Experimental evidence of relaxation arising from the motion of geometrical kinks on screw dislocations in iron

Abstract

Internal friction measurements with a superimposed bias stress have provided evidence for geometrical kink migration on screw dislocations in iron. This intrinsic process causes a relaxation phenomenon in internal friction which has been identified with the occurrence of a subpeak (below 20 K) of the α-peak. The effect of different bias stress has allowed us to evaluate the kink migration energy, E ^m _k ? 0·001eV.     

Unusual room-temperature compressive plasticity in nanocrystal-toughened bulk copper-zirconium glass

Cast Cu₅₀Zr₅₀ alloy rods with a diameter of 1?mm have been found to consist of a glassy phase containing fine crystalline particles with a size of about 5?nm. They have a glass transition temperature T _g of 675?K, and a large supercooled-liquid region extending 57?K above T _g. The rods exhibit a high yield strength of 1860?MPa and a Young's modulus of 104?GPa. Because they contain a dispersion of embedded nanocrystals, the as-cast bulk metallic glass rods can sustain a compressive plastic strain at room temperature of more than 50%, an exceptional value which is explicable by compensation of any shear softening by nanocrystal coalescence and pinning of shear bands.     

Phonon–phason coupling in a Mg–Ga–Al–Zn icosahedral quasicrystal

Precise X-ray diffraction measurements have revealed that phonon (conventional) strain is introduced at the phase transition from an icosahedral quasicrystal to its orthorhombic crystal approximant in a Mg–Ga–Al–Zn alloy. From the magnitude of the measured phonon strain, the phonon–phason coupling constant has been evaluated. This constant is approximately ?0.03μ (μ: shear modulus) and it is in good agreement with the result of a theoretical calculation reported previously (W.-J. Zhu and C.L. Henley, Europhys. Lett. 46 748 (1999)). This is the first study that experimentally evaluates the phonon–phason coupling constant in any existing quasicrystalline phase.     

Dipole of misfit dislocations in axially symmetric structures

The nucleation of a pair of misfit dislocations of Burgers vectors b 1 and b 2 with b 1 + b 2 = 0 has been studied for the case of an axially symmetric two-phase structure. Considering a cylindrical inclusion epitaxially stressed in a unbounded matrix, the variation in the total energy due to the formation of the dipole has first been determined as a function of the radius of the inclusion and the epitaxial stress. The conditions for nucleation of the dipole on the interface have then been investigated as a function of the ratio of the shear modulus and of the misfit stress.     

Dynamic and quasi-static mechanical properties of fibre-reinforced metallic glass at different temperatures

We have investigated the dynamic and quasi-static mechanical properties of a tungsten fibre-reinforced Zr_41.25Ti_13.75Ni₁₀Cu_12.5Be_22.5 bulk metallic glass composite (W/BMG) at temperatures ranging from 77 to 473?K. It was found that the yield stress and elastic modulus of the composite increase while strain-to-failure decreases with decreasing temperature. Tests under uniaxial dynamic compression showed that the W/BMG has a higher yield stress than under quasi-static compression. It was shown that yielding of the composite material is dominated by a shear banding process in the glass matrix, which is essentially a viscous flow as a consequence of local adiabatic heating. The interval between the nominal testing temperature and the temperature at which shear bands initiate is a key factor affecting the shear banding process, rendering the properties of the W/BMG very sensitive to temperature.     

Indentation hardnesses of semiconductors and a scaling rule

The Vickers hardnesses of 15 semiconductors, namely Si, Ge, SiC, AlN, GaN, GaP, GaAs, GaSb, InP, InAs, InSb, ZnO, ZnSe, ZnTe and CdTe, have been investigated from room temperature to their melting points. The temperature dependences of the Vickers hardness H V of 11 of these semiconductors, namely those with a cubic structure, obey a universal relationship when H V and the temperature T are scaled respectively by the shear modulus G and by Gb 3 / k B, with b being the magnitude of the Burgers vector. The scaling rule is the same as that found for the temperature dependence of the critical shear stress c for the {111}<110> slip system, satisfying the relationship H V = (70-100) c .     

