Microindentation Hardness Testing Research Articles

Mechanical Resistance in Decapod Claw Denticles: Contribution of Structure and Composition

The decapod crustacean exoskeleton is a multi-layered structure composed of chitin-protein fibers embedded with calcium salts. Decapod claws display tooth-like denticles, which come into direct contact with predators and prey. They are subjected to more regular and intense mechanical stress than other parts of the exoskeleton and therefore must be especially resistant to wear and abrasion. Here, we characterized denticle properties in five decapod species. Dactyls from three brachyuran crabs (Cancer borealis, Callinectes sapidus, and Chionoecetes opilio) and two anomuran crabs (Paralomis birsteini and Paralithodes camtschaticus) were sectioned normal to the contact surface of the denticle, revealing the interior of the denticle and the bulk endocuticle in which it is embedded. Microhardness, micro- and ultrastructure, and elemental composition were assessed along a transect running the width of the cuticle using microindentation hardness testing, optical and scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS), respectively. In all species tested, hardness was dramatically higher—up to ten times—in the denticle than in the bulk endocuticle. Likewise, in all species there was an increase in packing density of mineralized chitin-protein fibers, a decrease in width of the pore canals that run through the cuticle, and a decrease in phosphorous content from endocuticle to denticle. The changes in hardness across the cuticle, and the relationship between hardness, calcium, and magnesium content, however, varied among species. Although mechanical resistance of the denticles was exceptionally high in all species, the basis for resistance appears to differ among species. Statement of SignificanceUnderstanding the diverse mechanisms by which animals attain exceptionally high mechanical resistance may enable development of novel, biologically inspired materials. Decapod crustacean claws, and particularly the tooth-like denticles that these claws display, are of interest in this regard, as they must be especially resistant to wear. We assessed mechanical, elemental, and structural properties of the claw cuticle in five decapod species. Without exception, microhardness was dramatically higher in the denticle than in the bulk endocuticle. Multivariant statistical analyses, however, showed that the relationships among microhardness, elemental content, and structural variables differed among species. Such patterns likely result from strong evolutionary pressure on feeding and defensive structures and a trade-off between mechanical properties and energetic cost of exoskeleton formation.

Effect of Hydrogen Electrosorption on Mechanical and Electronic Properties of Pd80Rh20 Alloy.

The interaction of hydrogen with Pt-group metals and alloys is at the center of research in the fields of electrochemistry, electrocatalysis, hydrogen technologies and fuel cells developed under the Hydrogen Economy. In this work, the material under study was Pd80Rh20 alloy (50 μm foil) subjected to hydrogen electrosorption at potentials corresponding to formation of α, α-β and β phase in 0.1 M H2SO4 at 25 °C. The total amount of hydrogen adsorbed at the surface and absorbed in octahedral interstitial positions of fcc Pd80Rh20 alloy, was determined from the oxidation charges. The H/(Pd+Rh) was 0.002, 0.4 and 0.8 for α, α-β, and β Pd80Rh20H, respectively. Microindentation hardness testing and nanoindentation showed weakening of mechanical properties of the Pd80Rh20 alloy after hydrogen electrosorption due to internal stresses. Decrease of work function with increasing amount of hydrogen absorbed occurred due to the surface roughness changes and the presence of electropositive hydrogen atoms absorbed in the crystal lattice responsible for the dipole interaction. The detailed mechanism of hydrogen absorption/diffusion in the Pd80Rh20 alloy structure is discussed. The obtained results give a new insight into the relationship between the amount of absorbed hydrogen and mechanical and electronic properties of the Pd80Rh20 alloy at the micro- and nanoscale.

