航空紧固件用Ti-5553合金的组织和性能

采用扫描电镜和透射电子显微镜研究不同热处理制度对Ti-5553高强钛合金显微组织与力学性能的影响。结果表明:在(α+β)两相区进行固溶处理时,随着固溶温度的升高,Ti-5553合金组织中的初生α相含量逐渐减少,β相的尺寸和体积分数均增加,合金强度逐渐降低。时效后β基体发生转变,晶界和晶内析出大量次生α相。次生α相的尺寸对力学性能产生重要影响,随着时效温度的升高,次生α相逐渐粗化,导致抗拉强度逐渐下降。1240MPa级航空紧固件用Ti-5553的固溶温度应选择Tβ以下,使组织中留有足够的β相,从而时效时在β相中有大量次生α相析出,获得需要的高强度。同时,保留一定含量的初生α相,以便获得良好的塑韧性。经810~820℃,1.5h,水淬+510℃,10h,空冷热处理后,合金可以获得较好的综合性能,抗拉强度达1500MPa,伸长率达14.8%,断面收缩率为38.6%。固溶和时效态的拉伸断口均存在大量韧窝,材料具有良好的塑韧性。

Microstructure and Properties of Ti-5553 Alloy for Aerospace Fasteners

The effect of heat treatment on microstructure and mechanical properties of Ti-5553 alloy was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The results show that when the alloy is treated in α+βphase zone,tensile strength decrea-ses with raising solution temperature due to decreasing the content of primary α-phase and increasing the size and volume fraction of β phase.A lot of secondary α-phase precipitates from grain boundary and intragranular with βphase transformation during aging treatment.The size of secondary α-phase has significant influence on tensile strength,secondaryα-phase coarsens gradually with the increase of aging temperature,resulting in the decrease of tensile strength.It is suggested that for 1240MPa aer-ospace fasteners the solution temperature of Ti-5553 should be under Tβ,thus adequate β phase, where a lot of secondaryαphase precipitates from,is good for the required high strength.Meanwhile, a certain percentage of primaryα-phase is kept for acquiring good ductility and toughness.After solu-tion treatment at 810-820℃ for 1.5h,water quenching plus aging at 510℃ for 10h,Ti-5553 shows a better mechanical property with tensile strength 1500MPa,elongation 14.8% and reduction of cross-section area 38.6%.Lots of dimples can be found in tensile fracture after solution treatment and solu-tion+aging treatment,which demonstrate Ti-5553 with good ductility and toughness.