Complementary Microstructure Research Articles

Functional properties of expanded austenite generated on AISI 316L by plasma nitrocarburizing using different active screen materials

Abstract This study investigates the functional properties of the expanded austenite layers generated on AISI 316L austenitic stainless steel resulting from active screen plasma nitrocarburizing using different active screen materials, i.e. steel or solid carbon. Treatments were conducted at 460 °C for 5 hours in a nitrogen-hydrogen feed gas, whereas for the treatments using a steel active screen, methane was added as carbon precursor. Additionally, the bias plasma conditions applied at the samples were varied between 0 kW and 1.25 kW. Samples were characterized by complementary microstructural and compositional investigations, surface roughness and hardness measurements, pin-on-disk tribological tests as well as potentiodynamic polarization tests in H2SO4 and NaCl electrolytes. The functional properties of the case are discussed based on the contents of nitrogen and carbon in the expanded austenite and on their effective diffusion depths. The results show that the usage of a carbon screen generally produces surfaces with uniform layer thickness, high hardness, improved wear resistance and a delayed tendency to pitting corrosion independent of the bias condition applied to the samples. When applying both screen materials at non-biased condition, the general corrosion resistance is slightly reduced under the conditions used, however, the layers generated using the carbon screen have a wear rate that is 3 times lower. It can be concluded that the carbon screen represents a robust treatment variant for austenitic stainless steels to produce sufficiently thick and wear-resistant surface layers in a short treatment duration, which still have the potential to maintain the corrosion resistance in different environments.

Monitoring the precipitation of the hardening phase in the new VDM® Alloy 780 by in-situ high-temperature small-angle neutron scattering, neutron diffraction and complementary microscopy techniques

The hardening phase precipitation process plays an important role in the development of new Ni-base superalloys. In the present work, we apply a powerful combination of complementary characterization techniques to characterize in-situ the γ’ precipitation in the new VDM® Alloy 780. During the whole heat treatment process, in-situ time-of-flight (TOF) neutron diffraction (ND) unambiguously identified the γ’ phase as well as its weight fraction and the misfit with the matrix while in-situ small-angle neutron scattering (SANS) provided precise precipitates’ size analysis. Atom probe tomography (APT) and scanning electron microscopy (SEM) provided detailed microstructural characterization and chemical composition of the phases necessary for a proper neutron scattering data evaluation. This contribution reveals more detailed information on the nucleation, growth, and Ostwald ripening processes starting from the early precipitation stage in bulk samples using the complementary microstructure investigation methods. The nucleation and growth kinetics of precipitates at 720 °C depend on heating rates and the size distribution obtained in the pre-heating history of the sample. A subsequent heat treatment step at 620 °C, typically used in Ni-base superalloys, does not lead to similar progressive precipitation or growth. The expected matrix-diffusion-controlled Ostwald ripening process of the γ’ precipitates was in-situ monitored by SANS on a full precipitation hardened sample at expected operating temperatures (750 °C) showing slower coarsening kinetics than other reported Ni-based superalloys.

Controlled spreading of melted fillers and precision micro-brazing based on a micro-scale binary cooperative complementary interface design strategy

For improving the brazing joint precision of ceramics and metals, a micro-scale binary cooperative complementary interface was used to achieve precise control of the wetting and spreading of melted fillers. By analytical calculation and numerical simulation, the study revealed the influence of structural parameters of the binary cooperative complementary interface on the wetting behavior of fillers, which was verified by the wetting experiment. The experimental results showed that the Ag–28Cu filler was difficult to wet on smooth ceramic substrates. For ceramic with the binary cooperative complementary microstructure, the inhibitory effect of the ceramic phase zone on the wetting and spreading of fillers was dominant when the width of copper phase zone is small. With increasing the width of cooper phase zone, the copper phase zone gradually played a leading role in the wetting and spreading of fillers. A good wetting and spreading of fillers in the joint area and precise control of the fillers boundary were achieved by the micro-scale binary cooperative complementary interface.

