纯钛挤压管坯内表面缺陷分析

摘要

The internal surface pits usually occur in the extruded pure titanium tube blanks.The composition and phases of the secondary phase of the cracked copper canning surface and the titanium tube blanks after etch cleaning were analyzed by OM,EDS and XRD.Furthermore,the reasons were also investigated.Results show that the secondary phase was Cu3Ti on the contacting interface between copper canning and pure titanium tubes.Under the bad lubricant condition,the extrusion ratio increased from 14.2 to 22.9,leading to bigger friction heat and deformation heat; as a result,the local temperature increased to above 850 ℃,and in a short time less than 10 s the Ti-Cu liquid phase reaction happened,resulting in the copper canning tearing and dropping.The shearing copper canning had thick wall and lower running speed than titanium tube blank.Its irregular shape caused lots of spot-liked or strip-liked pits on the internal surface of titanium tubes.In conclusion,the thermal extrusion parameters should be improved to reduce the friction heat and deformation heat.%针对纯钛挤压管坯内表面凹坑缺陷现象,通过金相、能谱及XRD分析对破裂铜包套表面和酸洗后钛管坯表面的第二相分别进行了成分、物相和成因分析.结果表明:铜包套和纯钛锭坯相接触表面的第二相是Cu3Ti；凹坑缺陷产生的主要原因是润滑条件不良时,挤压比增大(从14.2提高到22.9)引起摩擦热和变形热增大,进而使铜包套和纯钛管坯局部温度升高(＞850℃),并在短时间内(＜10 s)发生Ti-Cu液相反应,导致铜包套撕裂脱落.被撕裂的铜包套壁厚较大,且流动速度小于钛管坯的流动速度,其不规则的外形在钛管坯的内表面形成了大量点状或条形凹坑缺陷.提出改进热挤压工艺参数减少摩擦热和变形热是消除管坯内表面缺陷的有效措施.