TA15钛合金模锻件低倍组织中局部粗晶的形成机理
|
摘要
在TA15钛合金模锻件应以模糊晶为主的低倍组织中发现了局部粗大的清晰晶。利用金相拼接和逐点统计方法,结合微拉伸、SEM等手段,分析对比了粗大清晰晶区、模糊晶区的显微组织与力学性能,着重探讨了局部粗晶的形成机制。结果表明:各晶区内显微组织均呈典型双态组织,显示了两相区变形的基本特征。与模糊晶区相比,粗大清晰晶区内初生等轴α相(α_p)含量略低,且存在粗大片层组织;存有大量的粗大原始β晶粒(连续的晶界α相包围的晶粒),平均尺寸可达124μm,是模糊晶区平均尺寸(32μm)的近4倍。这些异常粗大的β晶粒是导致低倍粗晶的最主要因素,同时也是导致合金的强度和塑性均下降的主要原因之一。热物理模拟结果表明,双相区变形后出现的粗大清晰晶对应变速率敏感。慢速率变形会增大形成低倍粗晶的倾向,这主要与变形过程中动态α_p→β相变有关。对于模锻件而言,局部粗大清晰晶区火次应变小使其较模糊晶区应变速率慢,再经多火次小应变(慢速率)累积导致了β晶粒明显粗化。
A local coarse-grained macrostructure which was identified as the clear structure, was found in the TA15 titanium alloy die forging. Usually, the macrostructure of TA15 titanium alloy forging was required to display a fuzzy structure with fine microstructures. The microstructure and mechanical properties in the coarse-grained areas were investigated by means of optical microscope(OM), scanning electron microscope(SEM) as well as micro-tension tests.The formation mechanism for the local coarse-grained macrostructure was discussed. The results show that the microstructures in various areas of forging display a duplex microstructure of titanium alloy which typically shows the microstructural characteristics of titanium alloy during hot deformation in the(α+β) region. Compared with the fuzzy structure area, the fraction of primary equiaxed α(α_P) in the clear structure area is slightly lower, and a coarse lamellar microstructure is found. Especially, a large number of coarse original β grains which are surrounded by α phase on grain boundaries are found in the clear structure area, and their average grain size reaches 124 μm, which is nearly 4 times of that(32 μm) in the fuzzy structure area. The abnormal coarse β grains are considered to be a critical factor for the formation of local coarse-grained macrostructure, and meanwhile, they can cause a decrease in strength and plasticity.Furthermore, the results of thermal-mechanical tests show that the coarse-grained macrostructure is sensitive to the strain rate. Lower strain rate causes an increase in the probability of such coarse-grained macrostructure. This is mainly related to the occurrence of α_p→β dynamic transformation during deformation. For the forging with the clear structure,the lower strain rate in each forging step, which is caused by the small strain within the same deformation time as compared to the fuzzy structure area, as well as the further cumulative effect of small strain in subsequent forging steps results in a significant coarsen of original β grains.
A local coarse-grained macrostructure which was identified as the clear structure, was found in the TA15 titanium alloy die forging. Usually, the macrostructure of TA15 titanium alloy forging was required to display a fuzzy structure with fine microstructures. The microstructure and mechanical properties in the coarse-grained areas were investigated by means of optical microscope(OM), scanning electron microscope(SEM) as well as micro-tension tests.The formation mechanism for the local coarse-grained macrostructure was discussed. The results show that the microstructures in various areas of forging display a duplex microstructure of titanium alloy which typically shows the microstructural characteristics of titanium alloy during hot deformation in the(α+β) region. Compared with the fuzzy structure area, the fraction of primary equiaxed α(α_P) in the clear structure area is slightly lower, and a coarse lamellar microstructure is found. Especially, a large number of coarse original β grains which are surrounded by α phase on grain boundaries are found in the clear structure area, and their average grain size reaches 124 μm, which is nearly 4 times of that(32 μm) in the fuzzy structure area. The abnormal coarse β grains are considered to be a critical factor for the formation of local coarse-grained macrostructure, and meanwhile, they can cause a decrease in strength and plasticity.Furthermore, the results of thermal-mechanical tests show that the coarse-grained macrostructure is sensitive to the strain rate. Lower strain rate causes an increase in the probability of such coarse-grained macrostructure. This is mainly related to the occurrence of α_p→β dynamic transformation during deformation. For the forging with the clear structure,the lower strain rate in each forging step, which is caused by the small strain within the same deformation time as compared to the fuzzy structure area, as well as the further cumulative effect of small strain in subsequent forging steps results in a significant coarsen of original β grains.