Unravelling chloride transport/microstructure relationships for blended-cement pastes with the mini-migration method

A chloride mini-migration method is proposed to estimate effective diffusion coefficients at the scale of the cement paste and to investigate mechanisms with complementary microstructure analyses on the same material. Blended-cement pastes with a wide range of properties were investigated in this study: systems at w/b = 0.3–0.5 including Portland cement, white Portland cement, slag-Portland cement, fly ash, glass powder, and/or limestone and calcined clay. Comparisons showed the relative and combined importance of three main parameters on the effective diffusion coefficient: the porosity, the pore connectivity parameter and the conductivity of the pore solution (low values of the latter two are generally key aspects of the high resistance of blended-cement systems against chloride ingress). Notably, a general correlation for all the investigated systems was established between the effective diffusion coefficient and the bulk conductivity (whereas no simple correlation was observed between the effective diffusion coefficient and the formation factor or the pore connectivity parameter).

Enhancement of fatigue resistance by overload-induced deformation twinning in a CoCrFeMnNi high-entropy alloy

We examined fatigue-crack-growth behaviors of CoCrFeMnNi high-entropy alloys (HEAs) under as-fatigued and tensile-overloaded conditions using neutron-diffraction measurements coupled with diffraction peak-profile analyses. We applied both high-resolution transmission electron microscopy (HRTEM) and neutron-diffraction strain mapping for the complementary microstructure examinations. Immediately after a single tensile overload, the crack-growth-retardation period was obtained by enhancing the fatigue resistance, as compared to the as-fatigued condition. The combined mechanisms of the overload-induced larger plastic deformation, the enlarged compressive residual stresses and plastic-zone size, the crack-tip blunting ahead of the crack tip, and deformation twinning governed the pronounced macroscopic crack-growth-retardation behavior following the tensile overload. A remarkable fracture surface of highly-periodic serrated features along the crack-propagation direction was found in the crack-growth region immediately after the tensile overload. Moreover, a transition of plastic deformation from planar dislocation slip-dominated to twinning-dominated microstructures in the extended plastic zone was clearly observed at room temperature in the overloaded condition, in accordance with the simulated results by a finite element method (FEM). The above tensile overload-induced simultaneously combined effects in the coarse-grained CoCrFeMnNi shed light on the improvement of fatigue resistance for HEAs applications.

Effect of lead on the machinability of brass alloys using polycrystalline diamond cutting tools

The international safety regulations are pushing the manufacturers of water systems and equipment to remove lead from material compositions due to the potential human hazard of lead absorption. The usage of green lead-free brass alloys is becoming mandatory in many important markets, demanding the manufacturers to quickly adapt their production techniques both casting and machining to this new reality. Regarding machining, lead has been used to facilitate the chip control, working as a natural chip breaker and reducing the tool wear. Therefore, the reduction of lead composition in brass alloys contributes to a machinability decrease of the materials leading to higher cutting forces, long chips and higher tool wear. This work focuses on the machinability characterization of three different brass alloys (leaded, medium-leaded and minimally leaded) by means of cylindrical external turning process with polycrystalline diamond inserts. A parametric study covering three different depths of cuts, three feed rates and four cutting speeds was conducted for three brass alloys with two repetitions. Cutting forces, chip morphology and surface roughness were analysed and compared between alloys. Complementary microstructural and mechanical characterization of the alloys were performed. Analysis of variance was performed to analyse the results. Cutting forces, power consumption, specific cutting pressure, roughness and chip morphology identification were used as comparison criteria among the tested materials. Results have demonstrated the decrease of machinability with the lead reduction, with higher cutting forces and longer chips. Polycrystalline diamond tools used in this work could be a good option to overcome the machinability challenges of the lead-free brass alloys.

Optical and Microstructural Investigation of Heavy B-Doping Effects in Sublimation-Grown 3C-SiC

In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000°C have been cross-correlated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects.

