Mechanical Behavior Of Alloys Research Articles

Effect of Ultrasonic Shot Peening on Surface Mechanical and Wear Behavior of Aluminum 7075-T651 Alloy

Effect of Ultrasonic Shot Peening on Surface Mechanical and Wear Behavior of Aluminum 7075-T651 Alloy

Origin and Potentialities of the Selective Host‐Matrix Effect in Hydrogenated III‐V‐N Alloys.

AbstractIn a previous study, puzzling experimental results regarding the neutralization of N effects on the bandgap energy in the hydrogenated In0.21Ga0.79As0.975N0.025 alloy were explained by theoretical investigations revealing the occurrence of a novel phenomenon: thermal annealing changes the InGaAs host‐matrix by making it able to exert a selection of the N–H complexes responsible of the N neutralization. In view of technological applications of this effect, the underlying selective host‐matrix model was carefully checked here by theoretically investigating InGaAsN alloys of different compositions ranging from Ga‐rich to In‐rich. As a most important result, such an extensive investigation inspired a comprehensive explanation of the origin of the host‐matrix effect which clarifies how the effect works, firmly establishes its occurrence, gives indications for a bandgap tuning based on a matrix design, sets conditions for its extension to other III‐V‐N alloys and suggests ways to induce fine changes of the alloy mechanical behavior.

Atomic simulation for the effect of short-range order and twin boundary on mechanical behavior of FeNiCrCoAl high-entropy alloys

Short-range order (SRO) structure has been considered a potential strengthening method to improve the mechanical properties of high-entropy alloys (HEAs). However, the reinforcement mechanism of SRO structure on the HEA is still unclear. Here, the effect of SRO degree, twin boundary (TB) and temperature on the mechanical properties of the FeNiCrCoAl HEAs with different Al contents under uniaxial tensile is investigated using molecular dynamics/Monte Carlo simulations. The results indicate that the strengthening effect caused by the SRO structure and the softening effect caused by the addition of Al atoms coexist in the HEAs, and their competition determines the mechanical properties of the HEAs. And the softening caused by Al atoms dominates the mechanical properties of the HEAs, and the mechanical properties of the HEAs decrease with the increase of Al content. The results show that Al content has a significant impact on the SRO structure of the HEAs and the degree of SRO decreases in the HEAs with the increase of Al content. It is worth noting that under the same alloy composition, the strengthening effect of the SRO structure on the alloys first increases and then decreases with increasing the degree of SRO. The results indicate that the strengthening effect of the SRO structure and TB together is greater than that of TB or SRO alone. In addition, the results also show that higher temperature is not conducive to the stability of SRO structure, and the strengthening effect of SRO on the HEAs decreases with the increase of temperature.

Effects of residual stress on the isothermal tensile behavior of nanocrystalline superelastic NiTi shape memory alloy

The residual stress greatly affects the mechanical behavior of a material. In this work, the effect of residual stress on the isothermal tensile behavior of a NiTi shape memory alloy is studied. The focused ion beam and digital image correlation are combined to measure the two-dimensional residual stress in nanocrystalline NiTi plates processed with prestrain laser shock peening. A four-point bending experiment verified the accuracy of this measurement method. The FIB-DIC method is an attractive tool for measuring the two-dimensional residual stress in phase transition nanocrystalline materials. The internal residual stress significantly decreases the phase transition stress, and the mechanism is studied via finite element and theoretical analyses. This work implies that the mechanical behavior of NiTi shape memory alloys can be tailored via residual stress engineering.

Effect of grain size on mechanical characteristics and work-hardening behavior of fine-grained Mg-0.8Mn alloy via adjusting extrusion temperature

