Phase formation under non-equilibrium processing conditions: rapid solidification processing and mechanical alloying

Rapid solidification processing (RSP) of metallic alloys, involving solidification of liquid metals at very high rates, results in the formation of a variety of metastable phases such as supersaturated solid solutions, crystalline intermetallic compounds, quasicrystalline phases, and metallic glasses. Additionally, significant refinement of the grain sizes and segregation patterns also occurs. Mechanical alloying (MA), another powerful non-equilibrium processing technique, utilizes repeated cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill. MA also results in the formation of metastable phases and microstructural refinement similar to what happens during RSP. Consequently, comparisons are frequently made between the phases produced by RSP and MA and the general understanding is that they both result in similar metastable effects. A detailed analysis of the metastable phases produced by RSP and MA is made in the present work, and it is shown that even though the effects may appear similar, the mechanisms of formation and the composition ranges in which particular phases form are quite different. These two methods also have some unique features and produce different phases. The differences have been ascribed to the fact that RSP involves solidification from the melt while MA is a completely solid-state process that is not restricted by the phase diagram.     

Evaluation of a phenomenological elastic‐plastic approach for magnesium alloys under multiaxial loading conditions

Magnesium alloys are greatly appreciated due to their high strength to weight ratio, stiffness, and low density; however, they can exhibit complex types of cyclic plasticity like twinning, de‐twinning, or Bauschinger effect. Recent studies indicate that these types of cyclic plastic deformations cannot be fully characterized using the typical tools used in cyclic characterization of steels and aluminium alloys; thus, it is required new approaches to fully capture their cyclic deformation and plasticity. This study aims to propose and evaluate a phenomenological cyclic elastic‐plastic approach designed to capture the cyclic deformation of magnesium alloys under multiaxial loading conditions. Series of experimental tests were performed to characterize the cyclic mechanical behaviour of the magnesium alloy AZ31BF considering proportional loadings with different strain amplitude ratios and a nonproportional loading with a 45° phase shift. The experimental results were modulated using polynomial functions in order to implement a cyclic plasticity model for the AZ311BF based on the phenomenological approach proposed. Results show good correlations between experiments and estimates.     

Relationships between processing conditions and mechanical properties of PA12 tubes. The EWF approach

In polyamide 12 (PA12) tube extrusion, calibration is the key step of the process that affects the subsequent mechanical properties. In previous work it has been shown that according to the calibration conditions, a very oriented skin layer may be created, which has been correlated to an important decrease of elongation at break. In this paper, we present new results showing a good correlation between molecular orientation and fracture toughness, as evaluated by the EWF (Essential Work of Fracture) approach. They concern notched specimens and confirm the results obtained in classical tensile testing. The specific essential work of fracture is very sensitive to the orientation generated in the skin region by appropriate processing conditions: it decreases from the external to the inner regions of the tube, and increases with skin orientation.     

A phenomenological constitutive modelling of polyethylene foam under multiple impact conditions

This paper extends the knowledge into the mechanical behaviour characterizations and constitutive modelling of polyethylene (PE) foam under multiple loading and unloading. The mechanical properties of PE foam subjected to single loading cases can be obtained by uniaxial compressive tests at quasi‐static and dynamic states. And the multiple loading and unloading behaviours of the foam can be revealed by consecutive drop tests. The major objective of this research is to propose a phenomenological model consists of shape function and modulus function, which can be predicted compressive response of PE foam for single loading cases. The constitutive models of foamed PE under multiple loading and unloading conditions are established by both using hyperbolic function, where the relations between coefficients and residual strain are introduced. And then, experiments are conducted to validate the proposed model by comparing the constitutive models proposed in this paper and those predicting by finite element software ABAQUS with those by experiments, showing that the proposed models are more accurate for predicting acceleration‐times curves of multiple drop scenarios.     

70 nm: The most unstable grain size in Cu prepared by surface mechanical grinding treatment

The stability of Cu with different average grain sizes prepared by surface mechanical grinding treatment were investigated under the conditions of isothermal annealing and uniaxial tension.In both conditions,experimental results revealed that the stability of the grains decreased with the decrease of grain size when the grain size was above 70–75 nm,while the stability of the grains increased with the decrease of grain size when the grain size was below 70–75 nm.The grains of about 70–75 nm in size showed the worst stability in both thermal and mechanical conditions due to having the highest level of average atom free energy and their large amount of high energy grain boundary with large curvature.This size was very close to the calculated smallest size achievable by severe plastic deformation based on the grain refinement mechanism of dislocation evolution under present processing condition,at which both the highest density of dislocation and highest energy should be produced and induces poor stability.Below 70 nm,the deformation mechanism of nanograined Cu was transformed into a partial dislocation motion,which activated mechanically induced grain boundary(GB)relaxation accompanied by GB flattening and GB energy decrease and resulted in enhanced stability.This discovery offers the potential for developing nanograined metals with high strength and high stability.     

