Room Temperature Mechanical Properties Research Articles

Re-evaluation of the mechanical properties and creep resistance of commercial magnesium die-casting alloy AE44

This paper presents a re-evaluation of the room temperature mechanical properties and high temperature creep resistance of magnesium die-casting alloy AE44 (Mg-4Al-4RE) in light of the influence of minor Mn addition. It is shown that the Mn-containing AE44 exhibits distinct age hardening response upon direct ageing (T5) due to the precipitation of nanoscale Al-Mn particles, as reported previously in a similar alloy. The T5 ageing leads to a significant improvement in strength with similar ductility. Consequently, the T5-aged AE44 has a remarkably better strength-ductility combination than most Mg die-casting alloys and even the Al die-casting alloy A380. Minor Mn addition is also shown to be critical for the creep resistance of AE44 whereas the influence of the RE constituent is not as significant as previously thought, which reaffirms that precipitation hardening of the α-Mg matrix is more important than grain boundary reinforcement by intermetallic phases for the creep resistance of die-cast Mg alloys. The findings in this work could provide new application perspectives for AE44, particularly in the automotive industry.

Strengthening Mechanism of Room Temperature Mechanical Properties for AZ31 Magnesium Alloy by Continuous Variable Cross section Direct Extrusion

Strengthening Mechanism of Room Temperature Mechanical Properties for AZ31 Magnesium Alloy by Continuous Variable Cross section Direct Extrusion

The effect of low-power laser on micro-forming of 316 stainless steel additive manufacturing part

316 stainless steel was fabricated with novel low-power pulsed laser-induced gas tungsten arc additive manufacturing (LGTA-AM). Compared with gas tungsten arc additive manufacturing (GTA-AM) process, the microstructure, phase composition and room temperature mechanical property were investigated. Compared with the micro-molding of walls fabricated by GTA-AM, the room temperature micro-structure of the two processes are composed of A and δ ferrite. The austenite grains show cell-like crystals → columnar crystals → dendrites → equiaxed crystals from bottom to top of 8-layer wall. The ferrite morphology of the GTA-AM specimens captured by SEM was strip-shaped, skeleton-shaped, sieve-shaped, and worm-shaped in order from bottom to top. The ferrite morphology of LGTA-AM specimens captured by SEM is strip-shaped, fine-mesh-shaped, reticulate-shaped, and fish-scaled in order from bottom to top. LGTA-AM can uniformly refine the micro-structure and accelerate the transformation rate from ferrite to austenite. The hardness value of the AM wall from the bottom to the top shows a trend of decreasing first and then increasing. The LGTA-AM process can improve the uniformity of the interlayer transition and reduce the anisotropy of the grains.

The effect of hot rolling on the strength and fracture toughness of 90W–7Ni3Fe tungsten heavy metal alloys

Due to their balance of strength, ductility and toughness, liquid-phase sintered tungsten heavy metal alloys (WHAs) are considered to be an attractive alternative to monolithic polycrystalline tungsten (W) for plasma facing components. Here we explore the effect of hot rolling (HR) on the room temperature (RT) mechanical properties of a 90W–7Ni3Fe (by wt%) WHA, at different thickness reductions of 0, 62, 74 and 87%. High elastic-plastic KJm maximum load toughness for LS-oriented pre-cracked bend bars is observed in the 0 and 87% HR WHA, along with stable crack growth. In contrast, the 62 and 74% HR WHA experience elastic fracture, at much lower KIc. The opposite trend is observed in the microhardness, as well as the tensile yield and ultimate stresses, which are lowest in the 0 and 87% HR condition and highest in the 62 and 74% HR WHA. The reason for the difference in strength at 87 versus 74% HR reductions is not fully understood. However, the strength differences partially rationalize the toughness trends. Unfortunately, HR results in highly anisotropic brick-and-mortar microstructures, leading to much lower elastic KIc in the LT-orientation.

Synthesis and characterisation of Cf/SiC composites with modified silicon carbide matrix

Cf/SiC composites with multilayer [(PyC/SiC)n; n = 4] interface and modified silicon carbide matrix were prepared through isothermal isobaric chemical vapor infiltration (ICVI) technique and characterised room temperature mechanical properties. The monotonic tensile properties were studied at elevated temperature (i.e. 1250 °C, and 1350 °C) and compared with room temperature tensile properties. The tensile strength at RT, 1250 °C, and 1350 °C of the composite was found to be 193 ± 10 MPa, 238 ± 14 MPa, and 189 ± 20 MPa respectively. This paper also focusses the effect of thermal exposure of composites on residual tensile strength. The enhanced strength and toughness behaviour observed for the prepared composites because of the presence of multi-layer interface and modified matrix (SiC/Si-B-C/SiC). SEM microstructural studies carried out on tested specimens and cross section of prepared composites revealed the evidence for the self-healing behaviour from the modified matrix.

