Loss Of Ductility Research Articles

Fundamental cracking performance of asphalt-filler mastics with hydrated lime

This study evaluates the impact of hydrated lime (HL) on the cracking performance at intermediate temperature of asphalt-filler mastics, specifically as a partial replacement for limestone filler (LF). HL, is an active filler known for its multiple benefits in asphalt applications. The Double Edge Notched Tension (DENT) test was used to assess fracture properties, including specific total work of fracture, plastic work of failure, essential work of fracture, and average critical tip opening displacement. The results revealed several key findings: a notable loss of ductility and toughness with increasing HL dosages, a stiffening effect evidenced by increased peak loads and reduced failure deformation, and a decrease in the specific total work of fracture, indicating a loss of fracture energy. However, an enhancement in fracture resistance to plastic deformation is observed with HL addition, although identifying trends at high dosages remains challenging due to complex interactions between HL and LF. Furthermore, using low volumetric concentrations of HL minimizes the adverse impact on fracture performance while leveraging its other beneficial active filler properties. These findings suggest that while HL can improve certain fracture properties, optimal dosages are crucial to avoid adverse effects. Overall, this paper provides an updated and comprehensive study of the fracture of mastics at intermediate temperatures, which adds up to the understanding of asphalt-filler interactions, which can potentially lead to further investigations, such as how the partial replacement of LF with HL affects asphalt mixtures’ performance-related characteristics, particularly the fatigue cracking resistance.

Evading intermediate temperature embrittlement of FeCoCrNiMn high entropy alloy via N-doping

High entropy alloys (HEAs) exhibit high strength and excellent ductility at both room and low temperatures. The loss of ductility with increasing the tensile temperature above room temperature has been widely observed in single phase face-centered cubic structured HEAs. In this work, a N and Si doped FeCoCrNiMn-(N,Si) HEA with preexisting nano-sized Cr2N particles was fabricated by laser powder bed fusion (LPBF) and subsequent cold-rolling and annealing treatment. Tensile testing was conducted on the alloy at 298 K, 573 K, 773 K, 873 K, and 973 K, respectively. It has been shown that the FeCoCrNiMn-(N,Si) alloy with preexisting Cr2N phase exhibits a steady ductility with increasing the tensile temperature. The intermediate temperature embrittlement is evaded in the FeCoCrNiMn-(N,Si) alloy via N-doping. The widely reported loss of ductility with increasing deformation temperature was avoided in present FeCoCrNiMn-(N,Si) HEA by shifting fast segregation of element Cr from GBs into preexisting Cr2N phase due to the high affinity between N and Cr elements, leading to the increases in the content and size of Cr2N particles after high temperature deformation.

A self-consistent void-based rationale for hydrogen embrittlement

Solely based on the failure process of metallic materials containing voids, we propose a straightforward rationale for a self-consistent void-based hydrogen embrittlement (CVHE) predictive framework that effectively captures ductile failure, hydrogen-induced loss of ductility, and most importantly, the ductile-to-brittle transition. While the coupling effect of homogenously distributed secondary voids is well-documented, the rigor of our approach lies in the precise definition of an array of equally sized and spaced secondary voids nucleated aligning with the hydrogen embrittlement mechanisms HEDE, HELP and HESIV, in the ligament between primary voids. The CVHE model can quantitatively predict the full range of embrittlement; it naturally reveals the brittle inter-ligament decohesion associated with an intrinsic lower bound of ductility, when the secondary voids are sufficiently small. Counterintuitively, our results show that ductility reduction accelerates with a decrease in the secondary void volume fraction, and that smaller voids lead to greater embrittlement.

Parametric optimization of SIP connection geometry in CFS-MRF structures: A finite element study

