Search

The structure-property relationship, one of the central themes in materials science, is far from being well understood for metallic glasses (MGs) due to the great complexity of their amorphous structures. Based on the analysis of published experimental data for 165 MGs from more than 15 different alloy systems, the present study reveals a universal dependence of mechanical properties (Young’s moduli, shear moduli and yield strength) on simple structural parameters (the inter-atomic distance and/or valence electron density) originating from the interatomic potential and Fermi sphere-Brillouin zone interaction. This work establishes a structure-property relationship for metallic glasses and provides insights into the fundamentals of the mechanical properties of disordered systems.

The chemical composition and structural state of advanced alloys are the decisive factors in optimum biomedical performance. This contribution presents unique Ti-Zr-Ge metallic glass thin-film compositions fabricated by magnetron sputter deposition targeted for nanocoatings for biofouling prevention. The amorphous nanofilms with nanoscale roughness exhibit a large relaxation and supercooled liquid regions as revealed by flash differential scanning calorimetry. Ti\textsubscript{68}Zr\textsubscript{8}Ge\textsubscript{24} shows the lowest corrosion (0.17 \textmu A cm\textsuperscript{\textminus2}) and passivation (1.22 \textmu A cm\textsuperscript{\textminus2}) current densities, with the lowest corrosion potential of \textminus0.648 V and long-range stability against pitting, corroborating its excellent performance in phosphate buffer solution at 37 {\textdegree}C. The oxide layer is comprised of TiO\textsubscript{2}, TiO\textsubscript{\emph{x}} and ZrO\textsubscript{\emph{x}}, as determined using X-ray photoelectron spectroscopy by short-term ion-etching of the surface layer. The two orders of magnitude increase in the oxide and interface resistance (from 14 to 1257 {\textOmega} cm\textsuperscript{2}) along with an order of magnitude decrease in the capacitance parameter of the oxide interface (from 1.402 x 10\textsuperscript{\textminus5} to 1.677 x 10\textsuperscript{\textminus6} S s\textsuperscript{n} cm\textsuperscript{\textminus2}) of the same composition is linked to the formation of carbonyl groups and reduction of the native oxide layer during linear sweep voltammetry., 34 Pages, 5 Figures, 4 Tables, 13 Supplementary Figures

Bulk metallic glasses (BMGs) are materials with outstanding strength and elastic properties that make them tantalizing for engineering applications, yet our poor understanding of how their amorphous atomic arrangements control their broader mechanical properties (hardness, wear, fracture, etc.) impedes our ability to apply materials science principles in their design. In this work, we uncover the hierarchical structure that exists in BMGs across the nano- to microscale by using nanobeam electron diffraction experiments. Our findings reveal that local hardness of microscale domains decreases with increasing size and volume fraction of atomic clusters with higher local medium range order (MRO). Furthermore, we propose a model of ductile phase softening that will enable the future design of BMGs by tuning the MRO size and distribution in the nanostructure.

A composite of two different medium entropy alloys (MEAs, i.e., CoCrFeNi and AlCoCrFe) was synthesized using ball milling and spark plasma sintering. The composite microstructure contains a homogenous distribution of fcc and bcc phases with submicron-sized grains and exhibits excellent microstructural and phase stability even after 100 h heat treatment at 800 °C. The composite provides a combination of high compressive strength, adequate plastic strain, and multiple strain-hardening stages at room temperature. This first exploratory study on a MEA composite can be used as a template to other systems and illustrates the feasibility of combining two or more MEAs.

In this study, high entropy metallic glasses (HEMGs) were developed through a combination of concepts for designing metallic glasses (main element + transition metal + metalloid element) and high-entropy alloys (more than five elements, each element having an atomic concentration between 5 at.% and 35 at.%). The developed metallic glass alloys are composed of Co-Fe-Ni main elements, transition metals (Cr, Mo) and metalloid elements (C, B). Moreover, the present work reports the thermal, mechanical and magnetic properties of (CoFeNi)50(CrMo)50-x(CB)x alloys with x = 20, 25, 30. The developed as-spun HEMGs exhibit typical paramagnetic properties even for a high amount of ferromagnetic elements (Co, Fe, and Ni) and have high elastic modulus (103–160 GPa) and hardness (14–27 GPa), thus possessing mechanical properties similar to well-known Co-based metallic glasses (Co-Cr-Mo-C-B system). In addition, some of the bulk samples prepared with a diameter of 2 mm form bulk metallic glasses with a high compressive strength around 3.5 GPa. The mechanisms determining the stability of the supercooled liquid, as well as the paramagnetic and mechanical properties for the developed non-equiatomic HEMGs, are discussed.

