The high temperature behavior of solute strengthening has previously been treated approximately using various scaling arguments, resulting in logarithmic and power-law scalings for the stress-dependent energy barrier Delta E(tau) versus stress tau. Here, a parameter-free solute strengthening model is extended to high temperatures/low stresses without any a priori assumptions on the functional form of Delta E(tau). The new model predicts that the well-established low-temperature, with energy barrier Delta E-b and zero temperature flow stress tau(y0), transitions to a near-logarithmic form for stresses in the regime 0.2 < tau/tau(y0) <= 0.5 and then transitions to a power-law form at even lower stresses tau/tau(y0) < 0.03. Delta E-b and tau(y0) remains as the reference energy and stress scales over the entire range of stresses. The model is applied to literature data on solution strengthening in Cu alloys and captures the experimental results quantitatively and qualitatively. Most importantly, the model accurately captures the transition in strength from the low-temperature to intermediate-temperature and the associated transition for the activation volume. Overall, the present analysis unifies the different qualitative models in the literature and, when coupled with the previous parameter-free solute strengthening model, provides a single predictive model for solute strengthening as a function of composition, temperature, and strain rate over the full range of practical utility.
The finite-temperature yield stress of Mg-Al alloys undergoing basal slip is investigated using a recently developed parameter-free solute strengthening model. The model takes input from first-principles calculations of the dislocation/solute interaction energy and evaluates the solute strengthening due to fluctuations in solute concentration, taking into account the correlation of these fluctuations as a function of dislocation roughening. Due to the wide partial separation of the Mg basal edge...
Alloys containing substitutional solutes exhibit strengthening due to favorable solute fluctuations within the alloy that hinder dislocation motion. Here, a quantitative, parameter-free model to predict the flow stress as a function of temperature and strain rate of such alloys is presented. The model builds on analytic concepts developed by Labusch but introduces key innovations rectifying shortcomings of previous models. To accurately describe the solute/dislocation interaction energies in and...
Experimental Charecterization of Dislocation Mechanisms, Interactions Between Dislocations and Small-size Obstacles, Frictional Forces in Metals, Dislocation Cross-slip, Experimental Studies of Peierls-Naborro-Type Friction Forces in Metals and Alloys, The Peierl-Nabarro Mechanisms in Covalent Crystals, Dislocations Climb, Dislocation Multiplication, Exhaustion and Work Hardening, Mechanical Behaviour of some ordered intermetallic
Last. Dallas R. Trinkle(UIUC: University of Illinois at Urbana–Champaign)H-Index: 28
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Abstract Solid-solution strengthening results from solutes impeding the glide of dislocations. Existing theories of strength rely on solute/dislocation interactions, but do not consider dislocation core structures, which need an accurate treatment of chemical bonding. Here, we focus on strengthening of Mg, the lightest of all structural metals and a promising replacement for heavier steel and aluminum alloys. Elasticity theory, which is commonly used to predict the requisite solute/dislocation i...
The mixing of metals to form alloys with enhanced properties has been known at least since the Bronze Age, although being able to predict their properties remains difficult. An analytical model using computational input is now able to quantitatively predict the mechanical properties of metal yield stress in solute-strengthened alloys.
Strengthening of dislocations by multiple obstacle types occurs in many engineering alloys. Theories have rationalized two different scaling laws for the total strength, \( \tau_{t}^{\alpha } = \tau_{1}^{\alpha } + \tau_{2}^{\alpha } , \) with α = 1 or 2, where τ1 and τ2 are the strengths of the two individual obstacle types. Simulations have clearly demonstrated α = 2, while “friction” strengthening must correspond to α = 1. Here, line-tension simulations of dislocation glide through two types ...
#1Johan Zander(KTH: Royal Institute of Technology)H-Index: 5
#2Rolf Sandström(KTH: Royal Institute of Technology)H-Index: 30
Abstract Models for strength properties are proposed for commercially aluminium alloys. The alloy group investigated are the hardenable alloys from the 2000 (Al–Cu and Al–Cu–Mg), 6000 (Al–Mg–Si) and 7000 (Al–Zn–Mg) series. The same model for solid solution hardening that has successfully been applied to non-hardenable alloys has been used. For precipitation hardening, particle cutting and the Orowan mechanism have been considered. The same basic model is used for all strength properties. It is d...
#1Johan Zander(KTH: Royal Institute of Technology)H-Index: 5
#2Rolf Sandström(KTH: Royal Institute of Technology)H-Index: 30
Last. Levente Vitos(KTH: Royal Institute of Technology)H-Index: 57
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A range of mechanical properties have been investigated for non-hardenable aluminium alloys. Commercially pure aluminium, Al-Mn, and Al-Mg alloys in five tempers have been covered. In the models so ...
