Elastic Recovery Research Articles

The mechanics of prestress and elastic recovery resulting from dimple formation in steel sheets: Comprehensive numerical and experimental studies

Residual stress is rarely considered as an initial condition for Finite Element Analysis (FEA), or used in the component design. A comprehensive numerical and experimental investigation into prestressed steel sheets is conducted. Residual stresses at specific locations were introduced into the steel sheets by dimple formation. FEA is used to simulate dynamic dimple forming of a mild steel disk due to a tool impact and detect the existence of prestress after dimple formation. A physical drop-hammer was used to form a range of dimple sizes in disks to experimentally validate the FEA predictions associated with dimple depth. Dimples were then created using a screw press and the prestress was measured by strain gauges beyond the zone of permanent out-of-plane deformation associated with a dimple. The experimental strain gauge measurements during dimple formation were found to be consistent with FEA predictions. The results demonstrated that the predicted and measured radial and tangentially projected stress components remain in steel sheets after forming a dimple. Furthermore, the predicted prestress was greater near to the dimple formation and occurred at higher magnitudes in the tangential direction than the radial direction. The highest prestress remaining in the disk was at the magnitude of the material’s ultimate tensile stress, predicted in the tangential direction at the edge of the dimple. The numerical and experimental results showed the three stages of prestress formation: the development of stresses during dimple formation, the elastic recovery after the dimple forming, and the final prestressed equilibrium state of the rimmed disk.

Flours from microwave-treated buckwheat grains improve the physical properties and nutritional quality of gluten-free bread

Microwave (MW)-assisted hydrothermal treatment of buckwheat grains was explored to improve the physical properties and nutritional quality of gluten-free (GF) bread. A mixture of 80% rice flour and 20% corn starch was used as control recipe (CR), whereas for fortification, 50% of the rice flour was replaced with native buckwheat flour (BN) or buckwheat flour from grains treated with several MW cycles (exposure/rest cycles of 10/50 s, BT1, 20/40 s, BT2, or 30/30 s, BT3, at 30% moisture content and 8 min MW exposure). The BN fortified dough showed increased consistency and elastic response, compared to CR, with the MW treatment further enhancing these effects. Due to the enormous increase in complex modulus (G1*) (from 1060 Pa for CR to 10,679 Pa for BT3), the hydration of doughs was subsequently adjusted to obtain similar G1*. The inclusion of MW-treated flours led to higher consistency and elastic recovery. The lower specific volume (SV) and higher crumb hardness encountered for BN (3.88 mL/g and 1.45 N) were alleviated by the inclusion of MW-treated flours (4.61 mL/g and 0.90 N for BT1, 4.39 mL/g and 0.85 N for BT3), resulting in similar SV and lower staling than CR. Moreover, compared to BN and CR, the BT2 and BT3 breads showed a significant reduction in glucose release during in vitro starch digestion (up to −25%), and an increase in protein digestibility (up to +23%). Overall, the experimental findings pointed to the feasibility of using MW to improve the physical and nutritional quality of buckwheat flour-enriched GF bread.

The influence of spark plasma sintering on multiscale mechanical properties of nickel-based composite materials

The paper presents a comprehensive investigation of the influence of the main process parameters of spark plasma sintering on the mechanical and microstructural properties of nickel-silicon carbide composites at various scales. Microstructure analysis performed by scanning and transmission electron microscopy revealed a significant interfacial reaction between nickel and silicon carbide due to the decomposition of silicon carbide. The chemical interaction of the matrix and reinforcement results in the formation of a multicomponent interphase zone formed by silicides (Ni31Si12 or/and Ni3Si) and graphite precipitates. Furthermore, several types of structure defects were observed (mainly nano/micropores at the phase boundaries). These significantly influenced the mechanical response of nickel-silicon carbide composites at different levels. At the macroscopic scale, uniaxial tensile tests confirmed that applying a 1000 °C sintering temperature ensured that the manufactured composite was characterised by satisfactory tensile strength, however, with a considerable reduction of material elongation compared to pure nickel. Moreover, the fractography study allowed us to identify a significant difference in the damage mode for certain nickel-silicon carbide samples. Secondly, the interface of the nickel matrix and silicate interphase was tested by bending with microcantilevers to evaluate its deformation behaviour, strength, and fracture characteristics. It was confirmed that a diffusive kind of interface, such as Ni-NiSi, demonstrates unexpected bonding properties with a relatively large range of plastic deformation. Finally, the nanoindentation of three main components of the nickel-silicon carbide composite was executed to evaluate the evolution of nanohardness, Young's modulus, and elastic recovery due to the application of various spark plasma sintering conditions.