The structural buildings should be designed to resist both static and dynamic loads. There are different types of structural systems that can support seismic loads. Moment-resisting frames (MRFs) are widely used for seismic purposes, relying on the plastic deformations occurring between the beam and column. The main problems of cold-formed steel sections in MRFs during seismic loads are premature local and distortional buckling, which cause severe damage under strong earthquakes, such as early loss of connection strength, low ductility, and low energy dissipation. This paper clarifies the performance of the CFS section with steel interconnected part (SIP) in moment-resisting frames (MRFs) in many aspects using finite element (FE) procedures. The study summarizes the required dimensions of SIP to achieve optimal behavior for the beam-column connection. Additionally, an advanced connection consisting of SIP and four pairs of out-of-plane stiffeners has been examined. The locations of the out-of-plane stiffeners have been carefully selected to stabilize the connection. A cantilever beam connection has been used to represent an MRF in an advanced way. The connection consists of 2 C channel back-to-back beams connected with a through plate with sixteen bolts. Numerical models have been developed and verified with experimental tests under both monotonic and cyclic loading. The characteristics and creation of the numerical model are well illustrated in this paper. Cyclic loading has been applied according to AISC protocol, which is used to test the performance of the steel connections, as well as to classify the connection according to different design codes. The results show that increasing the plastic moment capacity of the CFS section decreases the required SIP dimensions to achieve optimal behavior by the connection. Additionally, it has been found that using out-of-plane stiffeners in particular locations with SIP increases energy dissipation on average by 74 %. Using stiffeners with SIP can upgrade the classification of the connection from an ordinary or intermediate moment connection to a special moment connection without the need to increase the CFS cross-section area or reduce the slenderness ratio, which in turn reduces the overall costs of construction.

Microstructure and high temperature tribological behavior of nickel-based superalloy with addition of revert

The recycling of revert plays a crucial role in cost-efficiency and green manufacturing of superalloy. In this study, optical microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, tensile test, and tribological analysis were employed to investigate the microstructure, mechanical properties, and tribological behaviors of vacuum induction melted superalloys of 100% original material (Sample 1) and 40% original material + 60% revert (Sample 2). Dry sliding tests were conducted at 300 and 730 °C. The addition of revert promotes microstructure refinement, hardness increase, and carbide formation, at the cost of 18.5% ductility loss. During the high-temperature dry sliding process, abrasive, adhesive, and oxidative wear mechanisms were observed on the contact surfaces. Sample 2 exhibited a lower wear rate and coefficient of friction at both 300 and 730 °C. Additionally, a more continuous and wear-resistant tribolayer was formed on the wear track of Sample 2, effectively mitigating matrix oxidation compared to Sample 1. At 730 °C, a thick tribolayer developed on the wear surface of Sample 2, characterized by a hard and wear-resistant glaze layer on the outermost surface. The continuous sliding induced matrix heating, which facilitates recrystallization in the subsurface of Sample 2, induced by increased inclusions and carbides from the revert. The analysis of wear debris further illustrated the variations of wear mechanism at different temperatures. These findings are meaningful for understanding the high-temperature behavior of superalloys and optimizing alloy recycling process.

Nanoparticle-Enabled Zn-0.1Mg Alloy with Long-Term Stability, Refined Degradation, and Favorable Biocompatibility for Biodegradable Implant Devices.

Zinc-based alloys, specifically Zn-Mg, have garnered considerable attention as promising materials for biodegradable implants due to their favorable mechanical strength, appropriate corrosion rate, and biocompatibility. Nevertheless, the alloy's lack of mechanical stability and integrity, resulting from ductility loss induced by age hardening at room temperature, hampers its practical bioapplication. In this study, ceramic nanoparticles have been successfully incorporated into the Zn-Mg alloy system, leading to a significant improvement in long-term stability as well as mechanical strength and ductility. In addition, this study represents the first investigation of Zn-based nanocomposites both in vitro and in vivo to comprehend the influence of nanoparticles on the degradation behavior and biocompatibility of the Zn system. The findings indicate that the incorporation of WC nanoparticles effectively refines and stabilizes the degradation behavior of Zn-Mg without negatively impacting the cytocompatibility of the alloy. The subcutaneous implantation and femoral implantation further prove the benefits of nanoparticle incorporation and found no negative effects. Collectively, Zn-Mg-WC nanocomposites yield great potential for implant usage.

