Showing papers by "Daniel B. Miracle published in 2004"

A structural model for metallic glasses

Abstract: Despite the intense interest in metallic glasses for a variety of engineering applications, many details of their structure remain a mystery. Here, we present the first compelling atomic structural model for metallic glasses. This structural model is based on a new sphere-packing scheme—the dense packing of atomic clusters. Random positioning of solvent atoms and medium-range atomic order of solute atoms are combined to reproduce diffraction data successfully over radial distances up to ∼1 nm. Although metallic glasses can have any number of chemically distinct solute species, this model shows that they contain no more than three topologically distinct solutes and that these solutes have specific and predictable sizes relative to the solvent atoms. Finally, this model includes defects that provide richness to the structural description of metallic glasses. The model accurately predicts the number of solute atoms in the first coordination shell of a typical solvent atom, and provides a remarkable ability to predict metallic-glass compositions accurately for a wide range of simple and complex alloys.

A Structural Model for Metallic Glasses

Abstract: Despite the intense interest in metallic glasses for a variety of engineering applications, many details of their structure remain a mystery. Here, we present the first compelling atomic structural model for metallic glasses. This structural model is based on a new sphere-packing scheme—the dense packing of atomic clusters. Random positioning of solvent atoms and medium-range atomic order of solute atoms are combined to reproduce diffraction data successfully over radial distances up to ∼1 nm. Although metallic glasses can have any number of chemically distinct solute species, this model shows that they contain no more than three topologically distinct solutes and that these solutes have specific and predictable sizes relative to the solvent atoms. Finally, this model includes defects that provide richness to the structural description of metallic glasses. The model accurately predicts the number of solute atoms in the first coordination shell of a typical solvent atom, and provides a remarkable ability to predict metallic-glass compositions accurately for

The effect of matrix to reinforcement particle size ratio (PSR) on the microstructure and mechanical properties of a P/M processed AlCuMn/SiCp MMC

Abstract: Matrix to reinforcement particle size ratio (PSR) is the main factor governing the homogeneity of the reinforcement particle distribution in composites manufactured by the powder metallurgy route. To improve the homogeneity of the distribution, reinforcements with larger average particle size should be used. At the same time, increasing the reinforcement particle size leads to worsening of the mechanical properties due to lower work hardening and higher damage accumulation rates. It is therefore important to optimize the microstructure somewhere in between a smaller reinforcement particle size and a more homogeneous spatial distribution. The effect of PSR on the reinforcement spatial distribution, fabricability, and resulting mechanical properties of a P/M processed AlCuMn/SiC/15p composite was investigated. It was shown that increasing the PSR results in a less-uniform reinforcement distribution, which in turn leads to a decrease in the material fabricability and a general worsening of the mechanical properties. A close to linear dependence of the mechanical properties (yield stress, UTS, elongation before fracture, Young’s modulus) on PSR was found. Tensile elongation shows the highest sensitivity to the worsening of the homogeneity of the reinforcement spatial distribution caused by increasing the PSR. The effect of microstructural homogeneity on the relative change of mechanical properties does not seem to depend on matrix alloy plasticity.

