Reduction In Ductility Research Articles

Effect of grain size on deformation behavior of pure rhenium

A comprehensive study of grain size effect on twins, slips and work hardening of rhenium during tension was conducted using EBSD and SEM analysis. Slip/twinning trace and Schmid factor (SF) were analyzed to elucidate the activities of deformation modes. The deformation behavior was found to be sensitive to grain size. Non-basal slips and {112¯1} <1¯1¯26> extension twins were found to be the dominated deformation modes in the samples with large grain size. Large KAM values are located in twin GBs and severely deformed grains. Basal slip with low SFs was also activated to adapt strain-compatibility. With the decrease of grain size, non-basal slip was suppressed and an obvious transition from non-basal to basal slip-dominated flow occurred. The pure Re with coarse grain size (d = 67 μm) had a high elongation (27.6%) and ultimate strength (1168 MPa). In contrast, intergranular compatibility became difficult with decreasing grain size due to the progressively lower activation ability of deformation mechanisms, resulting in a reduction of ductility and ultimate strength. The exceptionally high work hardening rate of rhenium was mainly attribute to twin formation and basal slip activity during the initial straining. With the increase of grain size, high density cross-slip and twins provide additional work hardening, leading to extrapolated work hardening limit.

Tribological Properties of High-Entropy Alloys under Dry Conditions for a Wide Temperature Range-A Review.

High-entropy alloys (HEAs) are composed of multiple elements with equimolar or near equimolar composition that have superior mechanical and tribological properties. In this article, we present a review on the tribological performance of HEAs. The tribological properties of different HEAs systems have been evaluated, and it has been found that the wear rate strongly depends on the crystal structure of the phases. The most common structures are face-centered cubic (FCC), body-centered cubic (BCC), and dual-phase (FCC + BCC) alloys due to the high entropy of mixing instead of forming intermetallic phases. In general, HEAs with a BCC structure showed superior hardness and wear properties compared to FCC and FCC + BCC alloys. The lesser wear rate of HEAs with a BCC structure is attributed to the reductions in ductility, resulting in strong but brittle alloys. In addition to the crystal structure, the effect of temperature on the tribological performance of the HEAs is also discussed, which highlights their potential applications for high temperatures. Moreover, various other factors such as grain size, formation of an oxide layer, and wear mechanisms are discussed.

Influence of Si content on the microstructure and mechanical properties of silicon stainless steel

The influence of Si addition on the microstructure and mechanical behavior of cast silicon stainless steel alloys was investigated. It was recognized that after incorporation of Si in the range of ∼ 2–6 wt%, microstructure changes significantly. It transforms from single-phase austenitic to duplex microstructure containing ferrite and austenite. In addition, TiC precipitates with angular and spherical morphology were observed in all the sample conditions. Uniaxial tensile tests suggested that the incorporation of Si improved the strength and ductility as long as the microstructure remains primarily austenitic. However, at much higher silicon content (∼6 wt%), microstructure transformed to duplex structure, followed by the drastic reduction in ductility and toughness. Overall, the alloy with ∼4 wt% Si exhibited comparatively better strength, ductility as well as toughness. The mechanical properties of the individual phases, characterized using nanoindentation, indicated that the hardness and modulus of the austenite phase improved significantly after Si incorporation up to ∼6 wt%. Concomitantly correlation between the mechanical properties and crystallographic orientation of grains was also established by performing post-nanoindentation EBSD analysis. The results indicated that the average hardness and modulus of each phase are significantly related to the crystallographic orientation of grains, i.e., it is highly anisotropic. Finally, the nanomechanical properties of the individual phases were utilized to predict and compare the bulk mechanical properties using the ECM model. A reliable quantitative comparison between nanomechanical and bulk mechanical properties of alloys with single-phase microstructure was obtained, whereas a more refined ECMs are required for envisaging the bulk characteristics of the materials with duplex microstructure.

