Alloy Specimens Research Articles

Local oxynitriding of AZ31 magnesium alloy by atmospheric-pressure plasma treatment at room temperature

A surface-hardening treatment for AZ31 magnesium alloy using an atmospheric-pressure plasma jet (APPJ) at room temperature was developed. Magnesium is a potential engineering material because it is lightweight; however, magnesium alloys are difficult to heat-treat because of their low flaming temperature. Magnesium alloy specimens were irradiated with a localized atmospheric-pressure plasma jet generated by dielectric-barrier discharge for 180 s in air. The APPJ excited oxygen and nitrogen molecules in the ambient air, resulting in the formation of an oxynitrided layer; oxygen and nitrogen diffusion layer, on the surface of the magnesium alloy. The hardness and elemental distribution for the treated surface were examined. The top surface of the APPJ-treated magnesium alloy achieved a maximum hardness of 108 HV, which was ∼1.7 times greater than that of the untreated surface. Elemental analysis using an electron-probe microanalyzer revealed strong oxygen and nitrogen signals corresponding to the hardened region of the magnesium alloy, meaning that the hardness increased as a result of the formation of the oxynitrided layer. The proposed APPJ treatment is a promising approach for locally hardening magnesium alloys without using a heat treatment.

High cycle fatigue life prediction on TC4 titanium alloy after overload treatment

In this study, single edge notched specimens of TC4 titanium alloy are overloaded and then employed to perform high cycle fatigue tests. It is shown that overload treatment has a significant improvement on fatigue life, with a range of 2.28–2.81 times increase. Considering the theory of critical distance brings relatively big error, a critical distance method modified by high stress zone is proposed to describe the difference both in high stress zone and critical distance after overload treatment. The scatter factor is improved from 4.0 to 3.0 without introducing additional parameters, demonstrating a higher accuracy of the proposed model.

Effect of Dispersions of Al2O3 on the Physical and Mechanical Properties of Pur ties of Pure Copper and Copper-Nick e Copper and Copper-Nickel Allo el Alloy

This paper illustrates the mechanical and physical properties of pure Cu and Cu-Ni (50-50 wt. %) alloy mixed with Al2O3 (1-4 wt. %) as micro-particles reinforcement materials. The attained composite alloy specimens' characteristics were estimated such as microstructure, relative density, electrical and thermal conductivity, hardness, and compression yield stress properties to adjust the suitable optimum percentage of reinforcing material which has the best physical and mechanical properties with different main matrix materials whether pure Cu powder or Cu-Ni mechanical alloy. The micron-sized Al2O3 was added to enhance the mechanical and physical properties of the pure Cu and Cu-Ni alloy composites. The electrical and thermal conductivity for pure Cu alloy composites were improved compared to the copper-nickel alloy matrix composites material. The hardness and compression yield stress of pure copper has enhancement values and for Cu-Ni alloy composites have enhancement values and for Cu-Ni base composites, hardness and compression yield stress have improved with the most positive enhancement values.

This paper illustrates the mechanical and physical properties of pure Cu and Cu-Ni (50-50 wt. %) alloy mixed with Al2O3 (1-4 wt. %) as micro-particles reinforcement materials. The attained composite alloy specimens' characteristics were estimated such as microstructure, relative density, electrical and thermal conductivity, hardness, and compression yield stress properties to adjust the suitable optimum percentage of reinforcing material which

The recent booming in the power network industry inspired a lot of researchers to develop models to estimate the optimum cost of transmission towers. Unlike previous researches which depended on design the tower from scratch, this research depends on collecting actual database from several projects around the globe and applying the well-known (GP) technique to develop a model to predict the tower weight. The accuracy of the developed formula was about 84%. The developed model could be used in early tender stage or to check design economy.

