铂改性铝化物涂层的热生长层内应力研究

TGO Stress Growth for Pt-Modified Aluminide Bond Coats during High Temperature Oxidation

摘要:

研究了镍基高温合金热障涂层系统中铂改性铝化物粘结层在空气中非连续高温氧化生成的Al2O3层内应力状态及相应的粘结层微观结构。利用Raman光激发荧光谱技术，发现铂铝粘结层在900 ℃氧化初期生成了θ-和α-Al2O3，而在1100 ℃氧化时，表面则形成连续致密的α-Al2O3层。通过α-Al2O3的光激发荧光谱偏移量，计算得到了热障涂层中热生长层的内压应力略高于3.0 GPa。铂改性铝化物涂层表面Al2O3“背脊”处的内应力相对较低，同时由于没有陶瓷层的压制，生成的Al2O3起伏较大，并发生局部的Al2O3脱落。随氧化时间延长，由于Al元素沿晶界扩散较快，导致更多的γ′-Ni3Al在粘结层晶界处形成，粘结层中基本相β-NiAl向γ′-Ni3Al转变，改变了粘结层本身的热膨胀系数，引起热生长层中内应力变化

Abstract:

Microstructure and compressive stress in thermal growth oxide (TGO) of Pt-modified aluminide coating on nickel base superalloy CSMX4 for thermal barrier coating (TBC) application after discontinuous oxidation at high temperature in air have been studied. Using a micro Raman instrument technology, photo-stimulated-luminescence-spectra (PSLS) of θ- and α-Al2O3 formation are obtained for Pt-modified aluminide coating after 20 h oxidation exposure at 900 °C in air; however, a compact and protective α-Al2O3 layer is formed over the coating at 1100 °C in air. Thermal growth stress in α-Al2O3 was calculated according to the spectra shift compared with stress-free alumina spectra, a little higher than 3.0 GPa for TGO in TBC system after oxidation exposure. The stress within “ridges” of alumina surface over the coating is lower due to cracks’ formation during high temperature oxidation. Alumina rumpling is obvious for Pt-modified aluminide coating due to absence of ceramic layer. At the same time, Al element’s quick diffusion along substrate grain boundary results in more γ′-Ni3Al phase formed along boundary during oxidation. Coefficient of thermal expansion for the coating is changed with phase transformation from β-NiAl to γ′-Ni3Al, and finally affects the stress in TGO and coating lifetime during high temperature oxidation.