Stacking fault and dislocation glide on the basal plane of graphite

Generalized stacking-fault energies for the basal plane of graphite are calculated from first principles for slip along two high-symmetry directions. The rhombohedral fault energy compares well with experiment and the anisotropy in behaviour is consistent with observed dislocation network geometry. Utilizing these calculated fault energies within a modified Peierls-Nabarro model, we estimate the barrier for basal dislocation motion based on lattice friction. This is found to be extremely small, from which we conclude that dislocation network interaction and pinning, rather than the Peierls barrier, must determine the practical shear strength of graphite. However, at low dislocation densities or over small crystallite regions, the shear strength should tend to this lower limit. We discuss the relevance of this to the mechanism of lubrication.     

Energy,compressibility and covalency in the carbon subgroup

It is shown that a scaling relation of the type K V ₀/ E ₀ constant, where K₀, V₀ and E₀ are the bulk modulus, volume and total energy respectively at normal pressure, holds for the C subgroup of the Mendeleev periodic table of elements, which consists of C itself, Si, Ge, Sn and Pb. This means that so-called covalency does not contribute significantly to the compressibility of the corresponding substances. The extreme high value of the bulk modulus of diamond is clearly the result of its highest known atomic density.     

Psychological Reactance: Factor Structure and Internal Consistency of the Questionnaire for the Measurement of Psychological Reactance

Abstract

Psychological reactance, the theory that people resist attempts to constrain either their thoughts or their behaviors (J. W. Brehm, 1966), has been an influential concept in social psychology. In an attempt to measure reactance, J. Merz (1983) developed the Questionnaire for the Measurement of Psychological Reactance (QMPR). Subsequent researchers (S.-M. Hong & R. Ostini, 1989; R. K. Tucker & P. Y. Byers, 1987) have debated both the exact factor structure and the psychometric stability of the QMPR. In the present study, 898 undergraduates completed the QMPR. Factor analysis suggested that psychological reactance is multidimensional. The authors found 3 factors underlying the QMPR, but the QMPR provided unreliable estimates for each of those factors. According to the results, the QMPR as currently written is psychometrically unsatisfactory.     

Experimental investigations of TB2 alloy by pack boriding with rare-earth oxides

ABSTRACT

An orthogonal test with four factors, namely temperature, time, type of rare-earth oxides (REOs) and REO content, was performed to obtain the optimised boriding parameters of TB2 alloy by pack boriding with REOs. It is found that temperature has the strongest effect on the boride layer thickness, while time has the strongest effect on the surface hardness and coefficient of friction. The optimum parameters for pack boriding of TB2 alloy with REO are a temperature of 1373?K, a time of 20?h, La₂O₃ as the REO with a content of 4?wt.%.     

Books: Briefly noted

Abstract

Transcend by Morton Kelsey (The Crossroad Publishing House, New York N. Y. 1981)     

Crystallographic analysis of the fcc-to-fct martensitic transformation in an In22.73at.%Tl alloy

Analytical solutions for various crystallographic parameters have been obtained from the application of the infinitesimal deformation (ID) approach to the fcc M fct martensitic transformation with the (101) g [101] g twinning shear as the lattice invariant shear deformation. All crystallographic parameters were calculated for an In-22.73at.%Tl alloy. In order to compare numerical solutions between the ID approach and phenomenological crystallographic theory, the corresponding crystallographic parameters were also calculated using the Wechsler-Lieberman-Read (WLR) theory. Agreement between the two results obtained from the ID approach and the WLR theory is found to be excellent.     

Revealing texture architecture in a surface gradient nanostructured Al-Cu-Mg alloy

ABSTRACT

A multiscale crystallographic texture architecture in a surface gradient nanostructured Al-Cu-Mg alloy after surface sliding friction treatment (SSFT) has been revealed by a combination of electron backscatter diffraction and precession electron diffraction (PED)-assisted transmission electron microscopy (TEM) orientation mapping. Accompanying a grain structure variation from lamellar coarse grains to equiaxed nanograins, the major texture components evolve from brass {110}<112> in the coarse-grain matrix, Goss {110}<001> at a depth of ～80?μm, E {111}<011> and F {111}<112> at a depth of ～20?μm, to a mixture of rotated cube {001}<110>, E and F in the topmost surface layer. The through-thickness textural development and evolution are attributed to the cyclic loading of concurrent shear and compression during the SSFT processing. The PED-assisted orientation mapping shows good capability in mapping severe plastic-deformation-induced nanostructures with large residual strains and high defect density.     

On the shape of a dislocation shear loop in stable equilibrium

It is demonstrated that the shape of a dislocation shear loop held in stable equilibrium by an infinitesimal shear loop of the same sign at its centre is a circle. This unexpected result may help to explain some discrepancies between the shape of loops predicted by de Wit and Koehler and experimental observation.     