In this study, the Mg-0.8Mn (M08, wt%) alloy is subjected to hot extrusion at various temperatures ranging from 150 ℃ to 300 ℃, and the correlations between the microstructure evolution, tensile properties, and work hardening behavior at ambient temperature are elaborated. The M08 alloy extruded at 150 ℃ exhibits a bimodal microstructure, which included undynamic recrystallized (unDRXed) grains and fine dynamic recrystallized (DRXed) grains with an average size of 1.4 μm. As the extrusion temperature exceeds 210 °C, fully DRXed grains can be observed with grains growth becoming more pronounced with the increase of extrusion temperature. Notably, Mn atomic segregations are evident at the grain boundaries (GBs) in the M08 alloy extruded at 150 °C. It is also essential to highlight that the propensity for GB segregation is diminished with higher extrusion temperature, and the amount of α-Mn precipitates within grain interiors is increased in the M08 sample extruded at 300 ℃. An intriguing observation is the abnormal rise in yield strength (YS) with grain size as the extrusion temperature is increased. This phenomenon can be attributed to the diminishing effect of GB sliding and the concurrent enhancement of GB strengthening effect. However, as the extrusion temperature is raised from 150 °C to 300 °C, the ductility of M08 alloy experiences a substantial decline from 74 % ± 4–16 % ± 3 %. Meanwhile, the grain growth can bring about an increased strain hardening rate, which is primarily dependent on the transition in the dominant deformation mechanism from grain boundary sliding (GBS) to dislocation slip. This transition leads to a more substantial accumulation of dislocations within the coarser grains, thereby affecting the mechanical behavior of M08 alloy. This work provides valuable insights into the influence of extrusion temperature on the microstructure evolution and mechanical properties of Mg-0.8Mn alloy, offering a foundation for optimizing the processing parameters to achieve desired mechanical performance.

Parametric Analysis and Improvement of the Johnson-Cook Model for a TC4 Titanium Alloy

Titanium alloys are widely used in the manufacture of gas turbines’ compressor blades. Elucidating their mechanical behavior and strength under damaged conditions is the key to evaluating the equipment’s reliability. However, the conventional Johnson-Cook (J-C) constitutive model has limitations in describing the dynamic response of titanium alloy materials under the impact of a high strain rate. In order to solve this problem, the mechanical behavior of a TC4 titanium alloy under high strain rate and different temperature conditions was analyzed by combining experiments and numerical simulations. In this study, the parameters of the J-C model were analyzed in detail, and an improved J-C constitutive model is proposed, based on the new mechanism of the strain rate strengthening effect and the temperature softening effect, which improves the accuracy of the description of strain sensitivity and temperature dependence. Finally, the VUMAT subroutine of ABAQUS software was used for numerical simulation, and the predictive ability of the improved model was verified. The simulation results showed that the maximum prediction error of the traditional J-C model was 23.6%, while the maximum error of the improved model was reduced to 5.6%. This indicates that the improved J-C constitutive model can more accurately predict the mechanical response of a titanium alloy under an impact load and provides a theoretical basis for the study of the mechanical properties of titanium alloy blades under subsequent conditions of foreign object damage.

Mechanical behavior of shape memory alloys considering the effects of body fluids corrosion for biomedical applications

Abstract Shape memory alloys (SMAs) are widely used in biomedical engineering, including cardiovascular stents, artificial skeletons, and orthodontic implants. For the above applications, the body fluids corrosion processes will inevitably cause deterioration in the mechanical properties of the SMAs actuator during its service life, which will threaten the safety of human health. To analyze such problems, experimental measurements have been carried out to investigate the influence of body fluid corrosion on the mechanical properties of SMAs. Changes in the mechanical properties, such as Young’s modulus and phase transformation temperatures of SMAs under body fluids corrosion were tested firstly in the simulated body environment with the 0.9 wt. % NaCl solution at 37. With an increase of the immersion time, the results show that the Ti (titanium) percentage, austenitic (reverse) transformation start temperature, austenitic (reverse) transformation finish temperature, and maximum residual strain all increase, the Ni (nickel) percentage, martensitic transformation finish temperature, tensile strength, and yield strength decrease, and the martensitic transformation start temperature first decreases and then increases. The research in this work can provide an experimental basis for further study of the SMAs materials in biomedicine applications.

A molecular dynamics study on mechanical performance and deformation mechanisms in nanotwinned NiCo-based alloys with nano-precipitates under high temperatures

Abstract Molecular dynamics simulations are performed to investigate the mechanical behavior of nanotwinned NiCo-based alloys containing coherent L12 nano-precipitates at different temperatures, as well as the interactions between the dislocations and nano-precipitates within the nanotwins. The simulation results demonstrate that both the yield stress and flow stress in the nanotwinned NiCo-based alloys with nano-precipitates decrease as the temperature rises, because the higher temperatures lead to the generation of more defects during yielding and lower dislocation density during plastic deformation. Moreover, the coherent L12 phase exhibits excellent thermal stability, which enables the hinderance of dislocation motion at elevated temperatures via the wrapping and cutting mechanisms of dislocations. The synergistic effect of nanotwins and nano-precipitates results in more significant strengthening behavior in the nanotwinned NiCo-based alloys under high temperatures. In addition, the high-temperature mechanical behavior of nanotwinned NiCo-based alloys with nano-precipitates is sensitive to the size and volume fraction of the microstructures. These findings could be helpful for the design of nanotwins and nano-precipitates to improve the high-temperature mechanical properties of NiCo-based alloys.