Titanium carbonitride fabricated by spark plasma sintering: Is it a ceramic model of carbon-induced Friedel-Fleisher strengthening effect?

This work is devoted to the analysis of the composition, microstructure and room-temperature mechanical properties of a carbonitride ceramics: the case of Ti(C,N) ceramics fabricated by spark plasma sintering (SPS). Particular attention has been given to know whether there is a possible composition change under electric field, finding all the computed lattice parameters of SPS-ed TiN1-xCx ceramics lay within tiny interval (∼TiC0.43N0.57), hence following Vegard’s law. The analysis of the strengthening effect of substitutional carbon, making use of our own results and those available in literature shows that a classical x1/2 dependence could account for experimental data. This fact reveals that a Friedel-Fleisher mode of strong localized carbon pinning points might describe the hardening effect of those impurities. However, the large scattering of experimental data and the fact that tiny deviations of stoichiometry might play a relevant role on the hardening force us to leave this as an open problem.

Indentation-derived mechanical properties of Ti-6Al-4V: Laser-powder bed fusion versus electron beam melting

Employing a depth-sensing indentation testing technique, the room temperature mechanical properties of Ti-6Al-4V (Ti64) alloy fabricated through laser powder-bed fusion (L-PBF) and electron beam melting (EBM) additive manufacturing processes were studied. Mechanical properties including nano-hardness (in GPa), reduced elastic modulus, yield pressure, elastic recovery, and wear resistance were extracted. The microstructure of the fabricated materials was correlated with the indentation-derived characteristics. It was observed that the nano-hardness and reduced elastic modulus values were 3.66 ± 0.06 GPa and 118 ± 3 GPa, for the L-PBF, and 3.43 ± 0.22 GPa and 136 ± 4 GPa, for the EBM materials, respectively. The higher strength of the L-PBF alloy is due to the finer microstructure of this alloy. While α laths with an average width of 3.61 ± 0.92 μm developed in the EBM-Ti64, the microstructure of L-PBF-Ti64 consisted of α′ martensite with an average width of 0.37 ± 0.10 μm.

Microstructure, texture, and mechanical properties of the extruded and multi-directionally forged Mg–xGd alloys

The microstructural and textural evolutions as well as room-temperature mechanical properties of three binary Mg–Gd alloys with 1, 2, and 3 wt% of Gd were studied in the as-extruded condition and after two, four, and six passes of multi-directional forging (MDF). Microstructural observations of the extruded samples were indicative of partial dynamic recrystallization resulting in bimodal grain structures comprised of elongated un-recrystallized patches and fine recrystallized grains. After six passes of the MDF process, the fraction of the un-recrystallized regions decreased because of dynamic recrystallization, and thus, relatively uniform microstructures were achieved in all alloys. The greater fraction of the un-recrystallized patches and the finer grains in the recrystallized regions of the Mg–3Gd alloy confirmed the more pronounced retardation of recrystallization via solute drag mechanism at the higher Gd concentrations. Evaluation of crystallographic texture revealed that by applying the MDF process, the conventional fiber texture of the extruded condition was replaced with a new randomized texture, in which the basal planes had a tendency to rotate at angles of lower than 90° to the transverse direction. Mechanical properties were evaluated using shear punch testing (SPT) and the results showed that with increasing the number of MDF passes in each alloy, the achieved finer grain structure was responsible for improving the shear strength. In addition, increasing the Gd content of the alloys resulted in finer grain size, more solute atoms, and higher fraction of Mg 5 Gd second phase particles, all of which led to the enhancement in shear strength.

Tensile strength and fracture mechanics of two-dimensional nanocrystalline silicon carbide