The Influence of a Field-Aged Asphalt Binder and Aggregates on the Skid Resistance of Recycled Hot Mix Asphalt

The application of asphalt hot mix recycling is one challenge in sustainable road pavement research. In addition to the vast amount of research on the performance of recycled asphalt–concrete, the research on the frictional resistance of recycled hot mix asphalt is still limited. The effects of aged asphalt and aged aggregates on the skid resistance of recycled hot mix asphalt were investigated in this research. The aged asphalt and aged aggregates were carefully extracted from the field-reclaimed asphalt pavement, and the engineering and mechanical properties of aged and virgin aggregates were measured. The degradation of recycled hot mix asphalt was simulated using an accelerated polishing machine to mimic road surface abrasion. Accordingly, the initial and final skid resistances of the recycled hot mix asphalt were determined and correlated with the properties of the aged asphalt and aggregates. The initial skid resistance of recycled hot mix asphalt decreased with reductions in penetration and ductility of the blended asphalt. However, the changes in the blended asphalt properties contributed only small variations to the final skid resistances of the recycled hot mix asphalt. The gradations of recycled hot mix asphalt correlated only with the final skid resistances. The aggregate gradations controlled the characteristics of the final skid resistance since the covered binder was partially polished off from the road surface at this stage.

Transition of creep damage region in P91-Alloy800-SS316LN dissimilar metals weld joint

The creep behaviour of P91-Alloy800-SS316LN dissimilar metals weld joint (DMWJ) has been assessed at 823 K in the stress range of 180–260 MPa. Creep strain accumulation in the DMWJ was higher under high stress regime than the low stress regime. Transition of creep damage and fracture in the DMWJ occurred from P91 steel base metal at high stress regime to the interface region of P91 CGHAZ-IN182 weld metal at lower applied stress with significant reduction in ductility. Kernel average misorientation indicates that the localized increase in strain at the P91 CGHAZ-IN182 weld metal interface region under creep loading in comparison to that of the pre-creep condition. Enhanced heterogeneity in strain distribution, carbon migration, coarser precipitates and soft zone formation at the P91 CGHAZ-IN182 interface region have been attributed to the premature failure of DMWJ in comparison to P91 steel.

Effect of Laser Welding on Microstructure and Mechanical Behaviour of Dual Phase 600 Steel Sheets

Dual Phase steels are one of the most used advanced high-strength materials in the industry, due to its combination of a ductile ferritic matrix and disperse hard martensite islands, which provide outstanding mechanical properties for components to be cold stamped. This work investigated fiber laser welding applicability in Dual Phase 600 1.6 mm thick steel sheets, evaluating potential welding impacts on properties of the material for industrial applications. A first set of bead-on-plate welds was generated to define best parameters for subsequent tests. A second set was prepared, consisting of butt joints welded in the optimized condition. Weld microstructure was characterized as 100% martensitic at fusion zone (FZ), with growing fractions of ferrite at Heat Affected Zone (HAZ) as one moves away from fusion line. Hardness is around 60% higher at FZ than at BM, being maximum at supercritical HAZ due to its highly refined microstructure and HAZ softening was not observed. Tensile and Erichsen cupping tests presented similar strength results between welded and non-welded specimens, with slight ductility reduction. Finally, numeric simulations based on Finite Element Analysis were carried out to estimate temperature evolution, phase proportions, residual stresses and distortion levels, achieving excellent agreement with experimental results.

Manipulation of Microstructure and Mechanical Properties in N-Doped CoCrFeMnNi High-Entropy Alloys

Herein, we carefully investigate the effect of nitrogen doping in the equiatomic CoCrFeMnNi high-entropy alloy (HEA) on the microstructure evolution and mechanical properties. After homogenization (1100 °C for 20 h), cold-rolling (reduction ratio of 60%) and subsequent annealing (800 °C for 1 h), a unique complex heterogeneous microstructure consisting of fine recrystallized grains, large non-recrystallized grains, and nanoscale Cr2N precipitates, were obtained in nitrogen-doped (0.3 wt.%) CoCrFeMnNi HEA. The yield strength and ultimate tensile strength can be significantly improved in nitrogen-doped (0.3 wt.%) CoCrFeMnNi HEA with a complex heterogeneous microstructure, which shows more than two times higher than those compared to CoCrFeMnNi HEA under the identical process condition. It is achieved by the simultaneous operation of various strengthening mechanisms from the complex heterogeneous microstructure. Although it still has not solved the problem of ductility reduction, as the strength increases because the microstructure optimization is not yet complete, it is expected that precise control of the unique complex heterogeneous structure in nitrogen-doped CoCrFeMnNi HEA can open a new era in overcoming the strength–ductility trade-off, one of the oldest dilemmas of structural materials.