Effect of solution and cooling methods on the high-temperature mechanical behavior of Ti60 alloy

The influence of solution treatment temperature and cooling rate on the mechanical behavior of Ti60 alloy at 600℃ was investigated. Five different solution treatment temperatures and five different cooling methods were used for the Ti60 alloy. The study revealed that, at the same solution treatment temperature the ultimate tensile strength (UTS) and elongation (Z%) of the water-quenched (WQ) microstructure were 32 % and 61 % higher, respectively, compared to the furnace-cooled (FC) microstructure. The WQ microstructure exhibited significantly superior strength and ductility. This phenomenon was primarily attributed to the differences in microstructural morphology caused by varying cooling methods. The effects of different cooling methods on high-temperature tensile behavior were discussed in terms of fracture morphology, high-angle grain boundaries, and void distribution. On the other hand, the UTS of the air-cooled (AC) microstructure initially increased and then decreased with decreasing solution treatment temperature, while the UTS of the FC microstructure decreased with decreasing solution treatment temperature. This phenomenon was mainly due to the competing effects of effective slip length (colony size) and elemental distribution. The correlation between solution treatment temperature and cooling rate parameters and high-temperature mechanical properties was established using the response surface methodology (RSM). The optimized solution cooling scheme was determined to be at 1012℃ with a cooling rate of 4238℃/min.

Effect of hot-rolling process on the microstructure, mechanical and corrosion behaviors of dual-phase Co-based entropic alloys

Two compositions from dual-phase Co-based entropic alloys with high corrosion resistance were chosen, and the effect of hot-rolling process on the microstrcture, mechanical property and corrosion resistance was investigated in this work. The processing parameters were designed and optimized by CALPHAD calculations. For the case of hot-rolled alloys, fcc + hcp dual-phase structures were confirmed by different characterization techniques, including XRD, ECCI, and EBSD. After testing various mechanical properties and electrochemical corrosion behaviors at room temperature, the hot-rolled alloys exhibit an outstanding mechanical and corrosion resistance property. The hot-rolling process improves the electrochemical corrosion resistance slightly and promotes hardness as well as strength-ductility greatly. The experimental characterizations provide plentiful information about microstructure, crystallographic orientation, lattice misorientation, grain boundaries, and so on. More details for the strengthening and hardening mechanisms could be obtained from the EBSD analysis. The current work shed lights on the design of new alloy recipe as well as the synthesis of novel grade dual-phase entropic alloys with excellent combination of mechanical properties and corrosion resistance which could be applied in harsh environments.

Mechanical characterization of nanocrystalline Cu-Ag alloys subjected to shear deformation

ABSTRACT This study investigates the mechanical behaviour of nanocrystalline Cu-Ag alloys using molecular dynamics simulations combined with detailed analyses of dislocation densities, atomic populations, and deformation characteristics. Shear tests were conducted across three different atomic compositions at temperatures ranging from 10 K to 500 K. The influence of temperature and Ag impurities on the mechanical properties of nanocrystalline Cu is explored. Elevated temperatures are found to promote plastic deformation by increasing atomic mobility, resulting in reduced dislocation densities and flow stresses. Increasing Ag content correlates with lower dislocation densities, highlighting enhanced plastic activity between grain and grain boundaries. Structural population analysis underscores the significant impact of Ag species on the mechanical response of nanocrystalline Cu. Further investigations are warranted to explore additional deformation mechanisms. These findings contribute to a deeper understanding of nanocrystalline Cu-Ag alloys, informing the design of novel materials with tailored mechanical properties.

