Decrease In Ductility Research Articles

Investigation of the joinability of single- and multi-layered AA6014 sheets produced by accumulative roll bonding in the shear-clinching process

Accumulative roll bonding belongs to the severe plastic deformation processes and is suitable for producing multi-layered as well as high-strength sheets through repeated rolling. After four accumulative roll bonding-cycles, the strength of the investigated AA6014-T4 alloy is elevated due to strain and fine grain hardening by 170% in yield strength and by 37% in ultimate tensile strength. This is accompanied by a significant decrease in material ductility which is disadvantageous for joining processes based on forming operations. Shear-clinching, however, can be used to join high-strength and low-ductile materials on the die side. Thus, it is a promising method for the mechanical joining of accumulative roll bonding components. The multi-layered and more brittle material is located on the die side whereas the single-layered base material with higher ductility is positioned on the punch side. At present, there is no scientific knowledge how the multi-layered material behaves in the shear-clinching process. Since the material is cut in the process, delamination effects could occur at the interfaces produced via accumulative roll bonding. Additionally, the investigation aims at the influence of the accumulative roll bonding process on the properties of the joints. They are expected to depend on the number of process cycles and thus on the change of mechanical properties of the multi-layered material. The bond strength of the shear-clinched joints is determined by shear and tensile tests. The areas of material failure are analysed via metallographic methods. From the failure behaviour and load-bearing capacity it is determined which number of accumulative roll bonding cycles is ideal for joining multi-layered sheets via shear-clinching.

Phase formation, texture evolutions, and mechanical behaviors of Al0.5CoCr0.8FeNi2.5V0.2 high-entropy alloys upon cold rolling

The cold rolling (CR) reduction dependence of microstructure evolutions and mechanical properties for Al0.5CoCr0.8FeNi2.5V0.2 high-entropy alloy (HEA) were investigated. The HEA remains FCC structures consisting of nanoscale ordered L12 phase, confirming the phase formation prediction. With increasing CR reduction, the textures transform from random ones to FCC rolling ones accompanied by dense slip bands and deformation twins. Under a 50% CR reduction, the deformation textures started to become evident and were governed by typical {111}<112>F, {110}<100>Goss and {112}<111>Cu texture components. When the CR reduction approached 90%, the deformation textures mainly contained the {110}<111>A, {114}<110>X, and {112}<111>Cu texture components. As a result, both Vickers hardness and ultimate strength increased, but the ductility decreased roughly. The enhanced strength should be attributed to the anisotropy and work hardening behavior from textures. The plastic deformation for the samples under low CR reductions was dominated by deformation twins and slip bands. However, under high CR reductions, the textures severely impeded the further propagation of pre-existing slip bands, leading to the rapid decrease of ductility. Therefore, the CR reduction should be carefully designed before optimal heat treatments to enhance the strength and ductility synergy.

The effect of hydrogenation on the fracture of Ti2AlNb-based alloy during ball milling

In this work we have studied the effect of phase composition and microstructure of a rapidly solidified Ti2AlNb-based alloy containing hydrogen on deformation of the alloy during ball milling and production of a fine-dispersed powder. Hydrogen is introduced into the alloy up to a concentration of 2.0 wt%. The X-Ray diffraction (XRD) analysis and Scanning Electron Microscopy (SEM) show that the alloy has the following phase compositions depending on hydrogen content: β + O, β/β-hydride, β/β-hydride + intermetallic hydride (Ti2AlNbHx) or a single-phase intermetallic hydride. It is found that in the hydrogenated β + O alloy containing a small amount of hydrogen a strong decrease in ductility occurs, but this does not affect the ball milling and synthesis of the fine-dispersed powder. Efficient milling of the rapidly solidified alloy has been achieved when hydrogen content was 1.2 wt% and exceeding this value when a transformation from the H-saturated solid solution into a hydride phase is observed in the alloy or the formation of a single phase hydride occurs.