Evaluation of nano mechanical properties and corrosion behavior of diffusion welded CoCrNi medium-entropy alloy (MEA) and SUS 304 stainless steel joints

The study mainly focused on examining nanomechanical properties and corrosion behavior of the weld interface formed by diffusion welding of CoCrNi MEA and SUS 304 stainless steel. Three different bonding temperatures (i.e. 950 °C, 1000 °C, and 1050 °C) were utilized in producing diffusion welded joints. The influence of bonding temperatures on nanomechanical properties of the weld interface was characterized through Nanoindentation tests under various loads (i.e. 20 mN to 100 mN). Additionally, electrochemical properties of the weld interface were also examined using a 0.5 M HCl solution. Results clinched that with the increase of bonding temperature significant suppression in carbide formation occurred along with the weld interface. This instigated a reduction in nano hardness and elastic moduli which resulted in maximum elastic recovery along with the weld interface. The indentation size effect was also evident below 40 mN load after which nano hardness became stable while elastic moduli remained impervious to the change of indentation load. Furthermore, based upon electrochemical properties (i.e. Icorr, Ep, and Rp) samples welded at 1000 °C bonding temperature offered excellent corrosion resistance under 0.5M HCl environment.

Modifying Effect and Mechanism of Polymer Powder on the Properties of Asphalt Binder for Engineering Application.

For achieving the better modifying effect of polyurethane on asphalt pavement materials, the PUA powder modifier was prepared with fine grinding at the glass transition temperature, and polyurethane-modified asphalt (PUA-MA) with different dosages of modifier was prepared. The impact of the PUA on the physical properties of asphalt binder was studied. The modifying mechanism of PUA on asphalt was explored by investigating the thermal performance and chemical composition of asphalt (thermogravimetric analysis, differential scanning calorimetry test, and Fourier transform infrared spectroscopy). The micrograph of the interactive interface was characterized by scanning an electron microscope. Furthermore, the rheological properties of PUA-MA were also investigated and analyzed. The results indicated that the PUA had a dense structure with few pores on the surface. After mixing with asphalt, it altered the asphalt's internal structure via physical fusion and chemical reaction (carbamate formation). PUA improved the thermal stability of asphalt, enhanced the asphalt's thermal decomposition temperature, and further reduced the thermal mass loss while decreasing the glass transition temperature. The addition and dosage increase in the PUA modifier significantly improved the softening point, viscosity, complex shear modulus, and rutting factor of asphalt. Also, the PUA could improve the elastic recovery ability of asphalt and enhance the rutting resistance of asphalt at high temperatures. However, the crack resistance at low temperatures was not effectively improved (ductility and penetration decreased). When the dosage was 6-9%, PUA-MA had the best high-temperature performance, but asphalt showed poor low-temperature performance at this dosage. This study provides a theoretical reference for popularizing and applying polyurethane as an asphalt modifier in road engineering.

Achieving Record-High Stretchability and Mechanical Stability in Organic Photovoltaic Blends with a Dilute-absorber Strategy.

