Hardness across the Multi-Scales of Structure and Loading Rate: Applications I
Sponsored by: MS&T Organization
Program Organizers: Ronald Armstrong, University of Maryland; David Bahr, Washington State University; Naresh Thadhani, Georgia Institute of Technology; Stephen Walley, Physics and Chemistry of Solids Cavendish Laboratory
Wednesday 2:00 PM
October 19, 2011
Room: C210
Location: Greater Columbus Convention Center
Session Chair: Ronald Armstrong, University of Maryland; Lawrence Murr, University of Texas at El Paso
2:00 PM Invited
A Comparative Nanoindentation Study of the Metal Particles and Thin Films on a Sapphire Substrate: Eugen Rabkin1; Dan Mordehai1; Michael Kazakevich1; Julia Deuschle2; David Srolovitz3; 1Technion; 2University of Stuttgart; 3Institute of High Performance Computing, Singapore
We report a combined experimental/molecular dynamics study of the indentation of faceted Au and Ni nanoparticles, of polycrystalline Au and Ni films, and of single crystalline Ni film on a sapphire surface. The particles were created via the agglomeration of respective polycrystalline thin films. Both simulations and experiment show that the particles are softer than the film and that the deformation behavior is nearly independent of particle size. Deformation is controlled by dislocation nucleation near the indenter, followed by fast dislocation glide toward the surface. In some of our indentation tests of the polycrystalline ultrathin Ni film, a single large displacement burst was observed slightly below of, or at the maximal load. These large displacement bursts were interpreted as manifestations of intergranular brittle fracture in the indented region. We formulated a criterion of brittle intergranular fracture based on the theory of strain gradient plasticity.
2:20 PM Invited
Hardness of 1D and 2D Nanostructured Materials Characterized by Nanoindentation: Han Huang1; 1The University of Queensland
The characterization of hardness of 1D and 2D nanostructured materials is extremely challenging due to their small feature sizes. Our recent works involved the nanoindentation hardness of micro whiskers (1D) and thin film (2D) materials. The nanoindentation of tungsten whiskers revealed that the hardness of 1D single crystal tungsten is considerably higher than that of the bulk counterpart. The significant increase in hardness could be due to the lacking of dislocation avalanche that is the typical yielding characteristic of bulk tungsten. The determination of hardness of 2D materials was concerned with the nanoindentation of silicon nitride thin films deposited on silicon substrate. A deconvolution method that relates the hardness of the film/substrate bilayer to those of the constituent materials via a power-law relation was proposed. Geometrical dependence of hardness was wholly contained in the power-law exponents, expressed as empirical functions of indenter penetration relative to film thickness.
2:40 PM
Microhardness Characterization in Developing a High-Strength, High-toughness, and Superior Ballistic Resistance Low-Carbon 10% Ni Steel: Xian Zhang1; 1Naval Surface Warfare Center
In our effort to develop steels that exceed the ballistic resistance, strength, and toughness of current ship steels, we developed optimally QTL treated low-carbon 10Ni steel samples. These plates displayed exceptional properties, showing an improvement of more than 15% in FSP ballistic limit and strength as well as superior toughness over a widely used naval steel. A vibrating sample magnetometer study on the effect of QLT process and dynamic deformation on 10Ni steel led to the discovery of the underlying mechanisms that result in improved properties of the steel. This study yielded data leading us to conclude that dynamic deformation during ballistic perforation induced an austenite to martensite transformation, which improves the global dynamic plasticity and ballistic resistance of steel targets. This mechanism, similar to the TRIP effect, might be appropriately named BIP (ballistic induced plasticity). This theory is supported by the microhardness maps of sectioned craters of ballistic samples.
3:00 PM Invited
Mechanics of Material Removal in Chemical Mechanical Planarization: Sinan Muftu1; 1Northeastern University
In chemical mechanical polishing (CMP), a rigid wafer is forced on a rough, elastomeric polishing pad, while abrasive containing slurry flows through the interface. Applied pressure on the wafer is carried partially by the 2-body pad-wafer contact and by 3-body pad-wafer-abrasive contact. Fraction of the applied pressure carried by particle contacts is significant for material removal rate (MRR). A model will be presented for pad-wafer-abrasive interactions at different contact scales, ranging from particle-pad interactions to rough contact of pad and wafer. Effects of surface forces (e.g., van der Waals and electrical double layer) are included in the model. The wafer surface is modeled as consisting of layers with different hardness to include slurry chemistry. MRR rate is calculated based on the wafer-abrasive particle contact force, and by considering adhesive and abrasive wear mechanisms. A general overview of CMP will be presented along with model results and comparison with experiments.