Metallic Materials with High Structural Efficiency

Abstract: Preface. Introduction. 1: General Overviews. Opportunities and approaches for doubling the structural efficiency of metallic materials D.B. Miracle. The challenge for materials design: integrating modeling and computation C.S. Hartley. The main tendencies in elaboration of materials with high specific strength S. Firstov. 2: Amorphous, Nanocrystalline and Quasicrystalline Materials. Nanostructured materials produced by severe plastic deformation H.P. Stuwe. Development of nanostructured and nanoparticle dispersion-reinforced metallic systems P.R. Subramanian, et al. Nanostructured and nanocomposite light metal-based compounds for hydrogen storage R.A. Varin, et al. Strength and ductility of nanostructured SPD materials R.Z. Valiev. Consolidation of Cu and amorphous Zr-based powders by severe plastic deformation K.T. Hartwig, et al. Structure and properties of carbon-based nanocomposite films G. Radnoczi, et al. Nanocrystallization in iron alloys induced by friction treatment and nitrogen diffusion A. Yurkova, et al. Influence of scandium on amorphization of aluminum alloys A. Slipenyuk, et al. Structure peculiarities of Al63Cu25Fe12 ingots with a quasicrystalline component M. Yefinov, et al. Consolidation of Al-Cu-Fe powders with quasicrystalline component by using high quasihydrostatic pressures O. Bykov, et al. 3: Advanced Aluminum and Magnesium Alloys. High strength aluminum alloys for cryogenic applications O.N. Senkov, et al. Effect of Fe and Si on structure and mechanical properties of complex Al-Zn-Mg-Cu alloys produced by P/M casting techniques Yu. Milman, et al. Study of a zirconium modified 2014 aluminumalloy: analysis of the best warm forming conditions P. Cavaliere. Study of fatigue resistance properties of a zirconium modified 2014 aluminum alloy P. Cavaliere. High strain rate superplastic behavior of Al-Li-Mg-Cu-Sc alloy subjected to severe plastic deformation M.R. Shagiev, et al. Microstructure and mechanical properties od Al-Al4C3 materials M. Besterci, L'. Parilak. Creep behavior and strength of magnesium-based composites V. Sklenicka, et al. 4: Advanced Titanium Alloys and Composites. Multicomponent Ti-Si-based systems M. Bulanova, et al. Effect of Zr on structure and mechanical behavior of Ti-Al-Si alloys I. Gornaya, et al. High-temperature fatigue crack growth resistance of thermo-mechanically and heat treated cast Ti-Si-Al-Zr composites B. Vasyliv, et al. Structure and fracture features of Ti-Si- and Ti-B-based in situ composites O.D. Vasylyev, M.D. Bega. Effect of thermomechanical treatment on structure and properties of titanium-boride eutectic alloys T. Velikanova, et al. New high-strength weldable titanium alloy T110 V.N. Samkov, et al. Features of application of high-strength materials for units of the landing gear of aircrafts 'AN' A.G. Molyar, V.A. Trofimov. 5: Advanced Refractory Alloys. Structures and properties of the refractory silicides Ti5Si3 and TiSi2 and Ti-Si-(Al) eutectic alloys G. Frommeyer, R. Rosenkranz. Refractory metal/silicide multiphase systems for high temperature structural applications M.G. Mendiratta, et al. Microstructural effects and kinetics of high temperature oxidation in Nb-Si base alloys E.S.K. Menon, et al. Development of ductile Cr-Re alloys for high temperature application

Efficient Local Packing in Metallic Glasses

Abstract: A simple topological model in an earlier manuscript has provided additional support for the concept that efficient atomic packing is a fundamental principle in the formation of metallic glasses. In that work, an approach for defining and quantifying the local packing efficiency, P, was developed for solute-centered clusters that contained only solvent atoms in the first coordination shell. In the present work, this methodology is extended to allow quantification of P when more than one atomic species is present in the first coordination shell. This analysis is applied to several metallic glasses using published experimental data of partial coordination numbers. It is shown that packing in the first coordination shell is generally very efficient, even though the systems studied have significant differences in atomic species, compositions and relative atomic sizes. It is shown that packing is generally efficient around both solute and solvent atom species. Local packing efficiencies much less than unity are expected to be uncommon, since the global average packing efficiency is near unity and local packing efficiencies greater than unity are physically improbable. Deviations from efficiently packed configurations are discussed with respect to the local packing efficiencies in competing crystalline structures and with poorer glass forming ability. The values of P obtained for metallic glasses are essentially identical to the values obtained from a similar analysis of the competing crystalline structures. These results are consistent with frequent earlier reports of topological short range ordering in metallic glasses and with developments that have established the relationship between dense atomic packing and glass formation.

Powder metallurgy Ti-6Al-4V-xB alloys: Processing, microstructure, and properties

Abstract: This article describes processing of Ti-6Al-4V-xB alloys via pre-alloyed and blended elemental powder metallurgy techniques. The influence of processing on the microstructural evolution and mechanical properties of the alloys produced by these two routes is summarized, and the thermo-mechanical response and optimization of processing parameters to produce defect-free engineering shapes in these alloys is also discussed. Potential applications and issues involved in the development of these materials for damage-critical components are highlighted.

