3,546 research outputs found
Plastic properties and microstructure evolution of 20CrMoA steel during warm deformation
The plastic properties and microstructure evolution of 20CrMoA steel was analyzed at 600-750 °C and strain rate of 0,01-10 s-1.The result reveals that the deformation behavior is hardening followed by softening at low strain rates(0,01 s-1 and 0,1 s-1), but hardening is dominant in the whole deformation process at high strain rates(1 s-1and 10 s-1) and low temperature(600 °C and 650 °C). The strain rate sensitivity exponent increases with the increasing deformation temperature except for 650 °C and high strain rate. The spheroidization mechanism of cementite is the mechanical fracture and the dissolution of cementite particles. At 700 °C, spheroidized particles are finer and their distribution is more uniform than that at 750 °C
Quenching and reactivation of electroluminescence by charge trapping and detrapping in Si-implanted silicon nitride thin film
In this brief, quenching of electroluminescence (EL) from Si-implanted silicon nitride (SNR) thin film under a forward bias has been observed. The quenching phenomenon is shown to be due to charge trapping in the defect states involved in the radiative recombination. The composite EL bands have different quenching rates, causing a change in the EL spectrum shape by the EL quenching. Release of the trapped charges by a low-temperature annealing at 120 °C or an application of a reverse gate bias can partially recover the quenched EL both in the intensity and spectrum shape. The quenching phenomenon poses a serious challenge to the application of Si-implanted SNR thin films in light-emitting devices. © 2009 IEEE.published_or_final_versio
Evolution of electroluminescence from multiple Si-implanted silicon nitride films with thermal annealing
Influence of thermal annealing on electroluminescence (EL) from multiple-Si-implanted silicon nitride films has been investigated. A reduced injection current and an enhanced EL intensity have been obtained simultaneously by increasing the annealing temperature, which results in a higher EL quantum efficiency. In addition, four emission bands are identified, and their peak energies, intensities, and full widths at half maxima are found to change with annealing temperature. A model is proposed to illustrate the carrier transport, the mechanisms of the four emission bands, and the evolution of the EL bands with annealing as well. The two major bands and the minor ultraviolet band are explained in terms of the recombination of the injected electrons in either the silicon dangling-bond (≡ Si 0) states or the nitride conduction band with the injected holes in either the band tail states above the nitride valence band or the valence band itself, while the minor near infrared band is attributed to the Si nanocrystals formed in the thin film. © 2009 American Institute of Physics.published_or_final_versio
Segregation of Mn, Si, Al, and oxygen during the friction stir welding of DH36 steel
This work investigates the role of welding speed
in elemental segregation of Mn, Si, Al, and oxygen during
friction stir welding (FSW) in DH36 steel. The experimental
work undertaken showed that when the speed of the
FSW process exceeds 500 RPM with a traverse speed of
400 mm/min, then elemental segregation of Mn, Si, Al,
and O occurred. The mechanism of this segregation is not
fully understood; additionally, the presence of oxygen
within these segregated elements needs investigation. This
work examines the elemental segregation within DH36
steel by conducting heat treatment experiments on unwelded
samples incrementally in the range of 1200–1500 °C
and at cooling rates similar to that in FSW process. The
results of heat treatments were compared with samples
welded under two extremes of weld tool speeds, namely
W1 low tool speeds (200 RPM with traverse speed of
100 mm/min) and W2 high tool speeds (550 RPM with
traverse speed of 400 mm/min). The results from the heat
treatment trials showed that segregation commences when
the temperature exceeds 1400 °C and Mn, Si, Al, and
oxygen segregation progress occurs at 1450 °C and at a
cooling rate associated with acicular ferrite formation. It
was also found that high rotational speeds exceeding
500 RPM caused localized melting at the advancing-trailing
side of the friction stir-welded samples. The study aims
to estimate peak temperature limits at which elemental
segregation does not occur and hence prevent their occurrence
in practice by applying the findings to the tool’s
rotational and traverse speed that correspond to the defined
temperature
- …