Advanced Engineering Materials

Large area micro and sub-micrometer structuring of TCO thin film layers is performed using a laser based one-step procedure. The fabricated hexagonal arranged surface patterns with 800 nm spatial period show a higher performance in both transparency and diffraction properties compared to line-like textured and non-patterned substrates. Furthermore, non-significant variations of the electrical resistance are observed after the laser treatment.

This study is focused on the effects of material strengthening and reinforcing mechanisms on the crush resistance, deformability, and energy absorption capability of square-celled TRIP steel and TRIP steel/zirconia composite honeycomb structures under quasi-static out-of-plane compressive loading over a wide range of test temperatures. The microstructure and phase evolution in the cell wall material is investigated by magnetic force balance and EBSD measurements considering different deformation stages.

The ZrO₂–MgO phase diagram is experimentally studied using XRD, SEM-EDX, and DTA. The ZrO₂-based solutions are modeled as ionic solutions using compound energy formalism. The thermodynamic parameters are optimized using own and literature experimental data. The calculated ZrO₂–MgO phase diagram is used to interpret the microstructure and phase transformations observed in the industrial Mg-PSZ material in as-received and heat treated states.

CVD diamond electrodes have been extensively studied in recent years, from the point of view of fundamental electrochemical properties as well as that of applications. Diamond electrodes are found to be attractive for electrochemical applications due to their physical, chemical, and electronic properties, e.g. high thermal conductivity; high hardness, and chemical inertness; a wide electrochemical potential window in aqueous and non-aqueous media; a very low capacitance and a very high electrochemical stability.

A novel micro- and nanoweaving method based on the electroactuation properties of microfibers is developed. Poly(vinyl alcohol) microfibers are bent using electrical stimuli, with high electrosensitivity. The generated actuation force guide the fiber (monofilament) up or down by more than 5 mm, to provide a shedding motion for weaving ultrathin, uniform micro- or nanofabrics.

The microstructure evolution during deformation and the mechanical behavior of an austenitic Cr–Mn–Ni as cast steel are investigated at various temperatures. The deformation-induced twinning and ε/α′-martensite formation – the TWIP and TRIP effects – occur in the investigate steel depending on the deformation temperature. For characterization and illustration of the TRIP/TWIP effects the STT and DTT diagrams are developed. Finally, the α′-martensite nucleation threshold is determined, and an equation is proposed to describe the volume fraction of strain-induced α′-martensite as a function of the total driving force.

Despite their high silicon content up to 17–25 ma% spray-formed Al alloys are well nitridable. The present paper deals with the influence of the chemical composition, initial surface roughness and the nitriding parameters on the nitriding behavior, especially the surface coverage with aluminum nitride. Furthermore, the hardness and wear behavior are investigated both after the single plasma nitriding treatment as well as an additional subsequent heat treatment (age hardening).

The ceramic mask-assisted flame spray pyrolysis (CMA-FSP) is a method for creating accurate micron sized spots of different shapes by depositing of metal oxide nanoparticles directly onto user defined substrates. The patterning process uses free-standing alumina thin films with well-defined holes as reusable ceramic masks.

Strength and work hardening of TRIP matrix composite materials depend strongly on the testing temperature. Due to a temperature dependent driving force for the α′-martensite formation and a changing stacking fault energy in the metastable austenitic matrix, completely different deformation mechanisms can be observed at room temperature and at 100°C. With the transition from the formation of intrinsic stacking faults at 20°C to extrinsic stacking faults at elevated temperatures, the TRIP effect is substituted by mechanical twinning. The stress induced martensitic transformation in the reinforcing zirconia particles increases the stress level of the MMC further.

Wrinkling vs. long-wavelength instability envelope for multi-layered soft composite: Predictive analytical and finite element models are presented to reveal the instability mechanics governing reversible wrinkling of interfacial layers. The biomimetic guidelines for the design of reversible, tunable, and multi-functional layered soft composites with transforming interfacial layers are developed and verified via 3D printed prototypes.

We use X-ray tomography to investigate the fracture behavior of an ERG open cell aluminum foam. Local tomography has in particular been used to image the microstructure at high resolution showing the inter-metallic particles present in the struts. A FE model is also developed using the 3D data obtained by the tomography in order to simulate the damage process.

Influence of the welding geometry on the mechanical characteristics of light metal/carbon fiber reinforced polymer overlapped structures is analyzed. An elastoplastic model with Lemaitre-type damage is used for the simulation of the mechanical behavior of the interface material. An interfacial traction–separation law is applied. Finite element method is used for the simulation of force–displacement curves of ultrasonically welded AA5754/CF-PA66 joints.

Lower structural perfection of W-Ta single crystals is associated with considerable disturbance of the melt by plasma arc, great temperature gradients and cooling rate of the growing single crystal due to “air rinsing” of its surface by plasma-forming gas. In the peripheral areas of this sample a large number of small sub-grains is presented, which confirms the trend towards fragmentation of the structure at crystallization from the beginning to the end of the ingot.

