Laser Cladding vs Thermal Spray for Marine Shaft Repair (Corrosion Resistance & Adhesion)

1 Introduction

Marine shafts are continuously exposed to seawater and mechanical stresses, accelerating corrosion and wear. Surface repair is critical to extend service life and minimize downtime. Among repair methods, laser cladding and thermal spray are widely applied. Previous research quantified deposition efficiency, microstructure, and adhesion properties; however, comparative evaluation under controlled marine-simulated conditions remains limited. This study objectively assesses both methods with standardized experiments, providing data-driven guidance for maintenance decision-making.

2 Research Methodology

2.1 Experimental Design

• Samples: AISI 316 stainless steel shafts (50 mm diameter × 200 mm length), polished to Ra ≤ 0.4 μm.

• Laser Cladding (LC): Ni-based alloy powder, fiber laser 2 kW, 5 mm/s scan speed, preheated at 150°C.

• Thermal Spray (TS): HVOF spray of identical Ni-based powder, target thickness 500 μm.

2.2 Data Acquisition

• Corrosion Resistance: Salt spray chamber (ASTM B117) for 720 h; periodic weight loss measurements; SEM surface inspection.

• Adhesion Strength: Pull-off adhesion test (ASTM D4541); five replicates per method.

• Microstructure Analysis: Optical microscopy and cross-sectional SEM; porosity, thickness, and interface quality quantified.

2.3 Reproducibility

All deposition parameters and environmental conditions were documented. Experiments were conducted in triplicate to ensure statistical reliability.

3 Results and Analysis

3.1 Microstructure and Coating Quality

• Laser Cladding: Dense, low-porosity (~1.5%), metallurgical bonding observed.

• Thermal Spray: Higher porosity (~7%), lamellar structure with occasional microcracks.

Figure 1: Cross-sectional SEM images of LC and TS coatings

3.2 Corrosion Performance

• LC exhibits significantly lower weight loss.

• Pitting primarily observed in TS coatings.

Table 1: Corrosion weight loss comparison

3.3 Adhesion Strength

• LC adhesion is statistically higher (p < 0.01), consistent with metallurgical bonding.

4 Discussion

• Corrosion Resistance: LC’s dense microstructure reduces electrolyte penetration, resulting in superior long-term resistance.

• Adhesion: Metallurgical bonding in LC improves mechanical anchoring. TS’s lamellar, porous structure reduces adhesion and introduces vulnerability to pitting.

• Practical Implications: LC is recommended for critical shafts requiring long-term reliability; TS is suitable for rapid, cost-effective surface restoration.

• Limitations: Laboratory-scale testing and controlled conditions; real marine environments may introduce additional variables such as biofouling and impact loading.

5 Conclusion

• Laser cladding demonstrates superior corrosion resistance and adhesion for marine shaft repair compared to thermal spray.

• LC is preferred for critical shafts; TS can serve non-critical, rapid repair purposes.

• Future studies may explore hybrid approaches and real-time monitoring for enhanced surface repair strategies.