Property-microstructure Relationship Research Articles

Experiment and finite element modelling on compressive and damage evolution of graphene nanoplatelet reinforced Porous cement composites

As reinforcing nano-fillers, graphene nanoplatelets (GNPs) have shown considerable promise for developing high-performance cement composites. However, the influence of GNP orientation and pores on the compressive and damage evolution of the GNP reinforced cement composites (GNPRCCs) remains unclear. This work employs three-dimensional finite element modeling along with experiments to provide fundamental insights into the property-microstructure relationships in the GNPRCCs. The model which incorporates GNP and pore as individual phases with cohesive interactions is developed and validated. The simulations reveal that the alignment of GNPs at 45° has the most significant effect on improving the load-bearing capacity and damage resistance of the GNPRCCs. A larger GNP diameter-to-thickness ratio is more beneficial for enhancing crack bridging and propagation control. The orientation and porosity of pores are evidenced to have significant effects on the damage behaviours of the GNPRCCs, where the pore shape shows negligible effects. These findings elucidate the underlying mechanisms that underpin the mechanical behavior of GNPRCCs, providing key guidelines to tailor and optimize the microstructural features for advanced construction materials with superior performance and durability.

Experimental study and simulation of the interface shear deformation behavior in AISI304/Q235 clad plate with thin cladding layer

The mechanical properties and interface damage characteristics of hot-rolled bonded stainless steel/carbon steel (SS/CS) clad plate with thin cladding were investigated. The focus is on mechanical property-microstructure relationships in shear deformation. In detail, the mechanical response of the cladding components and clad plate were characterized. Then a hybrid numerical–experimental identification procedure for the cohesive zone model (CZM) in the simulation of heterogeneous SS/CS interface using finite element (FE) method was developed. A mixed-mode bilinear CZM, considering the anisotropy of the thin cladding was coupled FE model, showing a high accuracy for predicting the shear deformation behavior. The results showed obvious differences in the microstructure and mechanical properties of the SS and CS layers and the formation of an inhomogeneous interfacial layer. Additionally, the bond strength and delamination position of SS/CS clad plate are highly dependent on the interfacial oxide distribution and elemental diffusion behavior. Interestingly, the thin cladding is subjected to bending moments in shear deformation, resulting in delamination of the interface that is not completely dominated by one shear mode. And these abrupt interfacial failures could be clarified via stress-strain state and local damage analysis of the well-reproduced FE model of cladding material.

Mechanical property-microstructure relationships of an X70 pipeline steel at elevated temperatures

Mechanical property-microstructure relationships of an X70 pipeline steel were evaluated at temperatures up to 400 °C using tensile testing, scanning and transmission electron microscopy, and synchrotron wide-angle X-ray scattering characterization techniques. The X70 steel had a bainitic microstructure consisting of quasi-polygonal ferrite, retained austenite, martensite-austenite islands, and carbide/nitride microconstituents. Results are compared to an X52 steel with a ferrite-pearlite microstructure. Both steels exhibited dynamic strain aging (DSA) as evidenced by serrated yielding, reductions in strain rate sensitivity, increased strengths, and reduced dutilities in the approximate temperature ranges of 100–250 °C. For temperatures above the DSA range, the X70 steel exhibited unique properties of an increase in strength simultaneously with an increase in uniform strain, both features interpreted due to microstructural changes during testing due to dynamic tempering, indicated by decomposition of the retained austenite and associated cementite and transition carbide nucleation and coarsening, i.e. microstructural changes normally associated with static tempering at temperatures above 400 °C. However, if the X70 steel was tempered at the test temperature prior to testing, dynamic microstructural changes were absent and the steel exhibited behavior similar to that observed for the X52 steel, i.e. a decrease in strength and increase in ductility at temperatures above the DSA range. New alloying strategies are suggested to improve microstructure stability during isothermal holds at elevated temperature, while maintaining the strength benefits from strain assisted bainitic tempering during plastic deformation.

Understanding the mechanism of thermal-stable high-performance piezoelectricity

Lead zirconate titanate (PZT) ceramics have been widely used because of their large piezoelectric response and good temperature-stability in the vicinity of morphotropic phase boundary (MPB). However, the understanding on the mechanism of temperature-stable piezoelectricity in PZT is still blur and thus needs to explore properly since the urgently-needed Pb-free systems designed by the same MPB method commonly show poor temperature stability. In this paper, we investigate the property-microstructure relationship for the thermal-stable piezoelectricity through comparative studies of the phase diagram, in-situ piezoelectricity and microstructure evolution in both Pb-based and Pb-free systems. Our results show that the piezoelectric thermal-stability is closely related to the verticality of MPB and the doping elements. Tilted MPB shows worse thermal-stability as compared with that of the vertical MPB. While acceptor doped commercial PZTs show better thermal-stability when compared with that of the donor doped PZT. Moreover, our in-situ TEM reveals that it is the thermal-stable fine microstructure (i.e., no degeneration) that corresponds to the thermal-stable high-performance piezoelectricity. Our work provides an in-depth understanding of the relationship between the phase diagram, microstructure and thermal-stable piezoelectricity, which shall benefit the designing of new lead-free temperature-stable piezoelectric materials.

