Effect of amorphous-crystalline interfaces on the martensitic transformation in Ti 50 Ni 25 Cu 25

Abstract A partially crystallized amorphous Ti 50 Ni 25 Cu 25 melt-spun ribbon showing spherical particles in martensite has been investigated. Microstructural observations support the hindering of the martensitic transformation as well as the production of additional autoaccommodated structures nearby the interface compared with the ones used inwards

Two way shape memory effect in NiTiHf high temperature shape memory alloy tubes

[eng] Two-way shape memory effect (TWSME) in nano-precipitation hardened, Ni50.3Ti29.7Hf20 high temperature shape memory alloy (HTSMA) thin walled tubes and its thermal stability were investigated. Torsional TWSME was induced in the thin wall tubes by repeated thermal cycling across their martensitic transformation under applied shear stress. The effects of training parameters and geometric factors, such as the number of training cycles, shear stress levels, and thickness of the tube walls, on the resulting TWSME were evaluated. Thermal stability of TWSME was characterized as a function of annealing treatments at elevated temperatures. It was found that under 200MPa, 600 thermal cycles were sufficient to reach a two-way shape memory strain (TWSMS) as high as 2.95%, which was shown to be stable upon annealing up to 400°C for 30 minutes. This TWSMS was 85% of the maximum measured actuation strain under 200MPa. The microstructure after thermo-mechanical training was investigated using transmission electron microscopy (TEM), which did not indicate a significant change in precipitate structure and size after the training. However, small amount of remnant austenite was revealed at 100°C below the martensite finish temperature, with notable amount of dislocations. Overall, it was found that nanoprecipitation hardened Ni50.3Ti29.7Hf20 shows relatively high TWSMS and stable actuation response after much less number of training cycles as compared to binary NiTi and nickel lean NiTiHf compositions. Tube wall thickness and training stress levels have been found to have negligible effect on shape memory strains and number of cycles to reach the desired training level, for the ranges studied

Strain glass state in Ni-rich Ni-Ti-Zr shape memory alloys

[eng] This work reports the existence of the strain glass state in Ni-rich Ni-Ti-Zr shape memory alloys induced by the precursor stages of the H-phase precipitation, typical of this alloy system. The strain glass is detected from dynamic mechanical testing and microstructural observations by electron diffraction and Transmission Electron Microscopy (TEM). The elastic modulus measurements also suggest the elinvar effect in these alloys. The strain glass state of this material exhibits superelastic effect in compression with recoverable strain levels over 4% and very little temperature dependence of the stress-strain curves over a temperature range of 230 to 300 K

Forward jet production in deep inelastic ep scattering and low-x parton dynamics at HERA

Differential inclusive jet cross sections in neutral current deep inelastic ep scattering have been measured with the ZEUS detector. Three phase-space regions have been selected in order to study parton dynamics where the effects of BFKL evolution might be present. The measurements have been compared to the predictions of leading-logarithm parton shower Monte Carlo models and fixed-order perturbative QCD calculations. In the forward region, QCD calculations at order alpha_s^1 underestimate the data up to an order of magnitude at low x. An improved description of the data in this region is obtained by including QCD corrections at order alpha_s^2, which account for the lowest-order t-channel gluon-exchange diagrams, highlighting the importance of such terms in parton dynamics at low x.Comment: 25 pages, 4 figure

Ingeniería Forestal y ambiental en medios insulares

Las Islas Canarias a pesar de su reducida extensión y del relativo poco peso específico a nivel mundial, no es ajena a los problemas globales detectados en la conservación de bosques y en la importancia que éstos tienen para obtener beneficios económicos, socioculturales y ambientales. La gestión forestal sostenible es en este sentido esencial para asegurar y compatibilizar los diversos beneficios del bosque. El papel específico de los bosques y su gestión son sin embargo temas aún por conocer en nuestras islas, por lo que el Año Internacional de los Bosques ha representado una oportunidad única para dar a conocer el mundo forestal y acercarlo a nuestra sociedad. El presente libro consta de 25 capítulos donde se ha contemplado la mayoría de los aspectos a tener en cuenta en la planificación y gestión del medio forestal y natural. Desde la historia forestal del archipiélago, hasta el uso y técnicas de manejo de los recursos naturales, incluyendo el agua, la energía en forma de biomasa y la selvicultura

Effects of training on the thermomechanical behavior of NiTiHf and NiTiZr high temperature shape memory alloys

[eng] The effects of constant load thermal cycles (training) on the thermomechanical behavior of nanoprecipitation strengthened Ni50.3Ti29.7Hf20 (NiTiHf) and Ni50.3Ti29.7Zr20 (NiTiZr) high temperature shape memory alloys (HTSMAs) were compared. Thermomechanical properties were determined as a function of the number of training cycles, which consisted of up to 2000 isobaric thermal cycles at 300 MPa, between lower and upper cycle temperatures of 35 and 300 °C, respectively. In addition, the stability of the trained alloys was determined after exposure to thermal treatments at temperatures above the upper cycle training temperature. Training at 300 MPa significantly improved the actuation strain capability of the NiTiHf HTSMA at low stresses (i.e., 50 MPa) and resulted in a two-way shape memory strain (TWSMS) up to 1.9%, but essentially had no effect on the 300 MPa response. Training had less notable benefits in the case of the NiTiZr, producing negligible TWSMS, and resulting in a decrease in actuation strain capability at 300 MPa with repeated cycling. The benefits of training to the NiTiHf HTSMA were maintained after aging at 400 °C but were lost after exposure to 500 °C and above. Since training was not notably beneficial to the NiTiZr alloy and resulted in a loss in strain capability at 300 MPa, the high temperature annealing treatment actually recovered strain capability in the alloy under high stresses. Thesuperior TWSM response of the NiTiHf HTSMA as compared to the NiTiZr, was attributed to the highermelting temperature, and thus the lower homologous operating temperature of the former, when bothalloys were tested over the same temperature range