Organic solar cells (OSCs) have potential for applications in wearable electronics. Except for high power conversion efficiency (PCE), excellent tensile properties and mechanical stability are required for achieving high-performance wearable OSCs, while the present metrics barely meet the stretchable requirements. Herein, this work proposes a facile and low-cost strategy for constructing intrinsically stretchable OSCs by introducing a readily accessible polymer elastomer as a diluent for all-polymer photovoltaic blends. Remarkably, record-high stretchability with a fracture strain of up to 1000% and mechanical stability with elastic recovery>90% under cyclic tensile tests are realized in the OSCs active layers for the first time. Specifically, the tensile properties of best-performing all-polymer photovoltaic blends are increased by up to 250 times after blending. Previously unattainable performance metrics (fracture strain >50% and PCE >10%) are achieved simultaneously for the resulting photovoltaic films. Furthermore, an overall evaluation parameter y is proposed for the efficiency-cost- stretchability balance of photovoltaic blend films. The y value of dilute-absorber system is two orders of magnitude greater than those of prior state-of-the-art systems. Additionally, intrinsically stretchable devices are prepared to showcase the mechanical stability. Overall, this work offers a new avenue for constructing and comprehensively evaluating intrinsically stretchable organic electronic films.

Investigating the rheological behaviour of styrene–butadiene–styrene modified asphalt

The rheological properties of the styrene–butadiene–styrene modified asphalt (SBSMA) binder have not been thoroughly investigated yet. In this study, SBSMA binders with various SBS contents and base asphalt types were prepared and analysed. Fluorescence microscopy, temperature sweeping, and multiple stress creep recovery (MSCR) tests were conducted to analyse the phase structure and rheological behaviour of SBSMA. The results indicate that the special rheological behaviour of a decreasing phase angle value in SBSMA as the temperature increases is a result of the gradual dominance of the network structure over SBSMA’s rheological behaviour. Results from MSCR tests indicate that with the increase in stress levels, the elasticity of the network structure gradually diminishes, signifying a significant stress sensitivity in the network structure. Consequently, due to the stress sensitivity of the network structure, traditional rheological indicators measured at low stress levels (such as phase angle, elastic recovery rate) may overestimate the elasticity of SBSMA at high temperatures (40–80°C).

High molecular weight bimodal polyethylene elastomers using N,N'-nickel catalysts appended with methoxy and trifluoromethoxy functionality

Polyolefinic materials displaying bimodal molecular weight distributions are of interest since they can potentially provide mechanical toughness from the high molecular weight component without losing processability on account of the low molecular weight component. With this in mind, a series of nickel(II) complexes, [1-[2,6-{(4-MeOC6H4)2CH}2–4-(F3CO)C6H2N]-2-(ArN)C2C10H6]NiBr2 (Ar = 2,4-Me2C6H3Ni1, 2,6-Et2C6H3Ni2, 2,6-iPr2C6H3Ni3, 2,4,6-Me3C6H2, Ni4, 2,6-Et2-4-MeC6H2Ni5, 2,6-Me2C6H3Ni6) have been synthesized and have shown, following treatment with MMAO or Et2AlCl, excellent activity for the polymerization of ethylene (up to 19.87 × 106 g (PE) mol−1 for Ni4/Et2AlCl) generating high molecular weight branched polyethylene. More importantly, the elastomeric material produced using Et2AlCl as activator displays bimodal characteristics as well as low crystallinity and a medium to high branching density. By contrast, the material prepared using MMAO was more unimodal and showed higher crystallinity and lower branching density. Stress–strain and stress–strain recovery tests performed on the bimodal PE’s revealed a range of tensile properties with a sample prepared using Ni5/Et2AlCl combining both high tensile strength and high fracture strength (σ = 20.3 MPa, ε = 892.0 %). Conversely, a PE sample prepared using Ni4/Et2AlCl showed the highest elastic recovery with a stress relaxation (SR) value of 67.6 %. Besides branching analysis, molecular weight determinations and mechanical tests on the polymers, all nickel complexes and precursor 1,2-bis(arylimino)acenaphthenes, have been characterized by a combination of spectroscopic techniques, elemental analysis and in the cases of Ni1(OH2) and Ni4 by single crystal X-ray diffraction. A theory is also proposed to explain the observed bimodality.

