Xiongjun Liu

Glass formation mechanism of minor yttrium addition in CuZrAl alloys

Effects of yttrium additions on glass-forming ability of the model system (Cu0.48Zr0.48Al0.04)100−xYx (x=0–7at.%) were studied in detail by using a “perturbation theory” approach. Introduction of the atomic-level strain energy into the driving force for the crystal nucleation well explained the beneficial effects of yttrium additions. It was found that the atomic-level strain energy is related closely to the atomic packing efficiency of the precipitated crystals and less yttrium amount is needed to suppress the precipitation of crystal phase with a higher atomic packing efficiency, which is consistent with the experimental observations.

Molecular dynamic simulations and atomic structures of amorphous materials

A long-standing issue of using molecular dynamics (MD) to simulate local atomic structures in nonequilibrium metals and alloys is the huge difference in cooling rates used in experimental studies and theoretical calculations. In this study, a unique approach was introduced to correct the fast time steps involved in the MD calculations. This approach has demonstrated various medium-range ordered zones with imperfect ordered packing, which are verified experimentally by high-resolution transmission electron microscopy and its selected simulation imaging of Zr2Ni glass.

Microstructural Control via Copious Nucleation Manipulated by In Situ Formed Nucleants: Large-Sized and Ductile Metallic Glass Composites

A novel strategy to control the precipitation behavior of the austenitic phase, and to obtain large-sized, transformation-induced, plasticity-reinforced bulk metallic glass matrix composites, with good tensile properties, is proposed. By inducing heterogeneous nucleation of the transformable reinforcement via potent nucleants formed in situ, the characteristics of the austenitic phase are well manipulated.

Thermoelectric performance of PbSnTeSe high-entropy alloys

ABSTRACT In our study, we designed the PbSnTeSe high-entropy alloy (HEA) and investigated its microstructure and thermoelectric properties. It was found that the PbSnTeSe HEA has a simple face-centered cubic structure and possesses quite low lattice thermal conductivity at low temperatures, which could be ascribed to the strong phonon scattering due to its severe lattice-distortion. Minor additions of La not only enhanced both Seebeck coefficient and electrical conductivity at high temperatures, but also suppressed the bipolar effect to some degree. Our results indicate that the HEA concept could be applied for developing promising thermoelectric materials, which merits further investigation. GRAPHICAL ABSTRACT IMPACT STATEMENT The high-entropy alloy-design concept was employed to develop novel thermoelectric materials. Our findings indicate that this strategy effectively reduced the lattice thermal conductivity, which have important implications for the field.

Ageing behaviour of spray-deposited 18Ni(250) maraging steel + 10 vol.% Al2O3 particulate-reinforced metal matrix composites

Abstract The ageing behaviour of spray-deposited 18Ni(250) maraging steel+10 vol.% Al2O3 particulate-reinforced metal matrix composites (MMCs) was investigated by microhardness and nanoindentation techniques. Compared to the control steel, the composite material showed an accelerated ageing kinetics. Nanoindentation investigation revealed observable gradient distribution of elastic modulus and hardness around Al2O3 particulates inside the plastic zone in the matrix. Around a reinforcement particulate, the gradient distribution of the properties is steeper at the sharp corner than that at the flat interface. Theoretical Avrami-type precipitation model was successfully modified to calculate the distribution of precipitates around an Al2O3 particulate. The calculation results showed a gradient distribution of precipitates similar to the experimentally measured distribution of elastic modulus and hardness, which can attributed to the gradient distribution of dislocations within the plastic zones around the reinforcements.

Crystallization Kinetics of Zr65Ni25Ti10 Metallic Glass Alloy

The crystallization reaction of Zr65Ni25Ti10 (at. %) metallic glass was studied by using differential scanning calorimetry (DSC) at constant heating rate. Two distinct exothermic peaks were observed from the continuous heating DSC curves, implying the crystallization process undergoes two different stages. The crystallization kinetic parameters, including activation energy (E), Avrami exponent (n) and frequency factor (K0), were determined with non-isothermal analysis method based on the DSC data. The values of E are 267.353 KJ/mol and 224.293 KJ/mol, n 4.0±0.1 and 6.8±0.1, K0 4.4±0.05E+20 and 2.0±0.08E+15, for the first and second crystallization stage, respectively. The results suggest that the crystallization mechanism is governed dominantly by interface controlled growth with constant nucleation rate for the first crystallization stage and with increasing nucleation rate for the second stage.

Effects of Nitrogen on the Glass Formation and Mechanical Properties of a Ti-Based Metallic Glass

Effects of nitrogen addition on glass formation and mechanical properties of the Ti42.5Cu40Zr10Ni5Sn2.5 metallic glass were systematically investigated. It was found that a small amount of nitrogen addition facilitated the glass formation by suppressing formation of the competing eutectic structure. Unlike large atomic size elements such as Hf and Pd which usually deteriorate specific strength, nitrogen can also increase the specific strength of the current Ti-based BMGs. The results are not only helpful for understanding glass-forming ability in general, but also useful in developing cost-effective, high-performance Ti-based bulk metallic glasses with enhanced glass-forming ability.

High-performance hybrid electrode decorated by well-aligned nanograss arrays for glucose sensing

The worldwide boost in glucose related diseases such as diabetics over the last decade leads to an overwhelming demand for development of advanced electrochemical glucose sensors with high sensitivity, fast response and excellent selectivity. Herein we report a novel freestanding microelectrode comprising well-aligned Cu(OH)2 nanograss arrays and uniform nanoporous copper (NPC) substrate. Such a cost-effective hierarchical hybrid structure entails a unique combination of good conductivity of NPC and high electrocatalytic activity of Cu(OH)2. As a result, the glucose sensor based on the hybrid nanostructure exhibits extraordinary performance towards the oxidation of glucose with a high sensitivity of ~2.09mAcm-2mM-1, wide linear range of 0.2-9mM, low detection limit of 197nM, fast response time of less than 1s and excellent selectivity. The current work not only provides novel hybrid materials with great potential to be commercialized in blood glucose sensing, but also has important implications for designing enhanced nanostructured electrocatalysts for engineering applications in general.

Influences of Au ion radiation on microstructure and surface-enhanced Raman scattering of nanoporous copper

In this work, effects of Au ion irradiation on microstructure and surface-enhanced Raman scattering (SERS) performance of nanoporous copper (NPC) were investigated. It is found that the microstructure of NPC could be tailored by the ion irradiation dose, i.e., the pore size decreases while the ligament size significantly coarsens with the increase of the irradiation dose. In addition, the SERS enhancement for rhodamine 6G molecules was improved by Au ions irradiation at an appropriate dose. The underlying mechanism of the increase of SERS enhancement resulted from ion irradiation was discussed. Our findings could provide a new way to tune nanoporosity of nanoporous metals and improve their SERS performance.

Ion Irradiation-Enhanced Raman Scattering on Nanoporous Copper

Nanoporous copper (NPC) is the potential affordable surface-enhanced Raman scattering (SERS) substrate in practical use, although restricted by a relatively small enhancement factor. In this report, Cu ion irradiation is applied to effectively increase the enhancement factor of NPC. Two levels of surface roughness in NPC after ion irradiation are proposed to account for the improved SERS effect by careful characterization of microstructures. This study provides a new strategy to acquire a higher Raman enhancement factor in NPC, which perhaps can be extended to other SERS substrate systems.