Lack Of Ductility Research Articles

Mechanisms of elevated temperature galling in hardfacings

The galling mechanism of Tristelle 5183, an Fe-based hardfacing alloy, was investigated at elevated temperature. The test was performed using a bespoke galling rig. Adhesive transfer and galling were found to occur, as a result of shear at the adhesion boundary and the activation of an internal shear plane within one of the tribosurfaces. During deformation, carbides were observed to have fractured, as a result of the shear train they were exposed to and their lack of ductility. In the case of niobium carbides, their fracture resulted in the formation of voids, which were found to coalesce and led to cracking and adhesive transfer. A tribologically affected zone (TAZ) was found to form, which contained nanocrystalline austenite, as a result of the shear exerted within 30μm of the adhesion boundaries. The galling of Tristelle 5183 initiated from the formation of an adhesive boundary, followed by sub-surface shear in only one tribosurface, Following further sub-surface shear, an internal shear plane is activated. internal shear and shear at the adhesion boundary continues until fracture occur, resulting in adhesive transfer.

An in-depth look at the stability, electronic structure, mechanical properties, and thermodynamics characteristic of Ir3TM (TM: Sc, Ti, V) compounds

In this paper, the structural, mechanical, electronic, and thermodynamic properties of Ir3TM (TM = Sc, Ti, and V) intermetallic compounds in the cubic (L12) and hexagonal (D019 and D024) phases are presented. The outcomes of the simulation rely on density functional theory (DFT) within the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) based on the full-potential linearized augmented plane wave (FP-LAPW) approach. The existing study was performed on the L12 cubic phase. in addition to hexagonal D024 and D019 phases, which may be relative but differ in the way that the atomic layers are stacked. The calculated total, cohesive energy, and heat formation suggest that the Ir3Sc compound can be stable in the D024 phase because of an overlap between the L12 and D024 phases with a total energy difference of around 0.026 eV/atom. Ir3Ti and Ir3V are more stable in L12 and D019, respectively. From elastic constants calculations, it reveals that the studied compounds are mechanically stable and harder in the cubic phase than hexagonal phase. However, Ir3Sc has the lowest hardness due to its relative ductility. Inversely, Ir3V has the maximum hardness with a lack of ductility. It was observed that these compounds have an elastic anisotropy based on the three-dimensional Young's modulus surface, and Ir3Sc has the strongest anisotropy, while Ir3V has the weakest in the L12 phase. The total density of state (TDOS) calculations shows that Ir3Ti and Ir3V are stable in the L12 and D019 phases, respectively, except for the Ir3Sc compound which might undergo a martensitic transition. Also, the pseudogap for Ir3V moves quite close to the Fermi level, indicating that the covalent bonding in this compound is sharper than the other compounds. Moreover, via the quasi-harmonic Debye model within the Gibbs computational code, thermodynamic properties are calculated and analyzed with temperature and pressure.

Deformation mechanisms and their role in the lack of ductility in the refractory-based high entropy alloy AlMo0.5NbTa0.5TiZr

The deformation mechanisms in the refractory high entropy alloy AlMo0.5NbTa0.5TiZr have been investigated, with their potential impact on ductility. Specifically, the modes of plasticity active in the B2 matrix and in an alloyed version of the phase Al4Zr5 found at grain and subgrain boundaries were explored by use of nano-indentation. For the B2 phase, a combination of weak-beam dark-field and superlattice imaging revealed dissociation of 〈111〉 superdislocations into two superpartial dislocations, bounding an anti-phase boundary (APB), following the reaction: a〈111〉= a/2〈111〉+APB+a/2〈111〉. The dislocations in the B2 phase exhibited long, relatively straight screw segments and short edge segments, such that the mobility of the edge dislocations appears to be higher than that of the screw segments. Evidence of a B2 to bcc slip transmission process has been observed through use of stereo-pair imaging and anaglyph construction. This process involves the transmission of slip from the B2 matrix, followed by the decorrelated motion of the two a/2〈111〉 dislocations in the bcc precipitate, demonstrated by the increased separation of the dislocations within the bcc phase. Regarding the deformation of the Al4Zr5 intermetallic phase, it was found that indentation of this phase resulted in no evidence of dislocation generation and motion, and cracking at the edges of the given indent. It has been concluded that the lack of plasticity of this phase is the cause of the room temperature brittle nature of this alloy.

