High Strength Metallic Alloys Research Articles

Exceptional strength paired with increased cold cracking susceptibility in laser powder bed fusion of a Mg-RE alloy

Additive manufacturing (AM) of high-strength metallic alloys frequently encounters detrimental distortion and cracking, attributed to the accumulation of thermal stresses. These issues significantly impede the practical application of as-printed components. This study examines the Mg-15Gd-1Zn-0.4Zr (GZ151K, wt.%) alloy, a prototypical high-strength casting Mg-RE alloy, fabricated through laser powder bed fusion (LPBF). Despite achieving ultra-high strength, the GZ151K alloy concurrently exhibits a pronounced cold-cracking susceptibility. The as-printed GZ151K alloy consists of almost fully fine equiaxed grains with an average grain size of merely 2.87 µm. Subsequent direct aging (T5) heat treatment induces the formation of dense prismatic β' precipitates. Consequently, the LPBF-T5 GZ151K alloy manifests an ultra-high yield strength of 405 MPa, surpassing all previously reported yield strengths for Mg alloys fabricated via LPBF and even exceeding that of its extrusion-T5 counterpart. Interestingly, as-printed GZ151K samples with a build height of 2 mm exhibit no cracking, whereas samples with build heights ranging from 4 to 18 mm demonstrate severe cold cracking. Thermal stress simulation also suggests that the cold cracking susceptibility increases significantly with increasing build height. The combination of high thermal stress and low ductility in the as-printed GZ151K alloy culminates in a high cold cracking susceptibility. This study offers novel insights into the intricate issue of cold cracking in the LPBF process of high-strength Mg alloys, highlighting the critical balance between achieving high strength and mitigating cold cracking susceptibility.

Metal 3D-Printed Bioinspired Lattice Elevator Braking Pads for Enhanced Dynamic Friction Performance.

The elevator industry is constantly expanding creating an increased demand for the integration of high technological tools to increase elevator efficiency and safety. Towards this direction, Additive Manufacturing (AM), and especially metal AM, is one of the technologies that could offer numerous competitive advantages in the production of industrial parts, such as integration of complex geometry, high manufacturability of high-strength metal alloys, etc. In this context, the present study has 3D designed, 3D printing manufactured, and evaluated novel bioinspired structures for elevator safety gear friction pads with the aim of enhancing their dynamic friction performance and eliminating the undesired behavior properties observed in conventional pads. Four different friction pads with embedded bioinspired surface lattice structures were formed on the template of the friction surface of the conventional pads and 3D printed by the Selective Laser Melting (SLM) process utilizing tool steel H13 powder as feedstock material. Each safety gear friction pad underwent tribological tests to evaluate its dynamic coefficient of friction (CoF). The results indicated that pads with a high contact surface area, such as those with car-tire-like and extended honeycomb structures, exhibit high CoF of 0.549 and 0.459, respectively. Based on the acquired CoFs, Finite Element Models (FEM) were developed to access the performance of braking pads under realistic operation conditions, highlighting the lower stress concentration for the aforementioned designs. The 3D-printed safety gear friction pads were assembled in an existing emergency progressive safety gear system of KLEEMANN Group, providing sufficient functionality.

Изотермическое прессование в конической матрице релаксирующего материала

The relations for calculating the deformation mode and force conditions of isothermal extrusion of blanks made of high-strength metallic alloys are proposed. Under isothermal deformation, the material is hardened and softened, which is associated with the manifestation of the viscous properties of the material (creep). In this regard, the state of viscoplasticity is taken on. The deformation state is accompanied by stress relaxation, which is greater the lower the speed (longer duration) of the operation. Based on the mechanics of deformation, the dependence of moulding conditions (deformation, force, damage to the work material) is expressed by analytical relations. The power balance of activity of forces results in a pressure estimation for isothermal exposure. In this case, a discontinuous field of path velocities is used, which consists of a block of deformations and rigid blocks. The blocks are separated by slip surfaces. Deformations occur in the deformation block and on slip surfaces. Since pressing leads to the occurrence of micro-damages, the damage rate of the coating material was estimated. In this case, the criteria of fracture kinetics are used: energy and deformation equations. The damage rate of the material depends on the speed and degree of deformation, or solely on the degree of deformation. For a number of materials, reducing the speed helps to reduce damage and, consequently, the possibility of increasing the degree of shaping of the primary blank. The relations for stiffness analysis of the stress pattern are given, on which the damage also depends. Calculations of the pressure and damage of the material under compaction for blanks made of titanium and high-strength aluminum alloys have been performed. It is shown that at low operation speeds on the appropriate hydraulic forging equipment, the exposure pressure decreases significantly. The aluminum alloy damaging is also reduced, and for titanium it depends only on the degree of forming.

