【作者】 周宇；

【导师】 杨贤金；

【作者基本信息】 天津大学 ， 材料学， 2005， 硕士

【摘要】 本文通过试验对TC21钛合金的锻造工艺及锻后热处理工艺做了系统的研究。研究发现TC21钛合金采用第一火T_β+15℃准β锻造,第二火采用Tβ加热的准β模锻工艺能获得最佳的综合力学性能及损伤容限性能; 锻后热处理采用900℃×1h+(570℃-590℃)×4h的热处理制度能最大程度的保持原始网篮组织并获得细小致密的二次α相。研究表明,TC21钛合金经近β自由锻造与准β自由锻造后得到的组织分别为双态组织和典型的网篮组织。准β锻造工艺在强度、塑性以及疲劳裂纹扩展速率相差不大的情况下与近β锻造工艺相比能获得较高的断裂韧性。通过对5种不同准β锻造工艺参数的研究发现,合金的强度随第二火锻造温度升高而升高,塑性和强度的变化趋势相反,而断裂韧性和裂纹扩展速率相差不大。另外,第二火70%的大变形量对网篮组织形貌的变化影响不大。在模锻工艺深化研究中,采用第一火锻造温度Tβ+15℃,第二火锻造温度T_β+15℃及Tβ两种方案,并通过对其力学性能、显微组织及疲劳裂纹扩展速率的分析发现后者的综合力学性能优于前者,在强度、塑性和韧性的搭配上比较合理。第一次退火温度影响着合金最终显微组织中初生α相形态。随第一次退火温度升高,合金中网篮组织中片状α相逐渐有逐渐变成短棒状的趋势。合金在T_β-50℃第一次退火可最大程度使第二次退火后的组织保持网篮组织,从而获得优异的综合力学性能以及损伤容限性能匹配。次生α相的形态随着第二次退火温度的升高而变长变粗。因此合金的强度随第二次退火温度的升高而降低,拉伸塑性则随着第二次退火温度的升高而增加。在570℃和590℃第二次退火时可以得到比较细小致密的二次α相,因而也应获得最优的力学性能。第二次退火时间也影响着合金中次生α相的数量、尺寸和形态,但效果不如第二次退火温度对其的影响明显。合金在590℃第二次退火4小时次生α相比较致密细小。之后,次生α相开始逐渐增粗变厚,超过16小时后没有明显变化。因此,合金的第二次退火时间应在4小时左右比较适宜。更多还原

【Abstract】 This paper carried out systematic study on the forging technique and post-forging heat treatment of TC21 titanium alloy. The results shows that TC21 alloy could get optimum overall mechanical properties and damage tolerant properties adopting the quisi-β forging temperature of Tβ+15°C for the first time forging and Tβ for the second time forging; The best post-forging heat treatment under study is 900℃×1h+(570℃-590℃)×4h which could keep basketweave at maximum extent and get fine and compact second precipitating α phase. The microstructures of TC21 alloy undergone near-β forging and quisi-β forging were bimodel and typical basketweave respectively. Quisi-β forging technique could get better fracture toughness while keeping strength, plasticity and fatigue crack propagaton rate at the same level with near-β forging technique. Further investigation on quisi-β forging technique focuses on five different compound quisi-β forging parameters. It is found that the strength of TC21 alloy grows higher when the forging temperature of the second time forging rises, and the trend of plasticity is contrary to that of strength, but there is little difference for fracture toughness and fatigue crack propagation rate of the two techniques. Moreover, great deformation amount to 70% didn’t change the basketweave. In the experimental manufacture of forged pieces, two scheme were adopted: the temperature of first time forging was both Tβ+15°C, but the temperature of second time forging were T β +15°C(scheme 1) and T β (scheme 2). After comparing mechanical properties, microstructures and fatigue crack propagation rate of the two schemes, it was found that scheme 2 was superior to scheme 1 because scheme 1 had the combination of high strength, excellent plasticity and toughness. Solutioning temperature greatly affects the amount and shape of pre-α. As the solutioning temperature rising, the pre-α gradually spheroidizing from the original basketweave. Solutioning at Tβ-50°C could keep basketweave at maximum extent, thus acquiring excellent combination of overall mechanical properties and damage tolerant properties. The shape of second precipitation α grows longer and thicker as the aging temperature rises. Hence, the strength of TC21 alloy drops while tensile plasticity grows as the aging temperature rises. Aging at 570℃ and 590℃ could get fine and compact second precipitating α phase. Aging time also influences the amount, dimension and shape of the second precipitating α phase, but the effect was not so evident as that of aging temperature. Aging at 590℃ for 4 hours could get the proper dimension and shape of second precipitating α phase. After that, second precipitating α phase begins to become thicker. When aging time lasts beyond 16 hours, no observable change happens. Thus, the aging time should be around 4 hours.更多还原