Degree-based topological indices and entropies of diamond crystals.

High hardness, low friction coefficient and chemical resistance are only a few of the exceptional mechanical qualities of diamond. Diamonds can be artificially created to have different levels of conductivity, or they can be single, micro or nanocrystalline and highly electrically insulating. It also has high biocompatibility and is famous for being mechanically robust. Due to its high hardness, lack of ductility and difficulty in welding, diamond is a challenging material to construct devices with. Diamonds have experienced a rise in attention as a biological material in recent decades due to new synthesis and fabrication techniques that have eliminated some of these disadvantages. In general, entropic measurements are used for investigating the chemical or biological properties of molecular structures. This study calculates several important -Banhatti entropies, redefined Zagreb entropies and atom-bond sum connectivity entropy for diamond crystals. We also present a numeric and graphical explanations of obtain indices.

Mechanisms for Introduction of Pseudo Ductility in Fiber Reinforced Polymer Composites- A Review

Advanced polymer matrix composites are gaining the market in their way due to their exceptional specific stiffness, specific strength, fatigue, and corrosion resistance in the field of Auto-Tech, Aero-Tech, Biotech, etc. However, the lack of ductility and catastrophic failure has limited their application in these areas. Hence there is a need to explore means and protocols for designing the reduced factor of safety with high-performance toughened composites. To address this problem, a new generation of high-performance composites with pseudo-ductile or ductile behavior is needed. The ongoing High-Performance Ductile Composite Technology (HiPerDuCT) program jointly between the University of Bristol U.K and Imperial College London to address this challenge by developing newer materials. The fiber architectures made under this project gave a more gradual failure rather than catastrophic failure which improves the mechanical properties. This paper mainly focuses on addressing this evolution of pseudo ductility in fiber-reinforced composites. In addition to this, an attempt has been made to newer possible fiber positions in matrix materials for inducing reasonable ductility in composites.

Role of geometric dynamic recrystallization in nanocrystalline alloys

Nanocrystalline and near-nano-grained metals are plagued with an overall lack of ductility and formability. This is in part due to their inability to support the dislocation mechanisms or undergo the same types of transformations that conventional coarse-grained metals access inorder to increase their workability. Therefore, despite their advanced properties such as high strength, the manufacturing of such fine-grained metals, which exposes them to multi-axial states of stress in operations such as rolling, drawing, extrusion, forging, and bending, has not been possible. In this work, we address this limitation and highlight an important aspect of geometric dynamic recrystallization (GDRX) in nanocrystalline materials as a way to improve manufacturability. In particular, using two different alloy compositions and two different processing techniques, this study points to the fact that if nanocrystalline or near nano metals can be truly stabilized, they can repeatedly undergo the same types of processes that conventional coarse-grained metals endure, increasing both their formability and hence manufacturability. The results reveal that due to a large number of initial high-angle grain boundaries and large applied compressive strains, GDRX is activated in the absence of any discontinuous dynamic recrystallization (DDRX) or continuous dynamic recrystallization (CDRX). This is a unique aspect of stabilized nanocrystalline materials, as traditionally fine-grained metals are not microstructurally stable enough to accommodate such an event.

Prediction of failure of hybrid composites with ultra-thin carbon/epoxy layers using the Coupled Criterion

Composites are rapidly increasing in an extensive range of structural applications, but further growth is limited by their lack of ductility. Fiber hybridization is a promising strategy to toughen composite materials. The coupled criterion of the finite fracture mechanics is applied here to describe the sequential damage mechanisms that occur in a hybrid composite under tension. The studied specimens are made of an unidirectional thin layer reinforced with long carbon fibers, embedded between two unidirectional layers reinforced with glass fibers. The first damage is usually translaminar cracking of the carbon/epoxy layer, which can be followed by different mechanisms depending on the stacking lay-up: failure of the glass/epoxy layer, delamination of the interface between carbon/epoxy and glass/epoxy layer, or fragmentation of the carbon/epoxy layer. Once the first translaminar crack has appeared into the carbon/epoxy layer, it impinges on the interface and the crack tips undergo a strong singularity, which plays an important role in predicting the mechanisms that follow. The competition between the different mechanisms is studied here by the novelty of including the principle of maximum dissipation into the Coupled Criterion. The predictions obtained by this approach show a good agreement with the experimental and computational results found in the literature.