Two-dimensional Silicon Carbide (SiC) has opened the route to a cornucopia of advanced functionalities in the realm of quantum condensed matter. It holds great promise for highly efficient nanoelectronic, optoelectronic, renewable energy, and spintronic applications thanks to the confluence of a wide spectrum of mesmerizing physical properties like a wide direct bandgap with high exciton binding energy, robust spin–orbit-coupling, excellent photoluminescence, suitable mechanical strength, and thermodynamic stability. Nonetheless, it is still a daunting challenge to incorporate SiC in functional systems since extensive analyses of the mechanical properties, and fracture mechanism of nanocrystalline (NC)-SiC is still obscure. In this light, this work is an attempt to report detailed information concerning the room-temperature tensile mechanical properties and fracture phenomena of NC-SiC executing Molecular Dynamics (MD) simulations. In particular, effects of grain size on the stress–strain profile, fracture strength, fracture strain, and Young’s modulus of the NC-SiC have been thoroughly investigated. It has been found that the strength as a function of grain size can be characterized by the inverse pseudo Hall-Petch relation. Increasing grain size brings about more elasticity in the structure, albeit at the price of fracture strain. The NC-SiC encounters a substantial degradation in mechanical properties relative to its single-crystal counterpart. Afterward, we performed an exhaustive fracture analysis on two NC-SiC samples of different grain sizes. The single-crystal SiC can endure more tensile strain before rupture compared to that of the NC-SiC. At last, the nanosheet exhibits more immunity to fracture with decreasing grain size. This study would lay the groundwork for NC-SiC to be successfully realized in functional systems as well as serving as a solid roadmap for engineering the mechanical properties of nanocrystalline materials.

10 μm-Thick High-Strength Solid Polymer Electrolytes with Excellent Interface Compatibility for Flexible All-Solid-State Lithium-Metal Batteries.

An ultrathin solid polymer electrolyte (SPE) consisting of modified polyethylene (PE) as the host and poly(ethylene glycol) methyl ether acrylate and lithium salts as fillers is presented. The porous poly(methyl methacrylate)-polystyrene interface layers closely attached on both sides of the PE effectively improve the interface compatibility among electrolytes and electrodes. The resultant 10 μm-thick SPEs possess an ultrahigh ionic conductance of 34.84mS at room temperature and excellent mechanical properties of 103.0MPa with elongation up to 142.3%. The Li//Li symmetric cell employing an optimized solid electrolyte can stably cycle more than 1500h at 60°C. Moreover, the LiFePO4 //Li pouch cell can stably cycle over 1000 cycles at 1C rate and with a capacity retention of 76.4% from 148.9 to 113.7mAhg-1 at 60°C. The LiCoO2 //Li pouch cell can stably operate at 0.1 and 0.2C rate for each 100 cycles. Furthermore, the LiFePO4 //Li pouch cell can work stably after curling and folding, which proves its excellent flexibility and safety simultaneously. This work offers a promising strategy to realize ultrathinness, excellent compatibility, high strength, as well as safe solid electrolytes for all-solid-state lithium-metal batteries.

Effects of hydrogen as a solid solution element on the deformation behavior of a near-alpha titanium alloy

The effects of hydrogen on the room-temperature mechanical properties and the deformation behavior of near-alpha alloy Ti–6Al–3Nb–2Zr–1Mo were systematically investigated. It was found that hydrogen addition increased the strength and plasticity of titanium alloy, while the impact toughness firstly increased for the sample with 65 wppm hydrogen and then decreased at higher hydrogen content. The strength was increased due to the pinning effect and the solid-solution strengthening effect of hydrogen, while the plasticity was improved by the increase of dislocation mobility and the breakage of beta laths. The increase of impact toughness at 65wppm hydrogen resulted from the enhancement of dislocation motion and multiplication, but further increasing hydrogen addition would reduce impact toughness by decreasing the cohesion strength at interfaces and grain boundaries and the breakage of beta laths. In addition, deformation behaviors of titanium alloys with different hydrogen content were discussed. Hydrogen inhibited twinning and enhanced dislocation slip to some extent. Cross-slip was hindered and planar slip was favored due to the decrease of stacking fault energy after hydrogenation. Further, basal slip and pyramidal slip were activated while prismatic slip was suppressed by hydrogen addition.

Sn microalloying Al–Cu alloys with enhanced fracture toughness

Abstract Effect of minor Sn additions (0.05, 0.10 wt%) on the microstructure and room-temperature mechanical properties of Al-3.0 wt%Cu alloy was studied by using transmission electron microscopy (TEM), atom probe tomography (APT), tensile testing, and fracture toughness measurement, respectively. TEM experimental results showed that the Sn addition promoted the dispersion of θ′ -Al2Cu precipitates with refined size and increased number density. APT examinations revealed that the Sn microalloying mechanism was mainly the heterogeneous nucleation of θ′ precipitates on Sn particles. The microstructural evolution with Sn addition resulted in a decrease in ductility but an increase in both yield strength and fracture toughness. In particular, the fracture toughness was increased by over 60% at 0.1 wt% Sn addition, indicative of a significant microalloying effect. The ductility inversely scaled with the strength, while the fracture toughness simultaneously increased with the strength. These relationships are rationalized by considering a competition between dislocation-precipitate interaction and precipitate-matrix deformation discrepancy as the dominant strain localization mechanism, which is modulated by the Sn-affected precipitation as well as the constraint condition.

