Advanced Engineering Materials

The cover shows the in-situ diffraction setup. A fine synchrotron beam transmits the sample situated in a (heated) load frame and scatters into Debye-Scherrer cones. Large crystallites map onto spots onto the 2D detector rather than continuous rings. In the background, the intensity distribution of one selected reflection - here beta-Zr 110 - is plotted in color scale as a function of azimuthal angle (horizontal axis) and time (vertical axis) revealing the different states during thermo-mechanical processing. More details can be found in the article by K.-D. Liss on page 637.

The cover shows life and dead assay demonstrating living cells within a cellulose sulfate capsule. More information can be found in the article by J. M. Lohr et al. on page B129.

This review gathers together details on the processing of piezo-ferroelectric ceramic materials by spark plasma sintering. Results here reported clearly indicate that SPS is a powerful technique, opening the possibility of processing functional ceramics with a controlled (sub-micron or even nanoscale) grain size and, therefore, investigating size effects in this kind of system.

Bulk titanium foams were prepared by emulsion templating during slip casting. The emulsion template was stabilized using partially hydrophobized titanium particles while the continuous phase consisted of a titanium hydride powder suspension. Sintering was performed in inert atmosphere. The use of titanium hydride resulted in lower sintering temperatures and denser, stronger struts. Both homogeneous foams with high compressive strength and structures with a gradient in pore size were obtained.

Dynamic recrystallization and related effects have been followed in situ and in real time while a metal undergoes rapid thermo-mechanical processing. Statistics and orientation correlations of embedded/bulk material grains were deduced from two-dimensional X-ray diffraction patterns and give deep insight into the formation of the microstructure. Applications are relevant in materials design, simulation, and in geological systems.

The modulated structure of the AlCrFeCoNiCu high-entropy alloy consists of NiAl intermetallics (β′) and a (α-Fe, Cr) solid solution (β). The formation of the NiAl intermetallics greatly affects the strengths and magnetic properties of the Al_xCrFeCoNiCu alloys. Evidently, the AlCrFeCoNiCu alloy cannot be treated as a solid-solution alloy.

The nanomechanical behavior of NiAl derived from explosively RNLs in reactive solder joints is studied using in situ nanocompression and nanoindentation. We report the direct analysis of <011> slip and discuss the role it plays in the much disputed ductility of NiAl. The hardness, modulus, and residual stress in the NiAl layer are studied by load-displacement curve analysis.

FSP is used to introduce Al₂O₃ nano-sized particles to an Al 6061 alloy surface to form a hard, strong, and wear-resistant Al-Al₂O₃ nanocomposite layer. The residual stresses in the FSP zones (with and without Al₂O₃ particles) have been quantitatively analyzed using neutron diffraction. Results indicated tensile macro-level residual stresses in all three directions with peak values around 100 MPa longitudinally.

The evolution of microstructure and hardness with equivalent strain was studied in magnesium alloy AZ31 bars fabricated using a process of multi-pass caliber rolling at 473 K. The inhomogeneity of hardness throughout the cross section in the rolled bars was very similar to that of the strain predicted from FE simulation. The caliber rolling produced a fine-grain structure below 2.5 µm in a bulk sample with a length of over 1000 mm.

The infiltration mechanism of X3CrNi13-4 in titanium activated porous alumina preforms has been studied. Investigations revealed isolated steel-covered titanium particles beyond the infiltration front. The only transport path possible for the steel to form such wetted islands is through the gas phase. Supersaturation due to the mixing of the steel gas phase with the titanium rich gas phase over the activator particle surfaces is proposed as condensation mechanism. Progressive condensation leads to the formation of a melt network, which serves as pathway for the original steel melt to infiltrate the preforms and to fill the remaining pore space in the non-wetting X3CrNi13-4/Ti-Al₂O₃ sytem.

In this study, CrSiN/ZrN multilayer coatings were prepared by a reactive magnetron sputtering system. The evolution of their microstructure, mechanical, and tribological properties as a function of the multilayer modulation period was studied. The results showed that the multilayers had a good modulation structure. CrSiN and ZrN individual layer in the multilayers were “amorphous-like” and amorphous structure, respectively.

PVD coated metal forming tools may enormously reduce tool and work piece wear, friction and forming capacities. A PVD deposited TiZrN/CrN + CrN material system is presented for application on incremental sheet forming tools. This work reports on coating process development and tribological investigations leading to a clear friction reduction and wear protection.

The present work deals with the chemical removal of the α-case layer formed during precision casting of cellular TiAl6Nb7 sponges for biomedical applications. The major part of the brittle α-case layer can be attributed to chemical reaction between titanium and the investment mold components. To improve the ductility of the cell struts by eliminating the brittle surface, a pickling-vibration treatment was developed by which the α-case layer is chemically removed.

Matrix assisted pulsed laser evaporation (MAPLE) was used to coat Bioglass-based tissue engineering scaffolds with poly(D,L lactide). The polymer penetrated to some extent from the surface producing a graded porous composite material. This structure can be beneficial for application in osteochondral tissue engineering, where composite scaffolds are required exhibiting two distinct regions, one for cartilage integration (biopolymer) and the other one for bone contact (bioactive glass).

To mimic natural bone, a tissue engineering scaffold was developed that combines inorganic and organic components of natural bone, its pore diameter, and its interconnected structure. Collagen was coated onto a PLLA/PCL scaffold and hydroxyapatite particles were delivered throughout the polymer matrix much more easily than with other techniques thanks to the porosity-forming method of combining two porogens, namely, salt leaching and supercritical CO₂ extraction. Compared with other coating techniques, this procedure can be performed readily and homogeneous 3D hydroxyapatite coating was achieved.

Cellulose-based scaffolds osteoactivated with different sodium silicate coatings (pure and bisphosphonate or strontium enriched respectively) can serve as long-term depots for a slow drug-release. Thus they are a promising and cost-saving alternative to the short-lived drug delivery systems of recombinant bone promoting proteins.

The control of the in vitro and in vivo bioactivity, as well as the chemical reactivity of melt-derived glasses is an important state in the biomaterials field. The present work explores the local structure of bioactive glasses before and after in vitro assays in simulated body fluid. This study by solid-state MAS–NMR constitutes an original approach to the understanding of the bioactivity process.

Surface chemistry and geometry have a strong influence on adhesion and proliferation of various cell types, including human embryonic stem cells (ES). Visceral endoderm like cells (END-2) is an important cell line which induces ES cells to differentiate into cardiomyocytes. In this study, we have investigated the effect of surface chemistry and geometry on the END-2 cell adhesion and proliferation on gold surface.

Despite significant advances in orthopedic surgery, no perfect bioresorbable bone-filling material has yet been clinically established. A new candidate material based on hydroxyapatite, chitosan and oxidised starch, which has the potential to covalently bind to bone in a watery milieu was tested in a new murine model. A special focus lies on the in vivo biocompatibility and bioresorbability of the new material.

The current study focuses on the nanostructuring of our new drug-eluting porous films and its effect on the drug release profile of both hydrophilic and hydrophobic drugs. Nanostructuring was obtained using both the dispersion and the condensation methods of emulsion processing. These new highly porous nanostructured films can be used as basic elements of various drug-eluting medical devices.

Cell encapsulation represents an innovative technique. However, clinical applications are sparse. Most experiments and clinical studies have been performed with either alginate or cellulose sulfate capsules, containing several cell lines and a broad variety of applications, ranging all the way from substitution for impaired organ function and release of cytokines or growth factors to gene-directed enzyme prodrug therapy. A few clinical studies have been conducted and/or are under way.