Effects of Deformation Twinning on Energy Dissipation in High Rate Deformed Zirconium

The posit that deformation twinning can result in energy storage is examined by measuring the temperature increase of zirconium during adiabatic compression at high strain rates and correlating the response with the resulting microstructure. After examining the underlying assumptions of homogeneous deformation via microscopy and numerical modeling, it is determined that the occurrence of twinning does not correlate with significant energy storage relative to dissipation, and the appearance of storage may be caused by inhomogeneity in the deformation. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Dynamic Recrystallization: The Dynamic Deformation Regime

Severe plastic deformation (PD), especially involving high strain rates (>10³ s^–1), occurs through solid-state flow, which is accommodated by dynamic recrystallization (DRX), either in a continuous or discontinuous mode. This flow can be localized in shear instability zones (or adiabatic shear bands (ASBs)) with dimensions smaller than 5 μ, or can include large volumes with flow zone dimensions exceeding centimeters. This article illustrates these microstructural features using optical and electron metallography to examine a host of dynamic deformation examples: shaped charge jet formation, high-velocity and hypervelocity impact crater formation, rod penetration into thick targets (which includes rod and target DRX flow and mixing), large projectile-induced target plug formation and failure, explosive welding, and friction-stir welding and processing. The DRX is shown to be a universal mechanism that accommodates solid-state flow in extreme (or severe) PD regimes. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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<Emphasis Type="Italic">In-Situ</Emphasis> Electrochemical Investigations of a Nickel-Based Alloy Subjected to Fatigue

The HASTELLOY C2000 superalloy is a commercially designed superalloy manufactured to function in reducing and oxidizing corrosive solutions. The industrial applications have tremendous potential in automotive, structural, aviation, and storage components. Although C2000 demonstrates good reducing and oxidizing traits in extremely aggressive media (which are attractive features of its chemistry), changes in the mechanical properties are believed to be insignificant due to its strong propensity to passivate under corrosive conditions. The ductility behavior and corrosion properties of C2000 are superior to those of stainless steels. The objective of the present study is to examine the corrosion-fatigue behavior of C2000 in a 3.5 wt pct sodium-chloride (NaCl) solution. C2000 submerged in 3.5 wt pct NaCl at room temperature is not susceptible to localized corrosion, such as pitting, during fatigue. At an accelerated potential of 350 mV, the current responses show an increase in the current due to slip steps emerging to the surface as a result of fatigue. The crack-initiation site and the examination of the fracture morphology are discussed. This article is based on a presentation given in the symposium entitled “Deformation and Fracture from Nano to Macro: A Symposium Honoring W.W. Gerberich’s 70th Birthday,” which occurred during the TMS Annual Meeting, March 12–16, 2006 in San Antonio, Texas and was sponsored by the Mechanical Behavior of Materials and Nanomechanical Behavior Committees of TMS.

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Comparison of the Influence of Temperature on the High-Strain-Rate Mechanical Responses of PBX 9501 and EDC37

Many high-strain-rate compression measurements (2000 per second) using a specially designed split Hopkinson pressure bar (SHPB) for the plastic-bonded explosive PBX9501 have been reported in the literature, but there is a sparsity of data for a United Kingdom polymer-bonded explosives (PBX) known as EDC37. Both EDC37 and PBX9501 are cyclotetramethylenetetranitramine-based (HMX-based) PBXs with high filler contents. The binder systems for the PBXs are very different: EDC37 consists of a nitroplasticized nitrocellulose and PBX9501 a nitroplasticized ESTANE. PBX9501 exhibits nearly invariant fracture strains of ∼1.5 pct as a function of temperature at high strain rates, whereas EDC37 fails at ∼2 to 2.5 pct. The maximum compressive strengths for both PBXs were measured at 150 Mpa at −55 °C, but at +55 °C, the PBX was found to have a maximum strength of ∼55 MPa compared with ∼20 MPa for EDC37. Both PBXs exhibit an increasing loading moduli, E, with increasing strain rate or decreasing temperature. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Fragments Produced When Tungsten Penetrates Aluminum

