Mechanical Properties Of High-strength Research Articles

Microstructure evolution and mechanical properties of high strength and high conductivity Cu[sbnd]Fe alloy wire prepared by cold drawing

CuFe alloy wire is widely used in the field of electronic information because of its high strength and high conductivity. In this study, Cu-5Fe-0.1Si-0.3 Mg-0.05RE (La, Ce) alloys were prepared by cold drawing and heat treatment. The microstructure evolution of the alloy during deformation was studied by optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). Three kinds of second phases with different sizes and shapes were successfully constructed in the designed alloys, including fibrous iron phase, submicron spherical iron phase and nano spherical phase. The strength of the alloy is greatly improved by drawing deformation, with only slight reduction of the conductivity. Through joint addition of Mg, Si and rare earth elements, the designed CuFe alloy wire rod has excellent overall properties. It's electrical conductivity, tensile strength, yield strength and elongation reached 63.8% IACS, 831 MPa, 730 MPa and 6.1%, respectively. Detailed characterizations of the alloys reveal that: the addition of Mg reduces solid solubility limit of iron in matrix and spaces between iron phases; the FeSi phase formed by Si and Fe promotes the precipitation of iron phase; and the addition of rare earth inhibits segregation of second phase, recovery and recrystallization of the alloy, and the coarsening of Fe phase. The mechanical properties of the alloy are improved by fiber strengthening, Hall-Petch strengthening and precipitation strengthening, respectively. The contributions of precipitation strengthening, fiber strengthening and Hall-Petch strengthening to yield strength are 65 MPa, 59 MPa and 277 MPa, respectively. The microstructure of dislocation and fibrosis is the main factor of alloy strengthening.

Study on Mechanism of Cumulative Directional Blasting of Brittle Karst Limestone in the Guizhou Province

The theoretical analysis, mechanical test, numerical simulations, and model tests are carried out on the Taoziya tunnel in Guizhou to investigate the influence law of cumulative blasting technology on directional rock breaking and fracture propagation of brittle limestone. The penetration effect of the triangular-shaped charge cover angle on the metal jet, the expansion law of the main explosion crack, and the influence of the limestone directional damage effect are explored. The results show that high-energy metal jet is formed when the initial velocity of the shaped charge cover is lower than the sound velocity of the shaped charge cover material. The values of B1 and B2 of the original rock are 22.1 and 248.76, respectively, demonstrating the mechanical properties of high strength, high brittleness, and easy fracture. The evaluation index is brittle limestone, and the directional precracking effect of shaped charge blasting technology is remarkable. When the angle of the shaped charge cover is 90°, a penetrating crack is almost consistent with the direction of the precrack generated after the explosion. Moreover, the width of the slit is approximately 2 cm. The borehole imager scans show that the rock wall in the hole is smooth and stable, the test results are consistent with the simulation results, and the angle of the shaped charge cover is 90°. The results have certain guiding significance for rock blasting technology, surrounding rock control technology, and similar directional fracturing engineering in the karst area of Guizhou province.

Influence of tungsten particle size on microstructure and mechanical properties of high strength and tough tungsten particle-reinforced nickel-based composites by laser-direct energy deposition

Tungsten (W) particle-reinforced nickel (Ni)-based composites were fabricated via laser-direct energy deposition (L-DED). The influence of the W particle size on the microstructure and mechanical properties of the deposited samples was systematically studied. The results indicate that refining the W particle size could refine the γ-Ni grains and subgrains, thin the (Ni, Cr)4 W interface layer, and increase the dislocation density of the intergranular matrix, thus improving the tensile strength and elongation of the L-DED samples. As W particle size decreased from 75 to 150 μm to 6.5–12 μm, the tensile strength and elongation of the deposited samples increased by 150 MPa and 2.9 times to 1347.6 ± 15.7 MPa and 17.5 ± 0.4%, respectively. Based on the properties of the interface (Ni, Cr)4 W, a load-transfer efficiency factor suitable for this composite was proposed and the load-transfer strengthening formula was optimized. A quantitative analysis of the strengthening mechanisms was established considering load-transfer strengthening, Hall–Petch strengthening, thermal-mismatch strengthening, and solid-solution strengthening. The calculated contribution of each strengthening mechanism to the yield strength and theoretical calculations were in good agreement with the experimental data. The article breaks the bottleneck of poor plasticity of W particle-reinforced Ni-based composites prepared by L-DED and provides a theoretical basis for the construction design of W particle-reinforced Ni-based composites with excellent mechanical properties.

