Nanoindentation test was employed to measure the actual hardness and yield strength of the stir zone in the friction stir-welded single-phase brass joints. For this aim, different joints were prepared according to an experimental matrix based on the central composite rotatable design. In this design matrix, the tool rotational speed, tool traverse speed, and tool axial force were the input parameters. The outputs were the hardness and yield strength of the joints. To measure the hardness and tensile strength of the joints, the nanoindentation test was employed. Moreover, electron back scattered diffraction and transmission electron microscopy techniques were used to study the microstructural features. The results showed that by decreasing rotational speed and axial force, and by increasing the traverse speed, the hardness and yield strength of the joints were increased. In other words, lower heat inputs caused higher strength in the joints. Finer grain sizes, larger grain average misorientation amounts, i.e., existence of more dislocations, and greater Taylor factors in the lower heat input joints revealed that the influence of grain boundaries, dislocations, and texture were the origins of better mechanical properties.

中文翻译：

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纳米压痕在评估FSW黄铜接头的硬度和屈服强度中的应用：微观结构和强化机制

纳米压痕试验用于测量搅拌摩擦焊接单相黄铜接头中搅拌区的实际硬度和屈服强度。为了这个目的，根据基于中央复合旋转设计的实验矩阵准备了不同的接头。在此设计矩阵中，刀具转速，刀具移动速度和刀具轴向力是输入参数。输出是接头的硬度和屈服强度。为了测量接头的硬度和拉伸强度，采用了纳米压痕测试。此外，电子背散射衍射和透射电子显微镜技术被用来研究微观结构特征。结果表明，通过降低旋转速度和轴向力，并增加横向速度，增加了接头的硬度和屈服强度。换句话说，较低的热量输入导致接头的强度更高。较小的晶粒尺寸，较大的晶粒平均取向错误量（即，存在更多的位错）和较低的热输入接头中存在更大的泰勒因子表明，晶界，位错和织构的影响是更好的机械性能的起源。