Metallic Structural Materials Research Articles

Assessment of the degree of damage in structural materials using the parameters of structural acoustic noise

ABSTRACT The study considers the features of controlling the degree of structural metallic material degradation at the stage of scattered damage accumulation before the appearance of macrocracks using an approach based on the analysis of structural acoustic noise. Various methods of measuring the parameters of structural noise have been analysed from the point of view of their information content and the stability of the used calculation algorithms. Refined calculation algorithms for determining the spectral-energy parameters of structural noise are proposed, and the results of their experimental verification are presented. Comparative results of the stability of these algorithms are given. On the example of API X70 steel samples, cut from the main gas pipeline after long-term operation, and the sample of 08Cr18Ni10Ti steel, tested for low-cycle fatigue, the effectiveness of the proposed algorithm application for assessing the degree of critical material technical objects damage and the possibility of constructing a method for diagnosing products from these materials is shown.

Effect on microstructure and properties of LA103Z Mg–Li alloy plate by multi-pass friction stir processing

As the lightest metal structure material, Mg–Li alloy possesses many advantages and promising applications, but the low strength at room temperature limits its application. Multi-pass friction stir processing (MFSP) is expected to be an effective and simple method to overcome this shortcoming. In this study, the plate of LA103Z Mg–Li alloy was treated using MFSP. The mechanical properties, microstructure, and corrosion resistance of the plate before and after MFSP were compared. It was found that MFSP can effectively improve the mechanical properties of the plate, and the tensile strength and microhardness have been enhanced. Meanwhile, the plasticity of the material was also significantly improved, and the elongation increased by up to 109.2%. Furthermore, the corrosion resistance of the plate after MFSP was also increased.

Improving the Young's modulus of Mg via alloying and compositing – A short review

Lightweight, high-modulus structural materials are highly desired in many applications like aerospace, automobile and biomedical instruments. As the lightest metallic structural material, magnesium (Mg) has great potential but is limited by its low intrinsic Young's modulus. This paper reviews the investigations on high-modulus Mg-based materials during the last decades. The nature of elastic modulus is introduced, and typical high-modulus Mg alloys and Mg matrix composites are reviewed. Specifically, Mg alloys enhance Young's modulus of pure Mg mainly by introducing suitable alloying elements to promote the precipitation of high-modulus second phases in the alloy system. Differently, Mg matrix composites improve Young's modulus by incorporating high-modulus particles, whiskers and fibers into the Mg matrix. The modulus strengthening effectiveness brought by the two approaches is compared, and Mg matrix composites stand out as a more promising solution. In addition, two well-accepted modulus prediction models (Halpin-Tsai and Rule of mixtures (ROM)) for different Mg matrix composites are reviewed. The effects of reinforcement type, size, volume fraction and interfacial bonding condition on the modulus of Mg matrix composites are discussed. Finally, the existing challenges and development trends of high-modulus Mg-based materials are proposed and prospected.

Revealing the cryogenic-temperature toughness and deformation mechanisms in high manganese austenitic steels

High-Mn austenitic steels are promising structural metallic materials for cryogenic-temperature industries due to their good properties and economy. In this work, the cryogenic-temperature toughness and deformation mechanisms were revealed by Charpy impact testing and checking the microstructural characteristics in deformed Fe-(13– 30) Mn C steels. The results show that all studied steels showed good toughness at room temperature (i.e., 293 K), while an appropriate γ SFE level was essential for their low temperature toughness at 77 K. The plastic deformation mechanisms depended on stacking fault energy and accumulated strain or dislocation density levels simultaneously. Twinning-induced plasticity (TWIP) mechanism was found for the three studied steels at 293 K, which was beneficial for good Charpy impact toughness. Enhanced TWIP mechanism was found at 77 K owing to the decreased γ SFE values. Meanwhile, both strain-induced ε HCP martensite and α' BCC martensite were indicated in Fe-13Mn-0.9C steel, and few ε HCP martensite was examined in Fe-22Mn-0.9C steel. The α' BCC martensite was generally nucleated from prior strain-induced ε HCP martensite. The cryogenic-temperature toughness would deteriorate remarkably when strain induced α' BCC martensite was introduced or mechanical twins were delayed. The statistical dislocation densities in Fe-13Mn-0.9C steel were found to accumulate faster than Fe-22Mn-0.9C steel and Fe-30Mn-1.0C steel, especially at 77 K. And a full nonadditive strengthening mechanism between dislocations and varies obstacles were observed in the deformed steels. • The cryogenic-temperature toughness and deformation mechanisms in Fe-(13– 30) Mn C austenitic steels were revealed. • The temperature dependent Charpy impact energies showed special correlations with the stacking fault energies. • The plastic deformation mechanisms were the close functions of both stacking fault energies and accumulated dislocations. • The cryogenic-temperature toughness would deteriorate with strain induced α ' BCC martensite or delayed mechanical twins. • A full nonadditive strengthening mechanism between dislocations and varies obstacles were observed in the deformed steels.