Stabilizing austenite via intercritical Mn partitioning in a medium Mn steel

In this study, a novel processing route of intercritical Mn partitioning is proposed to stabilize the reverted austenite in a medium Mn steel. The Fe-5Mn-0.2C-1.5Al (wt.%) steel is annealed unceasingly at two intercritical temperatures to produce a compositional core-shell structured reverted austenite which consists of a core in low Mn content and a shell in relatively high Mn content. This distinctive microstructure can not only allow much more retained austenite to be obtained compared with the conventional processing route, but also produce active transformation induced plasticity effect over a broad strain range, leading to excellent mechanical properties of high strength and enhanced ductility.

Effect of yttrium on the cellular precipitation kinetics, grain growth behavior and mechanical properties of high strength Cu-15Ni-8Sn alloy

The effects of yttrium on the cellular precipitation kinetics, grain growth behavior and mechanical properties of Cu-15Ni-8Sn alloy are investigated. Results show that the added yttrium leads to the formation of NiSnY and Ni2Y compounds, which increases the strength, refines the grains and slows the grain growth rate of the Cu-15Ni-8Sn alloy. Also, the addition of yttrium changes the nucleation rate and crystal growth type of the γ phase, postponing cellular precipitation in the early stages of aging treatment. Compared with the peak-aged Cu-15Ni-8Sn alloy, the peak-aged Cu-15Ni-8Sn-0.2Y alloy possesses higher hardness and strength. The hardness increases from 348 HV to 372.2 HV, the yield strength increases from 960 MPa to 1098 MPa, and the ultimate tensile strength increases from 1044 MPa to 1166 MPa.

Effect of Intercritical Tempering Temperature on Microstructure Evolution and Mechanical Properties of High Strength and Toughness Medium Manganese Steel.

The effect of intercritical tempering temperature (TT) on the microstructure evolution and mechanical properties of 3.6Mn medium manganese steel, which contained martensite and austenite, was investigated by X-ray diffraction, electron backscattering diffraction and transmission electron microscopy, as well as Thermo-Calc calculation. The results showed that the volume fraction of reversed austenite (RA) increased firstly and then decreased with the increasing TT in the range of 550~650 °C. When the TT was below 620 °C, lath-like RA with good stability was mainly displayed between martensite laths and its size is about 100 nm. When the TT was higher than 650 °C, larger-size and block RA was formed in the martensite block boundaries, and part of the RA transformed into fresh martensite during cooling. The yield strength and tensile strength of the experimental steels decreased gradually as the TT increased, but the tensile strength increased gradually with the formation of block RA and fresh martensite. Lath-like RA could significantly improve the toughness and plasticity with slight loss of yield strength, but block RA decreased slightly them.

Effect of Yttrium on Cellular Precipitation Kinetics, Grain Growth Behavior and Mechanical Properties of High Strength and Toughness Cu-15ni-8sn Alloy

Effect of Yttrium on Cellular Precipitation Kinetics, Grain Growth Behavior and Mechanical Properties of High Strength and Toughness Cu-15ni-8sn Alloy

Effect of Yttrium on Cellular Precipitation Kinetics, Grain Growth Behavior and Mechanical Properties of High Strength and Toughness Cu-15ni-8sn Alloy

Effect of Yttrium on Cellular Precipitation Kinetics, Grain Growth Behavior and Mechanical Properties of High Strength and Toughness Cu-15ni-8sn Alloy

Comparison of Microstructure and Mechanical Properties of High Strength and Toughness Ship Plate Steel.