Hot Ductility Analysis and Flow Stress Prediction of (C-Mn-S-Al-Nb-V-Ti) Micro-alloyed Steel

The objective of this work is to study the hot ductility of (C-Mn-S-Al-Nb-V-Ti) micro-alloy steel of industrial production whose initial structural state is rolling stock. To simulate the thermomechanical treatments imposed we have deformed by pulling our samples after subjecting them to a solution treatment at 1200 °C and a precipitation treatment cycle before deformation. Hot deformations were carried out at temperatures from 700 °C and 1150 °C and deformation rates ranging between 10-2 s-1 and 5.10-4 s-1. The results show a decrease in hot ductility. Minimum values of hot ductility are determined at 800°C, and another decrease in hot ductility was observed at 900°C. Ferrite precipitation is observed at austenitic grain boundaries in the intercritical temperature range, causing intergranular embrittlement. Precipitation makes the hot ductility curve wider and deeper around 900°C. Hot ductility losses can explain by the presence of precipitates in the austenitic region and the presence of the two-phase structure in the intercritical region. Finally, based on experimental stress-deformation data, artificial neuron network (ANN) methods were used to predict flow stress of (C-Mn-S-Al-Nb-V-Ti) micro-alloy steel. This model is more effective in predicting flow stress and results can also be used in the mathematical simulation of hot metal formation processes.

Effect of welding consumables on shielded metal arc welded ultra high hard armour steel joints

Abstract Materials with high hardness are usually preferred in armour applications and are difficult to weld due to high Carbon Equivalent (C.E). In this investigation, an attempt was made to weld Ultra-high Hard Armour (UHA) steel (having C.E of 0.91) by Shielded Metal Arc Welding (SMAW) process using three electrodes (i) austenitic stainless steel (ASS- E307-16), (ii) super duplex stainless steel (SDSS-E2594-16) (iii) low hydrogen ferritic (LHF-E12018M-low-alloy steel electrode). The mechanical properties (tensile, impact toughness, and microhardness) were evaluated and correlated with microstructural features along with Cr eq /Ni eq ratio of weld metal. The joints fabricated using LHF electrodes showed superior strength of 962 MPa and hardness of 341 HV. The joints made using ASS electrode showed superior impact toughness of 72 J and Notch Strength Ratio (NSR) of 1.32 due to the higher energy absorption capability of the austenitic phase. At the weld interface, joints fabricated using ASS and SDSS electrodes show the unmixed zone (UMZ) and martensitic band (MB) due to sudden change of crystal structure (Face Centred Cubic (FCC) / Body Centred Tetragonal (BCT)). It is also found that the strength property increases (651 MPa to 856 MPa) with an increase in Cr eq /Ni eq ratio (1.87 to 3.2) of weld metal and with a decrease in ductility.

Studies on mechanical behaviour and tensile fractography of boron carbide particles reinforced Al8081 alloy advanced metal composites

Metal composites are advanced materials in the field of automotive and aero applications like wing root fittings of an aircraft. Al8081 alloy with 3 and 6 wt% of micro B4C composites were produced with vortex process. The prepared Al8081 with micro B4C composites were microstructural characterized by SEM micrographs. Further, mechanical behaviors of these composites were studied to know the influence of boron carbide particles on hardness and tensile properties of Al8081 alloy. SEM micrographs revealed the uniform distribution of particles in the Al8081 matrix. The hardness of Al8081 alloy was enhanced with the addition of B4C particles. Ultimate and yield strengths were improved with the incorporation of hard boron carbide particles with slight decrease in ductility. Tensile fractured surfaces revealed the ductile mode of fracture in Al8081 alloy and B4C added composites exhibited both ductile and brittle nature of fracture.

Cyclic Behavior of Reinforced Concrete Slab‐Column Connection Using Numerical Simulation

Nonlinear finite element (FE) simulation was employed to look into the behavior of flat slab‐column connections exposed to lateral cyclic loading. The study focused on the effect of drop panel and concrete grade by taking into consideration the element size sensitivity on the response of the joint. The study considered twelve specimens for the investigation. Four concrete grades having a magnitude of 47.7, 60, 75, and 90 MPa were selected. Three element sizes of 30 mm, 40 mm, and 60 mm were undertaken to access the mesh size sensitivity of the outputs. Six specimens are with drop panels, and others are without drop panels. The concrete‐damaged plasticity model has been used to model the specimens. Reduced eight noded bricks (C3D8R) and two noded trusses (T3D2) elements have been used for modeling concrete and steel, respectively. Cracking pattern, slab vertical deflection, strain distribution, ductility, load‐drift ratio, cracking load capacity, yielding load capacity, and ultimate load capacity are the main outputs of the FE simulation. The study confirmed a considerable increase in load‐carrying capacity and a decrease in ductility as the concrete grade increased. In another way, the load‐carrying capacity and ductility were slightly increased and decreased, respectively, as the slab‐column connection is provided with a drop panel. As element size decreases, the result obtained becomes more realistic.

