# Evaluating the Degradation of WE43 for Implant Applications: Optical and Mechanical Insights
## 4 Results and Discussion
### Results from the Degradation Experiments
Due to the position, more particles can detach from the degradation layer, which results in greater roughness and greater dispersion; therefore, samples from this position have been used for analyses with the Triboindenter. Based on the information from the roughness measurements and the analysis of the HBSS flow conditions, only position X\({}_{2}\) can be recommended for further analyses. In addition, investigations related to hardness and Young's modulus were carried out on sample geometry 2 (of position X\({}_{1}\)) as an example (Figure 12). It should be noted that the degradation products were not removed before measuring. The central area (MP 2) on the sample surface of the covered part was analysed (Figure 12a,c). Additionally, the edge area (MP 1) of the borehole that had contact with HBSS was investigated (Figure 12b,d,f). In the  
Figure 11: Images of the flow behaviour of the HBSS in one experimental chamber (back section), with the colour added to clarify the flow, without a sample present in the chamber. Figure 10: Roughness development (**a**) of all positions; an image of the roughness (**b**) of geometry 2 of sample position X\({}_{1}\). area that had no contact with HBSS, equal values for [PERSON]'s modulus of approximately 45 GPa can be measured (Figure 12a). In the edge area, the measurements are placed in such a way that an area with localised degradation is also examined. This ensures that a possible degradation layer is also investigated, which can also be recognised in the post-image in Figure 12f. In the area at the edges where surface corrosion was present, the degradation layer was removed due to the process. Consequently, it was not possible to measure this layer. Therefore, the focus was directed towards localised degradation. Through the analysis of [PERSON]'s modulus, it was indicated that the degradation progressed from the outside towards the inside, rather than originating internally (Figure 12b). In the area with the local degradation, lower values of around 25 GPa were determined. In some instances, these values are also slightly lower, but it is important to note the increased roughness in areas of localised degradation. This roughness might introduce minor distortions in the results; however, the overall trend remains consistent. It was to be expected that there would be a reduction in the mechanical properties in the area of degradation,  
Figure 12: Investigations with the Triboindenter after five days in the body replacement fluid of sample geometry 2 ((**a**,**c**) a region without contact to the fluid; (**b**,**d**) with contact to the fluid; (**f**) postscan of the investigations (**b**,**d**)) and (**e**) metallographic image of the centre side with contact to the fluid. as the degradation layer is described as brittle and lacking in strength. When analysing the middle sample area, a hardness of around 1.5 GPa was determined (Figure 12c). Only individual small areas with higher values of a maximum of 3 GPa and lower values of 0.75 GPa were measured. These local differences can be attributed to alloy precipitations, which were visible both in the analysis before the degradation experiments (chapter 4.1) and in the metallographic image Figure 12e. In the area of the local degradation, an average hardness of approximately 0.6 GPa was determined (Figure 12d). Occasionally, higher hardness values can be recognised around the local degradation, up to a maximum value of 4 GPa. The metallographic image in Figure 12e shows a slight change in the outer surface layer (green box). There is no uniform surface, and it appears that the outer grains have bonded together. This may indicate the presence of a degradation layer. The examination of the local degradation showed a reduction of [PERSON]'s modulus. However, this should be analysed again in further experiments to determine possible influencing factors. In addition to the surface roughness, the influence of geometry on the mass loss can also be recognised (Figure 13a).