Jaime Taha-Tijerina

The degradation of steel used in the oil industry has become a serious problem due to the high costs associated with material loss from corrosion. Applying thin layers of corrosion-resistant material promises to be a viable alternative for extending the service life of pipelines. ERCuAl-A2 electrode claddings were applied to API X70 carbon steel using the MIG brazing process with direct current (DC) and pulsed current (P). The cladding was applied under three conditions: base material (BM) at room temperature, BM preheated to 120 °C, and Ni-buttered BM. Microhardness profiles and Charpy impact tests were performed on the MB and all cladding conditions. The API X70 carbon steel showed a microhardness value of 186.95 ± 11.17 Vickers, while the microhardness profiles of the ERCuAl A2 cladding showed values that differed in the intermetallic zone generated by the welding process. Likewise, the impact behavior of the base material and the applied claddings was ductile, except for conditions C2PF and C3PF, which showed a brittle–ductile behavior. The highest values of absorbed energy obtained from the tests were found in the conditions applied with DC, with values of approximately 50 MJm-3, due to the transfer mode of application of the cladding and/or the position in which the notch was made.

The development of advanced high-strength steels (AHSS) for the automotive industry requires optimizing the balance between mechanical properties and durability in aggressive environments. This study investigates the effects of two heat treatment routes on the microstructure and corrosion resistance of a transformation-induced plasticity (TRIP) steel (Fe-0.2C-1.75Mn-0.5Si-1Al). Route A includes a full austenitizing step at 1000 °C prior to intercritical annealing, whereas Route B omits this step and begins directly with intercritical annealing at 800 °C. Microstructural characterization (SEM/XRD), electrochemical assays, and eddy current tests were employed. The results revealed that Route A yields a homogeneous microstructure with 12.7% retained austenite, higher than the 7.7% obtained with Route B. Electrochemically, the steel from Route A exhibited the greatest resistance, with the lowest corrosion current density (i_corr) of 3.72 µA/cm² and a more noble corrosion potential (E_corr) of −743 mV compared to SCE. The improvement mechanism is that the homogeneity induced by complete austenitization minimizes the formation of internal galvanic cells between phases; likewise, the higher austenite fraction provides superior chemical stability, which favors denser passivation. Finally, Route A exhibited the lowest loss of electrical conductivity (16%), validating the use of eddy currents for monitoring the integrity of advanced steels.

Recent innovations with the aid of nanotechnology are more frequently seen in the industrial sectors. Lubricants are a high-end commodity resource used in many manufacturing processes; unfortunately, most of these lubricants are petroleum-based, which come with certain drawbacks, such as environmental aspects, handling issues and high costs. With the incorporation of nanostructures within fluids and lubricants, novel material alternatives are replacing conventional lubrication systems, maintaining the required thermophysical and tribological characteristics. This research provides an analysis of vegetable lubricant, castor oil (CO), and the effects of the incorporation of WS₂ nanofiller at diverse filler fractions. A TEMPOS thermal analyzer device and a four-ball tribotester are used for the analysis of thermal conductivity and tribological assessments, respectively. Results showed the enhancement of thermal conductivity as the filler concentration and the evaluation temperature of the nanolubricants increased. The best thermal conductivity improvement was 27%, at 60 °C with merely 0.20 wt.% of nanofillers. For tribological performance, a decrease of 6% in the coefficient of friction (COF) and 31% in the wear scar diameter (WSD) was observed at 0.10 wt.% and 0.20 wt.%, respectively. Adhesion of the nanostructures to the steel surfaces creates a protective layer, preventing direct contact of the friction pairs. These results are an outcome of applied theoretical concepts such as Brownian motion and nano-layering of the lubricant–nanostructure interface.

Pullulan‐based microfibers containing 0.25 wt% of h‐BN, MoS ₂ , and their hybrid (h‐BN/MoS ₂ ) were successfully produced by the Centrifugal Force Spinning Method (CFSM) and characterized by TGA, SEM, XRD, XPS, DSC and tensile tests. The nanofiller‐loaded fibers exhibited thermal behavior comparable to neat pullulan, with similar T _g and stability. Tensile stress–strain tests showed up to ~45% and ~30% increases in ultimate tensile strength and modulus, respectively, while maintaining elongation. The hybrid h‐BN/MoS ₂ system achieved the most balanced reinforcement, evidencing a synergistic effect. Moreover, the microfibers preserved high HaCaT cell viability and inhibited Escherichia coli and Staphylococcus aureus growth by up to 67%, highlighting their multifunctional potential for biomedical and technological applications. This approach imparted the multifunctional character to these microfibers, with balanced thermal, mechanical, and biological properties, enabling their potential use in various technological fields.

