一种单晶镍基合金热处理期间的组织演化与分析

Microstructure Evolution and Analysis of a Single Crystal Ni-Based Superalloy during Heat Treatment

通过对一种单晶镍基合金的差热曲线分析和不同条件热处理后的组织形貌观察,结合有限元分析,研究了合金中γ′相在热处理期间的组织演化规律。结果表明:实验用合金的热处理‘窗口’是48℃,在1300℃γ′相有最大的溶解速度,1040℃析出的γ′相最为稳定;确定出该合金的热处理工艺为1280℃,4h,AC+1300℃,4h,AC+1040℃,4h,AC+870℃,24h,AC。一次时效期间,在界面能和共格应变能的作用下,γ′相长大呈立方体形貌;二次时效期间,γ′相略有长大,立方度增加,排列更加规则。其中,时效期间,共格界面的γ′相按“台阶机制”优先沿〈100〉取向扩散生长呈立方体形貌,而晶格错配应力的对称分布是使立方γ′相得以稳定存在的主要原因。

The regularity of microstructure evolution for a single crystal nickel-base superalloy have been investigated by means of the analysis of the differential thermal curve （DTA） and microstructure observation of SEM. The results show that the ＂window＂ of heat treatment for the experimental superalloy is detected to be 4812. There is a maximal solution rate of γ＇ phase at about 130012, and a better stability of the precipitated γ＇ phase occurs at about 1040℃. In the further, heat treatment conditions of the alloy are determined as follows： 1280℃, 4 h, A C ＋ 1300℃, 4 h, AC ＋ 1040℃, 4 h, A C ＋ 870℃, 24 h, A C. In the role of interface and lattice misfit strain energies, the γ＇ phase has grown into the morphology with cubic shape during first aging at 1040 ℃. After second aging, the cubic γ＇ phase has slightly grown in the form of the regular arrangement, improving the cubic degree of the γ＇ phase. Thereinto, it is according to ＂steps＂ mechanism, the coherent γ＇ phase grows into the cuboidal morphology along the 〈100〉 orientation during aging treatment. Moreover, the main reason of the stable existance of the regular and cuboidal γ＇ phase is attributed to the symmetrical distribution of the lattice mismatch stress in the cuboidal γ＇ phase.