Effect of quenching and partitioning time on microstructure and mechanical properties of low carbon micro-alloyed steel

In this present study, quenching and partitioning (Q&P) process was applied to rolled low carbon microalloyed steels. The Effect of partitioning time after quenching below martensite start temperature (Ms) on microstructure and mechanical properties is investigated. The resulting microstructure was investigated by using optical microscopy, Scanning Electron microscopy and X-ray diffraction techniques. The mechanical properties are evaluated. The microstructure consists of lath martensite, temper- martensite and retained austenite. The retained austenite is identified by XRD analysis. The tensile strength of Q&P processed steel significantly increases than rolled sample, but ductility decreases. The quenching below Ms temperature and portioning for 10 min shows a good strength and ductility combination.

Toward qualification of additively manufactured metal parts: Tensile and fatigue properties of selective laser melted Inconel 718 evaluated using miniature specimens

• A “microstructure unit” that can well reflect the microstructure characteristic of SLM materials is defined. • As the ratio of specimen thickness( t ) to the "microstructure unit" size( d ) is reduced below one, a dramatic decrease in tensile ductility occurs. • A criterion of t/d ≥ 4 for reliable mechanical properties determined by the miniature specimens is obtained. Combined with the topology optimization, additive manufacturing can be used to fabricate metal parts with complex shapes. However, due to the geometrical variations and microstructure heterogeneities of the additively manufactured metal parts, new standards with the use of miniature specimens are required for the evalutation of the spatial distribution of mechanical properties throughout the parts. Here, we conduct a systematic investigation on tensile and fatigue properties of selective laser melted Inconel 718 specimens with different thicknesses ranging from 0.1 mm to 1 mm. A “microstructure unit” that can well reflect the microstructure characteristic of selective laser melted materials is defined. The results reveal that premature necking with a dramatic drop in uniform elongation occurs if the ratio ( t/d ) of specimen thickness ( t ) to the "microstructure unit" size ( d ) is less than one. Premature necking is mainly attributed to the transition of strain localization behavior. We also propose a probabilistic statistical model for fatigue limit prediction based on the available fatigue data. It is recommended that the criterion of t/d ≥ 4 should be satisfied to ensure that the yield strength, the uniform elongation, and the fatigue limit determined by the miniature specimens are comparable with those determined by standard specimens. The findings may provdie a guide to the establishment of miniature specimen-based standards toward the qualification of additively manufactured metal parts.

Microstructure evolution and tensile properties of as-rolled Ti-Mo-Si composite

There is a keen interest in developing discontinuously reinforced titanium matrix composites (DRTMCs) as lightweight structural materials for aerospace and automotive industries. However, a long-standing problem for these materials is the conflict between strength and ductility. To address this challenge, a novel Ti-Mo-Si composite with network microstructure is successfully fabricated by spark plasma sintering and hot rolled in the β region (900 °C) with different statin rate. We find that a thickness reduction of 20% is optimal for improving the strengthening efficiency and corresponding ductility. However, with the reduction of thickness in the hot rolling process, the strength increases while the ductility decreases, which is mainly because of the spheriodiation of α-Ti and reinforcements, as well as the strengthening of the interface between reinforcement and matrix. In addition, the composite after hot rolling follows fractured reinforcement and dimple mechanisms at small thickness reduction, while it obeys a quasi-cleavage fracture mechanism with significant thickness reduction.

The effect of different levels of pre-damage loading on the strength and structural behavior of CFRP strengthened R.C. beams: Experimental and analytical investigation.

