This study presents a comprehensive investigation of the formation, composition, and behaviour of oxide layers during the high-temperature oxidation of four different steel alloys (16Mo3, 13Cr, T24 and P91) at a uniform temperature of 650 °C. The research combines CALPHAD (CALculation of PHAse Diagrams) calculations, thermogravimetric analysis (TGA) and advanced microscopy techniques, including scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), to elucidate the complex mechanisms controlling oxidation kinetics and oxide layer development. CALPHAD calculations were used to determine the thermodynamically stable phases for each steel type at 650 °C. The results showed different phase compositions, highlighting the importance of steel composition in the formation of oxide layers. Each steel grade exhibited different kinetics, with 16Mo3 steel showing the highest oxidation rate, followed by 13Cr, T24 and P91. This variability highlights the role of steel composition, particularly chromium content, in determining oxidation behaviour. These results have significant implications for temporary overheating in industrial applications and contribute to a deeper understanding of oxidation processes in steels.

We investigated the micro-threaded stem taper surface and the impact on premature failures, aseptic loosening, and infection. We have focused on the fretting, and crevice corrosion of micro-threaded tapers, as well as the characterization of microstructure and surface properties of two new and three retrieved Zweymüller stem tapers of cementless hip endoprostheses selected from a set of 45 stems. The retrievals examined were those in which the sole source of modularity with a metallic component was the head-stem taper interface between the Ti alloy taper stem and the ceramic head. To determine the surface chemistry and microstructures of both new and retrieved hip endoprostheses stem taper titanium alloy, scanning electron microscopy (SEM) was employed for morphological and microstructural analyses. At the same time, energy dispersive spectroscopy (EDS) was utilized for characterizing chemical element distribution, and electron backscattered diffraction (EBSD) was used for phase analysis. The micro-threated stem taper’s roughness for different manufacturers was investigated using an optical profilometer. Standard roughness pa-rameters Ra (average surface roughness) and Rz (mean peak to valley height of the roughness pro-file) were used in this investigation.Additionally, profile depth and peak spacing for different samples were investigated. The surface roughness results indicate no significant difference in roughness associated with varying survivorship times, ranging from 3 to 239 months, and across different manufacturers. Electrochemical studies revealed no fretting corrosion in retrieved stem tapers (ceramic head) that prematurely failed due to aseptic loosening after 239 months, infection after 3 months, and low-grade infection after a 32-month lifetime. Therefore, three retrieved ta-pers and two new ones for comparison underwent potentiodynamic measurements in Hank’s so-lution to ascertain the corrosion rate of new and retrieved stem taper surfaces. The results show a low corrosion rate for both new and retrieved samples that failed prematurely due to aseptic loosening. However, the corrosion rate of infected and low-grade infected tapers was higher. In conclusion, our study aligns with existing literature, suggesting that the use of ceramic heads de-creases the problem of taper corrosion and subsequently reduces premature failures in total hip arthroplasty.