Adjust operating conditions of an in-made house horizontal hydraulic press for a 90° cold bending process

During the cold-bending process, the tooling suffers considerable damage due to excess pressure. This also causes the machines to break down, causing problems in the precision and quality of the metal parts formed. The precision depends on the operating conditions of the press, the tooling employed, and the elastic recovery effect of the material. This study determines the working conditions for a made-in-house horizontal hydraulic press through an experimental design (DOE). This research carried out the V-forming to 90° (ISO 2768-1) of a hot-rolled carbon steel plate, considering pressure, piston permanence time, and recovery factor (Kr). The experimental and statistical analysis ensures accurate forming while the work pressure decreases by 17% and 33%, respectively, regarding the maximum. This reduction will delay the appearance of fatigue damage and have the operating parameters well established; in turn, it will be possible to design tools according to commercial standards.

Effects of temperature, punch angle, and loading velocity on mechanical properties of nanoimprinted FeNiCoCrCux high-entropy alloys

In this work, we use molecular dynamics simulations to study the effects of temperature, loading velocity, the taper angle of the punch on mechanical characteristics and deformation behavior of FeNiCoCrCu high-entropy alloys (HEAs) in nanoimprinting process. The impact of these factors is evaluated through loading force, atomic shear strain, structural change, dislocation evolution and elastic recovery rate. It points out that the primary deformation mechanism during imprinting of FeNiCoCrCu HEAs materials is the occurrence and propagation of dislocation and stacking faults. Increasing the temperature reduces the loading force, and the nanopatterning ability is better. When the imprinting speed increases, the stacking fault and dislocation increase, and the loading force improves. The results show that the higher the imprinting speed, the smaller the elastic recovery ratio. That proves the pattern forming at high imprinting speed will be better. As the mold angle increases, the depth of the forming groove increases. With the change of mold angles, the stress changes not only its value but also its distribution. As the taper angle of the punch increases, the high-stress region increases. The lower the concentration of Cu in the compound, the higher the forming ability and the pattern is sharper and clearer. While, the total dislocation and the residual stress in the substrate after withdrawing the punch from the substrate will gradually decrease on the order of FeNiCoCrCu0.2, FeNiCoCrCu1.3, FeNiCoCrCu0.7, FeNiCoCrCu0.4, FeNiCoCrCu1.0.

Effect of gas temperature on the interfacial bonding of cold-spray additive-manufactured Ti6Al4V

The mechanism of the bonding between the particles deposited in cold spraying (CS) is still under debate. Particularly for Ti and its alloys, bonding often occurs without evident jetting at the edge, which is difficult to explain using the traditional bonding theory. To date, a detailed microstructural understanding of the particles has been lacking. Therefore, in this work, the deposition behavior of cold-spray additive-manufactured Ti6Al4V (Ti64) was investigated as a function of gas temperature, and the microstructure of the surface particle interface was analyzed in depth. The results showed that with increasing gas temperatures, particle deformation and bonding between the surface particles and the previously deposited particles improved; accordingly, the porosities of the deposits decreased. Microstructural analysis revealed that abundant fine grains and amorphous phases formed at the interface between the surface particle and the subsurface particles, and that oxygen is likely to concentrate in this area. Therefore, a new bonding mechanism involving nano-recrystallized grains and amorphous structures is proposed. Moreover, the numerical simulation results showed that the maximum interfacial temperature is close to the melting point of Ti64, which plays a significant role in the nanocrystalline- and amorphous-phase formation. In addition, several nanosized cracks were observed at the interface at 700 °C, and the sample interface split at 800 °C. These results, combined with the evolution of the elastic recovery energy and velocity of the surface particle with impact time, lead us to speculate that the continuous fluctuating elastic recovery process may cause microcracks and interfacial tears.

