Metallographic Techniques Research Articles

Archaeometallurgical investigation of the Nebra Sky Disc

The world heritage object Nebra Sky Disc is one of the best investigated archaeological objects. The origin of the raw materials it is made of is well known. However, its manufacturing process was not completely clear. Investigations were made in order to clarify the steps of manufacturing from the initial casting to the finished disc using the latest metallographic techniques. Therefore, a small piece from the outer part of the disc was investigated and compared with a replica. Both were prepared regarding the metallographic procedure. Microstructural analysis was made by optical microscopy on a colour etched surface, EDS and electron backscatter diffraction. For the investigation of mechanical properties microhardness measurements were made. It could be found that the Nebra Sky Disc was manufactured from a flat cast followed by hot forging process. During the forging process the disc was heated and forged for approximately 10 times.

Effect of Intercritical Austenitization and Starting Matrix on Martensite Start Temperature and Austenite Carbon Concentration in Ductile Iron

AbstractIn this work, the effect of the intercritical austenitization temperature and time, Ni + Cu concentration and starting matrix (fully ferritic or fully pearlitic) on the volume fraction of austenite (fγ), martensite start temperature (Ms) and carbon concentration of the parent austenite (C0) in ductile iron was investigated using standard metallographic techniques and high-resolution dilatometry. The results showed that a fully pearlitic starting matrix gives higher fγ and C0 and lower Ms than a fully ferritic starting matrix at the same austenitization temperature under continuous heating. On the other hand, the austenitization time has an effect on the parameters under study only during the first minutes of intercritical austenitization. Finally, at the same intercritical austenitization temperature, the addition of Ni + Cu increases the volume fraction of austenite.

Study on the Tribological Properties of DIN 16MnCr5 Steel after Duplex Gas-Nitriding and Pack Boriding.

DIN 16MnCr5 is commonly used in mechanical engineering contact applications such as gears, joint parts, shafts, gear wheels, camshafts, bolts, pins, and cardan joints, among others. This study examined the microstructural and mechanical properties and tribological behavior of different surface treatments applied to DIN 16MnCr5 steel. The samples were hardened at 870 °C for 15 min and then quenched in water. The surface conditions evaluated were as follows: quenched and tempered DIN 16MnCr5 steel samples without surface treatments (control group), quenched and tempered DIN 16MnCr5 steel samples with gas-nitriding at 560 °C for 6 h, quenched and tempered DIN 16MnCr5 steel samples with pack boriding at 950 °C for 4 h, and quenched and tempered DIN 16MnCr5 steel samples with duplex gas-nitriding and pack boriding. Microstructure characterization was carried out using metallographic techniques, optical microscopy, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction. The mechanical properties were assessed through microhardness and elastic modulus tests using nanoindentation. The tribological behavior was evaluated using pin-on-disc tests following the ASTM G99-17 standard procedure under dry sliding conditions. The results indicated that the surface treated with duplex gas-nitriding and pack boriding exhibited the highest wear resistance and a reduced coefficient of friction due to improved mechanical properties, leading to increased hardness and elastic modulus.

Optimized Compound Layer Design for Highly Loaded Nitrided Gears

Nitriding is a thermochemical surface hardening process, which can be used to improve the performance properties of gears. In particular, the tooth flank and tooth root load-carrying capacity can be significantly increased by nitriding. Previous work has shown that tribological dominated failure modes and limits, such as the micro-pitting and wear load-carrying capacity of gears, can be significantly increased by a suitable compound layer structure. In this work, the relationship between compound layer design and macro-pitting load-carrying capacity of nitrided gears is explored based on experimental investigations. For this purpose, the materials EN31CrMoV9 and EN42CrMo4 were nitrided under varying nitriding conditions to produce compound layers with different structures and properties. The characteristics of the compound layer such as phase composition, compound layer thickness and pore seam were extensively characterized by means of metallographic techniques, XRD, GDOES, and EBSD. Experimental investigations of the macro-pitting load-carrying capacity were carried out on an FZG back-to-back gear test rig with center distance a = 52 mm. It was shown that the pitting load-carrying capacity depends to a large extent on the characteristics of the compound layer, in particular on the formation of the pore seam. A minimum pore seam thickness of CLTP ≥ 1.8 µm has a positive effect on the pitting load-carrying capacity. The test results for the pitting load-carrying capacity are above (σH lim ≥ 1690 N/mm2) or, in some cases, significantly above (σH lim = 1979 N/mm2) the strength values specified in ISO 6336-5:2016 for nitrided nitriding steels (σH lim = 1450 N/mm2; material quality ME) and case-hardened alloy steels (σH lim = 1650 N/mm2; material quality ME).