The Roles of Ni and Co in Dendritic Growth and Tensile Properties of Fe‐Containing Al–Si–Cu–Zn Scraps under Slow and Fast Solidification Cooling

Studies of Fe‐contaminated Al‐based scraps have drawn attention for years. However, little has been researched about the effects of cobalt (Co) and nickel (Ni) additions to contaminated scraps both under slow solidification (directional solidification, DS) and fast solidification regime (copper mold centrifugal casting, CC). As such, the current study examines a representative low‐alloy Al–Si chemistry from industrial scraps, i.e., the Al–7%Si–0.6%Fe–0.35%Cu–0.25%Zn (% by weight). This alloy is changed independently using Ni and Co. It is observed that a mixture of uneven distributed α and β Fe‐bearing particles prevails for all tested alloys and solidification conditions. The coexistence of both phases agrees with the charts proposed by Gorny's work for the range of secondary dendritic spacing, λ 2, observed. Although the Fe‐containing particles are smaller for fast‐solidified samples, they still maintain the acute morphology and, in some cases, the Chinese script shape. This results in a reduction in ductility of the order of 65% for the nonmodified and Ni‐modified samples considering mean λ 2 varying from 20 μm (DS) to 6.5 μm (CC), despite improvements in mechanical strength. Furthermore, addition of Co results in a higher number of Fe‐based particles within the microstructure. In this case, the largest particle/α‐Al interfacial area results in slightly poor ductility (~6–8%) and higher strength (175–205 MPa), with less ductility loss when DS and CC samples are compared.

Refined simulation of eccentric compression behavior of corroded reinforced concrete columns

In this paper, concrete is considered a three-phase composite material composed of aggregate, a mortar matrix, and an interface transition zone to investigate the eccentric compressive behavior of corroded reinforced concrete (RC) columns from the mesoscopic perspective. The deterioration of the material properties of steel bars, concrete cover, and bond strength was considered to be caused by corrosion, and a three-dimensional refined finite element analysis model was established. The numerical results are in good agreement with the experimental results, which verifies the rationality of the numerical analysis model. The effect of corrosion level and eccentric ratio on the eccentric performance of corroded RC columns is explored and discussed. The simulation results indicate that the corrosion of steel bars increases the critical eccentricity, which may make the structure tend to brittle failure. The increased corrosion level would obviously cause a reduction of stiffness, ductility, and ultimate bearing capacity of the columns. In addition, increased eccentricity causes a reduction in axial bearing capacity, and the failure mode of columns changes to large eccentric compression failure. Eventually, based on the unified formula for the bearing capacity of RC members in good condition and in consideration of the influence of steel corrosion, a calculation formula for the bearing capacity of corroded RC members was developed. The accuracy of the proposed formula was verified in comparison with the experiment results.

Bond behaviour between crumb rubberized concrete and deformed steel bars

This study presents a systematic investigation of the bond behaviour of rubberized concrete. The local and global bond behaviours of rubberized concrete are studied experimentally using concentric pull-out test and beam end test, respectively. The test parameters include concrete strength grade, bar embedded length, bar diameter and rubber content. In addition to the bond tests and the ancillary material property tests, six large-scale reinforced rubberized concrete beams are also tested under flexural bending to evaluate the influence of the alteration of bond behaviour owing to rubber incorporation on the flexural performance of the beams. The higher deformability of rubberized concrete compared to conventional concrete at each strength grade results in altered local and global bond behaviour, where the reduced peak bond stress and an increase in the slip at the peak bond stress are observed. The altered bond in conjunction with the other reduced mechanical properties of rubberized concrete subsequently led to a reduction in the flexural stiffness at the elastic stage and a reduction in ductility at the post-peak stage of a corresponding reinforced concrete beam containing rubber. The results of the mechanics-based and code-based models for predicting the development length for a reinforced bar in rubberized concrete indicated that the code-based model to design the anchorage length in rubberized concrete could be used with confidence.

