He Jingjun, Yang Haiou, Huang Linhao, Man Jingyu, Wu Yuhan, Lin Xin
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China.
Shenzhen Research Institute of Northwestern Polytechnical University, Northwestern Polytechnical University, Shenzhen 518057, China.
Materials (Basel). 2025 Jun 14;18(12):2806. doi: 10.3390/ma18122806.
The density of SLMed (Selective Laser Melting) Ti-22Al-25Nb alloy was improved through hot isostatic pressing (HIP) treatment, and the influence of HIP and solution aging on the microstructure of Ti-22Al-25Nb alloy in the as-deposited state was examined. The results indicate that following (1100 °C + 300 MPa)/3 h-HIP, the specimen densities have risen to 99.71%, porosity has markedly decreased, and internal flaws have been eradicated. Microstructural analysis reveals a significant presence of GBα (GB, Grain Boundary) along grain boundaries, with GBLO + α (GBL, Grain Boundary Lath; O, Orthorhombic) laths extending parallel from the grain boundaries into the intragranular region. Additionally, a limited number of cross or snowflake O + α lath clusters and acicular O phases are precipitated within the B2 (B, Body-centered cubic) phase in the HIPed state, characterized by isotropic and linear grain boundaries. The GBLα and GBLO exhibit two growth modes: sympathetic nucleation and interfacially unstable nucleation. During the solid solution treatment following HIP, as the solid solution temperature rises, the acicular O phase, GBLO, lath O phase, lath α and GBα sequentially dissolve, increasing the volume fraction of the B2 phase. After HIP, the aging microstructure is primarily characterized by the proliferation of the acicular O phase precipitated from the B2 phase and retaining the lath O phase in a solid solution. The precipitation of GBLO in the original solid solution is suppressed, and the GBLα in the original solid solution partially decomposes into rimO, resulting in coarse grain size and significant internal decomposition of α. Following solution treatment and aging at 920 °C, the proliferation of the acicular O phase enhances ductility, resulting in ideal overall characteristics with a yield strength (YS) of 760.81 MPa, ultimate tensile strength (UTS) of 869.32 MPa, and elongation (EL) of 2.683%. This study demonstrates that the HIP treatment and the modification of solution aging parameters can substantially increase the density and refine the microstructure of Ti-22Al-25Nb alloy, hence enhancing its mechanical properties.
通过热等静压（HIP）处理提高了选择性激光熔化（SLMed）Ti-22Al-25Nb合金的密度，并研究了HIP和固溶时效对沉积态Ti-22Al-25Nb合金微观结构的影响。结果表明，在（1100 °C + 300 MPa）/3 h-HIP处理后，试样密度提高到99.71%，孔隙率显著降低，内部缺陷得以消除。微观结构分析显示，沿晶界大量存在GBα（GB，晶界），GBLO + α（GBL，晶界板条；O，正交）板条从晶界平行延伸到晶内区域。此外，在HIP态的B2（B，体心立方）相中，有少量交叉或雪花状O + α板条簇和针状O相析出，其特征为各向同性和线性晶界。GBLα和GBLO呈现两种生长模式：协同形核和界面不稳定形核。在HIP后的固溶处理过程中，随着固溶温度升高，针状O相、GBLO、板条O相、板条α和GBα依次溶解，B2相的体积分数增加。HIP后，时效微观结构的主要特征是从B2相析出的针状O相增多，并在固溶体中保留板条O相。原始固溶体中GBLO的析出受到抑制，原始固溶体中的GBLα部分分解为rimO，导致晶粒粗大和α相内部显著分解。在920 °C进行固溶处理和时效后，针状O相的增多提高了延展性，屈服强度（YS）为760.81 MPa、抗拉强度（UTS）为869.32 MPa、伸长率（EL）为2.683%，从而具有理想的综合性能。本研究表明，HIP处理和固溶时效参数的调整可大幅提高Ti-22Al-25Nb合金的密度并细化其微观结构，进而提高其力学性能。