In order to investigate the effect of pre-loading damage on the structural performance of Carbon Fiber Reinforced Polymer (CFRP) strengthened Reinforced Concrete (R.C.) beams, experimental and Finite Element Modelling (FEM) investigation was carried out on six R.C. beams. Five of the R.C. beams were damaged up to different levels of strain in the main steel bars before Flexure CFRP strengthening. One of the R.C. beams loaded up to failure and was kept as a control beam for comparison. The experimental results showed that the failure mode of the CFRP strengthened specimen was controlled by CFRP debonding followed by concrete crushing; however, the control beam failed in concrete crushing after yielding the steel bars, which is a ductile failure. The CFRP sheet increases the strength and initial stiffness of the R.C. beams and reduces ductility and toughness. Also, CFRP application increases the first crack and yielding steel bars load by 87.4% and 34.4%, respectively. Furthermore, the pre-damage level does not influence the strength and ductility of the strengthened R.C. beams except for the highest damage levels, which experienced a slight decrease in load capacity and ductility. However, the initial stiffness decreases with increasing pre-damage levels by 40%.Design guideline ACI 440.2R (2004) predicts the ultimate load capacity marvelously for externally bonded Fiber-Reinforced Polymer (FRP) beams compared to the experimental maximum load capacity. The excellent agreement between experimental and FEM results indicates that the constitutive models used for concrete and reinforcement and the cohesive interface model can well capture fracture behavior. However, The FEM analysis predicts the beam to be slightly stiffer and more robust, probably because of the assumed perfect bond between concrete and reinforcement. The developed FEM can be used for further parametric study.

Microstructure and tensile properties of a cost-affordable and ultrahigh-strength metastable β titanium alloy with a composition of Ti-6Al-1Mo-1Fe-6.9Cr

A cost-affordable and ultrahigh-strength metastable β titanium alloy with a composition of Ti-6Al-1Mo-1Fe-6.9Cr has been designed by high-throughput diffusion couple technique. The alloy was heat treated along different regimes to investigate the effects of heat treatments on phase transformation, microstructure evolution, and tensile properties. The results showed that the aging strength of the alloy after solution treatment at 840 °C was higher than that at 800 °C due to the more αs precipitation during aging, while solution treatment at 840 °C and aging caused slight decrease of tensile ductility because of the lower αp-phase fraction during solution treatment. Moreover, the formation TiCr2 Laves phase at aging temperatures above 540 °C resulted in remarkable reduction of tensile ductility. Owing to the multiple-hierarchy α precipitations dispersed into the β matrix, two excellent strength-ductility combinations were successfully obtained for the alloys after solution treatment at 800 °C/840 °C and aging at 470 °C with the ultimate tensile strength and tensile elongation values of 1395 MPa/16.0% and 1614 MPa/9.7%, respectively.

Microstructures and Mechanical Properties of As Cast (Al7.5Co21.9Cr10.9Ti5.0Fe21.9Ni32.8)100-xCux High-Entropy Alloys

This study focused on the role of Cu in the microstructure characteristics and tensile properties of novel L12-strengthened multicomponent high-entropy alloys (HEAs). A series of as-cast (Al7.5Co21.9Cr10.9Ti5.0Fe21.9Ni32.8)100-xCux (x = 0.5, 2.5, 5.0) high-entropy alloys (HEAs) were prepared. The microstructures and mechanical properties of HEAs were investigated using X-ray diffraction, a scanning electron microscope, a transmission electron microscope, and atom probe tomography. The XRD patterns of HEAs confirmed that all HEAs consisted of the FCC phase and the L12 phase. As Cu content increased, the dendritic was gradually coarsened. The spherical L12 size decreased, and number density increased in the interdendritic regions (ID). The L12 mainly contained Ni, Ti, Al, and Cu. The acicular L12 size increased and was continuously distributed in the dendritic regions (DR) as the Cu content increased gradually. The ultimate strength and elongation decreased from 1,002 MPa, 20.0% to 906 MPa, 13.1%, respectively. The segregation rates of Ti, Cu, and Al increased in the DR and ID. The L12 nano-precipitates in the DR become denser and finer, while the L12 islets in the ID region increase and elongate. Large lattice distortion caused by Cu addition weakens the strength of the L12-FCC phase boundary, leading to the premature fracture of the three HEAs, which were the main reasons for the decreases in strength and ductility as Cu content increased.

Mechanical Behaviors of Microalloyed TRIP-Assisted Annealed Martensitic Steels under Hydrogen Charging.