Effect of the notched foreign object damage depth on the HCF strength of titanium alloy TC11

In this study, the effects of different incident foreign object damage (FOD) depths on the high-cycle fatigue (HCF) performance of TC11 titanium alloy specimens with compressor leading edge blades were studied. FOD values were obtained through high-speed ballistic impact tests at different aiming positions under the same impact conditions. HCF tests of smooth and FODed specimens were conducted via the step-loading test method, and the HCF strength was determined via experiments and numerical analysis. The results indicated that with increasing damage depth, the stress concentration factor significantly increased. There occurred greater material losses on the exit side of the resultant notch damage than those on the incident side. The maximum damage depth ranged from 0.23 to 1.51 mm, and the fatigue strength of the FODed specimens reached approximately 21.77–84.99 % of that of the smooth specimens. With increasing depth, the material loss increased, and the fatigue strength decreased. According to the Kf = 3 empirical criterion for FOD tolerance design, the determined serviceable limit of notch-type damage was 0.84 mm, which is expected to be useful for quick assessment of the notch-type FOD degree of TC11 titanium alloy leading edge blades.

Material parameters identification of 3D printed titanium alloy prosthesis stem based on response surface method

3D printed Titanium alloy is widely used as a material of artificial joints and its mechanical properties is a key factor for improving operation results. Because the elastic modulus of the 3 D printed titanium alloy specimen was related to the size of the metal blank. It is very difficult to identify mechanical parameters by traditional mechanics experiments. In this paper, according to the inverse analysis principle of the parameter estimation, a response surface methodology (RSM) was proposed to identify the mechanical parameters, based on finite element inverse analysis. The finite element models of femoral prosthesis stem were established in line with compression experiments. The material parameters were combined by central composite design (CCD), and the response surface (RS) models were constructed using a quadratic polynomial with cross terms and optimized using a genetic algorithm (GA). Finally, the best mechanical parameter combination of the femoral prosthesis was calculated. The calculated elastic modulus and Poisson's ratio of a 3 D printed titanium alloy femoral prosthesis stem were 109.07 GPa and 0.29, respectively, with the elastic modulus error being very small. The proposed method is effective and can be extended for the identification of mechanical parameters in other 3 D printed models.

Influence of particle content on the ductility of extruded non-recrystallized aluminium alloys subjected to shear loading

In-plane shear tests were conducted on two extruded 6000-series aluminium alloys to investigate the influence of constituent particles on ductile fracture. The two alloys have previously been characterized and found to have different area fraction of constituent particles while having similar grain structure, crystallographic texture, strength, and work hardening. Specimens of both alloys were machined from flat profiles with their gauge section oriented along either the extrusion direction or the transverse direction. The specimens were loaded in shear until fracture and an experimental-numerical approach was employed to analyse the stress and strain fields, which involved digital image correlation and crystal plasticity finite element analysis. The fracture mode was determined by examining digital images captured during the experiment, while the fracture surface of representative specimens was examined in a scanning electron microscope. The shear strain across the gauge section at failure was substantially lower for the alloy with higher fraction of constituent particles, and the negative effect of the particle content on the ductility was found to be more pronounced for the tests in the transverse direction. The crystal plasticity finite element analyses showed an extensive texture development within the gauge region and that the local shear strain at failure was somewhat different in the two loading directions.

Enhanced corrosion resistance, antibacterial activity and biocompatibility of gentamicin-montmorillonite coating on Mg alloy-in vitro and in vivo studies

Implant-associate infection (IAI) is a major cause of failure of bone implant materials, and one of the significant challenges in clinical managements. A synergistic coating strategy combining montmorillonite (MMT) sustained release, adsorption of bacteria and gentamicin (GS) bactericidal is proposed herein to tackle infection issues. Surface morphology, microstructure and chemical composition of the samples were investigated using SEM, XRD, FT-IR and XPS. Electrochemical experiments and immersion experiments reveal that corrosion resistance of Mg samples with GS/MMT coatings was higher than that of bare Mg alloy substrate in DMEM solution. In vitro studies demonstrated that the GS/MMT coating had a significant inhibitory effect on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The viability of MC3T3-E1 cells was 92.7% after a co-culturing for 72 h. After a subcutaneous transplantation of 90 days, the survival rate was 100% for GS/MMT-coated Mg alloy specimens with no infection at the implantation sites and no toxic damage to liver, kidney and local muscles pathological sections. This study provides a novel method for the preparation of sustained-release antimicrobial coatings on biodegradable Mg alloys as promising candidates for orthopedic implant materials.

