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研究了低合金化、中等强度、全片层γ-Ti Al合金Ti-45Al-2Mn-2Nb-0.8vol%TiB2在10 000 h、700℃大气热暴露处理下的热稳定性。研究发现,长期的大气热暴露导致合金通过渐进的α2层片消解、减薄模式实现α2→γ相变,且α2层片的分解、转化、消失的趋势较弱。相对于高合金含量的Ti-Al合金,该合金的枝晶偏聚不严重,α2层片不平衡分布的趋势较小。除极个别α2→β外,没有发生融合型α2+γ→β相变。热暴露10 000 h后,α2层片厚度约为热暴露前的一半,体积分数下降约为1/4,相应的“释氧脆化”和“B2+ω共生脆化”的影响较弱,使得合金的拉伸强度变化不大,塑形降低不严重,热暴露后的S-N疲劳强度反而增加了30%。疲劳强度的热暴露增强现象是因为热暴露导致的应力弛豫效应所致。长期的热浴浸泡导致样品表层的应力值降低,次表层的缺陷和微裂纹钝化,内部铸态α2-γ层片间的应力集中降低,这些均有利于提高合金抵抗疲劳微裂纹萌生的抗力。
The thermal stability of Ti-45Al-2Mn-2Nb-0.8vol% TiB2 with low-alloyed, medium-strength and full-thickness γ-Ti Al alloy exposed to atmospheric heat at 700 ℃ for 10 000 h was investigated. The results show that long-term exposure to atmospheric heat leads to the α2 → γ phase transformation of the alloy by progressive α2-layer digestion and thinning mode, and the decomposition, transformation and disappearance of α2 layer are weak. Compared with Ti-Al alloy with high alloy content, the dendrite segregation of the alloy is not serious, and the tendency of the unbalanced distribution of α2 lamellae is small. Except a few α2 → β, no fusion α2 + γ → β phase transition occurred. After heat exposure for 10 000 h, the thickness of α2 ply was about half of that before thermal exposure, and the volume fraction decreased by about 1/4, corresponding to “oxygen releasing embrittlement” and “B2 + ω intergrowth embrittlement” The impact is weaker, the tensile strength of the alloy does not change much, the shape reduction is not serious, the SN fatigue strength after heat exposure instead increases by 30%. The increased thermal fatigue of fatigue is due to the stress relaxation effect caused by thermal exposure. Long-term immersion in the hot bath resulted in lower stress on the sample surface, sub-surface defects and microcracking passivation, and lower stress concentration in the as2 as-cast α-γ layer, which all contributed to improve the resistance of the alloy against fatigue microcracking .