Multiscale composition modulated Ti–Al composite processed by severe plastic deformation

Using severe plastic deformation processes to consolidate and co-deform powder mixtures to make ultrafine grain composites is a very attractive approach because it offers an almost non-limited room for combinations of phases and composite structures. The aim of this work was to investigate the mechanisms operating at different length scales and leading to multiscale structures, namely co-deformation, fragmentation and mechanical mixing. A Ti–Al composite was processed from a Ti–Al powder mixture prepared by ball milling and subsequently deformed by equal channel angular pressing. Microstructures were characterized at all length scales, down to the nanometre, using optical microscopy, scanning electron microscopy and transmission electron microscopy. It was found that the final structure exhibits unique features at various length scales. Chemical heterogeneities at the micron scale are the result of co-deformation, while at the sub-micron scale they result from the fragmentation and necking of the Ti hard phase. Then, at the nanometer scale, intermixing occurred and nanoscaled intermetallic particles were discovered. This work highlights the possibilities offered by all these mechanisms to design ultrafine grain composite structures for optimized properties.     

Corrosion resistance of model ultrafine-grained Al–Li alloys produced by severe plastic deformation

The influence of grain boundaries and fine precipitation on the corrosion behavior was investigated in two model aluminum–lithium alloys, namely (in wt%) Al–1.6Li (lithium in a solid solution) and Al–2.3Li (lithium in the form of Al₃Li precipitation), subjected to three different severe plastic deformation (SPD) treatments which refined the microstructure of the alloys to the ultrafine grain size. The SPD techniques used in the experiments were equal channel angular pressing (ECAP), hydrostatic extrusion (HE), and extrusion-torsion (ET). The corrosion behavior was examined using a potentiodynamic polarization test, electrochemical impedance spectroscopy, and an immersion test followed by a SEM surface analysis. The electrochemical tests were conducted in a 0.1 M Na₂SO₄ solution added with 100 ppm of Cl⁻. The immersion tests (48 h) were performed in a 3.5% NaCl solution at room temperature. The results indicate that the pitting potential, pit number, and stability of the passive layer formed on the surface of the substrates undergo changes depending on the average grain size and the presence of precipitation or its lack. The corrosion resistance, examined in the solution mentioned above, appears to increase with decreasing average grain size. The ET method gave the microstructure with the lowest corrosion resistance.     

Structure and mechanical properties of nanostructured Al–Mg alloys processed by severe plastic deformation

Structural features, microhardness, and mechanical properties of three binary Al–Mg alloys and a commercial AA5182 alloy subjected to high pressure torsion at room temperature were comparatively investigated using transmission electron microscopy, high-resolution transmission electron microscopy, and quantitative X-ray diffraction measurements. Average grain sizes measured by dark-field images are in the range 71–265 nm while the sizes of coherent domains decreased tremendously from 86 to 46 nm as the Mg content increased from 0.5 to 4.1 wt%. The average dislocation density in the deformed alloys is in the range 0.37 × 10¹⁴–4.97 × 10¹⁴ m^?2. Both the microhardness and tensile strength of all the deformed alloys increased dramatically as compared to the undeformed counterparts. The yield strength with values ranging from 390 to 690 MPa in the deformed alloys is typically five to seven times higher than that of the same undeformed alloys. Calculations based on the Hall–Petch and Taylor equations suggest that the strengthening mechanisms contributing to the very high strength may depend not only on the conventional mechanisms of grain size strengthening and dislocation strengthening, but also on the additional mechanisms related to the contributions from stacking faults and nanotwins, and nonequilibrium GBs observed in the deformed alloys.     