Transformation Induced Plasticity (TRIP)-assisted annealed martensitic (TAM) steel sheets with various microalloying additions such as niobium, vanadium, or titanium were prepared on laboratory scale and subjected to a double-quenching and austempering heat treatment cycle. Slow strain rate tensile (SSRT) was tested on the investigated TAM steels with and without hydrogen charging to reveal their tensile behaviors and hydrogen induced embrittlement effects. Microstructure observations by scanning electron microscope (SEM) are composed of a principal annealed martensitic matrix and 11.0–13.0% volume fraction of retained austenite, depending on the type of microalloying addition in the different steels. SSRT results show that these TRIP-assisted annealed martensitic steels under air media conditions combine high tensile strength (>1000 MPa) and good ductility (~25%), while under hydrogen charging condition, both tensile strength and ductility decrease where tensile strength ranges between 680 and 760 MPa, down from 1000–1100 MPa, and ductility loss ratio is between 78.8% and 91.1%, along with a total elongation of less than 5%. Hydrogen charged into steel matrix leads to the appearance of cleavage fractures, implying the occurrence of hydrogen induced embrittlement effect in TAM steels. Thermal hydrogen desorption results show that there are double-peak hydrogen desorption temperature ranges for these microalloyed steels, where the first peak corresponds to a high-density dislocation trapping effect, and the second peak corresponds to a hydrogen trapping effect exerted by microalloying precipitates. Thermal desorption analysis (TDS) in combination with SSRT results demonstrate that microalloying precipitates act as irreversible traps to fix hydrogen and, thus, retard diffusive hydrogen motion towards defects, such as grain boundaries and dislocations in microstructure matrix, and eventually reduce the hydrogen induced embrittlement tendency.

Laser Welding of AISI 316L Stainless Steel Produced by Additive Manufacturing or by Conventional Processes

Among all the additive manufacturing techniques, Laser Powder Bed Fusion (LBPF), also called Selective Laser Melting (SLM), is the most common technique due to its high capability of building complex parts with generally improved mechanical properties. One of the main drawbacks of this technique is the sample size limitation, which depends on elaborating chamber dimensions. In this study, we investigate the viability of obtaining large parts with the laser welding of additive manufactured plates. A comparison of the microstructure and the tensile mechanical properties of SLM-welded plates and cold-rolled welded plates was performed. This paper shows the possibility of obtaining defect-free parts. Even if welding has a low impact on the microstructure of the SLM samples, fractures are located on the fusion zone, and a decrease in ductility of around 30% compared to the base metal is observed.

Mechanical Properties of Polyester Toughened with Nano-Silica

The fabrication of nanocomposites has played role to the development of the nanotechnology and the technology of advanced composite materials. Thermoset polymers are used in engineering applications widely. Their mechanical properties can be change with adding particles. The mechanism of toughening polymers has been suggested recently by reinforcing well dispersed particles to the plain polymer. Nano-silica particles were added to thermoset polymer of polyester to evaluate their influence on the mechanical properties of the toughened polymer using both experimental and numerical methods. The Representative Volume Element (RVE) approach, which employs finite element models, has been developed to achieve that aim numerically for various types of nano-particle reinforcement ratios. In each case, the stiffness has been calculated with using the equivalent homogeneous material concept. Experimentally, toughened thermoset polymers of polyester reinforced with nano-silica were prepared with different particle content ratio. Several tests were conducted on the nanocomposite, and it was observed increasing nano-silica ratio caused increase in Young’s modulus and decrease in ductility.

Effect of Sn alloying and cold rolling on microstructure and mechanical properties of Mg 14Li alloy

Mg-14Li-(0, 2, 4, 6)Sn alloys were prepared. Effect of Sn alloying and cold rolling on microstructure and mechanical properties of Mg14Li alloy have been studied. It is found that the introduction of Sn into Mg14Li alloy effectively promotes the grain refinement and columnar-to-equiaxed grain transition (CET). The alloys contain three kinds of compounds, Mg2Sn, MgLi2Sn and Li13Sn5. Mg2Sn is mainly distributed at the grain boundaries, MgLi2Sn is mainly distributed on the stacking faults inside Mg2Sn, and Li13Sn5 is distributed inside the grains. With the increase of Sn content from 2 wt% to 6 wt%, the grain size gradually decreases. Both the strength and ductility increase. However, when the Sn content reaches 6 wt%, the ductility decreases. After 50% cold rolling, due to the work hardening effect, the strength of Mg-14Li-(0, 2, 4) Sn alloys increases and their ductility decreases. As for Mg-14Li-6Sn alloy, due to the dynamic recrystallization, both the strength and ductility after 50% cold rolling are improved.

