Porosity optimization in Yb2Si2O7-CaF2-PHB high-temperature abradable sealing coatings for enhanced thermal shock resistance

Abstract

The design and deposition of well-matched abradable sealing coatings (ASCs) on ceramic matrix composites (CMCs) are currently a difficult challenge to improve engine efficiency and performance. The influence of the high porosity characteristics of ASCs on residual stress and thermal shock resistance has not been clarified. Therefore, this study investigated residual stress and thermal shock resistance in atmospheric plasma-sprayed Yb₂Si₂O₇-20 vol% CaF₂-(0/10/15/20 vol%) PHB/Si ASCs system. The simulation results indicated that higher porosity led to larger maximum radial tensile stress at the top-coat layer (TC). Moreover, alternating tensile and compressive stresses were observed near the pores. Thus, microcracks around the pores of the TC in experimental results deflected towards the location of pores, which stopped rapid propagation of cracks. Besides, the introduction of pore prevented the formation of large radial tensile stress concentration regions at the TC, while reducing penetrating cracks and contributing to enhanced thermal shock resistance. However, higher porosity gradually increased the stress fluctuations at the interface between the TC and the Si bond-coat layer (BC). Among these, radial tensile stress was particularly affected, promoting more interfacial cracks. Therefore, an appropriate porosity of about 35 vol% was beneficial for improving thermal shock performance. The pore model proposed could provide a foundation for optimizing Yb₂Si₂O₇-CaF₂-PHB ASCs for CMCs compatibility.