Surface form memory by indentation and planarization of NiTi: displacements and mechanical energy density during constrained recovery

Indentation-induced two-way shape memory leads to pronounced temperature dependence of the depth of spherical indents made in martensitic NiTi shape-memory alloys. They are shallower when austenitic, and depth varies during both M → A and A → M transformations. If the impression is planarized, by metallographic grinding at T < M _f , a protrusion rises at the site when warmed past A _f . If cooled again this “exdent” retreats, restoring optical flatness. The cycle is repeatable, and exdent heights can exceed 15% of prior indent depth. Since it maps between macroscopically distinguishable topographies, or forms, at orders greater length scale than the surface roughness, we call the effect “surface form memory”—SFM. Notable regarding potential applications is that, when loaded in compression by planar contact with a strong base metal, exdents exert sufficient pressure to indent the latter, suggesting that subsurface transformational mechanisms operate at volumetric work-energy densities >10⁷ J/m³, fully ~10% of the M → A enthalpy.     

Pressure-dependent electronic properties of MgO polymorphs: a first-principles study of Compton profiles and autocorrelation functions

The first-principles periodic linear combination of atomic orbitals method within the framework of density functional theory implemented in the CRYSTAL06 code has been applied to explore effect of pressure on the Compton profiles and autocorrelation functions (AF) of MgO. Calculations are performed for the B1, B2, B3, B4, B8₁, and h-MgO polymorphs of MgO to compute lattice constants and bulk moduli. The isothermal enthalpy calculations predict that B4 → B8₁, h-MgO → B8₁, B3 → B2, B4 → B2, and h-MgO → B2 transitions take place at 2, 9, 37, 42, and 64 GPa, respectively. The high-pressure transitions B8₁ → B2 and B1 → B2 are found to occur at 340 and 410 GPa, respectively. The pressure-dependent changes are observed largely in the valence electrons Compton profiles, whereas core profiles are almost independent of the pressure in all MgO polymorphs. Increase in pressure results in broadening of the valence electrons Compton profiles. The principal maxima in the second derivative of Compton profiles shifts toward high-momentum side in all structures. Reorganization of momentum density in the B1 → B2 structural phase transition is seen in the first and second derivatives before and after the transition pressure. Features of the AFs shift toward smaller distances when pressure increases.     

Coherent elastic energy calculation of ω particles in β matrix for Zr–Nb alloys

The misfit and coherent elastic energy caused by ω particles in β matrix is quantitatively calculated in this study. First, the coherent strain matrixes for four ω variants are established including the misfit parameters based on Khachaturyan’s theory. Then, the misfit and coherent elastic energy in athermal β → ω transition, and isothermal β → ω transition are calculated, respectively. The calculation results indicate that the coherent elastic energy gets maximum value when x _Nb = 0.08 (Nb content) and gets minimum value when x _Nb = 0.1518 in quenching Zr–Nb alloys, which are in fair agreement with experimental results. For isothermal β → ω transition, the misfit and coherent elastic energy depend on composition and aging temperature. The misfit caused by isothermal ω phase is much larger than the one caused by athermal ω phase. This results in larger coherent elastic energy in isothermal β → ω transition. In addition, the misfit is found as an approximate linear function of temperature and composition for Zr–Nb alloys, and the coherent elastic energy is revealed as an increasing function of |v _F –v _S | for the two kinds of transition.     

