bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nano-Hardness, Nano-Friction and Nano-Wear of Ultra-Thin Overcoats
Authors: Bogy D. B. , Jiang Zhaoguo 
Published: April 2011

AbstractThin film magnetic disks require protective overcoats, usually some form of carbon, to guard against corrosion and wear from interaction with the read/write transducer. In current products these films are less than 25 nm in thickness. This paper summarizes developments using scanning probe microscopes with sharp diamond tips (15 – 100 nm radius) to obtain indentation hardness tests with 5 nm deep indentations. We discuss an accelerated wear test that can measure wear at depths on the order of 1 nm. Finally material characterizations related to friction over sub-micron scans are discussed.A novel observation has been made when studying the dependence of friction coefficient on normal load: below a critical load, which is material and tip dependent, no observable wear occurs, and the coefficient of friction is about 0.05. Above the critical load the coefficient is load dependent and increases to a value more usually associated with the materials being tested. A study of fatigue wear was made in the “no-wear” regime with three different results. For some materials, fatigue wear occurred with multiple passes, when none was apparent for a single pass. Other materials showed no fatigue wear, and one material, silicon, showed a build-up or “negative-wear” under multiple passes. Interpretations and implications of these results are discussed.
Studies on Wear Mechanism of Ultrathin Protective Carbon Overcoat by Micro-Wear Scan Technique
Authors: Wu T. W. 
Published: April 2011

AbstractBy combining the micro-wear and microscratch techniques in a microindenter, a new methodology to investigate the mechanical properties of ultrathin coatings has been developed. With a 0.18 μm/sec scratch speed along a Y-direction while oscillating the indenter tip along the X-direction at a 6.55 Hz frequency, uniform wear tracks of approximately 20 μm × 90 μm in dimension can be created under either a constant or a gradually increased applied normal load. The wear-scan methodology has rendered several immediate advantages over the conventional micro-scratch technique, offering features such as a much larger testing area thus facilitating the failure and morphology analyses afterwards, the possibility of studying the wear debris generation and the flexibility in testing characteristics. Two thin film disks with different hydrogenated carbon overcoats have been tested by using the micro-wear scan technique. The results in the mechanical measurements, the wear processes and the morphology evolution are illustrated and discussed.
Tribology and Surface Mechanical Properties of Excimer Laser Nitrided Titanium
Authors: Jervis T. R. , Hirvonen J. P. , Zocco T. G. , Tesmer J. R. 
Published: April 2011

AbstractWe have nitrided Ti-6A1-4V alloys using excimer laser pulses at 1.2 J-cm−2 in high purity N2 at approximately one atmosphere. Substantial nitrogen and oxygen incorporation resulted from multiple pulse processing. The surface microstructure that results is of fine grained precipitates in the Ti alloy matrix. Formation of a TiN surface film was not observed. We have examined the tribological and mechanical properties of these surfaces using pin-on-disk and nanoindenter techniques respectively. Nitrogen alloying results in a period of reduced friction and torque noise in the pin-on-disk measurements. At higher N concentrations, abrasive wear of the pin is observed, but with little deterioration of the disk surface. This is consistent with the formation of a transfer film at the sliding interface. Nanoindenter measurements of the surfaces show increasing hardness proportional to nitrogen incorporation. The tribological properties can therefore be understood to result from a combination of tribochemical effects and increased surface hardness.
Hardness and Tribological Effects of Ion Implantation on Electroplated Chromium
Authors: Noll Kathryn , SteinbrÜchel Christoph 
Published: April 2011

AbstractThe effects of ion implantation on two types of electroplated chromium were studied. Both hard chromium and low contraction chromium were plated onto samples of AISI 4340 grade steel and subsequently implanted with N2+ or Ar+ at ion energies of 150 keV and 75 keV, respectively. The dose was varied from 9.4 x 1015 to 3.1 x 1018 atoms/cm2 and the implantation was conducted at both room temperature and 500 °C. The properties of the resulting surface layers were characterized using secondary ion mass spectrometry and Knoop microhardness. The dry sliding wear and friction behavior was also compared between implanted and unimplanted layers. An increase in hardness was observed for both types of electroplated chromium. The wear rate and friction coefficient were reduced in the nitrogen implanted samples. At the intermediate doses tested, the elevated temperature condition provided improved wear and friction properties compared to the room temperature condition.
Thermo-Mechanical Properties of Terfenol-D Thin Films
Authors: Su Quanmin , Zheng Y. , Wuttig Manfred 
Published: April 2011

