钛及钛合金高温氧化行为研究

对工业纯钛TA2、TC4及Ti60合金分别在600、700、800℃进行氧化,得到氧化增重曲线。利用SEM、XRD等手段对氧化表面形貌、氧化产物构成及分布进行研究并分析了3种钛材在不同温度下的氧化机制。结果表明:随着温度升高,TA2、TC4以及Ti60三种钛材的抗氧化能力均有所下降,且抗氧化能力由强到弱依次为Ti60>TA2>TC4。工业纯钛TA2的氧化产物为TiO2,TC4合金在600℃氧化产物为TiO2,700、800℃为TiO2/Al2O3,Ti60合金氧化产物为TiO2/Al2O3。TA2和TC4钛合金在600℃时的氧化反应均受扩散过程控制,随温度升高(700、800℃),逐渐转变为界面反应控制。由于氧化产物组织结构疏松且Al2O3、TiO2和基体由于热膨胀系数不同导致的应力,TC4合金氧化膜易剥落,抗氧化能力较差。Ti60合金在700、800℃的氧化反应也受扩散过程控制,Zr、Si及稀土元素的添加得到保护能力较强的致密氧化膜Al2O3,抗氧化能力较好。然而800℃时,富Sn、Nd相的析出诱导氧化膜剥离,抗氧化能力有所下降。

High temperature oxidation behavior of titanium and titanium alloys

Oxidation behavior of TA2,TC4and Ti60alloys at 600,700,800℃were investigated.The oxidation kinetics curves including weight gain versus time and temperature have been studied.Surface morphologies,microstructures and cross-sectional morphologies were examined by means of SEM,EDS and X-ray diffraction.The results show that the oxidation resistance decreases with increasing temperature,and followed by Ti60>TA2>TC4.The oxidation product of TA2is TiO2.The oxidation product of TC4alloy is TiO2 when oxidized at 600℃and is TiO2/Al2O3when oxidized at 700,800℃.For the Ti60alloy,the oxidation product is TiO2/Al2O3.The oxidation process of TA2and TC4alloy at 600℃is controlled by the diffusion process,and gradually changes to the interface reaction control with the increase of temperature(700and 800℃).Due to the loose microstructure of TC4alloy and the stress induced by different thermal expansion coefficients of Al2O3,TiO2and TC4substrate,the oxide film of TC4alloy is very easy to fall off,leading apoor oxidation resistance.The oxidation process of Ti60alloy at 700and 800℃is controlled by the diffusion process,too.The addition of Zr,Si and rare earth element provides the protective oxide film(Al2O3)with good resistance.However,at 800℃,the Sn,Nd-riched phase precipitates at the grain boundaries and deteriorates the oxidation resistance.