Use of simple experiments in the classroom, for teaching of phases and solutions, introduction to phase diagrams

This article brings together various experiences aimed at achieving a better understanding of learning by students through the application of simple and easy experiments, oriented especially to understanding what Phase and Component concepts represent in an alloy system, so that they can approach the topic of Phase Diagrams in their Materials (Science, Engineering, Technology) courses with better background. Thus, experiences are presented that allow, initially, to recognize, solute and solvent concepts, to distinguish an unsaturated , a saturated, and a supersaturated solution. From this, it is sought that, through experimentation, students distinguish systems of total solubility, partial solubility, and insolubility and thus, fully understand what a phase, a phase transformation, and a component in a system means. Finally, a connection of these concepts is made with metallographic techniques as a methodology to distinguish the phases in real systems. These experiences have made it possible to improve student learning and to more easily address the topic of Phase Diagrams.

Characterization of Microstructural and Mechanical Properties of 17-4 PH Stainless Steel by Cold Rolled and Machining vs. DMLS Additive Manufacturing

The 17-4 PH stainless steel is widely used in the aerospace, petrochemical, chemical, food, and general metallurgical industries. The present study was conducted to analyze the mechanical properties of two types of 17-4 PH stainless steel—commercial cold-rolled and direct metal laser sintering (DMLS) manufactured. This study employed linear and nonlinear tensile FEM simulations, combined with various materials characterization techniques such as tensile testing and nanoindentation. Moreover, microstructural analysis was performed using metallographic techniques, optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The results on the microstructure for 17-4 PH DMLS stainless steel reveal the layers of melting due to the laser process characterized by complex directional columnar structures parallel to the DMLS build direction. The mechanical properties obtained from the simple tension test decreased by 17% for the elastic modulus, 7.8% for the yield strength, and 7% for the ultimate strength for 17-4 PH DMLS compared with rolled 17-4 PH stainless steel. The FEM simulation using the experimental tension test data revealed that the 17-4 PH DMLS stainless steel experienced a decrease in the yield strength of ~8% and in the ultimate strength of ~11%. A reduction of the yield strength of the material was obtained as the grain size increased.

Long-term corrosion of copper alloys in the soil: new aspects of corrosion morphology in archaeological vessels from south-western Iran

A group of copper-based objects excavated at Deh Dumen cemetery, in south-western Iran, was studied and analysed to examine the long-term corrosion morphology and mechanism in the soil burial environment. For this purpose, twenty-two samples from twenty-one copper-based vessels were studied and analysed using X-ray diffraction, scanning electron microscopy—energy dispersive X-ray spectroscopy, micro-Raman spectroscopy and metallography techniques. The results of the analyses showed that the majority of vessels are made of tin bronze, along with two arsenical copper samples. The extent of corrosion observed ranges from very thin corrosion crusts to thick crusts and entirely corroded structures. These three identified corrosion morphologies display a multi-layered corrosion stratigraphy as well as the preserved limit of the original surface. The corrosion crusts include internal tin-rich and external copper-rich layers, and the main corrosion mechanism for the formation of multi-layered corrosion crusts is decuprification or selective dissolution of copper during the long-term burial time in a moderately Cl-contaminated soil. The three identified corrosion morphologies are similar to the previously published morphologies, but some clear deviations are apparent and are discussed here.

The influence of Gd content on the solidification and microstructure of AlSi7Mg0.3 casting alloy

The effects of Gd content on the solidification path and microstructure of an AlSi7Mg0.3 alloy have been studied. Two different Gd levels, 0.1 and 0.5 mass%, respectively, have been investigated while the material has been solidified at low (0.2 °C s−1) and high (1.3 °C s−1) cooling rates. Computer-aided thermal analysis and metallographic techniques have been used to study the solidification and microstructural evolution of the alloy at different Gd contents and cooling rates. The results show how Gd has no effect on the grain refinement at both cooling rates. The eutectic structure is unaffected at Gd level of 0.1 mass%. A concentration of 0.5 mass% Gd promotes the precipitation of the gadolinium phosphide (GdP) phase instead of aluminium phosphide (AlP) compounds, thus suppressing the eutectic plateau during the solidification and serving as nucleant for the GdAl2Si2 phase. The eutectic Si crystals solidified at low cooling rate are refined at 0.5 mass% Gd content, while the morphology of Si crystals is only partially modified at high cooling rate.