AbstractThe thermo-mechanical properties of Terfenol-D thin films deposited on Si substrates werestudied by static and dynamic measurements of film/substrate composite cantilevers. The Curie transition, δE effect and mechanical damping of the film were measuredsimultaneously. The stress in the film was controlled by annealing below the recrystallization temperature and determined to vary from -500 MPa, compression, in as deposited films to +480 MPa, tension, in annealed films. The Curie temperature shifts from 80ºC to 140ºC as the tension increases while the structure of the film remains amorphous. The stress change induced by annealing also drastically effects the film's damping characteristics. The δE effect of the amorphous material, about 20%, wasused to estimate the magnetostriction, λs≈4.10-3.
Smart Thin Film TiNi/Pzt Heterostructures
Authors: Mercado Peter G. , Jardine A.Peter 
Published: April 2011

AbstractThin film layers of shape memory alloys and ferroelectric ceramics can produce a family of ‘smart’ heterostructures capable of performing both sensing and actuating functions. Important issues in the synthesis of these active structures are the ability to generate the appropriate crystalline phases of each material, while producing defect-free homogeneous high quality films. The compatibility of sol-gel processed Pb(Zr,Ti)O3 (PZT) thin films with thin film shape memory effect TiNi substrates were investigated. Thin film TiNi was deposited on quartz substrates by physical sputter deposition utilizing a TiNi target in a ultra-high vacuum chamber, and followed by in-situ vacuum annealing. PZT was deposited on TiNi by sol-gel and spin coating processes. The ferroelectric tetragonal phase of PZT was obtained by a 600 °C anneal for 5m in air. The heterostructures were nominally defect-free, unlike those obtained through deposition onto bulk TiNi substrates.x
Evolution of the R-Phase Transformation Temperature of Ti50Ni50-xFex Shape Memory Alloys with Iron Concentration
Authors: GÓmez R , Marquina V. , Ridaura R. , Marquina M.L. , JimÉnez M. , Aburto S. , Escudero R. , Morales F. , Rios-Jara D. , Canales A. 
Published: April 2011

AbstractThe evolution of the R-phase transformation temperature with iron concentration is studied by Mössbauer spectroscopy (MS), magnetic susceptibility and calorimetric measurements in a series of three Ti50Ni50-xFex, samples, with x = 1, 2 and 3. The changes in the Mössbauer spectra, from a single line at room temperature to a quadrupole doublet when the temperature is lowered below 280 K, are related to structural transformations occurring in the system. The temperature changes in the magnetic susceptibility are interpreted in terms of a gap opening characteristic of charge density waves (CDW) formation when the R-phase transformation takes place. The calorimetric measurements show specific heat fluctuations near room temperature in two of the samples (x = 1 and 3) whose peaks shift during the cooling and heating cycles.
Deformation and Failure Modes Under Compressive Loading in Lamellar Tial
Authors: Dao Ming , Kad Bimal K. , Asaro Robert J. 
Published: April 2011

AbstractA physically based micromechanical model is applied to study finite compressive deformation and failure in lamellar TiAl microstructures. Orientation dependent yielding of lamellar TiAl single crystals is specifically modeled. Finite element computations show that deformation is inherently non-uniform in the lamellar microstructure. Intergranular fracture (at low strains) and internal buckling (at high strains) are found to be two of the most important failure modes.
Grain Size Effect on the Creep Behavior of Monolithic MoSi2
Authors: Feng C.R. , Sadananda K. 
Published: April 2011

AbstractThe grain size effect on the creep behavior of hot-pressed monolithic molybdenum disilicide was investigated at 1200°C in a 19–255 MPa stress range. The creep-stress exponent, n, increased from 1 at low stresses to 4 at high stresses. The grain size exponent, p, varied from 0, to 3.5 and to 8 depending on the grain size, the creep-stress exponent, and creep history.
Microstructure of Zr-25at. %Al Melt Spun Ribbons.
Authors: Lutterotti L. , Pradhan S. K. , Gialanella S. , Yavari A. R. 
Published: April 2011

