1：Experimental Design and Method Selection:

Ab initio Molecular Dynamics (AIMD) simulations of TiAlN reacting with oxygen were carried out using the Vienna ab initio Simulation Package (VASP) using the generalized-gradient approximation (GGA) and the projector augmented plane-wave (PAW) method. The time step was

2：0 fs and the total simulation time for each simulation was 2000 fs. Sample Selection and Data Sources:

The (0 0 1) surface of TiAlN was modeled by periodic slabs consisting of five atomic layers separated by of 15 ? of vacuum. A 3 × 3 surface unit cell was employed in the AIMD simulation, totaling to 189 atoms in the simulation box.

3：List of Experimental Equipment and Materials:

Vienna ab initio Simulation Package (VASP), Special Quasi-random Structures (SQS) supercells.

4：Experimental Procedures and Operational Workflow:

The simulations focus on the bonding between O and metal atoms of TiAlN(0 0 1) surface at different Al contents and temperatures. The Nosé-Hoover thermostat controlling the temperature, to 773 K and 1123 K to simulate TiAlN(0 0 1) surfaces interacting with O as a function of time, respectively, within the canonical ensembles (NVT).

5：Data Analysis Methods:

The temporal evolution of displacement height of metal atoms of TiAlN coating has been investigated.