"Corrosion Performance of Laser Clad Overlays and Thermal Spray Coatings: A Comparison" Part 1 of 8

Eight part series on the relative effectiveness of laser cladding and HVOF spraying for corrosion resistance.

Index of Parts

1.  Introduction
2. Open circuit potential measurement
3. Potentiodynamic test
4. Gravimetric Measurement
5. SEM
6. XRD
7. Vickers
8. Conclusion

Part 1

Introduction

This series is based on the work of Sunil Musali, George Kim Ph.D., Peter Longobardi and Michael Breitsameter of FW Gartner, Houston Texas. The conclusions of this research were presented at the TSS NACE symposium in San Paulo Brazil Nov. 8 – 10 2010.

As technology has progressed, the ability to modify the corrosion resistance of the surface of components has allowed the production of cheaper, stronger and/or more easily manufactured components. With the rapid improvements in materials and application techniques, there is an ongoing need to produce empirical evidence of the efficacy of the applications systems. Selecting the right coating for an application  requires the balancing of process capability, cost and desired service life. The focus of the researchers in this study is on relative performance of the two application methods outlined below. The data derived from this study will enable more informed consideration of application method used to produce coatings for corrosion applications.

The researchers investigated the relative corrosion resistance of three commercially available wear/corrosion protection materials, 316 Stainless Steel, Stellite® 6 and Inconel 625 (In 625). They used both laser cladding (1kw Precitec Fiber coupled Laser) and the High Velocity Oxygen Fuel (Jetkote® JK3000, HVOF) thermal spray process.  This resulted in 6 sample coupons for testing.

The corrosion resistance of each coating was determined by measuring the Corrosion Penetration Rate (CPR) using three different experimental methods: (1) open circuit potential measurements, (2) potentiodynamic tests, and (3) gravimetric measurements of anodic corrosion rate. In addition, coating properties like surface morphology, phase analysis, structure and hardness are examined using SEM, XRD and Vickers micro hardness tester respectively.

Results show that laser cladding generates superior corrosion resistant coatings in comparison to thermal spray coatings. It is evident from the results that the laser clad overlays show corrosion resistance equivalent to wrought material.

Fig. 1: (A) 1kW Laser, (B) Jet Kote 3000 HVOF gun