An application of composite soft material microstructure in development and formability of multi-axis dynamic transfer technology

This study examines the application of composite soft material microstructure in the technical development of multi-axis dynamic transfer, conducting forecast research aimed at the complementary microstructure. This study uses the PDMS soft materials of different proportions for multi-layer composition to research the characteristics of many composite inner-layer disperse materials and to discuss the mechanical properties of the composite soft materials. One innovation from this research is a multi-axis dynamic mold clamping system, which allows for a discussion of the anisotropic asymmetric dynamic regulation microstructure within the elastic range; controls its appearance characteristics effectively within the elastic range of the microstructure soft mold materials; deduces the appearance characteristics after multi-axis dynamic regulation transfer through the mathematical and geometrical principles; and makes a comparison with the result after the actual impression. The result shows that the composite soft mold proposed in this experiment has a better material mechanical property versus the traditional soft mold, and that the dual-axis dynamic clamping system developed and designed in this research can effectively regulate the microstructure dynamically. Finally, the deduced forecast method also conforms to the experiment result and provides more microstructure-oriented usage and innovation procedures for application in the microstructure industry.

Advanced characterization methods for wear resistant hard coatings: A review on recent progress

Abstract Due to economical demands to further increase the efficiency of production processes, it is essential to exploit the full potential of wear resistant hard coatings. This is, however, possible only if the coating microstructure and properties are well characterized. Thus, in the present work, recently suggested advanced characterization techniques for coatings are reviewed. The application of atom probe tomography, electron backscatter diffraction and synchrotron X-ray nanodiffraction enables previously unrevealed insights in their chemical composition, microstructure and crystallographic structure. For the determination of mechanical and tribological properties at elevated temperatures, high-temperature nanoindentation and high-temperature ball-on-disk tests in combination with in-situ measurement techniques are discussed. Utilization of micromechanical tests for coatings provides information about their fracture toughness and rupture strength. High-temperature X-ray diffraction and biaxial stress temperature measurements for the determination of the coefficient of thermal expansion are compared. The thermal conductivity as well as the specific heat capacity of coatings can be studied using the 3- ω technique, time domain thermoreflectance and differential scanning calorimetry. The introduced portfolio of characterization techniques enables the determination of a complementary microstructural, mechanical and thermo-physical fingerprint of wear resistant hard coatings, which allows to understand the complex structure–property relations in these materials and subsequently to further improve their performance.

First evidence of heat treatment during the early Neolithic in northeastern Italy

The site of La Vela sector VII (Trentino-Alto Adige – Italy), provides one of the few complete stratigraphic sequences, ranging from the Mesolithic to the middle Neolithic, in northwestern Italy. The site is located in the Adige valley, a way of communication between the Po plan and the Alps. This research focuses on the early Neolithic lithics ascribable to the Gaban facies, dated to 5000–4700 cal BC. Different rocks, coming from local exposures, have been exploited. The goal of the reduction sequence was the production of blades by pressure knapping technique. The technological study of the assemblage raised a particular interest for the presence of flint artifacts suggesting the usage of controlled heat treatment. The presence of this technique has been tested by an experimental approach based on Fourier-Transform infrared (FT-IR) spectroscopy. Complementary microstructural and analytical characterizations with low-vacuum scanning electron microscopy (LVSEM) observations combined with energy dispersive X-ray spectroscopy (EDXS) have been performed. The analyses confirm the presence of artifacts intentionally heat treated. The thermal treatment, achieved in order to increase the quality of the blade production, is the first evidence of this technique in northeastern Italy during the early Neolithic.

X-Ray Analysis of Residual Stress in Weld Region of X70 Pipeline Steel

X-ray diffraction method has been used to analyze the residual stress distribution in weld region of an X70 pipeline steel before and after heat treatment. The welding process has been realized by industrial arc welding with circular weld seams. The effect of heat treatments on the level and the distribution of residual stresses were investigated. Stress distribution was characterized by relative high compressive stresses in weld seam just after welding. However, residual stress relaxation phenomenon was observed in weld region after heat treatments due to microstructure restoration and recrystalization. Optical microscope observation and Vickers hardness measurements were also realized as complementary microstructure characterization techniques.

Residual Stress and Microstructures Characterization in Welded Al-Si-12Cu Alloy

X-ray diffraction method has been used to analyze the residual stress distribution across the joint of Al-Si-12Cu alloy just after welding process. On the other hand, isothermal heat treatments have been applied in order to study the residual stress evolution in this material. Optical microscope observation and Vickers hardness measurement have been carried out as complementary microstructure techniques. The different zones of welded joint have been analyzed, where the fusion zone was characterized by dendritic structure and different to heat affected zone. We have found a softening phenomenon in welded joint after heat according to microhardness results.