Tungsten rods were shot through blocks of 6061T6 aluminum. The rods were partially eroded, and the remaining length emerged from behind the aluminum accompanied by a large number of small tungsten particles. These constitute behind-armor debris, which is of great practical importance. Analysis of data shows that most debris is generated near the exit face of the aluminum, the particle number increases with velocity, and the particle size increases with rod diameter. The latter two observations are consistent with the Grady–Kipp theory for rate effects on fracture. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Improved Pulse Shaping to Achieve Constant Strain Rate and Stress Equilibrium in Split-Hopkinson Pressure Bar Testing

Assuring a constant strain rate during dynamic testing is highly desirable to support the development of physically based predictive, constitutive material models. Many dynamic tests conducted on high-work-hardening materials, or materials that do not display a classic power-law-type hardening behavior, such as materials exhibiting complex sigmoidal concave-upward hardening (shape-memory alloys or a number of textured hexagonal metals due to deformation twinning), often result in continuously decreasing strain rates as a function of strain throughout the test. Incident pulse shaping has not been fully developed or successfully demonstrated over a large range of strain in high work hardening or complex-hardening materials. To shape an incident pulse for a constant strain rate in a split-Hopkinson pressure bar (SHPB) test, a high-strength, high-work-hardening rate (HSHWHR) material was selected to fabricate the pulse shaper. Several test sample materials, namely, 50-50 NiTi superelastic alloy, higher strength 60NiTi alloy, tungsten single crystals, interstitial-free (IF) steel, and MACOR (a glassy ceramic), which display a range of strength levels, work-hardening rates, and superelastic hardening behavior in the case of 50-50 NiTi, were tested in the SHPB with and without a pulse shaper at different temperatures and strain rates. The current experiments demonstrate that HSHWHR pulse-shaper materials are ideally suited to shape the incident pulse to achieve constant strain rates and achieve stress state equilibrium, while inherently dampening high frequency oscillations in the incident pulse. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Influence of Microstructure on the Spall Failure of Aluminum Materials

Laser-shock-induced spall failure is studied in thin aluminum targets at strain rates from 2 to 5 × 10⁶ s⁻¹. Targets were prepared from high-purity aluminum in the recrystallized condition and a low-impurity aluminum alloy containing 3 wt pct magnesium in both recrystallized and cold-rolled conditions. The effects of material and microstructure on spall fracture morphology are investigated. Recrystallized pure aluminum produced spall fracture surfaces characterized by transgranular ductile dimpling. Recrystallized aluminum-magnesium alloy with a 50-μm grain size produced less ductile spall surfaces, which were dominated by transgranular fracture, with some isolated transgranular ductile dimpling at fast strain rates. Transgranular ductile dimpling regions disappeared in recrystallized alloy specimens with a 23-μm grain size tested at faster rates. Cold-rolled alloy material produced spall failure surfaces consisting of brittle intergranular and transgranular fractures. Measured spall strength increases with increasing ductile fracture character. Spall failure preferentially follows grain boundaries, making grain size an important factor in spall fracture surface character. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Microstructural Effects in Face-Centered-Cubic Alloys after Small Charge Explosions

Effects on metal targets after an explosion include the following: fracture, plastic deformation, surface modifications, and microstructural crystallographic alterations with ensuing mechanical properties changes. In the case of small charge explosions, macroscopic effects are restricted to small charge-to-target distances, whereas crystal alterations can still be observed at moderate distances. Microstructural variations, induced on gold-alloy disk samples, as compared to previous results on AISI 304Cu steel samples, are illustrated. The samples were subjected to blast-wave overpressures in the range of 0.5 to 195 MPa. Minimum distances and peak pressures, which could still yield observable alterations, were especially investigated. Blast-related microstructural features were observed on the explosion-exposed surface and on perpendicular cross sections. Analyses using X-ray diffraction (XRD) were performed to identify modifications of phase, texture, dislocation density, and frequency of mechanical twins, before and after the explosions. Optical metallography (OM) and scanning electron microscopy (SEM) observations evidenced partial surface melting, zones with recrystallization phenomena, and crystal plastic deformation marks. The latter marks are attributed to mechanical twinning in the stainless steel and to cross-slip (prevalent) and mechanical twinning (possibly) in the gold alloy. This article is based on a presentation given in the symposium “Dynamic Behavior of Materials,” which occurred February 26–March 1, 2007, during the TMS Annual Meeting in Orlando, FL, under the auspices of the TMS Structural Materials Division and the TMS/ASM Mechanical Behavior of Materials Committee.

