B4C添加Ti-43Al-6Nb-1Mo-1Cr合金高温压缩蠕变性能与机理研究

High-Temperature Compressive Creep Properties and Mechanisms of Ti-43Al-6Nb-1Mo-1Cr Alloy Reinforced with B4C

摘要:

研究了B₄C添加对一种β凝固γ-TiAl基合金在250 MPa/800~850 ℃下和850 ℃/200~250 MPa下高温压缩蠕变行为的影响机制。结果表明，B₄C的改性使Ti-43Al-6Nb-1Mo-1Cr合金的高温压缩蠕变性能显著提升，其稳态蠕变速率平均降低38.42%，50 h后的蠕变应变值平均下降46.32%。合金稳态蠕变速率与应力和温度之间的关系符合Norton-Bailey幂律模型，其应力指数由1.96增加至4.16，蠕变激活能从335.02 kJ/mol提升至368.52 kJ/mol，这表明合金主导变形机制从晶界滑移转变为位错攀移。合金抗压缩蠕变性能的显著提升归因于多种强化机制：析出的棒状TiB作为硬质第二相，通过阻碍位错运动和钉扎晶界强化基体，并与固溶于基体中的C元素协同细化了片层团。0.2at% B₄C的添加显著抑制了合金的动态再结晶行为，延缓其片层组织的退化，从而有效减弱动态再结晶所引起的软化效应。此外，在高温压缩蠕变过程中动态析出的Ti₂AlC和Ti₂Al颗粒分别钉扎于α₂相界面与B2相内，强化晶体结构，增强了合金显微组织的稳定性。

Abstract:

The effect of B₄C addition on the high-temperature compressive creep behavior of a β-solidified γ-TiAl-based alloy under the conditions of 250 MPa/800?850 ℃ and 850 ℃/200?250 MPa was investigated. The results show that the reinforcement of the Ti-43Al-6Nb-1Mo-1Cr alloy with B₄C significantly enhances its high-temperature compressive creep property. This improvement is reflected by a reduction in steady-state creep rate of 38.42% and a decrease in creep strain after 50 h of 46.32%. The steady-state creep rate of alloys as a function of stress and temperature follows the Norton-Bailey power-law model. With the addition of B₄C, the stress exponent increases from 1.96 to 4.16, and the creep activation energy rises from 335.02 kJ/mol to 368.52 kJ/mol. This change indicates a transition in dominant deformation mechanism from grain-boundary sliding to dislocation climb. The remarkable enhancement in compressive creep resistance is attributed to multiple strengthening effects. The precipitated rod-like TiB acts as a hard second phase that strengthens the matrix by hindering dislocation motion and pinning grain boundaries. In synergy with C dissolved in the matrix, it also refines the lamellar clusters. The addition of 0.2at% B₄C notably suppresses dynamic recrystallization, thereby delaying degradation of the lamellar structure and mitigating the softening effect induced by recrystallization. Furthermore, Ti₂AlC and Ti₂Al particles precipitate dynamically during high-temperature compressive creep, pinning at the α₂ phase interfaces and within the B2 phase, respectively. These precipitates strengthen the crystal structure and improve the microstructural stability of the alloy.