Simultaneous Increase In Ductility Research Articles

Enhancing strength and toughness in a pearlitic rail steel via multi-alloying and accelerated cooling

The demand for higher speeds and heavier loads has emphasized the necessity to tackle the inherent trade-off between strength and toughness in pearlitic rail steels. Herein, the co-additions of Cr, Ni and Cu and accelerated cooling rate on the microstructure and mechanical properties of a medium carbon pearlitic steel were systematically investigated. In comparison with base alloy, the new steel exhibits smaller prior austenite grain size (PAGS) due to the drag effect of Cu and Ni solutes. The finer PAGS and lower C content increased the volume fraction of proeutectoid ferrite. The finer pearlitic nodule size (PNS) and pearlitic colony size (PCS) were attributed to the small PAGS and greater extent of undercooling due to the combined effect of multi-alloying and accelerated cooling. Additionally, the synergistic effects of multi-alloying and accelerated cooling rate decrease the pearlitic phase transformation temperature, accountable for the finer interlamellar spacing (IS). Compared with the base steel, the yield strength and ultimate tensile strength of the new steel increased from 587 MPa and 1069 MPa to 740MPa and 1178MPa, respectively, with a simultaneous increase of ductility from 12.4% to 14.7%. The strength increments are mainly attributed to the finer IS in the new steel. Meanwhile, the new steel possesses a higher impact toughness compared to the base steel due to the increased volume fraction of proeutectoid ferrite, and finer PNS and IS.

Влияние состояния границ зерен на эффект пластификации в ультрамелкозернистом сплаве Al-0.4Zr

The influence of small additional deformation by cold rolling (CR) on the microstructure and mechanical properties of ultrafine-grained (UFG) Al–0.4Zr alloy structured by high pressure torsion (HPT) has been studied. The results are compared with the application of small additional deformation by HPT, which, after low-temperature annealing, leads to a substantial increase in ductility (plasticization effect) with small decrease in strength. It is shown that, in contrast to the additional deformation of HPT, the deformation of CR after intermediate low-temperature annealing leads to a sharp drop in plasticity to ~2%, while the strength increases to ~275 MPa. The key role of the nonequilibrium state of grain boundaries in the manifestation of the plasticization effect in the UFG Al–0.4Zr alloy is revealed. A new approach is proposed for simultaneously increasing the strength and ductility of the UFG Al–0.4Zr alloy due to a small additional deformation by CR without intermediate annealing. As a result of this approach, a significant increase in strength by ~30% (ultimate tensile strength ~223 MPa) was achieved with a simultaneous increase in ductility up to ~26%, which is associated with an increase in the strain hardening rate due to an increase in the density of lattice dislocations in the UFG structure with nonequilibrium grain boundaries. The strain rate sensitivity and strain hardening coefficients have been determined for the UFG Al–0.4Zr alloy in various states.

Hardening Mechanism in Low-Carbon Low-Alloy Steels with a Simultaneous Increase in Ductility and Fracture Toughness

The paper analyzes the nucleation and growth of bainite in low-carbon low-alloy 09Mn2Si steel doped with titanium carbonitride nanoparticles in impact toughness testing. The analysis shows that such particles segregate at low-angle boundaries, retarding the formation of high-angle ones, and when impacted into the steel, they curve the lattice and generate a new bainite phase at the curvature interstices. The mechanism of bainite nucleation and growth is sympathetic, obeys the angular momentum conservation law, and provides the formation of multilayered packets of bainite plates capable for unlimited thinning to sub-sub-subunits during deformation. Such bainite plates can respond to their stress-strain state by one or another rotation, showing a high relaxation capacity and providing a high impact toughness of the steel at low temperatures.

Novel insight into dry sliding behavior of Cu-Pb-Sn in-situ composite with secondary phase in different morphology

The Cu-24Pb-xSn (wt%) (x = 0, 2, 4, 6) alloys with Pb-rich second-phase particles (SPPs) in different shapes show obviously differently mechanical and self-lubricating properties. The influence of the SPPs’ shape difference on the alloys’ mechanical and self-lubricating properties was revealed. Cu-24Pb alloy with continuously netty SPPs shows much more intensive stick-slip phenomenon during dry sliding than the other three alloys with independently rodlike SPPs. That is mainly due to insufficient lubrication resulted by the netty SPPs’ splitting matrix. With the SPPs transforming from netty to rodlike shape under the addition of Sn, the stick-slip phenomenon was notably weakened, which was proven to be related to the higher self-lubricating property of alloys with rodlike SPPs. Simultaneously, the simultaneous increase of ductility and tensile strength was observed in the Cu-24Pb-xSn alloys with increasing Sn content, which is because the netty SPPs’ splitting behavior will be weakened with them replaced by the rodlike SPPs.

Enhancement of the microstructure homogeneity and mechanical performance of the As-Cast Mg/Mg2Si in-situ composite through friction stir processing

Multipass friction stir processing (FSP) with 100% overlap was applied to in situ Mg/Mg2Si composite in an effort to modify its as-cast microstructure. The results indicated that FSP eliminates porosities, breaks up the massive high aspect ratio Mg2Si particles and refines and homogenizes the microstructure. Uniform microhardness was observed in the FSP stir zone of the composite which was not the case for the as-cast material. As compared to the as-cast specimen, the results of the tensile test revealed the simultaneous increase in ductility by 4.5 times and in strength by 2 times by performing one pass of FSP. Investigating the fracture surface of FSP samples showed a high density of cracked primary Mg2Si particles which shows that load transfer to reinforcing particles has occurred due to the high strength of their interface.