E36 ship plate steel was, respectively, produced by as rolling and normalizing process (ARNP), and EH36 and FH36 ship plate steel was produced by the thermo-mechanical control process (TMCP) with low carbon and multi-element micro-alloying. The microstructure of the three grades of ship plate steel was composed of ferrite, pearlite, and carbides at room temperature. The average grain size on 1/4 width sections (i.e., longitudinal sections) of the three grades of ship plate steel was, respectively, 5.4 μm, 10.8 μm, and 11.9 μm. EH36 and FH36 ship plate steel had the higher strength due to precipitation and grain boundary strengthening effect, while the E36 ship plate steel had the lower strength due to the recovery phenomenon in the normalizing process. EH36 and FH36 ship plate steel had higher impact toughness due to lower carbon (C) and silicon (Si) content and higher manganese (Mn) content than E36 ship plate steel. E36 ship plate steel had the best plasticity due to the two strong {110} and {111} texture components. The fracture toughness KJ0.2BL(30) values of E36 and EH36 and KJ0.2BL value of FH36 ship plate steel were, respectively, obtained at 387 MPa·m1/2, 464 MPa·m1/2 and 443 MPa·m1/2. EH36 and FH36 ship plate steel had higher KJ0.2BL(30) due to lower C and Si and higher Mn, niobium (Nb), vanadium (V), and aluminum (Al) content than the E36 ship plate steel. The fatigue crack growth rate of E36 ship plate steel was higher than that of EH36 and FH36 ship plate steel due to its higher carbon content and obviously smaller grain size. The analysis results and data may provide a necessary experimental basis for quantitatively establishing the relationship between fracture toughness, yield strength and impact toughness, as well as the relationship between fatigue crack growth rate and both strength and fracture toughness.

Experiment on control measures of shrinkage and cracking of high strength manufactured sand concrete containing a large amount of high absorbency stone powder

The early-age shrinkage, crack resistance and mechanical properties of high strength manufactured sand concrete containing a large amount of high absorbency stone powder were conducted in order to solve the early-age shrinkage and cracking problem of concrete by adding expansion agent, shrinkage reducing agent, polyvinyl alcohol (PVA) fiber, super absorbent polymer (SAP). The mechanism of inhibiting shrinkage and cracking of high strength manufactured sand concrete containing a large amount of high absorbency stone powder was revealed by testing pore structure and microstructure morphology using low-field nuclear magnetic spectroscopy and scanning electron microscope. The test results show that the addition of expansion agent, shrinkage reducing agent, PVA fiber and pre-absorbent SAP can all effectively inhibit the early-age shrinkage and cracking of concrete. Compared with the benchmark group concrete, incorporating pre-absorbent SAP is the best measure to reduce the early-age shrinkage of concrete and the shrinkage strain will be reduced by 93%. The most obvious inhibitory effect on the cracking of concrete is incorporating PVA fiber and the total cracking area can be reduced by 68.26%. The mechanical properties of the concrete are improved because of pre-absorbent SAP and PVA fiber. However, the mechanical properties of concrete have a certain decrease because of incorporating expansion agent and shrinkage reducing agent. SEM images show that SAP can release the pre-absorbed water into the concrete and promote the cement hydration reaction, while the incorporation of PVA fiber improves the internal pore structure of the concrete and has a good filling and bridging effect. The low-field nuclear magnetic resonance experiments show that the mechanism of inhibiting shrinkage and cracking is to improve the pore structure of concrete and enhance the compactness of the interface, thereby reducing early shrinkage and improving crack resistance.

