Alloy Bars Research Articles

Experimental Study on Flexural Behavior of Seawater Sea-Sand Concrete Beams Reinforced with Superelastic Shape Memory Alloy Bars

In order to research the flexural behavior of shape memory alloy (SMA)-reinforced seawater sea-sand concrete (SWSSC) beams and improve their self-healing ability, three SMA SWSSC beams and one anti-corrosive steel bar SWSSC beam were designed. The influence of the reinforcement ratio, strength grade of SWSSC and type of reinforcement on the flexural performance of the beam were considered. The failure process, maximum crack width, mid-span deflection, displacement ductility and stiffness degradation of beams were studied by cyclic loading tests. The test results showed that the number of cracks in SMA-reinforced beams were significantly smaller than that in anti-corrosive-reinforced beams, and the crack width and mid-span deflection recovery effect were better after unloading. However, the effect of increasing the SMA reinforcement ratio on crack recovery was not obvious. The increase in SMA reinforcement ratio and the strength grade of SWSSC can significantly improve the bearing capacity of the beam and the stiffness, but the stiffness degradation rate decreased. Moreover, the ductility of concrete beams with SMA bars was significantly increased.

Experimental Study of Chip Shrinkage in Turning Titanium Alloy VT6

The article proposes an analysis of the study of turning a titanium-based alloy used for the manufacture of surgical implants. The main focus is on machinability problems associated with the choice of rational cutting parameters, which determine the quality and durability of pedicle screws. The conclusion is made about the need for research aimed at ensuring maximum performance and application of practical data for the manufacture of medical implants. To carry out experimental studies, non-free cutting of a titanium alloy bar was performed with a cutter fixed in a turning dynamometer. Graphs of cutting forces versus cutting speed and feed were used to select an effective combination of machining parameters. A thermal imaging camera was used to evaluate the effect of processing parameters on the temperature of the processed sample. Conclusions are drawn about the dependence of the coefficients of longitudinal and transverse chip shrinkage on the processing parameters. The results of the research analysis show that when turning titanium alloy VT6, the coefficient of transverse chip shrinkage, which characterizes the broadening with increasing cutting speed, remains unchanged. The goals of further research aimed at clarifying the optimal cutting conditions for turning transpedicular fixation screws from VT6 were determined.

Tension-compression asymmetry and Bauschinger-like effect of AZ31 magnesium alloy bars processed by ambient extrusion

Ambient extrusion was used to introduce different pre-strains in billets of AZ31 magnesium alloy. The effect of the pre-strain on tension-compression asymmetry and Bauschinger-like effect were studied. During ambient extrusion, the experimental material experienced {101‾2} twinning, {101‾2} detwinning and {101‾1} twinning sequentially. During tension and compression tests, the dominating deformation mechanisms are different, thus the tensile and compressive yield strength are improved with different trends. The extruded billets showed the strongest tension-compression asymmetry and Bauschinger-like effect when the pre-strain was ∼11%. With further increase of pre-strain, the plastic deformation became more homogeneous and caused a higher strengthening effect on {101‾2} twinning. As a result, the tension-compression asymmetry and Bauschinger-like effect got gradually weakened.

The Effect of Initial Grain Size on the Nanocrystallization of AZ31 Mg Alloy during Rotary Swaging.

Nanograins were obtained in the AZ31 Mg alloy bars with different initial grain sizes via cold rotary swaging. Microstructure evolution during deformation was investigated through electron backscatter diffraction analysis and transmission electron microscopy studies. The results indicate that initial grain size had little effect on the mechanism of grain refinement during swaging. The nanocrystallization process of the alloys with different initial grain sizes included extensive twinning followed by the further refinement of the twin lamellae through the formation of massive dislocation arrays. However, as the initial grain size decreased, the formation rate of nanograins increased, resulting in a higher degree of nanocrystallization after the same swaging pass. The mean grain size and yield strength of the sample with the smallest initial grain size were about 91 nm and 489 MPa, respectively. The slower rate and lower degree of nanocrystallization in the alloy with a larger initial grain size were mainly attributed to the less grain boundary areas and higher activity of twinning.