Enhanced work hardening from oxygen-stabilized ω precipitates in an aged metastable β Ti-Nb alloy

High levels of oxygen in solid solution in Ti alloys are considered detrimental to mechanical properties because of embrittlement concerns. In metastable β titanium alloys, the formation of isothermal ω precipitates is also known to cause severe embrittlement and ductility reduction. However, oxygen has been shown to partition to the ω phase during ageing, and this partitioning behavior may potentially impact ω’s mechanical contribution. Using micropillar compression, we compared the deformation behavior of Ti-20Nb (at. %) with oxygen-stabilized ω precipitates to the behavior of oxygen-free specimens. The oxygen-stabilized microstructures showed increased compressive yield strength and enhanced work hardening behavior compared to oxygen-free specimens. In the absence of oxygen, the compressed pillars showed slip band formation and catastrophic failure, and transmission electron microscopy imaging revealed that ω precipitates were sheared within the continuous deformation channels resulting in slip localization. In contrast, oxygen-stabilized ω precipitates were harder to shear and the formation of continuous deformation channels was suppressed during compression, leading to improved work hardening behavior up to 15% strain. This counter-intuitive role of oxygen may offer design strategies to address the significant embrittlement and loss of ductility observed for ω-strengthened β Ti alloys without oxygen and avenues to expand the use of β Ti alloys.

Influence of silicon on the structure and properties of high-strength cast aluminum alloy AZ5NF

The phase composition and the mechanical properties of the AZ5NF with various contents of silicon impurities alloy were investigated by both calculation and experimental methods. For evaluation of the alloy phase composition and the effect of the chemical composition, CALPHAD method integrated in Thermo-Calc software was applied. Further scanning electron microscopy technique a significant increase of the volume fraction of Mg2Si phase with an increase of silicon content from 0.1% to 0.3%. It is shown that in case of silicon content higher than 0,2 wt.% Mg2Si phase starts forming during equilibrium crystallization. This phase forms as the thin layers at the grain boundaries. This leads to brittle intergranular fracture and significant reduction of the alloy ductility both in the as-cast state and in T6 temper. Based on this limits for the silicon content in AZ5NF have been proven. It is shown that dissolution of Mg2Si phase (full or partial depending on silicon content) requires solid solution treatment. Following quenching and artificial ageing provide high strength and ductility.

Development in mechanical and fatigue properties of AA6061/AL2O3 nanocomposites under stirring temperature (ST)

Aluminum is expected to remain the core material for many critical applications such as aircraft and automobiles. This is due to the high resistance to different environmental conditions, desired and manageable mechanical properties, as well as high fatigue resistance. Aluminum nanocomposites such as AA6061/Al2O3 can be made in many ways using a liquid metallurgy method. The main challenges for this method in the production of nanocomposites are the difficulties of achieving a uniform distribution of reinforcing materials and possible chemical reactions between the reinforcing material and the matrix. For structural applications exclusive to aerospace sectors. The growing cost-effective nanocomposites mass production technology with essential operational and geometric flexibility is a big challenge all the time. Each method of preparing AA6061/Al2O3 nanocomposites can provide different mechanical properties. In the present study, nine nanocomposites were prepared at three stirring temperatures (800, 850, and 900 °C) with the level of Al2O3 addition of 0, 5, 7, and 9 wt %. The results of tensile, hardness and fatigue tests revealed that the composite including 9 wt % Al2O3 with 850 °C stirring temperatures has the best properties. It was also revealed that the 850 °C stirring temperature (ST) with 9 wt % Al2O3 composite provide an increase in tensile strength, VHN and reduction in ductility by 20 %, 16 % and 36.8 % respectively, compared to zero-nano. Also, the fatigue life at the 90 MPa stress level increased by 17.4 % in comparison with 9 wt % nanocomposite at 800 °C (ST). Uniform distributions were observed for all nine microstructure compositions.

Earthquake Response Modeling of Corroded Reinforced Concrete Hollow-Section Piers via Simplified Fiber-Based FE Analysis

The effect of corrosion-induced damage on the seismic response of reinforced concrete (RC) circular bridge piers has been extensively investigated in the last decade, both experimentally and numerically. Contrarily, only limited research is presently available on hollow-section members, largely employed worldwide and intrinsically more vulnerable to corrosion attacks. In this paper, fiber-based finite element (FB-FEM) models, typically the preferred choice by practitioners given their reduced computational expense, are validated against previous shake-table and quasi-static cyclic tests on hollow-section RC columns, and then used to investigate the influence of corrosion-induced damage. To this end, modeling strategies of varying complexity are used, including artificial reduction of steel rebar diameter, yield strength and ductility, as well as that of concrete compressive strength to simulate cover loss, and ensuing dissimilarities quantified. Pushover and incremental dynamic analyses are conducted to explore impacts on collapse behavior, extending experimental results while accounting for multiple corrosion rates. Produced outcomes indicate a minimal influence of cover loss; substantial reductions of base shear (up to 37%) and ultimate displacement capacity (up to 50%) were observed, instead, when introducing relevant levels of deterioration due to corrosion (i.e., 30% rebar mass loss). Its predicted impact is generally lower when considering more simplified assumptions, which may thus yield non-conservative predictions.