引文
[1]赵永庆,辛社伟,陈永楠,毛小南.中国战略性新兴产业-新材料-新型合金材料-钛合金[M].北京:中国铁道出版社,2017.ZHAO Yong-qing,XIN She-wei,CHEN Yong-nan,MAOXiao-nan.China's strategic emerging industries-new materials,new alloy materials-Titanium alloys[M].Beijing:China Railway Publishing House,2017.
[2]金和喜,魏克湘,李建明,周建宇,彭文静.航空用钛合金研究进展[J].中国有色金属学报,2015,25(2):280-292.JIN He-xi,WEI Ke-xiang,LI Jian-ming,ZHOU Jian-yu,PENG Wen-jing.Research development of titanium alloy in aerospace industry[J].The Chinese Journal of Nonferrous Metals,2015,25(2):280-292.
[3]陈强,王庆娟,王鼎春,刘继雄,李强,周晓,梁博.锻件组织不均匀性对新型近β钛合金组织与力学性能的影响[J].中国有色金属学报,2018,28(1):87-96.CHEN Qiang,WANG Qing-juan,WANG Ding-chun,LIUJi-xiong,LI Qiang,ZHOU Xiao,LIANG Bo.Effect of microstructure in homogeneity of forgings on microstructure and mechanical properties of new nearβtitanium alloy[J].The Chinese Journal of Nonferrous Metals,2018,28(1):87-96.
[4]张旺峰,王玉会,颜孟奇,张庆玲.锻造方法对TA15钛合金组织和性能的影响[J].中国有色金属学报,2013,23(s1):15-19.ZHANG Wang-feng,WANG Yu-hui,YAN Meng-qi,ZHANG Qing-ling.Effect of forging method on microstructure and mechanical properties of TA15 titanium alloy[J].The Chinese Journal of Nonferrous Metals,2013,23(s1):15-19.
[5]马济民,贺金宇,庞克昌.钛铸锭和锻造[M].北京:冶金工业出版社,2012.MA Ji-min,HE Jin-yu,PANG Ke-chang.Titanium ingot and forging[M].Beijing:Metallurgical Industry Press,2012.
[6]中国锻压协会.特种合金及其锻造[M].北京:国防工业出版社,2009.Confederation of Chinese Metal Forming Industry.Special alloys and their forging[M].Beijing:National Defense Industry Press,2009.
[7]曹京霞,黄旭,孙贵东,方波.一种Ti-6Al-2Zr-1Mo-1V合金锻件的宏观与微观组织特征分析[J].钛工业进展,2004,21(2):23-26.CAO Jing-xia,HUANG Xu,SUN Gui-dong,FANG Bo.Macro-and microstructure feature analysis of Ti-6AI-2Zrl Mo-l V titanium alloy forging[J].Titanium Industry Progress,2004,21(2):23-26.
[8]LIN Yong-cheng,JIANG Xing-you,SHUAI Ci-jun,ZHAOChun-yang,HE Dao-guang,CHEN Ming-song,CHEN Chao.Effects of initial microstructures on hot tensile deformation behaviors and fracture characteristics of Ti-6Al-4V alloy[J].Materials Science and Engineering A,2018,711:293-302.
[9]NIINOMI M,KOBAYASHI T,SASAKI N.Toughness and microstructural factors of Ti-6Al-4V alloy[J].Materials Science and Engineering,1988,100(4):45-55.
[10]李萍,薛克敏,姚彭彭,李成铭.热变形TA15钛合金的显微组织和室温力学性能[J].稀有金属材料与工程,2016,45(6):1495-1499.LI Ping,XUE Ke-min,YAO Peng-peng,LI Cheng-ming.Microstructure and mechanical properties of hot deformed TA15 titanium alloy at room temperature[J].Rare Metal Materials and Engineering,2016,45(6):1495-1499.
[11]LIU Rui,HUI Song-xiao,YE Wen-jun,XIONG Bai-qing,YOU Zhen-ping.Effects of annealing temperature on dynamic fracture toughness for TC4 titanium alloy[J].Rare Metal Materials and Engineering,2011,40(10):1799-1803.
[12]OBASI G C,FONSECA J Q D,RUGG D,PREUSS M.The effect ofβgrain coarsening on variant selection and texture evolution in a near-βTi alloy[J].Materials Science&Engineering A,2013,576(9):272-279.
