Microindentation Hardness Measurements Research Articles

Testibiopalladite, PdSbTe: A Valid Mineral and Sb-Analogue of Michenerite

Abstract Testibiopalladite was reported from two unnamed deposits in China by Anonymous (1974) to be ideally PdSbTe. The description of the mineral included an indexed X-ray powder diffraction pattern, space group determination, electron probe micro-analyses, reflectance, and micro-indentation hardness measurements. This description was published without prior submission to the IMA, which was the norm at the time before China became a member. It is unknown as to why the Commission for New Minerals and Mineral Names (CMNMN) did not examine and vote on the mineral as had been done for all other Chinese mineral descriptions published at the time. It is surprising because the chairman of the CMNMN at the time had reviewed the mineral (Fleischer et al. 1976) and concluded it was a valid species, i.e., the Sb analogue of michenerite (PdBiTe). Further, the same article included a description of “hexastibiopanickelite” which was voted on and rejected by the CMNMN in 1976. From 1981 to 2021 there were many papers published reporting testibiopalladite from several deposits in different countries (e.g., Hudson et al. 1978, Chen et al., 1993, Stepanets et al. 2019, 2020), as well as a single-crystal structure analysis of synthetic PdSbTe which confirmed the assigned space group (Foecker & Jeitschko 2001). The published data (e.g., Barkov et al. 2002, Liang et al. 2019, 2023) suggest that testibiopalladite is a valid mineral species, ideally PdSbTe, and is the Sb analogue of michenerite, PdBiTe, both crystallizing in space group P213. Both the name testibiopalladite and the mineral, ideally PdSbTe, were approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (CNMNC-IMA), Nomenclature Voting Proposal 23-H. Liang et al. (2019, 2023) studied samples from the type locality (Yangliuping deposit, PRC) that are to be considered as a neotype.

Effect of High-Temperature Tempering on Microstructure and Mechanical Strength of Laser-Welded Joints between Medium-Mn Stainless Steel and High-Strength Carbon Steel

The strengthening effect due to high-temperature tempering (HTT) at 700 °C on the microstructure and mechanical properties of welded joints between medium-Mn stainless steel (MMnSS) and high-strength carbon steel (CS) was studied. The microstructure of the weldments was investigated using Laser and scanning electron microscopes. An Electron probe microanalyzer (EPMA) was used to assess quantitatively the elemental distribution profiles of alloying elements within the weld zone. The strengthening precipitates induced during welding and HTT were characterized by transmission electron microscopy (TEM). Uniaxial tensile tests and microindentation hardness (HIT) measurements of the weld joints were conducted to evaluate the strengthening effect. Fully fresh-martensite and fine-tempered martensitic structures were promoted in the as-weld and HTT processes, respectively. The HTT structure exhibited a remarkable improvement in mechanical properties (a better combination of yield and tensile strength together with moderate ductility) compared to its weld counterpart. TEM investigation revealed that various types of precipitates have been promoted in the structures of the weld and HTT, e.g., nanosized vanadium and chromium carbides. It is apparent that the proposed HTT of the joints is an effective treatment for improving the mechanical properties due to inducing the formation of fine interphase precipitates, resulting in enhanced mechanical strength of the joints.

Enhancement of strength in laser-joined Al-TRIP and Si-TRIP steels: Microstructural insights and deformation analysis

This study highlights the strengthening mechanisms observed during the metal joining of high-strength grade steels (Al-TRIP and Si-TRIP) by providing a concise investigation of microstructural features, mechanical strength evaluation, and employing Finite Element Method (FEM) analysis to understand the deformation behaviour in the joint. The base metals (BMs), Al-TRIP and Si-TRIP are cold-rolled sheets with thicknesses of 0.9 mm and 1.3 mm, respectively. Al-TRIP contains 2.4 wt% Al, while Si-TRIP contains 1.5 wt% Si. The Al-/Si-TRIP joint was processed by laser welding at low energy input 24 J/mm. Electron backscattering diffraction and transmission electron microscopy extensively characterized the microstructural features in the fusion zone (FZ) and heat-affected zone (HAZ) to study strengthening mechanisms induced by welding. Uniaxial tensile tests examined joint mechanical strength, while microindentation hardness (HIT) measurements evaluated mechanical response in the weld zones. The FZ showed a fully martensitic structure, while the HAZs displayed refined grains. Ultrafine-grained structures with an average size of 1 μm were observed in the HAZs, resulting in higher HIT hardness values (∼6.7 GPa) compared to the FZ (∼6.3 GPa). Interestingly, the mechanical tensile properties of the joint were unaffected as failure occurred in the thinner Al-TRIP steel. Finite Element Method (FEM) analysis simulated the tensile testing, revealing localized plasticity in the thinner Al-TRIP and explaining the observed fracture.

