Effect of boronizing, aluminizing, and boroaluminizing treatments on the microstructure, mechanical properties, and high-temperature wear behavior of SLM Inconel 718

This study presents a comprehensive comparative assessment of thermochemical diffusion coatings produced on selectively laser-melted IN718 (SLM-IN718) at 980 °C via single-step boriding (SSB), single-step aluminizing (SSA), sequential aluminizing followed by boriding (SAB), sequential boriding followed by aluminizing (SBA), and co-deposited boroaluminizing (CBA) processes, with particular emphasis on their effects on surface characteristics, mechanical properties, and high-temperature wear behavior. The resulting coatings were systematically characterized using XRD, SEM–EDS, nanoindentation, and wear tests conducted over a wide temperature range from room temperature to 750 °C. Phase analysis revealed the formation of NiAl, Ni₃Al, and Al₂O₃ in the SSA coatings; Ni₂B, Fe₂B, and CrB in the SSB coatings; complex assemblies of aluminides, borides, and Ni₂₀Al₃B₆ in the SAB and SBA coatings; and a dense, compact boroaluminide layer in the CBA coatings. The coating thickness was strongly dependent on the processing sequence, with the maximum thickness observed in SBA coatings (175–180 μm) and the minimum in CBA coatings (25–35 μm). Nanoindentation tests demonstrated pronounced enhancements in surface hardness (H), H/E, and H 3 /E 2 ratios for all thermochemically treated specimens compared to the untreated alloy. At temperatures below 250 °C, the wear resistance of SSB and SBA specimens exhibited a strong correlation with hardness. On the other hand, at elevated temperatures of 500 °C and 750 °C, the CBA coating provided the highest wear resistance, attributed to reduced friction resulting from high-temperature aluminum oxidation. Wear mechanism analysis indicated that abrasive–adhesive wear dominated in the 25–250 °C range, oxidative–abrasive wear prevailed between 250 and 500 °C, and oxidative–tribochemical wear became the governing mechanism at 750 °C. • Thermochemical SSB, SSA, SAB, SBA, and CBA coatings were grown on SLM-IN718. • Aluminide, boride and boroaluminide phases increased SLM-IN718 surface hardness and H/E. • Hardness-controlled wear dominated at temperatures up to 250 °C. • CBA coating showed superior wear resistance at 500–750 °C due to Al₂O₃ formation • Wear mechanisms evolved from abrasive to oxidative–tribochemical with temperature.