Equiaxed microstructure design enables strength-ductility synergy in the eutectic high-entropy alloy

Eutectic high-entropy alloys (EHEAs) represent attractive candidate materials for overcoming the strength-ductility trade-off, which can be enhanced through the directional alignment of the lamellar structure along the loading direction. Here, we put forward a new route to optimize the strength-ductility synergy without orientation dependence. Through a combination of severe plastic deformation and annealing, we convert the initially lamellar structure into a dual-phase structure comprised of ultrafine equiaxed grains. The significant grain refinement improves the yield strength from 703 MPa to 1199 MPa without sacrificing any ductility. During deformation, the localized softening resistance of the achieved dual-phase microstructure avoids necking, and the intrinsic microcrack-arresting mechanism effectively improves the fracture resistance. Grain boundaries and phase boundaries provide nucleation sites for dislocations and restrict dislocation transfer while the strain incompatibility is accommodated by geometrically necessary dislocations. This work demonstrates that dual-phase alloys comprised of ultrafine equiaxed grains provide a pathway for strengthening without loss of ductility.

Impact toughness of LPBF 316L stainless steel below room temperature

The fracture behavior of LPBF 316L stainless steel in rapid loading conditions was characterized from room to cryogenic temperatures. Instrumented impact toughness tests allow to determine the influence of the microstructural features of this material on its crack initiation and propagation behavior. In the stress-relieved, homogenized/partially recovered and recrystallized states, LPBF 316L exhibit gradual impact toughness decreases between 20 °C and – 193 °C, with close toughness loss ranging from 0.38 to 0.55 J cm−2/°C. These values were similar to those reported by the literature for hot isostatically pressed (0.35–0.58 J cm−2/°C) and wrought (0.45–0.51 J cm−2/°C) 316L stainless steels, meaning that the microstructural features of LPBF 316L (segregations cells, dislocations cells, oxide particles, etc.) did not significantly influence the temperature sensitivity of its fracture properties. Whatever the testing temperature and microstructural state, fully ductile fracture occurred by decohesion at the oxide/matrix interfaces and void growth into dimples. The martensitic transformation during deformation at low temperature did not appears to play a significant role in the temperature sensitivity of the decrease in impact toughness of these materials. The latter is likely a consequence of the loss of ductility of the austenitic matrix, especially, under localized strain conditions.

Precipitation suppression of refractory high-entropy alloys at intermediate temperature via adding oxygen

Due to the excellent mechanical properties, TiZrNb-based refractory high entropy alloys (RHEAs) show great potential application prospects in aviation, aircraft and petrochemical. However, the RHEAs are usually thermally metastable and brittle phases can be precipitated in intermediate temperature (such as 500–700℃), which severely limit the preparation of large-sized RHEAs ingots in industrial production. In this paper, we propose an alloy optimization strategy to suppress the precipitation of TiZrNb-based RHEAs by adding interstitial atomic oxygen (O). The results show that the precipitation temperature region of brittle phases can be reduced from 500°C∼650°C to 550°C∼600°C after adding oxygen, and the temperature region is reduced by more than 66 %. Moreover, the growth rate of precipitated phase decrease from 4.1 × 10−23 m3/s to 1.9 × 10−24 m3/s after adding oxygen, which is reduced by more than ten times. The analysis shows that adding oxygen inhibits the diffusion rate of Zr at intermediate temperature, thus delaying the formation of Zr-rich phase. Based on this, TiZrNb-based RHEAs with oxygen can well keep the outstanding ductility even after annealing at intermediate temperature for 4 hours, while the TiZrNb-based RHEAs without oxygen show ∼50 % ductility loss after the same annealing treatment. Our results not only provide new insights into the phase stability and mechanical stability of RHEAs, but also provide a new strategy for improving the phase stability of large-size ingots for engineering applications.

Reassessment of Thor® 115 parent metal performance including consideration of notch behavior

In recent years, the waning of creep rupture ductility in the long term, and sensitivity to creep damage tolerance of creep strength-enhanced ferritic (CSEF) steels were put under the spotlight. The loss of ductility and damage accumulation at stress concentrations may result in early failures of boiler components, and potentially result in severe economic impact and/or safety concerns. To address the potentially undesirable materials performance, the ASME Boiler and Pressure Vessel Code has recently introduced rules for identification of damage intolerant behavior by means of testing, and for design of boiler components with creep damage-intolerant CSEF steels, as Code Case 3048. As of today, only Grade 91 Type 2 material has been classified as a damage tolerant steel.The Thor® 115 (T115) CSEF steel has entered the market in recent years and has since been used for the construction of several combined cycle power plants. This CSEF steel was developed as an evolution to Grade 91, with chemical composition modifications to enhance the resistance to steam oxidation while ensuring long-term microstructural stability, and therefore permitting its use for the higher temperature boiler components, as an alternative to stainless steels. While chemical composition and manufacturing precautions prescribed for Grade 91 Type 2 also apply to T115, an assessment of the materials’ damage tolerance following design standards criteria, and including extensive metallurgical characterization, has not yet been published.This work presents up-to-date uniaxial creep testing results of T115 CSEF, and the derived creep-rupture ductility and damage tolerance parameter evaluation. In addition, results from notched bar creep testing are presented, illustrating the material's response to multiaxial stress states. Post-test metallographic examination of ruptured specimens was also performed and findings are discussed.