Statistical Comparison of Mechanical Properties of VT6 Alloy Bars with Different Structures

Statistical Comparison of Mechanical Properties of VT6 Alloy Bars with Different Structures

Behavior of RC Beams Strengthened with Near-Surface Mounted Aluminum Alloy Bars under Fully Reversible Cyclic Loads

Behavior of RC Beams Strengthened with Near-Surface Mounted Aluminum Alloy Bars under Fully Reversible Cyclic Loads

Low-cycle fatigue behavior of Cu–Al–Mn superelastic alloys at different temperatures

Superelastic alloy (SEA) bars are widely used in structures subjected to moderate and strong earthquakes. Compared with conventional nickel-titanium (NiTi) SEAs, Cu–Al–Mn (CAM) SEAs has received increasing attention recently due to their cost-effectiveness and easier machinability. The authors’ previous research showed that despite their lower strength and limitations in the maximum length, the CAM SEAs have comparable superelastic strain recovery, a wider temperature range, and superior strain rate stability compared to NiTi SEAs. However, the previous research was limited to a few specimens and only conducted to a few hundred cycles without considering the full deterioration in the material properties. Besides, the existing research on CAM SEA was only limited to small sample sizes at room temperature, while the fatigue performance of large diameter CAM SEAs under low and high temperatures relevant for civil engineering structures has not been reported. To fill this knowledge gap, low-cycle fatigue performance of 20 mm diameter CAM SEAs was studied at room temperature 25 °C, low temperature, −40 °C, and high temperature, 50 °C. Both single crystal and polycrystal CAM SEAs were investigated to determine their feasibility as concrete reinforcement under repeated high strain loading cycles expected during an earthquake. Strain cycles up to 50 000 have been applied at a tensile strain amplitude of 5%. Variations in the superelastic properties were observed and analyzed, including the stress–strain curves, elastic modulus, transformation stresses, damping ratio and recovery strain. Stable hysteresis has been observed for cycles exceeding tens of thousands at all temperatures demonstrating the suitability of CAM SEAs for seismic applications in civil engineering structures.

Compound purification of nickel base superalloy cutting waste through special cleaning agent attached to ultrasonic stirring

The GH4169 nickel-based superalloy is a type of alloy that exhibits excellent properties. It has high creep strength, fracture strength, as well as good corrosion resistance, fatigue resistance, and oxidation resistance under high-temperature conditions, allowing it to be widely used in the aerospace, nuclear reactor, and oil industries. However, it is challenging to process superalloys because of their high hardness and considerable processing wastes, such as cutting fluid. Many processing wastes cannot be directly used for remelting due to issues like surface stains. However, the production of GH4169 superalloys requires low carbon content for recycling, so the alloy scraps that meet the standard after pre-cleaning can be obtained. This study explores the ultrasonic cleaning effect of superalloy scraps with different liquid-solid ratios, cleaning times, and cleaning temperatures to obtain the optimal cleaning conditions of GH4169 superalloy scraps. The content of carbon in unwashed superalloy scraps is as high as 0.2%, far exceeding the carbon content of the alloy itself (0.015–0.036%). After ultrasonic cleaning at 60 °C for 30 min with a cleaning solution having a solid-liquid ratio of 1:2.5, the carbon content of the scraps decreased from over 0.2%–0.048%, and the decarburization rate reached above 77%. After remelting the cleaned scraps into alloy bars, the composition content and properties of the bars meet the production requirements. The cleaning mechanism is analyzed, and the cavitation effect, saponification, and emulsification mode in the ultrasonic cleaning process are explained. This paper positively promotes recycling GH4169 nickel-based superalloy waste to protect environmental resources.