Influence of addition of TiAl particles on microstructural and mechanical property development in a selectively laser melted stainless steel

316L stainless steel is well known for its excellent corrosion resistance and ductility. However, its relatively low strengths restrict its application in many load-bearing fields. In this study, Ti–48Al–2Cr–2Nb powder particles were mixed with 316L powder particles and then processed by selective laser melting (SLM) with the aim of developing intermetallic nano-particles reinforced 316L. It was found that the addition of 2 wt.% TiAl particles led to formation of numerous nano-sized cuboidal γ-TiAl precipitates in the austenite matrix and ferrite in the bottom regions of solidified melt pools. The majority of ferrite shows no particular orientation relationships with austenite that are characteristic of austenite → ferrite (γ-Fe → α-Fe) solid phase transformation, indicating that they should have formed during solidification. The α-Fe domains and surrounding γ-Fe regions were found to have experienced significant dynamic recrystallization during thermal cycling, resulting in fine α-Fe and γ-Fe equiaxed grains and massive twins in the γ-Fe. The addition of TiAl has moderately improved 0.2% yield strength and significantly increased ultimate tensile strength, thanks to the refined grain structure and massive γ-TiAl nano-particles which have acted as effective dislocation motion barriers. Some un-melted TiAl particles acted as preferential crack initiation and propagation sites during deformation, leading to reduction in ductility.

Behaviour of square concrete filled FRP tube columns under concentric, uniaxial eccentric, biaxial eccentric and four-point bending loads

This study investigated the behaviour of short square concrete filled fibre reinforced polymer tube specimens under concentric, uniaxial eccentric, biaxial eccentric and four-point bending loads. Seven concrete filled glass fibre reinforced polymer (GFRP) tube specimens (GFRP-CFFT) and seven traditional steel bar reinforced concrete (steel-RC) specimens of 200 mm x 200 mm cross-section were tested. The GFRP-CFFT specimens obtained a larger P-M interaction surface (higher maximum axial loads and higher bending moments) than the steel-RC specimens. In addition, the GFRP-CFFT specimens exhibited a lower average reduction in ductility under eccentric axial loads than the steel-RC specimens.

Tailoring microstructure and tensile properties of Mg-Si alloys varying solidification cooling rate and Si content

Mg-Si alloys were investigated in terms of their microstructural characteristics and tensile properties, by varying solidification cooling rate and Si content. This type of investigation becomes essential since these alloys are considered potentially base alloys for new biocompatible and biodegradable materials that might be used to produce a variety of temporary implants. This because Silicon (Si) has been recognized as a vital mineral in the human body, aiding both the healing process and the development of the immune system. Despite these characteristics provided by Si, Mg-Si alloys typically have low ductility and tensile strength due to the presence of coarse Mg2Si particles. Therefore, efforts to understand and improve these properties are most welcome. In order to deepen the knowledge of these alloys, the present research analyzed three Mg-Si alloys: Mg-0.6 wt% Si, Mg-1.3 wt% Si and Mg-1.7 wt% Si regarding their microstructures and phase's morphologies produced in a broad range of solidification rates' samples and their corresponding tensile properties. The predominance of dendritic arrangement with the interdendritic region composed of the (Mg + Mg2Si) eutectic was noted for the Mg-0.6 wt% Si and Mg-1.7 wt% Si alloys. Eutectic cells prevailed for the Mg-1.3 wt% Si alloy, with cells varying from squarer and hexagonal to a more rounded shape with the decrease in cooling rate. Experimental influences of the microstructural parameters on the tensile properties have been verified. Except for the Mg-1.3 wt% Si alloy, the tensile properties of the other alloys were found to be roughly independent of the dendritic length scales in the verified ranges. In general, increased Si content led to a reduction in strength and ductility, probably due to the increase in the fraction of Mg2Si particles, which is an effective phase in the stress concentration during loading, shortening the break.