Effect of high-pressure torsion processing on the microstructure evolution and mechanical properties of consolidated micro size Cu and Cu-SiC powders

In this paper, micro size Cu and Cu-SiC composites powders were consolidated by powder metallurgy (PM) followed by sintering or high-pressure torsion (HPT) to study the effect of the different processing methods on microstructure evolution and mechanical properties. HPT contributes in producing fully dense samples with a relative density higher than those processed by PM followed by sintering. Bimodal and trimodal microstructures with a mixture of ultrafine grain (UFG) and micro or nano grain sizes were noted in the case of Cu and Cu-SiC HPTed samples, respectively. The increase of the SiC volume fraction (SiC%) produces smaller grain size with higher fractions of high angle grain boundaries (HAGBs) in the HPTed Cu-SiC samples than that in the case of HPTed Cu sample. The HPT under a pressure of 10 GPa and 15 revolutions was effective to achieve a complete fragmentation of SiC particles down to ultrafine particle size. HPT processing of Cu and Cu-SiC composites enhanced the mechanical properties (hardness and tensile strength) with conserving a reasonable degree of ductility (elongation%). The yield strength of the samples was estimated based on the microstructure observations and processing parameters by different models correctly with an error range of 5.1–1% from the experiential results.     

Radiometric calibration of SUMER: refinement of the laboratory results under operational conditions on SOHO

The radiometric calibration of the solar telescope and spectrometer SUMER was carried out in the laboratory before delivery of the instrument for integration into the SOHO (Solar and Heliospheric Observatory) spacecraft. Although this effort led to a reasonable coverage of the wavelength range from 53.70 to 146.96 nm, uncalibrated portions of the sensitivity curves remained before SUMER became operational in early 1996. Thereafter it was possible to perform extrapolations and interpolations of the calibration curves of detector A to shorter, longer, and intermediate wavelengths by using emission line pairs with known intensity ratios. The spectra of the stars alpha and rho Leonis were also observed on the KBr (potassium bromide) photocathode and the bare microchannel plate (MCP) in the range from 120 to 158 nm. In addition, the sensitivity ratios of the KBr photocathode to the bare MCP were determined for many solar lines as well as the H i Lyman and the thermal continua. The results have been found to be consistent with published laboratory data. The uncertainty is +/-15% (1 varsigma) in the wavelength range from 54 to 125 nm.     

UHMWPE初生态微观结构及不同成型条件下制品力学性能研究

超高分子量聚乙烯(UHMWPE)极高的分子量及线性分子链特性使其具备很多的优异性能,在军工、医药卫生等领域的应用越来越广泛的同时,对UHMWPE树脂的性能不断提出更高的要求。故利用高分辨扫描电镜(SEM)、高温凝胶色谱-红外联用(GPC-IR)、拉曼光谱(Raman)及差式扫描量热仪(DSC)对树脂初生态粒子的结晶结构、分子特性及热力学性能进行了研究,并通过控制模压过程中的冷却速率来研究UHMWPE样品的结晶行为,进而分析UHMWPE微观特性与宏观性能之间的关系。研究发现由次级颗粒和微纤组成的UHMWPE初生态粒子中具有大量的片晶和伸直链,分子链排列规整,结晶度高;但在熔融再结晶加工成制品的过程中,分子链的规整性遭到破坏,与初生态粒子相比,结晶度下降、缠结密度变大。另外,不同降温速率的样品中淬冷样品的分子链缠结密度最低,而低缠结、小的晶粒能够提升制品的耐冲击性能及断裂时的真应力。     

The promising aspects of processing nanomaterials under mechanical stressing for physicochemical viewpoints

Solid-state mechanochemical processing of nanomaterials offers unique opportunities for the creation of value-added materials. The present review reexamines physicochemical aspects of these processes and identifies the merits of leveraging local deformation derived phenomena such as symmetry loss of ligand field, charge-transfer across the grain boundary, reaction-induced amorphization and the consequences of intimate mixing for the creation of new materials. Case studies are also presented that include ligand exchange of transition metal coordination compounds, anion substitution of metal oxides, organic synthesis and drug amorphization. All these studies provide promise for solid-state mechanochemical processing in the future as a cornerstone of powder technology.     

Continuum based modeling of silicon integrated circuit processing: An object oriented approach

Continuum based integrated circuit process modeling is the dominant tool used to investigate and understand integrated circuit (IC) development. This paper describes the commonly used models for implantation, diffusion, and material growth. In addition, the supporting numerical techniques are described. This paper focuses on the implementation in object oriented code, Florida Object Oriented Process Simulator (FLOOPS). The software architecture is described for implementing models and numerics. A number of process examples are introduced and discussed.     