Microstructure and Mechanical Properties of the EN AC-AlSi12CuNiMg Alloy and AlSi Composite Reinforced with SiC Particles

There is growing interest in developing more advanced materials, as conventional materials are unable to meet the demands of the automotive, aerospace, and military industries. To meet the needs of these sectors, the use of advanced materials with superior properties, such as metal matrix composites, is essential. This paper discusses the evaluation of microstructural and mechanical properties of conventional eutectic EN AC-AlSi12CuNiMg aluminum alloy (AlSi12) and advanced composite based on EN AC-AlSi12CuNiMg alloy matrix with 10 wt% SiC particle reinforcement (AlSi12/10SiCp). The microstructure of these materials was investigated with the help of metallographic techniques, specifically using a light microscope (LM) and a scanning electron microscope (SEM). The results of the microstructural analysis show that the SiC particles are uniformly distributed in the matrix. The results of the mechanical tests indicate that the tensile properties and hardness of the AlSi12/10SiCp composite are significantly higher than those of the unreinforced eutectic alloy. For AlSi12/10SiCp composite, the tensile strength is 21% higher, the yield strength is 16% higher, the modulus of elasticity is 20% higher, and the hardness is 11% higher than unreinforced matrix alloy. However, the unreinforced AlSi12 alloy has a percentage elongation that is 16% higher than the composite material. This shows that the AlSi12/10SiCp composite has a lower ductility than the unreinforced AlSi12 alloy. The tensile specimens of the tested composite broke apart in a brittle manner with no discernible neck development, in contrast to the matrix specimens, which broke apart in a ductile manner with very little discernible neck formation.

Effects of preheating on laser beam–welded NSSC 2120 lean duplex steel

AbstractDuplex stainless steels show sustainable alternative for the conventional austenitic grades, with higher strength, higher resistance against stress corrosion cracking, and lower purchase cost. Thus, duplex stainless steel gains more attention in construction, oil and gas, and chemical industries. Among duplex stainless steels, low nickel and low molybdenum alloyed lean duplex stainless steel are a cost-effective substitution of austenitic grades. However, keeping the balanced ferrite/austenite phase ratio in the weld metal can be challenging, mostly for autogenous and low heat input welding processes. In our research, a newly developed NSSC 2120 lean duplex stainless steel grade was welded autogenously by fiber laser welding process. Different welding parameters and preheating temperatures were used during the experiments. The welds were evaluated by microscopic and metallographic techniques, and also by electrochemical corrosion measurements. The welding parameters and the preheating temperature greatly influenced the weld shape and the austenite content in the weld metal. It was found that the focus point distance from the sheet surface had significant effect on the weld geometry. Changing the focus point distance to + 2 mm, the penetration depth increased from 4.96 to 5.53 mm, and increased the austenite content by 2.6%. Due to the preheating the welds became wider and shallower, e.g., from 4.96 to 4.08 mm penetration depth, while the cross-section are increased from 5.10 to 6.12 mm2 at the same sample. The preheating resulted in more intergranular austenite formation, which meant maximum 4% increase in the weld metal. The increasing austenite content resulted in increasing pitting corrosion resistance in 3.5% NaCl electrolyte, the highest increase was 90 mV.

Failure analysis and factors influencing spline wear in hydraulic motors of charging pumps in nuclear power plants

Metallographic analysis techniques such as optical microscopy and scanning electron microscopy were used to observe the morphology of spline wear, confirming the presence of fretting wear characteristics. Microstructural analysis of spline cross sections using a metallographic microscope revealed surface carburization treatment on the splines. Hardness tests conducted from the surface to the core of the splines showed a gradual decrease in hardness, consistent with the observed microstructural features. The chemical composition of the spline was analyzed using a spectrometer, and the main component content was analyzed.By combining finite element analysis techniques, this study analyzed the effects of factors such as forces, eccentricity, and lubrication on spline wear. The results indicated that the varying degrees of spline wear in the hydraulic motors of charging pumps in the on-site conditions of the nuclear power plant were primarily attributed to differences in spline eccentricity after manufacture and assembly. Further investigation revealed that the fundamental cause of spline wear in hydraulic motors was the operation of the equipment under conditions deviating from the rated operating points, resulting in poor circulation of oil within the motors and insufficient spline lubrication. Specifically, operating the equipment at lower pressures and away from the rated operating points resulted in reduced oil flow velocity, increasing the friction between the spline mating surfaces. The poor lubrication of the spline and eccentricity are the primary reasons for spline wear, and the combination of these two factors exacerbates spline wear. To address the wear issue of the hydraulic motor, we replaced it with a linear-axis hydraulic motor and conducted a comprehensive analysis of the linear-axis hydraulic motor. The results indicate that the linear-axis hydraulic motor can effectively reduce wear, and after testing at the nuclear power plant, it meets the operational time requirements on-site.These findings offer valuable guidance for the maintenance and operation of charging pumps in nuclear power plants, facilitating the prevention of similar issues and enhancing equipment reliability and operational efficiency.