This study presents detailed microstructural investigations on single and bilayer thin films of two medium entropy alloys (MEAs) synthesized using magnetron sputter deposition. Single layer thin films of CoCrFeNi and AlCoCrFe show single-phase face-centered cubic (fcc) and body-centered (bcc) structure, respectively. The bilayer thin film consisting of CoCrFeNi (fcc) and AlCoCrFe (bcc) has a sharp interface between them with an equiatomic composition. Nanodiffraction was used to characterize planar defects in the fcc films. Plausibly, this maiden study on bilayer film of two MEAs is transformative to other systems and will help fundamental studies on high entropy alloys.

Using molecular dynamics simulations, we provide an atomistic description of the shear band multiplication mechanisms in a heterogeneous metallic glass consisting of two distinct amorphous regions with different amounts of free volume and degrees of short-range order. The structural differences and elastic fluctuations encountered by the developing shear band while crossing the interface between the two regions alter the autocatalytic activation of the shear transformation zones (STZs) and, subsequently, lead to shear band branching. The two-unit STZ-vortex mechanism sheds light on the correlation between the strain distribution during tensile deformation and the directional characteristics of the STZ activation process.

An Al-12Si/Al-3.5Cu-1.5Mg-1Si bimetal with a good interface was successfully produced by selective laser melting (SLM). The SLM bimetal exhibits four successive zones along the building direction: an Al-12Si zone, an interfacial zone, a texture-strengthening zone and an Al-Cu-Mg-Si zone. The interfacial zone ( fiber texture. Electron backscatter diffraction analysis shows that the grains grow gradually from the interfacial zone to the Al-Cu-Mg-Si zone along the building direction. Additionally, a strong fiber texture develops at the Al-Cu-Mg-Si side of the interfacial zone and disappears gradually along the building direction. The bimetal exhibits a room temperature yield strength of 267 ± 10 MPa and an ultimate tensile strength of 369 ± 15 MPa with elongation of 2.6% ± 0.1%, revealing the potential of selective laser melting in manufacturing dissimilar materials.

A refractory ReTaWNbMo high-entropy alloy (HEA) with an equal atomic ratio prepared by rapid solidification displays a BCC crystal structure. After annealing the as-quenched samples at 673, 873, 1073, and 1273 K for 12 h, respectively, the crystalline phase still keeps its BCC structure, but the crystalline morphology transforms from coarse dendrites to fine equiaxed crystals together with gradual grain refinement. The intragranular regions are enriched in W and Ta, while the crystals in the intergranular regions are enriched in Nb, Mo, and Re. With the increase in annealing temperature, the yield strength increases, and the compressive plasticity and fracture strength are obviously enhanced. The failure mode gradually changes from transgranular to intergranular fracture. Furthermore, the corrosion behaviors of the as-cast ReTaWNbMo HEA and the annealed states in a 3.5 wt.% NaCl solution were also studied. The samples annealed at 1273 K exhibit the best corrosion resistance due to the elemental re-distributions within grains.

Carbon nanotube reinforced titanium (CNT/Ti) composites with high tensile strength (872 ± 5 MPa) were synthesized by the high pressure torsion process (HPT). Cs-corrected high resolution transmission electron microscopy (TEM) revealed face centered cubic titanium (FCC–Ti) distributed in the grains and at the grain boundaries of a hexagonal close packed titanium (HCP–Ti) matrix, with an orientation relationship of [0002]HCP//[11 1 ¯ ]FCC and {2 1 ¯ 1 ¯ 0}HCP//{011}FCC between FCC-Ti and HCP-Ti. The phase transformation from a HCP-Ti structure to a FCC-Ti structure in the CNT/Ti composites during the HPT process made a significant impact on the mechanical properties. Combining experimental results with density functional theory calculations, the stability of FCC-Ti and HCP-Ti under external pressure were analyzed. Moreover, the nucleation and growth mechanisms of FCC-Ti phase in HCP-Ti matrix were identified. The results showed that the stress-induced phase transformation from HCP-Ti to FCC-Ti in the CNT/Ti composites during the HPT process is associated with the source of Shockley partial dislocations. This work helps to the better understanding of the phase transformation mechanism from a HCP-Ti structure to a FCC-Ti structure in CNT/Ti composites.