Influence of two kinds of clearance joints on the dynamics of planar mechanical system based on a modified contact force model

This study takes the slider-crank mechanism with revolute joint and translational joint as the research object and studies the contact force model of the clearance joint and the influence of the hybrid clearance joints on the nonlinear dynamic behavior of the mechanism. A modified contact force model is established based on the simplified elastic oscillator model, which can be used as a normal force in clearance joint. In the new contact force model, the component n of the indentation depth can be arbitrarily selected and it can support the calculation of contact force for both fully elastic recovery, non-elastic recovery and fully inelastic recovery. Based on the LuGre friction model, the tangential friction model of the clearance joint is given. Thus, the normal force and tangential force during the dynamic contact of the clearance joint are formed. Combining Lagrange’s equations of the first kind with the modified normal force and tangential friction force, the dynamic equations of the multi-body system with clearance joints are established. The Baumgarte stabilization method is used to improve the numerical stability. The correctness of the dynamic prediction model in the mechanism with clearance joint is verified by experiment. The dynamic analysis of the slider-crank mechanism with mixed clearance joints shows that the revolute clearance joint has a greater influence on the mechanism than the translational clearance, and the revolute clearance joint plays a leading role in the dynamic response.

Characteristics of atomic removal and mechanism of damage formation in vibration-assisted nano cutting of copper-nickel alloy

Vibration-assisted machining technology can effectively improve the quality and efficiency of nano cutting, but the characteristics of atomic removal and the mechanism of damage formation have not been systematically studied. In this paper, copper-nickel alloy material is taken as an example. The characteristics of vibration-assisted nano cutting and the plastic deformation behavior of materials were revealed by molecular dynamics simulation. The simulation results show that vibration-assisted nano cutting reduces tangential force, lateral force, and total force, strengthens the anisotropy of atomic motion, and causes greater displacement and removal of Cu/Ni atoms. The intermittent contact is beneficial for the elastic recovery of workpiece atoms, releasing internal stress and atomic strain, reducing the depth of damage and the length of dislocation lines. The difference in surface/subsurface damage to the workpiece is relatively small with an amplitude of 1 Å. With amplitudes of 3 Å and 5 Å, and as the frequency increases, the complete lattice structure is destroyed, resulting in a significant decrease in the number of FCC structural atoms and RDF peak. However, an appropriate increase in frequency can increase the removal of Cu/Ni atoms, improve the topological structure, and reduce RMS. The HCP and BCC structural atoms affect the generation of dislocation lines, with an amplitude of 3 Å and a frequency of 7.5 GHz, achieving the minimum damage depth and dislocation line length. Excessive amplitude of 10 Å results in irreversibly severe damage to the surface/sub-surface of the workpiece. This study will provide a new approach for optimizing vibration-assisted nano-cutting technology and achieving low-damage nano cutting of alloy materials.

Modeling of oscillating bone sawing forces with instantaneous cutting speed and depth of cut

Oscillating bone sawing is a crucial procedure in orthopedic surgery, but excess sawing forces are often detrimental to implant fixation and postoperative patient recovery. Therefore, understanding and controlling sawing forces are critical. However, the conventional bone cutting model is not applicable to the oscillating sawing process, as it requires variable speed cutting with a negative rake angle, which is affected by the difference in viscoelasticity of the bone at different speeds. In this study, an oscillating sawing force model was developed that considered variations in cutting speeds and depth of cut for each saw tooth. A speed-related cutting force model, including ploughing force in the tool edge and rake face, was developed, considering the effect of speeds on fracture toughness and normal stress based on orthogonal cutting experiments. Moreover, the model accounted for each saw tooth's instantaneous depth of cut by considering the depth of elastic recovery and interference effect of adjacent saw teeth, based on a kinematic model of the saw tooth tip. The impact force in the blind groove cut and the acceleration effect on cutting force were also considered in the model. The proposed model accurately predicts sawing forces, offers insights for reducing them through design parameter modifications, and has potential applications in medical training simulations, robotic-assisted surgery, and the optimization of saw blade shapes or movement to reduce sawing forces.

