*3.3. Mechanical Durability of the Coatings*

The results of scratch adhesion tests performed on samples after the process trial confirmed the observations made on the appearance of coatings. Representative results are shown in Figure 7. T1–T3 coatings showed good adhesion with no flaking after the process studies. U1–U2 coatings showed some flaking, which in most cases was confined to the area immediately next to the scratch track. Some of the samples, however, showed a more widespread flaking. This was most likely caused by the lack of a Ti base layer, which can enhance the adhesion of TiO2 to the stainless steel substrate or alternatively could be a result of the heat treatment. The MC coating from Breweries A and C showed some flaking near the scratch track. Samples removed from Brewery B showed no flaking. EDX analysis of these samples showed a Ti peak which had been greatly reduced compared to that of the control samples, suggesting that the coating had been heavily worn. This could be due to the different cleaning regimes, e.g*.*, chemicals and scrubbing methods used in the different breweries, with some conditions exceeding the chemical and mechanical resistance of the coating.

**Figure 7.** SEM micrographs showing the scratch tracks of coatings before and after process tests at Brewery C.