Laser finishing of polycrystalline diamond as strengthening mechanism

Abstract Polycrystalline diamonds are widely used in the cutting tool industry for machining of aluminium alloy and metal matrix composites as they exhibit superior wear resistance. However, their wear characteristics are dependent on their microstructural features (i.e. percentage of binder phase and size of grains) which are defined during the sintering process. Low-energy fibre laser process of polycrystalline diamond composites with different grain dimensions is proposed to promote microstructural changes, enhance their hardness, and retain surface finish. Specimens were processed with a nanosecond pulsed fibre laser (ytterbium-doped) at a wavelength of 1064 nm. Samples treated at various fluences, beam speeds and pulse durations were characterised via 3D interferometry, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and micro-indentation hardness test. At a fluence below the composite’s ablation threshold (i.e. 20 J cm2), the investigated finishing/polishing process for a coarse grain polycrystalline diamond resulted in a change of diamond grain size, a surface integrity of 140 nm and increased micro hardness (i.e. 240 GPa). The laser treatment caused plastic deformation of the grains, changing the intergranular boundaries area therefore impeding dislocation movements and enhancing hardness.

Optimization of resistance spot welding process applied to A36 mild steel and hot dipped galvanized steel based on hardness and nugget geometry

Resistance spot welding (RSW), a process intensively used for thin metal sheets assembly in automotive, railway, and aeronautical industries, has always presented technical and economic challenges. Thermal distortions and difficulties caused by the presence of anticorrosive coating on galvanized steels are among the major issues. An evaluation of effects of welding parameters on overall nugget quality will be of great importance in solving these issues. Two grades of steel were used in this study, A36 mild steel and A653 hot dipped galvanized steel. Welding experiments were done in overlap configuration, grade for grade, while following complete factorial plans of three factors at two levels. Micrographic analyses revealed weld microstructure, while micro-indentation hardness tests enabled to establish the hardness profile along weld nuggets. Analyses of variance (ANOVA) were done in order to evaluate the effect of each parameter on nugget hardness and diameter. Response surface models combining hardness in the fusion zone and nugget diameter were plotted as function of welding parameters. These response surfaces showed that current is the predominant parameter and should be maximized in order to achieve strong welds while force and time should be minimized for A36 mild steel and maximized for galvanized steel.

Electro-discharge Machining (EDM) of Superalloy Inconel 718 Using Triangular Cross-Sectioned Copper Tool Electrode: Emphasis on Topography and Metallurgical Characteristics of the EDMed Work Surface

A case experimental research towards investigating aspects of electro-discharge machining on Inconel 718 superalloy using copper tool electrode (triangular cross section) has been delineated herein. Based on three controllable process variables, viz. peak discharge current, pulse duration and gap voltage, experiments have been carried out to investigate their effects on surface crack density and white layer thickness observed onto the top surface of the EDMed end product. Additionally, EDS analysis has been carried out to investigate the extent of carbon enrichment incurred onto the machined surface caused by pyrolysis of the dielectric media. XRD tests have been carried out to compare metallurgical features (various phases/precipitates present, extent of grain refinement, crystallite size and dislocation density) of the EDMed work surface with respect to as-received Inconel 718. Results, thus obtained, have also been compared to those of micro-indentation hardness test data.

Prooxidant activity of phenolic stabilizers in polyolefins during accelerated photooxidation