Microstructures and growth characteristics of polyelectrolytes on silicon using layer-by-layer assembly

Abstract Growth processes of nanocomposite layers obtained by polyelectrolytes, poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC), self-assembled on silicon surface using layer-by-layer (LbL) technique were investigated, and theoretical and experimental data are herein reported. Complementary microstructural and compositional analyses techniques (scanning electron microscopy, ellipsometry, X-ray reflectivity, zeta (ξ) potential measurements and attenuated total reflection infrared spectroscopy) were used for deep characterization of the multilayer structure formation. Electrophoretic zeta (ξ) potential measurements indicated that the surface charge was either positive or negative, depending on the polyelectrolyte used (PDADMAC or PSS). ATR-IR spectra confirmed the successfully silanization process and then, the building up of the nanocomposite layer. Morphological investigation and X-ray reflectivity demonstrated the growth process and cross-section size of the bilayers. Ellipsometric measurements were in very good agreement with SEM and XRR, showing once again the successful deposition of polyelectrolyte multilayers.

Permeation Properties of Poly(m-xylene adipamide) Membranes

The permeation properties of a semiaromatic polyamide, the poly(m-xylene adipamide) (MXD6), were investigated by water and carbon dioxide permeation experiments (pervaporation and gas permeation tests). Complementary microstructure informations were obtained from calorimetric measurements. Amorphous and semicrystalline MXD6 membranes were studied. The analysis of the water flux through amorphous MXD6 membranes showed a plasticization phenomenon followed by a water-induced crystallization. It resulted that the role played by water in these materials was complex because of the dependence of the water diffusivity on water concentration and time. Because of the presence of crystalline phase, a significant reduction of water and gas permeability of MXD6 and an increase in the delay of diffusion were observed. In terms of barrier properties for water and carbon dioxyde, MXD6 membrane crystallized at high temperature were more performant than water-induced crystallized ones. Correlations between microstructure and transport properties had been so established.

Microstructure and Thermal Diffusivity of Ceramic Powders

For the first time, the thermal diffusivity (α) in red clay samples has been determined as a function of the annealing time, for a furnace temperature above 900 ◦ C. The thermal diffusivity measurements on the samples were obtained by means of the photoacoustic technique in a heat transmission configuration. A complementary microstructure analysis using X-ray diffraction (XRD) and energy dispersion spec- troscopy (EDS) has been performed. The ceramic material used in this work is widely used in the fabrication of several kinds of building materials such as bricks and roof tiles in the north oriental region of Colombia (Cucuta). The importance of these results is in the determination of conditions to obtain manufactured products with the desired heat transport capacity.

Hydrothermal Synthesis of Monodisperse Magnetite Nanoparticles

Magnetite particles with an average size of 39 nm and good monodispersity have been synthesized by coprecipitation at 70 °C from ferrous Fe2+ and ferric Fe3+ ions by a (N(CH3)4OH) solution, followed by hydrothermal treatment at 250 °C. The magnetite nanoparticles before the hydrothermal step display an average size of 12 nm and are highly oxidized when they are in contact with air. Complementary microstructural and magnetic characterizations of nanoparticles after hydrothermal treatment show unambiguously that they consist of magnetite with only a slight deviation from stoichiometry (δ ≈ 0.05), leading to Fe2.95O4.

Interface magnetism in Fe-based nanocrystalline alloys

Nanoscale materials exhibit properties that can not be find in larger scale system due to the crystal size effects as well as structural variations between the interfacial regions and the crystalline interior. In this paper the consideration of the finite-size effects are limited to a special class of nonconventional granular materials produced by the devitrification of Fe-based amorphous ribbons. The complementary microstructural and magnetic studies show that in such mesoscopic systems the interfaces exhibit identifiable properties. The data presented do not provide the detailed picture of the internal structure of the boundary regions but bring information about their basic structural and magnetic properties. In particular the influence of the magnetic state of the intergranular amorphous matrix (ferro-or paramagnetic) on the local magnetic behavior of the interfaces is considered. The effect of the symmetry restriction at grain boundaries on the structurally sensitive parameter such as a magnetostriction is also presented and discussed.