Development of a supramolecular accelerator simultaneously to increase the cross-linking density and ductility of an epoxy resin

The development of a novel accelerator capable of simultaneously enhancing the cross-linking density and ductility of an epoxy resin without sacrificing the reaction rate is reported. The basic concept comprises the synthesis of a tertiary amine-functionalized polyrotaxane (PRX_NR1) accelerator: a molecular necklace structure that induces a high cross-linking density as well as active molecular movement. Fourier transform infrared spectroscopy and differential scanning calorimetry measurements confirmed that the PRX_NR1-containing epoxy resin afforded a high reaction rate. Furthermore, the cross-linking density and mechanical properties of the epoxy resin were confirmed by dynamic mechanical analysis and tensile testing. Consequently, the PRX_NR1-containing epoxy resin greatly increased the cross-linking density, thereby resulting in an increase in tensile strength and glass transition temperature. Interestingly, the epoxy resin exhibited a simultaneous increase in ductility which is important to avoid brittle fracture (low toughness) of the epoxy resins. These results indicate that the proposed molecular necklace-like supramolecular PRX_NR1 accelerator is highly effective to overcome the traditional drawbacks of an epoxy resin that pose significant problems in the industrial field.

Impact toughness of 12Cr1MoV steel. Part 1 – Influence of temperature on energy and deformation parameters of fracture

In the paper, the study of the impact toughness of 12Cr1MoV steel Charpy specimens at the temperature range from 20°C to 600°C is presented. It was revealed that the increase of the testing temperature from 20°C to 375°C and then to 600°C causes the impact toughness to decrease by 1.2 and 2.42times, respectively. The maximum energy of crack propagation during impact loading was observed at T=375°C, which is related to the increased resistance to crack propagation (cracking resistance) and sufficient strength (load capacity) of 12Cr1MoV steel. An approach to the quantitative description of impact fracture process was developed that includes the measurement of shear lip size as a quantitative fracture parameter. Scanning electron microscopy (SEM) was used to reveal and justify the reduction of load capacity at increased testing temperature and simultaneous increase of ductility and to describe the rival influence of such factors on the behavior and work of impact fracture.

Microstructure, texture, grain boundary characteristics and mechanical properties of a cold rolled and annealed ferrite–bainite dual phase steel

Abstract The microstructural, textural evolution and changes in grain boundary character distribution during annealing of a prior cold worked (30 %, 50 % and 80 %) ferrite–bainite dual phase steel have been studied and correlated with mechanical properties. It has been shown that submicron sized subgrains can be obtained by selecting the appropriate amount of cold rolling and annealing cycle. Increasing the annealing temperature in all the materials produces the expected results, namely decrease in strength with a simultaneous increase in ductility. Although reasonably sharp γ-fibres were obtained in 80 % cold rolled and its 500 °C annealed counterpart, the very low values (< 1.0) make the steel unsuitable for the purpose of deep drawing. It is envisaged that grain boundary engineering may lead to better strength–ductility combinations in this steel for an enhanced range of applications.

Poly(ε-caprolactone) filled with electrospun nylon fibres: A model for a facile composite fabrication

Electrospun fibres are very rarely used as reinforcing agents in polymer-based composites. A fabrication approach is presented that allows to easily prepare composites based on polycaprolactone (PCL) filled with nylon 6 electrospun fibres by compression moulding. At very low filler contents (3%), the obtained composites exhibited improved stiffness with a simultaneous increase in ductility, differently from what is usually found in PCL nanocomposites with a variety of fillers, in which increases in modulus happen at the expense of elongation at break. The presence of fibres with a very small diameter, typical of the products of electrospinning, favoured a good interfacial adhesion between matrix and filler. Being of a similar order of magnitude than polymer lamellae, electrospun fibres can be used to shape the morphology of lamellar stacks, and therefore the final properties of the composites.

Bulk Ultrafine and Nanostructured Materials from Consolidation of Particles by Back Pressure Equal Channel Angular Pressing

Severe plastic deformation (SPD) has received considerable attention for its capability to produce ultrafine and nano structured materials. On the one hand, SPD, especially in the forms of equal channel angular pressing (ECAP) and high pressure torsion (HPT) is able to refine bulk materials with coarse grain structures. On the other hand, SPD has been used to synthesise bulk materials from particles. It enables particles from nano to micro scales to be consolidated into fully dense materials at much lower temperatures and shorter times, compared to the conventional sintering processing. It is particularly relevant to consolidating particles with non-equilibrium microstructures and to producing complex multiphase alloys. In this summary, ECAP as an effective process to synthesise a range of light metal based materials from particles with various sizes and structures, including aluminium and aluminium composites, titanium and magnesium, will be demonstrated. Full density and good bonding are achieved easily with the application of a back pressure. Microstructures from nano to ultrafine scales have been produced, resulting in significantly enhanced strength. Simultaneous increase in ductility has also been achieved in some alloys by virtue of multi-scale structures.

Tailoring stacking fault energy for high ductility and high strength in ultrafine grained Cu and its alloy

Bulk ultrafine grained (UFG) materials produced by severe plastic deformation often have low ductility. Here the authors report that simultaneous increases in ductility and strength can be achieved by tailoring the stacking fault energy (SFE) via alloying. Specifically, UFG bronze (Cu 10wt.% Zn) with a SFE of 35mJ∕m2 was found to have much higher strength and ductility than UFG copper with a SFE of 78mJ∕m2. Accumulations of both twins and dislocations during tensile testing play a significant role in enhancing the ductility of the UFG bronze. This work demonstrates a strategy for designing UFG alloys with superior mechanical properties.