The extraordinary combination of strength and toughness attained by nature's highly sophisticated structural design in nacre has inspired the synthesis of novel layered nanomaterials. The object of the present paper is a nanostructured layered TiO₂/PE-composite, mimicking the nacre's structure. In the present work, the influence of the thickness ratio between organic and inorganic phases and the influence of mineral bridges on the Young's modulus of the composites is analyzed analytically and numerically. By application of these findings in a modeling approach, the mechanical properties of artificially produced materials can be predicted.

The impact of a single micro crack on the fracture strength of PV silicon wafer is investigated based on a controlled flaw method by introducing radial/median cracks with controllable scales through microindentation. Results indicate that the fracture strength of PV silicon wafer decreases linearly with the increasing of the microindentation load. It is also found that carbon plays an important role in the contact cracking-fracture process.

The surface tension of copper, AISI 304 and the Cr-Mn-Ni steels are determined via the maximum bubble pressure method using zirconia capillary tubes. Oxygen adsorption in Cr-Ni steel decreases surface tension. Manganese is responsible for a decrease of surface tension values in Cr-Mn-Ni alloys. For Cr-Ni and Cr-Mn-Ni stainless steels temperature coefficient of surface tension changed to positive.

Composite bearings are normally produced with sintered bronze between the polymer coating and the metallic substrate, omitting the bronze layer would reduce complexity. Thermal impact welded metal-polymer composite specimen without bronze are shaped to U-half shells to test them tribologically. Wear rates and friction coefficient are measured. The effects of the shaping are examined by surface analysis. Beside those shaping effects the heat balance is a very important influencing parameter.

The paper gives a summary of several processes inside the material during and affecting the result of the diffusion welding process. The relation between the materials microstructural defects, the materials history arising from manufacturing processes as well as the surface condition of the material and its impact on diffusion processes are discussed in detail. Specific considerations of diffusion welding for microsystem technology are considered. The literature and different approaches of diffusion welding are evaluated.

Mechanical in situ investigations on cruciform members of square-celled TRIP-steel/Mg-PSZ honeycomb structures are presented under uniform compressive load in a computer tomograph (XCT). The mechanical and structural characteristics of the cell wall node elements are compared to the damage mechanisms of the complete honeycomb specimens. Phase transformations in the Mg-PSZ particles are determined by EBSD.

Interaction with water at the ultra-large surface area of nanoporous material (zeolite ZSM-5) is utilized to establish a nanoporous energy dissipation system and studied experimentally in this paper. Results show that the pretreatment temperature of about 1000 °C, and higher ratio of ZSM-5 with larger particle size are desired for an optimum energy dissipation performance, which enables a reusable cushioning device.

Microstructure defects and their interactions contributing to the high energy absorption in highly alloyed austenitic CrMnNi TRIP steels: dislocations, stacking faults, Lomer-Cottrell locks, stacking fault tetrahedra, dislocation clusters; the ε-martensite, twinned austenite and the α′-martensite, caused by the fluctuation of the stacking fault density and the lattice shearing within deformation bands, are analyzed using REM and TEM/ HRTEM.

The hot workability of Mg-3Sn-2Ca-1Al alloy has been established through the development of its processing map based on dynamic materials model. Domains 1–3 are considered as desirable processing windows for forming this alloy due to extensive dynamic recrystallization and grain refinement. Domain 4 represents extensive grain boundary sliding, and should be avoided under stresses of tensile nature due to flow instability.

The mechanical properties of graphene are modified by g-BN concentration, providing guidance to optimize graphene-based nanodevices. The in-plane stiffness and third order elastic constants can be linearly tuned. The longitudinal mode elastic constants are sensitive to the BN modification. The third, fourth, and fifth order elastic constants are required for strains larger than 0.02, 0.06, and 0.12, respectively.

High-pressure torsion is now a major processing method for the production of metals with ultrafine grain sizes. Experiments using a two-phase duplex stainless steel show that the flow patterns on the disk surfaces vary depending upon the amount of anvil misalignment. Specifically, shear vortices are visible when processing with a misalignment of x = 100 µm but not when the anvils are in perfect alignment.

The fatigue behavior of particle reinforced MMCs with high-alloyed CrMnNi steels as matrix reinforced with partially stabilized zirconia (Mg-PSZ) is investigated. It is shown, that the fatigue behavior is influenced significantly by the chemical composition of the steel matrix and Mg-PSZ volume fraction. Depending on the chemical composition, the high-alloyed steels show the TWIP and TRIP effect under cyclic loading.