Corrosion resistance of 6061-T6 aluminium alloy and its feasibility of near-surface reinforcements in concrete structure

Abstract The durability of concrete structures is often reduced owing to the corrosion of reinforcement in an aggressive environment. Ordinary reinforcement methods, such as wrapping section steel or steel plate, are also vulnerable to corrosion. Using 6061-T6 aluminium alloy as near-surface reinforcement of the concrete structure is a feasible method. In this study, the corrosion resistance of 6061-T6 aluminium alloy bars was studied by simulating the coastal environment, atmospheric environment, and concrete internal environment with chloride solution, simulated acid rain solution, and saturated Ca(OH)2 solution. The corrosion rate of the 6061-T6 aluminium alloy in the above environments was tested using a weight loss method, and its corrosion resistance was evaluated using the metal corrosion resistance classification standard. Based on the electrochemical reaction mechanism, the polarisation properties and AC impedance spectra of steel and 6061-T6 aluminium alloy were compared, and the corrosion resistance mechanisms of steel and the 6061-T6 aluminium alloy in the above corrosive environments were obtained. The results show that the 6061-T6 aluminium alloy has better corrosion resistance than steel bars in chloride and atmospheric environments, with corrosion currents of 0.012 and 0.037 µA·cm−2, and 8-day corrosion rates of 0.051 and 0.031 mm·a−1, respectively. However, owing to the activity of the aluminium alloy, its corrosion resistance in an alkaline environment inside concrete is poor; the corrosion current is 0.22 µA·cm−2 and the 8-day corrosion rate is 16.166 mm·a−1. The research results can provide a reference for applying aluminium alloy bars as external prestressed concrete bars and near-surface steel bars.

Effect of Fe addition on the glass-forming ability, stability, and mechanical properties of Zr50Cu34-xFexAl8Ag8 metallic glasses

Zr50Cu34-xFexAl8Ag8 (x = 0, 2, 4, 6, and 8) alloy bars of different diameters were prepared by copper mold suction casting and copper mold casting. The compressive mechanical properties of metallic glass samples with different Fe contents were determined by a universal testing machine. The microstructure and thermodynamics of the alloy samples were analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. According to the experimental results, Fe doping had a significant effect on the glass-forming ability, stability, and mechanical properties of these metallic glasses. The maximum diameter of the Zr50Cu32Fe2Al8Ag8 metallic glass bar was 15 mm, and the cooling rate of the alloy sample was 7.7 K/s. The addition of Fe inhibited the formation of stable crystalline phases inside the alloy sample and improved the glass-forming ability of the metallic glass. With the addition of Fe, the DSC curve of the alloy sample moved to higher temperatures, and the characteristic temperatures and the stability of the metallic glass increased. The fracture strength (σmax) and ultimate strain (εf) of the metallic glass samples reached their maximum values of 1917.6 MPa and 3.97 %, respectively, for Zr50Cu30Fe4Al8Ag8. Compared with the Fe-free Zr50Cu34Al8Ag8 metallic glass, σmax and εf increased by 51.4 MPa and 1.19 %, respectively. With the addition of Fe, the change in the distribution and content of free volume inside the metallic glass sample is the main reason for the improvement of its mechanical properties. This study shows that trace element doping has an important effect on the properties of metallic glasses.

The Microstructures and Mechanical Properties of a Welded Ni-Based Hastelloy X Superalloy

The Hastelloy X superalloy is a widely used solid-solution Ni-based sheet alloy for gas turbines, aero-engine combustion chambers, and other hot-end components. To investigate the effect of microstructure, especially grain size, on its weldability, Hastelloy X alloy bars are homogenized, cold-rolled to thin sheets, and recrystallized under different conditions to obtain equiaxed grain microstructures with average grain sizes of ~5 μm, ~12 μm, and ~90 μm. The laser welding process is used for joining the alloy sheets, and then the alloy’s weldability is investigated through microstructural and mechanical property characterizations. The microstructures in weld consist of coarse columnar grains with dendrite, and grain sizes of these columnar grains are almost the same when grain size of Hastelloy X base metal increases from ~5 μm to ~90 μm. Moreover, although all welds exhibit lower yield strengths (YS), ultimate tensile strengths (UTS), and elongations to fracture (EF) than the base metal, the degrees of reduction in them become slight when the grain size of base metal increases from ~5 μm to ~90 μm.