Solutes have been added to strengthen elemental metals, generating usable materials for millennia; in the 1960s, solutes were found to also soften metals. Despite the empirical correlation between the “electron number” of the solute and the change in strength of the material to which it is added, the mechanism responsible for softening is poorly understood. Using state-of-the-art quantum-mechanical methods, we studied the direct interaction of transition-metal solutes with dislocations in molybd...
Abstract The thermally activated motion of a dislocation through an array of randomly distributed solute atoms is studied. The influence of fluctuations in the solute density on the activation energy for dislocation motion is investigated, and the stress dependences of the effective activation energy and the activation volume are determined. It is shown that, in creep deformation, fluctuations in the activation energies may lead to a creep strain which increases with time according to a power la...
#1R. E. Kubilay(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 1
#2A. Ghafarollahi(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 4
Last. William A. Curtin(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 79
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Recent theory proposes that edge dislocations in random body-centered cubic (BCC) high entropy alloys have high barriers for motion, conveying high strengths up to high temperatures. Here, the energy barriers for edge motion are computed for two model alloys, NbTaV and MoNbTaW as represented by interatomic potentials, using the Nudged Elastic Band method and compared to theoretical predictions. The average magnitude of the barriers and the average spacing of the barriers along the glide directio...
Last. Sean R. Agnew(UVA: University of Virginia)H-Index: 54
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Abstract The principle of “stress equivalence” proposed by Basinski et al. offers insight regarding the nature of thermally activated plasticity of solid solution alloys of FCC and HCP (Mg) crystal structures at low temperatures. More recently, Leyson and Curtin have developed a theoretical framework which builds upon the Labusch solute strengthening model. The current work analyzes some recent results from the literature (for single crystal Mg-Zn, Mg-Y, and Mg-Dy) which permit a further examina...
Last. Xiaowang Zhou(SNL: Sandia National Laboratories)H-Index: 26
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Abstract Using molecular dynamics simulations, we compute the mobility of an edge dislocation in a random FCC Fe0.70Ni0.11Cr0.19 alloy over temperatures from 100 to 900 K and shear stresses up to 600 MPa. Dislocation mobilities are shown to be intrinsically length-dependent when the line length is below a minimum value, with shorter lines having a reduced mobility. We show that this minimum line length is sensitive to both temperature and stress. We develop a drag model with terms accounting for...
Abstract Plastic deformation of HfNbTaTiZr body-centered cubic high-entropy alloy (BCC HEA) was investigated at 77 K. Tensile stress-strain curves showed strong temperature dependence of yield strength. Characteristics of dislocation slip at 77 K was analyzed using slip traces which confirmed active slip on {112} planes. The apparent activation volume (V*) suggested thermally activated kink/kink-pair nucleation at 77 K (V*~7b3). V* values of BCC HEA and pure Nb were nearly same at 77 K. Low-temp...
#1Shankha Nag(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 2
#2William A. Curtin(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 79
Abstract The yield strength of random metal alloys, i.e. alloys with random occupation of the crystalline lattice sites by the elemental constituent atoms all considered as solutes, is primarily understood as controlled by solute/dislocation interactions. Solute-solute interactions exist and provide the energetic driving force for both short-range and long-range order but can then also affect yield strength even in the random alloy. Here, a recent theory for random alloys is extended to include ...
The fundamental interactions between an edge dislocation and a random solid solution are studied by analyzing dislocation line roughness profiles obtained from molecular dynamics simulations of Fe0.70Ni0.11Cr0.19 over a range of stresses and temperatures. These roughness profiles reveal the hallmark features of a depinning transition. Namely, below a temperature-dependent critical stress, the dislocation line exhibits roughness in two different length scale regimes which are divided by a so-call...
Last. Chuang Deng(UM: University of Manitoba)H-Index: 18
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Abstract In this work, the homogeneous and heterogeneous nucleation of dislocations in a representative face-centered-cubic high entropy alloy (HEA) CoNiCrFeMn is studied by combining molecular dynamics simulations and continuum mechanics modeling. It is found that as compared to conventional metals such as Cu, HEAs have relatively low activation energy but require high athermal stress for dislocation nucleation. This seemingly odd behavior originates from the uniquely low (even negative) stacki...
#1H.R. Leonard(UConn: University of Connecticut)H-Index: 3
#2S. Rommel(UConn: University of Connecticut)H-Index: 4
Last. Mark Aindow(UConn: University of Connecticut)H-Index: 43
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Abstract A series of three Al–Cr–Mn–Co–Zr alloys with total alloy contents of 3.58, 4.41 and 4.90 at.% has been produced by blind-die compaction of gas-atomized nano-composite powders. The alloy microstructures consist of a face-centered cubic (FCC) Al matrix with characteristic distributions of quasicrystalline I-phase dispersoids giving hardness values of up to 162 HV. The consolidated alloys were forged uniaxially to upsets of 30-90% at temperatures of 300-370 °C to investigate the effects of...