Atomistic study on effects of solute atoms on energy profile of edge dislocation mobility in FCC-Cu alloys

Solid-solution strengthening is an effective method to increase the mechanical strength of metal alloys. Revealing the solid-solution strengthening mechanism based on the energy profile of the dislocation motion is vital for the non-empirical development of high-strength metal alloys. This study provides detailed energy profiles (i.e., energy surfaces) of the edge dislocation gliding motion under the effect of solute atoms, as well as the atomic-scale origin of solute strengthening in face-centered cubic (FCC) Cu alloys. The maximum shear stress (τmax) required for the dislocation to leave the solute atoms (Ni, Co, and Mo, all with different sizes and stacking fault effects) was qualitatively evaluated by finite temperature molecular dynamics simulations. By the nudged elastic band (NEB) analysis, we determined the atomistic origin of the energy barrier for the edge dislocation motion and the maximum force required to overcome the solute pinning effect (i.e., depinning force, FNEB) in binary Cu alloys. By linking FNEB to the size misfit, a theoretical prediction model based on size effects and the volumetric strain field was used and can qualitatively explain the increment in the maximum shear stress (Δτmax) by the solute atoms. These results provide an atomistic basis for the prediction of the solute-strengthening effect correlated with the edge dislocation motion in wide FCC systems.

An advanced approach to improve the high-temperature property for Ni-based superalloys: Interface segregation manipulation

In response to the requirements for the long-term service reliability of Ni-based superalloys, the correlations between the microstructure and creep property are investigated in present work. Creep experiments were conducted on a designed Ni-based single crystal superalloy at 900 °C/330 MPa, the results indicate that the creep rupture properties deteriorated following thermal exposure at both 900 °C and 1000 °C. The γ′-phase, γ-matrix and γ/γ′ interface undergo varying degrees of degradation, including the coarsening and the decrease in the volume fraction of γ′-phase, the decrease in the γ-matrix strength, the decrease in the lattice misfit and the increase in the dislocation network spacing. When the values of the microstructural parameters (γ′-phase size and volume fraction) were numerically similar for different thermal exposure times at 900 °C and 1000 °C, taking 900 °C/10,000h and 1000 °C/2000h samples as examples. The experimental alloy exhibited better creep resistance after being exposed to 1000 °C compared to 900 °C. Through the combination of atom probe tomography and first-principles calculations, an interface strengthening mechanism driven by interface segregation is identified. Finally, a design concept for high-strength metal alloys based on the decoration of solutes interface segregation is proposed, also called “Interface Segregation Manipulation”.

Correlative high-resolution imaging of hydrogen in Mg2Ni hydrogen storage thin films

Nanometer scale imaging of hydrogen in solid materials remains an important challenge for the characterization of advanced materials, such as semiconductors, high-strength metallic alloys, and hydrogen storage materials. Within this work, we demonstrate high-resolution imaging of hydrogen and deuterium within Mg2Ni/Mg2NiH4 hydrogen storage thin films using an in-house developed secondary ion mass spectrometer (SIMS) system attached to a commercially available dual-beam focused ion beam - scanning electron microscope (FIB-SEM) instrument. We further demonstrate a novel approach to measure the size, shape, and distribution of the hydride phase in partially transformed films using laser scanning confocal microscopy (LSCM) to measure surface topography changes from the hydride phase volume expansion. Combining these techniques provides new insights on hydride nucleation and growth within the Mg2NiHx system. Finally, we demonstrate the efficacy of tracking deuterium as a hydrogen analog to reduce the background for SIMS imaging of hydrogen in high-vacuum chambers (∼10−6 mbar).