Microstructure evolution and mechanical property of directionally solidified Cu-9Ni-6Sn alloy wire during aging

A Cu-9Ni-6Sn alloy bar with axial columnar grains was prepared by directional solidification. The effects of aging on the microstructure and mechanical properties of the alloy were studied. The results showed that the alloy had columnar grains oriented along the axis and underwent continuous cold-drawing with a total deformation amount of 85%, a fibrous structure along the axis was formed. For the homogenized alloy, the tensile strength is 385 MPa, the hardness is 80 HV, and the elongation after fracture can reach 38.5%. After aging at 360 °C for 120 min, (Cu, Ni)3Sn phase precipitated intermittently along the grain boundary, and the tensile strength and elongation of the alloy were 1057 MPa and 7.1%, respectively. With increasing aging time to 240 min, the number of (Cu, Ni)3Sn phase increased and coarsened obviously, forming a precipitation-free zones, with occurrence of recrystallization of the Cu matrix. The preparation of Cu-9Ni-6Sn alloy billet by directional solidification, combined with large-deformation drawing and aging, is a new method to prepare high performance Cu-9Ni-6Sn alloy wire.

Behavior of Smart Reinforced Concrete Beam Column Joints by Using Shape Memory Alloy Reinforcement Under Repeated Loading

Using the super elastic materials in structures design is becoming very important in the research field because of their rare ability in sensing the around effect and reacting against the mechanical and thermal react. The major intent in this research is designing smart concrete beam column joints reinforced by Shape Memory Alloy (SMA) bars. The suggested systems use the (super elastic) Pseudo Elastic (PE) react of the SMA as reinforcement after being subjected under monotonic and repeated load. The behaviors of systems were explored experimentally and by using finite element simulation. In order to estimate load-displacement relationships of these specimens in this study, Analytical models were developed. A comparison of the reinforced specimens by SMA was carried out and it contained that the variation in percentage of the SMA in flexural reinforcement (25%, 50%, 75%) of the total flexural reinforcement by using this substitution get a clear effect on the failure load and the ultimate displacement of the specimens with these different ratios. The Finite Element models were developed by using the software ABAQUS. The models have been checked with the experimental results in the load-displacement terms in the top reinforcement. The models showed reasonable response. Where the ultimate load decreased by using SMA bars in (25%, 50%, 75% ) percentage of total flexural reinforcement about (50.51%, 28.32%, 38.15%) respectively, in case of static loading and (20.7%, 10.7%, 9.3%) respectively in case of repeated loading, and the deflection is increasing by using SMA in (25%, 50%, 75% ) percentage of total flexural reinforcement about (1.2%, 8.4%, 0.36%) respectively, in case of static loading and (9.6%, 5.28%, 10.9%) respectively in case of repeated loading

Seismic behavior of RC columns strengthened with near-surface-mounted aluminum alloy bars and CFRP wraps

This paper proposed a near-surface-mounted (NSM) strengthening technique by using aluminum alloy (AA) bars and carbon fiber-reinforced polymer (CFRP) wraps to improve the seismic behavior of square reinforced concrete (RC) columns. Eight strengthened concrete columns with square cross sections of 250 mm × 250 mm and 1600 mm shear span were tested under axial compression and reversal cyclic loading to investigate the effects of NSM reinforcement ratios (0.36–1.29%), layers of CFRP wraps (0 and 3), and axial compression ratios (0.1 and 0.4) on the seismic behavior. The failure mode, hysteretic response, load-bearing capacity, ductility, stiffness degradation, and energy dissipation capacity of those column specimens were analyzed. Results indicated that the lateral load-bearing capacity, stiffness, and cumulative energy dissipation capacity increased with the increase of the NSM reinforcement ratio. The CFRP wraps in the NSM technique can provide hoop confinement to avoid the buckling failure of NSM AA bars, and improve the seismic behavior by mitigating spalling of concrete. When increasing the axial compression ratio from 0.1 to 0.4, the lateral load-bearing capacity and cumulative energy dissipation capacity increased significantly, while the stiffness degradation became obvious. In addition, three-dimensional (3D) finite element (FE) models were developed and verified by comparisons in the deformation and lateral loads at characteristic points, as well as the strain distribution along NSM AA bars. The verified FE models can be used to analyze the damage of concrete and the stress distribution at the interface between epoxy and concrete.

