Microstructure and porosity evaluation in laser-cladding deposited Ni-based coatings

• Porosity was measured on a region that has the same magnitude as a RVE cross section.
• The porosity data followed a Weibull distribution best rather than a normal or lognormal distribution.
• The severity of porosity may not show a monotonous change with the increasing laser power.
• The statistically based evaluation of porosity might account for the variations in material properties.

Microstructure and porosity characteristics were studied for the laser cladding process. A series of Ni-based coatings were prepared at different laser powers. The damage caused by porosity was defined according to the theory of the continuum damage mechanics (CDM). Porosity measurements of the coatings were made using an image analysis method. Special attention was given to the influence of laser power on the porosity. Results showed that the laser cladding process can form a strong metallurgical bonding at the interface between the substrate and the clad coating. However, micro pores may be unavoidable in the clad coating. Porosity damage in the coating followed the Weibull distribution best rather than a normal or lognormal distribution. From the statistical trend, the severity of porosity may not show a monotonous change with the increasing laser power. This study implied that a statistically based evaluation of the porosity might account for the variations in material properties that were practically observed. In addition, the CDM-based definition of porosity may have shown the ability to bridge the gap between conventional porosity study and studies of material properties.