Partially recrystallized heterostructure via Mo-doping endows CoCrNi medium-entropy alloy with exceptional strength and ductility

CoCrNi medium-entropy alloy (MEA) has excellent ductility, but the low strength at room temperature limits its practical usage. This study proposes an effective strategy to enhance the strength of CoCrNi MEA without apparent loss of ductility via partially recrystallized heterostructures resulted from doping of large atomic radius element, which was substantiated in a Mo-doping (CoCrNi)98Mo2 MEA. Compared with CoCrNi, the strength of (CoCrNi)98Mo2 is remarkably improved, maintaining the high uniform elongation of ∼24%. The yield strength and ultimate tensile strength increased from 950 MPa, 1287 MPa to 1131 MPa, 1564 MPa, respectively. The difference in deformation between the soft recrystallized region (SRR) and the hard non-recrystallized region (HNRR) leads to an excellent hetero-deformation induced (HDI) strengthening. Additionally, it is easier to reach the critical stress of twinning caused by high HDI stress at the interface of SRR/HNRR, which contributes to activation of high-density twins and produce dynamic Hall-Petch strengthening effect.

Microstructure and mechanical properties of extruded Mg–Zn–Mn–Ca alloys

In this work, the influence of Mn and Ca doping on the microstructure and mechanical properties of Mg–3Zn, Mg–3Zn-0.5Mn, and Mg–3Zn-0.5Mn-1.2Ca alloys is systematically investigated. The addition of Mn elements is shown to exert no obvious effect on the microstructure of as-cast, as-homogenized, and extruded Mg–3Zn alloys. In contrast, the introduction of Ca into the extruded Mg–3Zn-0.5Mn alloy promotes the formation of nano-sized compounds and enhances grain refinement compared to the other two alloys. The extruded Mg–3Zn-0.5Mn alloy exhibits the higher yield strength (YS, 155 MPa) and ultimate tensile strength (UTS, 183 MPa) but the lower elongation (13%) than the extruded Mg–3Zn alloy (YS of 130 MPa, UTS of 175 MPa, and elongation of 25%). The improved strength of the extruded Mg–3Zn-0.5Mn alloy is mainly attributed to the refined grains, while both the lack of twinning deformation and strong texture result in ductility loss. The most optimal combination of strength and ductility is achieved in an extruded Mg–3Zn-0.5Mn-1.2Ca alloy (YS of 180 MPa, UTS of 250 MPa, and elongation of 26%). This suggests that fine grains and high volume fraction of nano-sized MgZn2 compounds contribute mainly to the strength of Mg–3Zn-0.5Mn-1.2Ca alloy. Although the grain refinement also facilitates the suppression of twinning in the extruded Mg–3Zn-0.5Mn-1.2Ca alloy, the weak texture and fine homogeneous grains are conducive to the high ductility.

Multiscale oxide dispersion strengthened refractory high entropy alloys with superior mechanical properties

Refractory high-entropy alloy (RHEA) is one of the most promising materials for high-temperature applications. However, their application is inhibited by insufficient strength at elevated temperatures and brittleness at ambient temperatures. Herein, we proposed a multiscale oxide dispersion strengthened (ODS) NbTaTiV RHEA with an excellent combination of strength and plasticity at both room and elevated temperatures. The multilevel microstructures are composed of a fine-grained BCC phase matrix (∼1.2 μm), submicron Ti-(O, N) particles (∼330 nm), and nanoscale Y2Ti2O7 particles (∼18 nm). Owing to the strengthening of combinatorial multilevel microstructures, the yield strength of the RHEA was found as high as 1626 MPa, which exhibits a significant improvement (∼46%) in comparison with the NbTaTiV RHEA, without significant loss of ductility. The ODS NbTaTiV RHEA also shows superior thermal-softening resistance, with yield strengths of 945 MPa at 700 °C and 482 MPa at 1000 °C. The enhanced strength is mainly attributed to the multilevel microstructures that mediate the collaborative strengthening mechanism among dispersed strengthening, precipitation strengthening, and grain boundary strengthening. This work presents a new insight to develop multiscale microstructures in RHEAs for high-temperature structural materials.