3:20 PM Break
4:00 PM Invited
Mechanical Properties of Sputtered, Highly Textured Cu/Ni Multilayers: Yue Liu1; Daniel Bufford1; Haiyan Wang1; Cheng Sun1; Xinghang Zhang1; 1Texas A&M University
We report on the synthesis of sputtered, highly (111) and (100) textured Cu/Ni multilayers with individual layer thickness, h, varying from 1 to 200 nm. When, h, decreases to 5 nm or less, X-ray diffraction spectra show epitaxial growth of Cu/Ni multilayers. High resolution TEM studies confirm the coexistence of twin and coherent layer interfaces in highly (111) textured Cu/Ni multilayers at smaller h. Film hardnesses increase with decreasing h, approach a maxima at h of several nm, and show softening thereafter. Detailed comparisons of interface and size dependent strengthening mechanisms are provided for (111) and (100) textured Cu/Ni multilayers. The formation mechanisms of twin interfaces as well as their significance on strengthening mechanisms are also discussed.
4:20 PM
Characterization of Indentation-Induced Hydrogen Cracking Using Cohesive Zone Modeling: Akio Yonezu1; Takuma Hara1; Toshiyuki Kondo1; Kohji Minoshima1; 1Osaka University
This study investigates hydrogen embrittlement cracking (HEC) upon indentation in a high-strength steel. When an indentation test is applied to the high-strength steel, i.e., steel that has absorbed hydrogen, several cracks appear around the impression, whereas as-received steel with no hydrogen absorption does not produce any cracks. It is also found that the crack length is depended on hydrogen content. An experimental/computational framework is used to elucidate the mechanism of such indentation cracks caused by hydrogen embrittlement. The crack propagation is computed based on cohesive zone model in finite element method in order to investigate stress intensity factor around the crack tip. It is found that crack initiates at loading, and then it propagates under unloading. The value of stress intensity factor at indentation crack tip agrees well with the threshold value of crack propagation of HEC. This indicates that the length of the indentation crack can roughly estimate KISCC.
4:40 PM Invited
Effect of an Electric Field on Solute Solubility in Al Alloys Measured by Hardness: Hans Conrad1; Jun Wang1; 1NC State University
The influence of a DC electric field on the pertinent solute solubility during the solution heat treatment of three AA6XXX (Mg2Si) Al alloys was determined employing Vickers hardness. Thermodynamic analysis of the results gave that the field decreased both the entropy ∆Ss and enthalpy ∆Hs of solution, but still gave a reduction in the Gibbs free energy ∆Gs = ∆Hs – T ∆Ss. Employing the relation Cs =αexp (- n ∆Gs /kT). The reduction in ∆Gs gave that the field increased the solubility Cs of the pertinent solutes, the magnitude depending on valence. The decrease in ∆Gs by the field and it`s dependence on valence indicates that there can exist a significant electronic component to the Gibbs free energy of solution in addition to the size misfit.
5:00 PM
Nanoindentation of Pure Tin: Effect of Electric Current: Guangfeng Zhao1; Fuqian Yang1; 1University of Kentucky
The pass of an electric current through a conducting material causes electromechanical interaction, which plays an important role in controlling structural reliability of devices and systems. Nanoindentation was performed to investigate the effect of direct electric current on the indentation behavior of pure tin at ambient temperature. The indentation load was in the range of 50 µN to 200 µN and the current density in the range of 726 to 2899 A/cm2. It was found that the surface temperature of tin with an electric current passing through is proportional to the square of the current density. The contact modulus decreased with increasing current density, while the hardness decreased slightly with increasing current density. This electromechanical behavior might be due to Joule heating and the momentum exchange between high speed electrons and atoms.
5:20 PM Invited
A Mystery of Current Spike: Nanoscale Plasticity Revised: Roman Nowak1; Dariusz Chrobak1; Sijo Nagao1; David Vodnick2; Michael Berg2; 1Nordic Hysitron Laboratory, Aalto University; 2Hysitron Inc.