Predictive model of chip segmentation in machining of high-strength metallic alloys

Chip segmentation is the dominant chip formation mechanism during the machining of high-strength metallic alloys which directly affects the machining productivity and the final product’s quality. This paper investigates the mechanism of shear band formation and its contact with the cutting tool for different titanium and nickel alloys. First, we reveal that the shear bands are in direct contact with the cutting tool due to rolling on its rake face, although the contact mechanism is different for titanium and nickel alloys. In addition, the effect of the stored energy at the tool-chip interface, which is believed to be the reason for chip segmentation in some studies, is investigated theoretically. We found that the stored energy at the tool-chip interface affects the strain rate temporarily and has minimal impact on the chip segmentation. Moreover, we provide a theoretical prediction of the workpiece material’s displacement, its distribution, and degree of segmentation for the first time without any post-mortem analysis of the produced shear bands. To this end, the rolling process must be taken into account for accurate prediction. We show that the segmented chip’s displacement can be accurately predicted without any fracture criterion since the shear band itself is a type of ductile material failure. It is shown that the shear bands can accommodate large strains (for example, around 45 when cutting Ti-6Al-4V at 60 m min−1 cutting speed) without fracture presumption.

Suppressed hydrogen embrittlement of high-strength Al alloys by Mn-rich intermetallic compound particles

The pursuit of strong and ductile Al alloys with superior resistance to hydrogen embrittlement (HE) is practically significant across the aerospace and transportation industries among others. Unfortunately, effective ways to progress on the strength-HE trade-off for Al-alloys remain elusive. A strategy of suppressing HE by introducing intermetallic compound (IMC) particles to achieve hydrogen redistribution in various trapping sites was proposed. Here, we systematically induce the precipitation of a constant volume fraction of intermetallic compound (IMC) particles by adding one of 14 elements in a ternary Al-Zn-Mg high-strength alloy. We show a strong correlation between hydrogen trapping energies of the IMC obtained from ab initio calculations with the resistance to HE. Mn-rich Al11Mn3Zn2 particles exhibit the highest hydrogen trapping energy (0.859 eV/atom), leading to a decrease by approximately 5 orders of magnitude in the hydrogen occupancy in η2 (MgZn2) phase interfaces and grain boundaries, where HE cracks initiate. The Mn-addition did not deteriorate the ductility and most Al11Mn3Zn2 particles remained intact during plastic deformation which was revealed by in-situ 3D X-ray tomography. Hydrogen-induced strain localization at η2 phase interfaces and grain boundaries were inhibited due to strong hydrogen trapping capacity of Al11Mn3Zn2, hence preventing HE cracks initiation. Our approach effectively suppresses hydrogen-induced cracks without sacrificing the ductility, and our strategy can help the design roadmap of HE-tolerant high-strength metallic alloys.

A state-of-the-art review of the fabrication and characteristics of titanium and its alloys for biomedical applications.

Commercially pure titanium and titanium alloys have been among the most commonly used materials for biomedical applications since the 1950s. Due to the excellent mechanical tribological properties, corrosion resistance, biocompatibility, and antibacterial properties of titanium, it is getting much attention as a biomaterial for implants. Furthermore, titanium promotes osseointegration without any additional adhesives by physically bonding with the living bone at the implant site. These properties are crucial for producing high-strength metallic alloys for biomedical applications. Titanium alloys are manufactured into the three types of α, β, and α + β. The scientific and clinical understanding of titanium and its potential applications, especially in the biomedical field, are still in the early stages. This review aims to establish a credible platform for the current and future roles of titanium in biomedicine. We first explore the developmental history of titanium. Then, we review the recent advancement of the utility of titanium in diverse biomedical areas, its functional properties, mechanisms of biocompatibility, host tissue responses, and various relevant antimicrobial strategies. Future research will be directed toward advanced manufacturing technologies, such as powder-based additive manufacturing, electron beam melting and laser melting deposition, as well as analyzing the effects of alloying elements on the biocompatibility, corrosion resistance, and mechanical properties of titanium. Moreover, the role of titania nanotubes in regenerative medicine and nanomedicine applications, such as localized drug delivery system, immunomodulatory agents, antibacterial agents, and hemocompatibility, is investigated, and the paper concludes with the future outlook of titanium alloys as biomaterials.Graphic abstract