Effects of Aging Processes on the Dynamic Impact Mechanical Behavior of Mg-Gd System Alloys

Effects of Aging Processes on the Dynamic Impact Mechanical Behavior of Mg-Gd System Alloys

High-temperature mechanical behavior and microstructural destabilization evolution of the lightweight refractory high-entropy alloy prepared by laser additive manufacturing

Lightweight refractory high-entropy alloy (LRHEA) has lower density and higher specific strength, which makes it very promising for future applications in rocket engine components. Their high-temperature resistance to softening and high microstructure stability in a wide temperature range are also essential to sustaining their performance due to being used in harsh, high-temperature situations. In this work, the high-temperature tensile behavior of Al0.3NbTi3VZr1.5 LRHEA fabricated by laser additive manufacturing has been systematically investigated from 400 °C to 800 °C, and the relationship between the deformed microstructure and the mechanical behavior was revealed, and analyzing the reasons for the thermodynamic instability of the solid solution in LRHEA are discussed in detail. It is found that the weakening of the high entropy effect at intermediate temperatures reduces the stability of the solid solution, and the accelerated diffusion between elements further promotes the solid solution destabilization, mainly manifested as the Laves phase and the local chemical fluctuation (LCFs). The high dislocation density introduced by the additive manufacturing technology leads to the irregular connection of the Laves phases within the grains, and it can be improved by grain growth. The high negative mixing enthalpy competes with the high-entropy effect, and temperature is the decisive factor. In this situation, the atomic clusters were promoted and induced spinodal decomposition for generating LCFs. The formation of LCFs exhibits solute competition with the emergence of the C14 Laves phase, and the phase proportions fluctuate at different temperatures. This work provides new thinking and attention for developing lightweight, heat-resistant materials.

The effect of various Sn and Ca equal proportional addition on the microstructure, mechanical behavior and corrosion performance of Mg alloys

In the present study, the effects of various Sn and Ca equal proportional addition (0.3:0.1, 0.6:0.2, 1.2:0.4, wt%) on the microstructure, mechanical properties and corrosion behavior of Mg-Sn-Ca alloys were systematically investigated. With the increase of Sn and Ca content, microstructure uniformity of the Mg-Sn-Ca alloy was improved, the average grain size was refined (from 34.4 μm to 21.62 μm, 13.47 μm), and more CaMgSn phases were generated (from 0.39 % to 1.64 %, 4.53 %). With increasing Sn and Ca content, the tensile yield strength (TYS) and ultimate tensile strength (UTS) of Mg-Sn-Ca alloys were gradually increased (TYS: from 91.8 MPa to 98.24 and 125.05 MPa; UTS: from 187.48 MPa to 190.73 and 214.58 MPa), mainly due to the contribution of grain refinement. The electrochemical tests revealed that the corrosion resistance of the Mg-Sn-Ca alloy initially decreases and then increases with the increase of Sn and Ca contents. The hydrogen evolution volume of Mg-0.3Sn-0.1Ca alloy was 41.91 mL cm−2, and the corrosion current density was −1.54 × 10−3 A/cm2. As for Mg-0.6Sn-0.2Ca alloy, deteriorated corrosion resistance compared to the Mg-0.3Sn-0.1Ca alloy was mainly ascribed to the micro-galvanic corrosion between the CaMgSn phase and Mg-matrix. The Mg-1.2Sn-0.4Ca alloy had the best corrosion resistance, with the lowest hydrogen evolution volume of 34.09 mL cm−2 and a minimum current density of −1.15×10−3 mA cm−2, its high corrosion resistance could be attributed to the grain refinement and homogenous distributed CaMgSn phase and more generated Ca(OH)2 product film with dense-structure.

Mechanical behavior of GH4720Li nickel-based alloy at intermediate temperature for different strain rates

Mechanical behavior of GH4720Li nickel-based alloy at intermediate temperature for different strain rates

Effect of grain size on the deformation mechanism and fracture behavior of a non-equiatomic CoCrNi alloy with low stacking fault energy

Manipulation of stacking fault energy (SFE) plays a significant role in microstructure control and in turn mechanical properties of advanced alloys. In this work, we present the influence of grain size on the mechanical properties and fracture behavior of a non-equiatomic CoCrNi alloy with low SFE. Specimens with controlled grain sizes ranging from 0.61 to 6.4 µm were fabricated through rolling and annealing. A novel SFs-dominated plastic deformation mechanism was discovered. Tensile strength decreases monotonically with increasing grain size, while ductility achieves a peak value at the medium grain size, contradicting with the typical behavior observed in most single-phase face-centered cubic (FCC) metallic materials deformed primarily by dislocation slips and/or twinning. The fracture behavior changes from void coalescence to quasi cleavage with grain coarsening, and the fracture mechanisms were analyzed. Additionally, the evolution of SFs and phase transformation is explored at various deformation strains.

