TC4 ELI钛合金显微组织对低周疲劳性能的影响

Effect of Microstructure on Low Cycle Fatigue Properties of TC4 ELI Titanium Alloy

摘要:

本文通过分析TC4 ELI合金在不同应力幅下的应变-循环次数曲线，研究了双态和片层两种典型组织的低周疲劳性能。组织观察发现：双态组织中等轴α相体积分数约26.6%，等轴α相平均晶粒尺寸~7.8 μm。片层组织试样中，α相的片层厚度为0.5 ~ 2.0 μm。低周疲劳性能结果表明：在最大应力水平下，不同组织的TC4 ELI合金均表现出显著的循环软化现象，双态组织具有更加优异的疲劳性能，这主要是因为双态组织中有效的滑移程远小于片层组织，此外高位错密度等轴α相的存在也阻碍了疲劳裂纹的萌生和扩展。扫描断口形貌分析发现：双态组织试样的疲劳断口平整光滑，而片层组织断口则出现了与原始粗大的β晶粒有关的几何形刻面。

Abstract:

Low cycle fatigue behavior of TC4 ELI titanium alloy with bimodal and lamellar microstructure had been investigated by analyzation of strain-cycles curve with different stress amplitudes. Results indicated that the volume fraction of equiaxed α phase is about ~ 26.6% for the bimodal microstructure, the average grain size is approximate 7.8 μm. At the same time, the thickness of α phase layer is about 0.5 ~ 2.0 μm for lamellar microstructure. Cyclic softening phenomenon was observed for all the samples of TC4 ELI alloys with different microstructure at the maximum stress. Sample with bimodal microstructure exhibited higher low cycle fatigue life, which could be attributed to the shorter effective slip path than the one with lamellar microstructure. More than that, the presence of equiaxed α-phase with high dislocation density also could hinder the initiation and propagation of fatigue cracks for the bimodal microstructure. Fracture morphology shown flat and smooth for the sample with bimodal microstructure, however, some geometric facets associated with the original coarse-grained β were found for the sample with lamellar microstructure.