Analytical Modeling of Shear Localization in Orthogonal Cutting Processes

AbstractThis paper presents an analytical thermo-mechanical model of shear localization and shear band formation in orthogonal cutting of high-strength metallic alloys. The deformation process of the workpiece material includes three stages: homogeneous deformation, shear localization, and chip segmentation. A boundary layer analysis is used to analytically predict the temperature, stress, and strain rate variations in the primary shear zone associated with the shear localization. The predictions of shear band spacing and width from the proposed model are verified by experimental characterization of the chip morphology. The rolling of shear bands on the tool rake face is discussed from the experimental observations. The cutting tool temperature, which is influenced by the heat generated during the shear band formation, is simulated and compared with finite element simulations. The proposed analytical model reveals the fundamental mechanism of the complete shear localization process in orthogonal cutting and predicts the stress and temperature variations with high computational efficiency.

Machine learning for metallurgy III: A neural network potential for Al-Mg-Si

High-strength metal alloys achieve their performance via careful control of the nucleation, growth, and kinetics of precipitation. Alloy mechanical properties are then controlled by atomic scale phenomena such as shearing of the precipitates by dislocations. Atomistic modeling to understand the operative mechanisms requires length and timescales far larger than those accessible by first-principles methods. Here, a family of Behler-Parinello neural network potentials (NNPs) for the Al-Mg-Si system is developed to enable quantitative studies of Al-6xxx alloys. The NNP is trained on metallurgically important quantities computed by first-principles density function theory (DFT) leading to high-fidelity predictions of intermetallic compounds, elastic constants, dilute solid-solution energetics, precipitate/matrix interfaces, Al stacking fault energies, antisite defect energies, and other quantities. The generalized stacking fault energy surfaces for the three prevalent ${\ensuremath{\beta}}^{\ensuremath{'}\ensuremath{'}}$ precipitate compositions in peak-aged Al-6xxx are then computed with the NNP, and are validated by DFT computations at key points. A preliminary examination of early stage clustering kinetics and energetics in Al-6xxx is then made, showing the formation of low-energy Mg-Si structures and the trapping of vacancies in these clusters. The NNP thus shows significant transferability across structures, making it a powerful approach for chemically accurate simulations of metallurgical phenomena in Al-Mg-Si alloys.

Insights on tube rotary draw bending with superimposed localized thermal field

The manufacturing of hollow section profiles using high strength metallic alloys may suffer of relevant drawbacks such as springback, reduced formability as well as wrinkling, which often limit the process capabilities. Localized heating of cross section sectors may allow a significant reduction of these issues thanks to the neutral layer shift and lowered yield stress. The paper describes an analytical approach to provide a fast prediction of the stress and strain distributions in the cross-section and their effects on the springback as consequence of the process thermal and mechanical parameters. Experimental and numerical validations confirm the analytical model reliability.