Friction Stir Welding of Dissimilar Al 6061-T6 to AISI 316 Stainless Steel: Microstructure and Mechanical Properties.

The friction stir welding (FSW) process was recently developed to overcome the difficulty of welding non-ferrous alloys and steels. In this study, dissimilar butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel were welded by FSW using different processing parameters. The grain structure and precipitates at the different welded zones of the various joints were intensively characterized by the electron backscattering diffraction technique (EBSD). Subsequently, the FSWed joints were tensile tested to examine the mechanical strength compared with that of the base metals. The micro-indentation hardness measurements were conducted to reveal the mechanical responses of the different zones in the joint. The EBSD results of the microstructural evolution showed that a significant continuous dynamic recrystallization (CDRX) occurred in the stir zone (SZ) of the Al side, which was mainly composed of the weak metal, Al, and fragmentations of the steel. However, the steel underwent severe deformation and discontinuous dynamic recrystallization (DDRX). The FSW rotation speed increased the ultimate tensile strength (UTS) from 126 MPa at a rotation speed of 300 RPM to 162 MPa at a rotation speed of 500 RPM. The tensile failure occurred at the SZ on the Al side for all specimens. The impact of the microstructure change in the FSW zones was significantly pronounced in the micro-indentation hardness measurements. This was presumably attributed to the promotion of various strengthening mechanisms, such as grain refinement due to DRX (CDRX or DDRX), the appearance of intermetallic compounds, and strain hardening. The aluminum side underwent recrystallization as a result of the heat input in the SZ, but the stainless steel side did not experience recrystallization due to inadequate heat input, resulting in grain deformation instead.

Evolution of operable slip systems, lattice strain fields and morphological view of Bi-2223 ceramic system with optimum NiO addition

The current work extensively reveals the influence of different nickel oxide (NiO) impurity addition levels on the morphological, microstructural, key mechanical performance, and mechanical characteristic properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Oy (Bi-2223) ceramics using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and Vickers micro-indentation (Hv) hardness measurements. It was observed that the addition of NiO impurity in the Bi-2223 crystal structure affected seriously the fundamental characteristic features. In the case of the optimum NiO concentration level of x = 0.1, the Bi-2223 materials exhibited the best crystallinity quality and coupling strengths between the adjacent layers, the most uniform surface view, and the densest, and the smoothest crystal structure. Similarly, the compound was noted to possess the hardest, highest mechanical strength, durable tetragonal phase, resistance toward failure by fatigue, and elastic recovery properties. Besides, it was observed that the characteristic Bi-2223 superconducting phase fraction and stabilization of the tetragonal crystal system reached the maximum level for the optimum concentration. Moreover, optimum NiO particles brought about a considerable increase in the number of operable slip systems, surface residual compressive force regions, and lattice strain fields. Correspondingly, the mobility of defects was blocked significantly depending on the preference of defects through transcrystalline regions. Additionally, optimum addition strengthened the typical indentation size effect due to the improvement of the recovery mechanism. In this regard, the NiO-added sample exhibited the least response to the applied loads. Thus, the Bi-2223 sample with the optimum NiO concentration was found to present the highest hardness parameter of 0.496 GPa, greatest elastic deformation value of 16.493 GPa, largest stiffness value of 1.044 MN/m, and smallest contact depth of 5.849 µm. On the other hand, after the optimum concentration level of x = 0.1, there appeared serious increase in problems including internal defects, impurity residues, microscopic structural problems, and connection problems between the grains. All experimental findings were theoretically supported by semi-empirical mechanical methods. To sum up, the addition of NiO particles was noticed to increase the potential application areas of Bi-2223 ceramics.

