粉末高温合金Udimet720Liγ′强化相析出行为

Precipitation behavior ofγ′phase in P/M superalloy Udimet720Li

采用气淬炉模拟了粉末高温合金Udimet720Li经空冷、风冷及油冷等不同冷却路径的固溶处理过程,测试了经过两级时效处理的合金在650℃的拉伸性能,研究了拉伸变形后的位错组态,分析了冷却速率对γ′强化相析出规律及力学性能的影响。结果表明:粉末高温合金Udimet720Li的析出相强化机制为位错切过机制,二次γ′相尺寸越小,合金强度越高。合金二次γ′相的形核析出温度区间为900~1000℃,其尺寸与合金在该温度范围内的冷却速率成反比,冷却速率越大,γ′相尺寸越小,当冷速高于100℃/min时,合金强度达到应用要求。推荐粉末Udimet720Li合金盘件固溶处理的冷却方式为:在1000℃以上保持低冷却速率来降低淬火应力,然后选择油浴作为盘件淬火的冷却方式,入油温度应在1000℃左右。

P/M superalloy Udimet720Li specimens were solutioned and quenched at the different cooling rates in gas quenching furnace,following by the double aging treatment.The microstructures and elevated temperature tensile properties at 650℃were investigated,and theγ′precipitation behavior and strengthening mechanism were analysed.The effect of cooling rates on the microstructures and properties ofγ′phase were discussed.Results show that the secondaryγ′phases mainly precipitate between 900℃and 1000℃for the P/M superalloy Udimet720Li,and the size of the secondaryγ′phases are inversely proportional to the cooling rates.The secondaryγ′phase interacts with the dislocations by shearing mechanism,enhancing the strength of P/M superalloy Udimet720Li.The strengthening effect increases with the decrease of the secondaryγ′phase size.To meet the strength requirement in practical application,the cooling rate should be more than 100℃/min.Therefore,the recommended solution cooling path for P/M superalloy Udimet720Li is shown as follow:the cooling rate should be slow to reduce the quenching stress above 1000℃,then the specimen can be quenched in oil at 1000℃to obtain enough strength.