Antimicrobial Zr-based bulk metallic glasses for surgical devices applications

Zr58.6Al15.4(Co1-xCux)26 (at. %; x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8) bulk metallic glasses (BMGs) were designed and produced by copper mold casting. As a result of the partial substitution, Zr58.6Al15.4Co18.2Cu7.8 (x = 0.3) BMG showed the largest glass glass formation ability with a critical glass forming diameter of 10 mm. And the Zr58.6Al15.4Co18.2Cu7.8 BMG also showed excellent room-temperature mechanical property, corrosion resistance and antibacterial property. The compressive strength (σf) was about 1.95 GPa and the plastic strain was about 2.0%. The corrosion current density was two order of magnitude lower than that of Ti6Al4V alloy. Moreover, antibacterial test results showed the surface of the BMG is able to eradicate bacteria at a 99.99% level. Therefore, for Zr60.5Ti3Al9Fe4.5Cu23 BMG, the properties combine with larger GFA, outstanding mechanical properties, biocorrosion resistance and antibacterial properties is considered a potential biomedical material for surgical devices applications.

Strong work hardening in a high niobium-containing TiNi-based bulk glassy alloy composite

In this study, a high niobium-containing bulk glassy alloy composite Ti41Ni39Nb17.5Al2.5 consisting of amorphous, B2-TiNi and β-Nb phases was fabricated through in situ precipitation strategy by utilizing copper-mold suction casting. Upon compressive loading, the composite alloy showed a pronounced average plastic strain of (17.6 ± 3.5)% and a high fracture strength of (2279 ± 33) MPa together with a strong work-hardening deformation behavior. The volume fraction of the amorphous phase in the composite was determined to be around 23 vol%. The work softening caused by the formation of shear bands can be compensated by the work hardening arising from the pile-ups of dislocation and severe lattice distortion in the precipitated crystals and thereby stabilize the plastic deformation of the composite material. The findings imply that the room-temperature mechanical properties of bulk glassy alloy composites can be well tailored by selecting suitable reinforcers.

Microstructural stability and intermetallic embrittlement in high Al containing FeCrAl-ODS alloys

Abstract The effect of Al addition on the microstructural stability and intermetallic embrittlement in FeCrAl oxide dispersion strengthened (ODS) alloys was investigated in 1423 K solutionized and 748 K aged conditions by comparing their phase stability and room temperature mechanical properties. Microstructural characterization revealed that the microstructures of solutionized FeCrAl-ODS alloys containing 10 wt% Al. Contrary to this, the ordered B2 phase observed in alloys containing >20 wt% Cr and 16 wt% Al remained B2, even after prolonged ageing at 748 K. Ageing at 748 K up to 1000 h resulted in the precipitation of the ordered Fe3Al intermetallic but insignificant hardness increment in FeCrAl-ODS alloys as compared to the hardness increment due to α’ phase separation. The hardness values reached to their maxima after 100 h ageing at 748 K and thereafter either it attained a plateau or decreased slightly. Ageing also led to increase in strength and decrease in ductility due to intermetallic embrittlement; however, the loss of ductility was limited to 2–4% only.

Twinning Engineering of a CoCrFeMnNi High-Entropy Alloy

Deformation-induced twinning has been a notable example of overcoming the strength/ductility trade-off dilemma as a strengthening mechanism. By borrowing this concept from the area of TWIP steels, we designed a thermomechanical treatment for a CoCrFeMnNi high-entropy alloy to improve its mechanical characteristics. We used pre-straining at 77 K to introduce deformation-induced twins in the microstructure of the alloy, and then recovered it by annealing at 773 K, while avoiding recrystallization. The deformation-induced twins generated by pre-straining at 77 K were retained after this heat treatment, whilst partial recovery of dislocations occurred. As a result, the room-temperature mechanical properties of the alloy, including its strain hardening ability, were improved substantially.

Experimental characterization and molecular dynamics simulation of thermal stability, mechanical properties and liquid oxygen compatibility of multiple epoxy systems for cryotank applications

