【摘要】 钨（W）能够有效提升TiAl合金的高温力学性能，但其较低的扩散速率易导致组织偏析，使得W对TiAl合金显微组织的影响规律尚未得到系统阐明。为此，本文采用热等静压工艺制备了组织均匀且细小的TiAl/W合金，研究了W元素的扩散行为对TiAl合金组织演变与微纳力学性能的影响。结果表明：经固溶处理后，合金主要由类珠光体基体与B2相构成。其中，γ板条在B2相中的贫W区内以Kurdjumov-Sachs(K-S)位向关系析出，形成典型的B2(γ)区域。类珠光体组织的形成机制可归结为：在α→γ相变过程中，W元素被排挤至周围区域，导致邻近α相处于W过饱和状态，进而诱发α2相晶格畸变并转变为B2相，最终促成类珠光体组织的生成。预先进行的均匀化热处理促进了W元素的均匀分布，从而在后续固溶处理中抑制上述相变过程，促使合金最终形成稳定平衡的片层组织。微纳力学性能测试结果显示，随着固溶温度升高，B2相区域的显微硬度呈现先上升后下降的趋势，该变化与受W扩散控制的固溶强化机制及相应相变机制密切相关。实验表明，在1320℃固溶处理后，合金的显微硬度达到最高值，为HV 440.0。更多还原

【Abstract】 The addition of tungsten(W) improves the high-temperature mechanical properties of TiAl alloys by effectively suppressing atomic diffusion. However, its low diffusivity and high melting point lead to significant microstructural inhomogeneity and complications during melting and solidification. Consequently, the systematic understanding of how W influences the microstructure of TiAl alloys remains limited. To address these challenges, powder metallurgy offers a promising route for obtaining uniform and fine microstructures suitable for detailed investigation. In this work, the effect of W diffusion on microstructure evolution and micro-/nano-mechanical properties was investigated. To promote W redistribution, solid-solution treatments(ST) were performed at three different temperatures within(α+γ) phase region. After ST, all three alloys exhibited similar microstructures, consisting mainly of a pearlite-like matrix and B2 phase. Within B2 phase, γ laths(denoted γ_p) precipitated in W-deficient zones following the Kurdjumov-Sachs(K-S) orientation relationship, forming B2(γ) region. γ_p phase nucleated directly inside B2 grains, with its growth likely governed by discontinuous coarsening. The volume fraction of γ_p within the B2 phase increased with rising ST temperature. Higher temperatures enhance atomic mobility, increasing the diffusion coefficient of W and promoting γ phase precipitation in W-depleted areas. Moreover, reduced interfacial energy at elevated temperatures provides a stronger driving force for direct nucleation, explaining the observed increase in γ_p content. During ST, the α→γ phase transition expels W into adjacent regions, resulting in a supersaturated α phase and inducing lattice distortion. To relieve the distortion energy, the hexagonal structure transforms into a body-centered cubic(B2) phase, leading to the formation of a pearlite-like microstructure. Prior homogenization annealing at 1250 ℃ for 16 h effectively reduced micro-segregation, as confirmed by a residual segregation index δ close to zero. This homogenization promoted uniform W distribution, suppressed phase transformations during subsequent ST, and ultimately yielded a segregation-free lamellar structure. These observations indicate that W segregation significantly hinders the formation of equilibrium lamellar microstructures. Micro-and nano-mechanical tests revealed that microhardness first increased and then decreased with rising ST temperature. The highest hardness of HV 440.0 was achieved after ST at 1320 ℃, followed by a decline to HV 384.3 at 1340 ℃ and HV 365.8 at 1360 ℃. After prior homogenization, hardness remained stable around HV 350.5 regardless of ST temperature. Similarly, the microhardness of B2(γ) region peaked at HV 509.2 after ST at 1320 ℃, dropping to HV 427.0 and HV 430.0 at higher temperatures. In contrast, the pearlite-like matrix showed little dependence on ST temperature, averaging HV 354.0.Nanoindentation tests were conducted to clarify the mechanisms behind these trends. The nanohardness of B2 phase decreased slightly from(7.80±0.39) GPa(1320 ℃) to(7.49±0.37) GPa(1340 ℃) and(7.62±0.15) GPa(1360 ℃). Conversely, γ_p phase exhibited a notable increase from(5.94±0.53) GPa to(6.09±0.10) GPa and further to(6.73±0.48) GPa under the same conditions. Load-displacement curves showed that B2-phase curves nearly overlapped across temperatures, while γ_p-phase curves gradually approached those of B2 phase with increasing temperature. EDS point analysis indicated that higher ST temperatures raised W content in both B2 and γ_p phases, enhancing solid-solution strengthening and thereby increasing nanohardness. Concurrently, the volume fraction of the softer γ_p phase grew due to the elevated nucleation drive at higher temperatures. Thus, microhardness variation is governed by two competing mechanisms tied to W diffusion: solid-solution strengthening and phase-transformation-induced softening. Furthermore, the decreasing nanohardness difference between B2 and γ_p phases reflects improved micromechanical compatibility, which helps dissipate interfacial stress concentrations and promotes more uniform deformation. This work established a theoretical basis for microstructure control through W-diffusion engineering and provided a preliminary quantitative assessment of the associated strengthening effects, offering valuable guidance for the microstructural design of TiAl alloys.更多还原