In this study, the deformation behavior of a metallic glass under a cylindrical indenter is elucidated with in situ observations. The experimental observations for various indenter radii provide information on both macroscopic and microscopic details of the deformation. The deformation zones developed under indenters with different radii were found to be self-similar, in agreement with the predictions of the cavity expansion model. It will be shown that, the evolution of shear bands under the indenter resembles the solutions obtained from the slip line analysis. Finally, full field strain measurements can provide the detailed information regarding the temporal and the spatial evolution of the shear bands during the course of deformation.

The nanoindentation of a columnar grain boundary (GB) network in nanocrystalline Al has been examined by atomistic simulation. The goal of this study was to gain fundamental understanding on the relationship between structure evolution at GBs and incipient plasticity for indenter tips significantly larger than the average grain size. The nanoindentation simulations were performed by quasicontinuum method at zero temperature. A GB network made of vicinal and high-angle <110> tilt GBs was produced by generating randomly-oriented 5-nm grains at the surface of a 200 nm-thick film of Al. The major findings of this investigation are that (1) nanocrystalline GB networks profoundly impact on the nanoindentation response and cause significant softening effects at the tip/surface interface; (2) GB movement and deformation twins are found to be the predominant deformation modes in columnar Al, in association with shear band formation by GB sliding and intragranular slip, and crystal growth by grain rotation and coalescence; and (3) the cooperative processes during plastic deformation are dictated by the atomic-level redistribution of principal shear stresses in the material.

Consolidation of SiC nanopowder with stacking disordered structure was accelerated by milling with the AlN as the additive. SiC powders without the additive was sintered at 1900°C to a density of 99%. The grain size of the sintered material was approximately 500 nm. On the other hand, with AlN as additive, the sintering temperature to reach a density of 98% was reduced to 1700°C by the addition of 1.0 mol% AlN. The grain size of this material was less than 100 nm. The effect of AlN addition on SiC sintering with disorder-order transformation was evaluated by shrinkage profile, XRD analysis, and TEM observation.

From the reported experience, primary nanocrystallization in amorphous Al alloys involves transient kinetic behavior that is sensitive to the initial as-quenched structural arrangements. In order to examine the precursor effects, systematic studies outlining the evolving growth kinetics of primary aluminum nanocrystals (nc) during pre-crystallization annealing treatments, and investigations on the microstructure refining effect of specific alloying substitutions represent new approaches for an analysis of primary phase crystallization kinetics. In Al88Ni8Sm4 melt-spun ribbon (MSR), incremental substitutions of Cu for Ni (0 − 1at%) affect the thermal stability of the material (crystallization onset shifts to lower temperature) and refine the size of the primary phase nanocrystals. However, continuous heating calorimetry measurements indicate that the primary crystallization enthalpy remains approximately constant with increased Cu substitution. From a structural analysis standpoint, quantitative microstructure examinations applied in parallel with calorimetry measurements have been employed to characterize the as-quenched volume of MSR samples. The increased primary Al nanocrystal particle density with Cu substitution reflects the modification of local structural arrangements, necessitating an understanding of the local structure of the as-quenched sample in order to develop a description of primary phase nanocrystal growth kinetics.

Using a scalable electrodeposition process, nanocrystalline Ni-Cr alloy coatings have been produced on copper and steel substrates, and the roles of various processing variables on the resulting coating structure and properties have been investigated. The possibility of producing composite coatings of wear resistant nanostructured Ni-Cr alloys containing graphite or MoS2 particles has also been studied; the co-deposition of solid lubricant particles improved the tribological performance of the coatings in ball-on-disk testing. The combination of a hard material such as nanocrystalline Ni-Cr alloy with a solid lubricant has a great potential for new surface modification developments.

Diamond like carbon (DLC) coatings have attracted great attention for use in various applications in automobile industry and machinery because they have excellent properties such as low friction coefficient and ultra high strength. The low friction coefficient of DLC comes from anti-adhesion with other materials, smooth surface, lubrication of graphite structure at the contacting point of films, and the hydrogen content of the films. Many researches have been focused on the microstructure effects on the tribological properties of DLC films but few have been reported on the effect of hydrogen content. In this study, the effect of hydrogen content on the friction coefficient of DLC films has been investigated.

DLC films have been deposited on D2 steel by plasma enhanced CVD (Pulsed DC PECVD) method with different precursor gas of C2H2 and CH4 and different gas pressure. The effects of gas composition on the hydrogen content in DLC films and the resulting tribological properties have been reviewed. Si interlayer was deposited on D2 to improve adhesion of DLC on steel substrates. The characteristics of microstructure were evaluated by Raman spectroscope and composition was measured by RBS and EDS. The tribological behaviors of DLC films were investigated using ball on disk tribometer. The hardness of films was examined by nano-indenter. The failure mechanism of DLC deposited on steel substrates was examined using optical microscope and SEM/EDS. The results showed that the friction coefficient of DLC films deposited with C2H2 was 0.06 and that of the film with CH4 was 0.15. The friction coefficient improved with decreasing hydrogen content in DLC films.

