Study on the thermal deformation behavior and microstructure of FGH96 heat extrusion alloy during two-pass hot deformation

The change rules associated with hot deformation of FGH96 alloy were investigated by isothermal two-pass hot deformation tests in the temperature range 1050–1125°C and at strain rates ranging from 0.001 to 0.1 s^(-1) on a Gleeble 3500 thermo-simulation machine. The results showed that the softening degree of the alloy between passes decreases with increasing temperature and decreasing strain rates. The critical strain of the first-pass is greater than that of the second-pass. The true stress–true strain curves showed that single-peak dynamic recrystallization, multi-peak dynamic recrystallization, and dynamic response occur when the strain rate is 0.1, 0.01, and 0.001 s^(-1), respectively. The alloy contains three different grain structures after hot deformation: partially recrystallized tissue, completely fine recrystallized tissue, coarse-grained grains. The small-angle grain boundaries increase with increasing temperature. Increasing strain rates cause the small-angle grain boundaries to first increase and then decrease.

Microstructure and mechanical performances of CGHAZ for oil tank steel during high heat input welding

Microstructure and mechanical performances of the coarse grain heat-affected-zone （CGHAZ） for oil tank steel with different Ti content were investigated through Gleeble-3500, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometer. The results show that the strength and low- temperature toughness of base material are significantly improved for the high titanium content steel, but the impact toughness of CGHAZ is seriously deteriorated after the high heat input welding and declined sharply with the heat input increasing, while the effects of heat input on impact toughness are very weak for the low titanium content steel, impact toughness of which is gradually larger than that of high titanium content steel with the welding heat input increasing because of the granular bainite increasing, TiN particle coarsening, and （Ti, Nb） N composition evolution during the high input welding for high titanium content steel.

Preparation and radar-absorbing properties of Al2O3/TiO2/Fe2O3/Yb2O3 composite powder

Al2O3/TiOe/FeeO3/Yb2O3 composite powder was synthesized via the sol-gel method. The structure, morphology, and ra- dar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes （100-200 rim） and the other is spherical A1203 particles （smaller than 80 rim）. Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 （at 15.68 GHz） in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increas- ing matching thickness. The effective absorption hand covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.

Study on the preparation of Pt nanocapsules

Ag@Pt core-shell nanoparticles（Ag@Pt NPs） were prepared by a co-reduction method. Pt nanocapsules with diameters of less than 10 nm were obtained by an electrochemical method. Cyclic voltammetry（CV） scanning was used to cavitate the Ag@Pt NPs, and the morphology, structure, and cavitation conditions were studied. The results indicate that the effective cavitation conditions to obtain Pt nanoparticles from Ag@Pt NPs are a scanning voltage of 0 to 0.8 V and continuous CV scanning over 2 h. This cavitation method is also applicable for the syntheses of Ir, Ru, and Ru-Pt nanocapsules.

Influence of Plastic Deformation on Thermal Stability of Low Carbon Bainitic Steel

Bainite is metastable due to its high dislocation density, and consequently bainitic steel structures have the problem of thermal stability. Plastic deformation of bainite can further increase dislocation density and change dislo- cation configuration at the same time. The influence of plastic deformation on thermal stability of low carbon bainitic steel during isothermal holding at 650 ℃ was investigated with hardness analysis, in-situ tracing metallographic analysis and transmission electron microscopy, Bainite in the low carbon steel evolves into polygonal ferrite via recov- ery and reerystallization during isothermal holding at 650 ℃. There is a considerably long period （about 20 h） be tween end of recovery and commencement of recrystallization of undeformed bainite, in which the hardness of the sample maintains a constant value slightly lower than that before reheating. Slight plastic deformation of bainite in- duces rearrangement of pre existing dislocations and forming of low-energy dislocation cells inside bainite laths, which has little influence on thermal stability of bainite, whereas heavy plastic deformation results in obvious dislocation multiplication and accelerates recrystallization of bainite. Recrystallization of heavily-deformed bainite occurs preferen tially at prior austenite grains boundaries. The samples subjected to heavy torsion exhibit obviously higher thermal stability than the samples subjected to heavy compression despite their same initial hardness, which can be attributed to different influences of torsion and compression on dislocations and boundaries of bainite.