AbstractFollowing a previous study in which we presented some microstructural aspects of meltspun ribbons having a composition close to Zr-25 at.% Al, we discuss now the crystallography of the phases observed in similar samples. We performed X-Ray diffraction analyses of ribbons and refined the observed crystallographic structures. We could identify a number of stable and metastable structures, according to the actual composition of the ribbons. We also estimated the percentage of each one of these phases. We did the same for some ribbons annealed at 750°C for several times. In this way we could follow the kinetics leading from the initial as-spun condition to the final one, featuring the L12 ordered Zr3Al, as the major phase, and other intermetallic phases of the Zr-Al phase diagram.
Metastable Phase Transformations in Ti-40Al-10V Alloy
Authors: Shao G. , Tsakiropoulos P. , Miodownik A. P. 
Published: April 2011

AbstractThe microstructures in arc melted ingots and melt spun ribbons have been investigated by electron microscopy and thermodynamic modelling has been used to study the phase transformations. In the ingot, solidification starts with the bcc β phase and at room temperature the structure consists of B2, ωordered, γ and α2 phases. The calculated equilibrium phase transformation sequence during cooling is L → L+ β→β→β + α→β2+α → α+β2+γ → α2+γ + B2. The phase transformation sequence is dramatically changed by rapid quenching from the melt. Athermal ordered w phase is formed in metastable B2 and the α→α2 ordering process is completely suppressed in the melt spun ribbons. The volume fraction of the α precipitates is also dependent on cooling rates.
Dynamic Restoration Mechanism of a Fe3Al Based Alloy During Elevated Temperature Deformation
Authors: Chen Mingwei , Shan Aidang , Lin Dongliang 
Published: April 2011

AbstractBy TEM and metallographic examination, we found that dynamic recovery and following continuous recrystallization, which connects with the elevated temperature ductility, takes place in a Fe3Al based alloy during elevated temperature deformation. Dynamic restoration consists of the following process: (1) by climbing or cross-slipping, glide dislocations change into dislocation arrays, (2) the dislocation array attracts lattice dislocations, (3) with increasing dislocation density, a non-equilibrium subboundary forms, which is easy to migrate, slide or rotate under external force, and (4) when the misorientation angle of the subboundary increases to a critical value, the subboundary changes into a grain boundary with continuous misfit. By relaxation, the boundary then changes into a grain boundary consisting of periodical structure units.
Mechanical Properties of Polycrystalline NiAl from Miniaturized Disk-Bend Tests
Authors: Eck S. J. , Ardell A. J. 
Published: April 2011

AbstractDisk-shaped specimens of polycrystalline NiAl (grain size ∽25 μm), 3 mm in diameter and ranging in thickness from 165 to 370 μm, were indented in their centers to various indentation loads, F, using a Vickers indenter. The yield stress, σy, and apparent fracture stress, σfa, were measured as a function of F, with the indented side in tension, using a miniaturized disk-bend test (MDBT). Fracture does not originate at the indentation for F ≤ 39.2 N. Within this regime of behavior both σy and σfa are slightly larger than in unindented specimens, although σfa passes through a sharp minimum for F < 10 N. For F ≥ 39.2 N fracture originates at the indentations. In this regime σy is essentially constant, but significantly larger than σy at smaller values of F, while σfa decreases steadily with increasing F. We attribute the larger values of σy to strain hardening within the relatively large plastic zone surrounding the indentation. The reduction of σfa with increasing F in this regime occurs because the indentation serves as the point of failure. Fractography reveals NiAl fractures primarily in an intergranular manner. A preliminary estimate of the fracture toughness is 8.54 MPa·a.m1/2, which overestimates the true fracture toughness because σfa exceeds the true fracture stresses.
Intermediate Temperature Creep of Ni3Al
Authors: Rong T. S. , Jones I. P. , Smallman R. E. 
Published: April 2011

AbstractThe creep behaviour and dislocation structure of polycrystalline Ni3Al have been investigated at intermediate temperatures, where macroscopic inverse creep may or may not be present depending upon both the temperature and the stress applied. Microstructural observations indicate that superdislocations slip on the cube cross-slip plane more easily at lower temperatures, and is one of the reasons causing the creep strength to vary anomalously with temperature. Although inverse creep is produced by the operation of cube cross-slip, it is a necessary but not sufficient condition, i.e. the operation of cube cross-slip may not necessarily result in macroscopic inverse creep.
Trends in Dislocation Core Structures and Mechanical Behavior in B2 Aluminide
Authors: Vailhe C. , Farkas D. 
Published: April 2011

