热处理过程中DD6单晶高温合金的组织演化规律与力学性能

研究了DD6单晶高温合金在热处理过程中的显微组织演化规律以及初熔组织的生成机理。通过研究不同固溶时效处理对γ′相形貌、尺寸分布和体积分数的影响且分析了完全热处理后合金的显微硬度和拉伸性能,从而确定了合金最佳的热处理工艺。结果表明,通过差热分析法和金相观察法确定合金的初熔温度在1300~1310 ℃。在1315 ℃固溶处理4 h,枝晶间/枝晶干γ′相尺寸趋于一致,呈立方状均匀排列。在固溶处理过程中,γ/γ′共晶组织熔化生成了不规则初熔组织。在不同的一次时效工艺下,1120 ℃时效4 h空冷后,γ′相立方度更好,尺寸分布更均匀。合金最佳的热处理工艺为1290 ℃×1 h+1300 ℃×2 h+1315 ℃×4 h, AC+1120 ℃×4 h, AC+870 ℃×32 h, AC。合金在完全热处理后,随拉伸温度从室温升高至850 ℃时,强度达到峰值,温度继续升高,强度下降;在760 ℃拉伸时塑性最差,随着拉伸温度从760 ℃升高到950 ℃,塑性提高。

Microstructure evolution and mechanical properties of DD6 single crystal superalloy during heat treatment process

Evolution of microstructure during heat treatment and the formation mechanism of incipient melting microstructure of DD6 single crystal superalloy were studied. The effects of different solution and aging treatments on morphology, size distribution and volume fraction of γ′ phase were studied. The microhardness and tensile properties of the alloy after complete heat treatment were analyzed to determine the optimum heat treatment process. The results show that the incipient melting temperature of the alloy determined by differential scanning calorimetry(DSC) and the metallographic observation method is 1300-1310 ℃. The sizes of dendritic core and inter dendritic of γ′ phase are equivalent after solution treatment at 1315 ℃ for 4 h, and γ′ phase is uniformly arranged in cubic form. The melting γ/γ′ eutectic produces irregular incipient melting microstructure during the solution treatment. Under different primary aging processes, γ′ phase has better cubic degree and more uniform size distribution after aging at 1120 ℃ for 4 h and air cooling (AC). The optimum heat treatment of the alloy is 1290 ℃×1 h+1300 ℃×2 h+1315 ℃×4 h, AC+1120 ℃×4 h, AC+870 ℃×32 h, AC. After complete heat treatment, the strength of the alloy reaches the peak as the tensile temperature increases from the room temperature to 850 ℃. As the tensile temperature further increases, the strength decreases. The plasticity is the worst at 760 ℃, and as the tensile temperature raises from 760 ℃ to 950 ℃, the plasticity improves.