Polymer plaques made of high density polyethylene (HDPE) and of two types of cycloolefin copolymer (COC) differing in glass transition temperature, were stabilized with 0.2 or 1.0 wt % of natural (α-tocopherol) or synthetic (Irganox®1010) phenolic stabilizer or hindered amine stabilizer (Tinuvin®770) and aged using accelerated weathering technique (WOM). The efficiency of the phenolic stabilizers was compared among themselves and with well-established Tinuvin®770. Concentration profiles of radicals generated inside polymer plaques during WOM exposure were determined by ESRI, profiles of oxidation products and crystallinity inside the HDPE plaques were determined by IR microspectroscopy, oxidation products in COC copolymers were identified using ATR, the changes of local mechanical properties of the polymer plaques were characterized using microindentation hardness testing, and their morphology was studied by light and/or scanning electron microscopy. All the techniques evidenced high stability of neat COC against photooxidation processes, whereas neat HDPE exhibited fast photooxidation of the surface layers. Tinuvin®770 was found to provide long term protection to both HDPE and COC against photodegradation. In contrast, the same polymers stabilized with the natural phenolic antioxidant α-tocopherol (the most active component of vitamin E) or synthetic phenolic antioxidant Irganox®1010 exhibited an increase in the surface oxidation in comparison with the neat polymers during WOM exposure, proving prooxidant activity of phenolic stabilizers during WOM exposure in all polymers studied. The prooxidant activity α-tocopherol was stronger in comparison with Irganox®1010. We conclude that neither of the two phenolic stabilizers was able to provide long term protection of the investigated polymers against photooxidation.

Optimization of arc-sprayed iron-based tungsten carbide hard coatings on harvester blades

This research investigated the viability of improving the performance of agricultural harvester blades by thermal spray, utilizing the arc spray process. A cored iron-based wire with recycled WC was used with several process parameters in order to determine the best WC distribution in the coating. The effect of 40 V voltage was compared to 30 V on electric arc-sprayed coatings, and the results show that 40 V provides higher tungsten carbide (WC) content. Flame remelting of the arc-sprayed iron-based WC coatings on sugarcane harvester blades was studied, and the changes in the microstructure and impact abrasion wear behavior were analyzed. The coatings were characterized by utilizing microstructural analysis and microhardness indentation tests. In order to verify the coating adhesion strength, a special machine was built to simulate field conditions. This machine, called impact abrasion test machine, was used to test the blades for coating detachment due to low adhesion strength. The results showed that the flame remelting provided metallurgical bonding between the coating and substrate, improving the impact wear resistance and potentially extending the lifetime of sugarcane harvester blades.

Bone Hardness of Different Anatomical Regions of Human Radius and its Impact on the Pullout Strength of Screws.

ObjectiveTo investigate the bone hardness of different anatomical regions of the human radius and its impact on the pullout strength of screws.MethodsFresh radius bones were obtained from three donated cadavers. They were divided into three parts: proximal metaphysis, shaft, and distal metaphysis. The proximal metaphysis contains the head, neck, and radial tuberosity. The distal metaphysis includes the palmaris radius and the styloid process. The shaft of the radius was divided into nine segments of equal length. The bone hardness of three radiuses, one from each cadaver, was measured by Vickers microindentation hardness tests, and the screw pullout strength was examined in the other three radiuses using a materials testing machine. The trend between radius hardness and pullout strength was analyzed by using an analysis of variance randomized block design. Pearson correlation analysis was performed to evaluate the linear correlation between the bone hardness and the pullout strength of the human radius.ResultsThe mean hardness ranged from 33.30 HV (the head) to 43.82 HV (the diaphysis). The hardest part of the radius was the shaft, with a value of 42.54 ± 5.59 HV. The proximal metaphysis had a hardness value of 34.15 ± 6.48 HV, and the distal metaphysis hardness value was 35.24 ± 5.17 HV. The shaft was 23.5% harder than the proximal metaphysis and 20% harder than the distal metaphysis. The microhardness test demonstrated that the bone hardness value of the diaphysis was significantly higher than those of both the proximal and distal metaphysis of the radius (both P < 0.05). The mean pullout strength values ranged from 552 N (the distal metaphysis) to 2296 N (the diaphysis). The greatest pullout strength of the radius was observed for the shaft, with a pullout strength of 1727.96 ± 111.44 N. The pullout strength of the proximal metaphysis was 726.33 ± 236.39 N, and the pullout strength of the distal metaphysis was 590.67 ± 36.30 N. The pullout strength of the shaft was 138% greater than that of the proximal metaphysis and 190% greater than that of the distal metaphysis. The pullout strength was also higher in the diaphysis than at both ends of the radius (both P < 0.05). A positive correlation was found between bone hardness and pullout strength (R = 0.927, P < 0.001).ConclusionsBone hardness and screw pullout strength are higher in the diaphysis of the radius than at either end. The pullout strength is positively related to bone hardness in the human radius.

