【作者】 黄灿；

【导师】 李聪； 陈飞；

【作者基本信息】 长沙理工大学 ， 工程硕士（专业学位）， 2022， 硕士

【摘要】 钛合金由于其所具有的优异的力学性能广泛应用于工业生产的各个领域。汽轮机叶片长时间在高温环境下运行容易产生失效,其叶片性能的好坏很大程度决定了汽轮机的发电效率,因此先进钛合金叶片制造技术成为衡量汽轮机发展水平的重要标志之一。目前国内外使用较多的末级叶片钛合金为Ti-6Al-4V(TC4钛合金),但由于加工性能有所欠缺阻碍了该合金的进一步发展。Ti-4.5Al-3V-2Mo-2Fe(SP-700钛合金)作为研制的一种新型α+β型钛合金,在Ti-6Al-4V合金的基础上添加了 Mo和Fe两种β稳定化元素,减少了 Al、V两种元素的含量,合金的超塑性、耐腐蚀性、强度、韧性都有所提高,因此SP-700钛合金有希望替代Ti-6Al-4V合金成为一种新型的汽轮机叶片材料。本文以SP-700钛合金作为研究对象,研究了冷却速率(β相区固溶)、固溶时间和固溶温度(β+(α+β)相区固溶)、时效时间和时效温度(单级和双级时效)对SP-700钛合金显微组织、硬度和压缩性能的影响,确定了不同热处理条件下的最佳强塑性配比,为SP-700钛合金叶片的制造和在汽轮机中的应用提供了一定的参考依据。主要结论如下:(1)SP-700钛合金在β相区进行固溶处理,当冷却速率较慢时,易发生β相向α相转变,冷却速率较快时易发生β相向马氏体转变。当冷却速率为3℃/s时,可以获得最好的强、塑性匹配。(2)SP-700钛合金在β+(α+β)相区进行固溶处理时,当α+β相区固溶温度一定,固溶时间越长,α相析出越多,合金硬度与固溶时间呈非线性关系。当β固溶温度为850℃、固溶时间为5min时,α+β相区固溶时间在3-10min的区间内,SP-700钛合金可以获得最好的强、塑性匹配。(3)SP-700钛合金在β+(α+β)相区进行固溶处理时,当α+β相区固溶时间一定,固溶温度越低,α相析出越多,合金的硬度与固溶温度呈非线性关系。在α+β相区固溶温度为650-900℃的区间,当固溶温度为650℃,固溶时间为5min时,SP-700钛合金可以获得最好的强、塑性匹配。(4)SP-700钛合金进行单级时效及双级时效热处理时,基本组织都是由β晶粒、α相、针状马氏体组成,且双级时效时的显微组织更均匀。在单级时效热处理的时效温度为650℃、时效时间为90min时,合金的强、塑性匹配最好;双级时效热处理时效温度为650℃、效时间为15min时,能获得较好的强塑性匹配。更多还原

【Abstract】 Titanium alloys are widely used in various fields of industrial production due to their excellent mechanical properties.Turbine blades are prone to failure when operating in a high temperature environment for a long time,the performance of its blades largely determines the power generation efficiency of the steam turbine,so advanced titanium alloy blade manufacturing technology has become one of the important indicators to measure the development level of steam turbines.At present,Ti-6Al-4V(TC4 titanium alloy)is widely used at home and abroad,but its further development is hindered by the lack of processability.Ti-4.5Al-3V-2Mo-2Fe(SP-700 titanium alloy)is a new type of α+β titanium alloy.On the basis of Ti-6Al-4V alloy,two β stabilizing elements Mo and Fe are added,which reduces the content of Al and V,and improves the superplasticity,corrosion resistance,strength and toughness of the alloy,so SP-700 titanium alloy is expected to replace Ti-6Al-4V alloy as a new type of turbine blade material.In this thesis,SP-700 titanium alloy is used as the research object.The effects of cooling rate(β phase zone solid solution),solid solution time and solution temperature(β+(α+β)phase zone solid solution),aging time and aging temperature(single and double stage aging)on the microstructure,hardness and compression properties of SP-700 titanium alloy were studied.The optimal strong plasticity ratio under different heat treatment conditions was determined,which provided a certain reference basis for the manufacture of SP-700 titanium alloy blades and the application in steam turbines.The main conclusions are as follows:(1)SP-700 titanium alloy is treated by solution treatment in β phase zone.When the cooling rate is slow,β phase transformation is easy to occur β phase to the a phase,and when the cooling rate is fast,β phase transformation is easy to occur β phase to martensitic.When the cooling rate is 3℃/s,the best matching between strength and plasticity can be obtained.(2)SP-700 titanium alloy for β+(α+β)phase zone solid solution treatment,when the α+βphase zone solid solution temperature is a certain,the longer the solid solution time,the more a phase precipitation.The hardness of the alloy and the solid solution time is nonlinear relationship.When the β solid solution temperature is 850℃,the solid solution time is 5min,the α+β phase area solid solution time in the range of 3-10min,SP-700 titanium alloy can obtain the best strong and plastic match.(3)SP-700 titanium alloy for β+(α+β)phase zone solid solution treatment,when the α+βphase zone solid solution time is certain,the lower the solid solution temperature,the more a phase precipitation.The hardness of the alloy and the solid solution temperature is nonlinear relationship.In the range of α+β phase zone solid solution temperature of 650-900℃,when the solid solution temperature is 650℃,the solid solution time is 5min,SP-700 titanium alloy can obtain the best strong and plastic match.(4)When SP-700 titanium alloy is treated with single-stage aging and double-stage aging,the basic structure is composed of β grains、α phases、martensitics,and the microstructure of the two-stage aging is more uniform.When the aging temperature of the single-stage aging heat treatment is 650℃ and the aging time is 90min,the strong and plasticity matching of the alloy is the best.When the aging temperature of the two-stage aging heat treatment is 650℃and the aging time is 15min,a good strong plasticity match can be obtained.更多还原