Advanced Engineering Materials

The front cover shows macroscopic morphology, computer tomography model and microscopic structure of Al foams produced by a novel dissolution-sintering process. Further details can be found in the article by N. Michailidis et. al. on page 29.

The back cover shows the color optical microstructure of as-cast Fe-18Mn-5.5Si-9.5Cr-4Ni alloy deformed by 6%. Further details can be found in the article by Y. Wen et. al. on page 48.

Endothelial cells form the inner lining of the cardiovascular system. It seems clear, that their surface structure and biochemistry is of critical importance for the vessels' unique blood compatibility. A logical first step to mimic these properties is the analysis of the native endothelial structure. Further details can be found in the article by J. Bossert et. al. on page 54.

An overview is provided of our current understanding of SCC of Mg alloys. TGSCC is caused by an interaction of H with the microstructure so a detailed study of H-trap interactions is needed in order to design alloys resistant to TGSCC. This understanding is urgently needed because prior research indicates that many Mg alloys have a threshold stress for stress corrosion cracking of the order of half the yield stress in common environments including high-purity water.

The surface condition of a glass melt has significant influence on the melting process. Thus it is important to keep the surface in a state of high optical transmission. This paper describes a new approach that has been tested out to obtain information about the melt surface using “small angle backscattered laser radiation”. The self-radiation of the melt however is something that complicates optical measurements.

Electrocoating of open cell aluminum foams with thin films of nanocrystalline nickel brings about a substantial enhancement of the energy absorption properties, the stiffness and the strength of the foams both under quasi-static and under impact loading.

Crystalline carbohydrate, commonly known as raw cane sugar, can be used as a new space-holder material for manufacturing metal foams with porosities in the range of 40–70%. The proposed method is capable of producing low-cost, environmentally friendly, net-shape metal foams with tailored distribution of pore size or relative density making them suitable for potential industrial applications.

Two types of new cellular metals are fabricated by assembling layer by layer helically-formed wires with metal hollow sphere (MHS) arrays. Compression tests reveal excellent energy absorption, which is attributed to combination of suppression of strut buckling in the WBK and moving plastic hinge occurring in the MHSs. The WBK-MHS hybrids outperform competitors in deformation energy absorption.

By applying an electrical current between the molten alloy and the Cu-mold during the copper mold casting, the surface tension of the conductive liquid is modified. By modifying the surface tension, the contact angle modifies as well, the global behavior of the molten alloy being drastically changed: (i) the alloy flows better into the mold and (ii) for the short casting time the cooling rate is smaller and the alloy remains liquid until the cavity is completely filled.

Iron aluminides show many properties useful for applications in power generation using fossil fuels, but suffer from relatively low ductility and poor creep strength at high temperatures. This short overview describes recent efforts, from the US and from Europe, aimed at removing such limitations by modification of alloy chemistry and by microstructure control.

A novel training-free cast FeMnSiCrNi shape memory alloy has been developed based on the formation of stress-induced ε martensite bands in a domain-specific manner realized by lathy ferrite phase. Before deforming, lathy ferrite phases subdivide grains into smaller domains. After deforming, the lathy ferrite phases make stress-induced ε martensite bands form in a domain-specific manner. Such a finding will provide a novel method for developing training-free FeMnSi shape memory alloys.

Cu₅₀Zr₅₀ and Cu_46.5Zr_48.5Al₅ rods are obtained by suction mould casting. Despite their similar compositions and identical preparation conditions, these two materials exhibit very different microstructures and mechanical properties. Nanoindentation tests performed in the different phases of the alloys indicate that the amorphous matrix is harder than the crystalline phases. The nanoindentation measurements also confirm that the austenite phase in the Cu_46.5Zr_48.5Al₅ alloy undergoes a martensitic phase transformation during compression.

Measurements of the practical adhesion of screen-printed Ag films on BaTiO₃ substrates have been completed, showing that the interfacial crack propagation energy decreases rapidly with increasing silver volume porosity. A geometrical model is proposed to estimate the interface porosity, which is relevant for adhesion concerns, in function of the volume porosity of the sintered silver layer. Experimental results present more consistent tendencies after this transcription.

The possibility of pressure slip casting of coarse granular suspensions is shown for laboratory and scale up trails. A commercial pressure slip casting machine which is remodeled for suspensions containing coarse grain is presented. A newly developed falling sphere viscometer is introduced to investigate the rheology of coarse granular suspensions. Fundamental characteristics of cake filtration are adopted to highlight the significant influences on the pressure slip casting process. Computer tomography is used to investigate the segregation of coarse particles.