Simultaneously enhancing strength and toughness of graphene oxide reinforced ZK60 magnesium matrix composites through powder thixoforming

Simultaneously realizing high strength and ductility has been a hot but also difficult subject for structural metal materials, especially Mg alloys, it is always unavoidable to sacrifice ductility as strength improvement and vice versa. Here, we report an effective technology, namely powder thixoforming, to attempt to overcome the trade-off between strength and ductility of a ZK60 Mg alloy based composite reinforced by graphene oxide. It is found that the composite prepared by utilizing segmented ball milling exhibits a tensile yield strength of 177 MPa, which is 21.2% and 36.2% higher than those of the corresponding ball-milled and un-milled ZK60 alloys, respectively, while maintaining a high tensile elongation to failure of 23.09%, being equivalent to that of the unreinforced counterpart and 20.3% higher than that of the un-milled ZK60 alloy. This work represents a promising technology for fabricating carbon nanomaterials reinforced metal-based composites with both high strength and ductility.

Thermal, Sound and Fire Performance Properties of Prefabricated Facade Panels with Massive, Sandwich and Frame Design Concepts

Many reasons such as the Industrial Revolution and the need for rapid building production after the Second World War have led to an acceleration of developments in the construction sector and new construction systems have emerged. These construction systems have brought forth the need for new facade designs. Prefabricated facade panels designed with the aim of quickly closing a building whose structure is completed so that it is least affected by external environmental conditions and ensuring that the facades created can exhibit good performance are also among these innovations. In this study, thermal and sound insulation, and fire resistance performance characteristics of prefabricated facade panels with wood, concrete, metal, or terracotta-based structure material, made with three different design concepts as massive, sandwich, and frame, were examined. The study is considered important because it examines the characteristics of facade elements aimed at improving the quality of the indoor environment.

(Digital Presentation) Investigation of Microgalvanic Corrosion in Magnesium Alloys Using Theoretical Analysis and Phase-Field Modeling

Magnesium and its alloys are the lightest structural metallic materials known, and therefore, hold vast potential for reducing the weight for various transportation modes such as airplanes, cars, buses, etc. Although the alloying of Mg with elements such as Al, Mn, and rare earth elements is known to improve the mechanical properties of Mg, the process is often detrimental to the corrosion performance of Mg. This increase in the corrosion rate occurs because of the microgalvanic couple that forms between the Mg-rich phase, which acts as an anode, and the alloying-element-rich phase, which acts as a cathode. Using both experiments and modeling, it has been reported that the rate of microgalvanic corrosion in the Mg alloys depends on the alloying element and microstructure. However, a deeper understanding is required for quantifying the effect of microstructure characteristics such as the fraction of the two phases, spacing between the two phases, the geometry of the two phases, etc., on the corrosion rate. This understanding is crucial for designing Mg alloys with optimal mechanical properties and high corrosion resistance. To bridge this gap in our understanding, we perform the continuum-scale phase-field modeling of different microstructures observed in Mg alloys. Furthermore, we complement the modeling work with theoretical analysis, where we develop analytical relations for studying the effect of various material and microstructural parameters on the characteristic corrosion length scale. The results from both these efforts will be summarized in our presentation.