Crucial role of sidewalls in velocity distributions in quasi-two- Dimensional granular gases

Abstract: Our experiments and three-dimensional molecular dynamics simulations of particles confined to a vertical monolayer by closely spaced frictional walls (sidewalls) yield velocity distributions with non-Gaussian tails and a peak near zero velocity. Simulations with frictionless sidewalls are not peaked. Thus interactions between particles and their containers are an important determinant of the shape of the distribution and should be considered when evaluating experiments on a constrained monolayer of particles.

Structure-forming principles for amorphous metals

Abstract: The purpose of this research is to establish structure-forming principles that govern the atomic structures of metallic glasses. A structural model based on efficient atomic packing will be discussed and applied to the topological systems that represent most metallic glass alloys. The concept of efficient atomic packing has direct and specific implications regarding the local structure and composition of metallic glasses. Specific solute-to-solvent atomic radius ratios and specific solute concentrations related to these ratios are shown to be preferred in this model, and analysis of a wide range of metallic glass systems shows a very strong correlation with these predicted values. Relationships between atomic size and concentration are discussed, and new insights are proposed based on the current structural model. Possible local atomic configurations (i.e., atomic clusters) are defined based on topological constraints that are derived from the requirement of efficient atomic packing. Experimental observations drawn from the literature that provide support for this model are presented.

Titanium alloy microstructural refinement method and high temperature, high strain rate superplastic forming of titanium alloys

Abstract: A method for refining the microstructure of titanium alloys in a single thermomechanical processing step, wherein the titanium alloy comprises boron. In some embodiments, the method comprises the steps of first adding boron to the titanium alloy then subjecting the boron-containing titanium alloy to a thermomechanical processing step. Also provided is a method for achieving superplasticity in titanium alloys comprising the steps of selecting a boron-containing titanium alloy, determining the temperature and strain rate necessary to achieve beta superplasticity, and applying sufficient temperature and strain rate to the boron-containing titanium alloy to deform the alloy to the desired shape. Also provided methods of forming titanium alloy parts and the parts prepared by these methods.

Beta phase superplasticity in titanium alloys by boron modification

Abstract: Addition of boron to titanium alloys produces fine TiB whiskers in situ with excellent thermal stability and good chemical compatibility with the matrix. These whiskers stabilize a fine-grain microstructure by restricting grain growth at high temperatures in the β phase field. The hot deformation behavior in the β phase field (temperature range 1050–1200 °C) of Ti-6Al-4V alloys modified with two different levels of B additions (1.6 and 2.9 wt.%) produced by powder metallurgy was investigated using hot compression tests in the strain rate range of 10−3 to 10−1 s−1 and hot tensile tests at a nominal strain rate of 6×10−4 s−1. The β phase exhibits superplasticity, which occurs due to stabilization of a fine-grain microstructure by the TiB. Matrix grain boundary sliding and β/TiB interface sliding appear to contribute to the β superplasticity. The ability to achieve superplasticity at higher temperatures enable lower flow stresses, improved chemical homogeneity, and high strain rate capability due to enhanced accommodation processes.

The influence of solute distribution on the high nucleation density of Al crystals in amorphous aluminum alloys

Abstract: An extension of a previous model that describes the role of solute atoms on glass formability leads to the conclusion that solute distribution plays an important role in the formation and stability of amorphous metals. A random distribution of solutes is shown to produce local solute-depleted regions (on the size scale of the mean inter-solute spacing) that provide preferred sites for the formation of crystalline nuclei. The possibility that these solute-depleted regions are responsible for the exceptionally high number density of critical Al nuclei is explored for three Al–Y binary alloys using a computer simulation. Up to 10 7 Y atoms were placed at random locations in the system, and the number of solute-free regions were counted as a function of the size of these regions. The experimentally observed number density of critical nuclei (∼3 × 10 21 m −3 ) is reproduced for a critical nucleus about 5 Al atoms in diameter, containing ∼60 Al atoms in an fcc array. Good agreement with previous suggestions of the size of a critical nucleus (about 6 atoms in diameter, containing about 100 atoms) support the conclusion that the current model provides a reasonable physical explanation for the quenched-in features responsible for the exceptionally high nucleation density in some amorphous Al alloys.