The microstructure and mechanical properties of welded joints of API 5L X-52 steel plates cladded with AISI 316L-Si austenitic stainless steel were evaluated. The gas metal arc welding process with pulsed arc (GMAW-P) and controlled arc oscillation were used to join the bimetallic plates. After the root welding pass, buttering with an ERNiCrMo-3 filler wire was performed and multi-pass welding followed using an ER70S-6 electrode. The results obtained by optical and scanning electron microscopy indicated that the shielding atmosphere, welding parameters, and electric arc oscillation enabled good arc stability and proper molten metal transfer from the filler wire to the sidewalls of the joint during welding. Vickers microhardness (HV) and tensile tests were performed for correlating microstructural and mechanical properties. The mixture of ERNiCrMo-3 and ER70S-6 filler materials presented fine interlocked grains with a honeycomb network shape of the Ni–Fe mixture with Ni-rich grain boundaries and a cellular-dendritic and equiaxed solidification. Variation of microhardness at the weld metal (WM) in the middle zone of the bimetallic welded joints (BWJ) is associated with the manipulation of the welding parameters, promoting precipitation of carbides in the austenitic matrix and formation of martensite during solidification of the weld pool and cooling of the WM. The BWJ exhibited a mechanical strength of 380 and 520 MPa for the yield stress and ultimate tensile strength, respectively. These values are close to those of the as-received API 5L X-52 steel.

This study investigated the control of porosity during gas metal arc welding with pulsed arc (GMAW-P) of complex-phase 780 (CP780) galvanized steel. Due to the Zn coating on this type of steel, porosity forms during welding as a result of Zn vaporization. The objective was to optimize the welding parameters to minimize porosity with a design of experiments using an L9 orthogonal array to analyze the effects of peak current (I_p), pulse time (t_p), and pulse frequency (f) in high-speed welding conditions. The results showed that porosity was significantly reduced with a peak current of 313 A, a frequency of 10 Hz, and a pulse time of 10 ms, achieving ~0% porosity in the validation welding trials. A microstructural analysis identified allotriomorphic ferrite, Widmanstätten ferrite, acicular ferrite, bainite, and martensite in the heat-affected zone (HAZ). A predictive model to anticipate the percentage of porosity with an R² of 99.97% was developed, and an ANOVA determined the peak current as the most critical factor in porosity formation.

Nanocomposites containing low wt% of oxidized multi‐walled carbon nanotubes (MWCNT‐OXI), nanosilica (NS), and its hybrid (MWCNT‐OXI/NS) in epoxy resin were produced and evaluated. The used nanoparticles were studied by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Raman spectroscopy while the nanocomposites were investigated in relation to its morphology, thermal, and mechanical properties. The results demonstrated significant improvements in the storage modulus (E′), glass transition temperature (T_g), and cross link density (CD), for the produced nanocomposites. Increases in thermal conductivity (TC) of up to 85% at 90°C were observed for the nanocomposites containing 1.0 wt% of the hybrid MWCNT‐OXI + NS nanofiller, when compared with neat polymer. It was also verified increases in the resistance to plastic deformation for the nanocomposites, maintained the polymer thermal stability with the addition of these nanoparticles. Finally, the use of MWCNT‐OXI and NS, combined or not, significantly improved the thermal and mechanical properties of polymer, showing multifunctional characteristics for the produced nanocomposites.

In this study, the theoretical welding parameters influencing porosity formation were examined with the aim of reducing or minimizing porosity levels. An experimental design was implemented using the Taguchi methodology for data analysis, resulting in an L9 orthogonal array matrix of experiments. The welding variables considered in the orthogonal array were peak current, peak time, and frequency. Nine lap welds were performed on CP780 steel using the gas metal arc welding process with pulsed arc (GMAW-P), employing an ER70S-3 electrode as filler metal. The percentage of porosity was determined as a response variable, and the actual heat input was treated as a covariable, thereby identifying the welding parameters with the predicted values. Three repetitions were conducted with the optimal welding parameters to validate the Taguchi prediction. The quality of the welds was assessed through radiographic inspection, and metallographic preparation was performed, revealing the microstructure with 5% Nital for 12 s. The samples were analyzed using an optical microscope, and images were obtained with the collage technique. The results showed that the welding parameters predicted by the Taguchi statistics were favorable for all three predicted welded joints. The maximum percentage of porosity obtained was 19%, which was reduced to 1% using the Taguchi methodology, demonstrating the effectiveness of this statistical tool for process optimization. It was observed that for heat input values of 230 to 250 J/mm, the presence of porosities is dramatically reduced, finding a very small window that allows the gases generated by the burning of zinc to be expelled to the surface.