Influence of Cryogenic Temperatures on the Microstructure and Mechanical Properties of Magnesium Alloys: A Review

Magnesium alloys have been used in the automotive industry and 3C (computer, communication, and consumer electronics) for many years. Their room temperature properties combined with their low density offer a wide range of applications, especially when processed by High Pressure Die Casting (HPDC). The use of magnesium alloys at higher temperatures is well-studied; special creep resistant alloys containing the rare earth elements silver or yttrium are needed. However, when it comes to very low temperatures, only a few studies have been performed to determine the property-microstructure relationship. The possible fields of application at low temperatures are aerospace and satellite parts and tanks for liquefied gases. This review shall not only examine mechanical properties at low temperatures, but also the permanent effects of cyclic or long-lasting cryogenic treatment on the microstructure and mechanical properties. It was found that cryogenic treatment is able to influence the precipitate concentration and grain orientation in some magnesium alloys. Reduction in the number of brittle phases is improving ductility in some cases. It is well-known that high speed tool steels, in particular, can be influenced by cryogenic treatment. Whether this is possible with magnesium alloys and what the mechanisms are shall be reviewed.

Investigation of thermal aging effects on the tensile properties of Alloy 617 by in-situ synchrotron wide-angle X-ray scattering

The nickel-base Alloy 617 has been considered as the lead candidate structural material for the intermediate heat exchanger (IHX) of the Very-High-Temperature Reactor (VHTR). In order to assess the long-term performance of Alloy 617, thermal aging experiments up to 10,000h in duration were performed at 1000°C. Subsequently, in-situ synchrotron wide-angle X-ray scattering (WAXS) tensile tests were carried out at ambient temperature. M23C6 carbides were identified as the primary precipitates, while a smaller amount of M6C was also observed. The aging effects were quantified in several aspects: (1) macroscopic tensile properties, (2) volume fraction of the M23C6 phase, (3) the lattice strain evolution of both the matrix and the M23C6 precipitates, and (4) the dislocation density evolution during plastic deformation. The property–microstructure relationship is described with a focus on the evolution of the M23C6 phase. For aging up to 3000h, the yield strength (YS) and ultimate tensile strength (UTS) showed little variation, with average values being 454MPa and 787MPa, respectively. At 10,000h, the YS and UTS reduced to 380MPa and 720MPa, respectively. The reduction in YS and UTS is mainly due to the coarsening of the M23C6 precipitates. After long term aging, the volume fraction of the M23C6 phase reached a plateau and its maximum internal stress was reduced, implying that under large internal stresses the carbides were more susceptible to fracture or decohesion from the matrix. Finally, the calculated dislocation densities were in good agreement with transmission electron microscopy (TEM) measurements. The square roots of the dislocation densities and the true stresses displayed typical linear behavior and no significant change was observed in the alloys in different aging conditions.

Ti-Mo Alloys Used in Medical Applications

Metallic biomaterials are used in various applications of the most important medical fields (orthopedic, dental and cardiovascular). The main metallic biomaterials are stainless steels, Co-based alloys and Ti-based alloys. Recently, titanium alloys are getting much attention for biomaterials because these types of materials have very good mechanical properties, good corrosion resistance and an excellent biocompatibility. The paper contains important information about titanium alloys used for biomedical applications, which are considered the most widely. It is very important to understand the microstructural evolution and property-microstructure relationship in implant alloys. In the present paper, authors present a short literature review on general aspects of promising biocompatible binary Ti-Mo alloys compared with CoCr and stainless steel alloys, as an alternative of the known metallic biomaterials. This alloys show superior mechanical compatibility and very good biocompatibility. The aim of this review is to highlight the mechanical properties for several types of biomaterials, their application in medical field, especially the Ti-Mo group.