A thermodynamic model for high temperature corrosion applications: The (Na2SO4 + K2SO4 + ZnSO4 + PbSO4) system

The (Na2SO4 + K2SO4 + ZnSO4 + PbSO4) salt system is important for deposit buildup, fouling and associated corrosion of metallic structural and heat exchanger materials of municipal solid waste incinerators, low-grade fuel firing boilers, as well as metallurgical heat recovery boilers. In this study, a complete critical evaluation of all available phase diagram and thermodynamic data has been performed for all condensed phases of the (Na2SO4 + K2SO4 + ZnSO4 + PbSO4) system, and optimized model parameters have been found. The Modified Quasichemical Model for short-range ordering was used for the molten salt phase while most of the relevant solid solutions were modeled using the Compound Energy Formalism. The (Na2SO4 + K2SO4) sub-system has been critically evaluated in a previous article. A (60 mol% PbSO4 + 40 mol% ZnSO4) binary mixture was investigated by DTA-TGA since no thermodynamic data were available in the literature for this particular sub-system. The model parameters obtained for the binary and ternary sub-systems of the (Na2SO4 + K2SO4 + ZnSO4 + PbSO4) system can be used to predict thermodynamic properties and phase equilibria for the multicomponent system. In particular, ternary and quaternary eutectics (corresponding to the formation of a liquid phase at low temperatures) may be predicted, thus permitting to avoid “catastrophic” corrosion. This work is part of a large thermodynamic model for the Na+, K+, Zn2+, Pb2+ // Cl−, SO42− system.

Effect of Carburizing Helium Environment on Corrosion Behavior of the High-Temperature Alloys for High-Temperature Gas-Cooled Reactor

The primary coolant of High-Temperature Gas-cooled Reactor (HTGR) is expected to contain impurities that can make corrosion to structural metallic materials at elevated temperatures. According to the chemical thermodynamics and kinetics, the carbon activity of helium can be calculated, and it is indicated that a high “CH4/H2O” ratio may lead to severe carburizing of the alloys. On this basis, corrosion tests were conducted on the three heat-resistance alloys Inconel 617, Hastelloy X, and Incoloy 800H at 950°C using helium environment with impurities, and mainly the effect of carburization was investigated. The corrosion samples were observed by Scanning Electron Microscopy (SEM) with Energy Disperse Spectroscopy (EDS), Electron Probe Microanalyzer (EPMA), and Carbon-sulfur Analyzer. These all alloys showed the oxidation and carburizing behavior, in which the carburized depth of Hastelloy X was shallow due to the dense oxide scale.

Metallographical and Thermodynamic Investigation of the Microstructures at 1200°C of TaC–Containing Co–Based Alloys

Among the wide variety of current metallic structural materials able to work at elevated temperatures in severe chemical and mechanical conditions, some superalloys based on cobalt play a particular role: the ones rich in chromium for resisting hot corrosion by gases and melts and strengthened by tantalum carbides. They are able to demonstrate good behavior in contact of molten salts or glasses and simultaneously under mechanical stresses. Their refractoriness as well as the characteristics of their TaC population are key points for their sustainability at high temperature in working conditions. The present study aims to anticipate the long time microstructure behavior at high temperature by testing three similar cast Co–based superalloys strengthened by TaC carbides but different from each other in the field of the chemical compositions of their matrix. Thermodynamic calculations and long time exposure at 1200°C were carried out to predict their microstructure evolution at this very high temperature, with special focus of the influence on TaC carbides of the chemical compositions of the alloys, notably of their matrix.

N-doped carbon dots as a multifunctional platform for real-time corrosion monitoring and inhibition

The occurrence of corrosion can’t be completely eliminated. To prevent the failure of structural materials, corrosion has to be easily identified, visualized and detected at early-stage, in order to intervene at the point where it is necessary. In this view, fluorescent N-doped CDs have been synthesized to synergistically inhibit and monitor corrosion of iron. The as-prepared CDs were fabricated by simple solvothermal process using citric acid as carbon source and ammonia as dopant. It is found that the active groups on the surface of the CDs promote the formation of adsorption film of CDs on iron plates and effective fluorescence emission. As a result, the CDs could readily inhibit the corrosion of iron and exhibit an inhibition efficiency of 88 % at 180 mg/L. As the degree of corrosion increases, the CDs-adsorption film can sensitively, visually and effectively respond to released Fe3+ due to the complexation between CDs and Fe3+. Due to this dual function of CDs for corrosion monitoring and inhibition, they can readily trace early-stage corrosion and prevent its development. This is a synergistic strategy to prevent critical engineering failures and to ensure the safety of structural metal materials.