Flexural behaviour of CFRP RC beams having a ductile cementitious composite layer in compression zone: an analytical study

Today, the use of fibre reinforced polymer (FRP) bars has received considerable attention. However, concrete beams reinforced with FRP bars suffer from a lack of ductility. The addition of steel bars to the beams has been widely studied to improve ductility. In this study, the idea of using a ductile cementitious composite layer (DCCL) in the compression zone is investigated. In fact, the ductility of DCCL comes from the bridging action of fibres and confinement concepts rather than the yielding of steel members. First, an analytical model is proposed to predict the behaviour of the beams. Then, the behaviour of concrete beams reinforced with FRP bars having various DCCL layers is investigated. It is shown that using DCCL can improve the ductility of the beams. The ductility ratio of the beam with a layer of DCCL is 3.5 times more than that of the control beam.

Embedment properties of Japanese cedar (Cryptomeria japonica) treated with resin impregnation

To strengthen the embedment properties of wood, this study applied the resin impregnation technique, which fills the resin into wood cells. The urethane prepolymer and acrylic monomer were selected in this study. A mechanical test by a round steel bar loaded to the wood specimen was conducted. The characteristics showed higher values in the resin-impregnated groups than in the control specimen group, especially in the stiffness. The urethane- and acryl-impregnated group showed 3.78 and 2.27 times the stiffness values of the control groups in the parallel-loaded condition, and 1.94 and 1.24 times those of the control group in the perpendicularly loaded condition, respectively. Although the stiffness was significantly increased, there was a lack of ductility, which seems to be a serious problem for construction application.

Experimental evaluation of concrete confined with hand laid carbon FRP grids

In many cases structures serve in highly corrosive environments and as a result the service life of the elements is significantly reduced. An alternative could be the use of fiber reinforced composites. The skepticism behind using this material has to do with the lack of ductility. A different approach must be followed in the design of such structures to achieve a behavior similar to regular reinforced concrete. In this case failure should initiate and end in concrete with confinement providing ductility. This paper investigates concrete confinement through experimental testing of concrete specimens utilizing embedded custom made, hand laid carbon FRP (CFRP) grid. The grid was formulated into the shape of a tube and embedded in concrete specimens to evaluate the grid tube effect on concrete properties. Typically, the FRP material is applied externally using an adhesive. In this case the hand laid CFRP grid was pre-manufactured and was embedded into concrete. Standard sized cylindrical specimens were manufactured using hand laid CFRP grid. Some of the specimens were made using plain concrete and served as reference specimens. The specimens were loaded axially in compression. This allowed the evaluation of the extent to which the hand laid tubular shaped grid positively affected the ultimate capacity and deformation of concrete. This application is unique and its confinement effectiveness needs to be investigated and evaluated. Experimental results show a very significant change in the maximum capacity and deformability for confined concrete. Depending on the amount of CFRP reinforcement in the grid strands the enhancement in strength was between 42 % and 58 %. The deformability of the specimens with the hand laid CFRP grid was between 134 % and 196 % higher compared to the reference specimens, with higher values associated with higher amounts of the CFRP grid.

A new ductile iron for mechanically and thermally strained rolls Part 2: material development varying Ni, Mo, Cr content using DoE

ABSTRACT For manufacturing of steel wires, tubes and profiles in hot rolling mills, the toughest conditions occur in the front rolling stands where the mechanical load comes along with a constant change of hot rolling stock and cooling liquid. Conventional roll materials as pearlitic or acicular cast irons are not able to overcome these intense conditions because of their lack of ductility. A fine selection of alloying elements leads to a new material with a microstructure uniting bainite, austenite and martensite inducing high hardness and strength, without lacking elongation. For this purpose, a full-factorial design of experiments was created consisting of three alloying elements in two concentrations each. The alloys were cast, heat-treated and underwent extensive investigations on mechanical properties and microstructure. The results were analysed and implemented in mathematical models whose combination and optimisation led to the identification of the ideal alloy meeting the required strength, hardness and elongation.