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Advances in X-ray Computed Tomography Diagnostics of Ballistic Impact Damage

With the relatively recent introduction of quantitative and volumetric X-ray computed tomography (XCT) applied to ballistic impact damage diagnostics, significant inroads have been made in expanding our knowledge base of the morphological variants of physical impact damage. Yet, the current state of the art in computational and simulation modeling of terminal ballistic performance remains predominantly focused on the penetration phenomenon, without detailed consideration of the physical characteristics of actual impact damage. Similarly, armor ceramic material improvements appear more focused on penetration resistance than on improved intrinsic damage tolerance and damage resistance. Basically, these approaches minimize our understanding of the potential influence that impact damage may play in the mitigation or prevention of ballistic penetration. Examples of current capabilities of XCT characterization, quantification, and visualization of complex impact damage variants are demonstrated and discussed for impacted ceramic and metallic terminal ballistic target materials. Potential benefits of incorporating such impact damage diagnostics in future ballistic computational modeling are also briefly discussed. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.

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Slip-System-Related Dislocation Study from <Emphasis Type="Italic">In-Situ</Emphasis> Neutron Measurements

A combined experimental/computational approach is employed to study slip-system-related dislocation-substructure formation during uniaxial tension of a single-phase, face-centered-cubic (fcc), nickel-based alloy. In-situ neutron-diffraction measurements were conducted to monitor the peak-intensity, peak-position, and peak-broadening evolution during a displacement-controlled, monotonic-tension experiment at room temperature. The measured lattice-strain evolution and the macrostress/macrostrain curves were used to obtain the material parameters required for simulating the texture development by a visco-plastic self-consistent (VPSC) model. The simulated texture compared favorably with experimentally-determined texture results over a range of 0 to 30 pct engineering strain. The grain-orientation-dependent input into the Debye-intensity ring was considered. Grains favorably oriented relative to the two detector banks in the geometry of the neutron experiment were indicated. For the favorably oriented grains, the simulated slip-system activity was used to calculate the slip-system-dependent, dislocation-contrast factor. The combination of the calculated contrast factor with the experimentally-measured peak broadening allows the assessment of the parameters of the dislocation arrangement within the specifically oriented grains, which has a quantitative agreement with the transmission-electron-microscopy results. This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,” which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee.

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Effect of Titanium on Microstructure and Mechanical Properties of Cu50Zr50? x Ti x (2.5?≤ x ≤?7.5) Glass Matrix Composites

The microstructure and mechanical properties of Cu₅₀Zr_50−x Ti _x (2.5 ≤ x ≤ 7.5) glass matrix composites have been investigated. The presence of austenitic (Pm-3m)/martensitic phases (P2₁/m and Cm) enhances the plastic deformability significantly. These composites show high yield strength up to 1753 MPa and large plastic strain over 15 pct. Their high strength scales with the volume fraction of glassy matrix and crystalline phase. When the austenitic phase forms instead of the martensite, the work hardening of the composite material increases. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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Rate-Dependent Temperature Increases in Shear Bands of a Bulk-Metallic Glass

Using an infrared (IR) camera, we observed in situ the dynamical shear-banding processes of the geometrically constrained specimens of a Zr-based bulk metallic glass in a quasi-static compression at various strain rates, measured the temperature evolutions within the specimens, and calculated the temperature increases in shear bands. Strain-rate-dependent serrated plastic flow is a result of shear-banding operations. The average temperature increases in the specimens are observed during the plastic deformation and their magnitudes are strain rate dependent. The temperature increases in shear bands are related to strain rates. The higher the strain rates, the larger the temperature increases in a shear band. The shear strain in a shear band may be responsible for the strain-rate-dependent temperature increase in a shear band. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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Structure of Zr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript>100−<Emphasis Type="Italic">x</Emphasis></Subscript> (73 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 77) Metallic Glasses