Micromechanical Properties of UHMWPE’S with Different Molecular Weights

Ultrahigh molecular weight polyethylene (UHMWPE) is used as a key component of total joint replacements (TJR) and its mechanical performance is one of the factors influencing TJR lifetime. Micromechanical properties of three model UHMWPE samples with different molecular weights were evaluated from both non-instrumented and instrumented microindentation hardness testing. The properties were correlated with molecular and supermolecular structure of the samples. We have demonstrated that molecular weight influenced the final micromechanical properties mostly indirectly – it changed the overall crystallinity, which strongly correlated with microhardness, indentation modulus, and also with the elastic part of the indentation work. Only microcreep was influenced predominantly by amorphous phase, in which the higher molecular weight resulted in higher amount of entanglements and slightly higher creep resistance.

Archaeometallurgical analysis of the bow drill from the fifth century BC Ma‘agan Mikhael shipwreck

Three bow drills were discovered in the 400 BC Ma‘agan Mikhael ship. Radiography revealed a square cross-section recess for the bit in the wooden stock of one of the drills. Metal particles, remains of a bit, survived in the recess. The metal composition, microstructure and manufacturing technology of the bit were studied using non-destructive and minimally destructive testing methods. These comprised digital radiography, light microscopy, X-ray fluorescence analysis, scanning electronic microscopy–energy-dispersive X-ray spectroscopy analysis, and micro-hardness indentation tests. The results demonstrated that the bit was made of wrought iron manufactured by the direct smelting process. A martensitic microstructure was observed after etching the external part of the bit. Examination of the iron oxide areas revealed a layered microstructure. Therefore, it is suggested that the bit was probably manufactured by forge-welding thin alternating layers of carburized wrought iron, which was heat-treated and quenched without tempering. This microstructure improved the hardness and strength of the metal. This is the first time that a metal bit found on a shipwreck of the period has been metallurgically investigated. It shows that the ancient blacksmiths produced the drill bit using the most suitable materials and advanced manufacturing processes. This information enlarges our limited knowledge about the use of carpenter’s tools in the East Greek/Phocaean fifth century BC shipbuilding tradition.

UV degradation of styrene-butadiene rubber versus high density poly(ethylene) in marine conditions studied by infrared spectroscopy, micro indentation, and electron spin resonance imaging

UV irradiation and thermal degradation were studied in marine conditions for styrene-butadiene rubber (SBR) and high density poly (ethylene) (HDPE) containing a Tinuvin® 770 hindered amine stabilizer. Electron spin resonance imaging (ESRI) was used to monitor degradation process in various depths and compare the polymers in terms of robustness to UV irradiation. In addition, both oxidative degradation and mechanical properties were studied by microscale methods, such as infrared microspectroscopy (IR) and microindentation hardness testing (MHI), enabling us to compare the material changes locally, i.e. both at the exposed surfaces and inside the samples. In SBR/Tin770 system, Tinuvin®770 stabilizer failed to protect the polymer matrix against photooxidation as clearly seen from IR/ATR spectra. The Weather-Ometer (WOM) aging resulted in strong oxidative degradation of both non-stabilized and stabilized SBR and caused remarkable changes in three regions of IR/ATR spectra. The strong photooxidative degradation was also manifested through the micromechanical properties of SBR/Tin770 systems. The change of the local properties was the same (within the standard deviations) for both stabilized and non-stabilized samples, which confirmed negligible stabilization efficiency of Tinuvin® 770 in the SBR system. In contrast to the SBR systems, similar experiments showed very dramatic stabilization effects in the HDPE/Tin770 system. ESR and 2D spectral-spatial ESRI directly proved the different degradation behavior of the two types of the composites: whereas in the SBR composites fast degradation was observed, high density poly (ethylene) showed much slower degradation. We attributed such striking difference to the modification of Tinuvin® 770 hindered amine stabilizer after vulcanization during preparation of SBR rubber, which apparently eliminated most of its protective activity.

