Failure Mechanism and Mechanical Characteristics of NiCrBSi Coating

Abstract

Mechanical properties of NiCrBSi coatings on plain carbon steel substrate prepared by HVOF (High velocity flame spraying) were studied in this work. Sprayed coatings with average thicknesses of 0.25 mm, 0.5 mm and 1 mm were prepared on preheated steel strips and steel strips without preheating. Chemical analysis of the coatings cross‑section offered information about material structure and distribution of chemical elements within the coating. Hardness of the coating was measured with the aim to reveal the influence of coating thickness and coated substrate preheating on coating hardness. Similar hardness was observed regardless coating preparation conditions and thickness. Bend test was used for characterization of failure character of NiCrBSi thermally sprayed coatings under different thermal conditions. Higher coating thickness was beside cracking, accompanied also by coating delamination from the substrate, while also some influence of testing temperature (laboratory temperature vs. ‑50 °C) on coating failure characteristics were observed. No influence of the coating preparation conditions on the coating pull‑off strength was observed.

Keywords

• thermal spraying
• NiCrBSi coating
• bend test
• coating failure mechanism
• cracks to centimetre ratio
• microstructure