The structure of hyper-eutectic Zr _x Pt_100−x (73 ≤ x ≤ 77) metallic glasses produced by melt spinning was examined with high-energy synchrotron X-ray diffraction (HEXRD) and fluctuation electron microscopy. In addition, details of the amorphous structure were studied by combining ab initio molecular dynamics and reverse Monte Carlo simulations. Crystallization pathways in these glasses have been reported to vary dramatically with small changes in compositions; however, in the current study, the structures of the different glasses were also observed to vary with composition, particularly the prepeak in the total structure factor that occurs at a Q value of around 17 nm⁻¹. Results from simulations and fluctuation electron microscopy suggest that the medium-range order of the amorphous structure is characterized by extended groups of Pt-centered clusters that increase in frequency, structural order, or spatial organization at higher Pt contents. These clusters may be related to the Zr₅Pt₃ structure, which contains Pt-centered clusters coordinated by 9Zr and 2Pt atoms. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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Multistage Fatigue Modeling of Cast A356-T6 and A380-F Aluminum Alloys

This article presents a microstructure-based multistage fatigue (MSF) model extended from the model developed by McDowell et al.[1,2] to an A380-F aluminum alloy to consider microstructure-property relations of descending order, signifying deleterious effects of defects/discontinuities: (1) pores or oxides greater than 100 μm, (2) pores or oxides greater than 50 μm near the free surface, (3) a high porosity region with an area greater than 200 μm, and (4) oxide film of an area greater than 10,000 μm². These microconstituents, inclusions, or discontinuities represent different casting features that may dominate fatigue life at stages of fatigue damage evolutions. The incubation life is estimated using a modified Coffin–Mansion law at the microscale based on the microplasticity at the discontinuity. The microstructurally small crack (MSC) and physically small crack (PSC) growth was modeled using the crack tip displacement as the driving force, which is affected by the porosity and dendrite cell size (DCS). When the fatigue damage evolves to several DCSs, cracks behave as long cracks with growth subject to the effective stress intensity factor in linear elastic fracture mechanics. Based on an understanding of the microstructures of A380-F and A356-T6 aluminum alloys, an engineering treatment of the MSF model was introduced for A380-F aluminum alloys by tailoring a few model parameters based on the mechanical properties of the alloy. The MSF model is used to predict the upper and lower bounds of the experimental fatigue strain life and stress life of the two cast aluminum alloys. This article is based on a presentation made in the symposium entitled “Simulation of Aluminum Shape Casting Processing: From Design to Mechanical Properties,” which occurred March 12–16, 2006 during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the Computational Materials Science and Engineering Committee, the Process Modeling, Analysis and Control Committee, the Solidification Committee, the Mechanical Behavior of Materials Committee, and the Light Metal Division/Aluminum Committee.

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Stress and Composition of Carbon Stabilized Expanded Austenite on Stainless Steel

Low-temperature gaseous carburizing of stainless steel is associated with a colossal supersaturation of the fcc lattice with carbon, without the development of carbides. This article addresses the simultaneous determination of stress and composition profiles in layers of carbon expanded austenite obtained by low-temperature gaseous carburizing of AISI 316. X-ray diffraction was applied for the determination of lattice spacing depth profiles by destructive depth profiling and reconstruction of the original lattice spacing profiles from the measured, diffracted intensity weighted, values. The compressive stress depth distributions correlate with the depth distribution of the strain-free lattice parameter, the latter being a measure for the depth distribution of carbon in expanded austenite. Elastically accommodated compressive stress values as high as −2.7 GPa were obtained, which exceeds the uniaxial tensile yield strength by an order of magnitude. This article is partly based on a presentation given at the “International Conference on Surface Hardening of Stainless Steels,” which occurred October 22–23, 2007 during the ASM Heat Treating Society Meeting in Cleveland, OH under the auspices of the ASM Heat Treating Society and TMS.

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Poisson Effects on X-Ray Diffraction Patterns in Low-Temperature-Carburized Austenitic Stainless Steel

Austenitic stainless steel was carburized at low temperature to generate a hard surface layer. X-ray diffractometry (XRD) revealed that this “case” contained an expanded fcc lattice and significant residual stresses due to the interstitial carbon. The XRD patterns also exhibit consistent variations with crystallographic orientation. Using published elastic constants for austenitic stainless steel and appropriate approximations for the XRD elastic constants, the XRD peak position variations can be accounted for by orientation-dependent Poisson effects due to biaxial residual stresses. The XRD patterns of specimens containing either compressive or tensile residual stresses were consistent with this hypothesis. This article is based on a presentation given at the “International Conference on Surface Hardening of Stainless Steels,” which occurred October 22–23, 2007 during the ASM Heat Treating Society Meeting in Cleveland, OH under the auspices of the ASM Heat Treating Society and TMS.

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