Microstructures and mechanical properties of high strength Ti-XAl-2Fe-3Cu alloys fabricated by powder compact extrusion

Ti-XAl-2Fe-3Cu (X = 2.7, 4 wt%) alloys with a high tensile yield strength of up to 1150 MPa were synthesized using powder compact extrusion from blended TiH2 and elemental powders. The microstructures and mechanical properties of the extruded rods without and with a homogenization heat treatment at 1000 °C for 1 h followed by furnace cooling were investigated. It was found that the Al content and heat treatment had significant effects on the microstructures and mechanical properties. With increasing the Al content from 2.7 to 4 wt%, the average lamellar colony size and lamellar thickness of the as-extruded Ti-XAl-2Fe-3Cu alloy decreased from 442.4 to 224.1 µm and 6.7–5.2 µm respectively. The heat treatment increased the lamellar thickness as well as the level of partitioning of Fe and Cu between α and β phases. As a result of the microstructural changes, increasing Al from 2.7 to 4 wt% caused a slight increase in the strength of Ti-XAl-2Fe-3Cu alloys without changing the ductility, while the heat treatment slightly reduced the strength of the alloys, but clearly increased their tensile ductility. The correlation between microstructures and mechanical properties is discussed.

Martensitic transformation in a α + β–Ti alloy after cryogenic treatment and its influencing to low elastic modulus biomaterials

The high strength titanium alloy is one of the most popular α + β-Ti type alloy and well responsive to the microstructure mainly depends on the processing history, heat treatment and selective faster cooling treatments. It has many engineering applications like military application, biomedical implant and aerospace application. The cryogenic treatment (CT) was typically done for faster cooling at low temperature (−20 to −100 °C) after solution treatment at 860 °C for 1 h then immediately quenched into liquid nitrogen bath with control manner. Subsequently, another identical sample quenched into the water to cool room temperature. After successfully solution treated both samples again preferred for ageing treatment at 500 °C for 5 h then air cooling. The examination of microstructures by SEM analysis revealed that after double steps heat treatment shows very fine α and β phases, with needle shape α are decomposed from α′ martensite tend to speed up by TiN or VN precipitates enhanced strength in the matrix. As well as, vanadium content is one of the important factors for martensite formation after solution treatment in the α + β phase field. The results show that after double steps heat treatment in CT obtained optimum mechanical properties such as 0.2% proof strength (PS) of 790 MPa, ultimate tensile strength (UTS) of 1200 MPa, strain (ε) of 70%, reduction area (RA) of 16.76%, and PS to UTS ratio of 0.66, respectively. To intuitive study estimate the effect in water quenching (WQ) as well as cryogenic treatment on microstructures and mechanical properties of high strength Ti-Al-V ternary alloy, which is potentially used in aerospace and structural applications owing to a high specific strength and high corrosion resistance. Meanwhile, after faster cooling in CT that martensite transformation tends to exhibit low elastic modulus for beneficial to orthopaedic implants in the human body.

A quantitative understanding on the mechanical behavior of AlCoCrFeNi2.1 eutectic high-entropy alloy

Eutectic high entropy alloys (EHEAs) possess the unique mechanical properties of high strength and ductility. However, the characterization of mechanical behavior and its theoretical verification of EHEAs remain to be solved. In this work, a constitutive mechanical model of AlCoCrFeNi2.1 eutectic high-entropy alloy is established. Mori-Tanaka’s homogenization method and Eshelby equivalent inclusion theory are adopted to analyze the problem of multiphase inclusion, and the excellent mechanical properties of the alloy are verified by theoretical methods. The theoretical results are consistent with the experimental date, which proves the authenticity of the model. And the results show that the eutectic phase interface and back stress can improve the strength and ductility of the material to a certain extent. In addition, our analysis found that mechanical properties of EHEAs are sensitive to the volume ratio of two phases, nano-precipitated phase and strain rate. This research has provided a theoretical framework to design excellent mechanical property of EHEAs by optimizing material structure parameters.

