氧化铝涂层垂直裂纹对热载荷下界面失效的影响

Effect of Vertical Cracks of Alumina Coating on Interface Failure under Thermal Load

目的探索氧化铝/铝在热载荷作用下的界面失效机理。方法基于内聚力有限元模型,预测热载荷下铝基氧化铝涂层材料界面处的残余热应力,并系统研究其失效过程。重点考虑涂层厚度、热载荷大小、预制涂层垂直裂纹密度对界面处应力场和界面损伤失效的影响,并同实验进行对比。结果试验和模拟结果都发现,加热到300℃冷却后,界面未产生平行裂纹,而加热到400℃冷却后,界面出现平行裂纹。涂层无裂纹缺陷时,界面处剪应力呈单曲线余弦分布,而有预制裂纹时,界面处的剪应力呈双曲线余弦分布。随着热载荷的增大,界面最大剪应力值由两端向界面中心处迁移。相比涂层有裂纹的情况,界面在涂层无裂纹时平均正应力最小。实际制备的氧化铝涂层不可能完美无裂纹缺陷,在考虑涂层有裂纹缺陷时,涂层裂纹密度为4 mm^(-1)时平均所受正应力较小,且界面只有拉应力作用,不容易产生脱层缺陷。结论存在特定的最佳临界预制垂直裂纹密度值,使得热载荷下界面损伤最小。有限元模拟结果也显示,相同热载荷和相同裂纹密度下,涂层越厚,对界面的防护力也越强。

To investigate the interface failure mechanism of alumina-coating/aluminum under thermal loads.The residual thermal stress at the interface under thermal loads was predicted,and the interface failure of the alumina-coating/aluminum was systematically studied by the finite element model with a cohesive zone.The effects of the coating thickness,the thermal load magnitude,and the vertical crack density of the coating on the stress field at the interface and the interface damage failure were considered and compared with experiments.Experimental and simulation results showed that,as the interface was cooled after heated to 300℃,no parallel cracks was observed at the interface.However,as the interface was heated to 400℃and then cooled,parallel cracks were observed at the interface.The shear stresses at the interface showed a single-curve cosine distribution when there was no crack defect in the coating,while the shear stresses showed a hyperbolic cosine distribution when there was vertical cracks in the coating.With the increase of thermal load,the maximum shear stress at the interface migrated from both ends to the center.Coatings without vertical cracks had a minimum average normal stress compared to coatings with verti cal cracks.However,the actually prepared alumina coating was unlikely to be free of defects.When the coating crack density was 4 mm?1,the average residual normal stress was small,and the interface had only tensile stress,which caused the interface to be less likely to delaminate.There is a specific optimum critical pre-fabricated vertical crack density value,which minimizes interface failure under thermal loading.The finite element results also indicate that,the thicker the coating is,the stronger the thermal protection of interface is under the same thermal load and the same density.