TA18钛合金管材织构对环向拉伸性能的影响

Effect of Texture on Circumferential Tensile Properties of TA18 Titanium Alloy Tubing

摘要:

利用织构增强原理，开发出了TA18(Ti-3Al-2.5V)钛合金860 MPa级高强度管材，保证了管材的工艺性能，同时又具有优异的力学服役性能。标准一般规定反映径向织构的管材收缩应变比(CSR)大于1.3，但对上限值未作规定。本文设计出小管径的环向拉伸夹具，测试了不同CSR管材的环向拉伸力学性能，分析织构对环向拉伸强度的影响，发现存在一个最有利的CSR值为1.75，强于或弱于该CSR值时都会导致管材环向屈服强度下降。进一步测定了对应管材的极图和ODF，从微观结构上可以解释这一规律和本质。环向拉伸强度下降会引起液压系统工作时疲劳强度降低，CSR值的上限在工艺设计时应当加以控制。本研究将对发展安全可靠的航空液压系统具有十分重要的理论意义和工程应用价值。

Abstract:

Taking advantage of texture strengthening, the TA18 (Ti-3Al-2.5V) titanium alloy tubing was developed with tensile strength of 860 MPa as well as high formability and a good combination of mechanical properties. While the contractile strain ratio (CSR) of such tubing must be greater than 1.3 to meet the current standard, the upper limit value is not specified. In this paper, a fixture was designed for the hoop tension of tubing with a small diameter, and the mechanical properties in the hoop direction of tubing with different CSR values was tested. The effects of texture on the circumferential strength was analyzed. It was found that the optimal CSR value for the yield strength is 1.75, higher or lower value would lead to a decrease of the strength. Additionally, based on the pole figures and the orientation distribution function (ODF), the essence of the above regulation was well explained from microscopic aspects. Lower circumferential strength of hydraulic tubing will result in poorer fatigue life of hydraulic system in service, hence the upper limit value, not just the lower limit value, of CSR should be controlled. This investigation will be of theoretical significance and application value for the development of safe and reliable aerospace hydraulic systems.