Influence of Zinc Chloride Exposure on Microstructure and Mechanical Behavior of Age-Hardened AZ91 Magnesium Alloy.

The AZ91 magnesium alloy was subjected to a complex treatment involving age hardening (supersaturation and artificial aging) and simultaneous surface layer modification. The specimens were supersaturated in contact with a mixture containing varying concentrations of zinc chloride, followed by cooling either in air or water. After supersaturation, the specimens were subjected to artificial aging and then air-cooled. This process resulted in the formation of a surface layer made of zinc-rich phases. The thickness and microstructure of the surface layer were influenced by the process parameters, namely, the zinc chloride content in the mixture and the cooling rate during supersaturation. The treated specimens exhibited favorable tensile strength and greater elongation compared to the as-cast AZ91 alloy, with values comparable to those of the alloy subjected to standard T6 tempering. No cracking of the layer was observed under moderate deformation, though greater deformation resulted in the formation of cracks, primarily in the areas containing the Mg5Al2Zn2 intermetallic phase. The produced layer demonstrated strong metallurgical bonding to the AZ91 substrate.

Nano hydride precipitation-induced disappearance of yield drop in zirconium alloy at elevated temperature

Hydrogen-induced variations in mechanical behavior of zirconium alloys impose detrimental influence on nuclear fuel cladding integrity. This work reports a disappearance of intrinsic yield drop in a recrystallized zirconium alloy following hydrogen-charging treatment. Microstructure characterizations reveal that the nano-hydrides precipitation, mediated by second phase particles Zr(Fe,Cr)2 acting as hydrogen trapping sites, leads to emission of substantial dislocations in α-matrix grains due to strong strain concentrations, as identified by high-angular resolution EBSD. These mobile dislocations preserved at elevated temperatures can maintain the applied plastic strain and impede rapid dislocation multiplication as well, a conclusion validated by comparative analysis of dislocation densities prior to and near yielding stage. These findings are expected to shed light on the underlying mechanisms governing the interaction between hydrogen and microstructural defects in Zr-based nuclear fuel cladding materials.

Validation of Experimental Data for the Application of the Magnesium Alloy “Elektron 43”

The behaviour of a structural component, such as the spreader installed on an aeroplane passenger seat made of the magnesium alloy Elektron® 43, is evaluated under a variety of load conditions. The purpose of this research project is to considerably reduce weight by employing the new alloy while keeping the strength and ductility necessary to meet the dynamic standards for both the 16 g forward and 14 g downward tests. A comprehensive campaign of static and dynamic testing on coupons was conducted to characterise the mechanical behaviour of the E43 magnesium alloy, from quasi-static to dynamic loading, and across a wide range of deformation rates. The elastic–plastic and strain rate sensitive material model of E43 is then calibrated using an FEA approach and LS-DYNA software, utilising stress–strain curves and properties determined from standardised experimental tensile and compression trials at varied strain rates. Finally, this material model was used to perform a finite element structural study of a major component of an aeroplane seat built using Elektron® 43 under typical in-flight stresses.

Tensile mechanical behavior of functionally graded NiTi alloy manufactured via laser powder bed fusion

Laser powder bed fusion (LPBF) offers the potential to modify the characteristics of NiTi alloys, allowing for the creation of bespoke solutions tailored to specific applications. In this study, four functionally graded NiTi alloys with varying martensite/austenite distributions were designed and manufactured. A comprehensive investigation was conducted into the local microstructure, phase transformation behaviour, and tensile mechanical behaviour. The findings illustrate that, in comparison to homogeneous NiTi, gradient NiTi displays a propensity for preferential deformation within the martensitic region, attributable to the presence of localised performance variations. Gradient NiTi exhibits evident strain hardening and a wider range of plateau stress due to its intricate step-by-step phase transformation behaviour. The strain gradient strengthening near the interface between martensite and austenite endows gradient NiTi with enhanced fracture strength. Furthermore, while ensuring a discernible gradient in strain, the design of the interface with narrow spacing and parallel to the tensile direction can effectively enhance the mechanical properties of gradient NiTi. This study validates that gradient design based on LPBF is an effective approach for controlling the macroscopic mechanical behavior of NiTi alloy.