A microstructure of gradient grains pinned by gradient δ phase was obtained within GH4169 by ultrasonic rolling followed by a post heat-treatment at either 900 °C or 954 °C for 5, 15 or 30 min, respectively. In order to evaluate the high temperature stability of such gradient microstructure, the variations of grain size and gradient microhardness of GH4169 were measured after being kept at 650 °C for 10–100 h. Hot tensile tests at 650 °C were conducted to reveal the effects of refined grains and δ phase on mechanical properties. The results showed that the amount of δ phase decreased with the depth increasing, while recrystallized grain size presented the opposite trend. And the cross-sectional microhardness within strengthened layer decreases as depth increases after post heat-treatment. The ultrasonic rolled sample treated at 900 °C for 15 min (900–15) brings a relatively finer δ phase which distributes both in grains and grain boundaries. Such microstructure results in a better pinning effect compared with the one treated at 954 °C for 15 min (954–15) with less δ phase only distributed in grain boundaries. The gradient refined grains and δ phase contributes to the improvement on tensile strength at 650 °C in Sample 900–15 with YS (Yield strength) = 903 MPa, UTS (Ultimate tensile strength) = 988 MPa (21% and 6% improvement compared with Sample 0-900-30, respectively). The gradient microstructure with refined grains pinned by δ phase showed good thermal stability and mechanical properties at 650 °C.

在GH4169中，通过超声轧制，然后在900°C或954°C下分别进行5、15或30分钟的后热处理，获得了由梯度δ相钉扎的梯度晶粒的微观结构。为了评估这种梯度微结构的高温稳定性，在650°C下放置10–100 h后，对GH4169的晶粒尺寸和梯度显微硬度进行了测量。进行了650°C的热拉伸试验，以揭示细化晶粒和δ相对机械性能的影响。结果表明，δ相的数量随深度的增加而减少，而再结晶晶粒尺寸呈现相反的趋势。后热处理后，随着深度的增加，强化层内的截面显微硬度会降低。超声轧制的样品在900°C下处理了15分钟（900-15），产生了相对更细的δ相，该相既分布在晶粒中，又分布在晶界中。与在954°C下处理15分钟（954-15）的显微组织相比，这种微结构具有更好的钉扎效果，而δ相较少，仅分布在晶界。梯度细化晶粒和δ相有助于样品900–15中650°C的抗拉强度的提高，其中YS（屈服强度）= 903 MPa，UTS（最终抗拉强度）= 988 MPa（相比分别提高了21％和6％）分别使用0-900-30样品）。在650°C下具有δ相固定的细晶粒的梯度微结构显示出良好的热稳定性和机械性能。与在954°C下处理15分钟（954-15）的显微组织相比，这种微结构具有更好的钉扎效果，而δ相较少，仅分布在晶界。梯度细化晶粒和δ相有助于样品900–15中650°C的抗拉强度的提高，其中YS（屈服强度）= 903 MPa，UTS（最终抗拉强度）= 988 MPa（相比分别提高了21％和6％）分别使用0-900-30样品）。在650°C下，具有δ相钉扎的细晶粒的梯度微结构显示出良好的热稳定性和机械性能。与在954°C下处理15分钟（954-15）的显微组织相比，这种微结构具有更好的钉扎效果，而δ相较少，仅分布在晶界。梯度细化晶粒和δ相有助于样品900–15中650°C的抗拉强度的提高，其中YS（屈服强度）= 903 MPa，UTS（最终抗拉强度）= 988 MPa（相比分别提高了21％和6％）分别使用0-900-30样品）。在650°C下具有δ相固定的细晶粒的梯度微结构显示出良好的热稳定性和机械性能。UTS（最高抗拉强度）= 988 MPa（与样品0-900-30相比分别提高了21％和6％）。在650°C下具有δ相固定的细晶粒的梯度微结构显示出良好的热稳定性和机械性能。UTS（最高抗拉强度）= 988 MPa（与样品0-900-30相比分别提高了21％和6％）。在650°C下具有δ相固定的细晶粒的梯度微结构显示出良好的热稳定性和机械性能。