Friction stir welding is a solid-state joining process widely used in several industrial applications. One of its variants, orbital friction stir welding, is of key importance in fundamental industries such as oil and gas and aerospace. For orbital friction stir welding, there is a need to develop not only new process parameters but also tools and ancillary mechanisms that can ensure sound, high-performing joints are obtained. This review assesses the current state of orbital friction stir welding, highlighting several key aspects related to this technology.

The influence of Nb on phase stability and microstructural evolution in an interstitial Fe-Mn-Co-Cr-C high-entropy alloy was investigated using in-situ synchrotron X-ray diffraction (SXRD) during laser melting. Scheil-Gulliver simulations predict the formation of σ and γ-f.c.c. phases in all three alloys, along with NbC in Nb-containing compositions. SXRD confirmed the presence of most predicted phases, but the σ phase was absent. Nb promotes crystallite refinement and increases dislocation density, though excessive additions reduce refinement efficiency due to solubility limits and secondary phase formation. Furthermore, Nb addition also enhances ε -h.c.p. phase formation by reducing stacking fault energy through NbC-induced carbon depletion. Analysis of intensity peak evolution reveals that Nb alters preferred grain orientations, reducing <!-- [if gte msEquation 12]> 111 γ <![endif]--> <!-- [if !msEquation]--> <!-- [if gte vml 1]> <![endif]--> <!-- [if !vml]--> <!--[endif]--> <!--[endif]--> intensity while enhancing <!-- [if gte msEquation 12]> 220 γ <![endif]--> <!-- [if !msEquation]--> <!-- [if gte vml 1]> <![endif]--> <!-- [if !vml]--> <!--[endif]--> <!--[endif]--> , leading to a more isotropic grain distribution. Overall, Nb plays a key role in phase selection, microstructure refinement, and preferred orientation evolution, allowing the tailored microstructure of high-entropy alloys via rapid solidification.

In this study, eletrolitical copper powder (Cu) was initially mixed with the aqueous solution of graphene oxide (GO); later, the mixture underwent mechanical stirring for 1 h, vacuum filtration, and drying for 42 h. The final concentration of GO in the composite was 0.3%wt. Through scanning electron microscopy (SEM), it was possible to observe the homogeneous dispersion of graphene sheets between copper particles, without the presence of agglomerates. In addition, X-ray diffraction (XRD) of the pure samples and after mixing revealed that there was no oxidation of the copper and the absence of peaks related to other elements, confirming the high purity of the copper used. Still, by XRD, it was possible to analyze that the graphene oxide produced was formed by stacking layers of graphene owing to the appearance of a diffraction peak referring to the plane (002), which was confirmed by Raman spectroscopy performed in GO from the appearance of the 2D bands. Fourier transform infrared spectroscopy (FTIR) allowed the identification of the vibrational spectra referring to the hydroxyl, carbonyl, and epoxy functional groups in GO, confirming that the oxidation process was effective in inserting functional groups in the basal graphical plane. Through the GO thermogravimetric analysis (TGA), it was possible to identify a significant loss of mass of approximately 30% at temperatures below 100 °C; referring to the elimination of water molecules, the most stable functional groups were eliminated at temperatures between 600 °C and 800 °C.