高强韧钛合金Ti700的冲击韧度研究

Observation on Impact Toughness of High Strength and Toughness Titanium Alloy Ti700

对Ti700合金在不同热处理制度下的冲击韧度与显微组织之间的关系进行了研究。结果表明,在其相变点以上的980℃热处理,炉冷可获得高于空冷的冲击韧度,主要是由于炉冷冷却速度慢,魏氏组织中的α片厚度和长度以及晶界α的宽度比空冷组织中的α相大,冲击断裂时,裂纹在α集束和β晶界发生大角度偏转,在α/β相界发生停滞和偏转,使裂纹扩展路径更曲折,因而吸收的能量更多,冲击韧度更高。相变点以下热处理的冲击试样微裂纹的形核位置主要集中于初生α相界和α/β相界。915℃处理可获得最高的冲击韧度,而其炉冷可获得高于空冷的冲击韧度,炉冷试样的晶间转变β相内次生α相发生明显宽化,强化效果明显较弱,相对于空冷组织中的次生α相是一种韧性相,当裂纹扩展与之相遇时,要产生塑性变形,消耗较多的能量,从而提高了韧性。750℃处理的Ti700合金炉冷和空冷的冲击韧度最低,550℃处理直接时效高于750℃处理的冲击韧度,但低于915℃处理的冲击韧度,固溶时效处理的韧性较低。

The relationship of impact toughness and microstructure of titanium alloy Ti700 under different treatments was investigated. The results shows that the impact toughness of the sample heat treated at 980℃ in the supertransus region followed furnace cool is higher than that of the sample heat treated at 980℃ followed air cool. The thickness and length of α-phase and the thinckness of grain boundary under furnace cool is wider and longer than that of the air cool microstructure. Therefore crack take places large angle deviation at the α-colony boundaries and grain boundaries, and crack arrest and deflect at oα/β interface. The crack prorogation path is tourouser and can absorb more energy, higher toughness is abtained. The microcrack of the sample in the subtransus region is nucleated at primary α grain boundaries or at the α/β interface.Heat treatment at 915℃ can achieved the highest impact toughness among all treatment. The impact toughness of heat treatment at 915℃ followed furnace cool is superior to that of the sample heat treated followed air cool. The second α phase in the transformed β phase is obviously widen because of low cool rate, so the second α phase has low strengthen effect, and is a toughness phase compareing with that of air cool microstructure. When crack is encounter the second ot phase, the large ductility deformation is created and more energy is consumed, consequently the toughness increase. The toughness of Ti700 alloy treated at 750℃ followed furnace cool and air cool is the lowest among all the treatments. The toughness of direct aging at 550℃ has higher than that of heat treatment at 750℃, but is lower than heat treatment at 915℃. Solution and aging treatment can achieve low toughness.