Electron beam welding of high alloy CrMnNi cast steels showing the TRIP and/or TWIP effect proved to be advantageous because of its short time energy input, which results in minimized thermal loading of the base material. Crack and pore-free welding seams with depths up to 26 mm were produced. EBSD investigations showed that the deformation mechanisms in the welding seam are qualitatively the same as in the base material.

The microstructure of ultrasonically welded Al/CFRP-joints is studied by microscopy and spectroscopy. Mechanically deformed areas near the hybrid interface are observed by HRTEM which lead to a reorientation of the crystal structure. Furthermore it is proven by EELS, that molten thermoplastic can penetrate into a cavernous, nanoscaled aluminum oxide layer corresponding to sub-microscopic interlocking and improved mechanical properties.

The effect of the manganese content (0–11%) on the transformation temperatures, the mechanical properties, and microstructure development of five highly alloyed 14Cr–XMn–6Ni cast stainless steels with 0.1% nitrogen is studied. The temperature dependence of tensile properties in alloys is explained on the basis of varying contributions to the strength and ductility of deformation-induced martensite and twin formation mechanisms.

Shape memory polymer Tecoflex™ is experimentally investigated by running DMA tests in three distinct deformation modes, uniaxial tension, three-point bending, and simple torsion, using two test rigs, Eplexor 500N of Gabo Qualimeter® and Modular Compact Rheometer MCR-301 of Anton Paar. It is observed that the temperature-dependent storage and loss moduli measured in different deformation modes show certain discrepancies that cannot be easily reconciled.

A novel principle of design of sandwich panels utilizing segmentation of a monolithic core into a set of building blocks with a specially designed shape is proposed. Our investigation shows that segmentation of a monolithic sandwich core made from polyurethane into an assembly of interlocked osteomorphic blocks brings about a remarkable increase in the deflection to failure and in the energy absorption capability of a sandwich panel.

The freeze-drying combining solid sintering is a good method to fabricate porous SiC ceramics with good high temperature mechanical properties. Though SiC ceramics are sintered at high temperature of 2150 °C, there are still large quantities of macropores and micropores. After being treated at a temperature of 1200 °C, the ceramics exhibit good thermal shock damage resistance.

Particle reinforced TRIP-matrix composites, consisting of partially stabilized zirconia particles embedded in a TRIP-steel matrix, show a very heterogeneous phase transformation behavior. It is due to both the stress concentration and the void formation as a result of interface decohesion. The figure depicts the distribution of martensite volume fraction in the matrix and the volume fraction of monoclinic zirconia in the particle after uniaxial compression ε = 0.35.

We report a new centimeter-sized Ti₄₀Zr₂₆Be₂₈Fe₆ bulk metallic glass with a large supercooled liquid region of 100 K. This glassy alloy also possesses excellent mechanical properties such as a high specific strength of 4.03 × 10⁵ Nm kg⁻¹ and an obvious compressive plastic strain of 7.4%, which make it possible to be used as novel aerospace materials.

In this work, magnesium matrix composites reinforced with a TiC–TiB₂ network have been fabricated using in situ reactive infiltration technique. Relatively uniform distribution of TiB₂ and TiC particulates in the Mg matrix was observed. Compared with those of the unreinforced AZ91D alloy, the elastic modulus, flexural and compressive strengths of the composite are greatly improved. However, their low ductility was improved by the addition of MgH₂ powder in the preform.

Nanoindentation tests were conducted on four commercial zirconia dental ceramics. For each material, the measured nanohardness exhibits significant indentation size effect. The so-called load-independent nanohardness was determined based on a second-order polynomial analysis of the variation of the contact depth with the peak load. Finally, a brief discussion was conducted on the reliability and the applicability of the determined load-independent nanohardness.

A optical micrograph showing some lenticular α′ martensite (dark) produced inside the block thermal ε martensite (white) and many granular α′ martensite (dark) introduced at the intersections of different direction ε martensite bands after 5% deformation in a quenched Fe14Mn5.5Si8.0Cr5.0Ni alloy.

Mylopharyngodon piceus, or black carp, is a species of fish mainly feeding on mollusks, which are commonly protected by hard exoskeleton. Why can the black carp crush the hard mollusk shells at ease? Does such unique diet imply that its teeth are superior to the mollusk shells in mechanical properties? Present mechanics-based study on the competition between black carp teeth and mollusk shells comes up with the answers.

An in-situ examination of hole exit delamination at the bottom-ply during drilling holes in the selected woven CFRP is presented. The advent, accruement and shape-pattern of the exit delamination are discussed via some experimental observations. A few illustrative models are also proposed. An attempt to correlate exit delamination results with the instantaneous cutting angle configurations right at the bottom-ply is also made in this article.

Geometrical inhomogeneities in seamless tubes result in a non-symmetric residual stress and texture distribution. Controlling the inhomogeneities leads to a change and even improvement of the mechanical status. As a point of investigation the effect of the thickness deviation over circumference in seamless tubes was analyzed by neutron diffraction for the residual stresses and by synchrotron radiation for the texture.