On the microstructure and tensile behaviour of nanostructured NiTi alloy produced by electroplastic rolling

Electroplastic rolling was employed to produce nanostructured (NS), near-equiatomic NiTi alloy from a coarse grained NiTi nugget (ingot), which was produced using vacuum induction melting, followed by quenching in water from a temperature of 800°C. The microstructure of NS NiTi was characterized using X-ray Diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis revealed that the NS NiTi is predominantly martensitic at room temperature, with less than ≈10 % of the austenite phase. The NS NiTi alloy has an average grain size of ≈36 nm. TEM investigation confirmed the presence of grains that are less than 10 nm in size and no amorphous zones were detected. The NS martensitic NiTi alloy specimens were tested in tension at two different strain rates (10−2 and 10−1 s−1). In contrast to a stress-strain profile expected in a martensitic NiTi alloy, the stress-strain curves show conventional tensile behaviour. The observed UTS was high, around ≈1800 MPa, with a less than usual elongation to failure of ≈6 %. The presence of dimples on the fracture surfaces can be seen in scanning electron microscopy (SEM) images, which is indicative of ductile fracture. The role of grain size in the observed deformation and fracture features is also discussed.

Investigating the thermal oxidation behavior of Ti–6Al–7Nb alloy in dry air

AbstractThe thermal oxidation behavior of a forged Ti–6Al–7Nb (Ti67) alloy was investigated in dry air conditions. The alloy specimens were oxidized for 50 h at different temperatures (650°C, 750°C, and 850°C) and the oxidation kinetics were analyzed. The microstructure of Ti67 after oxidation and the different phases and compounds were identified. A parabolic equation based on weight gain was used to define the oxidation rate. The parabolic rate constant increased from 1.10 × 10−8at 650°C to 2.10 × 10−8and 1.53 × 10−7g2/(cm4·h) at 750°C and 850°C, respectively. At 650°C, the oxidation behavior resumed the parabolic behavior until 40 h, a breakaway phenomenon. At 750°C, a linear behavior was observed in the periods of 20–50 h. This linear trend appeared also after 35–50 h at 850°C. The activation energy was found to be 238.4 kJ/mole. At the lowest oxidation temperature (650°C), a disconnected oxide layer was observed. These variations in the response of Ti67 alloy to the different thermal oxidation conditions are worthy of consideration when modifying the surfaces for biomedical applications.

Cavitation erosion behaviors and damage mechanism of Ti-Ni alloy impacted by water jet with different standoff distances

The cavitation erosion of Ti-Ni alloy is explored on a cavitating liquid jet with different standoff distances. The cavitation erosion characteristics of Ti-Ni alloy specimens are analyzed, and the influences that different standoff distances of the water jet have on cavitation erosion are explored. The results of cavitation erosion outcomes under different standoff distances of 6 mm, 8 mm, 10 mm, 12 mm, 14 mm and 16 mm show slight deformation, grain boundary cracking and formation of initial micro-pits, pits of maximum depth around 50 μm, more pits of maximum depth around 80 μm with micro-cracks, obvious plastic deformation traces with some pits, bulges and slip bands, respectively. When the Ti-Ni alloy is impacted by water jet with a standoff distance of 12 mm for 4 hrs, the surface microstructure undergoes substructural evolution and new fine grains form, with obvious stress concentration and dislocation accumulation appearing on the subsurface.