Nanoprecipitates of icosahedral phase in quasicrystal-strengthened Mg-Zn-Y alloys

Extensive microstructural studies have been performed with respect to the formation of the icosahedral quasicrystalline phase and its relationship to other phases in Mg 95 Zn 4.2 Y 0.8 alloy. The icosahedral phase forms as an intergranular eutectic phase as well as precipitates in the matrix. The precipitates are nanosized (typically 50 nm) with a definite orientation relationship with the matrix, sharply faceted on twofold planes which are on the basal and prismatic planes of the matrix. The detailed crystallographic relationship with the matrix is described. The icosahedral phase is occasionally found to coexist with the cubic W-Zn 3 Mg 2 Y 3 phase with a definite crystallographic relationship.     

First principles study of the temperature-dependent elastic properties of W

The temperature-dependent elastic constants of body-centred cubic (bcc) phase W are presented from first principles quasi-static approach. With the quasi-harmonic approximation model, the Hugoniot equation of state and temperature-dependence linear thermal expansion coefficient is successfully obtained. The adiabatic elastic constants show a normal behaviour with temperature: decrease with increasing temperature. Based on the obtained adiabatic elastic constants, the structural stability and polycrystalline aggregate properties including bulk modulus B, shear modulus G, and B/G ratio are analysed for bcc phase W. In addition, the sound velocities as a function of temperature for bcc phase W are predicted.     

Book reviews

Paul Ricoeur. Freud and Philosophy: An Essay On Interpretation (trans. Denis Savage). New Haven: Yale University Press, 1970. Pp. 1–551. Indexed. $15.00.

Keith Campbell. Body and Mind. Garden City, N.Y.: Doubleday, 1970. Pp. vi, 150. Indexed. $1.45 (paper).

D. J. O'Connor. Free Will. Garden City, N.Y.: Doubleday Anchor Books, 1971. Pp. 1–150. Indexed. $1.45.

Dwight van de Vate, Jr. (ed.). Persons, Privacy, and Feeling: Essays in the Philosophy of Mind. Memphis: Memphis State University Press, 1970. Pp. vii, 140. Indexed. $5.00.     

Strain localization in nickel single crystals cyclically deformed at 77 K

Nickel monocrystals oriented for single slip have been cyclically deformed at 77 K at plastic strain amplitude between 5 x 10^-4 and 1 x 10^-2 up to saturation of the stress amplitude. After unloading from maximum compression, the slip markings on the surface of the specimens were removed and the deformation continued for one half cycle in tension. As previously observed for room-temperature deformation, the plastic strain was found to be localized in narrow slip bands (SBs). Using atomic force microscopy at a given imposed strain amplitude, a wide spectrum of local plastic strains was found. The averaged resolved shear strain of the SBs was found to be independent of the imposed plastic strain amplitude and turned out to be a factor of three larger than the upper plateau strain limit of the cyclic stress-strain curve.     

Friction and wear behaviour of Inconel 718 alloy fabricated by selective laser melting after heat treatments

ABSTRACT

The effect of heat treatments (solution and double aging) on friction and wear behaviour of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) were studied. After heat treatment of solution and double aging, the friction and wear of the alloy have been improved. The worn surfaces of heat-treated IN718 alloy became smoother, and micro-ploughing became shallower. After solid solution hearting, a portion of the Laves phase ((Ni, Fe, Co)₂(Nb, Ti, Mo)) dissolves into the matrix, after which the γ″ phase (Ni₃Nb) andthe equilibrium phase of the δ phase (Ni₃Nb) precipitates during double ageing. After solution and double aging, nano-scale γ′ (Ni₃(Al, Ti)) and γ″ phases distribute homogeneously in the matrix, which improves the material hardness and wear resistance of the SLMed IN718 alloy.     

Influence of Guinier-Preston zones on deformation in Ti-rich Ti-Ni thin films

The deformed microstructure of a Ti-48.9at.%Ni thin film has been investigated by transmission electron microscopy. It was found that Guinier-Preston (GP) zones exist in the thin film and the martensite has (001) compound twins as substructure. The microstructure of the martensite shows that the GP zones do not stop both the shear deformation of martensitic transformation and the twinning shear of (001) deformation twin in the martensite phase. These results give a microstructural explanation for the previous result that Ti-rich Ti-Ni thin films with GP zones show a large transformation strain despite the presence of the GP zones.