Performance of concrete beams partially/fully reinforced with glass fiber polymer bars

One of the major advantages of using glass fiber-reinforced polymer bars as a replacement to the traditional steel-reinforced bars is its lightweight and high-resistant to corrosion. This research focuses on the performance of concrete beams partially/fully reinforced with glass fiber-reinforced polymer bars with 50% of GFRP bars were used to reinforce partially concrete beams at flexural zone. While 100% of GFRP bars were used to reinforce fully concrete beams at flexural and compression zones with different concrete compressive strength.This study reported the test results of 6 reinforced concrete beams with dimensions 150 × 200mm and a 1700-mm clear span length subjected to a four-point loading system. The tested beams were divided into three groups; the first one refers to the glass fiber-reinforced polymer bar effect. The second group is referring to the effect of concrete compressive strength, while the third group is referring to the effect of the GFRP bar volume ratio.Using longitudinal GFRP bars as a full or partial replacement of longitudinal steel bar reinforcement led to an increase in the failure load capacity and the average crack width, while a decrease in ductility was reported with a lower number of cracks. Increasing the concrete compressive strength is more compatible with GFRP bar reinforcement and enhanced the failure performance of beams compared with normal compressive strength concrete.

Tuning the strength-ductility synergy of nanograined Cu through nanotwin volume fraction

Nanograined (NG) metals with nanotwinned (NT) regions can overcome the inferior ductility of NG metals and achieve high strength and modest ductility. Based on the strain gradient plasticity and Johnson–Cook failure criterion, we simulate the dependences of their strength and ductility on volume fraction, twin spacing, as well as shape and distribution of NT regions in NG Cu. It is found that these factors have significant impact on the overall ductility. In particular, the overall ductility abnormally decreases with the increase in the volume fraction of NT regions, which is directly related to the failure modes of this material system. Interface debonding can explain the above abnormal decrease in overall ductility. In addition, with the increase in twin spacing, fracture of NT regions can cause different reversals of overall ductility. We also found that, when the NT regions are of the oblique square type, the overall ductility is significantly lower than when they are of the circular and square types. In most cases, the array arrangement of NT regions is superior to the staggered arrangement for the improvement of the overall ductility. It is believed that these reported results can contribute to a deeper understanding of this novel material system.

Strength enhancement of a bi-lamellar PM Ti–6Al–4V alloy without sacrificing ductility by Al partitioning and twinning-induced plasticity effect

Ti–6Al–4V alloy samples with two bi-lamellar microstructures were prepared by cost-effective thermomechanical powder consolidation and two inter-critical annealing treatments; one comprising of annealing at 900 °C followed by air cooling (900-AC alloy) and the other comprising of annealing at 910 °C followed by water quenching and aging (910-Q&A alloy), respectively. Both bi-lamellar microstructures encompass lamellae of primary α phase and β transformed structure which consists of ultrathin secondary α lamellae and β thin layers. Thanks to the higher Al concentration in the primary α lamellae associated with the higher annealing temperature and finer scale of βt structure lamellae, the α and βt lamellae of the 910-Q&A alloy exhibit a higher nano-hardness than that of the 900-AC alloy (5.4 and 4.6 GPa vs. 4.5 and 4.3 GPa) as well as a larger difference in nano-hardness between the α and βt lamellae (0.8 vs. 0.2 GPa). These microstructural and nano-hardness differences lead to a significant enhancement of the yield strength of the 910-Q&A alloy by 200 MPa compared to the 900-AC alloy with almost no decrease of tensile ductility. Quantitative analysis indicates that the hardening of α and βt lamellae accounted for approximately 35% and 28% of the total strength increment, respectively, while the heterostructure induced hardening associated with the inhomogeneity between the α and βt lamellae accounts for approximately 37% of the strength increment. Interestingly, the significantly higher flow stress of the 910-Q&A alloy during tensile deformation induces a significant higher degree of trans-lamellar twinning which is believed to be responsible for mitigating the strain localization and maintaining the good tensile ductility despite of a higher flow stress.