F. Almeraya Calderon

Effect of Boron Additions on Sintering and Densification of a Ferritic Stainless Steel

The effect of boron additions on the densification of a ferritic stainless steel during sintering was studied. Experimental results showed that density and microstructure changed with the boron content. Boron promotes the formation of a liquid phase, which resulted from a eutectic reaction involving iron and chromium. The presence of the liquid phase modified the microstructure morphology, shape of porosity, density, and hardness.

Effects of Heat Treatments in Corrosion Behavior of HVOF-Sprayed Ni-Based Alloy Coatings

It is well known that sprayed Ni-based alloy coatings show good corrosion resistance. They have good wear resistance after adding W and Mo elements to the alloy. High-velocity oxygen-fuel (HVOF) spraying is a thermal spray technique well matched to obtain corrosion- and wear-resistant coatings. Post-spray treatments such as laser remelting, shot peening, HIP, sealing, and furnace heat treatments are also used to improve the density and homogeneity of sprayed coatings. The corrosion properties of Ni-based alloy coatings processed by HVOF thermal spraying were studied as a function of annealing heat treatment at 850 and 950 °C in atmosphere of vacuum and air. Immersion tests in HCl, NaOH, and water media with various electrochemical techniques such as linear polarization resistance (LPR) and potentiodynamic anodic polarization curves (PAPC) were employed to perform such evaluation. The microstructural characterization of the as-sprayed coatings was analyzed by scanning electron microscopy (SEM). The results show that when the heat treatment temperature increases, the corrosion current density gradually decreases. This implies that thermally treated coatings increase its corrosion resistance relative to the coating of the substrate and heat treatment. Finally, it was found that a heat treatment at 950 °C in vacuum atmosphere improves the corrosion resistance of Ni-based coating applied by HVOF thermal spray.

Citric Acid Passivation of 15-5PH and 17-4PH Stainless Steel Used in the Aeronautical Industry

In the aeronautical industry, the effects of corrosion are reflected in high costs of maintenance and equipment inactivity, as well as in safety risks for personnel. Modern aircraft are manufactured using different types of metal alloys, for example, civil aircraft are constructed with heat-treated aluminum alloys and military aircraft with titanium alloys and stainless steels. The objective of this study is to use electrochemical techniques to determinate the layer passivate of stainless steel (SS) 304, 17-4PH, and 15-5PH. Passivation of the SS was performed in 15% citric acid at temperatures of 25 and 49 °C. The corrosion kinetics was obtained using the electrochemical technique as potentiodynamic polarization curves (PPC) in a three-electrode system: the electrolytes used were sodium chloride (NaCl) and sulfuric acid (H2SO4). Passivation in citric acid allows obtain passive layers at temperatures of 49 °C with immersion times of 30 min. Precipitation hardening steels allow to obtain passive layers up to 360 mV in sodium chloride (NaCl), and in sulfuric acid there is a mechanism of passivation-transpassivation-secondary passivation, this due to the high electropositive values ​​of potential above 1000 mV.

Electrochemical Study of 17-4 and 17-7 PH Stainless Steels Used in the Aeronautical Industry

In the aeronautical industry, precipitation hardenable (PH) stainless steels are accessories used in aircraft, turbine blades, and other parts. These alloys are alloys of iron, chromium, and nickel, characterized by mechanical strength obtained through age hardening by heat treatment. The addition of elements such as Al, Ti, Mo, and Cu lead to the appearance of intermetallic compounds. In this work, we performed electrochemical corrosion testing of 17-4 PH and 17-7 PH stainless steels with cyclic polarization and linear polarization resistance tests, showing the susceptibly of these stainless steels to pitting and intergranular corrosion. These tests were carried out in an electrochemical cell with a saturated calomel reference electrode at room temperature. The solutions were hydrochloric acid (HCl), sodium chloride (NaCl), and neutral (H2O) environments. The results in the neutral environment showed that 17-4 PH had more pitting than 17-7 PH; they had similar behavior in a salty environment. 17-4 PH and 17-7 PH generally presented corrosion in an acid environment. The susceptibility to corrosion of stainless steel types 17-4 PH and 17-7 PH was demonstrated; however, the environment is a vital factor in the behavior of this steel.

Design of Wind Tunnel for Testing Stress Corrosion Cracking

Corrosion is one of the greatest threats to civil and military aircraft. In general, the materials that make up aircraft structures are subjected to stresses, causing embrittlement and consequent cracks and fractures. Corrosion and erosion of the aircraft coating, induced by the dynamic chemical environment of the atmosphere, manifests as pitting on the surface material. Because they concentrate the stress, these pits are vulnerable to stress corrosion cracking. In current stress corrosion cracking tests on aeronautics materials, parts constructed from corrosive media are held in universal machines. However, the obtained results do not reflect the flight conditions of the aircraft. Therefore, we propose wind tunnel tests that can assess stress corrosion cracking under simulated flight conditions.

Efecto de tratamiento térmico en aleaciones feal1% at li expuestas a pruebas de oxidación en diferentes temperaturas

La adicion de Li en aleaciones intermetalicas base Fe3Al ayuda en la mejora de propiedades mecanicas y resistencia a la corrosion. Las aleaciones se producen con tecnicas convencionales de vaciado usando crisoles de SiC y se someten a un tratamiento termico de 400oC por 144h. Se realizaron pruebas de oxidacion de alta temperatura en termobalanza con atmosfera estatica a temperaturas de 650, 800 y 900 oC las cuales indicaron una diferencia en la cinetica de oxidacion entre las muestras con tratamiento termico y sin el. Por analisis de Microscopia electronica de barrido se pudo ver que la capa de oxidacion es mas uniforme cuando se tiene tratamiento termico.