This work reports on the densification of iron nanoparticles heated at moderate rates without applied pressure as observed by TEM imaging, gas adsorption pore size measurement, and X-ray diffraction. Despite a low packing density, the small pore size is amenable to significant densification by pressureless sintering. Carbon residues from the stabilizing ligands affect both the composition and processing of the particles. This approach is amenable to deposition on non-planar or fragile substrates. Additionally, large areas can be processed in parallel.

We report the equilibrium phase assemblage of two bulk-metallic-glass-forming alloys, Hf44.5Ti5Cu27Ni13.5Al10 and Hf44.5Nb5Cu27Ni13.5Al10. Using thermal analysis, scanning electron microscopy, and x-ray microanalysis, we examined the phase equilibria of the major components - Hf, Cu, and Ni. We then examined the effect of additions or substitutions of Nb, Ti, and Al on equilibrium phase assemblage and melting behavior.

Molecular dynamics simulations are used to study grain boundary sliding in pure and doped Cu bicrystals using both Lennard-Jones and Embedded-Atom Method potentials. Two tilt [100] grain boundaries are considered: the coincident site lattice Σ5 interface and a random high angle interface. Shear stress between 0.69 GPa and 1.61 GPa was applied to the bicrystals for a duration of 10 ps at ambient temperature (300K) and high temperature (800K). For the pure bicrystals, the sliding of the Σ5 interface with respect to the random interface was lower at 800K and higher at 300K. For the doped bicrystals, interstitial dopant atoms and substitutional dopant atoms with larger atomic radius were effective in retarding grain boundary sliding. These simulations will aid further work to determine how segregated dopant atoms alter the tensile properties of nanocrystalline metals.

Glass-forming Zr47Cu31Al13Ni9 (in atomic percent) films of various thicknesses were deposited on the C-2000 Ni-based alloy substrate by magnetron sputtering. Four-point-bending fatigue tests were conducted on the above system with the coated surface on the tensile side. It has been found that both fatigue life and fatigue-endurance limit can be considerably improved, while the degree of fatigue resistance enhancement depends on the maximum applied stress and the film thickness. Mechanisms of fatigue-resistance enhancements of the coated Ni-based alloy are discussed from the following aspects: reduction of surface roughness by the thin-film coating, good adhesion between thin film and substrate, development of residual compressive stress, and excellent ductility of glass-forming thin film (which would be otherwise brittle in bulk form). Of particular interest, we examine the interaction of substrate slip bands and the thin film ductile property, which would delay fatigue crack initiation process and thus extend the fatigue life.

The large bulk glassy [(Fe0.5Co0.5)0.75B0.20Si0.05]96Nb4 alloy specimens with the diameters up to 7.7 mm have been prepared by water quenching the melt immersed in the molten flux of B2O3. The maximum diameter of the obtained specimens is approximately 1.5 times as large as the pre-vious result for copper mold casting should be cooled at the higher rate than the of water quenching. The flux melting improves the glass-forming ability by the elimination of oxides and other inclusion in the molten metal which act as heterogeneous nucleation sites for crystallization.

We present an experimental evidence of concentric ring pattern formation in a metal. They form during a single electro-explosion event in a needle-plate configuration. By measuring the dynamic progression of current during the explosion, we discuss evolution of these ring structures. Atomic force microscopy provides details of nanostructures that constitute these rings. From fluctuations in the plasma current recorded during the process, micro and nanostructure evolution is seen to be a self-organization process.

The conventional concept of alloy design is based on the principal metallic element (>40 at.%); therefore, it is novel and challenging for a new alloy design to synthesize several (5∼7) principal elements (each <35 at.%), i.e. equal or near-equal molar ratio. With the design concept of multi-principal-element alloy, this paper will present the mechanical behaviors and workability of this alloy, Fe0.71Cr1.48Al0.38Ni1.42Co in molar ratio. The alloy possessed the simple FCC crystal structure even though these elements come from three categories of crystalline structures, FCC, BCC and HCP. The hardness can also reach 367(Hv) after precipitated treatment at 700°C for 24 Hr.. Meanwhile, the ultimate tensile strength (UTS) of Fe0.71Cr1.48Al0.38Ni1.42Co can be elevated to 1112 MPa as almost triple as the original sample, and the elongation rate can be kept at 20%.

