【作者】 王震；

【导师】 赵永庆； 洪权；

【作者基本信息】 东北大学 ， 材料学， 2010， 硕士

【摘要】 本文以损伤容限型TC4-DT合金为研究对象,通过光学金相组织观察、力学性能测试、扫描断囗分析及透射电镜观察等方法,系统地研究了不同机械热处理工艺对组织与性能的影响,讨论了TC4-DT合金组织遗传与演化规律,分析了不同组织状态与各种性能的关系。研究发现,锻造温度越高,等轴α相含量越少,但是等轴α尺寸大小变化不大。冷却方式对等轴α相的数量和尺寸影响不大,只改变片层α的尺寸与取向分布。片层α受多种机制共同作用逐级短化,包括末端迁移机制,热扩散,局部剪切,亚晶界分离,动态回复,动态再结晶及界面自由能降低,最终球化。在两相区锻造,960℃/1h WQ+540℃/6h AC热处理后的强度与塑性达到最佳匹配。普通退火后的拉伸性能主要由锻造工艺得到的组织决定。强化热处理后,根据固溶温度的不同,决定拉伸性能的机械热处理过程也不同。两相区固溶时效后的拉伸性能由锻造工艺与热处理制度共同决定。近β区固溶时效,强度主要受次生α相的分布和尺寸控制。980℃固溶时效后的强度与塑性主要与热处理制度有关,受β晶粒尺寸控制。随着锻造温度的升高,TC4-DT合金的条件疲劳强度呈下降趋势。在两相区锻造,980℃/1h WQ+540℃/6h AC固溶时效后的疲劳裂纹扩展速率远低于1000℃锻造,960℃/1h WQ+540℃/6hAC固溶时效的。p区锻造得到较高的冲击韧性,近β区锻造比两相区锻造的冲击韧性略低。更多还原

【Abstract】 The effect of thermomechanical processing (TMP) on microstructures and properties was systemtically investigated for TC4-DT alloy by means of optical microscope observation, mechanical property test, scanning electric microscope fractography analysis and transmission electric microscope observation. The structure heredity and evolution of TC4-DT alloy were discussed. The relastionship among different kinds of microstructures and properties was analysed.It was found that the higher the forging temperature, the fewer the content of equiaxed a phase is, however, the size of equiaxed a changed little. The cooling method after forging only changed the size and orientation distribution of lamellar a phase. Under the result of concurrent effects of various mechanisms, including lamellar termination migration, thermal diffusion, local shear, subgrain boundary sliptting,dynamic recovery, recrystallization and reduction of interfacial free energy, lamellar a gradually becomed short and was spheroidized finally.Optimal matching between strength and ductility in TC4-DT alloy was reached after forging at α+β filed and heat treatment with960℃/1h WQ+540℃/6h AC. After conventional annealing, the tensile properties were determined by the microstucture obtained from forging processing. Through the solution and aging treatment, the mechanical properties depended on the different step of TMP. When the solution temperature was in a+(3filed, the forging and heat treatment determined the tensile properties. With temperature rising to near-β field, they were controled by the distribution and size of secondary a phase, but strength had little relation to forgiong process. The tensile strength and ductility were restricted to β grain size after solution treat at980℃following aging at540℃. The fatigue strength of TC4-DT alloy decreased with the increasing of forging temperature. The fatigue crack growth of TC4-DT alloy after forging at a+(3field subsequent to heat treatment at980℃/1h WQ+540℃/6h AC was slower than that after forging at β field and heat treament at960℃/1h WQ+540℃/6h AC. The higher attack toughnes could be achieved after forging at β field. But when deformed below the transus temperature, attack toughnes after forging at near-β field slightly lower than that after forging at α+β field.更多还原