LASER CLADDING OF STRUCTURED BOND COAT ON NI-BASED SUPERALLOY

摘要

Structured bond coat (BC) is a generally accept method for improving the adhesion of thermal barrier coatings (TBCs) hence the thermal barrier effect. To manufacture structured BC with good adhesion the laser cladding method was used. The triangular structured BC (NiCrAlY) was clad on the substrate (Ni-based superalloy DZ4125) with optimized laser processing parameters. The top coat (TC) with ceramic material ZrO_2-8%Y_2O_3 was further deposited by atmosphere plasma spraying (APS). The microstructure of the cladded BC and the sprayed TC were detected by scanning electron microscope (SEM). Their adhesion or cohesion were measured by the tensile test. To explain the tensile stress induced fracture the distribution of stress in three different models were simulated by finite element method. The results show that the adhesion of laser cladded BC is 175MPa. It meets the requirement of metallurgical bonding. Unlike the non-structured TBCs the TC of the structured one is not fully spall off the substrate with the help of the triangular BC. However the cohesion of the latter TC is still lower due to the poor adhesions on the perpendicular interface of BC and TC, the interface of BC and the glue used in tensile test.