Deriving a dynamic-system eigenvalue spectrum under conditions of uncertainty by processing measurements

A method is given for determining the eigenvalue spectrum of a linear dynamic system under conditions of uncertainty. A method is described for deriving the characteristic parameters by analysis of measurement data that provide preliminary evaluations of the spectrum. An adaptive identification algorithm is proposed to refine the estimators. The task is handled in the class of static models.     

Relationships between processing conditions and mechanical properties of PA12 tubes

In polyamide 12 (PA12) tube extrusion, calibration is the key step of the process that affects the subsequent mechanical properties. In previous work it has been shown that according to the calibration conditions, a very oriented skin layer may be created, which has been correlated to an important decrease of elongation at break. In this paper, we present new results showing a good correlation between molecular orientation and fracture toughness, as evaluated by the EWF (Essential Work of Fracture) approach. They concern notched specimens and confirm the results obtained in classical tensile testing. EWF is very sensitive to processing conditions, and especially to induced orientation: it decreases from the external to the inner regions of the tube, and increases with skin orientation.     

Numerical modeling of crack growth under dynamic loading conditions

A framework for modeling crack growth is described that is based on introducing one or more cohesive surfaces into a continuum. Constitutive relations are specified independently for the material and for the cohesive surfaces. Fracture emerges as a natural outcome of the deformation process, without introducing an additional failure criterion. The characterization of the mechanical response of a cohesive surface involves both an interfacial strength and the work of separation per unit area, which introduces a characteristic length into the formulation. Finite element analyses are carried out for a plane strain block with an initial central crack, subject to impact loading. The crack is constrained to grow along the initial crack line. Numerical results are presented for elastic and elastic-viscoplastic solids using various degrees of mesh refinement.     

The phenomenological approach to estimating critical indices of critical fluid

High Temperature - This work presents a new phenomenological approach to estimating critical indices of critical fluid that are characterized by two components, regular and fluctuational. A direct...     

Influence of dislocations on magnon-phonon couplings: A phenomenological approach

On the basis of a nonlinear theory of finitely deformable elastoviscoplastic ferromagnetic crystals developed in a companion paper, the present work presents an attempt at a phenomenological study of the influence of dislocations and viscoplastic flow on the behavior of spin waves (the collective modes of oscillations typical of ferromagnetism). This is achieved by linearizing the above mentioned nonlinear theory about a fundamental ferromagnetic phase with a practically vanishing viscoplastic threshold. The main results obtained after a study of wave modes and asymptotic evaluations in terms of a piezomagnetic coupling parameter are the evidence of a magnetoacoustic resonance between spin waves and left circularly polarized transverse elastoviscoplastic disturbances, a slight shift towards higher wave numbers of the corresponding critical wave number as compared to the perfectly elastic-crystal case and the fact that spin waves suffer a damping which is directly proportional to the piezomagnetic coupling parameter and to the reciprocal primary relaxation time (the relaxation time associated with the viscosity processes inherent in viscoplasticity, in the absence of restoring effects.     

Mass transfer in a three-phase system under conditions of mechanical and pneumatic agitation

Mass transfer between a solid and a liquid, accompanied by the evolution of a gaseous phase, is studied experimentally in the presence of mechanical agitation. It is shown that for low concentrations of the reagent pneumatic agitation is more effective than mechanical.     

Optimization of ZnO sheets dimension in terms of ductility, micro-indentation, mechanical resistance, Amlouk-Boubaker optothermal expansivity and crystallites size

ZnO sheets with different thicknesses have been prepared using a simple spray pyrolysis technique. Parallel to classical characterization techniques like common XRD and AFM, a critical thickness has been proposed on the bases of micro-indentation related hardness, mechanical ductility, optothermal expansivity and crystallite sizes measurements.     

Effects of processing conditions on microstructure and mechanical properties of equal-channel-angular-pressed titanium

This review presents an investigation on effects of the processing conditions on the microstructural evolution and mechanical properties of commercial pure titanium processed by Equal Channel Angular Pressing (ECAP). An overview of ECAP processing is presented. A discussion on the microstructure evolution of ECAPed titanium emphasising effects of the ECAP-route type, processing temperature, number of ECAP passes, and mechanical/thermal treatments is presented. Moreover, the variations of the mechanical properties (yield strength, tensile strength, and ductility) of titanium as functions of the grain size are reported for the different conditions of ECAP processing. In addition, the best estimates of the Hall–Petch parameters for titanium processed by ECAP, ECAP followed by mechanical and/or thermal annealing are reported.