Self-Centering Hybrid GFRP-Steel Reinforced Concrete Beams for Blast Resilience

Despite having a high strength-to-weight ratio and being chemically inert, fiber-reinforced polymer (FRP) reinforcing bars are not currently used in reinforced concrete protective design due to their brittle nature and lack of ductility. This paper presents research on the innovative use of blended mixtures of FRP and steel rebar to activate self-centering behavior to return blast-loaded elements to their original position after the inertial loads are removed. Self-centering blast-resilient members promise reductions in residual damage, repair cost, and facility downtime after a terrorist bomb attack or accidental explosion. Large-scale reinforced concrete beams with different combinations of steel and glass FRP (GFRP) rebar were designed, constructed, and tested under progressively increasing blast loads generated by the Virginia Tech Shock Tube Research Facility. The results demonstrated that beams with hybrid reinforcing experienced reduced overall residual damage in comparison with similar conventionally reinforced concrete members. Increasing the self-centering ratio (SC) of beams, defined as the ratio of the restoring moment provided by the FRP to the resisting moment provided by energy dissipating steel rebar, increased the blast self-centering tendencies of the hybrid beams. Additionally, if the GFRP rebar ruptured during the blast, the presence of steel prevented a brittle failure mechanism and provided additional energy dissipation and redundancy. To encourage the use of hybrid FRP-steel reinforcement in blast-resistant construction, a series of protective design recommendations are made. Furthermore, a new response limit based on a blast self-centering index (BSI) is proposed to explicitly account for the residual damage state in the protective design process.

RETRACTED: Development of Bulk Metallic Glasses and their Composites by Additive Manufacturing - Evolution, Challenges and a Proposed Novel Solution

RETRACTED ARTICLE: Bulk metallic glasses (BMGs) and their composites (BMGMCs) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very large elastic strain limit. However, they suffer from lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which makes them amenable to failure without appreciable yielding. Various mechanisms and methods have been proposed to counter this effect out of which, recently Additive Manufacturing has gained widespread attention. It is proposed that additive manufacturing can overcome these difficulties in single step due to inherent existence of very high cooling rate in the process which is essential for glass formation. This, when coupled with careful selection of alloy chemistry is proposed to be the best solution to fabricate near net shape parts in a single step with excellent properties. In this report, an effort has been made to describe one possible route to achieve this. Solidification processing employing carefully selected inoculants based on edge to edge matching technique along with the carefuly controlled inoculation procedure is proposed to reflect upon enhanced mechanical properties. It is hypothesized that number density, size and distribution of ductile crystalline phase would best be able to improve microstructure and hence properties. This is meant to be controlled by manipulating type, size and the amount of inoculants. The proposed methodology is claimed to bear maximum potential.

The Influence of 3d and 4d Transition Metals on the Glass Forming Ability of Ternary FeCo-Based Alloys

Thermodynamic modeling was used to determine enthalpies of formation and other thermodynamic parameters describing glass forming ability of Fe-Co-TM (TM = V, Nb, Cr, Mo) alloys. FeCo-based alloys are considered as candidates for applications as high magnetic flux density materials due to their high magnetic saturation and low magnetic anisotropy. Nevertheless, mechanical properties, especially the lack of ductility, are their main weakness. Therefore, further optimization by vitrification, further heat treatment and alloying should be considered. As the most crucial step is the synthesis of amorphous precursors, discussion is concentrated on the effect of transition metal substitution on the glass forming ability. The highest glass forming ability was reported for Fe-Co-Nb alloys. It can be also noted that the driving force for vitrification can be improved by substitution of Fe by other transition elements, as glass forming ability parameter ∆PHS reaches the lowest values for Fe-less compositions.

Unveiling the Local Atomic Arrangements in the Shear Band Regions of Metallic Glass.

The prospective applications of metallic glasses are limited by their lack of ductility, attributed to shear banding inducing catastrophic failure. A concise depiction of the local atomic arrangement (local atomic packing and chemical short-range order), induced by shear banding, is quintessential to understand the deformation mechanism, however still not clear. An explicit view of the complex interplay of local atomic structure and chemical environment is presented by mapping the atomic arrangements in shear bands (SBs) and in their vicinity in a deformed Vitreloy 105 metallic glass, using the scanning electron diffraction pair distribution function and atom probe tomography. The results experimentally prove that plastic deformation causes a reduction of geometrically favored polyhedral motifs. Localized motifs variations and antisymmetric (bond and chemical) segregation extend for several hundred nanometers from the SB, forming the shear band affected zones. Moreover, the variations within the SB are found both perpendicular and parallel to the SB plane, also observable in the oxidation activity. The knowledge of the structural-chemical changes provides a deeper understanding of the plastic deformation of metallic glasses especially for their functional applications and future improvements.