Stochastic model describing evolution of microstructural parameters during hot rolling of steel plates and strips

Enhancing strength-ductility synergy of materials has been for decades an objective of research on structural metallic materials. It has been shown by many researchers that significant improvement of this synergy can be obtained by tailoring heterogeneous multiphase microstructures. Since large gradients of properties in these microstructures cause a decrease of the local fracture resistance, the objective of research is to obtain smoother gradients of properties by control of the manufacturing process. Advanced material models are needed to design such microstructures with smooth gradients. These models should supply information about distributions of various microstructural features, instead of their average values. Models based on stochastic internal variables meet this requirement. Our objective was to account for the random character of the recrystallization and to transfer this randomness into equations describing the evolution of dislocations and grain size during hot deformation and during interpass times. The idea of this stochastic model is described in the paper. Experiments composed of uniaxial compression tests were performed to supply data for the identification and verification of the model in the hot deformation and static recrystallization parts. Histograms of the grain size were measured after hot deformation and at different times after the end of deformation. Identification and validation of the model were performed. The validated model, which predicts evolution of heterogeneous multiphase microstructure, is the main output of our work. The model was implemented in the finite element program for hot rolling of plates and sheets and simulations of these processes were performed. The model’s capability to compare and evaluate various rolling strategies are demonstrated in the paper.

The Federal Institute of Materials Research and Testing (BAM) – 150 Years of Enabling Scientific and Technological Breakthrough

The Federal Institute of Materials Research and Testing (BAM) – 150 Years of Enabling Scientific and Technological Breakthrough

Effects of Ni content on microstructure and wear behavior of Al–13Si–3Cu–1Mg-xNi-0.6Fe-0.6Mn alloys

As one of the lightweight and wear-resistance metallic structural materials, cast Al–Si alloys have been widely studied in automobile and defense industries to meet the greater demands for elevated-temperature wear-resistance properties. In this study, the effect of Ni content on the microstructure and wear behavior of Al–13Si–3Cu–1Mg-xNi-0.6Fe-0.6Mn alloys were investigated by thermodynamic modeling, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and ball-on-disk reciprocating sliding test. The results show that the θ-Al2Cu and γ-Al7Cu4Ni phases are disappeared, while the δ-Al3CuNi, ε-Al3Ni, and T-Fe phases are formed with the increasing of Ni contents. The 3-D network structure is composed of α-Al matrix, eutectic Si, Q, Ni-rich, and Al15(Mn, Fe)3Si2 phases, which leads to the best hardness and wear-resistance of the alloy with 2 wt% Ni. The fracture and debonding of excessive coarse ε-Al3Ni phase deteriorate the wear-resistance and ductility of the 3Ni alloy. The main wear mechanisms of the tested alloys are abrasive, delamination and oxidative wear at 25 °C and convert to adhesive wear at 350 °C.

Significant improvement in creep property of a Mg–Yb based alloy via introducing nano-spaced stacking faults

Although magnesium alloys are the lightest structural metallic material, they have poor creep resistance. We present a new mechanism for increasing their creep resistance in this paper. Nano-spaced stacking faults were introduced into a Mg-3Yb-0.6Zn-0.4Zr (wt.%) alloy by the alloying of Y, resulting in a more than two orders of magnitude reduction in the minimum creep rate. The finding provides a reference for developing Mg alloys with superior creep resistance.

