Directed energy deposition (DED)-built titanium alloys have long suffered from the anisotropic mechanical properties induced by the long columnar prior β grains growing along the building direction, which restricts their applications. In this work, a special interlayer pause (SIP) strategy is designed to reduce the tensile property anisotropy by adjusting the grain morphology. The grain morphologies, microstructure, crystallographic texture, tensile properties and their anisotropy of DEDed TC11 titanium alloys were systematically investigated. The results show that the SIP strategy promotes the columnar-to-equiaxed transition of grain morphology, reduces grain sizes, and weakens the crystallographic textures. The microstructure of SIP samples consists of superfine basketweave and lamellar α laths and residual β phases. The average length of α laths increases with the SIP layer number. In addition, the maintained superfine α phases contribute to an ultrahigh yield strength of ∼1200 MPa of the SIP samples. The yield strength of the horizontal direction gradually decreases and that of the vertical direction increases with increasing the SIP layer number, resulting in a lowered strength anisotropy of less than 2%. When adopting an optimal SIP strategy, the as-deposited TC11 alloy exhibits a relatively small ductility anisotropy.

中文翻译：

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定向能量沉积技术制备TC11合金晶粒形貌和拉伸性能各向异性控制的特殊层间暂停策略

定向能量沉积（DED）构建的钛合金长期以来一直受到沿构建方向生长的长柱状原β晶粒引起的各向异性机械性能的影响，这限制了其应用。在这项工作中，设计了一种特殊的层间暂停（SIP）策略，通过调整晶粒形态来降低拉伸性能各向异性。对DEDed TC11钛合金的晶粒形貌、显微组织、晶体织构、拉伸性能及其各向异性进行了系统研究。结果表明，SIP策略促进了晶粒形貌从柱状到等轴的转变，减小了晶粒尺寸，削弱了晶体织构。SIP 样品的微观结构由超细篮纹和层状 α 板条和残余 β 相组成。α板条的平均长度随着SIP层数的增加而增加。此外，保持的超细 α 相有助于 SIP 样品具有~1200 MPa 的超高屈服强度。随着SIP层数的增加，水平方向的屈服强度逐渐降低，垂直方向的屈服强度逐渐增加，导致强度各向异性降低至2%以下。当采用最佳 SIP 策略时，沉积态 TC11 合金表现出相对较小的延展性各向异性。