In this study, plates of Inconel 600 superalloy were gas metal arc welded to investigate the effects of the welding process on the creep behavior of the welded samples and compare it to the creep behavior of samples in the as-received condition. Creep tests were performed at two temperatures (600 and 650 °C) with different stress levels. During the welding process, three distinctive microstructural zones are generated, i.e. welded material, heat affected zone, and base metal that may affect the properties of the welded joint. Microstructural, elemental analysis of samples was conducted using Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The experimental results show that creep rupture preferentially occurs in the heat-affected zone of the base metal at 4 mm from the fusion line and that the creep behavior of welded samples is different from that of the base metal. These results can be used in the design of structural components to assure their structural integrity.

ZnO films grown by ultrasonic spray pyrolysis with different Ga contents in the range of 1.0-6.5 at% on quartz substrates have been studied. The ZnO:Ga films were annealed at 400°C for 4h in a nitrogen flow. Morphology, emission, transmittance, absorbance and electrical resistivity were controlled. It is revealed that with a small content of Ga ≤ 4.0 at%, the ZnO:Ga films maintain a flat morphology, their transmittance increases to 86% together with the increase of the ZnO optical bandgap to 3.28 eV and the intensity enlargement of the near band edge (NBE) emission band A (3.188 eV). Furthermore, the new NBE emission band B (3.072 eV) appears in photoluminescence (PL) spectra at Ga contents ≥ 1.5 at%. Simultaneously, the process of decreasing electrical resistivity becomes saturating. The last effect is attributed to the self-compensation effect in n-type ZnO:Ga films related to the generation of acceptor type complexes (VZn2- - GaZn+). The thermal quenching of the PL intensities of the A and B PL bands is studded at 18-290K, which allows assigning the PL band A to the LO-phonon replica of the free exciton emission and the band B to the emission in donor-acceptor pairs: shallow donors - acceptor complexes (VZn2- - GaZn+). The NBE emission intensity drops and the ZnO optical bandgap demonstrates the shift to a lower energy at Ga doping up to ≤ 6.5 at%. Optimal Ga concentrations have been estimated to produce ZnO:Ga films with flat morphology, high optical transmittance and bright NBE emission.

In recent years there has been an increase in the field of research of advanced steels that have excellent mechanical properties combining high strength with excellent ductility. Within this range of advanced steels are the stable austenitic phase steels at room temperature of twinning induced plasticity known as TWIP. An important aspect to highlight about TWIP steels is their addition with different microalloying elements, generally less than 0.20 wt. %, which are forming precipitated phases such as carbides, nitrides and carbonitrides, and directly or indirectly control and/or modify microstructure and mechanical properties in these steels. Microalloying elements can cause a higher degree of hardening due to the formation of precipitates and grain refinement. The present research work studies the inclusions and second-phase particles formed in Fe–21Mn–1.3Si–1.6Al TWIP steels microalloyed with Ti, Nb, V, Mo and Ti/B in as-solution condition. TWIP steels melted in induction furnace were homogenized and hot-rolled at 1200 °C with reduction of 60 %. Subsequently, rolled plates were solubilized at 1100 °C followed by water quench. Thermodynamics-based predictions of inclusions and second-phases of different TWIP steels were carried out using JMatPro®V.9.1.2. Metallographic characterization was carried out by light optical and scanning electron microscopies (LOM, SEM), while second-phase particles characterization was performed using energy dispersion spectroscopy (SEM-EDS). Also, Vickers microhardness tests were carried out in accordance to ASTM E92 standard. In general, results showed the formation of inclusions of AlN and MnS at higher temperatures, which act as nuclei points for the precipitation particles of each type of microalloying element (TiN, TiC, Nb (C, N), VC and MoC) at lower temperatures. The studied TWIP steels exhibit similar microhardness values, since the microalloying elements are mostly dissolved in solid solution. The TWIP steels microalloyed with V and Ti exhibited the highest microhardness values.