[13]王杨,曾卫东,马雄,周建华,王晓英,王腾.BT25钛合金在两相区变形过程中的显微组织定量分析[J].中国有色金属学报,2013,23(7):1861-1865.WANG Yang,ZENG Wei-dong,MA Xiong,ZHOU Jian-hua,WANG Xiao-ying,WANG Teng.Quantitative metallography analysis of microstructure of BT25 titanium alloy deformed in two-phase field[J].The Chinese Journal of Nonferrous Metals,2013,23(7):1861-1865.
[14]ABBASI S M,MOMENI A,LIN Yong-cheng,JAFARIANH R.Dynamic softening mechanism in Ti-13V-11Cr-3Al beta Ti alloy during hot compressive deformation[J].Materials Science and Engineering A,2016,665:154-160.
[15]FAN Xiao-guang,YANG He,GAO Peng-fei,ZUO Rui,LEIPeng-hui,JI Zhe.Morphology transformation of primary stripαphase in hot working of two-phase titanium alloy[J].Transactions of Nonferrous Metals Society of China,2017,27(6):1294-1305.
[16]GUO Bao-qi,SEMIATIN S L,LIANG Jiang-tao,SUNBin-han,JONAS J J.Opposing and driving forces associated with the dynamic transformation of Ti-6Al-4V[J].Metallurgical and Materials Transactions A,2018,49(5):1450-1454.
[17]JONAS J J,JR C A,FALL A,JAHAZI M.Transformation softening in three titanium alloys[J].Materials&Design,2017,113:305-310.
[18]ABBASI S M,MOMENI A.Effect of hot working and post-deformation heat treatment on microstructure and tensile properties of Ti-6Al-4V alloy[J].Transactions of Nonferrous Metals Society of China,2011,21(8):1728-1734.
[19]石卫民,魏寿庸,王鼎春,李渭清,王青江,刘建荣.Ti60钛合金大棒材的显微组织及力学性能[J].中国有色金属学报,2010,20(S1):s75-s78.SHI Wei-min,WEI Shou-yong,WANG Ding-chun,LIWei-qing,WANG Qing-jiang,LIU Jian-rong.Microstructures and mechanical properties of Ti60 Ti alloy large-section bars[J].The Chinese Journal of Nonferrous Metals,2010,20(S1):s75-s78.
[20]张津,刘贞阳,郭海明.Ti8LC钛合金热处理工艺对硬度和组织的影响[J].稀有金属,2011,35(1):17-21.ZHANG Jin,LIU Zhen-yang,GUO Hai-ming.Effect of heat treatment on hardness and microstructure of Ti8 LC alloy[J].Chinese Journal of Rare Metals,2011,35(1):17-21.
[2]金和喜,魏克湘,李建明,周建宇,彭文静.航空用钛合金研究进展[J].中国有色金属学报,2015,25(2):280-292.JIN He-xi,WEI Ke-xiang,LI Jian-ming,ZHOU Jian-yu,PENG Wen-jing.Research development of titanium alloy in aerospace industry[J].The Chinese Journal of Nonferrous Metals,2015,25(2):280-292.
[3]陈强,王庆娟,王鼎春,刘继雄,李强,周晓,梁博.锻件组织不均匀性对新型近β钛合金组织与力学性能的影响[J].中国有色金属学报,2018,28(1):87-96.CHEN Qiang,WANG Qing-juan,WANG Ding-chun,LIUJi-xiong,LI Qiang,ZHOU Xiao,LIANG Bo.Effect of microstructure in homogeneity of forgings on microstructure and mechanical properties of new nearβtitanium alloy[J].The Chinese Journal of Nonferrous Metals,2018,28(1):87-96.
[4]张旺峰,王玉会,颜孟奇,张庆玲.锻造方法对TA15钛合金组织和性能的影响[J].中国有色金属学报,2013,23(s1):15-19.ZHANG Wang-feng,WANG Yu-hui,YAN Meng-qi,ZHANG Qing-ling.Effect of forging method on microstructure and mechanical properties of TA15 titanium alloy[J].The Chinese Journal of Nonferrous Metals,2013,23(s1):15-19.
[5]马济民,贺金宇,庞克昌.钛铸锭和锻造[M].北京:冶金工业出版社,2012.MA Ji-min,HE Jin-yu,PANG Ke-chang.Titanium ingot and forging[M].Beijing:Metallurgical Industry Press,2012.
[6]中国锻压协会.特种合金及其锻造[M].北京:国防工业出版社,2009.Confederation of Chinese Metal Forming Industry.Special alloys and their forging[M].Beijing:National Defense Industry Press,2009.