The Influence of Sealing Processes and Machining Operations on the Scratch and Wear Resistance of Anodized AlSi9Cu3(Fe) Diecasting Alloy

The effects of hydrothermal and cold sealing processes on the scratch and wear resistance of the anodic layer have been studied. High-pressure diecast AlSi9Cu3(Fe) alloy plates were anodized in a sulfuric acid electrolyte at 16°C and further sealed in boiled water or in a NiF2 solution at 25°C. To analyze the influence of pre-anodizing machining operations, the plates were studied in the as-diecast condition and after milling. Metallographic investigations and image analysis techniques were carried out to study the morphology and thickness of the anodic layer. Hardness, wear, and scratch measurements were also performed to characterize the surface mechanical properties. The results showed that the sealing processes enhanced the wear and scratch resistance of the anodized surfaces because of the precipitation of hydrates that sealed the surface porosity. The thicker oxide layer formed on the milled substrate led to a greater wear resistance compared to the as-diecast surface, owing to reduced wear of the underlying aluminum substrate. Finally, a cracked mechanically mixed layer, which was enriched with fragmented intermetallics and anodic layer debris, was formed on the anodized surfaces at the end of the wear tests.

Heat-Affected Zone Characterization of X2CrNiN22-2 Lean Duplex Stainless Steel by Metallographic and Electrochemical Techniques

This research aimed to investigate the heat-affected zone of lean duplex stainless steel grade X2CrNiN22-2. Different heat-affected zone microstructures and grain morphologies were developed by Gleeble simulations. The governing microstructures were evaluated by metallographic techniques and electrochemical corrosion measurements. It was found that the 1200-800 °C cooling time significantly affects the microstructure, austenite content, and corrosion properties. The average austenite content in the case of 1 s cooling time is 30.7 ± 1%, which increased with the longer cooling times up to 38.6 ± 0.9%. The rapid cooling times resulted in a more ferritic microstructure, which promoted nitride precipitation in the ferrite grains. The nitride precipitations acted as nucleation sites for pitting initiation in 3.5 wt.% NaCl solution. The lowest pitting potential was measured in the case of the most rapidly cooled sample: 573 ± 31 mV, while the balanced, annealed microstructure had much better pitting corrosion resistance, showing a pitting potential of 1308 ± 62 mV vs. the Ag/AgCl (KCl sat.) reference electrode. The results of this research can be used in designing welding parameters for the welding of the X2CrNiN22-2 lean duplex stainless steel.Graphical

Fretting wear behaviour in 6061-T6 aluminium alloy

Abstract In this study, fretting wear in riveted lap joints of aluminium alloy plates was investigated. For the fretting test, 6061-T6 aluminium alloy plates, which are widely used in aircraft construction, and blind rivets were used. Experiments were carried out using a computer controlled Instron testing machine. Fretting surface roughness, microhardness was investigated by metallographic techniques and scanning electron microscopy. Tensile load cycles in the riveted lap joint were found to cause damage to all surfaces. Two contact surfaces where friction occurs were investigated. The contact surface of the lower plate with the upper plate, and the contact surface of the lower plate with the rivet head. As load and cycles increased, fretting scars and surface roughness increased. Consequently, it has been determined that fretting damages occur between the contact surface of the plates and between the plate and the rivet contact surface.

Onset of Mechanical Degradation due to Transverse Compressive Stress in Nb3Sn Rutherford-Type Cables

In the framework of the High Field Magnets program at CERN, lower limits of degradative mechanical loads on reacted and impregnated Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn Rutherford-type cables are being studied with the goal of optimizing the pre-stress applied at room temperature on the accelerator magnets. Coils are loaded during assembly, for instance when transverse load is applied by using a collaring press or the bladder and key technique. Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn is susceptible to transverse compressive stress, which is the loading condition investigated for this study. The purpose of this work is to identify the maximum pressure that can be applied, at room temperature, to reacted cables without generating cracks in the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn subelements and to quantify the crack propagation with increasing pressure. Metallographic techniques are used to examine the onset and evolution of damage in the transverse planes of impregnated double-stacked Rutherford-type cable specimens with increasing stress. The damage pattern observed at subelement, strand and cable levels is described. Two reaction heat treatment cycles are analyzed.

