A Study on Interactions of Composition and Scratch Test Parameters in Nix-B-Based Electroless Alloy and Composite Coatings under Scratch Loading

Abstract

Recent studies have reported the incorporation of various alloying elements and lubricious phases into electroless nickel-boron (Ni-B) coatings to enhance hardness and frictional resistance. This research introduces a novel Nix-B (x = 1, 2, 3…) notation to reflect compositional complexity and investigates the mechanical and tribological durability of electroless Nix-B-W-hBN composite coatings, alongside binary Nix-B and ternary Nix-B-W alloy coatings, through scratch tests assessing hardness and fracture toughness. All three coatings consist of a finer nickel-based mixed phase structure containing both crystalline and amorphous or short-range ordered phases. The selection of input factors for studying these coatings is based on a combination of experiments and existing research, aiming to understand how factors like composition, scratch load (14N, 17N, 20N), and scratch speed (1, 3, 5 mm/s) impact mechanical properties such as fracture toughness and scratch hardness. While scratch load has been extensively studied, scratch speed is often overlooked, and this study aims to address this gap. Results show that Nix-B-W-hBN coatings exhibit the highest microhardness and critical load, with fracture toughness and scratch hardness increasing with scratch load and speed. Higher speeds induce strain-rate hardening in fine-grained materials, enhancing strength. Using response surface methodology (RSM), optimal conditions linking composition, load, and speed are determined for fracture toughness and scratch hardness, offering insights into the coatings’ responses to intrinsic and extrinsic parameters. This advances the design of high-performance Ni-B coatings for tribological applications. © ASM International 2026.