Microstructure and microhardness of an AlFe alloy subjected to severe plastic deformation and aging

A nanocrystalline structure was produced in an Al-11 wt.% Fe alloy with the use of the novel technique of severe plastic deformahon of ingots by torsion under high imposed pressure. This technique allows a large departure of materials from equilibrium. The microstructure of the alloys was studied with the use of TEM and EDS. The severe plastic deformation led to solid solubility extension of iron in the aluminum matrix, dispersion and dissolution of second phase particles, grain size reduction into the nanometer range, and partial amorphization. Microhardness of the alloy increased substantially after the deformation due to the grain refinement and the solid solubility extension. Aging of the severe plastically deformed samples at 100 °C led to further increase of the microhardness due to the decomposition of the supersaturated solid solution and precipitation-induced hardening.     

A combination of severe plastic deformation and ageing phenomena in Al–Mg–Si Alloys

In this paper static and dynamic strain ageing behavior in Al–Mg–Si alloys related to equal channel angular pressing (ECAP) was investigated. In order to examine the combined plastic deformation, solution treatment and ageing effects on strengthening characteristics, experimental results of ageing without ECAP, pre-ECAP ageing, post-ECAP ageing and dynamic ageing inside of ECAP die were compared. In particular, the effects of ageing temperature, ageing time, strain rate in ECAP, and sequence of heat treatment and ECAP on Vickers hardness were discussed. To achieve a higher hardness, an optimum ageing cycle combined with ECAP process is presented based on the results of current study. By employing the proposed schedule the hardness value was increased from 86 HV (as-solution treatment) to 138 HV (peak hardness of the current schedule).     

In vitro fibroblast response to ultra fine grained titanium produced by a severe plastic deformation process

The in vitro response of the mouse fibroblast cell line 3T3 on the surface of ultrafine grained titanium [produced by a severe plastic deformation (SPD) process] has been studied in this work. SPD Ti showed much higher strength than the coarse grained Ti and equivalent to that of Ti–6Al–4V alloy. Better cell proliferation was observed on SPD Ti compared to conventional Ti and Ti–6Al–4V alloy. This could be attributed to the increased surface free energy by reduction in the grain size and possibly the presence of a large number of nano size grooves at the triple point junctions in SPD Ti sample. There was no significant difference in the results of cytotoxicity tests of fine and coarse grained materials.     

Porous and strong bioactive glass (13–93) scaffolds fabricated by freeze extrusion technique

Scaffolds fabricated by current methods often lack the combination of high strength and high porosity for skeletal substitution of load-bearing bones. In this work, freeze extrusion fabrication (FEF), a solid freeform fabrication technique, was investigated for the creation of porous and strong bioactive glass (13–93) scaffolds for potential applications in the repair of loaded bone. The process parameters for forming three-dimensional (3D) scaffolds with a pre-designed, grid-like microstructure by FEF were determined. Following thermal treatment of the as-formed constructs at temperatures up to 700 °C, scaffolds consisting of dense glass struts and interconnecting pores (porosity ≈ 50%; pore width ≈ 300 μm) were obtained. These scaffolds showed an elastic mechanical response in compression, with a compressive strength of 140 ± 70 MPa and an elastic modulus of 5.5 ± 0.5 GPa, comparable to the values for human cortical bone. The scaffolds supported the proliferation of osteogenic cells in vitro, showing their biocompatibility. These results indicate that 13–93 bioactive glass scaffolds created by the FEF method could have potential application in the repair and regeneration of load-bearing bones.     

Effect of severe plastic deformation on creep behaviour of a Ti–6Al–4V alloy

This paper examines the effect of severe plastic deformation on creep behaviour of a Ti–6Al–4V alloy. The processed material with an ultrafine-grained (UFG) structure (d ≈ 150 nm) was prepared by multiaxial forging. Uniaxial constant stress compression and constant load tensile creep tests were performed at 648–698 K and at stresses ranging between 300 and 600 MPa on the UFG processed alloy and, for comparison purposes, on its coarse-grained (CG) state. The values of the stress exponents of the minimum creep rate n and creep activation energy Q _c were determined. Creep behaviour was also investigated by nanoindentation method at room temperature under constant load. The microstructure was examined by transmission electron microscopy and scanning electron microscope equipped with an electron back scatter diffraction unit. The results of the uniaxial creep tests showed that the minimum creep rates of the UFG specimens are significantly higher in comparison with those of the CG state. However, the differences in the minimum creep rates of both states of alloy strongly decrease with increasing values of applied stress. The CG alloy exhibits better creep resistance than the UFG one over the stress range used; the minimum creep rate for the UFG alloy is about one to two orders of magnitude higher than that of the CG alloy. The indentation creep tests showed that annealing had little effect on the creep behaviour in UFG Ti alloy at room temperature.     

