1：Experimental Design and Method Selection:

The study used a duplex coating system with electrodeposition in two baths. The inner layer was Ni coating, and the outer layer was Ni-P-TiO2 nanocomposite coating prepared using a sol-enhanced plating method to avoid nanoparticle agglomeration.

2：Sample Selection and Data Sources:

Brass substrates of size 20 × 30 ×

3：3 mm3 were used. Samples were cleaned and activated before electroplating. TiO2 sol was prepared as per previous methods. List of Experimental Equipment and Materials:

Equipment includes an ultrasonic cleaner, X-ray diffractometer (Bruker D2 Phaser), optical microscope, Vickers hardness tester, micro-tribometer (CETR, Brooke), and electrochemical workstation (CS2350H). Materials include NiSO4·6H2O, NiCl2·6H2O, H3BO3, NaCl, H3PO4, NaH2PO2·6H2O, TiO2 sol, NaOH, NaH2PO4·H2O, citric acid, ammonium citrate, and distilled water.

4：Experimental Procedures and Operational Workflow:

Substrates were cleaned ultrasonically, alkali washed, activated, and then electroplated with Ni coating (bath in Table 1) followed by Ni-P-TiO2 coating (bath in Table 2) with varying TiO2 sol concentrations. Characterization involved XRD for phase structure, optical microscopy for cross-section analysis, microhardness testing, wear tests, and potentiodynamic polarization for corrosion resistance.

5：Data Analysis Methods:

Data were analyzed using standard techniques for XRD patterns, microhardness measurements, friction coefficient calculations, wear track width measurements, and electrochemical parameters (Ecorr and Icorr) from polarization curves.