This work analyzes the effect of rare earth additions to an Inconel 718 superalloy; for this purpose, two 8 kg ingots of a commercial composition of Inconel 718 were made in a vacuum induction furnace. One of them (In718) with the base composition and the other one (In718RE) with an addition of 0.04wt% of mischmetal (rare earths alloy based on cerium and lanthanum). Both alloys were cast into metallic molds into the vacuum chamber and let to solidify. The alloys were then solubilized for two hours at 1155 °C to eliminate deleterious phases, rolled at 1100 °C to get a reduction of 50% in thickness, then aged for 16 hours at 720 °C and 620 °C by 8 hours each. A complete microstructural characterization was undertaken by optical and electronic (SEM and TEM) microscopy and X-ray diffraction. Mechanical characterization was done by hardness tests, tensile and Charpy impact tests. Results show a slight improvement of the tensile and hardness values for the alloy with rare earth additions. However, no notorious difference was observed during the impact tests, since both alloys show the same values. These mechanical results are discussed in terms of the obtained microstructure. Both alloys are mainly composed by γ, γ´, γ´´ and carbides. It was observed that primary carbides nucleate rare earth particles; therefore, higher number of carbides and of larger size (according to a size distribution) are observed in the alloy with rare earth additions. The presence of such carbides prevents the grain growth during the thermomechanical processing which in turn improve the mechanical properties.

Studies have shown that local laser heating/“drilling” of composite large-porous ceramics consisting of aluminosilicates and glass phase is based on melting and ablation processes that lead to the formation of holes in a porous specimen. The interaction of the components of the composite in the high-temperature heating zone is accompanied by the formation of glass-phase melt of new composition. The advance of the melt deep into the sample along channel-like pores of the main ceramic material depends on the viscosity of the melt (i.e., the irradiation mode) and the cooling rate of the melt (i.e., the thermo-physical properties of the ceramics and glass phase). The development of gas-dynamic impact in the laser heating zone leads not only to the ejection of a part of the melt from the channel, but also to the compaction of the ceramics adjacent to the walls of the vitrified channel. These effects depend heavily on the ceramic-to-glass phase ratio and the porosity of the initial ceramic. It has been established that “laser perforation” of highly porous aluminosilicate ceramics leads to the hardening of the coarse-porous ceramics due to the formation of holes with strong walls, consisting of layers of the glass phase and compacted ceramics in the sample.

The PA6G blue is a polymeric material for great versatility of engineering applications that required good mechanical and tribological properties such as gears. The focus of this study was to investigate the mechanical properties as well as the friction and wear resistance of a commercial PA6G blue under biodegradable external lubrication, to evaluate its potential use for gear applications. Firstly, the PA6G blue was characterized by FTIR analysis in order to identify the characteristic chemical groups of this polymer. The mechanical characterization was performed by tension and hardness tests according to the standards ASTM D638 and ASTM E10, respectively. Subsequently, friction tests were carried out on a tribometer with pin-on-disk configuration based on the ASTM G99 standard, in dry and lubricated conditions. Natural castor and canola oils were employed as bio-lubricants, as well as their mixture at 50% by volume. The results exhibited that the PA6G blue exhibit good mechanical performance as that required by gear fabrications. Besides, the friction performance showed a low friction coefficient of 0.11 in the dry condition that decreased about 50% in lubricated tests, obtaining a friction coefficient value of 0.054.

Titanium alloys have been successfully used in the energy industry due to their stability at high temperature service, good mechanical properties and corrosion resistance. The near-α Ti-6%Al-1.5%V-1.0%Mo-0.5%Zr-0.1%C alloy, has been successfully used in several parts for geothermal energy generation. Several studies have concluded that the wear behavior of Ti alloys is generally poor; however, the specific tribosystem must be analyzed. This work analyzes the additions of 0.3%Ru, and variations of the V and Mo contents on the wear performance of a Ti alloy. Different combinations of α+β and degrees of microstructural refinement were observed depending on the composition. Wear test were undertaken by using a dry sliding block-on-ring configuration under the ASTM G77 standard. Two different loads (7 and 25 N) were used against a M2 hardened steel ring as a counter face with a hardness of 790 HV. Results showed that for the 7N load, the wear behavior is related to the volume fraction and thickness of the α phase; on the other hand, for the 25N load tests, the wear losses are directly proportional to the bulk hardness of the alloys and the α plate thickness, for this condition, best wear performance was achieved by the alloy 3 which contains 1.0wt%V, 1.8wt% Mo and 0.25wt% Ru. From the experimental results of the present study, it has been found that the wear behavior is directly related to the microstructure, e.g. amount of phases, refinement degree, applied load, and, in a lesser extent to the bulk hardness.