Effect of loading modes on torsional behavior of an extruded Mg alloy bar

The torsional deformation with shear stress is crucial for improving mechanical performance of wrought Mg alloys. Consequently, the difference of mechanical behavior between fixed-end and free-end torsion was investigated. It is found that strain hardening behavior is affected by end constraint. The decreased hardening rate is exhibited which is dominated by prismatic slip during fixed-end torsion. For free-end loading, two stages of strain hardening are presented during torsion, i.e., constant hardening rate and slowly decreased hardening rate. The basal slip dominates the onset of plastic deformation. The prismatic slip becomes dominated mechanism at large shear strain. However, the axial effect is sensitive to forward and reversal torsion. The difference of axial stress between forward and reversal torsion under fixed-end is attributed to twin growth. The difference of axial strain is small during forward and reversal torsion under free-end, which is attributed to the activation of tensile twinning.

Effect of Furnace Cold Annealing on Microstructure and Tensile Properties of TC18 Titanium Alloy

TC18 alloy bars were annealed at different temperatures, and then the tensile properties were tested. The effects of different furnace cooling temperatures on the microstructure and tensile properties of the alloy were analyzed by optical microscope and scanning electron microscope. The results show that after furnace cooling at different temperatures, the size, distribution and appearance of α phase in the microstructure are changed to varying degrees. With the increase of temperature, the α phase in the microstructure disappears, the elongated α phase becomes thinner, the grain boundary α phase appears, and the obvious β grain appears. The strength of the alloy increases with the increase of temperature, and the plasticity shows the opposite trend. The maximum tensile strength is 1131 MPa, the maximum yield strength is 992 MPa, the maximum elongation is 14 %, and the maximum section shrinkage is 34 %. When the temperature is in the two-phase region, the morphology is mainly dimples, and the dimple morphology is large and deep. When the heating temperature is in the single-phase region, the fracture morphology is mainly crystalline, with tearing edges and a small amount of shallow dimples distributed on the surface.

Seismic performance of self-centering beam-column joints reinforced with superelastic shape memory alloy bars and engineering cementitious composites materials

This paper presents a preliminary experimental investigation of a self-centering beam-column joint reinforced with superelastic Ni-Ti SMA bars and ECC materials. As an alternative to the longitudinal bars in the beam plastic hinge, SMA is used to reduce the residual deformations and dissipate energy, whereas the ECC materials used in the critical region of the joints can improve the ductility of the structural member. Five 1/2 scale frame joints were designed and manufactured. The failure phenomenon, bearing capacity, energy dissipation capacity, displacement ductility, residual deformation, and self-centering performance of the joints were comparatively analyzed through a low cyclic loading experiment. A finite element model of SMA-ECC joints was established, and the influence of the SMA and ECC on the seismic behavior of the joints was investigated. The study results show that SMA bars can dramatically enhance their self-centering capability, enabling self-retrofitting damage. The ECC material is helpful for optimizing the development of the plastic hinge at the end of the beam and improving the ductility and energy dissipation capacity of the structure. The SMA-ECC composite materials exhibit good supplement to significantly improve the ductility, energy dissipation, and self-centering capabilities and delay the stiffness degradation of the structure under extreme events.