The rate-controlling mechanism(s) during plastic deformation of polycrystalline NaCl at 0.28–0.75 TM

The plastic deformation kinetics of polycrystalline 99.9% NaCl were determined in compression at 23–532°C (0.28–0.75TM) and a strain rate = 8.3 × 10–4 s–1. The rate-controlling mechanism at 0.28–0.65 TM (/ < 3 × 10–4) was deduced to be the intersection of forest dislocations with a Helmholtz free energy F* = 113 kJ/mol (0.16 b3). The forest dislocation obstacles become ineffective at 0.65TM. The kinetics at 0.75TM (/ > 3 × 10–4) were in accord with the Weertman-Dorn creep equation. At T > 0.5 TM the decrease in strain hardening with strain and temperature was attributed to cross slip, leading to a brittle-to-ductile transition at 0.5 TM. Dislocation climb was deduced to become more important at higher temperatures. The stress-strain curves were described reasonably well by the Bergström-Roberts dislocation multiplication model.     

Role of severe plastic deformation on the formation of nanograins and nano-sized precipitates in Fe–Ni–Mn steel

In this research, the effect of severe plastic deformation (SPD) on the formation of nano-scaled grains and precipitation of nano-sized particles which consequently control mechanical properties of Fe–Ni–Mn alloy was investigated. Fe–Ni–Mn martensitic steels show excellent age hardenability but suffer from embrittlement after aging. Discontinuous coarsening of grain boundary precipitates, resulting in the formation of precipitate free zone (PFZ) along prior austenite grain boundaries, has been found as the main source of embrittlement in the previous studies. In this paper, severe plastic deformation has been carried out on the Fe–10Ni–7Mn steel to improve its mechanical properties. It is found that substantial improvement of tensile properties in cold-rolled steels occurs at thickness reductions larger than 60% where formation of ultrafine grains is realized. According to transmission electron microscopy (TEM) observations, formation of nano-scaled grains less than 100 nm along with the copious precipitation of nanometer-sized precipitates take place in the severely-deformed steels.     

Ibuprofen-loaded poly(ε-caprolactone) layered silicate nanocomposites prepared by hot melt extrusion

Ibuprofen loaded poly(ε-caprolactone) (PCL) layered silicate nanocomposites were prepared by hot-melt extrusion. The morphology and extent of dispersion of ibuprofen and layered silicate was studied using a combination of wide-angle X-ray diffraction (WAXD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Exhaustive examination across the length scales revealed the composite to have both an intercalated and exfoliated morphology. The ibuprofen was well dispersed and distributed throughout the PCL matrix. Most significantly, the static tensile and dynamic mechanical properties of PCL can be manipulated as a function of nanoclay loading and is dependent on the aspect ratio of clay platelets. The glass transition of PCL increased by up to 16°C on addition of nanoclay, as determined from dynamic mechanical thermal analysis (DMTA). This behaviour was attributed to the constrained mobility of PCL chains intercalated between clay platelets and to the tethering of PCL chains by hydrogen bonding with platelet edges. As a consequence, PCL crystallisation was inhibited and confirmed from non-isothermal crystallisation experiments using differential scanning calorimetry (DSC). The fraction of PCL that was crystalline (X_c) decreased by 15% on addition of ibuprofen and nanoclay, although the temperature of crystallisation (T_c) did not change significantly. The dissolution of ibuprofen from PCL can be retarded by addition of layered silicates (nanoclays) to the polymer matrix.     