A novel high-entropy alloy with excellent mechanical properties, corrosion resistance, and antibacterial properties

Microbiologically influenced corrosion is a challenge problem involving many fields and causes great corrosion losses. Developing antibacterial structural materials is one of the effective strategies to solve above issues. The current study reports a novel Al0.2CoCrFeNiCu0.3Ta0.1 HEA with outstanding mechanical properties, corrosion resistance, and antibacterial properties. The HEA exhibited a face-centered cubic (FCC) structure with L12 nanoprecipitates enriched in Al–Ni–Ta–Cu that are dispersed in the FCC matrix. Antibacterial rate of the HEA against Bacillus subtilis was more than 99.99 %, which was far superior to that of the traditional antibacterial Cu-bearing 304 stainless steel (72.84 %). The ultimate tensile strength and yield strength of the HEA were 1053.5 MPa and 602.5 MPa, respectively, which were much higher than those of traditional antibacterial Cu-bearing 304 stainless steel (530.5 MPa and 242.8 MPa, respectively) without apparent loss of ductility. In addition, this HEA displayed an excellent corrosion resistance that was superior to that of 304 stainless steel and antibacterial Cu-bearing 304 stainless steel.

In-situ alloying of maraging steel with enhanced mechanical properties and corrosion resistance by laser directed energy deposition

Maraging steels are known for their exceptional strength derived from the martensite matrix and nano-precipitate strengthening. However, the trade-off to the high strength is often a loss of ductility and minimal strain hardening. Introducing metastable austenite to the matrix to activate transformation-induced plasticity (TRIP) is an effective approach to achieve high strength and ductility synergy. Existing methods to introduce TRIP into additively manufactured maraging steels are limited by the compositions of pre-alloyed powder or additional heat treatment steps. In-situ alloying via the laser directed energy deposition (L-DED) process allows flexibility in tailoring the alloying composition to achieve an austenite–martensite microstructure. Herein, we develop a TRIP–maraging steel by in-situ alloying of M789 with 316L (4–8 wt%) during the L-DED process. The addition of 316L facilitates austenite reversion in solution-treated maraging steel. As a result, the TRIP–maraging steel exhibits a 76 % increase in uniform elongation at the expense of a minimal sacrifice of strength. Furthermore, the corrosion resistance of the TRIP–maraging steel is enhanced. This work showcases a pathway to developing superior alloys by in-situ alloying via additive manufacturing.

Nanoindentation Test of Ion-Irradiated Materials: Issues, Modeling and Challenges.

Exposure of metals to neutron irradiation results in an increase in the yield strength and a significant loss of ductility. Irradiation hardening is also closely related to the fracture toughness temperature shift or the ductile-to-brittle transition temperature (DBTT) shift in alloys with a body-centered cubic (bcc) crystal structure. Ion irradiation is an indispensable tool in the study of the radiation effects of materials for nuclear energy systems. Due to the shallow damage depth in ion-irradiated materials, the nanoindentation test is the most commonly used method for characterizing the changes in mechanical properties after ion irradiation. Issues that affect the analysis of irradiation hardening may arise due to changes in the surface morphology and mechanical properties, as well as the inherent complexities in nanoscale indentation. These issues, including changes in surface roughness, carbon contamination, the pile-up effect, and the indentation size effect, with corresponding measures, were reviewed. Modeling using the crystal plasticity finite element method of the nanoindentation of ion-irradiated materials was also reviewed. The challenges in extending the nanoindentation test to high temperatures and to multiscale simulation were addressed.

