Browsing by Author "Gómez-Mitxelena, Xabier"
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Item Effect of Temperature on Mechanical Properties of 9%Cr Ferritic Steel(2016) Peñalba, Felix; Gómez-Mitxelena, Xabier; Jiménez, José Antonio; Carsí, Manuel; Ruano, Oscar Antonio; Tecnalia Research & Innovation; EXTREMATMechanical properties of a 9%Cr-ferritic steel grade P92 experimental alloy are studied. The effect of cooling rate on the hardenability was determined by means of continuous cooling diagrams and data provided by hardness measurements and microstructure observations. A fully martensitic microstructure after the solubilization treatment over a wide range of cooling rates was revealed. As this grade of steels is mostly supplied in tempered condition, tensile tests to determine the variation of the strength and ductility at temperatures ranging from 20 to 650°C were carried out after a treatment of 3 h at 760°C. In addition, Charpy V-notch tests were conducted to characterize the impact toughness of the steel and the ductile-brittle transition temperature. Finally, the creep strength was determined from creep tests in the range 550 to 650°C.Item Modelling the optimum hot workability of TiB reinforced Ti-6Al-4 V alloy by stability maps(2016-02-17) García de Cortázar, Maider; Peñalba, Felix; Silveira, Elena; Gómez-Mitxelena, Xabier; Carsí, Manuel; Ruano, Oscar A.; Tecnalia Research & Innovation; CIRMETAL; Caracterización y Validación. Materiales; EXTREMATHot workability of Ti-6%Al-4%V and two whisker discontinuously reinforced materials, Ti-6%Al-4%V/1.2%TiB and Ti-6%Al-4%V/8.9%TiB, have been investigated. Hot uniaxial compression tests were carried out using a computer controlled thermomechanical simulator Gleeble machine at temperatures in the range 850 °C to 950 °C and strain rates ranging from 1 to 50 s−1. The microstructures and the compression test results were compared among the three materials. The Ti-6%Al-4%V/8.9%TiB material presented extensive cracking after deformation. In contrast, the Ti-6%Al-4%V/1.2%TiB material showed an interesting compromise between flow stress and workability. The parameters of the Garofalo equation were calculated for the three materials revealing apparent activation energies that increased with increasing TiB content. The modelling is carried out by stability maps that gives the temperature at a given strain rate to obtain optimal workability and the stresses that has to bear the equipment. Taken 5 s−1 as a reference strain rate, the temperature required to obtain a quality product increased from about 1143 K (870 °C) for the Ti-6-4 alloy without TiB to 1228 K (955 °C) for the 1.2%TiB and to 1283 K (1010 °C) for the 8.9%TiB material. Therefore, the production of parts of the TiB composites should be conducted at a higher forming temperature to avoid the presence of cracks