Page 47 - MSAM-4-2

Materials Science in Additive Manufacturing Measuring the porosity of AM components

Table 8. Comparison of different aspects of the density and porosity measurement methods
Criteria Pycnometry Archimedes method Micrograph
Non-destructive testing ● ● ○
Geometry dependencies ◕ ◕ ◕
Measurement effort and costs ◕ ◕ ◕
Repeatability of measurements ● ◕ ○
Complexity of the process ◕ ◕ ◕
Accuracy of measurements and results ● ◕ ◕
Short measuring cycle ◕ ● ○
Direct density measurement ● ● ○
Detection of pore morphology ○ ○ ●
Detection of pore distribution ○ ○ ●
Ability to measure the true density ◕ ◕ ●
Ability to measure the apparent density ◕ ● ○
Note: ●: Denotes yes, good, low; ○: denotes no, bad, high. The symbols between the black full circle and the white full circle are gradations of the
respective designation. There is no direct description for this, it is more like visualizations that the criterion is closer to yes, etc. or no, etc.

as well as the density values calculated by micrograph effects and the surface tension of the infiltration fluid
analysis for the individual components. The individual on the component surfaces, smaller open pores cannot
diagrams clearly show the individual density values and be infiltrated as well with the Archimedes method and
the reference density for each measurement method and are therefore not included in the density calculation in
also roughly visualize the resulting range, the variance, and addition to the closed pores. This results in lower density
the deviation from the respective reference value. values than those with gas pycnometry. Air bubbles
The diagrams show that the gas pycnometry often adhering to the component surface in the measuring fluid
exhibits a low variance and range in the individual can also cause additional buoyancy, which falsifies the
measurements among each other as well as between the density calculation. The Archimedes method can therefore
measurements of the respective component geometries and be used more for direct measurement of the apparent
usually deviates only slightly from the reference values. The part density. The density here is lower than the material
gas molecules of the helium gas used are not prevented from density, as the enclosed air or porosity is partly considered
penetrating the pores by capillary effects or surface tensions and reduces the density. This usually corresponds better
and can therefore penetrate even the smallest open pores to the real conditions in the component and is also more
so that only the closed pores are not reached and are not advantageous, especially for technical aspects, as the
included in the density calculation. The resulting density mechanical properties of the component can be predicted
values often almost characterize the material density of the more realistically. Gravimetric density measurement
material used or come closest to it of all the measurement according to Archimedes method is also very reliable,
methods examined. This method can therefore usually be accurate, fast, and easy to automate, making it effective for
used to directly measure the true density. However, it should industrial component characterization.
be noted that gas pycnometry can tend to overestimate The micrograph analysis shows slightly higher values
the density values when the apparent density is actually of for the variance and the range of the results compared
interest. Depending on the application or further utilization to the other two measurement methods, but still at a low
of the measured values, the true density may not correspond level overall. Micrograph analysis is the only measurement
to the real conditions and the component may appear to method investigated that also includes the closed pores in
have better mechanical properties than it actually has. the calculations. However, the porosity is measured first
Compared to gas pycnometry, the density values of the and then calculated back to the density. Furthermore, the
Archimedes method always deviate more strongly from values are only meaningful for the area of the component
the reference density value and show lower part densities. under consideration and are not representative of the
In addition, the deviation between the component entire component. In most cases, they basically confirm
geometries is also higher in some cases. The variance and the values of gas pycnometry and buoyancy measurement
the range are comparatively small, especially between the and often lie between the measured values of these two
individual measurements of a component. Due to capillary methods.

Volume 4 Issue 2 (2025) 21 doi: 10.36922/MSAM025090010