显微组织对Ti-40Al-8Nb合金高温氧化性能的影响

Influence of microstructure on high-temperature oxidation properties of Ti-40Al-8Nb alloys

以超细晶(ω_(o)+γ)组织(as-HT800)和等轴双态(α_(2)+γ)组织(as-HT1000)为对象,研究了不同显微组织的Ti-40Al-8Nb合金在800℃下的等温氧化行为.结果表明:由于as-HT800试样的初始组织晶粒尺寸极小(仅有300 nm),在表面易形成致密的氧化膜.此外,as-HT800试样中的ω_(o)相促进了氧化膜与基体界面上富Nb钉状物的形成,不仅抑制了Ti、Al、O元素的互扩散,而且提高了氧化膜与基体之间的结合强度.对于as-HT1000试样而言,其组织晶粒尺寸粗大(约为5μm),且α_(2)相含量高,导致选择性氧化的发生,从而在表面生成了疏松多孔的氧化膜.因此,as-HT800试样的抗氧化性能优于as-HT1000试样.

In this work,the isothermal oxidation behavior of Ti-40Al-8Nb alloys with ultrafine(ω_(o)+γ)(as-HT800)and equiaxed duplex(α_(2)+γ)microstructures(as-HT1000)at 800℃was investigated.Results showed that due to the ultrarefined grain size of as-HT800 sample i.e.,only 300 nm,a dense oxide scale formed on the surface.In addition,ω_(o)phase in as-HT800 sample promoted the formation of Nb-rich pegs at oxide scale/substrate interface,which not only inhibited the mutual diffusion of Ti,Al,and O elements,but also improved the bonding strength between the oxide scale and substrate.In contrast,due to the coarse grain size(5μm)and high content ofα_(2)phase,a selective oxidation occurred in the as-HT1000 sample resulting in a loose and porous oxide scale.As a results,the as-HT800 sample presented an enhanced oxidation resistance comparing to the as-HT1000 sample.