The Microstructure Evolution of Mg-RE Alloy Produced by Reciprocating Upsetting Extrusion during Hot Compression

Mg-13Gd-4Y-2Zn-0.4Zr (wt. %) alloy bar produced by three passes reciprocating upsetting extrusion (named as RUE-ed bar) exhibited fine grain with the average grain size of 3.02 μm. Hot compression tests of the RUE-ed bar were carried out on Gleeble-3800 compression unit at different deformation temperatures (653, 683, 713, and 743 K) and strain rates (0.001–1 s, 0.01–1 s, 0.1–1 s, and 0.5–1 s). This alloy showed work hardening and softening stages in hot compression, the thermal activation energy of the RUE-ed bar was 150 ± 1 kJ/mol and the constitutive equation was: ε˙=1.80×109[sinh(0.0174σ)]2.47exp[−150×1038.314×T]. Numerous Mg5 (Gd, Y, Zn) phase re-dissolved in α-Mg matrix appeared in the RUE-ed samples during hot compression deformation. The movement of the dislocation stimulated the re-dissolution of the Mg5 (Gd, Y, Zn) phase. The re-dissolution of Mg5 (Gd, Y, Zn) phase promoted texture strengthening and DRX grains growth in this experiment. In addition, the transformation and kinking of LPSO phase played an important coordinating role in the process of hot compression; 18R-LPSO was changed to 14H-LPSO phase at low strain rate while the LPSO phase kinked dominant to coordinated deformation at high strain rate.

Drift limit state predictions of rectangular reinforced concrete columns with superelastic shape memory alloy rebars

This study derives empirical drift limit state expressions for rectangular concrete columns reinforced with nickel–titanium shape memory alloy (SMA) bars using numerical simulation results obtained from well-calibrated nonlinear finite element models. A parametric study is conducted to examine the effects of various design parameters, such as the axial load ratio, section information, and material properties of concrete and SMA on the drift limit states of the columns. For each limit state (LS), a multivariate stepwise regression analysis was performed. An expression was derived to estimate the associated drift capacity of the SMA-reinforced concrete columns. In addition, the precondition for the SMA-reinforced concrete columns to ensure ductile behavior was investigated. It turned out that the axial load and the amount of transverse reinforcement are the most influential parameters on the ductility of the columns. Finally, nonlinear static and dynamic analyses were conducted for an SMA-reinforced concrete building frame to demonstrate the application of the proposed drift LSs. Both analysis results revealed that the building model tends to experience core crushing or loss of lateral load capacity prior to SMA failure.

Seismic performance assessment of steel frames upgraded with shape memory alloy re-centering dampers for passive protection of structures subjected to seismic excitations using high-performance NiTiHfPd material

This study explores a super-elastic memory alloy re-centering damper device and investigates its performance in improving the response of steel frame structures subjected to multi-level seismic hazard. The configuration of the device was initially proposed by the authors in a different paper. The proposed super-elastic memory alloy re-centering damper (SMARD) counts on high-performance shape memory alloy (SMA) bars for re-centering capability and employs friction springs to augment its deformation capacity. First of all, this study explores the super-elastic response of NiTiHfPd SMAs under various conditions and illustrates their application into seismic applications. In order to collect experimental data, uniaxial tests are conducted on super-elastic NiTiHfPd SMAs in the temperature range of −35 °C–25 °C and at the loading frequencies of 0.05 Hz to 1.0 Hz with four different strain amplitudes. The effects of loading rate and temperature on super-elastic characteristics of NiTiHfPd SMAs are examined. Then, an analytical model of six-story and nine-story steel special moment frame buildings with installed SMARDs is developed to determine the dynamic response of the building. Finally, nonlinear response time history analyses are conducted to assess the behavior of controlled and uncontrolled buildings under 44 ground motion records. Results show that SMARDs can enormously mitigate the dynamic response of steel frame structures at different seismic hazard levels and, at the same time, enhance their post-earthquake functionality.