A constraint‐based approach to the modelling and analysis of packaging machinery

To enable packaging machinery manufacturers to compete at an international level, it is necessary to introduce them to more advanced design methods and technologies. For years, the evolution of packaging machinery has relied heavily on trial‐and‐error methods. The demands for continual increases in the performance capabilities of the machines, escalating legislation, environmental directives and changes in the characteristics of the product require rapid development of existing machine designs and the creation of new machines. This paper discusses the needs of SME packaging machinery manufacturers and identifies their requirements for methods in support of the design and redesign of packaging machinery. The need to identify, capture and manipulate design knowledge is critical for SMEs, where all too often design records are incomplete. Furthermore, a systems modelling approach that provides for support over the conceptual, embodiment and detailed design phases is essential for the rapid and effective development of designs. In order to meet these requirements, a methodology is proposed which incorporates ‘constraint modelling’ techniques. The methodology provides for experimental investigation and computer‐based modelling, which together aid the designer in gaining a fundamental understanding of the design problem. This enables the identification and representation of design knowledge, the determination of the limitations of an existing design, the evaluation of alternative designs and redesign strategies, as well as the embodiment, refinement and optimization of design solutions. The theory of ‘constraint modelling’ is discussed and the various phases of the methodology described. The applications of the methodology to a new machine design and a redesign program are also detailed. Copyright © 2001 John Wiley & Sons, Ltd.     

Mathematical Model for Transitional Processes in Josephson Cryotrons Based on Tunnel Junctions

In this work, we consider controlling of logical states of Josephson memory cells (cryotrons) based on superconductor-insulator-superconductor (SIS) Josephson tunnel junctions by external current impulses. A mathematical model for the transitional processes that take place during direct logical transitions “0” → “1” and inverse logical transitions “1” → “0” is proposed. By means of mathematical modeling, we investigate transitional processes in cryotrons during the change of their logical state and obtain their transitional characteristics for operational temperatures T ₁=11.6 K and T ₂=81.2 K, close to the boiling temperatures of helium and nitrogen, respectively. It is shown that such memory cells can efficiently operate under the temperature T ₂=81.2 K. The behavior of the Josephson cryotrons as well as their operational stability is explored.     

Luminescence properties and electronic structure of Sm<Superscript>3+</Superscript>-doped YAl<Subscript>3</Subscript>B<Subscript>4</Subscript>O<Subscript>12</Subscript>

The luminescence properties of Sm³⁺ ions in YAl₃B₄O₁₂ were studied upon synchrotron excitation in the 3.8–11 eV region. In addition to the 4f → 4f excitation bands, the excitation spectra of the Sm³⁺ emission contain broad bands at 6.1 and ~7.0 eV. These bands are attributed to charge transfer transition in Sm³⁺–O²⁻ complexes and 4f → 5d transition of Sm³⁺ ions, respectively. The optical absorption edge of YAl₃B₄O₁₂ was determined at 7.3 eV. A comparison with the results of electronic structure calculations on YAl₃B₄O₁₂ is also made.     

Effect of aging on martensitic transformation behavior of Ti48.8Ni50.8V0.4 alloy

In this article, the effect of aging on martensitic transformation of Ti_48.8Ni_50.8V_0.4 alloy was investigated. The results show that the martensitic transformation of the solution-treated shape memory alloy is a typical single-stage transformation process. The transformation temperatures of the samples aged at different temperatures for 0.5 h were lower as compared to that of the solution-treated alloy. With the increase of aging temperature, the transformation temperatures increase. After aging at 500 °C, the samples exhibit a multiple-stage transformation. The samples after aging at 500 °C for more than 5 h resulted in the transformation sequence of A → R→M1 and A → M2 upon cooling and M2 → A and M1 → A upon heating.     

Mixed convection flow near an axisymmetric stagnation point on a vertical cylinder

The mixed convection flow near an axisymmetric stagnation point on a vertical cylinder is considered. The equations for the fluid flow and temperature fields reduce to similarity form that involves a Reynolds number R and a mixed convection parameter λ, as well as the Prandtl number σ. Numerical solutions are obtained for representative values of these parameters, which show the existence of a critical value λ _c  = λ _c (R, σ) for the existence of solutions in the opposing (λ < 0) case. The variation of λ _c with R is considered. In the aiding (λ > 0) case solutions are possible for all λ and the asymptotic limit λ → ∞ is obtained. The limits of large and small R are also treated and the nature of the solution in the asymptotic limit of large Prandtl number is briefly discussed.     

