ABSTRACT
Zinc titanate phosphors containing Eu3+/ Mn4+ as active ions were synthesized by using the solid-state method. XRD patterns of the powders confirmed that the samples were a mixture of cubic Zn2TiO4 and hexagonal ZnTiO3 phases. The luminous intensity of ZTO: Eu3+phosphors and ZTO: Mn4+ phosphors both increased with the increase of doping concentration, reaching the maximum at 2 mol% Eu3+ and 0.3 mol% Mn4+, respectively. In the photoluminescence spectra of ZTO: Eu3+(2 mol%) phosphors with different Mn4+ doping amounts excited at 465 nm, the emission spectra revealed the characteristic peaks of Eu3+ with low Mn4+ content, and with the Mn4+ content increasing, the emission spectra contained both Mn4+ and Eu3+ luminescence peaks. In the variable temperature spectra, the relative sensitivity of the samples was improved with the concentration of Mn4+ increasing and achieved the maximum value of 3.2 %/K.
ABSTRACT
The hot deformation behavior and dynamic recrystallization (DRX) of Fe-15Mn-15Al-5Ni-1C low-density steel in the as-cast state was investigated via hot compression experiments over temperature and strain rate ranges of 925 to 1150 °C and 0.01 to 10 s-1, respectively. A constitutive equation and a critical DRX model of the Fe-15Mn-15Al-5Ni-1C low-density steel were also constructed. The results showed that higher strain rates resulted in significant work hardening and subsequent rapid softening of the Fe-15Mn-15Al-5Ni-1C low-density steel, while lower strain rates resulted in predominantly steady-state flow behavior. The activation energy of deformation for the Fe-15Mn-15Al-5Ni-1C low-density steel was Q = 540 kJ mol-1 and the stress index was n = 4. The hot deformation mechanism was solute dragging and dislocation climbing, which was controlled by the strain rate. Increasing the deformation temperature or strain rate reduced the critical stress value σc of the DRX of the Fe-15Mn-15Al-5Ni-1C low-density steel and contributed to the DRX of austenite and δ-ferrite. The Fe-15Mn-15Al-5Ni-1C low-density steel after the hot compression deformation was mainly composed of austenite, ferrite, and κ carbide phases.
ABSTRACT
A Gleeble-2000D thermal simulation machine was used to investigate the high-temperature hot compression deformation of an extruded Mg-16Al magnesium alloy under various strain rates (0.0001-0.1 s-1) and temperatures (523-673 K). Combined with the strain compensation Arrhenius equation and the Zener-Hollomon (Z) parameter, the constitutive equation of the alloy was constructed. The average deformation activation energy, Q, was 144 KJ/mol, and the strain hardening index (n ≈ 3) under different strain variables indicated that the thermal deformation mechanism was controlled by dislocation slip. The Mg-16Al alloy predicted by the Sellars model was characterized by a small dynamic recrystallization (DRX) critical strain, indicating that Mg17Al12 particles precipitated during the compression deformation promoted the nucleation of DRX. Hot processing maps of the alloy were established based on the dynamic material model. These maps indicated that the high Al content, precipitation of numerous Mg17Al12 phases, and generation of microcracks at low temperature and low strain rate led to an unstable flow of the alloy. The range of suitable hot working parameters of the experimental alloy was relatively small, i.e., the temperature range was 633-673 K, and the strain rate range was 0.001-0.1 s-1.