In the present work we have intentionally introduced significant amount of oxygen to Zr- based alloys. Samples were prepared either by high energy ball milling of the elemental powders and single phase α-ZrO0.43 at the appropriate stoichiometry, or by melting in an Zr-gettered arc melting facility, in both cases under purified argon atmosphere. The effect of small amounts of oxygen (∼1 at. %) on the amorphization process and the thermal stability of mechanically alloyed Zr54Cu19Ni8Al8Si5Ti5O1 powders and arc melted bulk samples was studied by X-ray diffraction and differential scanning calorimetry. It was found that the introduction of oxygen to the alloy composition does not inhibit the amorphization but enhances greatly the thermal stability of the mechanically alloyed amorphous powders. Compared to samples without oxygen prepared either by arc melting or mechanical alloying, samples with oxygen show an increase of the supercooled liquid region from ΔTx−g=Tx−Tg=117 °C to 141 °C where Tx is the crystallization and Tg the glass transition temperature. The glass transition for the mechanically alloyed samples (Tgma) remains unaffected at 336 °C.

The structural/mechanical behavior of zirconium-based (Vitreloy106) bulk metallic glass reinforced with tungsten particles is evaluated using elastic and plastic property measurements via static and dynamic compression tests performed on rod shaped samples. Anvil-on-rod impact tests combined with high-speed digital photography and velocity interferometry are used to obtain qualitative and quantitative information about the transient deformation and failure response of the composites. The deformation and failure mechanisms of recovered impacted specimens are also characterized and correlated with their structure and tungsten phase distribution. The results of these experiments and initial attempts at validating constitutive equations based on homogeneous/inhomogeneous plastic/viscous flow in glassy and glassy-crystalline composites will be presented.

The availability of high-energy synchrotron beamlines has made it possible to study the development of elastic strain in crystalline phases in metallic-glass-matrix composites in situ during loading, and to measure elastic strain in amorphous materials as well. In this paper, we discuss experimental techniques and data analysis for these measurements and give examples. We show that the strain in both the amorphous and crystalline phases in a metallic-glass-matrix composite can be extracted from a single scattering pattern.

The Dynamic Compacting (DC) method is promising method to produce considerable-size nonporous wares. The phenomenon is based on the impact of shock wave on the initial powders of amorphous alloys. Every time when the shock wave propagates through the bulk of substance then the temperature rises substantially. Therefore there is a need of study of the DC’s effect on the structure and properties of the amorphous alloys. The results of the thermal analysis (in particular, Differential Scanning Calorimetry) of the samples of the soft magnetic alloys are presented in the report. These results concern with amorphous alloys of 5BDSR, GM414, 10NSR trademarks before DC and after DC, respectively. It is shown there is single low-temperature endothermic peak (near 300C) and there are several high temperature exothermic peaks (near 540C, 650C, and 700C). The first peak is related to glass-transition, the following peaks are related to formation of nano-crystalline phases. It was proved by XRD analysis data. The optimal regimes of the thermal processing of final wares were chosen on the base of thermal- and XRD-analysis. The study of the effects of these regimes on the properties (magnetic conductivity, specific losses etc.) of the circular magnetic conductors was executed. In particular, thermal- as well as thermo-magnetic processing of magnetic conductors based on 5BDSR amorphous alloy (after DC) essentially improves their magnetic properties. For example, magnetic conductivity fÝ increases approximately by factor 17 with respect to the magnitude before DC.

Helical structures can be classified in accordance with the orientation of its cross-section with respect to the normal or binormal vectors. We investigate the geometric features of several nanosprings verifying the non-existence of normal nanohelices. In this work, using the VLS growth model, we explain not only the absence of normal nanosprings but also the growing process of binormal nanosprings. The dynamical stability of crystalline ZnO binormal nanohelices is also addressed.

Atom probe tomography is used to observe the solute distribution in electrodeposited nanocrystalline Ni-W alloys with three different grain sizes (3, 10, and 20 nm) and the results are compared with atomistic computer simulations. The presence of grain boundary segregation is confirmed by detailed analysis of composition fluctuations in both experimental and simulated structures, and its extent quantified by a frequency distribution analysis. In contrast to other nanocrystalline alloys, the present Ni-W alloys exhibit only a subtle amount of solute segregation to the intergranular regions. This finding is consistent with quantitative predictions for these alloys based upon a thermodynamic model of grain boundary segregation.

Understanding the mechanical behavior of nanoparticles has become a key factor for the success of many engineering applications. Classically, for polycrystalline materials one would expect an increase in the yield strength for smaller grain sizes according to the empirical Hall-Petch equation. However, at the nanoscale, this mechanism seems to break down. Despite the number of interesting papers published on this topic, controversy persists and consensus is still lacking. While this discussion is of great interest for polycrystalline nanoparticles, contemporary models for strengthening are inappropriate for single-crystal nanoparticles, which, altogether, pose a very different problem: the absence of grain boundaries to inhibit dislocations. In this context, we present a new model wherein the change in Gibbs Free Energy of an edge dislocation in a single-crystal particle provides a driving force for dislocation motion. These results show that dislocations become unstable and are spontaneously ejected from the particles below a certain critical size.