From the present study, vanadium additions up to 6.4% were added to a 14%Cr-3%C white iron, and the effect on the microstructure, hardness and abrasive wear were analysed. The experimental irons were melted in an open induction furnace and cast into sand moulds to obtain bars of 18, 25, and 37 mm thickness. The alloys were characterized by optical and electronic microscopy, and X-ray diffraction. Bulk hardness was measured in the as-cast conditions and after a destabilization heat treatment at 900°C for 45 min. Abrasive wear resistance tests were undertaken for the different irons according to the ASTM G65 standard in both as-cast and heat-treated conditions under a load of 60 N for 1500 m. The results show that, vanadium additions caused a decrease in the carbon content in the alloy and that some carbon is also consumed by forming primary vanadium carbides; thus, decreasing the eutectic M7C3 carbide volume fraction (CVF) from 30% for the base iron to 20% for the iron with 6.4%V;but overall CVF content (M7C3 + VC) is constant at 30%. Wear behaviour was better for the heat-treated alloys and mainly for the 6.4%V iron. Such a behaviour is discussed in terms of the CVF, the amount of vanadium carbides, the amount of martensite/austenite in matrix and the amount of secondary carbides precipitated during the destabilization heat treatment.

From the present work, the wear behavior of aged Ni-based superalloy was analyzed under dry sliding conditions. Such alloy was melted in a vacuum induction furnace and cast into a ceramic mold. Then the alloy was solubilized at 1080°C for 4 hours and then aged at 760°C for 4, 8, 16, 24, 48, 72 and 150 hours. The alloy was characterized as-cast and also in the heat-treated conditions by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Mechanical characterization included just Vickers hardness and wear resistance under dry sliding conditions by a block on ring configuration according to the ASTM G77 standard. Wear tests were undertaken for 2000 m at a speed of 0.7 ms-1 at two different loads (25 and 78 N). The worn samples were analyzed by an optical profiler to determine the wear volume and by SEM to analyze the worn surface and the microstructure below the worn surface. The main findings indicate the formation of an oxide layer mainly formed by Cr and Ni during sliding. The thickness of such a layer is about 10 μm for short aging times and about 5 μm for longer aging times. For this load, the wear resistance was 50% higher for the shorter aging times than that for the longer aging times. This behavior is described in terms of the thickness of the protecting layer, and on the availability of chromium to form such a layer since it forms Cr23C6 at long aging times. On the other hand, for a load of 78 N the wear behavior is in agreement with hardness. Wear resistance increases with aging time due to the higher precipitation of prime gamma phase.

Sintering of Si3N4 compounds requires additives that promote densification through the dissolution-precipitation mechanism in liquid phase sintering. The sintering of the Si3N4 with the SiO2-Y2O3-Al2O3 system has been extensively studied. Nevertheless, because SiO2 depends on the natural amount on the Si3N4 surface, little has been studied about SiO2 control. A pre-sintering treatment can increase the content of SiO2 through controlled oxidation of Si3N4. In this work the effect of the additive content on the densification of Si3N4 composite ceramics was evaluated. For this purpose, powder mixtures of Si3N4, Y2O3 and Al2O3 were prepared. The Y2O3 and Al2O3 ratio were modified in percentages of 4, 8 and 12% by weight. The mixtures were compacted and pre-sintered at 1300°C for 1 hour. Then, these were sintered at 1450°C for two hours. The samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results showed that during pre-sintering, the Y5(SiO4)3N phase is formed; then, it's subsequently oxidized at the sintering stage. A second phase identified as Y3Al5O12 was found in samples with higher proportions of Al2O3. Composition and quantity of the observed phases depend of Y2O3 and Al2O3 proportion in the added additive.