Stereological Evaluation of Precipitates within Ferrite Grains in Heat-Treated 1.25Cr0.5Mo Steel Previously Exposed to Service

The objective of this work was to study the effect of the heat treatment and further operation aging on the stereological parameters (size, quantity and volume fraction) of precipitates within ferrite grains of a creep-resistant 1.25Cr0.5Mo steel after long-term operation. The heat treatment was similar to the treatment that is carried out in industrial steam pipelines after welding (post weld heat treatment - PWHT) during installation and/or repairing. The operation aging corresponds to a subsequent long in-service operation after repairing. To determine the stereological parameters, SEM digital images were taken from samples of this material after conditions of in-service-aged (after long-term operation), in-service-aged and heat-treated (simulating repairing) and in-service-aged, heat-treated and in-laboratory aged (simulating subsequent long-term operation after repairing). The results indicate that the changes in the stereological parameters of the precipitates within ferrite grains after PWHT is associated with the coarsening process of the within-ferrite-grain precipitates as well as stabilizing the microstructure, since the material aging after PWHT of an in-serviced aged material would not change the stereological parameters

Fatigue behavior and physical characterization of surface-modified Ti-6Al-4V ELI alloy by micro-arc oxidation

Anodizing has proven an effective method for preparing bioactive titanium and has been the subject of many studies regarding the performance and biological characterization of the layers obtained. However, the fatigue behavior of titanium alloys, after undergoing this process is still poorly studied. This study aims to investigate the influence of MAO (Micro-Arc Oxidation) process on the fatigue properties of titanium alloy Ti-6Al-4V. Therefore axial fatigue tests were performed to obtain SxN curves, of specimens in polished and anodized (MAO processed, phosphate salt solution, potential of 290 V) conditions. Roughness measurements, SEM, Raman spectra and X-ray photoelectron spectroscopy (XPS) analyses were used to characterize the features of the modified surface. SEM was also used to analyze the fatigue fractures of the tested specimens. The MAO process, with the parameters used in this investigation, had no influence on the fatigue behavior of the Ti-6Al-4V alloy, when compared to specimens without surface modification