Ultrasonic peening for dieless metal deformation in vacuum conditions

Ultrasonic peening (UP) systems have recently attracted much attentions as a flexible dieless plastic deformation manner with merits of deep stress penetration and efficient shaping capability. Compared with conventional shot peening techniques, UP systems are promising for special processing in vacuum conditions but rarely explored before. In this paper, an ultrasonic peening system is designed, fabricated and finally characterized in vacuum conditions. The transducer can amplify the vibration amplitude and then trigger rod pin arrays to accelerate simultaneously towards the workpiece. Numerical results reveal that under high-speed impact one compressive residual-stress layer is created and results into the bulk deformation of the workpiece. Measurements on the prototype ultrasonic peening transducer confirm the vibration performance and captured rapid movement of rod pin arrays verifies the proposed impact principle. With the driving voltage of 100 V at resonance, one piece of 5 mm 7055 aluminum alloy specimen could be deformed with 0.61 mm arc height after 10 min peening. At last, the validation for ultrasonic peen forming in vacuum conditions is conducted and variation for the deformation level is obtained and analyzed. The proposed method and tested results open a new way for ultrasonic peen forming to be implemented for special processing in extreme environments.

Actual Marine Atmospheric Pre-Corrosion Fatigue Performance of 7075-T73 Aluminum Alloy

Actual marine atmospheric pre-corrosion behavior and its effect on the fatigue performance of 7075-T73 aluminum alloy were studied by means of marine atmospheric outdoor exposure testing and fatigue testing. The surface and cross-sectional microstructures of aluminum alloy specimens after different numbers of days of exposure were analyzed. Localized pitting, and intergranular and exfoliation corrosion occurred during the outdoor exposure of aluminum alloy specimens in a marine atmosphere. The degree of severity of atmospheric corrosion increased with increasing duration of exposure. The effects of Fe-rich constituent particles (Al23CuFe4) and grain boundary precipitates (MgZn2) on the marine atmospheric corrosion behavior were discussed. In addition, when the exposure time was increased from 0 days to 15 days, the average fatigue life of aluminum alloy specimens decreased dramatically from about 125.16 × 104 cycles to 16.58 × 104 cycles. As the exposure time was further increased to 180 days, the average fatigue life slowly decreased to about 6.21 × 104 cycles. The fatigue fracture characteristics and the effect mechanism of marine atmospheric pre-corrosion on the fatigue life of 7075-T73 aluminum alloy were also analyzed.

Buckling behaviors of aluminum foam-filled aluminum alloy composite columns under axial compression

In this study, a new 6082-T6 aluminum alloy composite column filled with aluminum foam was proposed. Thirteen axial compression tests were performed on the aluminum foam-filled 6082-T6 aluminum alloy specimens with various slenderness ratios and diameter–thickness ratios. The load–lateral displacement relationships, surface strain histories, failure modes, and buckling characteristics of the composite specimens were obtained. Finite element (FE) models of the aluminum foam-filled aluminum alloy columns under axial compression were established using the non-linear finite element analysis (FEA) software ABAQUS/Standard. After verifying the accuracy of the FE model, the influence of the aluminum foam on the stability and buckling bearing capacity of the columns was discussed, and the effect of the combination of the external aluminum column and aluminum foam filling was analyzed based on the numerical results. Parametric studies were also conducted to reveal the influences of the geometric parameters (including the slenderness ratio, diameterto-to-thickness ratio, and cross-section) and material properties (including aluminum alloy with different grades and aluminum foam with various densities) on the buckling behavior and buckling bearing capacity of the composite columns. In addition, the failure mechanism of this new type of composite column, considering the supporting effect of the aluminum foam on the foam-filled aluminum columns with thin walls, was investigated.

