Efecto de la precipitación en la tenacidad criogénica en aceros inoxidables con nitrógeno

Los aceros inoxidables austeníticos JK2, JJ1 y JN1 se envejecieron isotérmicamente a temperaturas de 600 a 900 ºC por distintos tiempos, para estudiar la evolución microestructural y su efecto en la tenacidad a la fractura a temperaturas criogénicas. La energía de fractura Charpy muesca-V a 77 K muestra una significante disminución con el tiempo de envejecido en los aceros JJ1 y JN1 debido a sus altos contenidos de C y N. Las fractografias de MEB de las muestras ensayadas por CMV muestran fractura frágil cuya fracción aumenta con el tiempo y temperatura de envejecido

Synthesis of TiB2-Ni3B nanocomposite coating by DC magnetron sputtering for corrosion-erosion protection

Significant contribution on corrosion-erosion resistance of Ni _3 B-TiB _2 nanocomposite coating of 1 μ m of thickness, deposited by DC magnetron Sputtering on stainless steel 304 substrates was studied. Nickel phase ( γ Ni) plus Ni _3 B-TiB _2 phases were synthesized previously by Mechanical Alloying (MA). Solid cathode (76.2 mm of diameter and 3 mm of thickness) used to grow thin films was manufactured with the alloyed powders, applying a uniaxial load of 70 MPa at room temperature and sintered at 900 °C for two hours. Microstructure and mechanical properties of the coatings were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation, and wear test with a ball-on-disc tribometer. Compact coating of Ni _3 B-TiB _2 with a microstructure of prismatic crystals after annealing treatment, showing a uniform coating with good adherence and low friction coefficient of 0.5, correlated with a low roughness of Ra ≈ 0.0439 ± 0.0069 μ m. The average hardness of 537.4 HV (5265.0 MPa) and wear coefficient at room temperature of 2.552E-10 m ^2 N ^−1 correspond with medium-hard phases with an elastic-plastic behavior suitable for fatigue applications. Geothermal fluid modified was synthesized in the lab with NaCl/Na _2 SO _4 to evaluate the corrosion resistance of the films in a standard three electrodes cell, characterizing a corrosion rate of 0.0008 and 0.001 mm*year ^−1 at 25 and 80 °C respectively during 86.4 ks (24 h) of exposition; showing a resistive coating without corrosion products and with good response to the geothermal environment

Thermal, Mechanical and UV-Shielding Properties of Poly(Methyl Methacrylate)/Cerium Dioxide Hybrid Systems Obtained by Melt Compounding

Thick and homogeneous hybrid film systems based on poly(methyl methacrylate) (PMMA) and CeO2 nanoparticles were synthesized using the melt compounding method to improve thermal stability, mechanical and UV-shielding properties, as well as to propose them for use in the multifunctional materials industry. The effect of the inorganic phase on these properties was assessed by using two different weight percentages of synthesized CeO2 nanoparticles (0.5 and 1.0 wt %) with the sol–gel method and thermal treatment at different temperatures (120, 235, 400, 600 and 800 °C). Thereafter, the nanoceria powders were added to the polymer matrix by single screw extrusion. The absorption in the UV region was increased with the crystallite size of the CeO2 nanoparticles and the PMMA/CeO2 weight ratio. Due to the crystallinity of CeO2 nanoparticles, the thermal, mechanical and UV-shielding properties of the PMMA matrix were improved. The presence of CeO2 nanostructures exerts an influence on the mobility of PMMA chain segments, leading to a different glass transition temperature