Improvement in deformation degree of Zr surface-layered Bi-2223 ceramics by diffusion annealing temperature

This study investigated the effects of different annealing temperatures (650 °C ≤ T ≤ 840 °C) on the surface morphological and mechanical performance properties of Zr surface-layered Bi-2223 materials with scanning electron microscopy (SEM) images, Vickers microhardness (Hv) measurements, and semi-empirical mechanical approaches. It was observed that the ceramic compound exposed to 650 °C annealing temperature exhibited the superior performance features due to the enhancement in the deformation degree. This is because the Zr ions behaved as the nucleation centers to prevent the propagations of cracks and dislocations throughout the main matrix depending on the decrease in the degree of granularity and distributions of crystal structure problems over a wider area. Similarly, the SEM pictures indicated that the diffusion mechanism increased the random distributions of the thinner plate-like granular structures (serving as nucleation centers), leading the decrease in the coupling problems between the grains. Among the materials, the highest surface densification was observed for the compound exposed to 650 °C. Namely, surface morphological analysis showed a strong correlation between microstructure and mechanical performances. Further, the zirconium ions were found to decrease in the non-recoverable stress concentration sites, crack-initiating defects, and dislocations in the ceramic system. Accordingly, the sensitivity to the applied test load was noted to decrease dramatically. Shortly, crack growth size and velocity were observed to be more easily under control. Correspondingly, the Zr ions delayed considerably the beginning points of saturation limit (load-independent) regions for the bulk Bi-2223 superconducting materials. Additionally, the Zr ions led to the change in the mechanical characteristic behavior from typical indentation size effect to reverse indentation size effect. Lastly, the microindentation hardness measurements were semi-empirically analyzed by the different models. According to the comparison, Hays-Kendall mechanical model was noted to provide the closest parameters to the load-independent microhardness results.

Evolution of dynamics of physico-chemical and mechanical properties of hydroxyapatite with fluorine addition and degradation stability of new matrices

This multidisciplinary study examined sensitively the change in the dynamics of main mechanical performance, stability of crystal structure, crystallinity quality, strength, corrosion resistance, biocompatibility, resistance to structural degradation/separations and mechanical durability features of hydroxyapatite (HAp) biomedical materials based on the fluorine addition and degradation process to guide future medical and dental treatment studies. In the study, the fluorine ions were used to be the dental coating, filling and supporting material for biologically or synthetically produced bone minerals. The general characteristic properties were investigated by means of standard spectroscopic, structural and mechanical analysis methods including RAMAN, SEM-EDS, TEM, Vickers micro-indentation hardness and density measurements. A time dependent release test was performed to evaluate possible fluorine ion release after the degradation process. It was found that the fundamental characteristic properties of HAp biomedical materials are noted to improve with the increase in the fluoride level up to 2% due much more stabilization of HAp crystal system. The combination of RAMAN spectra and powder XRD analyzes indicates that 2% addition level affects positively the formation velocity of characteristic HAP phase. Besides, fluorine doped HAp materials all exhibited the main characteristic peaks after degradation process. This is attributed to the fact that the fluorine ions enabled the hydroxyapatite to enhance the structural quality and stability towards the corrosion environment. However, in case of excess dopant level of 3% the degradation rates were obtained to increase due to higher contribution rate and especially electrostatic interactions. As for the surface morphology examinations, 2% fluorine added HAp with the highest density of 3.0879 g/cm3 was determined to present the superior crystallinity quality (smallest grain size, best smooth surface, honeycomb pattern, regular shaped particles and densest particle distributions through the specimen surface). Conversely, the excess fluorine triggered to increase seriously degree of micro/macro porosity in the surface morphology and microscopic structural problems in the crystal system. Thus, the HAp doped with 3% was the most affected material from the degradation process. Additionally, the fluorine ion values read after the release process were quite far from the value that could cause toxic effects. Lastly, the optimum fluorine addition provides the positive effects on the highest durability, stiffness and mechanical fracture strength properties as a consequence of differentiation in the surface residual compressive stress regions (lattice strain fields), amplification sites and active operable slip systems in the matrix. Hence, the crack propagations prefer to proceed in the transcrystalline regions rather than the intergranular parts. Similarly, it was found that Vickers micro-indentation hardness tests showed that the microhardness parameters increased after the degradation process. All in all, the fluorine addition level of 2% was noted to be good choice to improve the fundamental characteristic properties of hydroxyapatite biomedical materials for heavy-duty musculoskeletal, orthopedic implant, biological and therapeutic applications in medicine and dentistry application fields.