Numerical modelling of functionally graded adherends

The development of lighter structures and materials has been one of the main research concerns of the transportation industry during the last decade, driven by the necessity to decrease fuel consumption and emissions. Therefore, the use of several different new lightweight materials, such as special metal alloys, reinforced polymers and new advanced composite materials has been explored, leading to optimized structures which combine these novel materials. To manufacture these multi-material structures, adhesive bonding is one of best joining techniques available, as fasteners add weight to the structure and require holes to be drilled and welding is not easily applicable to reinforced plastics, composites and some high strength metal alloys. However, adhesive bonding also presents some limitations that need to be considered, such as the appearance of singularities and the resultant stress concentration at the edges of the bond line, which result in a reduction of the joint strength. In order to mitigate this effect, several techniques have been proposed, being the use of functionally graded adherends one of them. Functionally graded adherends consist in an adherend where the mechanical properties gradually change throughout the material, usually in the thickness or length direction. The present work introduces the concept of a layered functionally graded adherend, varying the flexibility of each layer through the thickness direction. Different ratios of stiffness variation, combined with different adhesive properties, were numerically evaluated for single lap joints, comparing the stress distribution of the adhesive layer and the resultant joint strength, using cohesive zone modelling. Moreover, an optimization process of typical graded material properties, where different distribution laws that consider material weight and strength are considered, is presented.

Machine learning for metallurgy I. A neural-network potential for Al-Cu

High-strength metal alloys achieve their performance via careful control of precipitates and solutes. The nucleation, growth, and kinetics of precipitation, and the resulting mechanical properties, are inherently atomic scale phenomena, particularly during early-stage nucleation and growth. Atomistic modeling using interatomic potentials is a desirable tool for understanding the detailed phenomena involved in precipitation and strengthening, which requires length and timescales far larger than those accessible by first-principles methods. Current interatomic potentials for alloys are not, however, sufficiently accurate for such studies. Here a family of neural-network potentials (NNPs) for the Al-Cu system are presented as a first example of a machine learning potential that can achieve near-first-principles accuracy for many different metallurgically important aspects of this alloy. High-fidelity predictions of intermetallic compounds, elastic constants, dilute solid-solution energetics, precipitate-matrix interfaces, generalized stacking fault energies and surfaces for slip in matrix and precipitates, antisite defect energies, and other quantities, are shown. The NNPs also captures the subtle entropically induced transition between ${\ensuremath{\theta}}^{\ensuremath{'}}$ and $\ensuremath{\theta}$ at temperatures around 600 K. Many comparisons are made with the state-of-the-art angular-dependent potential for Al-Cu, demonstrating the significant quantitative benefit of a machine learning approach. A preliminary kinetic Monte Carlo study shows the NNP to predict the emergence of GP zones in Al-4at%Cu at $T=300$ K in agreement with experiments. These studies show that the NNP has significant transferability to defects and properties outside the structures used to train the NNP but also shows some errors highlighting that the use of any interatomic potential requires careful validation in application to specific metallurgical problems of interest.

Residual Normal and Shear Stresses on Different Machining-Finished Surfaces of Martensitic Ultrahigh Strength Steel

Machining induced residual stresses are known to have influenced mechanical properties of high strength metallic alloys. In this paper, we have compared the surface residual stresses of an ultrahigh strength martensitic/bainitic steel grade 56NiCrMoV7 induced by two different machining processes, namely turning and milling. Using the established d~sin2ψ method, x-ray diffraction technique was employed to measure the residual stresses on both the axial and hoop directions of cylindrical samples. The results reveal that, turning finish led to tensile residual stress in the axial direction and compressive residual stress in the hoop direction. On the other hand, milling finish led to compressive residual stresses in both the axial and hoop directions. In addition, large splitting in the d~sin2ψ linear regressions has been interpreted by the presence of residual shear stresses.

Innovative setup for cryogenic mechanical testing of high-strength metallic alloys

Mechanical properties of two high-strength metallic alloys, fabricated using additive manufacturing (AM) technology, were characterised down to − 269 °C. A test setup has been developed to accommodate the specific sample geometry and manufacturing conditions for these tests. Tensile, compression, pin-bearing, and shear tests were performed at room temperature, − 73 °C, − 196 °C, and − 269 °C. Test equipment and fixtures were designed and optimized to survive the test loads up to 100 kN at low temperatures. Instrumentation for strain, temperature, and displacement was also carefully chosen to record the specimen behaviour and apply the test requirements. The KRP cryo apparatus provided fast cooling and temperature stability during the entire duration of testing. In this paper, we describe the design of the test apparatus, the challenges in development and some results of test runs.