Plating on acrylonitrile–butadiene–styrene (ABS) plastic: a review

ABS is an engineering plastic that has butadiene part uniformly distributed over the acrylonitrile-styrene matrix. It possesses excellent toughness, good dimensional stability, easy processing ability, chemical resistance, and cheapness. However, it suffers from inherent shortcomings in terms of mechanical strength and vulnerability to environmental conditions. Furthermore, it is non-conducting and easily fretted. Plating on ABS can serve to enhance the strength and structural integrity as well as to improve durability and thermal resistance resulting in metallic properties on the ABS material. ABS is described as the most suitable candidate for plating because it is possible to deposit an adherent metal coating on it by only the use of chemical pretreatment process and without the use of any mechanical abrasion. This article aims to review the history of ABS plastics, properties of ABS, processes and mechanisms of plating, and studies of plating on ABS involving mainly eco-friendly methods of plating by discussing the literature published in recent years. The details of electroplating of ABS carried out in the authors’ laboratory are also presented.     

Novel Evolution Process of Zn-Induced Nanoclusters on Si(111)-(7×7) Surface

Nano-Micro Letters - A tiny number of Zn atoms were deposited on Si(111)-(7×7) surface to study the evolution process of Zn-induced nanoclusters. After the deposition, three types (type I, II,...     

Cross-slip on the first order pyramidal plane (10\bar 11) of a-type dislocations [1\bar 210] in the plastic deformation of α-titanium single crystals

The nature of the cross-slip plane was determined by electron microscopy observations of α-titanium single crystal specimens, oriented for single prismatic slip (10 \(\bar 1\) 0) [1 \(\bar 2\) 10]. The occurrence of cross slip on the first order pyramidal plane (10 \(\bar 1\) 1) was proved for a-type dislocations [1 \(\bar 2\) 10]. Furthermore, two types of dislocation configuration due to the double cross-slip were observed: edge dislocation dipoles and loops elongated along the Burger's vector.     

Upcycling of plastic waste to carbon nanomaterials: a bibliometric analysis (2000–2019)

Clean Technologies and Environmental Policy - Due to the rapidly escalating generation of plastic wastes, the development of an effective management strategy is vital to reduce their adverse...     

Uniaxial deformation of face-centered-cubic(Ni)-ordered B2(NiAl) bicrystals: atomistic mechanisms near a Kurdjumov–Sachs interface

Creating tailored interfaces between soft and hard materials is a promising route to simultaneously enhance ductility and strength of multicomponent materials. Here, we study deformation mechanisms in a model bicrystal, with a Kurdjumov–Sachs (KS) interface, between face-centered-cubic Ni and ordered-B2 NiAl slabs using molecular dynamics simulations. The bicrystals were uniaxially deformed by strain rates of \(10^7\) and \(10^9\,\hbox {s}^{-1}\) by holding temperatures constant at 300, 500, 700, and 900 K for each strain rate. Our simulations reveal atomistic processes that create sessile and glissile dislocations, and their reactions during high-strain rate deformation. At \(10^9\,\hbox {s}^{-1}\) strain rates, dislocation processes enhance ductility and cause large-scale atomic rearrangements in the KS interfacial region. This subsequently causes nucleation, growth, and coalescence of nano-voids into cracks inside the harder B2-ordered phase bordering the interface. Our results suggest that interfaces between “soft”–“hard” materials likely withstand high-strain rates better.     

N—(对硝基苯基)—N’—(甲氧基羰基)硫脲及其铜(Ⅰ)配合物的NMR研究

利用~1H—~1H COSY,HMQC等2D NMR技术对一种新的配体N—(对硝基苯基)—N’—(甲氧基羰基)硫脲(H_2pmt(Ⅰ)进行~1H、~(13)C NMR谱数据分析与归属;对于它与Cu~+离子配位的化合物Cu(H_2pmt)_2Cl(2)也作了~1H、~(13)C NMR的测定,归属了它们的所有谱线,对于它们的化学位移与配位行为作了简单讨论。