Investigation of effect of voxel size choice for the measurement and analysis of porous coatings

This study aims to investigate the effects of voxel size change with measurement and characterisation of functional characteristics of a porous surface or coating. Prevalent across numerous fields, porous coatings and surfaces have been utilised and exploited for their unique characteristics, particularly in the biomedical field, where their osseointegrative potential is paramount. Due to the topographical nature of this surface type, the use of X-Ray Computed Tomography (XCT) is often dictated when re-entrant features are present. Voxel size is the indicative parameter in determining the resolution of the corresponding scan, with lower values resulting in increased scan times and data size implications but offer an increase in the scale of features that can be obtained. Topographical surface area information and amplitude parameters have been utilised in this comparative study to demonstrate the effects a change of voxel size has on the surfaces extracted from XCT measurements. 

Titanium Alloy (Ti6Al4V) coupon samples (12.7 mm diameter, 4.73 mm avg. thickness) were used for this study. They incorporate a porous plasma sprayed top coating with machining marks present on the opposing surface with a unique engraved identification mark present. A voxel size range of 8 μm to 76 μm was used, these resulted in a topographical surface area decrease, with values of 883 mm2 and 471 mm2 respectively. Amplitude parameters were used on the machining marks only, with root mean square roughness changing from 0.9 μm to 3.1 μm, with large variation between the voxel size intervals. Visible differences are instantly noticeable with the identification mark being only visible at voxel sizes below 25 μm.