Approaching ideal energy absorption through the multicellular structure with gradient material distribution

Energy absorption of traditional tubular energy absorbers is restricted by the low structure efficiency, which makes the mean crushing force of the structure usually much lower than its yield strength. The combination of a multicellular design and a gradient-thickness strategy significantly improves the energy-absorption ability of thin-walled energy absorbers while reducing weight. Gradient-thickness multicellular tubes (GTMT) were studied in this paper to demonstrate this advantage. Mechanical performances of GTMT with two material-distribution principles, sample gradient thickness (SGT) and modified gradient thickness (MGT), were investigated experimentally and numerically, primarily in terms of folding behaviors, energy-absorption ability, and load-carrying capacity undulation. Wire-cut electrical discharge machining technology was used to create a series of aluminum alloy specimens that were then compressed under quasistatic loading conditions.Following that, finite element method was used to run detailed numerical simulations. The effect of geometric configuration was determined after conducting parametric studies with different cell density and thickness gradient coefficients. The results showed that, compared to a traditional multicellular tube, a gradient-thickness one with MGT material distribution can improve structural efficiency with a stable loading history. Increases in cell density and thickness gradient coefficient have positive effects on energy-absorption ability; however, excessively high parameter values will lead to global bending deformation and weaken the mean crushing force. Therefore, reasonable parameter matching is vital. The result shows that when the cell density reached 9 × 9 and the thickness gradient coefficient reached 1.4, the mean crushing force was 98.16% of the full-plastic strength of the matrix, and there was no irregular deformation, indicating that ideal energy absorption is almost achieved. These achievements pave a way for achieving ideal energy absorption.

Experimental and numerical studies of fatigue behavior of Ti6Al4V alloy treated by laser shock peening

Laser shock peening (LSP) is applied as the laser surface treatment technology to improve the fatigue resistance of aircraft parts with complex geometric features. In this paper, the effects of laser energy inputs on residual stresses and fatigue properties for hole-structured specimens of Ti6Al4V alloy treated by LSP are studied. Changes of residual stress distributions, fatigue behaviors and fracture morphologies are analyzed with different laser-induced shock pressures. The results show the fatigue life is prolonged by 137% compared with the untreated specimens due to the introduction of compressive residual stresses. The sectional observations of fatigue fracture morphology show the inwards movement of fatigue crack initiation positions and the complexity of fracture cracks after LSP treatment. The simulation results confirm that the fatigue life with different laser energy inputs depends strongly on the three-dimensional stress distribution around the hole. Among them, high surface compressive stresses and deep stress affected layers play a decisive role in improving fatigue life. The results in this study broaden the knowledge of fatigue behavior and explore engineering potentials of improved fatigue life for complex industrial specimens.

Can the finite fracture mechanics coupled criterion be applied to V-notch tips of a quasi-brittle steel alloy?

Structures made of steel alloys with V-notches may fracture at the V-notch tip at which a small plastic zone usually evolves. Failure criteria for predicting fracture loads for such quasi-brittle alloys, as a function of the V-notch opening angle are very scarce and have not been validated, to the best of our knowledge, by a set of experimental observations.Herein we provide a database of experiments performed on AISI 4340 steel alloy specimens with three different V-notch opening angles and three different tempering temperatures, loaded in mode I. Material properties, failure load and plastic area at the V-notch tip are detailed.The experimental observations are used to investigate to which extent the finite fracture mechanics coupled criterion (FFMCC) for brittle materials may predict the failure load of quasi-brittle steel alloys, depending on the plastic zone size. Finite element analyses were used to compute the parameters required by the FFMCC. We compared the predicted versus the experimental fracture load for the different V-notch opening angles and tempering temperatures.For small opening angles (30°) for which the plastic area is very small, the FFMCC under-predicts the fracture load by about 20% which is within the experimental error range. The under-prediction of the failure load constantly increases to ∼ 50% as the V-notch angle increases to 90° and plastic zone area on the surface increases to ∼0.5mm2 (for a V-notch depth of 5 mm).The detailed experimental database is suggested to be used for validation purposes when new failure criteria for quasi-brittle materials are developed.