The coagulation of particles was observed after freezing and thawing of a particles suspension. Here we show how freezing of a suspension can create internal forces comparable with hundreds MPa of conventional pressure. The way of freezing and particle characteristics determine the quantity and character of formed aggregates. The morphology/particle packing of the green body after thawing and drying significantly influences the sintering behavior of the ceramic compact. Our results demonstrate a possibility to substitute an effect of high mechanical pressure by freeze pressing without shape limitations.

Electrophoretic deposition with simultaneous electrolytic gas bubble formation is used for fabricating porous ceramic structures. The resulting pore channels are unidirectionally aligned. When gauzes of suitable mesh sizes are used as deposition electrode, a very regular arrangement of the tubular pores corresponding to the structure of the gauze can be obtained.

Zr(N)O coatings being synthesized by cathodic arc evaporation (P3e™ technology) show that cubic zirconia, ZrO₂, can be formed at low substrate temperatures of 550°C using nitrogen-oxygen reactive gas mixtures during deposition. The structural properties of the coatings obtained for different nitrogen-oxygen ratios have been investigated by XRD techniques. The composition of the layers was studied by RBS and ERDA and the layers morphology by cross sectional SEM. The phase stability of the cubic ZrO₂ phase has been investigated by in situ high temperatures XRD studies in air and reveals a multi step phase transformation.

More effective targeted delivery of pharmaceutical drugs for bone restoration and infection prevention is needed. There is intensified interest in harnessing the design of natural skeletons for regenerative medicine, which often possess superior qualities to their man-made counterparts. In this study, bioresorbable calcium phosphate microshells from beach sand show promise for gradual elution of drug compounds required for clinically acceptable bone repair.

Silicon nanowires (SiNWs) have found a wide range of applications in the field of electronics and optics due to their unique chemical and physical properties. The biocompatibility of undoped and n-type SiNWs, synthesized by metal-catalyzed chemical vapor deposition, was investigated in vitro, and compared with that for SiO₂-coated silicon wafers. According to the in vitro biocompatibility test results, we conclude that SiNWs may be considered as potential materials for biomedical applications.

A multifunctional calcium phosphate (CaP) nanocomposite is prepared by encapsulating alendronate drug in CaP nanoparticle and modifying the surface with a fluorescent rhodamine B dye. The pH sensitive CaP nanocomposite is capable of controlled drug delivery, and also senses the release by change in the fluorescence property.

HA/YSZ gradient coatings are successfully prepared on a Ti6Al4V substrate by magnetron sputtering. The gradient-HA coating had a dense structure, without the appearance of cracks. Linear-scanning analysis on the fracture surface shows that the chemical composition of the HA/YSZ coating presents a perfect gradient distribution. The atomic (Ti, Ca, P, Zr) intermixed zone in the interfacial field indicates that there is a diffusion layer (∼3–5.0µm) between the gradient coating and the substrate.

Living yeast (Saccharomyces cerevisiae) and bacteria cells (Rhodococcus ruber) can be embedded within magnesium phosphate cement (MPC). MPCs are produced by using a water-based slurry system of Mg₃(PO₄)₂ powder and ammonium phosphate solution allowing the gentle admixture of living microorganisms. The resulting bioactive composite materials showing important advantages, like a high mechanical, chemical and thermal stability, a gentle preparation process and the fabrication of molded, crack-free parts with low shrinkage. They can be used as new stable biocatalysts, e.g., for the bioconversion of glucose and phenol, respectively.

Unveiling the biomineralization process in a 3D scaffold of insoluble chitosan. The image shows: Ca²⁺–citrate ion pairs in a 3D insoluble chitosan scaffold (A)→hydrated amorphous calcium carbonate (ACC) precursor with complete disorder (B)→stable ACC particles with short range order of calcite structure (C)→transient ACC phase with short range order of calcite structure→calcite nanocrystals (D)→calcite polycrystals (E)→rough calcite mesocrystals (F)→smooth calcite mesocrystals (G).

Vinculin illustrating a large number of focal contact sites with higher expression level at the edges and around the cells associated with dense actin stress fibers in silicone-titania hybrid network structure elastomer.

The ideal artificial vascular graft would mimic the surface structure of native blood vessels to accomplish excellent biocompatibility. A logical first step in designing such a vascular graft is the analysis of the native endothelial structure and determination of the endothelial cell dimensions. To address this need, we broaden the relatively small number of qualitative and quantitative data available on the endothelium of human blood vessels by using SEM and quantitative image analysis.