Macromechanical and micromechanical properties of polymers with reduced density of entanglements

AbstractThe macromechanical and micromechanical properties of polypropylene, polylactide, and polystyrene with different entanglement densities and different crystallinities were tested. The mechanical properties were characterized by macroscale compression tests and microindentation hardness measurements. The entanglement density modified the mechanical properties only in the high‐deformation region, above the yield point, when the strain‐hardening occurred, and ca 10% lower stresses were measured for disentangled polymers. In the low‐deformation region, the influence of the entanglement density was negligible. The stiffness of semicrystalline polymers increased with their crystallinity and the stiffness of amorphous polymers increased with their glass transition temperature. For example, the elastic modulus was equal to 1.59 MPa for entangled polylactide, 1.68 MPa for partially disentangled polylactide, and 2.20 MPa for semicrystalline, disentangled polylactide. The stiffness‐related properties in both macroscale (compressive modulus, E, and yield stress, Y) and microscale (indentation modulus, EIT and indentation hardness, HIT) showed very similar trends, which was in perfect agreement with theoretical predictions and confirmed the reliability of our results. The supplementary, viscosity‐related properties from microindentation experiments (indentation creep, CIT, and elastic part of indentation work, ηIT) supported the above‐mentioned conclusions in the sense that also these two low‐deformation region properties were independent on the entanglement density.

Failure Analysis of a Stainless Steel Pipe Elbow in a Purge Gas Line

A failure analysis was performed on a SA-312 TP304 stainless steel pipe elbow in a purge gas line at a petrochemical plant. Fatigue was confirmed to be the mechanism of the failure. Visual, dimensional, fractography, macrostructural, and vibrational evaluations; as well as microindentation hardness measurements, material characterization, and morphology analysis, were performed. The contributing factors for the fatigue were extreme steady-state piping vibration in the line of the elbow, a non-conformance weld joint, and improper pipe installation which caused external stress on the elbow. The fatigue most likely was originated by a crack at an inclusion in the grain boundary of the austenitic microstructure. The results emphasize that by not complying with adequate piping installation, with welding practices and without reducing or attenuating vibrations in equipment or at its proximity; failures associated with fatigue in this material will tend to be present, increasing the need of costly plant shutdowns.

Characterization of Vacuum Explosive Welded Joints between Titanium and Stainless Steel for Vacuum Applications

A two-layered vacuum explosive welded (EXW) plate, consisting of titanium-grade 1/stainless steel 304L (Ti/304L), was investigated for vacuum applications. The interface of the Ti/304L displayed a wavy shape characteristic of the EXW method, which reflects the existence of mass transfer during bonding. The aim of this study was to examine the feasibility of using Ti/304L EXW joints for vacuum application. The Ti/304L EXW plate was examined by non-destructive and destructive metallurgical methods, including visual testing, scanning acoustic testing, light microscopy and metallography, SEM-EDS examination, microindentation hardness measurements, ram tensile test, fractography, and leak testing. According to the metallurgical testing methods, the formation of brittle intermetallic phases took place adjacent to the bonding interface. The intermetallic phases formed at the interface of the Ti/304L, behave as the weakest part in the joint, and determine the brittle type of fracture received under tensile stresses. The measured typical tensile strength of the joint is around 300 MPa, similar to that of the Ti 1 alloy. Based on the leak test results, the examined EXW Ti/304L components were found to be feasible for vacuum applications.

