单晶高温合金DD6高温显微组织演化规律研究

Microstructure Evolution of Single Crystal Superalloy DD6 at High Temperature

摘要:

我国自主研发的低成本DD6镍基高温合金，具有优良的拉伸性能和高温蠕变性能等，在涡轮机部件等领域具有广阔的应用前景。本研究从建立单晶叶片使用失效评价方式的角度出发，模拟叶片实际使用温度对DD6进行了加热处理，研究和分析了DD6合金在模拟使用温度下保温50h后微观组织随温度的演化规律。研究发现，在模拟使用状态加热的过程中，随加热温度的升高，γ′相首先发生连接、合并，尺寸不断增大，随后向γ基体中溶解，这与Al、Nb等γ′相形成元素从γ′相向γ基体中的扩散有关。加热到1150℃以上在冷却到室温的过程中，较宽的基体通道内会析出颗粒状的二次γ′相，且二次γ′相颗粒随着加热温度的升高进一步长大。 二次γ′相的析出是因为γ基体中Al、Nb元素过饱和引起了成分过冷，而其长大从热力学上看是为了减小界面能，从动力学上看与加热温度及长大时间有关。

Abstract:

A low cost nickel-based superalloy DD6 has been independently developed in our country which has excellent tensile properties, high-temperature creep resistance, fatigue resistance, oxidation and corrosion resistance. DD6 superalloy has broad application prospects in fields of turbine components. In order to establish failure evaluation standard of single crystal turbine blades, heat treatments are given to DD6 in this study to simulate the actual operating temperature of turbine blades. The microstructure evolution with temperature of DD6 superalloy after heated for 50 hours is studied and analyzed. It is found that γ′ phase continuously dissolved into γ base with the increase of heating temperature. It is related to the diffusion of Al, Ti elements from γ′ phase to γ base. While DD6 are cooling from above 1150 ℃ to room temperature, the second γ′ phase particles will precipitate at wide base tunnels and grow bigger with temperature rises. The precipitation of second γ′ phase is due to composition undercooling caused by oversaturation of Al, Ti in γ base. From the point of view of thermodynamics, second γ′ phase grow to decrease interface energy. And it is related with heating temperature and cooling time from the point of view of kinetics.