Simultaneous spark plasma sintering (SPS) of metal powders (Fe and Ni) with their respective aluminide powders (FeAl and NiAl) was attempted to produce a cylindrical aluminide coating on a cylindrical metal core. The interdiffusion zone (IDZ) formed between the metal and the aluminide was analyzed to evaluate the diffusion coefficient. The composition variation and the actual temperature estimated at the interface were taken into consideration while evaluating the diffusion coefficient. The diffusion coefficients estimated based on the IDZ are found to be higher than those obtained by conventional methods but are in agreement with those obtained from previous SPS studies.

Single phase ternary (TiFe)100-xNix alloys were synthesized through high-energy ball milling. Ni solubility in equiatomic TiFe reaches 10 at. %, exceeding the values known from the equilibrium diagram of state and those obtainable by conventional arc melting. The reactivity of mechanically alloyed (TiFe)95Ni5 with hydrogen was investigated in detail by a combination of volumetric and calorimetric methods. The influence of Ni addition on the pressure-composition isotherms and the reaction enthalpies was evaluated. Finally, the hydrogenation behavior was compared with Ni-free mechanically alloyed TiFe and with literature data on different TiFe-Ni alloys.

A new series of Ti40Zr10Cu36−xPd14Gax (x = 2, 4, 8 and 10) alloys with improved plasticity and glass-forming ability (GFA) are produced. The strategy is to create local structural heterogeneity in Ti-based bulk metallic glasses (BMGs) by alloying with a soft element which has high negative enthalpy of mixing with Ti-atoms. The GFA of Ti40Zr10Cu36−xPd14Gax rods increases with increasing Ga content up to 4 at.%, and for more Ga it decreases. Minor addition of Ga (x = 2) is beneficial to improve the strength and ductility of the TiZrCuPd-based BMG due to the formation of local structural heterogeneities which facilitate the formation of a highly organized pattern of multiple shear bands under quasi-static compression. Ti40Zr10Cu34Pd14Ga2 BMG shows the best combination of compressive global strain and maximum compressive strength of ∼4.5% and ∼2000 MPa, respectively. Comparing the Young's modulus of Ga-containing alloys in amorphous and crystalline state we find that the amorphous state shows significant elastic softening (40–48% smaller) which is useful to reduce stress shielding effect for biomedical applications. The alloys show a remarkable thermoplastic formability as the viscosity decreases sharply by an order of magnitude in the supercooled liquid region.

This study investigates the effect, that replacing Zr in a glass-forming Cu47.5Zr47.5Al5 alloy by Sc (0–2 at.%) has on the phase formation as well as on the thermal and mechanical properties. Even though it is not reflected in the thermal data, the glass-forming ability (GFA) is significantly reduced. This originates from the increased tendency to precipitate the shape-memory phase B2 CuZr(Sc), which, in turn, promotes the formation of bulk metallic glass (BMG) matrix composites. Sc appears to be very effective in stabilizing the B2 crystals because it forms the stable B2 CuSc phase with a similar lattice constant like B2 CuZr. By adjusting the casting parameters, the composite microstructure of Cu47.5Zr46.5Al5Sc1 can be controlled to a certain extent. The yield strength and the plasticity of the present composites depend on the crystalline volume fraction. In-situ high-energy X-ray diffraction reveals that deformation proceeds in three stages: (i) martensitic transformation of the B2 phase, (ii) yielding of the amorphous phase and continuing martensitic transformation, (iii) completion of the phase transformation and plastic deformation of all phases. Our work suggests that Sc is a promising candidate to adjust the microstructure and, thus, the mechanical properties of CuZr-based composites consisting of a glassy matrix and shape-memory crystals.

High-entropy composites (HECs) were subjected to severe straining by high-pressure torsion (HPT) to evaluate their influence on the evolution of microstructure and deformation behavior. Severe straining leads to a homogeneously strained microstructure and inhomogeneous micro-shear bands in these HECs. Nb addition in HECs varies the microstructure from single phase to eutectic, and the Vickers microhardness in HPT HECs increases to 7.45 GPa. Nb addition up to x = 0.80 in as-cast HECs improves the strength of these materials at the expense of its plasticity. Nevertheless, severe straining provides a better combination of strength and ductility without sacrificing its plasticity. Such improvement in properties is attributed to the evolved microstructural features, formation of “transformation-shear bands (T-SBs)” and “deformation-shear bands (D-SBs)” at severe straining. This assures the homogeneous deformation by shear banding and suggests that shear banding is the dominant deformation mechanism when the lamellar spacing becomes saturated upon severe straining.