Martensite-austenite transformation in maraging steel alloys during tensile deformation and thermal cycling

The effect of simultaneous additions of tungsten on the martensite (M) ⇌ austenite (γ) transformation, taking place during tensile deformation under different constant stresses and thermal cyclic rates for Fe-Ni-Co based maraging steel alloys was studied. The strain rate sensitivity parameterm was found to be 1.0 and 0.6 for the M →γ andγ → M transformations, respectively. The interpretation of deformation results implied a preponderantly diffusional mechanism in the M →γ transformation and a dislocation mechanism in theγ → M transformation. The increase of the lattice parameters of maraging steel alloys indicated that the hardening element, which is tungsten, was dissolved after tensile deformation.     

Drop Calorimetry Studies on 9Cr–1W–0.23V–0.06Ta–0.09C Reduced Activation Steel

The temperature dependence of enthalpy increment (H _T − H ₂₉₈) of 9 mass% Cr–1 mass% W–0.23 mass% V–0.06 mass% Ta–0.09 mass% C reduced activation steel has been measured by inverse drop calorimetry in the temperature range 400 K to 1273 K. A critical comparison of present isothermal enthalpy measurements with the results of our previous dynamic calorimetry studies has been made to reveal clearly the occurrence of various diffusional phase transformations that occur at high temperature. These phase changes are marked by the presence of distinct inflections or cusps in an overall nonlinear variation of enthalpy values with temperature. The principal thermal relaxation step of the martensitic microstructure obtained through quenching from the high-temperature γ-austenite phase is observed around 793 K. The ferromagnetic-to-paramagnetic transition of the α-ferrite phase is found to occur at 1015 K. The equilibrium values of γ-austenite start (Ae ₁) and finish (Ae ₃) temperatures are found to be 1063 K and 1148 K, respectively. A value of 12 J · g⁻¹ has been estimated for Δ°H ^α→γ the latent heat associated with the α → γ transformation. The measured enthalpy increment variation of the α-ferrite phase with temperature has been fitted to a suitable empirical function to estimate the temperature-dependent values of the specific heat. A comparison of the drop calorimetry-based indirect estimate of the specific heat with the direct differential scanning calorimetry-based values revealed that the drop calorimetry estimates are systematically lower than its dynamic calorimetry counterpart. This difference is attributed to the fact that, under finite heating rate conditions that are typical of dynamic calorimetry, measurements are made under nonequilibrium conditions. Notwithstanding this limitation, there is a good overall agreement between the two C _p values and also among the phase transformation temperatures so that a reliable assessment of thermal properties and phase transformation characteristics of reduced activation steel can be determined by a combined analysis of the results of drop and differential scanning calorimetry.     

Photoluminescence and magnetic properties of β-Ni(OH)2 nanoplates and NiO nanostructures

Single-crystalline β-nickel hydroxide (β-Ni(OH)₂) nanoplates of hexagonal structure have been synthesized through hydrothermal process. The β-Ni(OH)₂ nanoplates possess well-defined hexagonal shapes with landscape dimension of 45–140 nm and thickness of 20–50 nm. Post-thermal decomposition of the β-Ni(OH)₂ nanoplates led to the formation of single-crystalline NiO nanostructures with landscape dimension of 25–120 nm including nanorolls, nanotroughs and nanoplates. The sizes of the central hole in NiO nanorolls and the low-lying ground in NiO nanotroughs are in the range of 10–24 nm. Two photoluminescence emission peaks appear at 390.5 nm and 467 nm in the photoluminescence spectrum of NiO nanostructures and were assigned to the ¹T_{1 g} (G) → ³A_{2 g} and ¹T_{2 g} (D) → ³A_{2 g} transitions of Ni²⁺ in oxygen octahedral sites, respectively. Temperature-dependent magnetic measurement results show that an antiferromagnetic-paramagnetic transition occur at 26.3 K in β-Ni(OH)₂ nanoplates.     

