Multilayered structures of dissimilar titanium alloys can achieve excellent fracture ductility and strength, while their fatigue characteristics especially dislocation networks and twin formation are rarely reported. Heterogeneous microstructures are observed in the multilayered TC4/TB8 alloys, including fine acicular α grains, continuous α layer at prior β grain boundaries (α) and β matrix on the TB8 layer, together with equiaxed α grains on the TC4 layer. High-cycle fatigue (HCF) and low-cycle fatigue (LCF) tests show that the initial fatigue damage appears at the α/β matrix interfaces on the TB8 layer instead of the boned TC4/TB8 interfaces. Since the stress concentration induced by dislocation pile-up is prone to micro-void formation and crack propagation at the α/β interfaces. For LCF, the α/β interfaces can not only act as impenetrable barriers and sources of lattice dislocations, but also allow the dislocations cross boundaries during cyclic tension and compression because of the high boundary energy. The formation characteristic of deformation twins that is beneficial for the plastic deformation of α grains in TC4 layer during cyclic strain is investigated. Furthermore, the hexagonal dislocation networks are also found within the equiaxed α grains of TC4 layer after LCF, and the role between interface barrier and slip direction in the formation mechanism is analyzed.

中文翻译：

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多层异种钛合金的高周和低周疲劳特性


异种钛合金的多层结构可以实现优异的断裂塑性和强度，但其疲劳特性尤其是位错网络和孪晶的形成却鲜有报道。在多层 TC4/TB8 合金中观察到不均匀的微观结构，包括细小的针状 α 晶粒、先前 β 晶界 (α) 处的连续 α 层和 TB8 层上的 β 基体，以及 TC4 层上的等轴 α 晶粒。高周疲劳（HCF）和低周疲劳（LCF）测试表明，初始疲劳损伤出现在TB8层的α/β基体界面，而不是TC4/TB8接骨界面。由于位错堆积引起的应力集中很容易在α/β界面处形成微孔洞和裂纹扩展。对于LCF，α/β界面不仅可以充当不可穿透的屏障和晶格位错源，而且由于高边界能，还允许位错在循环拉伸和压缩过程中跨越边界。研究了循环应变过程中TC4层中有利于α晶粒塑性变形的形变孪晶的形成特征。此外，LCF后TC4层等轴α晶粒内也发现了六方位错网络，并分析了界面势垒和滑移方向在形成机制中的作用。