Most bulk metallic glass systems with high glass-forming ability are doped with precious metal(s) or toxic element(s), like palladium and beryllium, leading to relatively high cost or low safety in use. In this work, the glass-forming ability, crystallization kinetics and mechanical properties of the Zr55Co25Al20 and Zr52Co25Al23 bulk metallic glasses prepared by water-cooled copper mold suction casting are investigated in detail. The results show that Zr52Co25Al23 has a wider supercooled liquid region, a higher thermal stability and a higher glass-forming ability than the Zr55Co25Al20 amorphous alloy. At the same time, Zr52Co25Al23 has a higher activation energy of crystallization than Zr55Co25Al20 amorphous alloy, indicating that Zr52Co25Al23 has a higher resistance to crystallization than Zr55Co25Al20. Investigation of the mechanical properties reveals that Zr52Co25Al23 also has a higher fracture strength of up to 2308 MPa and a higher specific fracture strength of up to 3.78 × 105 N m kg−1 compared with 316L stainless steel, Ti-6Al-4V, as well as Mg-, Ti-, and other Zr-based BMGs.

To uncover the physical correlation between intrinsic structural heterogeneity and mechanical properties of metallic glasses, we performed high-pressure torsion (HPT) to tailor their microstructure with a rejuvenated state. Nanoindentation results show that the change of mechanical properties results from the convolution of the intrinsic thermal activation process and the structural inhomogeneity in the glassy phase. The spatial heterogeneity induced by severe plastic deformation can markedly operate to reduce the energy barrier for shear transformation zone (STZ) activation and increase the number of STZ events during tensile testing to accommodate the plastic strain, leading to a brittle-to-ductile transition. We highlight that by properly controlling the distribution of structural heterogeneities, one can purposely tune the mechanical performance of metallic glasses.

The influence of annealing at different temperatures (573, 873, 1273, 1373 and 1673 K) on the stability of phases, composition and microstructure of 316L stainless steel fabricated by SLM has been investigated and the changes induced by the heat treatment have been used to understand the corresponding variations of the mechanical properties of the specimens under tensile loading. Annealing has no effect on phase formation: a single-phase austenite is observed in all specimens investigated here. In addition, annealing does not change the random crystallographic orientation observed in the as-synthesized material. The complex cellular microstructure with fine subgrain structures characteristic of the as-SLM specimens is stable up to 873 K. The cell size increases with increasing annealing temperature until the cellular microstructure can no longer be observed at high temperatures (T ≥ 1273 K). The strength of the specimens decreases with increasing annealing temperature as a result of the microstructural coarsening. The excellent combination of strength and ductility exhibited by the as-synthesized material can be ascribed to the complex cellular microstructure and subgrains along with the misorientation between grains, cells, cell walls and subgrains.

Evaluation of the diffusion coefficient of metal powders was attempted by using the power-law creep model in conjunction with the isothermal densification kinetics during spark plasma sintering (SPS). The diffusion coefficients obtained from the densification data of elemental Fe, Ni and Al powders are found to be higher than those reported in the literature. The higher values of diffusivity can be attributed to electric current effects. Our analysis demonstrates that it is possible to evaluate diffusion coefficients from experimental SPS densification data.

Journal of alloys and compounds 857, 157503 (2021). doi:10.1016/j.jallcom.2020.157503, Self-propagating exothermic reactions, for instance in the nickel-aluminum (Ni–Al) system, have been widely studied to create high performance intermetallic compounds or for in-situ welding. Their easy ignition once the phase spacing is reduced below the micron scale, makes top-down methods like high-energy ball milling, ideal to fabricate such reactive nanostructures. A major drawback of ball milling is the need of a sintering step to form bulk pieces of the reactive material. However, this is not possible, as the targeted reactions would already proceed. Therefore, we investigate the ability of high pressure torsion as an alternative process, capable to produce bulk nanocomposites from powder mixtures. Severe straining of powder mixtures with a composition of 50 wt% Ni and 50 wt% Al enables fabrication of self-reactive bulk samples with microstructures similar to those obtained from ball milling or magnetron sputtering. Samples deformed at ambient temperature are highly reactive and can be ignited significantly below the Al melting point, finally predominantly consisting of Al$_3$Ni$_2$ and Al$_3$Ni, independent of the applied strain. Although the reaction proceeds first at the edge of the disk, the strain gradient present in the disks does not prevent reaction of the whole sample., Published by Elsevier, Lausanne