In situ fracture observations of distinct interface types within a fully lamellar intermetallic TiAl alloy

Intermetallic γ‐TiAl‐based alloys are commonly used as structural materials for components in high‐temperature applications, although they generally suffer from a lack of ductility and crack resistance at ambient temperatures. Within this study, the process‐adapted 4th generation TNM+ alloy, exhibiting a fully lamellar microstructure, was examined using notched micro‐cantilevers with defined orientations of lamellar interfaces. These configurations were tested in situ using superimposed continuous stiffness measurement methods during loading with simultaneous scanning electron microscopy observations. Subsequently, the video signal was used for visual crack length determination by computer vision and compared to values calculated from in situ changes in stiffness data. Applying this combinatorial approach enabled to determine the J‐integral as a measure of the fracture toughness for microstructurally different local crack propagation paths. Thus, distinct differences in conditional fracture toughness could be determined from 3.7 MPa m1/2 for γ/γ‐interface to 4.4 MPa m1/2 for α2/γ‐interface.

Laser powder bed fusion of soda lime silica glass: Optimisation of processing parameters and evaluation of part properties

Glass has a number of attractive properties, such as transparency, chemical resistance, good thermal stability and high electrical resistivity, that make it a favourable material for a range of applications, including medical technology, electronics, chemical and pharmaceutical industries. However, compared to metals and polymers, the additive manufacturing of glass is still at a primitive stage. The inherent material properties of glass, i.e. its amorphous structure, lack of ductility and high processing temperatures, make processing of glass by additive manufacturing challenging. This paper describes the laser powder bed fusion of a soda lime silica glass. Optimisation of the laser powder bed fusion process was undertaken and the physical and mechanical properties of the manufactured parts were characterised revealing an average porosity of 12%, a mean flexural strength of 6.5 MPa and a fully amorphous structure. Feasibility examples were successfully demonstrated, indicating that geometrically complex shapes are possible. Even though the manufactured parts are opaque, they could potentially find use in applications where the need for chemical inertness and geometrical complexity surpass the need for transparency as in the chemical and pharmaceutical industries e.g. in the form of continuous flow reactors or structured catalysts.

In situ fracture observations of distinct interface types within a fully lamellar intermetallic TiAl alloy

Abstract

Strengthening and toughening mechanisms of metallic glass nanocomposites via graphene nanoplatelets

The lack of ductility, mainly due to shear localization, limits the full exploitation of metallic glasses (MGs). Such a weakness can be mitigated via introducing graphene nanoplatelets (GNs), which helps strengthen and toughen MG matrix. Using molecular dynamics simulations, we investigate the tensile deformation of Cu50Zr50 metallic glass-graphene nanoplatelet composites (MGGNCs) regarding the effects of graphene volume fraction and graphene layer number. Increasing fraction of GN in MGGNC enhances both tensile strength and fracture strain. The dominant component changes from MG matrix to GN, corresponding to a failure mode transition from shear banding in MG to brittle fracture in graphene. For a given volume fraction, single-layered GN behaves better than its double-layered counterpart, manifested as a higher fracture strain in MGGNCs. Our study illustrates the strengthening and toughening mechanisms in MGGNCs, and why single-layered GN performs better. All of these results can contribute to the synthesis of novel MG/graphene composites.

High temperature rise dominated cracking mechanisms in ultra-ductile and tough titanium alloy

Extensive use of titanium alloys is partly hindered by a lack of ductility, strain hardening, and fracture toughness. Recently, several β-metastable titanium alloys were designed to simultaneously activate both transformation-induced plasticity and twinning-induced plasticity effects, resulting in significant improvements to their strain hardening capacity and resistance to plastic localization. Here, we report an ultra-large fracture resistance in a Ti-12Mo alloy (wt.%), that results from a high resistance to damage nucleation, with an unexpected fracture phenomenology under quasi-static loading. Necking develops at a large uniform true strain of 0.3 while fracture initiates at a true fracture strain of 1.0 by intense through-thickness shear within a thin localized shear band. Transmission electron microscopy reveals that dynamic recrystallization occurs in this band, while local partial melting is observed on the fracture surface. Shear band temperatures of 1250–2450 °C are estimated by the fusible coating method. The reported high ductility combined to the unconventional fracture process opens alternative avenues toward Ti alloys toughening.