High-cycle fatigue induced twinning in CoCrFeNi high-entropy alloy processed by laser powder bed fusion additive manufacturing
High-cycle fatigue induced twinning in CoCrFeNi high-entropy alloy processed by laser powder bed fusion additive manufacturing
复制标题
激光粉末床熔融增材制造CoCrFeNi高熵合金高周疲劳诱发孪晶
DOI：
10.1016/j.addma.2022.103319
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发表时间：
2022-11
影响因子：
11
通讯作者：
Yinan Chen;Bo Li;Boxiong Chen;Fuzhen Xuan
中科院分区：
文献类型：
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作者：
Yinan Chen;Bo Li;Boxiong Chen;Fuzhen Xuan
研究了高周疲劳（R=0.1，室温）诱导的激光粉末床熔合（L-PBF）增材制备四元CoCrFeNi高熵合金（HEA）的显微组织演变。构建后的材料具有< 001 >和< 110 >的复合织构，低角度边界比例高。电子背散射衍射（EBSD）和透射电镜（TEM）分析结果表明，在σmax= 450 MPa （Nf=1.06 ×105）高周疲劳条件下，合金发生变形孪晶，而在300 MPa和200 MPa高周疲劳条件下，合金没有发生变形孪晶。变形孪晶导致循环软化，表现为应力控制疲劳状态下最大应变不断增大，后疲劳状态下硬度提高~ 80 hv0.2。EBSD结果显示，< 001 >和< 110 >取向均有利于双晶状体的形成。考虑到< 001 >和< 110 >取向的晶粒尺寸比其他取向的晶粒尺寸大2倍，晶粒尺寸效应对孪晶的形成可能起到一定的作用。高分辨率透射电镜显示，完全位错、晶格畸变、层错和部分位错与孪晶、胞状和迷宫壁状位错结构有关。高应力疲劳过程中形成纳米孪晶的潜在机制涉及1/2 < 110 >的完全位错解离为1/6 < 112 >的部分位错。高周疲劳加载后，原位状态下观察到的位错胞结构演变为亚晶，亚晶界位错密度极大。
High-cycle fatigue (R=0.1, room temperature) induced microstructural evolution in a laser powder bed fusion (L-PBF) additively manufactured quaternary CoCrFeNi high-entropy alloy (HEA) was studied. The as-built material exhibited a combined < 001 > and < 110 > texture and high proportion of low-angle boundaries. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) revealed that deformation twinning occurred under the high-cycle fatigue ofσmax= 450 MPa (Nf=1.06 ×105), but not for the stress level of300 MPa and 200 MPa. The deformation twins led to the cyclic softening, as manifested by the continuous increase of maximum strain under the stress-controlled fatigue, and the hardness increased by ∼80 HV0.2in the post-fatigued condition. EBSD revealed that both the < 001 > and < 110 > orientations were favorable for the twin formation. Given that the size of grains with the < 001 > and < 110 > orientations was twice larger than those of the other orientations, the grain size effect on twin formation could play a certain role. High-resolution TEM revealed that the full dislocations, lattice distortion, stacking faults, and partial dislocations were associated with the twin, cellular and labyrinth wall-like dislocation structures. The underlying mechanism for the formation of nano-twins during high-stress fatigue involved the dissociation of 1/2 < 110 > full dislocations to 1/6 < 112 > partial ones. Moreover, the dislocation cell structure as observed in the as-built condition evolved into sub-grains after the high-cycle fatigue loading, with the immensely dense dislocations at the sub-grain boundary.