Evolution of mechanical properties and corrosion resistance of Al0.6CoFeNiCr0.4 high-entropy alloys at different heat treatment temperature

The non-equiatomic Al0.6CoFeNiCr0.4 HEA with dual FCC + BCC structure was fabricated by arc-melting under high-purity argon atmosphere, and the mechanical behavior and corrosion resistance of these HEAs with heat temperature range of 550 °C–850°Cfor 24 h were investigated. By increasing the ageing temperature, the crystalline phase of these HEAs transformed from FCC + disordered BCC to FCC + disordered BCC + order B2 phase, and then to FCC + order B2 phase.The spherical B2 was firstly observed in the aged- 650°CHEA, and disordered BCC disappeared in aged-850°CHEA. The ageing hardening occurred at aged-650 °C, because of the growth of disordered BCC phase (α-Fe) and precipitation of spherical B2 phase (AlNi). Additionally, it can be found that the proper spinodal decomposition of FCC phase (Fe–Cr) can optimize mechanical properties of alloys, while excessive spinodal decomposition will cause the negative effect. The aged-750°Cdisplay an excellent mechanical properties of high strength and compress ductility due to the presence of proper spinodal decomposition and spherical B2 phase precipitation. When these HEAs were immersed in the 3.5 wt% NaCl solution, the corrosion resistance of these HEAs are gradually decrease with the Volume fraction of B2 phase increase, suggesting that crystalline phases with higher amount of Al element are prone to be corroded by Cl-ion.

Correlation between macroscale tensile properties and small-scale intrinsic mechanical behavior of Mo-added Fe–Mn–Al–C lightweight steels

Research and development for increasing the strength of steel materials has been in progress for a long time, but as the strength increases, the stiffness and impact characteristics are deteriorated, the weight reduction by reducing the thickness of steel is gradually reaching its limit. Therefore, lightweight steels having a low density by adding aluminum, which is a substituted element having a smaller atomic weight than iron atoms, has been proposed. These steels have exhibited favorable mechanical properties of high strength and good ductility, making it suitable for the automotive and defense industries. In this study, the effects of Mo addition on the microstructural evolution and mechanical properties of austenitic lightweight steel with Fe-1.1 wt% C-30 wt% Mn-10.5 wt% Al were investigated using a macroscopic tensile test and small-scale nanoindentation. The yield strength decreased as the Mo content increased to 3 wt%. This phenomenon was explained by the precipitation of κ-carbide. In contrast, the yield strength increased as the Mo content significantly increased to 4 wt%. This is due to grain refinement caused by Mo-enriched precipitation such as M6C and the formation of ferrite and ordered phase D03. In addition, the intrinsic mechanical properties inside grain and at the grain boundary were statistically evaluated using nanoindentation data. From the maximum shear stress at the elastic–plastic transition of the grain boundary during nanoindentation, we could determine the grain boundary strengthening due to M6C precipitation. From the grain boundary strengthening and the grain refinement, the effects of Mo on the microstructure evolution and mechanical properties of lightweight steel could be described.

The quantitative analysis of the crack propagation on the fatigue properties of dual-phase approximate equiaxial nanocrystalline AgCu alloy

Nanostructure dual-phase equiaxial alloy (DPEA) possesses the unique mechanical properties of high strength and ductility. However, the investigation of the fatigue properties in DPEA remains to be solved. In this paper, the mechanism of fatigue crack propagation in DPEA is explained by the interaction between dislocations and clusters in different grains of materials. The stress of dislocations on the slip plane and the time constant of pinned dislocation bypass the cluster can be calculated. The results show that the presence of clusters results in dislocations on the slip planes to induce different degrees of pile-up. The pile-up of dislocations is the dominant factor for hindering crack growth, which facilitates the crack blunting and improves the fracture toughness of alloy, during the plastic deformation of materials. In addition, based on the calculated results of the theoretical model, it is revealed that fracture toughness of DPEA is sensitive to the grain size, activation energy and the time constant of dislocation bypass the cluster. In a word, this research has provided a rational framework to amply explain the fatigue properties of DPEA based on theoretical model.

