Influence of ceramic particles and process parameters on residual stress of flame-sprayed Fe-based coatings

A series of Fe-based amorphous composite coatings, mixed with ceramic particles, are prepared by flame spraying water atomized powder. The morphology, structure and mechanical properties are investigated by scanning electron microscopy, X-ray diffraction and micro- and nano-indenter, respectively. The residual stress and influence of process parameters on residual stress, such as ceramic content, type and spraying distance, have been systematically studied. The results reveal that the coating with 30 wt% Al2O3 has shown excellent properties, such as porosity of 0.5% and micro-hardness of 794.7 HV. Furthermore, the results reveal that the residual stress decreased with the addition of ceramic particles, up to a threshold value, followed by a linear increase. The maximum value of 141 MPa has been achieved for FeBSiNb coating, with the Al2O3 content of 20%. However, the high melting point of feedstock powder and high thermal conductivity of impacting ceramic particles reduce the impacting effect because of the increased enthalpy of the coating and decreased kinetic energy of the impacting ceramic particles. In addition, spraying distance can also influence the residual stress of coatings. Once the spray distance was increased from 150 mm to 250 mm, the residual tensile stress of the coating decreased from 208 MPa to -115 MPa, where negative sign signifies that the residual stress has become compressive stress.