In the present work, interactions of nanoindentation-induced dislocations (NIDs) with a low-angle grain boundary (LAGB) are investigated in a single-crystalline CrCoNi medium-entropy alloy (MEA). Microstructural evolutions before and after nanoindentation were examined using accurate electron channeling contrast imaging (A-ECCI). In the as-grown state, the alloy microstructure consists of subgrains separated by LAGBs. After nanoindentation on the (001) plane far away from LAGBs, the load-displacement curves exhibit the typical behavior of metals and alloys with a pop-in marking the elastic-plastic transition. This pop-in is related to the nucleation of NIDs that are observed to form pile-ups on {111} planes. In contrast, when indents are performed in the vicinity of a LAGB with a low misorientation angle of 0.24° and consisting of dislocations spaced ~60 nm apart, different micromechanical responses and deformation mechanisms are observed depending on the distance between the LAGB and the nanoindenter tip. When the distance between the LAGB and the nanoindenter tip is larger than four times the size of the indent (corresponding ratio: R > 4), the LAGB does not affect the micromechanical response nor interact with NIDs. In contrast, when the indenter comes in direct or indirect contact with the LAGB (R < 1), the load-displacement curve deviates at low loads from the elastic stage, and pop-ins are not observed. In this case, the continuous deformation is accommodated by the movement of the pre-existing LAGB dislocations. For intermediate cases with 1 < R < 4, the load of the initial pop-in is dependent on the local defect density. In this latter case, the pile-ups of NIDs directly impinge on the LAGB. Microstructural analyses reveal that the LAGB accommodates plasticity by blocking the NIDs, activating a dislocation nucleation site in the adjacent subgrain/emission of dislocation from the LAGB, and inducing slight motions of its constituent dislocations.

在目前的工作中，在单晶CrCoNi中熵合金（MEA）中研究了纳米压痕诱导的位错（NID）与低角度晶界（LAGB）的相互作用。使用精确的电子通道对比成像（A-ECCI）检查了纳米压痕之前和之后的微结构演变。在成长期状态下，合金的微观结构由被LAGB隔开的亚晶粒组成。在远离LAGBs的（001）平面上进行纳米压痕后，载荷-位移曲线显示出金属和合金的典型行为，并带有弹跳标记，指示弹塑性转变。此弹出窗口与NID的成核有关，可以观察到这些NID在{111}平面上形成堆积。相反，当在低取向角为0的LAGB附近执行缩进时。由LAGB和纳米压头尖端之间的距离观察到的24°且由相距约60 nm的位错组成，观察到不同的微机械响应和变形机制。当LAGB与纳米压头尖端之间的距离大于压痕尺寸的四倍时（对应比例：R  > 4），LAGB不会影响微机械响应，也不会与NID相互作用。相反，当压头与LAGB直接或间接接触（R  <1）时，载荷-位移曲线在低载荷下偏离弹性阶段，并且没有观察到弹跳。在这种情况下，连续变形通过预先存在的LAGB位错的运动来调节。对于1 < R的中级情况  <4，初始弹出窗口的负载取决于局部缺陷密度。在后一种情况下，NID的堆积直接撞击LAGB。微观结构分析表明，LAGB可通过阻断NID，激活相邻亚晶粒中的位错成核位点/从LAGB释放位错并诱导其组成位错的轻微运动来适应可塑性。