AbstractIn an effort to understand the deformation mechanism in high temperature B2 intermetallics, atomistic simulations were carried out for dislocation cores in a series of compounds exhibiting the B2 structure (FeAl, NiAl, CoAl). A comparison was made on the basis of core structures, dislocation splittings and Peierls stress values. The (110) and (112) γ surfaces were computed for these three compounds. The importance of the APB values and the maximum shear faults for explaining the dislocation behavior is discussed.
Influence of Dislocation-Solute Interactions on The Mechanical Properties of Zirconium-Doped NiAl
Authors: Jayaram R. , Miller M.K. 
Published: April 2011

AbstractAtom probe field ion microscopy (APFIM) has been used to characterize NiAl microalloyed with molybdenum and zirconium. Field ion images and atom probe analyses revealed segregation of zirconium to dislocation strain fields and ribbon-like morphological features that are probably related to dislocations. These results provide direct experimental evidence in support of the suggestion that the tremendous increase in the ductile-to-brittle transition temperature (DBTT) in zirconium-doped NiAl is due to pinning of dislocations by zirconium atoms. Atom probe analyses also revealed segregation of zirconium to grain boundaries. This result is consistent with the change from an intergranular fracture mode in undoped NiAl to a mixture of intergranular and transgranular fracture mode in zirconium-doped NiAl. The NiAl matrix was severely depleted of the solutes molybdenum and zirconium. Small Mo-rich precipitates, detected in the matrix and grain boundaries, are likely to contribute to the significant increase in the room-temperature yield stress of microalloyed NiAl through a precipitation hardening mechanism.
Dislocation Motion in λ Tial Studied by in situ Straining Experiments in the Hvem
Authors: Messerschmidt Ulrich , Bartsch Martin , Häussler Dietrich , Aindow Mark , Hattenhauer Rainer , Jones Ian P. 
Published: April 2011

AbstractMicro-tensile specimens of coarse-grained Ti52at%Al crystals have been deformed in situ in a high voltage electron microscope at room temperature. In addition to some twinning, “simple” 1/2〈110] dislocations as well as superdislocations were moving, with the simple dislocations prevailing even if their orientation factor is lower than that of the superdislocations. Both types of dislocations are pinned, probably by small precipitates having a distance along the dislocations of about 100 nm. The precipitates consist most probably of Al2O3. Under stress, the dislocations bow out between the obstacles. The bowing is stronger for 1/2〈110] dislocations. An effective stress of about 41 MPa is estimated from their curvature. The kinematic behaviour of the dislocations is in accord with precipitation hardening. The dislocations are generated by the double-cross slip mechanism. Their density within the slip bands corresponds to a long-range internal stress of about 40 MPa. These data are consistent with the flow stress of PST crystals in the easy orientation, taken from the literature.
Influence of the Grain Size of Fully Lamellar Structure on the Mechanical Properties of a TiAl Based Alloy
Authors: Pu Z. J. , Ma J. L. , Wu K. H. 
Published: April 2011

AbstractA preliminary investigation was conducted for developing a thermomechanical procedure to refine the lamellar colony size of a fully lamellar structure and improve the balance of the mechanical properties of TiAl based alloys. The main experimental results are as follows: 1) The lamellar colony size in a fully lamellar structure can be reduced to 50 μm using a proper thermomechanical procedure. 2) The influence of colony size on the compressive yield stress of the fully lamellar structure is complex. In the large colony size region, the yield stress can be described by the Hall-Petch relation. In the small colony size region, the yield stress decreases as the colony size decreases. 3) The TiAl alloy, with a fine fully lamellar structure, has the best balance of tensile properties and fracture toughness.
Deformation Behavior and Dislocation Mechanisms in Tial Alloys
Authors: Sriram S. , Vasudevan Vijay K. , Dimiduk Dennis M. 
Published: April 2011

AbstractPolycrystalline Ti-50 and Ti-52A1 (in at.%) alloys, with large grain sizes (50Al-300μm, 52Al-500μm) and containing low (∼250 wt.ppm) levels of oxygen were deformed under compression over a wide temperature range (77-1173°K). The 0.2% proof stress-temperature profiles comprise of three distinct regimes: Regime I (between 77-∼600°K), regime II (between ∼600-1073°K), and regime III (above 1073°K). Deformation temperature influences the types of dislocations present, the nature of superdislocation dissociations, and the morphological characteristics of both ordinary and superdislocations. Collectively, experiment and theory suggest that the flow properties at low temperatures (regime I) are controlled by lattice friction, whereas at higher temperatures (regime II) the properties are dislocation obstacle controlled.
On the Correlation of the Hardness of B2 Compounds with Point Defect Concentrations
Authors: Pike L. M. , Chang Y. A. , Liu C. T. 
Published: April 2011