A New Approach Towards Life Prediction of Case Hardened Bearing Steels Subjected to Rolling Contact Fatigue

Abstract The failure of a bearing-raceway assembly is governed by the spatial distribution of subsurface stresses at the vicinity of a bearing-raceway contact and the evolution of these stresses during rolling contact fatigue (RCF) loading. In this paper, we propose an experimental methodology that allows one to accurately measure the location and magnitude of the cyclically evolving elastoplastic von Mises stresses in terms of microhardness numbers. An M50NiL steel rod is subjected to RCF by three silicon nitride (Si3N4) balls for over several hundred million cycles at 5.5 GPa contact stress level. Microindentation hardness measurements within the subsurface RCF-affected regions of the rod revealed significant material hardening. A mechanistic methodology to construct a stress-life (S-N) diagram for RCF loading is proposed. S-N diagrams are constructed based on maximum von Mises stress amplitude and volume average von Mises stress amplitude. The effects of elastic modulus and yield strength gradient on stress fields are also considered in this analysis. Comparison of S-N diagrams based on both stress amplitudes indicates that the maximum von Mises stress amplitude overpredicts the fatigue strength of material in S-N diagrams. The experimental results obtained by following this methodology can help construct material hardening models for RCF, which may lead to an improved estimate of bearing fatigue life.

A study on non-uniform deformation of backward flow forming and its influencing factors

Non-uniform deformation in the thickness of tubular spun parts is a common problem in the flow forming process and has a significant impact on the performance of spun parts. In this paper, the plastic strain distribution in the wall thickness of tubular spun parts made of Haynes230 superalloy was obtained by the finite element method and microindentation hardness measurements. Moreover, the causes of the non-uniformity in plastic strain distribution were analysed, particularly the effect of main processing factors such as thickness reduction, feed rate and forming passes on plastic strain distribution in the thickness direction. The results indicate that the factors that have significant impacts on uniformity of deformation are thickness reduction and forming passes; deformation in the material is mainly concentrated in the outer layer of the spun part and less so in the inner layer. Furthermore, the plastic strain increases with an increase in thickness reduction, and the number of forming passes with the former process more favourably increasing the plastic strain in the inner layer than the latter. Therefore, in order to improve deformation uniformity in the spun parts, thickness reduction should be increased and the number of forming passes should be decreased when determining the total thickness reduction. This study is equally applicable to other materials.

Metallurgical characterization of brass sheet from the 19th-century Akko Tower Wreck (Israel)

The Akko Tower Wreck is the remains of a 25-m-long merchant brig, dated to the first half of the 19th century. A well preserved piece of brass sheathing was found in the shipwreck, retrieved and examined by non-destructive and destructive metallurgical methods, including visual testing, XRF, OES, light microscopy, SEM-EDS examination, microindentation hardness measurements and lead isotope analysis. The results demonstrate that the sheet is made of α-brass, containing about 34wt% Zn. Its thickness (average 0.85mm) and microstructure indicate that it was produced as rolled sheet, annealed during its manufacturing process. Its composition and manufacturing process indicate that it was produced during the first half of the 19th century, thus supporting the dating of the ship. The lead isotope analysis suggests that the raw material most probably originated in Great Britain, similarly to brass nails retrieved from the ship. This is an example of the exploitation of the corrosion resistance of α-brass sheet for use as sheathing to protect a ship against Teredo navalis and to improve its sailing qualities by its anti-fouling properties.

Pro-oxidant activity of α-tocopherol during photooxidative degradation of polyolefins. ESRI and IR microspectroscopy studies

Photooxidation processes inside high-density polyethylene (HDPE) and cyclic olefin copolymer (COC) poly(ethylene-co-norbornene), both stabilized with biological antioxidant α-tocopherol (α-T-OH), has been investigated. Plaques made of the polymers stabilized with α-T-OH were subjected to long-term accelerated weathering in a Weather-Ometer (WOM). Concentration profiles of radicals generated in the plaques in dependence on WOM exposure time were determined by electron spin resonance imaging (ESRI). Concentration profiles of oxidation products and stabilizer, together with local crystallinity profiles inside the polymer plaques were determined by infrared (IR) microspectroscopy. The ESRI and IR profiles, supplemented by light microscopy (LM) and microindentation hardness measurements (MH), revealed the heterogeneity of the oxidation process and, surprisingly, the pro-oxidative activity of α-T-OH. Increasing concentration of products of polymer oxidation was found in the surface layers of the plaques stabilized with α-T-OH since the beginning of WOM treatment unlike the same control experiments with polymer plaques stabilized with HAS Tinuvin® 770, where no oxidation products were observed after the same treatment before HAS depletion. We have confirmed that α-T-OH exhibits antioxidant activity during thermooxidation but it acts as a pro-oxidant agent during photooxidation.

