Formation mechanisms of defects in additively manufactured GH4169/cast iron bimetal via a multiphysics coupling model

Under extreme service conditions, the high thermo–mechanical loads generated by high power density engines exceed the service limit of cast iron. Depositing GH4169 onto the combustion surface of cast iron cylinder heads combines the high performance of GH4169 with the cost-effectiveness of cast iron, thereby enhancing the service life of engine cylinder heads. Owing to the interface defects of the GH4169/cast iron bimetal, its application in high-power-density cylinder heads is limited. This study employs multiphysics field coupled simulation to elucidate the formation mechanism of defects, such as tracks and layers of non-fusion, and cracks caused by residual stress, which were observed during laser powder bed fusion (LPBF) experiments. Through simulation analysis of the multiphysics fields of heat, flow, and solid, it is demonstrated that the primary cause of fusion defects between melt tracks and layers lies in the mismatch between the geometric dimensions of the forming melt track and the process parameters. The keyhole formed under high energy density also affects the forming quality of the fabricated component. Further thermo-mechanical coupling studies found that the residual stress distribution of the GH4169/cast iron bimetal exhibits a ”tensile-compressive-tensile” distribution. Temperature gradients are identified as the primary cause of residual stress, while the difference in thermal expansion coefficients at the GH4169/cast iron bimetallic interface also contributes to the magnitude of residual stress. For GH4169/cast iron bimetal, cracking tends to occur in the cast iron due to its lower tensile strength. A corresponding defect suppression strategy is proposed based on the above mechanistic analysis. This study provides research ideas for LPBF manufacturing of high-reliability bimetals. It also gives data support and a theoretical basis for enhancing reliability in bimetal engineering applications. It is a reference for process optimization in high-reliability bimetals manufactured by LPBF and provides data support and a theoretical basis for enhancing reliability in bimetal engineering applications.