Seismic Performance of CFST Frame-Steel Plate Shear Walls Connected to Beams Only

The safety and cost of structures composed of concrete-filled steel tube (CFST) frame-steel plate shear walls (SPSWs) with two-side connections are governed by the seismic performance. The response modification factor R and displacement amplification factor Cd are important seismic performance factors. In this paper, nonlinear seismic responses of 10-story, 15-story, and 20-story CFST frame-SPSWs (CFST-SPSWs) are studied. A nonlinear finite element model which includes both material and geometric nonlinearities is developed using the finite element software OpenSees for this study. The accuracy of model was validated by comparing with experimental results. Nonlinear seismic analysis shows that CFST-SPSWs, in high seismic region, behave in a stable and ductile manner. Also, R and Cd of CFST-SPSWs were evaluated for the structure models using incremental dynamic analysis (IDA), and the average values of 3.17 and 3.05 are recommended, respectively. The recommended R value is greater than the value (2.8) in the “Chinese Code for seismic design of buildings” for composite structures, indicating the code is conservative. The structural periods provided by current code are generally lower than the periods calculated by finite element analysis. Research results show that R and Cd increase with increasing story number, span number, and structural period. Ductility reduction factor Rμ increases with increasing span number and decreasing story number. Overstrength factor Rs increases with increasing story number and decreasing span number.

The mechanical and oxidation properties of novel B2-ordered Ti2ZrHf0.5VNb0.5Alx refractory high-entropy alloys

A series of novel B2-ordered Ti2ZrHf0.5VNb0.5Alx refractory high-entropy alloys (RHEAs) was designed and prepared by vacuum arc-melting. The effect of Al alloying on the microstructure, mechanical properties, and oxidation properties was investigated. The Al addition triggers the transformation of the crystal structure from disordered BCC phase to ordered B2 phase, and the Al1 alloy present single B2 phase structure. This B2 ordering results in significant yield strength increase of the RHEAs, i.e., from 915 MPa to 1410 MPa at room temperature (RT, leading to an excellent specific strength of ~232.3 KPa·m3/kg for the Al1 alloy), 719 MPa to 1088 MPa at 873 K and 126 MPa to 278 MPa at 1073 K, respectively. However, in the expense, the near full and full B2-structured Al0.75 and Al1 alloys show dramatic reduction in compressive ductility down to 31.4% and 15.1% at RT. Four parameters, VEC, ΔHmix, Bo¯ and Md¯ are employed to predict the B2 ordering in the RHEAs, and the calculation shows that ordered phases are preferred in the realm of ΔHmix < −14 kJ·mol−1 and Bo¯ < 0.4Md¯+1.9. In addition, the introducing of Al also significantly enhances the oxidation resistance of the alloys. While the Al0 alloy shows catastrophic oxidation within 24 h in air at 1073 K, the Al1 alloy only gains 112 mg·cm−2 after 50 h. However, the constitution of the oxide layer remains loose and complex, consisting of multiple oxides including Al2O3, TiO2, (Zr,Hf)O2 and (Zr,Hf)V2O7.

Temperature Impact on Engineered Cementitious Composite Containing Basalt Fibers

Engineered cementitious composite (ECC) is a new generation of fiber-reinforced concrete with high ductility and exceptional crack control capabilities. However, ECC can suffer a substantial reduction in ductility when exposed to elevated temperatures resulting in a loss of crack-bridging ability. In this study, the effect of adding basalt fiber (BF), which is an inorganic fiber with high-temperature resistance for the production of ECC, was studied. Moreover, the change in the mechanical properties of ECC, including compressive, tensile, and flexural strength, was experimentally investigated under elevated temperatures up to 400 °C. The results showed that the addition of BF to reinforced ECC improved the tensile and flexural strength of concrete effectively, but compressive strength marginally decreased. A significant decrease was observed in the range from 300 to 400 °C, while it increased smoothly when heated up to 300 °C. The compressive and flexural strength diminished after a slight strain gained when heated up to 100 °C. This work paves the way for future investigations focusing on the development of high-temperature resistance ECC.