Effect of heat treatment on bonding mechanism and mechanical properties of high strength Cu/Al/Cu clad composite

The present study is aimed at fabricating Cu/Al/Cu tri-layered clad composite with one pass heavy reduction roll bonding and subsequent heat treatment. High strength clad composite was designed via introducing 7075 alloy. The interface bonding mechanism was discussed under different conditions. The mechanical properties of the Cu/Al/Cu clad composites were also studied. The results showed that thick interfacial intermetallic layer could be formed after certain heat treatments (annealing at 500 °C or T6 treatment). The peeling behavior was affected by the intermetallic layer. The interfacial bonding behavior was related with the state of Cu/Al/Cu clad composite. Peel strength could reach 78.1 or 62.2 N/cm after annealing at 500 °C or T6 treatment, respectively. Lamellar delamination traces were remained on the peel surface after peel process. The thickness of interfacial compounds was in proportional with the altitude of delamination remaining. During the peel process, peel gap sheared through the interfacial layer and transformed between two matrix layers periodically. The mechanical properties of present clad composite could reach a best comprehensive value after T6 treatment with strength of 458 MPa and elongation of 15.2%. The strength level increased clearly as compared with pure aluminum and copper “sandwich” clad composite.

Effect of cold rolling process on microstructure and mechanical properties of high strength β titanium alloy thin sheets

The microstructure and mechanical properties of Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe high strength titanium alloy sheets prepared by unidirectional cold rolling and two-step cross cold rolling were investigated. Results showed that the β phase grains were refined significantly by cold rolling followed by solution treatment for a short time. Compared to unidirectional cold rolling, the short time solution treatment after two-step cross rolling could significantly reduce the non-uniformity of the microstructure of the alloy sheets. After aging treatment at 550 °C, the anisotropy of the mechanical properties still existed in the unidirectional rolled sheets, and the tensile strength was highest along the rolling direction. After solution and aging treatment, the anisotropy of the mechanical properties of the two-step cross rolling process sheet was not obvious than unidirectional cold rolling, and alloy had good strength and plasticity matching.

Direct injection molding and mechanical properties of high strength steel/composite hybrids

Metal polymer hybrid technology is a promising way of automotive weight reduction and safety improvement. In this study, high strength steel and glass-fiber reinforced PA66 composite were integrated by direct injection molding process. The mechanical properties and failure behavior of steel/composite hybrids under tension, bending, mode I and II fracture loads were investigated experimentally, theoretically and numerically. The properties of the interface between steel and composite were measured using double cantilever beam and end-notched flexure tests for the first time. The analytical model and finite element simulation considering the interface mechanical behavior were proposed and validated. They can be utilized to predict the mechanical properties and progressive failure process of hybrid material cost-effectively and accurately. It is found that the cracks initiate at the interface, and then propagate through composite until the hybrid material loses load-carrying capacity completely. The steel dominates the load-bearing capacity, and the interface dominates the failure process. The results obtained in this study offer a scientific guidance and theoretical basis for the engineering application of metal polymer hybrid materials.

Microstructure and Mechanical Properties of High Strength Alloyed Steel for Aerospace Application

The high strength aerospace steel alloyed with Cr, Mn, Si, Ni, W and Mo was studied. The austenite transformations under continuous cooling conditions were investigated using the dilatometer analysis at the cooling rates 0.1...30 °C/s. The mechanical properties of the studied steel were determined after the conventional quenching and tempering heat treatment. The dependences of the mechanical properties on the tempering temperature were obtained. The novel quenching and partitioning heat treatment was applied to the steel under consideration. The microstructure and the mechanical properties were studied after three different modes of the quenching and partitioning (QP) treatment: single-stage QP, two-stage QP and single-stage QP with subsequent tempering (QPT).