Experimental and simulation research on hollow AZ31 magnesium alloy three-channel joint by hot extrusion forming with sand mandrel

Magnesium alloy is one of the lightest metal structural materials. The weight is further reduced through the hollow structure. However, the hollow structure is easily damaged during processing. In order to maintain the hollow structure and to transfer the stresses during the high temperature deformation, the sand mandrel is proposed. In this paper, the hollow AZ31 magnesium alloy three-channel joint is studied by hot extrusion forming. Sand as one of solid granule medium is used to fill the hollow magnesium alloy. The extrusion temperatures are 230 °C and 300 °C, respectively. The process parameters (die angle, temperature, bottom thickness, sidewall thickness, edge-to-middle ratio in bottom, bottom shape) of the hollow magnesium alloy are analyzed based on the results of experiments and the finite element method. The results are shown that the formability of the hollow magnesium alloy will be much better when the ratio of sidewall thickness to the bottom thickness is 1:1.5. Also when edge-to-middle ratio in bottom is about 1:1.5, a better forming product can be received. The best bottom shape in these experiments will be convex based on the forming results. The grain will be refined obviously after the extrusion. Also the microstructures will be shown as streamlines. And these lines will be well agreement with the mold in the corner.

Stress-accelerated softening in bulk nanocrystalline Mg-Gd-Y-Zr alloys

Exploring the microstructure and mechanical property evolution of metallic structural materials during stress annealing has scientific and engineering significance since these materials are usually used to bear coupled thermo-mechanical loads in their service life. Here, we report a stress-accelerated softening phenomenon in bulk nanocrystalline Mg-Gd-Y-Zr alloys. Transmission electron microscopy observation indicates that, compared with static annealing, stress annealing accelerates the grain coarsening and precipitation of the grain boundary β phases. The precipitation of β phases results in the depletion of intragranular solute atoms, which therefore weakens the solid solution strengthening effect. The stress-assisted β phase precipitation and grain coarsening lead to the accelerated softening of nanocrystalline Mg-Gd-Y-Zr alloys. That is, the mechanical properties of nanocrystalline Mg-Gd-Y-Zr alloys subjected to coupled thermo-mechanical loads deteriorate more rapidly compared with the statically-annealed alloys.

Conversion of the kinetic indentation diagrams of ball indenter into stress-strain curves for metallic structural materials

A brief review of known approaches to converting diagrams obtained by indentation into tension diagrams is presented. It is noted that most studies on the transformation of kinetic diagrams of indentation of a spherical indenter into tension diagrams are carried out within the limits of uniform deformation using both computational and experimental approaches including the finite element method (FEM) and neural networks. However, we consider that such a transformation from one diagram to another can be fulfilled successfully when using the proper relationship between indentation and tension deformations. This makes it possible to obtain both more reliable estimation of the mechanical properties from indentation tests and more accurate transformation of these results into the stress-strain curves. A relative indentation diameter is one of the main parameters used in the most frequently used formulas for determining plastic deformation. However, at the same values of the relative indentation diameters and a constant ratio of the average contact pressure (Meyer hardness) to the true tensile stress, the strain values upon indentation and tensile can differ significantly due to different ability of materials to strain hardening. We determined a relationship between the true elastoplastic deformation in tensile tests and the relative depth of unrecovered indent obtained in indentation tests with allowance for strain hardening. A methodology for converting the kinetic indentation diagram into a tension diagram in the region of uniform deformation has been developed with the possibility of determining the yield strength, tensile strength, and ultimate uniform elongation of tested materials. The developed method was verified by testing steels, aluminum, magnesium and titanium alloys which differ greatly in the modulus of normal elasticity, strength characteristics, ductility and strain hardening.

Preface to the Special Issue on “Lamellar Structure in Structural Metallic Material and Its Mechanical Property”

Preface to the Special Issue on “Lamellar Structure in Structural Metallic Material and Its Mechanical Property”

Austenitic stainless steels of high strength and ductility

Abstract High strength and high ductility together are prime requirements for modern structural metallic materials. Important industrial examples are steels for car components such as body sheets, tubes and forgings. The present paper traces two lines of alloy development, stable austenitic stainless steels and intentionally metastable austenitic stainless steels. Although both groups have different advantages and disadvantages, each one exceeds all other presently available structural metallic materials in terms of strength to density ratio at equal ductility.