Advanced Engineering Materials

Thermal conductivity images of thermal barrier coatings are measured using time-domain thermoreflectance at a single delay time with micron-scale resolution. We find that the thermal conductivity of electron-beam physical vapor deposited 8 wt% yttria-stablized zirconia coatings for heat flow along both the through-thickness and in-plane directions is isotropic and uniform throughout the depth of the coating.

Although corrosion performance is currently a severe problem with magnesium alloys, the prospect for magnesium alloys is promising because of their attractive advantages and potential applications. How to solve the corrosion problem has now become an important issue in the application of magnesium alloys. The aim of this overview is to deepen the current understanding of corrosion and protection of magnesium and its alloys and to provide a base for future research work in this field.

A significant improvement of the room temperature ductility of fully nanocrystalline/glassy material can be achieved by developing a composite microstructure incorporating second phase precipitates with a different length scale in Zr-base multicomponent alloys. The formation of such a composite microstructure through simple casting techniques is described with the help of a metastable phase formation diagram.

Nanoscale and nanocomposite lithium electrodes synthesized using hydrogen-driven metallurgical reactions demonstrate reversible lithium cycling at low temperature (298 °C). This novel synthesis technique may also be applied to the preparation of new, nanostructured, hydrogen storage compounds. These materials offer enhanced kinetics, material stability and gravimetric capacity, with respect to their bulk counterparts.

Evidence for deformation mechanism crossover, i.e. from dislocation nucleation and motion to grain boundary mediated plasticity, has been sought for many years, but direct experimental confirmation remains elusive. By employing in situ dynamics dark field transmission electron microscope investigation on nanocrystalline nickel films with an average grain size of about 10 nm, the authors show conclusive experimental evidence that grain boundary plasticity has begin to dominate the deformation of as deposited Ni. The physical mechanism that governs the observed phenomenon is discussed.

The deformation behavior of thin film metallic glasses (TFMG) both as-deposited and annealed at the supercooled liquid region (SCLR) near the T_g were investigated by bending TFMG microbeams. It was found that the shear banding behavior, the stress for operating the first shear band and the plastic shear displacement along the shear band plane were dependent on annealing time at the T_g. The deformation mechanism and the controlling of mechanical properties of the TFMG were discussed.

Three kinds of precipitates were newly found, which are Mg₃Zn₃Y₂, MgZn and MgZn₂, in Mg-Zn-Y alloys both as-cast and after extrusion due to the composition concentration of Zn and Y on nanometer scale. This figure shows the high-resolution TEM image of MgZn precipitate in Mg substrate with the crystallographic parameters labeled in details. The boundary between MgZn precipitate and Mg substrate is very clear, no second phases were observed.

A staple from nickel-titanium shape memory alloy for foot surgery was prepared by metal injection moulding (powder metallurgy). After a thorough characterisation with a multitude of physical, chemical, mechanical, and biological methods, the prototype appears to be well suited for clinical use where a shape-memory effect is useful.

The mass production of micro parts is an important step towards the fabrication of integrated micro systems in large scale. Powder injection molding allows to produce parts not only in high quantity but also with reduced or even without finishing. The presented results show that the production of micro parts even in the sub-millimeter range is possible with this process when specially designed feedstocks, an adapted tool concept and optimized post processing are used.

Thermal conductivity images of thermal barrier coatings are measured using time-domain thermoreflectance at a single delay time with micron-scale resolution. We find that the thermal conductivity of electron-beam physical vapor deposited 8 wt% yttria-stablized zirconia coatings for heat flow along both the through-thickness and in-plane directions is isotropic and uniform throughout the depth of the coating.

The effective elastic modulus of a laser-engineered composite TiB2 coating on AISI 1010 steel substrate has been computed using different micromechanics models and compared with the experimental values. The Hashin-Shtrikman Bound method evinced most consistent effective elastic modulus values compared to Eshelby and Mori-Tanaka models.

Composite coatings were fabricated on the surface of pure titanium by laser alloying with B and Ni mixed powders. X-ray diffraction (XRD) spectrum shows that compounds such as TiB, TiB₂ and NiTi are formed in the coatings. With surface microhardness of 1600–1700 HV_0.1, the coatings have excellent wear resistance compared with the as received sample. The corrosion resistance of the annealed coatings is improved, but the unannealed coatings just have similar corrosion resistance as original pure titanium.

Knowledge about the erosion mechanisms of spark plug materials is of fundamental interest for the development of materials with a high resistance against electrode erosion. Endurance tests were performed to study the wear behaviour of platinum, iridium, silver and nickel as electrode materials for spark plugs between 200 and 900 °C. Oxidation must be the dominating mechanism, irrespective of the material. Additional calculations resulted in the suggestion of a plasma-assisted oxidation process.