Effect of the impact angles on the erosion wear resistance of borided AISI 4140 steel

• Dual-phase FeB/Fe 2 B layers enhanced erosion resistance at low impact angles, reducing wear by up to 93.3 % compared to untreated AISI 4140 steel. • Erosive wear rates were predominantly influenced by particle geometry, size, and hardness, with Al 2 O 3 particles causing the highest material removal. • Wear mechanisms varied with impact angle, transitioning from abrasion at 30° to brittle erosion with cracking and fracture at 90°. • The interplay of boride layer composition and erosive particle properties provided valuable insights for optimizing erosion-resistant coatings in industrial applications. This study evaluates the erosive wear resistance of untreated AISI 4140 steel, borided AISI 4140 steel, and borided AISI 4140 steel subjected to diffusion annealing (DAP). Dual-phase FeB/Fe₂B and single-phase Fe₂B layers were obtained with thicknesses of 256 µm and 263 µm, respectively. Erosive wear tests were performed using Al₂O₃, SiC, and steel shot particles at impact angles of 30°, 60°, and 90°, following ASTM G-76 . Scanning electron microscopy and optical profilometry were used to analyze wear mechanisms and profiles. The brittle nature of FeB and Fe₂B layers increased erosive wear rates by up to ∼3.5 times compared to untreated AISI 4140 steel when using Al₂O₃ particles. However, under steel shot impact at 90°, the FeB/Fe₂B layer exhibited the lowest wear rate of 0.001 mg/g, representing a 93.3 % improvement compared to the untreated condition (0.015 mg/g). The single-phase Fe₂B layer achieved a 35.6 % lower wear rate than the dual-phase coating (0.0030 vs. 0.0047 mg/g), highlighting the beneficial effect of diffusion annealing. Additionally, the Fe₂B layer showed an overall wear reduction of 78 % compared to untreated steel under SiC particle testing. Wear mechanisms varied with impact angle, transitioning from abrasion at 30° to erosion at 90°. Observed failure modes included cracking, material detachment, and plowing, particularly in borided layers. These findings provide a framework for optimizing boride coatings in erosive environments.