Phase transitions and hard magnetic properties for rapidly solidified MnAl alloys doped with C,B, and rare earth elements

MnAl alloys are attractive candidates to potentially replace rare earth hard magnets because of their superior mechanical strength, reasonable magnetic properties, and low cost. In this study, the phase transitions and magnetic properties of melt spun Mn₅₅Al₄₅ based alloys doped with C, B, and rare earth (RE) elements were investigated. As-spun Mn–Al, Mn–Al–C, and Mn–Al–C–RE ribbons possessed a hexagonal ε crystal structure. Phase transformations between the ε and the L1₀ (τ) phase are of interest. The ε → τ transformation occurred at ~500 °C and the reversed τ → ε transformation was observed at ~800 °C. Moderate carbon addition promoted the formation of the desired hard magnetic L1₀ τ-phase and improved the hard magnetic properties. The Curie temperature T _C of the τ phase is very sensitive to the C concentration. Dy or Pr doping in MnAlC alloy had no significant effect on T _C. Pr addition can slightly improve the magnetic properties of MnAlC alloy, especially J_S. Doping B could not enhance the magnetic properties of MnAl alloy since B is not able to stabilize either the ε phase or the L1₀ hard magnetic τ phase.     

The Kramers-Kronig relations for permittivity, “True” screening radius,and critical point of a coulomb system

A correlation between the peculiarities of the electric permittivity (EP) ɛ(q, ω) of a homogenous and isotropic Coulomb system (CS) in the limit of ω → 0, q → 0 and q → 0, ω → 0 is established on the basis of exact limiting relations; general expression for static EP ɛ(q, 0) of a CS is obtained in the region of small wave vectors q. The concepts of a “true” dielectric and “ideal” conductor are introduced. The definition of a “true” screening radius is considered. A critical point of two-component CS is shown to correspond to either the “true” dielectric state or the “ideal” conductor one.     

Evolution and stability of texture during thermomechanical processing of Ti-24Al-11Nb alloy

The evolution of basal texture during thermomechanical processing of Ti-24Al-11Nb alloy has been studied as a function of different processing variables like hot rolling temperature, amount of deformation, cooling conditions etc. The stability of the deformation texture during post-rolling annealing and during theα ₂→β→α ₂ phase transformation cycle was also investigated. Unrestricted rolling of primaryα ₂ to maximum thickness reduction at the lowest rolling temperature has been found to be most favourable for obtaining a good basal texture. Texture of transformed (secondary)α ₂ is generally non basal when the transformation takes place from deformedβ. Rolling texture does not seem to change during annealing leading to recrystallization. Theα ₂→β→α ₂ phase transformation cycle does not change the starting basal texture and a starting non basal texture also does not give rise to basal texture due to this treatment.     

First report on observation of abnormal creep in a Zr–2.5wt.%Nb alloy at low stresses

Low-stress creep behaviour of a two-phase Zr–2.5%Nb alloy, differently heat treated, has been investigated using helical test specimens. The phase diagram of the α (hcp) + β (bcc) alloy is characterized by the monotectoid reaction at 893 ± 10 K: β ₁ → (α + β ₂) where β ₁ (Zr–20Nb) and β ₂ (Zr–80Nb) have widely differing compositions. At the creep testing temperature, 818 K, which is close to but below the monotectoid temperature, the creep rate for samples with the equilibrium α + β ₂ structure has been found to be considerably higher, over an order of magnitude, than that in samples with the metastable α + β ₁ structure. Microstructural changes accompanying the markedly enhanced creep rate for the α + β ₂ structure at stresses as low as 1–4 MPa have been explained in terms of the relative stability of the β ₁ and the β ₂ phases during the creep process. An attempt has been made to elicit the likely mechanism underlying the observed enhancement of creep rate and the changes in morphology, composition and volume fraction of the β phase.     