Study of tantalum-based coatings magnetron sputtered on NiTi alloy in argon and argon/nitrogen atmosphere

In this work, surface morphology, corrosion resistance, and mechanical properties of tantalum sputtered NiTi in Ar and Ar–N2 atmospheres as well as room and 200 °C temperatures have been investigated. FESEM studies showed the positive effect of heat on forming a uniform and dense Ta layer under the Ar atmosphere whereas it left an adverse mark on coatings in the Ar–N2 atmosphere. XRD patterns depicted amorphous coatings in all samples meaning 200 °C was not sufficient for the formation of crystallized Ta. AFM 3D images of surface topographies suggested that smooth and compact layers were produced in the Ar-injected chamber while the coatings containing N in their chemical composition owned irregular ups and downs with a higher porosity degree. Electrochemical measurements indicated that despite nonuniformity, Ar–N2 coatings were more resistive whereas polarization resistance was at least three times greater than that of Ar coatings. Finally, nanoindentation results showed that the coating formed at 200 °C and Ar condition had the highest nano-hardness, Young's modulus, and elastic recovery. The sample coated in Ar–N2 condition and the same temperature, however, expressed the least mechanically-favorable character.

Prediction of asphalt binder elastic recovery using tree-based ensemble bagging and boosting models

The Multiple Stress Creep Recovery (MSCR) test has been proposed and implemented over the last two decades as an alternative to traditional tests, especially the elastic recovery (ER) test, to better capture rutting resistance. This paper presents a study on predicting asphalt binder ER using MSCR test results through ensemble learning methods, based on a database of more than 700 points for mostly polymer-modified binders. The ensemble approach involved tree-based Bagging (Random Forest and Extra Trees) and Boosting (Adaboost, gradient boosted decision tree, XGBoost, LightGBM, and CatBoost). The findings revealed the effectiveness of ensemble learning methods in capturing complex relationships within the data. Extra Trees and XGBoost emerged as the most accurate models based on coefficient of determination, mean absolute error, and root-mean-square error, compared to the other mentioned models and Neural Networks. These models offer precise predictions of asphalt binder ER from MSCR test results, surpassing the ER-DSR test proposed in the literature. Recovery at stress levels of 0.1 and 3.2 kPa were identified as the top influential features. In addition, clustering methods were employed to detect patterns within the dataset. The outcomes highlighted difficulties in discerning binders based on existing MSCR parameters, suggesting opportunities for refining MSCR analysis, and exploring additional tests to improve the distinction among asphalt binders. This investigation provides practical implications for states still utilizing PG-Plus, promoting the adoption of MSCR specifications for asphalt binder characterization.

Formation and properties of zein Particle-GMS Co-stabilized pickering emulsions: Insights into the complex interface

The interplay between colloidal particles and surfactant co-adsorption plays a pivotal role in determining interface properties and emulsion stability. This study delves into the influence of the Zp/GMS ratio on the physical stability of Zein particle-GMS co-stabilized emulsions (CPEs) and how co-adsorption and interfacial interactions impact this stability. Results indicated that the preferential adsorption of GMS facilitated the diffusion (Kdiff increased from 0.083 mNm−1 s−0.5 to 0.206 mNm−1 s−0.5) and penetration of Zp (KP increased from −17.0 × 104 s−1 to −23.6 × 104 s−1), triggering interface rearrangement. Consequently, intricate interfaces formed, inducing a synergistic reduction in interfacial tension. Moreover, the decreased Zp/GMS ratio bolstered the lateral molecular interactions between Zp and GMS at the interface, while also enhancing the longitudinal relaxation of GMS during interface deformation. Therefore, the Zp/GMS ratio played a pivotal role in controlling the stiffness, elasticity, and deformability recovery of complex interfaces in both lateral and longitudinal dimensions. Furthermore, in both O/W and W/O CPEs, a decreased Zp/GMS ratio improved the physical stability of CPEs by reducing the rate of droplet coalescence. To summarize, the enhanced stability of CPEs can be attributed to the reduction in droplet aggregation. This reduction is influenced by a combination of improved mechanical properties resulting from lateral molecular interactions at the interface and enhanced deformability recovery due to the longitudinal relaxation of GMS. These findings not only deepen our understanding of particle-surfactant interactions in Pickering emulsions but also pave the way for formulating emulsions with specific textures and stabilities.