Normal-pressure microwave rapid synthesis of hierarchical SnO2@rGO nanostructures with superhigh surface areas as high-quality gas-sensing and electrochemical active materials

Hierarchical SnO2@rGO nanostructures with superhigh surface areas are synthesized via a simple redox reaction between Sn(2+) ions and graphene oxide (GO) nanosheets under microwave irradiation. XRD, SEM, TEM, XPS, TG-DTA and N2 adsorption-desorption are used to characterize the compositions and microstructures of the SnO2@rGO samples obtained. The SnO2@rGO nanostructures are used as gas-sensing and electroactive materials to evaluate their property-microstructure relationship. The results show that SnO2 nanoparticles (NPs) with particle sizes of 3-5 nm are uniformly anchored on the surfaces of reduced graphene oxide (rGO) nanosheets through a heteronucleation and growth process. The as-obtained SnO2@rGO sample with a hierarchically sesame cake-like microstructure and a superhigh specific surface area of 2110.9 m(2) g(-1) consists of 92 mass% SnO2 NPs and ∼8 mass% rGO nanosheets. The sensitivity of the SnO2@rGO sensor upon exposure to 10 ppm H2S is up to 78 at the optimal operating temperature of 100 °C, and its response time is as short as 7 s. Compared with SnO2 nanocrystals (5-10 nm), the hierarchical SnO2@rGO nanostructures have enhanced gas-sensing behaviors (i.e., high sensitivity, rapid response and good selectivity). The SnO2@rGO nanostructures also show excellent electroactivity in detecting sunset yellow (SY) in 0.1 M phosphate buffer solution (pH = 2.0). The enhancement in gas-sensing and electroactive performance is mainly attributed to the unique hierarchical microstructure, high surface areas and the synergistic effect of SnO2 NPs and rGO nanosheets.

Microstructural evolution and strengthening mechanisms in Ti–Nb–Zr–Ta, Ti–Mo–Zr–Fe and Ti–15Mo biocompatible alloys

The microstructural evolution and the strengthening mechanisms in the two quaternary alloys, TNZT (Ti–34Nb–9Zr–8Ta) and TMZF (Ti–13Mo–7Zr–3Fe), and one binary alloy, Ti–15Mo, have been investigated. In the homogenized condition both the quaternary alloys exhibited a microstructure consisting primarily of a β Ti matrix with grain boundary α precipitates and a low volume fraction of primary α precipitates while the binary alloy showed single-phase microstructure with large β grains. On ageing the homogenized alloys at 600 °C for 4 h, all the alloys exhibited the precipitation of refined scale secondary α precipitates distributed homogeneously in the β matrix. However, after ageing while the hardness of TMZF marginally increased, that of the TNZT and Ti–15Mo alloys decreased. Furthermore, the modulus of TNZT decreased while other two alloys showed opposite trends. TEM studies indicate that there is initially a B2 ordering in TNZT that is destroyed after ageing causing a reduction in both hardness and modulus of this alloy. Also in Ti–15Mo, dissolution of ω precipitates on ageing causes the hardness to reduce, while the precipitation of secondary α causes an increase in the modulus. Using these examples, the important influence of thermal processing on the property–microstructure relationships in orthopaedic alloys for implant applications will be highlighted.

Dielectric property-microstructure relationship for nanoporous silica based thin films

Low dielectric constant silica based films which incorporate a large amount of nanometer sized pores are attractive candidates as interlayer dielectrics in future gigascale integrated circuits chip technology. Nanoporous silica based films were deposited by surfactant templated self-assembly spin-on deposition (SOD). Other low-k materials with relatively low density silica based films were deposited by plasma enhanced chemical vapor deposition (PECVD), and some silica films were deposited by a CVD process. The SOD films have a higher porosity, compared to the PECVD/CVD films, as measured by x-ray reflectivity, Rutherford back scattering, and ellipsometry measurements. The SOD films have lower dielectric constants compared to the PECVD/CVD films, as derived from electrical (1 MHz) and optical (5×1014 Hz) measurements. The correlation between the dielectric constant and the porosity for the SOD films fits well to the lower prediction of the Lorentz–Lorenz model, and the PECVD/CVD films agree with the higher prediction of the Rayleigh model. These results suggest that the dielectric constant of the inhomogeneous two phase nanoporous silica based films deposited by SOD is significantly lowered by forming air voids, whereas the PECVD/CVD films consist of a homogeneous low density loose microstructure originating from the bonding nature alone, and therefore their dielectric constant is lowered to a smaller extent.