Gradient TiO₂ nanotubes with tube diameters ranging from 55 to 105 nm and lengths ranging from 300 nm to 500 across 12 mm of Ti foil are obtained by a new anodization based method in HF electrolyte using applied voltage as low as 5–20 V. In the method, the applied anodization voltage is increased step by step, while the Ti foil is immersed into electrolyte progressively during anodization.

The tailoring of surface properties requires a method being able to access structural sizes ranging from sub µm up to some 100 µm or even more. So far, several mechanical techniques such as embossing, cast moulding, or lithography based methods are needed to create the necessary structures on different scales. Therefore, a new technology combination is studied within this work on aluminum surfaces. The idea is based upon the combination of laser interference metallurgy for the advanced design of topographies and microstructures with micro-coining leading to superior hierarchical surface textures.

There is an evident difference in fatigue behavior of freestanding 40 µm-thick Ni foils loaded normal to and parallel to the rolling direction. An EBSD analysis reveals that fatigue cracking along grain boundaries (GBs) or slip bands in the foils depends on the difference in Schmid factor of the grains along GBs and the misorientation angle of the GB. A model is proposed to understand the fatigue damage mechanism.

With the technological evolution of the refractory materials and products, new testing technology and simulation methods are requested and developed, which can be used to investigate their thermomechanical properties and thermal shock behavior. The present work focuses on the development of a combined testing method based on physical and thermomechanical numerical simulation to study the thermal shock behavior of refractory ceramics.

New developments in using induction heating to join hybrids of metal and CFRPC are presented. An explanation of the process, the equipment, as well as first steps to automation is given. Variation of pretreatments and process parameters show great influence on the shear tensile strength. The documentation of the process parameters shows a high reproducibility and reliability of the developed equipment and demonstrator parts are successfully manufactured.

Using the direct-LIGA technology, nickel–iron micro-specimens are serially produced by a micro-gear drive manufacturer and subsequently annealed within the temperature range between 180 and 800 °C. The microstructure (grain size, lattice strain, and texture) is characterized using XRD measurements. Following electrodeposition, nano-crystalline microstructures result with grain size of approximately 10 nm. The transmission electron microscope images confirm the XRD results. The lattice strain decreases in the temperature range from 200 to 300 °C and grain growth results for an annealing temperature from approximately 260 °C. The annealing treatment produced no essential changes in the material's texture. Analysis of the indentation hardness and indentation modulus demonstrates considerable changes above 200 °C.

Surface nanocrystalline of martensite steel has been successfully prepared by using sandblasting technique at room temperature combined post-annealing and at 500 °C, respectively. The average grain sizes of surfaces are 112 and 30 nm, respectively. Fine grains and Fe₃C phase in situ form during sandblasting at 500 °C that is favor for producing nanoscale structure of the martensite steel.

This study presents the results from immersion tests of biodegradable Mg and Fe in simulated body fluid buffered with gaseous CO₂. The particular advantage of controlling the pH value by means of CO₂ is that the physiological conditions are better reproduced; hence the in vitro experiments are closer to the in vivo situation.

Low level silver (Ag) additions of 0.12 and 0.5 wt% to magnesium alloy AZ91 reveal that micro-alloying with Ag was capable of imparting an increment in hardness, with no significant increase in electrochemical corrosion kinetics. The alloy properties were reconciled with microstructural analyses and atom probe tomography.

The thermal conductivities (k) of three ZrB₂–SiC–B₄C compositions were determined over 25–2000 °C using the laser flash technique. Higher SiC concentration increased the k temperature sensitivity. Finite difference calculations of k based on microstructures correctly predicted temperature and phase concentration dependencies. The k of pure ZrB₂ and SiC as a function of temperature were iteratively back-calculated from the experimental results.

The influence of different heat treatments on mechanical properties and microstructure of ultrasonic welded AA 2024/CF-PA66-joints have been studied. A distinction was made between pre-weld and post-weld heat treatments. As a beneficial result a significant higher tensile strength of up to 113 MPa is observed for hybrid Al/CF-PA66 joints and solution annealed AA 2024 sheets which can be attributed to the specific oxide morphology with mechanical interlocking of polymer and aluminum, even on a sub-µm-scale.

Dual-growth-factor (TGF-β₂/BMP-7)-immobilized PCL/Pluronic F127 porous scaffolds were fabricated using a modified melt-molding particulate-leaching method followed with the binding of heparin and growth factors onto the pore surfaces of the scaffolds. From the in vitro chondrogenesis study, it was observed that the dual TGF-β₂/BMP-7-immobilized scaffold induced better chondrogenic differentiation than the single-growth-factor-immobilized scaffolds or control scaffold (without growth factor), probably owing to the synergistic effect of both growth factors.