Unlike crystalline alloys, disordered amorphous alloys lack long-range order. Even today, the creep mechanisms for amorphous alloys are far from being fully understood. In this work, an Fe–Cr–Mo–B–C (Cr: 25–27 wt%, Mo: 16–18 wt%, B: 2.0–2.2 wt%, and C: 2.0–2.5 wt%) amorphous coating was fabricated on the surface of a 304 stainless steel via atmospheric plasma spraying with a NiAl bonding layer. In this study, the effects of peak load and loading rate on the creep deformation behavior of the Fe-based amorphous coatings were investigated. The results demonstrated that a macroscopic viscous flow behavior was obtained at low peak loads, which led to a larger creep strain rate sensitivity m. At high loading rates, the accumulation of free volume led to an increase in the shear deformation zone and a more uniform plastic rheology. It indicated that at higher loading rates, the amorphous coating had higher m values under steady-state creep.

In this study, novel glassy Co-Fe-Ta-Si-C alloys were prepared by mechanical alloying, (MA) and the influence of annealing treatment and substitution of Fe for Co on glass-forming ability (GFA), thermal stability and magnetic properties were investigated. Quantitative X-ray diffraction (XRD) analysis by the Rietveld method showed that the new Co50Fe25Ta5Si5C15 powders have an enhanced glass formation rate, especially during the early milling stages compared to the Fe-free Co75Ta5Si5C15 alloy. In good agreement with the XRD measurements, the calculated PHSS thermodynamic parameter revealed that that the GFA is notably increased for the new powder. Thermal analysis demonstrated a high thermal stability and a rather wide supercooled liquid region (SLR) of 51 K for the Co75Fe25Ta5Si5C15 glassy alloy. The milling process and subsequent annealing treatment remarkably improved the soft magnetic behavior of the Co75Fe25Ta5Si5C15 powder. The results indicated that the Co75Fe25Ta5Si5C15 glass exhibits a slightly higher coercivity (Hc) and a notably larger saturation magnetization (Ms) than the Co75Ta5Si5C15 alloy in the as-milled state. Furthermore, in the relaxed state, the new alloy possesses a markedly lower Hc of 0.96 kA/m and a higher Ms of 108 Am2/kg than Co75Ta5Si5C15 and large number of ssoft magnetic glasy powders prepared before. The influence of milling time and annealing temperature on the evolution of the magnetic properties were discussed in detail.

Achieving effective load transfer at the interface between carbon nanotubes (CNTs) and aluminum (Al) is a crucial issue for fabricating high-performance CNTs reinforced Al matrix (CNT/Al) composites. In this work, CNT/Al composites with different Ti additions and the compared materials were prepared by powder metallurgy. Micro-sized Ti particles in which CNTs are well-dispersed firstly circumvent the difficulty of CNT dispersion, and subsequently act as nucleation site for sandwiched TiAl3 layers that lock the dispersed CNTs in place and improve the CNT-Al interface bonding. Additionally, Ti addition not only allows modification of the dispersed CNTs but also enhances the strength of the composites by enhancing the load-bearing capacity of the CNTs through in situ formation of nano-sized titanium carbide (TiC). This work provides a new approach to improve the load transfer efficiency of CNTs by strengthening the interface bonding for fabricating high strength CNT/Al composites.

Eutectic high entropy composites (EHECs) are novel class of material with excellent combination of strength and ductility, thus having a large potential for industrial applications. However, the mechanisms operating behind the trade-off between strength and ductility has not been investigated in detail. In this work, the influence of severe straining imposed by high-pressure torsion (HPT) was evaluated for a series of CoCrFeNiNbx alloys with varying Nb content (x molar ratio), hypoeutectic (x = 0.25), eutectic (x = 0.65) and hypereutectic (x = 0.80) compositions. Strain rate sensitivity (m) and activation volume (V*) calculations were calculated from constant strain rate (CSR) nanoindentation experiments, revealing that dislocation interaction with lamellae interfaces become the rate-limiting step for the strength-ductility trade-off in these EHECs.