Microwave dielectric property–microstructure relationships in Y 2Ba(Cu 1− xMg x)O 5 solid solutions

Y 2Ba(Cu 1− x Mg x )O 5 solid solutions were synthesized by the solid state reaction method and the microstructure was studied by using SEM in order to clarify the microwave dielectric property–structure relationship. From the variations in the lattice parameters obtained by Rietveld analysis and the least-squares method, it was clarified that the limit of Y 2Ba(Cu 1− x Mg x )O 5 solid solutions is approximately at x=0.2. Grain growth and the reduction of porosity in the samples increased with the composition x. The dielectric constants were constant and the quality factors were extremely increased from 3800 to 42 300 GHz, as the composition x increased from 0 to 0.2. Thus, it was found that the quality factors of the samples were closely related to the morphological changes and a formation of the porosity; the temperature coefficient of resonant frequency of the samples ranged from −35.0 to −56.5 ppm/°C. Moreover, compared to Y 2Ba(Cu 1− x Mg x )O 5 compound without cold isotropic pressure (CIP), that with CIP especially exhibited approximately 16% higher Q· f value.

Unique Features and Properties of Nanostructured Materials

AbstractIn this introductory paper an attempt is made to give an overview of the area of nanostructured materials irrespective of the synthesis process. The various microstructural features such as clusters or isolated nanoparticles, agglomerated nanopowders, consolidated nanomaterials and nanocomposite materials as well as all materials classes are considered. As an important component of modern research on nanomaterials a section describes the various characterization tools available. Based on these remarks some properties of nanostructured materials will be summarized emphasizing the property–microstructure relationships. Finally, a brief outlook on applications and initial industrial use of nanomaterials is presented.

PLD 방법에 의해서 증착된 ZnO 박막의 전기적 특성 및 접합 특성에 관한 연구

In this study, metal/ZnO contacts were thermally annealed at different temperatures (as-dep., 400<TEX>$^{\circ}C$</TEX>, 600<TEX>$^{\circ}C$</TEX>, 800<TEX>$^{\circ}C$</TEX>, 1000<TEX>$^{\circ}C$</TEX>) for the investigation of electrical properties, and surface and interface characteristics. The analysis of the element composition and the chemical bonding state of the surface was made by the XPS(X-ray photoelectron spectroscopy). An attempt was made to establish the electrical property-microstructure relationship for the (Ti, Au)/ZnO. The Ti/ZnO contact exhibits an ohmic characteristics with a relatively high contact resistance of 4.74<TEX>${\times}$</TEX>10<TEX>$\^$</TEX>-1/ <TEX>$\Omega$</TEX><TEX>$\textrm{cm}^2$</TEX> after an annealing at 400<TEX>$^{\circ}C$</TEX>. The contact showed a schottky characteristics when the samples were annealed at higher temperature than 400<TEX>$^{\circ}C$</TEX>. The transition from the ohmic to schottky characteristics was contributed from the formation of the oxide layers as was confirmed by the peaks for O-O and Ti-O bondings in XPS analysis. For the Au/ZnO contact the lowest contact resistance was obtained from the as-deposited sample. The resistance was slowly increased with annealing temperature up to 600<TEX>$^{\circ}C$</TEX>. The ohmic characteristics were maintained eden fort 600<TEX>$^{\circ}C$</TEX> annealing. The XPS analysis showed that the Au-O intensity was dramatically decreased with temperature above 600<TEX>$^{\circ}C$</TEX>.

Relationship between mechanical performance and microstructure in composites fabricated with flow-enhancing fabrics

The resin transfer moulding process involves the long-range flow of resin into a closed mould which is filled with dry reinforcement. High-performance composites require a high volume fraction of fibres, which results in low porosity of the fibre pack and therefore slow rates of mould filling. Commercial reinforcement fabrics are becoming available which promote faster resin flow than conventional fabrics, by engineering regions of large pore space into the reinforcement stack. However, theoretical models of the property-microstructure relationships have indicated that resin-rich areas (corresponding to filled large pore space) and fibre clustering will lead to degradation of the mechanical performance of the laminate. This report describes a series of compression and interlaminar shear tests on a range of twill-weave fabrics having ‘flow-enhancing’ tows substituted in the warp direction. The results provide some experimental support for existing theoretical models.

Property-Microstructure relationships in the

The tensile properties and fracture toughness levels found in forged and heat treated pancake forgings of the high strength titanium alloy, Ti6Al2Sn4Zr6Mo, were analyzed as to their relationship to microstructural features. The desired microstructure for the alloy, resulting in an optimum combination of both fracture toughness and tensile ductility at yield strengths of 170–180 k.s.i., is described as containing about 10 volume percent equiaxed or globular alpha (primary alpha) along with a matrix containing relatively coarse acicular alpha (secondary alpha) and aged beta. Although many combinations of forging procedures and/or heat treatments may exist which result in material having the above-described microstructure, two specific approaches for its attainment were investigated. One consisted of forging very high (1725°F) in the two-phase region, followed by a low (1525°F) temperature solution treatment; the other consisted of alpha+beta forging at a convenient temperature, followed by two solutions treatments. Aging to a desired strength level was the final step in each operation.