One of the fundamental questions in materials science concerns the nature of deformation of solids. The onset of plasticity has traditionally been understood in terms of dislocation nucleation and motion. A recent study using nanoindentation, a nanoscale deformation technique, has proven that initial displacement transient events occurring in metals are the direct result of dislocation nucleation [1]. Meanwhile, recent MD-calculations indicate that in GaAs this initial displacement transient is related rather to a pressure-induced crystal transition [2]. This never before seen nanoindentation-induced phase transformation of GaAs structure, is in consistent agreement with the curious electrical response of GaAs to nanoindentation [3]. This new discovery calls for a major shift in nanoscale plasticity.
5:40 PM Student
Strain Rate Dependence of the Indentation Stress of Heat-Treated AA 6061 Alloy over the Indentation Depth Range from 50 nm to 10.0 μm: Meysam Haghshenas1; Lin Wang2; Robert Klassen1; 1The University of Western Ontario; 2Beijing Institute of Technology
Room-temperature load-controlled pyramidal micro-indentation tests (loading rates of 10, 100, 500, 1000, 1500, and 2000 mN/sec to loads of 500, 1000, 1500, and 2000 mN) were performed on the AA 6061 in the annealed, partially aged, and fully aged conditions to assess the dependence of the activation energy ΔG upon indentation depth and strain rate. The dependence of the indentation stress upon depth from 50 nm to 10.0 μm and indentation strain rate of 10-4 to 1 sec-1 was analysed by applying an Arrhenius equation as a function of ΔG/kT. Results indicate that ΔG of the dislocation-obstacle interactions is dependent upon the indentation depth, strain rate, and the microstructure (i.e. the heat treatment). For indentations of depth greater than about 1 μm, ΔG ranged from 0.35 to 0.10 eV and decreased with increasing indentation rate. When the indentation depth was less than 1 μm, ΔG was observed to increase with increasing strain rate. Our findings present new, and important, information on the effect of high indentation strain rate, which is an inevitable occurrence during sub-micrometer depth pyramidal indentation, on the much reported length-scale dependence of the indentation hardness of ductile metals.
6:00 PM Cancelled
Measuring Creep Parameters Using Nanoindentation and Finite Elements: James Dean1; Angela Bradbury1; Bill Clyne1; 1University of Cambridge, UK
Nanoindentation is the established technique for characterising various material properties at small length scales (E and H). More recently indentation techniques have been used to determine the yield stress and initial work hardening rate of metallic materials. Procedures for measuring variations in surface residual stresses [2] have also been established. A method for inferring the uniaxial creep behaviour from indentation data is presented here. Creep dwell curves obtained from indentation experiments are presented for a range of temperature. These dwell curves contain information about the characteristic creep response of the copper being studied. Using iterative finite element simulations employing customised primary creep subroutines, the experimentally-measured creep dwell curves can be simulated by carefully controlling the creep parameters in the subroutine.
6:20 PM Cancelled
Tribology of Hardfaced Surfaces: Impact of Elastic and Plastic Indentation Work on Wear Performance: Ewald Badisch1; Markus Varga1; Thomas Koch2; Martin Kirchgaßner3; 1AC2T research GmbH; 2Vienna University of Technology; 3Castolin Ges.m.b.H.
The objective of the present work was the comparison of hardfacings applied by metal inert gas and plasma transferred arc cladding processes. Content of hardphases was kept in a similar range, whereas matrix composition and cladding process were varied in order to find the dominant parameters influencing wear behaviour. Microstructural procedure included nano-hardness mapping, scratch-tests and metallographic investigations. Additionally, instrumented macro-hardness tests were performed on the coarse multiphase microstructures in order to investigate the influence of mechanical support due to hardphases reinforcing the matrix. 3-body abrasion resistance under low-stress conditions was evaluated according ASTM G65. A continuous impact/abrasion test was implemented for evaluation of combined impact/abrasion behaviour. It was found out that micro wear mechanisms and mechanical properties of both metallic matrix and tungsten carbide are in strong interaction. A good correlation of elastic and plastic indentation properties of manufactured microstructures was found for pure abrasion and combined impact/abrasion conditions.