Eutectic high entropy composites (EHECs) can exhibit an excellent combination of high strength and high ductility; however, the mechanisms responsible for the strength-ductility trade-off remain unpredicted. The influence of strain rate ( e ˙ ) on the severe deformation imposed by high-pressure torsion (HPT) was used to evaluate the deformation mechanisms for a series of CoCrFeNiNbx (x molar ratio, 0 ≤ x ≤ 0.80) EHECs. Systematic and detailed micro-/nanoindentation investigations were performed and the results suggest that strain hardening (Taylor hardening) and grain-boundary strengthening (H-P strengthening) are the predominant strengthening mechanisms. Nanoindentation at different loading conditions (varying e ˙ ) revealed that the measured hardness in the eutectic regime increases gradually because of dislocation-lamellae-interface interactions. Based on the deformation mechanisms operating at different strain rates ( e ˙ ), the density of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs), determined by the Nix-Gao approach, are used to explain the strain hardening phenomena. The results reveal that a large volume fraction of lamellae-interfaces accommodate more dislocations upon straining these EHECs. Lamellae-interface GNDs ( ρ G G ) are activated at higher strain rates and can be effectively stored, thereby improving the global strain and strain hardening.

Investigation of the microstructural features and mechanical properties of the Al86Cu7Si7 nanostructure-dendrite composite revealed that the high yield strength of 615 MPa and its reasonable plasticity of ~ 20% at room temperature mainly originate from the evolution of dislocations in the micron-scale dendrites together with the cooperative deformation action of shear band and interfacial sliding throughout the whole volume of the material. Especially, shear band-induced rotation of dendrites was found to be an important deformation mechanism. Here, we sequentially elucidate the deformation behavior using atomic force microscopy, nanoindentation, and scanning electron microscopy to determine the surface topography of the deformed alloy.

A heat treatable TiB2/Al-3.5Cu-1.5Mg-1Si composite was successfully fabricated by selective laser melting (SLM). The results show that the Q phase forms in the matrix of the as-fabricated TiB2/Al-3.5Cu-1.5Mg-1Si composite. After T6 heat treatment, the Q phase disappears and the AlxMny, Mg2Si and Al2Cu(Mg) phases are formed. The same results can be observed before and after heat treatment in the unreinforced Al-Cu-Mg-Si alloy. EBSD and TEM analyses indicate that the addition of the TiB2 particles results in a remarkable grain refinement, leading to enhanced strength of the TiB2/Al-Cu-Mg-Si composite in comparison to the unreinforced Al-Cu-Mg-Si alloy in both the as-fabricated and heat-treated conditions. Both grain refinement and Orowan strengthening contribute to the high strength of the heat treated TiB2/Al-Cu-Mg-Si composite.

In this work, we investigated the effect of boron addition on glass-forming ability and mechanical properties of Co-Cr-Mo-C alloys. The starting alloy was (Co0.65Cr0.13Mo0.22)80C20 derived from the Co65Cr13Mo22 ternary eutectic composition. This alloy is almost fully crystalline and exhibits brittle mechanical properties. Replacing carbon with boron allows obtaining bulk metallic glasses (BMGs) and bulk metallic glass composites. The designed alloys show very high strength (∼4100 MPa), wide super-cooled liquid region (∼100 K) and large endothermic enthalpy of the supercooled liquid region (∼35 J/g), indicating high thermal stability. The electronegativity difference and supercooled liquid region of the present alloys are comparable to rare-earth elements containing BMGs. The physical properties of the present alloys corresponded well with the alloy design strategy based on the unified parameter using the glass transition temperature, fracture strength, and molar volume. Furthermore, we propose the optimum compositional condition for glass formation by controlling the carbon-to-boron ratio and the influence of carbon on phase formation in this alloy system is discussed.

The effect of chemical composition on microstructure and mechanical properties of heavily alloyed beta-titanium Ti-Nb(V)-Cu-Co-Al alloys was studied. The alloys were fabricated by casting into a water-cooled copper crucible employing relatively high cooling rates. The microstructure of these alloys consists of primary micrometer-sized bcc-structured (bcc – body centered cubic) dendrites surrounded by a minor amount of intermetallic phases. The morphology and volume fraction of the intermetallic phases are strongly affected by the alloys’ chemical composition. Particularly, the solubility of Cu and Co in the bcc dendrites of Ti-V-Cu-Co-Al is lower compared to that of Ti-Nb-Cu-Co-Al leading to a higher volume fraction of the intermetallic phase in the latter alloy. The high mechanical strength of the Ti-Nb(V)-Cu-Co-Al alloys (yield strength up to 1430 MPa) is mainly attributed to their multiphase nature and solid solution hardening of the supersaturated bcc-structured dendrites. Moreover, the large compressive plastic deformability supported by pronounced strain-hardening reaches several tens of percent. The alloys exhibit a significant strength asymmetry between compressive and tensile loadings, namely, they are weak and brittle under tensile loading. The tensile brittleness is associated with the lattice distortion in the bcc-structured dendrites as well as crack initiation at the interdendritic precipitates.

