You Wang

First-principles Study of NiAl Alloyed with Rare Earth Element Ce

The structural, elastic, and electronic properties of NiAl alloyed with rare earth element (REE) Ce have been investigated by using density functional theory (DFT). It is found that Ce has a strong AI site preference and causes lattice distortion of NiAl. The calculation of elastic constants shows that Ce increased both the hardness and the ductility of NiAl, which could be explained by the formation of new ionic bonds between AI (and Ni) and Ce and the enhancement of covalent bonds in Ni 8 Al 7 Ce. Our results are in good agreement with the available experimental data and other theoretical results.

Cutting Performance of WC-Co Alloys Modified by Nano-Additives

In this paper, the microstructure of WC-Co alloys with and without nano-additives was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The hardness and fracture toughness was tested by using a Vickers hardness tester and a universal testing machine. The cutting test was carried out at different feed velocities (250 r/min and 320 r/min), and the contact pairs are cutting tools and 45# steel bars. Results showed that the hardness and fracture toughness of WC-Co cemented carbides with nano-additives are higher than that of WC-Co cemented carbides without nano-additives, and they are increased 10.21% and 19.69%, respectively. The flank worn width and crater width of cutting tools decrease greatly with the addition of nano-additives. For the nano-modified specimen with WC grain size of 7 μ m , both the flank worn width and crater width are the minimum after the cutting process. And there are little built-up layers and some pile-up regions on the flank face leading to high cutting performance for the nano-modified cemented carbides. There are some melted regions on the flank face of cutting tools without nano-additives, and the WC grains on the cross section of alloys without nano-additives show severe fragmentation. The wear type of WC-Co is flank wear, and the wear mechanism is abrasive, adhesion and oxidation wear.

Characterization of Wear and Corrosion Protective Coatings Formed on AZ91 Magnesium Alloy and SiCw/AZ91 Magnesium Matrix Composite by Microarc Oxidation

The wear and corrosion protective coatings were synthesized on AZ91 Mg alloy and Mg matrix SiCw/AZ91 composite by a microarc oxidation (MAO) technique in an alkali-silicate electrolyte solution. The phase structure of the coatings was analyzed using X-ray diffraction (XRD). The tribological properties of the coatings sliding against GCr15 steel were investigated on a pin-on-disc friction and wear tester. The morphology and elemental composition of the worn coating surface were determined by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The potentiodynamic polarizing curves were measured to evaluate the corrosion resistance of the coatings. The results showed that the application of the coatings changed evolution tendency of friction coefficients and wear mechanism. For coated Mg alloy and Mg matrix composite, both the wear resistance and corrosion resistance were improved greatly.

Preparation of 8YSZ and Double-Ceramic-Layer La2Zr2O7/8YSZ Thermal Barrier Coatings on GH4169 Superalloy Substrates and their Static High Temperature Oxidation Behaviour

Thermal barrier coatings (TBCs) are very important ceramic coating materials due to their excellent performance at high temperature. Double-ceramic-layer (DCL) La2Zr2O7 (LZ)/8YSZ TBCs, nanostructured single-ceramic-layer (SCL) 8YSZ and conventional SCL 8YSZ TBCs with the same thickness were fabricated by atmospheric plasma spraying in the present work. The static high temperature oxidation behaviour of the three as-sprayed coatings at 1000 and 1200 was investigated systematically. The results indicated that the LZ/8YSZ has higher oxidation resistance than that of SCL 8YSZ. The addition of LZ ceramic layer can increase the insulation temperature, impede the oxygen transferring to the bond coat and decrease the formation rate of the thermally grown oxide (TGO). The formation of the oxidized isolated islands in the bond-coat has decreased the effective thickness of the TGO at the bond coat/ceramic layer interface due to the depletion of the metallic elements in the bond-coat.

The influence of (510) step surface on the segregation of (110)surface of O/Rh x Pt 1−x alloy system

The atomic cluster models of (110) surface of Rh<inf>x</inf>Pt<inf>1−x</inf> disordered binary alloy were constructed under the condition of O adsorption or not, and the coverage rate of O is 0.5. Also the (510)^[1] step surface were constructed on each model. The environment sensitive inlaid energy (E<inf>ESE</inf>) and the electronic structure of the (510) step surface of O/Rh<inf>x</inf>Pt<inf>1−x</inf> system were calculated by Recursion method. The results of E<inf>ESE</inf> show that, the exists of (510) step surface increases the segregation of Rh on the surface of Rh-Pt. The electronic structure shows that in the case of O adsorption, the two peaks in the total density states on the alloy surface is more obvious because of the step stage which also decreased the total density states on the alloy surface.