Full-operating-temperature tensile mechanisms of [111] oriented single-crystal superalloy: New intermediate temperature toughening behavior against ductility losing

Single crystal (SX) superalloys are required for full-operating-temperature mechanical properties. However, the quest for intermediate temperature (IT) resistance often encounters a perplexing phenomenon: anomalous yielding behavior coupled with an unexpected loss of ductility. This study delved into the tensile behavior of a [111]-oriented SX superalloy from room temperature (RT) to 1150 °C, uncovering temperature-dependent tensile mechanisms where the interplay among phases and deferent defects governs plastic deformation. Desirable high strength-ductility properties were observed at IT, showcasing comparable strength with increased ductility. Microstructural evidences show that the primary strengthening effects stem from coupled interface boundary strengthening and anti-phase boundary (APB) strengthening, while the plasticity arises from planer defects transitioning from the stacking fault (SF) within γ phase at small strains, to superlattice SFs, ultimately to the erasure of superlattice SFs, leaving cutting dislocation pairs in γʹ phase. Energy analysis of APB and SF, along with adherence to Schmid laws, reinforce the plausibility of such intricate defect interactions. The strength-ductility balance can be ascribed to the collective effect of preferentially generated dislocations and prompt formation of SF. This strategy of sequential defects’ competition provides a new route for solving the strength-ductility trade-off of alloys.

Improving the compressive properties of laser powder bed fusion Ti-6Al-4V containing oxygen and nitrogen by adding trace TiC+TiB nanoparticles

The oxygen and nitrogen interstitial solutes strongly resist the motion of dislocations in titanium alloys, which accounts for the improvement of strength and the loss of ductility. In this study, compressive properties of L-PBF Ti64 with high oxygen and nitrogen content are improved by adding trace nanoparticles (0.1 wt% TiC + TiB) and CALPHAD-based design of heat treatments for the first time. The strength and plasticity of Ti64 increase by 8.8 % and 29.2 % respectively with the addition of nanoparticles before heat treatment. A good combination between strength and plasticity is obtained by solution treatment at 1040 °C and subsequently air-cooling (1040-AC) with the addition of nanoparticles. Compared to the L-PBF Ti64, the plasticity of TiC + TiB/Ti64 increases by 100 % without losing compressive strength after 1040-AC. A bi-modal structure including hard primary α phase and ductile secondary fine α lamellae, was obtained after 1040-AC, which is beneficial for its ductility and work-hardening. The addition of nanoparticles promotes the refinement and uniform distribution of the secondary α lamellae during cooling, which results in high strength and the distribution of α/α boundary being close to the theoretical random frequencies. Therefore, the TiC + TiB/Ti64 after 1040-AC exhibits excellent compressive strength and plasticity.

Ti-Mo microalloyed medium Mn steels: Precipitation and strengthening mechanism

Medium-Mn steels possess an exceptional strength-ductility balance but normally relatively low yield strength, which hinders their practical applications especially in ultra-high strength structural components. In this study, the simultaneous addition of Ti and Mo was proposed to improve the yield strength of medium-Mn steels, together with the systematic experimental and theoretical investigations on the precipitation behavior of (Ti, Mo)C carbides and its effects on the microstructure-properties relationship. The addition of Ti and Mo increases yield strength by 150∼350 MPa and ultimate tensile strength by 55∼320 MPa without a significant loss of ductility. Based on the intercritically annealed microstructure close to equilibrium as well as the nucleation and growth kinetic theory, the Ti–Mo addition can reduce the fraction of austenite, but increase the mechanical stability of austenite by refining the mean grain size of austenite. Mo was found to increase the precipitate density of (TixMo1-x)C by lowering the interfacial energy between the nano-precipitates and the matrix, and reduce the mean size of precipitates. A maximum increment in yield strength (∼350 MPa) was achieved at 610 °C, which was mainly attributed to the combined effects of grain refinement and precipitation hardening due to the addition of Ti and Mo.

Enhanced strength and plasticity of 316L austenitic stainless steel through combined ECAP and annealing treatment

The mechanical properties of 316L austenitic stainless steel (ASS) were enhanced by equal channel angular pressing (ECAP) combined with annealing treatment. High-density dislocations, twins, and slip bands are generated during 4 passes ECAP. An appropriate annealing treatment is beneficial for overcoming ductility loss and maintaining strength of ECAP samples. In this study, we found that annealing at 700 °C for 1 h and 600 °C for 12 h can achieve this goal, mainly due to the recovery of stacked dislocations at boundaries and the retention of nanoscale twins and slip bands.