase. Mechanical testing revealed that hardness increased with heat treatment temperature, whereas both tensile strength and ductility at 750 °C decreased compared with the as-fabricated condition. The as- fabricated sample demonstrated superior high-temperature mechanical performance, achieving a tensile strength of 654.67 ± 17.01 MPa and an elongation of 42.5 ± 2.29%, primarily due to the fine γ grains and dense intragranular lamellae formed during rapid solidification. During heat treatment, the α? and γ phases coarsened through orientation-dependent growth to minimize interfacial energy, leading to lamellar thickening. The resulting coarsened lamellae and α? phase enrichment at grain boundaries and interlamellar interfaces served as preferential sites for crack initiation and propagation, thereby reducing ductility. This study elucidates the intrinsic correlations among heat treatment, microstructure, and mechanical behavior in EB-PBF TiAl-4822 alloy, providing valuable insights into tailoring the microstructure and optimizing the high-temperature performance of γ-TiAl alloys through thermal processing