Lishu Zhang

Effects of Mn and Ti on microstructure and inclusions in weld metal of high strength low alloy steel

Abstract The influences of alloying elements on chemical composition of non-metallic inclusions, impact toughness and microstructure in weld metals of high strength low alloy steels have been studied. Results indicated that microstructure had changed from a mixture of acicular ferrite, proeutectoid ferrite, ferrite side plates and microphases to a mixture of acicular ferrite, bainite and microphases due to the addition of Mn and Ti. The impact toughness of weld metal was improved correspondingly. The volume fraction and composition of inclusions both influenced the proportion of acicular ferrite. Mn and Si based oxide globular inclusions located at the boundary of acicular ferrite plates in the weld metal produced using C–Mn–Si–Cu wire. When Mn and Ti were added to welding wires, the inclusions within acicular ferrite plates permitted fewer primary acicular ferrite plates to grow into relatively larger dimensions. Secondary acicular ferrites nucleating on pre-existing ferrite plates refined microstructure effectively.

Effects of inclusions on formation of acicular ferrite and propagation of crack in high strength low alloy steel weld metal

Abstract High strength low alloy steel was welded by gas shielded arc welding process without preheating. Microstructural characteristics of the weld metal, morphology of inclusions and crack propagation paths were investigated by means of optical microscopy and scanning electron microscopy. The chemical composition of the inclusion and element distribution across the inclusion were analysed via energy dispersive spectroscopy system. Results indicated relatively large inclusions with diameters of about 0·6–0·8 μm are much more effective in providing nucleation sites for acicular ferrite transformation and refining the microstructure within austenite grain than small ones with diameters of about 0·3–0·5 μm. When the main crack tip encountered inclusion, more crack paths would be initiated from the interface between inclusion and acicular ferrite plates.

Electronic transport properties of PbSi Schottky-clamped transistors with a surrounding metal–insulator gate

Sustaining Moores law requires the design of new materials and the construction of FET. Herein, we investigated theoretically the electronic transport properties of PbSi nanowire Schottky-clamped transistors with a surrounding metal–insulator gate by employing MD simulations and the NEGF method within the extended Huckel frame. The conductance of PbSi nanowire transistors shows ballistic and symmetrical features because of the Schottky contact and the resonance transmission peak, which is gate-controlled. Interestingly, the PbSi(8,17) nanowire FET shows a high ON/OFF ratio and proves to be a typical Schottky contact between atoms as described by the EDD and EDP metrics.

CH 3 NH 3 PbX 3 (X = I, Br) encapsulated in silicon carbide/carbon nanotube as advanced diodes

We employ first-principles density functional theory (DFT) calculations to study CH3NH3PbX3 (X = I, Br) and its encapsulation into the silicon carbide nanotube and carbon nanotube (CNT). Our results indicate that these devices show diode behaviors which act on negative bias voltage but do not work under positive voltage. When they are encapsulated into SiC nanotube and CNT, their electronic properties would be changed, especially, electric currents mainly exist at positive bias region. Corresponding transmission spectra and density of states are provided to interpret the transport mechanism of the CH3NH3PbX3 (X = I, Br) as a diode. These findings open a new door to microelectronics and integrated circuit components, providing theoretical foundation for innovation of the new generation of electronic materials.

Electronic transport properties of heterojunction devices constructed by single-wall Fe2Si and carbon nanotubes

The electronic structures of the armchair Fe2Si nanotubes are calculated by using the SGGA+U method. Novel heterostructure devices are prepared composed of single-wall Fe2Si nanotubes (Fe2Si NTs) and carbon nanotubes (CNTs). The results indicate that the (4,4) Fe2Si NT is a ferromagnetic half metal with 100% spin-polarization ratio at the Fermi energy level. These heterojunctions have spin-polarized transport properties but their spin-polarization ratios are relatively low. Interestingly, the (13,0) CNT–(n,n) Fe2Si NT–(13,0) CNT devices are all semiconductors but others are metallic. This study suggests that adding the novel Fe2Si NTs endows the CNTs with spin-polarized property and provides very valuable results for better understanding of the electronic structures of the heterostructure.