[7]曹京霞,黄旭,孙贵东,方波.一种Ti-6Al-2Zr-1Mo-1V合金锻件的宏观与微观组织特征分析[J].钛工业进展,2004,21(2):23-26.CAO Jing-xia,HUANG Xu,SUN Gui-dong,FANG Bo.Macro-and microstructure feature analysis of Ti-6AI-2Zrl Mo-l V titanium alloy forging[J].Titanium Industry Progress,2004,21(2):23-26.
[8]LIN Yong-cheng,JIANG Xing-you,SHUAI Ci-jun,ZHAOChun-yang,HE Dao-guang,CHEN Ming-song,CHEN Chao.Effects of initial microstructures on hot tensile deformation behaviors and fracture characteristics of Ti-6Al-4V alloy[J].Materials Science and Engineering A,2018,711:293-302.
[9]NIINOMI M,KOBAYASHI T,SASAKI N.Toughness and microstructural factors of Ti-6Al-4V alloy[J].Materials Science and Engineering,1988,100(4):45-55.
[10]李萍,薛克敏,姚彭彭,李成铭.热变形TA15钛合金的显微组织和室温力学性能[J].稀有金属材料与工程,2016,45(6):1495-1499.LI Ping,XUE Ke-min,YAO Peng-peng,LI Cheng-ming.Microstructure and mechanical properties of hot deformed TA15 titanium alloy at room temperature[J].Rare Metal Materials and Engineering,2016,45(6):1495-1499.
[11]LIU Rui,HUI Song-xiao,YE Wen-jun,XIONG Bai-qing,YOU Zhen-ping.Effects of annealing temperature on dynamic fracture toughness for TC4 titanium alloy[J].Rare Metal Materials and Engineering,2011,40(10):1799-1803.
[12]OBASI G C,FONSECA J Q D,RUGG D,PREUSS M.The effect ofβgrain coarsening on variant selection and texture evolution in a near-βTi alloy[J].Materials Science&Engineering A,2013,576(9):272-279.
[13]王杨,曾卫东,马雄,周建华,王晓英,王腾.BT25钛合金在两相区变形过程中的显微组织定量分析[J].中国有色金属学报,2013,23(7):1861-1865.WANG Yang,ZENG Wei-dong,MA Xiong,ZHOU Jian-hua,WANG Xiao-ying,WANG Teng.Quantitative metallography analysis of microstructure of BT25 titanium alloy deformed in two-phase field[J].The Chinese Journal of Nonferrous Metals,2013,23(7):1861-1865.
[14]ABBASI S M,MOMENI A,LIN Yong-cheng,JAFARIANH R.Dynamic softening mechanism in Ti-13V-11Cr-3Al beta Ti alloy during hot compressive deformation[J].Materials Science and Engineering A,2016,665:154-160.
[15]FAN Xiao-guang,YANG He,GAO Peng-fei,ZUO Rui,LEIPeng-hui,JI Zhe.Morphology transformation of primary stripαphase in hot working of two-phase titanium alloy[J].Transactions of Nonferrous Metals Society of China,2017,27(6):1294-1305.
[16]GUO Bao-qi,SEMIATIN S L,LIANG Jiang-tao,SUNBin-han,JONAS J J.Opposing and driving forces associated with the dynamic transformation of Ti-6Al-4V[J].Metallurgical and Materials Transactions A,2018,49(5):1450-1454.
[17]JONAS J J,JR C A,FALL A,JAHAZI M.Transformation softening in three titanium alloys[J].Materials&Design,2017,113:305-310.
[18]ABBASI S M,MOMENI A.Effect of hot working and post-deformation heat treatment on microstructure and tensile properties of Ti-6Al-4V alloy[J].Transactions of Nonferrous Metals Society of China,2011,21(8):1728-1734.
[19]石卫民,魏寿庸,王鼎春,李渭清,王青江,刘建荣.Ti60钛合金大棒材的显微组织及力学性能[J].中国有色金属学报,2010,20(S1):s75-s78.SHI Wei-min,WEI Shou-yong,WANG Ding-chun,LIWei-qing,WANG Qing-jiang,LIU Jian-rong.Microstructures and mechanical properties of Ti60 Ti alloy large-section bars[J].The Chinese Journal of Nonferrous Metals,2010,20(S1):s75-s78.
[20]张津,刘贞阳,郭海明.Ti8LC钛合金热处理工艺对硬度和组织的影响[J].稀有金属,2011,35(1):17-21.ZHANG Jin,LIU Zhen-yang,GUO Hai-ming.Effect of heat treatment on hardness and microstructure of Ti8 LC alloy[J].Chinese Journal of Rare Metals,2011,35(1):17-21.