B2 CuZr exhibits a stress-induced martensitic transformation from a B2 to a B19 structure during tensile deformation, and that is believed to be the reason for the pronounced ductility and work hardening of CuZr-based bulk metallic glass (BMG) composites. In order to gain a better insight into the structural transformation of CuZr precipitates, the phase stabilities as well as the anisotropic elastic and thermodynamic properties of both B2 cubic (CsCl-type) CuZr and B19 (β-AuCd-type) CuZr structures under hydrostatic pressures up to 30 GPa are investigated by first principles calculations. Moreover, the effects of the hybridization between the electronic orbitals of the constituent atoms on the variation of the elastic properties of the B2 CuZr structure are discussed. The results show that the Young's modulus (E), bulk modulus (B) and shear modulus (G) increase significantly with increasing pressure. Noticeably, for pressures up to 30 GPa, the B2 CuZr structure shows a stronger anisotropy along the (1 1 0) plane than for the (1 0 0) plane. Under high pressure, the stability of both B2 CuZr and B19 CuZr phases decrease while the Helmholtz free energy (F) and the formation enthalpy (H) of B2 CuZr increase monotonically. However, the different stability decreasing trajectories of both B2 and B19 CuZr phases result in a high propensity of martensitic transformation from the B2 to B19 structure. Our results may have implications for better understanding the phase stability of B2 and B19 CuZr structures under high pressure and can shed light on the structure-property relationships of BMG composites reinforced with shape-memory crystals.

Positron annihilation spectroscopy and differential scanning calorimetry were used to evaluate the changes of the atomic configurations in Zr-based metallic glasses (MGs) due to alloying and plastic deformation. The correlation between the atomic configurations of MGs and the amorphous-to-icosahedral phase transition due to heating was investigated. The results indicate that the free volume frozen in the as-cast Zr60Al15Ni25, Zr65Al7.5Ni10Cu17.5, and Zr65Al7.5Ni10Cu17.5Ag5 MGs substantially decreases in sequence. More excess free volume is introduced in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling. The annihilation of free volume due to alloying considerably stabilizes the icosahedral structure of MGs, which enhances the nucleation and growth of quasicrystals upon heating. However, the nucleation and growth of quasicrystals are considerably suppressed in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling, during which the more introduced excess free volume results in substantial destruction of short-range order with 5-fold symmetry. The present work further provides direct evidence for the prevalence of icosahedral short-range order in MGs.

Systematic microstructural investigations of a series of Al81Ni13-xCuxSi6 alloys with x = 0, 3, 5, 8, and 10 at.% revealed that addition of Cu leads to a change of the primary intermetallic compound from Al3Ni to Al3Ni2. Moreover, Cu addition induces a multi-phase composite microstructure consisting of dual primary phases (Al3Ni2 + α-Al) and a eutectic matrix. The eutectic matrix is transformed from (α-Al+Si)eutectic to (α-Al+Al2Cu+Si)eutectic. In course of the microstructural evolution, the mechanical properties are enhanced, and the Al81Ni5Cu8Si6 alloy exhibits optimized room temperature mechanical properties such as an increased yield strength of ∼600 MPa and a remarkably improved fracture strain of ∼15% due to similar lattice parameters and crystal structures of the constituent phases. The large macroscopic plastic strain is attributed to a combination of impeded crack growth and wavy propagation of shear bands in the intermetallic compounds.

