Correlation of work function and stacking fault energy through Kelvin probe force microscopy and nanohardness in diluteα-magnesium

Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca,Mg-Sr and Mg-Ba systems.This investigation incorporated the difference in the‘Work Function'(ΔWF)measured via Kelvin Probe Force Microscopy(KPFM),as a property directly affected by interatomic bond types,i.e.the electronic structure,nanoindentation measurements,and Stacking Fault Energy values reported in the literature.It was shown that the nano-hardness of the solid-solutionα-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba.Thus,it was shown,by also considering the nano-hardness levels,that SFE of a solid-solution is closely correlated with its‘Work Function'level.Nano-hardness measurements on the eutectics andΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys.Correlation withΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree,relatively simple atomic models and a number of assumptions.As asserted by this investigation,if the results of measurement techniques can be qualitatively correlated with those of the computational methods,it can be possible to evaluate the electronic structures in alloys,starting from binary systems,going to ternary and then multi-elemental systems.Our investigation has shown that such a qualitative correlation is possible.After all,the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level,that is,free electron density distributions.Our study indicated that the principles of‘electronic metallurgy'in developing multi-elemental alloy systems can be followed via practical experimental methods,i.e.ΔWF measurements using KPFM and nanoindentation.

Unveiling the reaction products in heat treated Si3N4–Ti joined ceramics by transmission electron microscopy

Joining is a crucial process for the production of complex-shaped advanced engineering materials.Deep understanding of ceramic–metal interfaces during joining or following heat-treatment steps is therefore of important concern in designing the new systems.Capacitor discharge joining(CDJ)method was firstly carried out to compose the ceramic–metal joint material by silicon nitride(Si3N4)–titanium(Ti)constituents.Afterwards,heat treatment was performed on the Si3N4-Ti joints in air atmosphere at 1000℃temperature to reveal the interface reactions and phases.Reaction layer that occurred between the Si3N4 and Ti interfaces and new phase formations were examined by transmission electron microscopy(TEM)-based various imaging and chemical analysis techniques.Electron transparent samples for TEM characterization were prepared by focused ion beam(FIB)milling and lifting method.Based on the detailed TEM results,Si and N diffusion arising from the Si3N4 ceramic was observed towards Ti metal foil side and further interacted with Ti atoms.The upshot of current diffusion was that Ti3N2 reaction layer with 50 nm thickness was formed at the interface while titanium silicon nitride(Ti6Si3N)matrix phase including dendritic-shaped Ti2 N grains occurred in the Ti interlayer.It is believed that our TEM-based microscopy results not only provide the knowledge on ceramic–metal joint materials by CDJ method,but also contribute new insights on the development of various new joint systems.

Solution combustion synthesis and electrochemical properties of yttrium-doped LiMnPO4/C cathode materials for lithium ion batteries

Phospho-olivine pristine LiMnPO4/C and yttrium-substituted LiMn1-xYxPO4/C(x=0,0.01,0.03,0.05)were synthesized by a solution combustion method.The effects of Y-doped on structure,morphology and electrochemical performances were investigated.From powder X-ray diffraction pattern,all substituted materials adopt an identical structure to that of the LiMnPO4 olivine structure,suggesting that the yttrium ion was well inco rporated into the crystal lattice,without any changes in the host crystal structure.The electrochemical impedance spectroscopy provides clearly that yttrium-substituting reduces the charge transfer impedance and improves the lithium ion diffusion through the structure.When x=0.01,the material shows an excellent capacity and stability during charge/discharge process.The initial specific discharge capacity can reach up to 156.84 mAh/g at C/20,with a coulombic efficiency of about 96.11%,which is 14%higher than that of the pristine material.The results confirm that the cyclic stability and the electrochemical performances of LiMnPO4/C are highly improved by Y-doping.