Impact of particle morphology on structure, crystallization kinetics, and properties of PCL composites with TiO2-based particles

Crystallization kinetics of polycaprolactone (PCL) filled with TiO2-based particles (TiX) was shown to depend on the TiX particle type and concentration, which were associated with a slight polymer matrix degradation. The partially degraded, shorter, and more mobile polymer chains increased the overall crystallization rate at the initial stage of crystallization, while at the later stages, the non-nucleating TiX particles acted as a sterical hindrance, slowing down the crystallization process. The PCL/TiX composites were prepared by melt-mixing and contained 2.5 and 5 wt% of the filler. The investigated TiX particles included isometric anatase microparticles (mTiO2) and titanate nanotubes with high-aspect ratio (TiNT). Light and electron microscopy showed very homogeneous dispersion of the mTiO2 particles in the PCL matrix, while the TiNT formed large agglomerates. In situ polarized light microscopy displayed faster isothermal crystallization of all PCL/TiX composites, but the micrographs indicated that the TiX particles did not act as nucleation centres. Isothermal DSC experiments, evaluated in terms of Avrami theory, confirmed the PLM results and showed that the overall rate of isothermal crystallization increased in the following order: PCL <PCL/TiNT <PCL/mTiO2. Non-isothermal DSC and rheological measurements revealed the correlation between the crystallization rate and the polymer matrix degradation—the well-dispersed mTiO2 particles with high specific surface caused the highest PCL degradation and, consequently, the earliest start of non-isothermal crystallization as well as the fastest isothermal crystallization. Microindentation hardness measurements confirmed that the partial degradation of the polymer matrix did not have a significant impact on the mechanical performance of PCL/mTiO2 composites.

Influence of Residual Stress and Temperature on the Cyclic Hardening Response of M50 High-Strength Bearing Steel Subjected to Rolling Contact Fatigue

Microstructural and mechanical characterization investigations on three variants of a through-hardened M50 bearing steel are presented to compare and contrast their performances under rolling contact fatigue (RCF) loading. Baseline (BL) variant of M50 steel bearing balls is subjected to: (i) a surface nitriding treatment and (ii) a surface mechanical processing treatment, to obtain distinct microstructures and mechanical properties. These balls are subjected to RCF loading for several hundred million cycles at two different test temperatures, and the subsequent changes in subsurface hardness and compressive stress–strain response are measured. It was found that the RCF-affected subsurface regions grow larger in size at higher temperature. Micro-indentation hardness measurements within the RCF-affected regions revealed an increase in hardness in all the three variants. The size of the RCF-affected region and intensity of hardening were the largest in the BL material and smallest in the mechanically processed (MP) material. Based on Goodman's diagram, it is shown that the compressive residual stress reduces the effective fully reversed alternating stress amplitude and thereby retards the initiation and evolution of subsurface plasticity within the material during RCF loading. It is quantitatively shown that high material hardness and compressive residual stress are greatly beneficial for enhancing the RCF life of bearings.

Post-treatment of Plasma-Sprayed Cr2O3 with Methane-Containing Gas for Conversion to Binder-Free Cr3C2

In most applications, the performance of thermally sprayed Cr3C2-NiCr cermet coatings is known to be adversely affected by the presence of the NiCr binder phase. A processing technique for the rapid synthesis of Cr3C2 on industrial-scale components could improve the functionality of these coatings by eliminating the metallic binder phase. To form a thick, continuous surface layer of adherent, binder-free Cr3C2, the reduction of plasma-sprayed Cr2O3 with methane-containing gas was investigated. Conversion of the plasma-sprayed Cr2O3 to carbide resulted in a significant increase in coating porosity, yielding a highly microporous Cr3C2 surface layer. The physical characteristics of the reduction process appear to be dependent on the coating defect structure at the reduction temperature. Phase morphology and porosity evolution throughout the reduction process were qualitatively examined using x-ray diffraction and scanning electron microscopy. The utility of the resultant Cr3C2 coating is discussed with respect to these microstructural characterizations and microindentation hardness measurements.

