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首页> 外文期刊>Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing >Numerical simulations of crack formation from pegs in thermal barrier systems with NiCoCrAlY bond coats
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Numerical simulations of crack formation from pegs in thermal barrier systems with NiCoCrAlY bond coats

机译：NiCoCrAlY粘结涂层在热障系统中钉形成裂纹的数值模拟

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摘要

The high temperature exposure of thermal barrier systems with MCrAlY bond coats is accompanied by non-uniform thickening of the thermally grown oxide (TGO). The heterogeneities are manifest as intrusions into the bond coat, referred to as "pegs". The progressive growth and swelling of these intrusions, in conjunction with the thermal expansion mismatch from layer to layer, leads to the development of localized strains upon thermal cycling. A finite element study reports on the evolution of the stress state and of the plastic strains in the vicinity of the pegs, and on the conditions under which cracks may initiate and advance. It is demonstrated that large plastic strains accumulate near the peg. Moreover, large shear stresses arise that could motivate mode Ⅱ (shear) cracking along the interface between the bond coat and thermally grown oxide. However, for realistic sizes of peg, the energy release rate is always much less than the interface toughness. It is concluded that the pegs do not behave as imperfections that initiate cracks, but rather, serve a beneficial purpose of fastening the TGO to the bond coat.
机译：带有MCrAlY粘合涂层的热障系统的高温暴露伴随着热生长氧化物（TGO）的不均匀增稠。异质性表现为侵入粘结涂层，称为“钉子”。这些侵入物的逐渐生长和膨胀，以及层与层之间的热膨胀失配，导致热循环时局部应变的发展。有限元研究报告了钉附近的应力状态和塑性应变的演变，以及裂纹可能引发和发展的条件。事实证明，大的塑性应变在桩附近积累。此外，会产生较大的剪切应力，这会促使沿粘结层和热生长氧化物之间的界面的Ⅱ型（剪切）开裂。但是，对于实际大小的钉，能量释放速率始终远小于界面韧性。得出的结论是，钉子的行为不像是会引起裂纹的缺陷，而是将TGO固定在粘结层上的有益目的。

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