Browsing by Keyword "Electron microscopy"
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Item The initial stage of liquid phase sintering for an Al-14Si-2.5Cu-0.5Mg (wt%) P/M alloy(2010-06) Arribas, I.; Martín, J. M.; Castro, F.; TRAZABILIDAD CIRCULARThe present paper focuses on the initial stage of the liquid phase sintering (LPS) of a commercially available P/M Al-Si alloy, with nominal composition Al-14Si-2.5Cu-0.5Mg (in wt%). The microstructural examination of the as-received powder showed that it is constituted by pure Al particles and master alloy particles with composition Al-28Si-5Cu-1Mg (in wt%). Its compressibility is lower than for the conventional elemental P/M aluminium premixes, but it is still better than for prealloyed Al powders and other P/M powders. Thermogravimetry experiments showed that the elimination of the organic lubricant takes place between 275 and 490°C during heating to the sintering temperature. The phase transformations leading to the formation of the liquid phase were studied by differential scanning calorimetry (DSC). The dimensional changes associated with the generation of the liquid were measured by dilatometry. Samples quenched into water from different temperatures (between 450 and 575°C) and times (between 0 and 30min) were studied to reveal the microstructural evolution of the alloy. The first liquid is formed inside the master alloy particles at around 505°C. This liquid spreads across the compact, enhancing the chemical homogenization of the material. The alloying elements diffuse from the liquid inside the originally pure Al particles, reducing their melting temperature. This alloying process is almost concluded at around 535°C. When the temperature is increased the liquid starts to be formed also in the originally pure Al particles. The melting of the FCC Al-rich phase finishes around 575-590°C. The full melting of the alloy occurs at about 635-645°C. After analyzing the different possible causes, it is concluded that the main swelling mechanism is the volume change associated with the melting of a fraction of the material when the temperature is increased. The phases detected by X-ray diffraction (XRD) in the as-received powder and in the sintered compact are FCC Al-rich solid solution, Si, θ-phase (CuAl2), and Q-phase (Cu2Mg8Si6Al5).Item Roughening of metallic biomaterials by abrasiveless waterjet peening: Characterization and viability(2011-04-04) Barriuso, S.; Lieblich, M.; Multigner, M.; Etxeberria, I.; Alberdi, A.; González-Carrasco, J. L.; FABRIC_INTELThis study addresses the roughening of AISI 316 LVM and Ti6Al4V by waterjet peening (WJP) without abrasive particles, looking for rough surfaces free of embedded particles that could act as severe notches. Strong parameters have been selected to characterize and check viability of abrasiveless WJP; a water pressure of 360. MPa and two slow traverse velocities: 0.05 and 0.1. m/min. After processing, large number of pits with undercuts plus some larger intrusions are observed, which are more abundant and larger in the steel specimens and in those treated with the lower traverse speed. Cross sectional examination of 316 LVM reveals a significant grain size refinement in the subsurface zone, 10-20. μm wide, that exhibits a submicrometric/nanometric grain size, accompanied with a hardness gradient (50% increase) that extends to a depth of up to about 100. μm. The analysis of the magnetic hysteresis loops discards the presence of strain induced α-martensite. No hardness or microstructural gradient was developed in the Ti6Al4V alloy. The results indicate that in AISI 316 LVM the volume loss occurs through hardening of the subsurface, embrittlement, crack formation and erosion. In Ti6Al4V the material removal may take place first at the vanadium reach β-phase.Item Thermal shock performance of carbon-bonded carbon fiber composite and ceramic matrix composite joints for thermal protection re-entry applications(2017-02-15) Triantou, K.I.; Mergia, K.; Perez, B.; Florez, S.; Stefan, A.; Ban, C.; Pelin, G.; Ionescu, G.; Zuber, C.; Fischer, W.P.P.; Barcena, J.; POLIMEROS; EXTREMATHybrid thermal protection systems for aerospace applications based on carbon-bonded carbon fiber composite (CALCARB®) and ceramic matrix composites have been investigated. Two types of ceramic composite materials were considered, Cf/SiC (SiCARBON™) and C/C-SiC. The ablative material and the ceramic matrix composite were joined using alumina, graphite and zirconia-zirconium silicate based commercial high temperature adhesives and their performance on thermal shock tests was evaluated. Microstructural analysis of the joints after thermal shock tests was conducted using optical microscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Both material combinations survive the thermal shock tests for the structures in which zirconia-zirconium silicate and graphite based adhesives were employed.