Titanium-Boride Composites

Abstract: Alloy properties and phase constitutions for ternary Ti-Al-B and Ti-B-X, quaternary Ti-10 at% Al-B-X (where X=Si, Ge, Sn, Zr, V, or Nb) and some multi-component alloys were investigated on alloys prepared by arc melting Ascast and annealed samples were studied by metallography, electron probe microanalysis, XRD, DTA, Vickers hardness at temperatures up to 800°C and compression and bend tests Phase equilibria in the Ti-rich portions of the systems were studied in the two-phase (Ti)+(TiB) and conjugate three-phase fields Based on the experimental data obtained, contributions of alloying additions to the mechanical properties are estimated and discussed for eutectic alloys

Multicomponent ti-si-based systems

Abstract: The present paper provides a rewiev of our results on the phase equilibria and phase reactions in the Ti-corners of the Ti-Si-{Al,Sn,Zr}, Ti-Si-Al-{Ge,Sn,Zr} systems. The relation between the character of the phase diagrams, the crystal structure of the phases, mechanical properties of the individual phases and materials are discussed. It is shown that a basic understanding of phase equilibria can provide useful guidance for the selection and development of alloys for high temperature structural applications.

Opportunities and approaches for doubling the structural efficiency of metallic materials

Abstract: Significant reduction in system mass is required to achieve advanced aerospace objectives such as hypersonic flight, improved fuel efficiency and low cost access to space. The general needs for metallic materials with high structural efficiency will be outlined here, and current approaches for achieving significant improvements in specific strength and stiffness will be described.

Effect of Zr on Structure and Mechanical Behaviour of Ti-Al-Si Alloys

Abstract: Multicomponent alloys based on the Ti-Si system are attractive structural materials with high oxidation resistance and high temperature strength. Zr is one of the elements that may further improve these properties, but there is little systematic information about the combined influence of Si and Zr in wide concentration ranges on the structure and mechanical behaviour of titanium and titanium-aluminium alloys. The features of structure, phase composition, and mechanical properties of as-cast Ti-3Al-XSi alloys (where X=2,4,6-wt.%) vs. Zr content (0-18-wt.% ) have been studied in the present work. It is shown that Zr additions promote essential refinement of alloy microstructure and the formation of ternary (Ti,Zr)2Si silicides. It was found that hypoeutectic Ti-3Al-(4, 6)Si alloys with high Zr content have very refined microstructures based on an α-Ti+(Ti,Zr)2Si eutectic. Such alloys demonstrate high strength at room temperature and up to 400°C. Hypoeutectic alloys with 5-wt.% Zr reinforced by eutectic Ti5Si3 silicides are characterised by higher strength in the temperature range from 400 to 600°C.

Effect of Fe and Si on the Structure and Mechanical Properties of Complex Al-Zn-Mg-Cu Alloys Produced by P/M and Casting Techniques

Abstract: In order to establish the possibility of using recycled aluminum, which usually has an increased content of Fe and Si, the structure and mechanical properties of high-strength Al-Zn-Mg-Cu alloys additionally alloyed with only Fe and Si as well as additionally alloyed with Mn, Zr, Sc, Fe and Si were studied. Rods were manufactured from ingots cast into water-cooled copper molds as well as by a P/M technique using powders atomized from the melt by high-pressure water. The microstructure and distribution of elements in the starting condition and in the T6 treated extruded rods were studied by OM and SEM techniques and compared with rod tensile properties. An addition of Fe up to 1 wt.% led to a 5–7% increase in strength. This increase was accompanied by a decrease in ductility in the cast and cast-and-wrought alloys. In alloys prepared by P/M the technique, the addition of Fe led to about 20% increase in strength, as compared to the baseline alloy, without any detrimental effect on elongation. An addition of ≥0.5 wt.% Si to the P/M alloys decreased strength and slightly increased ductility. Thus, reasonable properties were obtained in high strength Al-Zn-Mg-Cu alloys containing significant amounts of Fe and Si.