AbstractPoint defects such as vacancies and anti-site atoms are known to strongly affect the mechanical properties of B2 compounds. The variations in the hardness of these compounds with composition and quenching temperature can often be correlated with the concentrations of these point defects. Simple themodynamic models using a quasi-chemical approach can be used to estimate the concentrations of point defects with composition and temperature. These estimates can often be supported by experimental methods. Knowledge of the concentrations of defects can then be compared to the variations in hardness using solid solution strengthening models. A consistent relationship is found for several B2 compounds. The hardening rates of vacancies are found to be greater than those of anti-site atoms. B2 compounds having the anti-structure defect structure (AuZn, FeCo) are investigated as well as those with the triple-defect structure (FeAl, NiAl, CoAl).
Quantitative Observations in Dislocation Mechanisms in Gamma TiAl
Authors: Viguier B. , Cieslar M. , Hemker K. J. , Martin J. L. 
Published: April 2011

AbstractQuantitative TEM observations have been made on a series of gamma Ti47Al51Mn2 polycrystals that were deformed at different temperatures. Special attention has been given to determining the statistical variation of defect densities that occur at the different temperatures. The results, which are in good agreement with mechanical testing [J], indicate that three different mechanisms control deformation in this alloy: lattice friction and the formation of faulted dipoles at low temperatures, the pinning of ordinary dislocations at intermediate temperatures, and the bowing and looping of dislocations at high temperatures. The anomalous flow strength of this alloy has been found to be related to the intrinsic pinning of ordinary dislocations. Details of this pinning and subsequent unzipping process, which are the basis for the new local-pinning-unzipping (LPU) models[2-4], are outlined within.
The Effect of Room Temperature Prestrain on the Yield Stress of Single Crystals of γ’ in the Anomalous Regime
Authors: Ezz S.S. , Hirsch P.B. 
Published: April 2011

AbstractThe yield stress of a specimen prestrained at 294 K increases only slowly or is constant up to a temperature above which the yield stress of a virgin specimen is greater. Above that temperature, the yield stress tends to increase as for a virgin crystal. For sufficiently high prestresses, the yield stress anomaly disappears completely. The results are interpreted in terms of a model in which the operation of Frank-Read sources is rate controlling.
The Microchemistry Studies of Ductile Ll2 Ni-Based Intermetallics
Authors: Masahashi Naoya 
Published: April 2011

AbstractAuger electron microscopy (AES) analysis of boron doped Ni3Al have shown boron segregation at grain boundary (GB). Boron segregation was enhanced with increasing bulk boron content independent of stoichiometry, suggesting that hypo-stoichiometric alloy is intrinsically ductile even without boron. A slight Ni cosegregation is confirmed using atom probe field ion microscope (APFIM). In Ni3(Si,Ti), no distinct composition fluctuation was identified between matrix and GB vicinity. These results suggest that atomic bonding atmosphere modification from covalent to metallic in the vicinity of GB is one of factors to modify ductility for Ll2-type intermetallics.
Oxide Dispersion in Direct-Cast Gamma TiAl-Based Alloy
Authors: Hanamura Toshihiro , Hashimoto Keizo 
Published: April 2011

AbstractThe objective of this study is to evaluate the high temperature behavior of γ TiAl-based alloy sheets containing AI2O3 particles, produced by a combination of vacuum induction melting, use of a CaO crucible, and direct sheet casting, over a wide temperature range. Alumina particles, having a tendency to coagulate during solidification of a TiAl ingot, are finely dispersed due to the disturbance of high frequency induction, and frozen without having enough time to grow in size by direct sheet casting. The TiAl sheet thus produced shows remarkable high temperature tensile strength which exceeds that of conventional ingots having the same composition and various different structures. This is determined to be attributable to the dispersion strengthening of finely dispersed AI2O3 particles whose diameter is from 100 to 500nm. Moreover, because of the small size of these alumina particles, the TiAl sheet does not show any significant retardation in high temperature ductility, which is often the case in conventional ceramic-reinforced intermetallic compound composites.