Processing and characterization of crack-free aluminum 6061 using high-temperature heating in laser powder bed fusion additive manufacturing

During solidification of many so-called high-performance engineering alloys, such as 6000 and 7000 series aluminum alloys, which are also unweldable autogenously, volumetric solidification shrinkage and thermal contraction produces voids and cracks. During additive manufacturing processing, these defects can span the length of columnar grains, as well as intergranular regions. In this research, laser powder bed fusion (LPBF) of aluminum alloy (AA) 6061 used powder bed heating at 500 °C in combination with other experimentally determined processing parameters to produce crack-free components. In addition, melt-pool banding, which is a normal solidification feature in LPBF, was eliminated, illustrating solidification process modification as a consequence of powder bed heating. Corresponding microindentation hardness and tensile testing of the as-fabricated AA6061 components indicated an average Vickers hardness of HV 54, and tensile yield, ultimate strength, and elongation values of 60 MPa, 130 MPa, and 15%, respectively. These mechanical properties and those of heat treated parts showed values comparable to annealed and T6 heat treated wrought products, respectively. X-ray diffraction and optical microscopy revealed columnar grain growth in the build direction with the as-fabricated, powder-bed heated product microstructure characterized by [100] textured, elongated grains (∼ 25 μm wide by 400 μm in length), and both intragranular and intergranular, noncoherent Al-Si-O precipitates which did not contribute significantly to the mechanical properties. The results of this study are indicative that powder bed heating may be used to assist with successful fabrication of AA6061 and other alloy systems susceptible to additive manufacturing solidification cracking.

Effects of Tool Electrode on EDM Performance of Ti-6Al-4V

Due to widespread application of Ti-6Al-4V especially in automotive, aerospace, defense, and biomedical industries; machinability of this alloy is of immense importance. Very low thermal conductivity of Ti-6Al-4V is mainly responsible for its poor machinability. During Electro-Discharge Machining (EDM), conductivity of the workpiece as well as electrode plays a vital role affecting process performance. In this context, choice of electrode also influences the machining efficiency. Therefore, selection of an appropriate electrode to enhance performance of EDM on Ti-6Al-4V alloy is indeed necessary. In the present reporting, an experimental work has been carried out to investigate ease of machining of titanium alloy (Ti-6Al-4V) for electro-discharge machining using Tungsten and Copper (normal and cryogenically treated) electrodes. Experiments have been performed at different values of peak discharge current to study EDM performance on Ti-6Al-4V in terms of material removal efficiency, surface roughness, surface crack density and white layer thickness observed for the EDMed end product prepared from Ti-6Al-4V work material. Influence of peak discharge current on topography of the EDMed work surface has been examined. EDS analysis followed by micro-indentation hardness test has been performed to examine the extent of carbon enrichment onto the machined surface during EDM operation. XRD tests have been carried out to comprehend metallurgical aspects of the EDMed work surface which are supposed to be affected by the thermo-electrical phenomenon of EDM operation. Results obtained thereof, have been analyzed in detail to understand effects of electrode in persuading machinability of Ti-6Al-4V while machining though EDM route. It has been found that among three tool electrodes selected (Tungsten, normal Copper and cryogenically treated Copper), cryogenically treated Copper electrode has been found the most superior in purview of EDM performance.