Study on rheological properties of POE/VO compound recycled asphalt.

In order to improve the high temperature performance of Vegetable oil recycled asphalt, this study used Polyolefin elastomer (POE) and vegetable oil (VO) to compound recycled aging asphalt. The properties of recycled asphalt were compared and analyzed by conventional physical properties and high & low temperature rheological tests. The results show that 8% VO content can achieve the best regeneration effect. Based on this VO dosage, a variety of POE/VO combination mixture schemes were designed and tested to obtain excellent deformation resistance of recycled aging asphalt under high temperature environments. The POE/VO combination with an appropriate dosage can restore the high temperature deformation resistance and elastic recovery performance even beyond the pre-aging level, and increase the critical temperature by 4~10°C. Considering the physical properties and rheological properties of asphalt, the recommended ratio of POE/VO composite recycled asphalt is 8% VO+4% POE and 8% VO+6% POE.

Investigation of the Al-Mo-B(CN) Coatings Deposited Using Magnetron Sputtering of Al-Mo-B4C Target Produced by Detonation Spray Coating

In this work, a metal–ceramic composite target for magnetron sputtering was manufactured by a robotic complex for detonation spraying of coatings equipped with a multi-chamber detonation accelerator. The powder composition (30Mo-30Al-40B4C) was sprayed onto the copper plate base of the composite target cathode. The obtained cathode target with Al-Mo-B4C coating (thickness 280–300 μm) was used to deposit the Al-Mo-B(CN) coating (DC mode) on flat specimens of AISI 316 steel and silicon using equipment for magnetron sputtering UNICOAT 200. The Al-Mo-B4C coating has a lamella-type structure with inclusions of boron carbide particles. The structure and morphology of the coatings were studied using methods of optical analysis, scanning electron microscopy, atomic force microscopy, X-ray analysis, and X-ray photoelectron spectroscopy. Mechanical and tribological properties of the Al-Mo-B(CN) thin coatings were studied using a nanoindenter, a scratch tester, and a tribometer under a fluid-free friction regime at room temperature. The Al-Mo-B(CN) coating (thickness ~1 μm) exhibited a dense homogeneous fine-grained design without columnar elements and had an amorphous structure. The formation of the MoB2 and AlN phase with an admixture of oxygen in the form of aluminum oxide, molybdenum oxide, and boron oxide was determined using XPS analysis. The Al-Mo-B(CN) coating possessed a hardness of 13 GPa, an elasticity modulus of 114 GPa, an elastic recovery of 45%, a friction coefficient of 0.8 against a steel 100 Cr6 ball, and an adhesion strength of 11 N.

Direct synthesis of polyethylene thermoplastic elastomers with high molecular weight and excellent elastic recovery via a hybrid steric bulky strategy

Recently, α-diimine nickel-catalyzed ethylene chain walking polymerization has enabled the direct preparation of polyethylene thermoplastic elastomers using ethylene as a single feedstock. In this study, a series of hybrid bulky butyl-based α-diimine nickel complexes constructed with o-aryl and -diarylmethyl anilines were synthesized and employed for the ethylene polymerization. All the nickel complexes showed high activities (level of 106 g mol-1h−1) and high molecular weight (Mn up to 1230.9 kg/mol) polyethylene with high branching density (82–118/1000C) were yielded in ethylene polymerization. The polyethylene obtained by Ni1-3 showed distinguished elastic properties (SR = 72–91 %) and the sample obtained by Ni1 at 50 °C exhibited optimal elastic recovery values (91 %), which is also the best reported so far in polyethylene elastomers. Compared to the corresponding nickel complexes with symmetrical ligand substituents, the complexes with unsymmetrical substituents (hybrid) in this study facilitate the synthesis of significantly higher branched polyethylene with much better elastic recovery. The hybrid cationic nickel catalysts are also capable of catalyzing the copolymerization of ethylene with methyl 10-undecenoate.