Experimental determination of the dynamic fracture-initiation toughness of high-strength metals

In the case of materials that may be subjected to dynamic loads or extreme conditions, it is crucial to be aware of the evolution of their fracture behaviour with the strain rate. This study describes the detailed design and careful development of a novel experimental technique that allowed measuring the dynamic fracture-initiation toughness for a wide range of loading rates based on a strong theoretical background. For such a purpose, two high-strength metallic alloys were studied: (i) a very mild strain rate dependent alloy, the AA7017-T73, and (ii) an armour steel with well-established rate effects the Mars 240. The former was selected in order to validate the newly established experimental technique. The measured dynamic fracture-initiation toughness, as expected, gave almost identical results, therefore validating the technique. Once the technique was established, the dynamic fracture-initiation toughness of the Mars 240 steel at different loading rates was obtained. The results showed an increase on the dynamic fracture-initiation toughness with increasing loading rates.

Spatial correlation of elastic heterogeneity tunes the deformation behavior of metallic glasses

Metallic glasses (MGs) possess remarkably high strength but often display only minimal tensile ductility due to the formation of catastrophic shear bands. Purposely enhancing the inherent heterogeneity to promote distributed flow offers new possibilities in improving the ductility of monolithic MGs. Here, we report the effect of the spatial heterogeneity of elasticity, resulting from the inherently inhomogeneous amorphous structures, on the deformation behavior of MGs, specifically focusing on the ductility using multiscale modeling methods. A highly heterogeneous, Gaussian-type shear modulus distribution at the nanoscale is revealed by atomistic simulations in Cu64Zr36 MGs, in which the soft population of the distribution exhibits a marked propensity to undergo the inelastic shear transformation. By employing a mesoscale shear transformation zone dynamics model, we find that the organization of such nanometer-scale shear transformation events into shear-band patterns is dependent on the spatial heterogeneity of the local shear moduli. A critical spatial correlation length of elastic heterogeneity is identified for the simulated MGs to achieve the best tensile ductility, which is associated with a transition of shear-band formation mechanisms, from stress-dictated nucleation and growth to structure-dictated strain percolation, as well as a saturation of elastically soft sites participating in the plastic flow. This discovery is important for the fundamental understanding of the role of spatial heterogeneity in influencing the deformation behavior of MGs. We believe that this can facilitate the design and development of new ductile monolithic MGs by a process of tuning the inherent heterogeneity to achieve enhanced ductility in these high-strength metallic alloys.

Experimental Investigation on the Effect of Process Parameters on Friction Stir Processing Of Aluminium

Light weight, high strength metallic alloys are of primary interest in the present day industries. Aluminium alloys occupy a unique position in industries because of its light weight. Lately much work has going on in enhancing the mechanical properties of the Aluminium by Friction Stir Processing (FSP), which is a surface modification technique. The various process parameters for FSP have a significant impact on the end result. The present study investigates the effect of various process parameters on Friction Stir Processing of Aluminium alloys. The process parameters selected for this study are speed (rpm), feed (mm/min) and depth of cut (mm). Three levels of speed, feed and depth of cut were selected and experiments were designed on the basis of Taguchi Orthogonal array. Experiments were conducted on CNC machine with specially designed FSP tool, having shoulder diameter of 20mm and pin diameter of 5mm. Optimum parameters value were obtained using Taguchi method. Confirmation experiments were also carried out. The documented results show that the micro hardness of the Aluminium gets improved during FSP.

High-strength silicon brass manufactured by selective laser melting

Generally, metallic alloys adaptive to selective laser melting (SLM) need to meet three basic physical properties, i.e. relatively high laser absorptivity, relatively low thermal conductivity, and especially non-containing low boiling point volatile elements. In this work, high-strength Cu-12.5Zn-2.9Si silicon brass, which does not meet these three requirements, was manufactured by SLM from gas-atomized powder. Interestingly, the SLM-manufactured silicon brass has high relative density (98.8%) thereby exhibiting higher strength than that for cast counterpart. Accordingly, this work substantiates, for the first time, the feasibility by SLM to manufacture high-strength metallic alloys with special physical properties.