Relations between morphology and micromechanical properties of alpha, beta and gamma phases of iPP

The relations between crystalline structure and micromechanical properties of α-, β- and γ-phase of isotactic polypropylene (iPP) were investigated. The iPP samples with various crystalline phase compositions were prepared by a controlled high-pressure crystallization that enabled us to obtain not only α-iPP and β-iPP modifications, but also a series of almost pure γ-iPP samples with gradually changing morphology, crystallinity and lamellar thickness. The micromechanical properties were assessed by instrumented microindentation hardness testing (MHI), from which we determined indentation hardness (HIT), indentation modulus (EIT), indentation creep (CIT) and elastic part of the indentation work (ηIT). It was demonstrated that γ-iPP does not necessarily exhibit better mechanical performance than α- and β-iPP, as suggested by some previous studies, because the final properties are strongly influenced not only by the phase composition (i.e. by the content of α-, β- and γ-phase), but also by the overall crystallinity.

Thermal and Mechanical Characterization of EMA-TEGDMA Mixtures for Cosmetic Applications.

Mixtures of methacrylic polymers are the most common materials for making composites to be used as resins for dental and cosmetic applications. Some of these mixtures are composed by poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA), which constitute a solid component to be mixed with a liquid component made out of methacrylate monomers. The reaction between the thermal initiator benzoyl peroxyde (BPO) present in the solid component and the activator of the polymerization process, N,N-dimethyl-p-toluidine (DMT) present in the liquid component, gives rise to thermoset materials. In the present study, different liquid formulations composed by a mixture of two methacrylic monomers, ethyl methacrylate (EMA) and triethylene glycol dimethacrylate (TEGDMA) for cosmetic applications, were prepared and characterized, using a commercial powder (POW) composed by PEMA and PMMA. With the aim of improving workability during final application of the material, it was necessary to slow down the polymerization rate of liquid formulations. Their thermal behavior was investigated by differential scanning calorimetric (DSC) in order to check the polymerization rate. Thermal stability of final materials was determined by thermogravimetric analysis (TGA). Dynamic mechanical thermal analysis (DMTA), microindentation hardness and impact tests were performed on final materials, to assess their performance with respect to standard formulation. The combination of thermal and mechanical properties allows choosing which formulations could be suitable for use in cosmetics.

Investigation of Fracturing and Adhesion Behavior of Hydroxapatite Coating Formed by Aminoacetic Acid-Sodium Aminoacetate Buffer Systems

Biomaterials utilized in implantation can be categorized into 4 main categories, as ceramics, polymers, metals and composites. Ceramic-based biomaterials are opted for, particularly in the field of orthopedics. These materials, also named as bioceramics, are usually employed by coating them onto the base material, inasmuch as they are far from the mechanical values of bone. In this study, a hydroxyapatite coating that is fully compatible with human blood plasma was applied on Ti6Al4V alloy through a biomimetic technique using aminoacetic acid-sodium aminoacetate buffer system for the first time in the literature, and examinations related thereto were carried out. The surface of the base material Ti6Al4V alloy was activated with various chemicals. Subsequent to activating the surface, a coating process whereby the base material was kept in simulated body fluid for 24, 48, 72, 96 h was carried out. Ultimate microhardness (indentation) tests were performed to determine the average indentation depths in maximum load, vickers hardness and elasticity modulus of the coatings obtained by using the biomimetic method, while scratch tests were performed to measure the surface bonding strengths of the coating layers. Furthermore, the fracture toughness values of the coating were calculated. The results obtained through the study are evaluated and discussed.

Understanding How Bonding Controls Strength Anisotropy in Hard Materials by Comparing the High-Pressure Behavior of Orthorhombic and Tetragonal Tungsten Monoboride

In this work, we investigate the high-pressure behavior of the stabilized high-temperature (HT) orthorhombic phase of WB using radial X-ray diffraction in a diamond-anvil cell at room temperature. The experiments were performed under nonhydrostatic compression up to 52 GPa. For comparison, the low-temperature (LT) tetragonal phase of WB was also compressed nonhydrostatically to 36 GPa to explore structurally induced changes to its mechanical properties. Although our microindentation hardness tests indicate that the HT WB possesses slightly higher hardness, synchrotron-based high-pressure compression data yield significant distinct incompressibilities. The ambient pressure bulk modulus of the HT phase of WB is 341 ± 5 GPa obtained by using the second-order Birch–Murnaghan equation of state, while for the LT phase of WB the incompressibility increased to 381 ± 3 GPa. The elastically supported differential stress was measured in a lattice-specific manner and analyzed by using lattice strain theory. Greater s...