Epoxy resins with high thermal stability, good mechanical properties and liquid oxygen compatibility are primary candidates in large cryogenic engineering projects, particularly for cryotank applications to avoid catastrophic accidents. Herein, an experimental characterization and molecular dynamics modeling are conducted for the thermal stability, mechanical properties and liquid oxygen compatibility of multiple epoxy systems. The multiple epoxy systems are synthesized to achieve a comprehensive evaluation of their thermal stability, room-temperature and cryogenic mechanical properties as well as liquid oxygen compatibility. Concretely speaking, the anti-oxidation properties of the degradation are investigated by thermogravimetric analysis (TGA) and the glass transition temperature (Tg) is measured by the differential scanning calorimetry (DSC). The tensile test and fracture toughness test under room-temperature/cryogenic conditions (90 K) are chosen for determining their mechanical performances. Moreover, limited oxygen index measurements and liquid oxygen impact tests are utilized to characterize the flame retardancy and liquid oxygen compatibility, respectively. In parallel, molecular dynamics models are established to construct the high cross-linking structures and predict thermomechanical properties, which helps reveal the relationship between the molecular structures and macroscopic properties. Finally, the synergistic effects of organic/inorganic flame retardants and polyurethane toughener are proven to be effective to balance the liquid oxygen compatibility and mechanical properties. The valuable and extensive evaluation data in this work could be beneficial to the epoxy resin system design for cryotank applications.

Improved ionic conductivity and Li dendrite suppression of PVDF-based solid electrolyte membrane by LLZO incorporation and mechanical reinforcement

High room-temperature ionic conductivity and mechanical property are essential for the application of solid electrolyte. In this work, a poly(vinylidene fluoride) (PVDF)-based composite polymer solid electrolyte membrane (CSE) incorporated with Li7La3Zr2O12 (LLZO) fillers and high-strength porous skeleton was prepared. The introduction of LLZO increased the ionic conductivity of PVDF at room temperature by reducing the crystallinity of PVDF matrix, and the addition of skeleton greatly improved the mechanical property of electrolyte membrane and inhibited the growth of lithium dendrites. The prepared PVDF-LLZO CSE has a room-temperature ionic conductivity of 1.75 × 10−4 S/cm, and the tensile strength reaches 95 MPa, which greatly enhanced the ability of lithium dendrite suppression. The assembled LiNi0.6Co0.2Mn0.2O2 (NCM622)/CSE/Li cell shows an initial capacity of 151 mAh/g with a retention capacity of 108 mAh/g after 100 cycles at the current density of 0.5 C. This ultrathin PVDF/LLZO CSE has a great application prospect in solid-state lithium batteries.

Characterization of Microstructure and Mechanical Properties of Ti-6Al-4V Alloy after Cyclic Heat Treatment

A cost-effective approach which consists of cyclic heat treatment (CHT) and annealing is used to refine the coarse lamellar structure of as-cast Ti-6Al-4V alloy. The coarse lamellar microstructure was significantly refined after the CHT process, α lamellae were broken up while the original orientations of α lamellae were maintained. After annealing treatment, a basketweave microstructure was achieved in Ti-6Al-4V alloy, and the formation of globular α grains was observed. The microstructure refinement mechanisms during CHT and annealing are mainly considered to be break-up of lamellar structure and static recrystallization. The room temperature mechanical properties of Ti-6Al-4V alloy were significantly improved. The microhardness of Ti-6Al-4V alloy increased from 306 HV to 402 HV. The values of yield strength (YS) and ultimate tensile strength (UTS) increased from 734 MPa and 740 MPa to 911 MPa and 1010 MPa, respectively. The value of ductility increased from 1.1 % to 3.3 %.

In-situ development of MB2 and their effect on microstructure and mechanical properties of refractory Hf0.5Mo0.5NbTiZr high entropy alloy matrix composites

To improve the room temperature comprehensive mechanical properties of the refractory high entropy alloy Hf0.5Mo0.5NbTiZr, boron element is added to form the boride phase as the strengthening phase. The Hf0.5Mo0.5NbTiZrBx (x = 0.1, 0.3, 0.5, 0.7, and 0.9) were produced by vacuum arc melting and effect of boron element on the microstructure and room temperature mechanical properties of Hf0.5Mo0.5NbTiZr alloy was investigated. The boride MB2 phase form and the volume fraction of boride phase increases with the addition of boron element. The microstructure exhibits the evolution from the hypoeutectic structure to the eutectic structure, and then to the hypereutectic structure with the increase of boron element. Because of the difference of the formation path, the morphology and chemical compositions of MB2 phase is different. The lamellar or needlelike MB2 phase forms through the eutectic reaction and is rich in Zr element but poor in Mo and Nb elements. The agglomerated or block sexangle MB2 phase forms as the proeutectic phase and is enriched with Nb element and are depleted with Mo and Zr elements. When the content of the boron is x = 0.1 and 0.3, both the strength and ductility are improved due to the refined structure, the clean interface between the BCC solid solution phase and MB2 phase and the precipitated strengthening of boride phase. And the strength increases dramatically at the expense of the decrease of the ductility with more addition of boron element, which is attributed to the formation of more brittle boride phase