Load-Driven Tribofilm Formation: Friction-Wear Trade-Off in Ti 2 AlN and Ti 2 NT x Multilayered Nanosheet Coatings

MXenes have gained considerable attention in solid lubrication due to their involved tribofilm formation offering low friction and extended durability at the same time. While the solid lubrication performance of carbide systems has been well explored, research on nitride MXenes remains considerably scarce. Therefore, we synthesized multilayer Ti2NTx from its parental Ti2AlN precursor. Coatings consisting of multilayer Ti2NTx were spray-coated onto AISI 304 steel substrates to assess their solid lubrication performance using linear reciprocating ball-on-disk tribometry varying normal loads (0.1–1.0 N) and durations (15–60 min). In case of Ti2NTx, the specific wear rates ranged between 5.09 and 6.79 ×10–8 mm3/(N·mm) for 15 min testing and decreased to about 1.30 × 10–8 mm3/(N·mm) for extended durations (60 min and 1 N). In contrast, the Ti2AlN coating exhibited substantially higher friction (COF ≈ 0.55 for 0.4 N), while demonstrating lower wear rates of (2.84–3.17) × 10–8 mm3/(N·mm) for a test duration of 15 min. To understand the involved friction and wear mechanism as well as tribochemistry, the corresponding wear tracks were assessed by complementary materials characterization. While bare steel exhibited a high, noisy friction, characteristic for abrasion- and debris-dominated tribosystems, the Ti2AlN coatings showed similarly high friction under low loads, which is consistent with a formation of a rigid, oxide-rich tribofilm. In striking contrast, the Ti2NTx coatings rapidly run into a low and remarkably stable friction, insensitive to both load and sliding time, thus evidencing the development of a more continuous, easy-to-shear tribofilm. The results indicated that the lamellar structure of Ti2NTx lamellae and its chemistry promote a self-replenishing tribofilm, whereas the Ti2AlN coating and the steel reference remain governed by abrasive circulation of oxide/debris. Using simple, scalable spray-coating, this MAX-to-MXene route delivers durable, low-friction surfaces thus extending the concept of 2D solid lubrication to Ti2NTx, highlighting their potential for tribological applications.