Surface Integrity and Metallurgical Characteristics of the EDMed Work Surfaces of A2 Tool Steel (SAE 304SS), Inconel 601 and Ti-6Al-4V: a Comparative Analysis

In the present work, a comparative analysis of surface integrity and metallurgical characteristics of the EDMed work surfaces of A2 tool steel (SAE 304SS), Inconel 601 and Titanium alloy (Ti-6Al-4V) has been attempted. Experiments have been conducted at different values of peak discharge current to study morphology as well as topographical features of the EDMed work surface in terms of surface roughness, surface crack density and thickness of the white layer. XRD analysis has also been carried out to understand metallurgical features (phases and precipitates, material migration) of the EDMed work surface. Results have been interpreted with relevance to EDS and micro-indentation hardness test data. The effect of peak discharge current on the EDMed work surface topography has also been examined. It was found that peak current has imposed a positive effect on surface crack density as well as white layer thickness irrespective of the work material chosen. Compared to 304SS and Inconel 601, cracks thus developed are more severe for the EDMed surface of Ti-4Al-6V due to formation of a hard TiC layer. The white layer is non-uniformly deposited over the EDMed surface of Ti-6Al-4V compared with 304SS and Inconel 601.

Strong synergistic improvement of mechanical properties in HDPE/COC blends with fibrillar morphology

High‐density polyethylene/cycloolefin copolymer (HDPE/COC) blends with fibrous morphology were prepared. Mechanical properties in the whole concentration range were measured in both macroscale (tensile measurements) and microscale (microindentation hardness testing). Strong improvement of mechanical performance was observed namely for the blends with soft HDPE matrix reinforced with the stiff oriented COC fibers. The combined results from scanning electron microscopy, mechanical properties measurements and theoretical calculations based on predictive models showed that the interfacial adhesion was unusually high, which could be attributed to the excellent compatibility or even partial miscibility of the blend components. The HDPE/COC blends with 10–40% of COC showed the synergistic improvement of the tensile energy to break (ETB) that exceeded the ETB of both individual components. Also the stiffness of the blends, represented by the elastic modulus, the yield strength and the microhardness were very high, above the theoretical values predicted by the equivalent box model. POLYM. ENG. SCI., 58:1955–1964, 2018. © 2017 Society of Plastics Engineers

Effect of Cation Composition on the Mechanical Stability of Perovskite Solar Cells

AbstractPhotoactive perovskite semiconductors are highly tunable, with numerous inorganic and organic cations readily incorporated to modify optoelectronic properties. However, despite the importance of device reliability and long service lifetimes, the effects of various cations on the mechanical properties of perovskites are largely overlooked. In this study, the cohesion energy of perovskites containing various cation combinations of methylammonium, formamidinium, cesium, butylammonium, and 5‐aminovaleric acid is reported. A trade‐off is observed between the mechanical integrity and the efficiency of perovskite devices. High efficiency devices exhibit decreased cohesion, which is attributed to reduced grain sizes with the inclusion of additional cations and PbI2 additives. Microindentation hardness testing is performed to estimate the fracture toughness of single‐crystal perovskite, and the results indicated perovskites are inherently fragile, even in the absence of grain boundaries and defects. The devices found to have the highest fracture energies are perovskites infiltrated into a porous TiO2/ZrO2/C triple layer, which provide extrinsic reinforcement and shielding for enhanced mechanical and chemical stability.