Ab initio calculations of the thermodynamics and phase diagram of ScSb

The hydrostatic pressure-induced transition phase of ScSb from the sixfold-coordinated NaCl-type (B1) to the eightfold-coordinated CsCl-type (B2) is investigated within the Perdew–Burke–Ernzerhof (PBE) form of generalized gradient approximation. It is found that the transition pressure from the B1 to B2 phase is at 42.8 GPa which agrees with experiment. Through the quasi-harmonic Debye model, the dependences of the relative volume V on the pressure P, the thermal expansion, the Grüneisen parameter ratio, (γ − γ ₀)/γ ₀, the Debye temperature Θ, and heat capacity C _V on the pressure P and temperature T are estimated. The quasi-harmonic Debye model for the first time is used to predict phase diagram of B1 → B2.     

Synthesis,photoluminescence and mechanoluminescence properties of Eu<Superscript>3+</Superscript> ions activated Ca<Subscript>2</Subscript>Gd<Subscript>2</Subscript>W<Subscript>3</Subscript>O<Subscript>14</Subscript> phosphors

A new series of Eu³⁺ ions-activated calcium gadolinium tungstate [Ca₂Gd₂W₃O₁₄] phosphors were synthesized by conventional solid-state reaction method. The X-ray diffraction patterns of the powder samples indicate that the Eu³⁺: Ca₂Gd₂W₃O₁₄ phosphors are of tetragonal structure. The prepared phosphors were well characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL), and mechanoluminescence (ML) spectra. PL spectra of Eu³⁺: Ca₂Gd₂W₃O₁₄ powder phosphors have shown strong red emission at 615 nm (⁵D₀ → ⁷F₂) with an excitation wavelength λ _exci = 392 nm (⁷F₀ → ⁵L₆). The energy transfer from tungstate groups to europium ions has also reported. Mechanoluminescence studies of Eu³⁺: Ca₂Gd₂W₃O₁₄ phosphors have also been explained systematically.     

Product Evolution: A Reverse Engineering and Redesign Methodology

New products drive business. To remain competitive, industry is continually searching for new methods to evolve their products. To address this need, we introduce a new reverse engineering and redesign methodology. We start by formulating the customer needs, followed by reverse engineering, creating a functional model through teardowns. The functional model leads to specifications that match the customer needs. Depending upon required redesign scope, new features are possibly conceived, or not. Next, models of the specifications are developed and optimized. The new product form is then built and further optimized using designed experiments. An electric wok redesign provides an illustration. The methodology has had a positive impact on results by using a systematic approach, both within design education and industrial applications.     

Synthesis and photoluminescence properties of Eu<Superscript>3+</Superscript>-activated SrZnO<Subscript>2</Subscript>

Synthesis, X-ray diffraction, and photoluminescence (PL) investigations of SrZnO₂ doped with Eu³⁺ were carried out in order to characterize the material. The emission spectra showed a broad band emission at 525 nm attributed to oxygen defect centers in the host matrix, along with peaks corresponding to the ⁵D₀ → ⁷F _j (j = 1, 2) transitions of Eu ion under 250 nm excitation. PL decay time studies were done to confirm these investigations. Time-resolved emission spectrometric (TRES) study was carried out to extract the emission spectra of the Eu ion which was buried under the broad band emission. After giving suitable delay times and by choosing a proper time gate, transitions due to ⁵D₀ → ⁷F _j (j = 0, 1, 2, 3, and 4) could be observed. Judd–Ofelt intensity parameters and other radiative properties for the system were evaluated from this emission spectrum and decay time data by adopting standard procedure. The color coordinates of the system were also evaluated and plotted on a standard CIE index diagram. The observations showed that the SrZnO₂:Eu³⁺material has near white light emission (also considering the emission from host) whereas, the extracted emission spectrum due to only Eu ions has a near red emission.