时效温度对Ti1023和Ti5553合金微观组织与析出硬化的影响规律

Effect of Aging Temperature on Microstructures and Precipitation Hardening in Ti1023 and Ti5553 Alloys

研究了Ti1023和Ti5553钛合金经过固溶与低温时效处理(ST-SQA)获得的微观组织和析出硬化行为。采用扫描电镜和透射电镜观察了不同温度时效处理后α相的析出形貌以及分布特点,统计了时效析出次生α相的析出密度和宽度随时效温度的变化情况,并测试了合金的维氏硬度。结果表明:Ti1023合金时效处理时次生α的析出温度低于Ti 5553合金。Ti1023合金在300℃时效时α相已经析出,400℃时效时α相析出密度到达峰值;Ti5553合金在450~500℃时效α相开始析出,在550℃时效α相的析出密度达到峰值。Ti1023合金硬度随着时效温度的增加先升后降,400℃时效硬度最高;在相同的时效温度范围,Ti5553合金硬度变化出现双峰规律,硬度峰值分别对应于350和550℃时效温度。2种合金的硬度变化规律源于合金时效中第二相的析出行为:时效温度低于400℃,Ti1023合金的硬度取决于α相和ω相,而Ti5553合金的硬度取决于ω相;时效温度高于400℃,2种合金的硬度均主要取决于次生α相的数量与尺寸。

The microstructures and precipitation hardening of Ti1023 and Ti5553 alloys after the same solution treatment and step-quench aging treatment(ST-SQA) have been studied. The morphology of α phase about precipitation and distribution in different aging treatment were observed by using SEM and TEM, and the variation of density and width of secondary α phase were analyzed. The hardness of these two alloys was measured. The result shows that Ti1023 alloy is more likely to precipitate α phase than Ti5553 alloy due to low stability of β phase. Ti1023 alloy precipitates α phase at 300℃ aging and gets the maximum density of precipitation at 400℃, while Ti5553 alloy precipitates α phase at 450℃, and gets the maximum density of precipitation at 550℃. As for Ti1023 alloy, the peak of hardness is obtained at 400℃ aging, while as for Ti5553 alloy, double peaks of hardness are shown at 350℃ and 550℃ aging. The variation of hardness was caused by the precipitation of secondary phase in β phase for different aging temperatures. When aging temperature is below 400℃, the hardness of Ti1023 alloy depends on both α phase and ω phase, and the hardness of Ti5553 alloy depends on only ω phase. As aging temperature is over 400℃, the hardness of both Ti1023 and Ti5553 alloys depend on the density of precipitation and the size of α phase.