In the present work, the influence of a minor Hf addition on the atomic structure, crystallization behavior, thermal stability and magnetic properties of a Co-based metallic glass was studied. Thermal analysis indicates that the thermal stability of new glassy ribbons microalloyed with 2.5 at.% Hf is notably enhanced through increasing the incubation time prior to devitrification and enlarging the width of the supercooled liquid region from 72 K to 96 K. Magnetic studies reveal that the new glass exhibits an excellent soft magnetic behavior, i.e., a very low coercivity of 0.26 A/m in the relaxed state, and a comparable saturation magnetization as the Hf-free ribbon. Structural relaxation of the Hf-containing alloy upon isothermal annealing below the glass transition temperature, Tg, was investigated by differential scanning calorimetry (DSC) and high-energy synchrotron X-ray diffraction (XRD). The evolution of the recovered enthalpy with annealing time can be expressed by the Kohlrausch-Williams-Watts (KWW) exponential function with a Kohlrausch exponent of 0.88, indicating a broad spectrum of relaxation times. Analysis of the reduced pair correlation functions, G(r), reveals volume shrinkage upon annealing caused by elimination of liquid-like sites including free-volume and anti-free-volume according to the shift in the positions of the G(r) maxima in the medium-range scale. The influence of structural relaxation on the variation of the Curie temperature and the coercivity of the new Hf-microalloyed glassy ribbon is discussed. A faster evolution of the Curie temperature with annealing time compared to the coercivity indicates a preferential dependence of the former on the chemical short-range order (SRO).

Ti-based metallic glass matrix composites (MGMCs) with a composition of Ti50Zr20V10Cu5Be15 (atomic percent, at. %) exhibit excellent tensile ductility and distinct work-hardening capability. A dislocation pile-up model (DPM) has been established to elaborate the dislocation motion near the yield point and to theoretically derive a linear Hall-Petch-like relationship between the yield strength, σ, and the inverse square root of the diameter of dendrite arms, d−1/2. The materials constant, k, in the present Hall-Petch-like relationship can be calculated on the basis of the pile-up model, and is very close to the experimental value. The hardness variation in the dendrites and the strengthening effect from unloading-reloading tests prove the reasonability of the DPM during tension. The Hall-Petch-like relationship is verified for a variety of MGMCs, whose plastic deformation is only dominated by dislocation motion. Mean-field theory (MFT) has been first utilized to build a relationship between the critical diameter of dendrites, dc, and the composition in MGMCs with the similar atomic percentages of low solubility elements. By tuning the composition, one can universally scale the Hall-Petch-like relationship, and accurately predict the yield strength of such in-situ MGMCs.

Nano-/ultrafine-grained carbon nanotube-reinforced titanium (CNT/Ti) composites were synthesized by ball milling and high pressure torsion (HPT) at room temperature. The effects of the number of HTP rotations and the weight fraction of CNTs on the microstructure, hardness and tensile properties of the CNT/Ti composites were investigated. Transmission electron microscopy (TEM) revealed that elongated grains with an average length of 100–250 nm parallel to the compression axis of HPT and a thickness of 10–25 nm are formed in CNT/Ti composites when CNT contents ranging from 0.3 wt% to 1.0 wt%. With increasing CNT contents, the grain size of Ti is refined, and the microhardness and tensile properties of the composites increase. Evaluating the mechanical properties of the CNT/Ti composites with 0.7 wt% CNTs after 20 rotations indicates a high tensile strength of 872 ± 5 MPa. Cs-corrected high resolution TEM of the interfaces between Ti and the CNTs after HPT reveals a gradual transition from the lattice planes of hexagonal Ti to those of the CNTs. The strengthening mechanisms are discussed from the aspects of matrix grain refinement, distribution of the CNTs and the CNT-Ti interfaces obtained during ball milling and HPT processing.

The appearance/disappearance of glass transition (GT) and supercooled liquid (SL) region was found to be affected for Zr-Al-(Ni, Cu, Co) glassy ribbons by changing the ejection temperature (Te) in the range from liquid temperature (Tl)+200 K (LT) to Tl+700 K (HT). The Te at which the disappearance occurs lies around 600–700 K above Tl. The oxygen contents increase from 240 to 550 ppm for LT samples to 990–4440 ppm for HT samples, but their contents are lower than those (4000–5000 ppm) for the samples with GT and SL region. The AES analyses show that the oxygen was segregated to the thin surface region. As compared with LT samples, HT samples exhibit higher hardness and glass transition temperature (Tg), while keep good bending ductility. Structure analyses using high energy X-ray diffraction and MD simulations show the change to looser atomic configurations for HT sample. The disappearance of GT for HT samples reflects the change of liquid structure from icosahedral-like medium-range ordered structure to a less-coordinated atomic structure. The GT appears again by ejection after the lowering of Te from Tl+700 K to Tl+300 K. The Te dependence of GT together with the changes in Tg and hardness is encouraging for novel material science/engineering field through the control of liquid structures.