Time-resolved micro-indentation hardness measurement to probe the Form II/Form I crystal polymorphism in random copolymers of butene-1 with either ethylene or propylene

Time-resolved micro-indentation hardness measurements have been performed on random copolymers of butene-1 with minor amount of ethylene or propylene during the room-temperature transition of the Form II mesophase into Form I crystals. The microhardness depends on the present crystal polymorph and increases during the Form II–Form I phase transformation, which is completed faster in the random copolymers than in the butene-1 homopolymer. It is furthermore observed that the microhardness decreases with increasing concentration of ethylene and propylene co-units in the random copolymers. This experimental result is comprehensively discussed in view of the observed decreases of the crystallinity and crystal perfection in copolymers containing ethylene or propylene, respectively. Analysis of a copolymer with about 11 mol% propylene revealed that the microhardness of copolymers containing Form I’ crystals, formed directly from the melt, is higher than the initial microhardness of samples of lower co-unit content containing only Form II mesophase.

Additive Manufacturing and Characterization of René 80 Superalloy Processed Through Scanning Laser Epitaxy for Turbine Engine Hot‐Section Component Repair

This article demonstrates single‐pass fabrication of thick, crack‐free deposits of René 80, a high gamma‐prime “non‐weldable” superalloy, atop like‐chemistry substrates through scanning laser epitaxy (SLE), a metal powder bed‐based laser additive manufacturing (AM) technique. Microstructural investigations and processing zone identification are presented. Optical microscopy and scanning electron microscopy reveal the segregated dendritic microstructure with the presence of finer carbides and primary γ′ particles. Transmission electron microscopy reveals a bimodal distribution of finer secondary γ′ particles in the deposit region. Microindentation hardness measurements show an increase in the hardness value by 25% in the deposit region compared to the cast substrate due to microstructural refinement. In addition to the achievement of metallurgical continuity across the interface and improved hardness in the deposit, the crack‐free deposits obtained here for René 80 represent one of the few successes reported for a non‐weldable alloy of its kind. The results presented here illustrate the significant potential of SLE for the AM‐based repair of existing and AM‐based construction of entirely new gas turbine hot‐section components utilizing powders of high γ′ nickel‐based superalloys that have long been known to have high tendency for cracking under the processing conditions associated with traditional welding, joining, and cladding approaches.

The Brass Nails of the Akko Tower Wreck (Israel): Archaeometallurgical Analyses

The shipwreck designated as the Akko Tower Wreck was discovered inside Akko harbor, Israel, in 1966. It was surveyed in 1975 and 1981, and excavated in 2012–2013. Hull planks were connected to the frames by brass nails, some of which were in situ, emerging vertically from the planking, where frames had disappeared, and others were detached. The 105 nails that were retrieved were tentatively divided into two groups (A and B) according to their general shape and size. Nails sampled from each group were characterized by non-destructive and destructive metallurgical methods, including XRF, light microscopy, SEM–EDS, microindentation hardness measurements, and lead isotope analysis, in order to reveal their composition and microstructure, as well as to determine their manufacturing process and date the origin of the raw material. All nails were manufactured by casting and made of binary copper-zinc alloy: Type A with 35–36 wt% zinc, and Type B with 33–34 wt% zinc (XRF results). These compositions confirmed the preliminary typing of the nails. Their microstructure indicates that they were manufactured differently: Type A nails have Widmanstatten thin lamellae plates, and Type B nails have α-brass grains containing a dendritic microstructure. Based on their zinc and lead concentrations it is suggested that the nails were manufactured in the first half of the nineteenth century. The lead isotope analyses of the nails suggest that the raw material most probably originated in Great Britain. Hence, it is suggested that the Akko Tower Wreck is the remains of a European merchantman which sank in Akko harbor about the middle of the nineteenth century.