Microstructure analysis and mechanical properties of electron beam powder bed fusion (PBF-EB)-manufactured γ-titanium aluminide (TiAl) at elevated temperatures

Abstract Additively manufactured γ-titanium aluminide has a high specific strength and temperature resistance. This opens new possibilities for future lightweight constructions for aerospace applications. The objective of this work was to characterize additively manufactured Ti–48Al–2Cr–2Nb alloy specimens, which were successfully manufactured by electron beam powder bed fusion. For microstructural characterization, the as-built state was investigated with light and scanning electron microscopy. In the electron backscatter diffraction analysis, the size and the orientation of the grains were observed. The pore size and distribution were examined in computer tomographic scans, which showed a near fully dense material with a relative density of >99.9%. Furthermore, the hardness curve over the building height was examined in hardness mappings. Thereby, a strong decrease in hardness could be observed with an increase in part height. To evaluate the reliability of the manufactured alloy, quasi-static compression tests were carried out at temperatures up to 650 °C. Within these tests, a high compression strength (σ c,p,0.2,650 °C = 684 MPa) was determined, which implicated a potential substitution of nickel-based superalloy components in aerospace applications under compressive loads.

Temperature-induced enhancement of tensile strength of perforated Ti–6Al–4V sheet revealed through mechanical-thermal coupling quasi-static tension

In order to investigate the effect of temperature on the tensile strength of perforated Ti–6Al–4V (TC4) alloy, the tensile mechanical properties of TC4 alloy with various micro-hole array distributions were obtained at a temperature in a range from 20 °C to 500 °C by using a novel mechanical-thermal coupling tensile test instrument developed by ourselves. The experimental results showed that the tensile strength of all types of TC4 alloy specimens decreased with the increase in temperature, and the elastic modulus of most types of TC4 alloy specimens decreased with the increase in temperature. The tensile strength of the perforated specimen iii was 14.8% lower than that of the solid specimen and the elastic modulus of perforated specimen ii was 5.5% lower than that of the solid specimen at room temperature (RT), and all types of the perforated specimens continued to exhibit relatively lower tensile strengths and elastic modulus at 180 °C and 340 °C. Abnormally, the tensile strength of the perforated specimen iii was 2.1% higher than that of the solid specimen and the elastic modulus of perforated specimen ii was 23% higher than that of the solid specimen at 500 °C. With the increase of temperature from 20 °C to 500 °C, the fracture mode of the solid specimen gradually changed from equiaxed dimple to shear dimple. Regarding the perforated specimens, the cracks and dimples adjacent to the holes gradually decreased as a function of temperature. The existence of prefabricated holes in the specimens dissipated part of the thermal stress, maintained the integrity of the micro-hole structure, and made the nearby section relatively flat, which induced a relatively higher tensile strength and structural stiffness at an elevated temperature. The relatively lower stress in the gauge section of the perforated specimens obtained through finite element analysis also indicated the temperature-induced enhancement of tensile strength.

The study on the overloading effect on fatigue crack growth considering residual stress relaxation in Al 5456-H38

A numerical and experimental study was conducted on fatigue crack growth (FCG) of metallic components to investigate the effect of redistribution of mechanical residual stresses induced by overloading in notched specimens. The compact tension (CT) specimens of an aluminum alloy were used, and mechanical residual stresses were introduced in them by applying tensile overload (OL). Then, the specimens were subjected to fatigue loading. In the calculations of finite element method (FEM), the modified cyclic J-integral was used as the crack growth parameter. Good agreement was observed between the numerical and experimental results. The FEM results demonstrated a clear redistribution of residual stresses during FCG process. It was observed that after a few cycles, the residual stress field reached a lower magnitude value confining in a small zone around the around the crack tip. Furthermore, the effects of stress ratio, load amplitude, and OL ratio (OLR) on the redistribution of residual stresses are studied in this research. It was observed that the residual stresses are considerably released during the initial cycles of fatigue loading.