Evaluation of the Interface of Green Bilayer Powder Compact (BPC) of Iron (Fe) Under Different Die Wall Conditions

The current work evaluates cross-sectioned green bilayer powder compact (green BPC) of iron (Fe) under different die conditions. At first, finite element-based (FE) simultaneous compaction modelling is used to model the uniaxial, one-sided compaction of the green BPC of Fe and its interface. A Tri-mesh of 0.03 mm and mesh refinement along the interfacial boundary is set up with the condition of each node from both sides of layers (namely lower layer, L and upper layer, U) is mapped precisely to ensure its mutual interconnection along the horizontal edges of interface. Additionally, the modelling part utilised and validated our recently proposed image analysis under the metallographic technique’s standard framework. Our approach to model the interface to gain the same effect as from the experimental result of green BPC of Fe is in good agreement. It is significantly found that the use of the lubricated die condition contributed to increasing the local RD distribution along the interface of the green BPC of Fe. In contrast, the distribution is gradually dissuaded from the interface for the unlubricated die condition as the applied height: diameter (H:D) ratio increases.

The Metallic Sounds: A Microanalytical Study on the Production of Armenian Church Bells from Iran.

There are a considerable number of church bells in museums, examples include the museum of the Vank Cathedral and the Treasury of Armenian Music in New Julfa, both located in Isfahan, Iran. These objects were collected from different Armenian churches and cathedrals in Iran and were dated to ca. 400-100 years ago. Due to the long history of Armenians in Iran and their important role in its cultural and architectural development, study of the production technologies they utilized is a subject of interest for art historians and scientists. Three metallic bells from the Treasury of Armenian Music in New Julfa were selected for a multianalytical study to investigate their manufacturing methods, using micro-XRF, scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and metallography techniques. The results showed that the bells were produced with a binary tin bronze alloy with 13 to 20 wt% of tin, classified as either low-tin or high-tin bronze, depending on the concentration. The analysis showed a two-phase cast microstructure consisting of the α solid solution with significant amounts of interdendritic α + δ eutectoid. The results also indicate that the bells are cast first, but some evidence of complementary thermomechanical operations is visible in their microstructure.

Enhancement of Elevated‐Temperature Strength in Al–Cu–Ce–Mn–Zr Cast Aluminum Alloy Through Ni Alloying

Herein, to enhance the elevated‐temperature strength of heat‐resistant aluminum alloys to satisfy application requirements, the effect of Ni content (0.5, 1.0, 2.0, 4.0 wt%) on the microstructures and tensile properties of Al–8.4Cu–2.3Ce–1.0Mn–0.2Zr alloy is investigated. The metallographic analysis techniques are used to quantitatively examine the microstructural changes. The skeleton‐like Al7Cu4Ni phase is formed after the addition of Ni and its morphology is gradually transformed into a coarse reticular‐like shape with Ni content increasing. However, the thermally stable Al8CeCu4 and Al24MnCu8Ce3 phases disappear when Ni content exceeds 1.0%. Al–8.4Cu–2.3Ce–1.0Mn–0.2Zr–0.5Ni alloy exhibits the optimal elevated‐temperature tensile performance at 400 °C, and its ultimate tensile strength, yield strength, and elongation at 400 °C reach 105, 85 MPa, and 16.5%, respectively. The optimal tensile performance is attributed to synergistic enhancing action of the thermostable Al8CeCu4, Al24MnCu8Ce3, Al16Cu4Mn2Ce, and Al7Cu4Ni phases at the grain boundaries and the nano‐sized Al20Cu2Mn3 and Al2Cu precipitates inside the grains. The typical brittle fracture is dominating in the five alloys with different Ni contents at ambient temperature, but the fracture mode at 400 °C is changed from ductile fracture to ductile and brittle mixed fracture with the increase of Ni.

Investigation of microstructure of fretting wear behavior in 6061-T6 aluminum alloy

PurposeThe purpose of this study is to investigate the microstructure of fretting wear behavior in 6061-T6 aluminum alloy. The fretting wear of blind riveted lap joints of 6061-T6 aluminum alloy plates, which are widely used in aircraft construction, was investigated. Fretting damages were investigated between the contact surface of the plates and between the plate and the rivet contact surface.Design/methodology/approachExperiments were carried out using a computer controlled Instron testing machine with 200 kN static and 100 kN dynamic load capacity. Max package computer program was used for the control of the experiments. Fretting scars, width of wear scars, microstructure was investigated by metallographic techniques and scanning electron microscopy.FindingsIt was found that fretting damages were occurred between the plates contacting surface and between the plate and rivet contact surface. As load and cycles increased, fretting scars increased. Fretting wear initially begins with metal-to-metal contact. Then, the formed metallic wear particles are hardened by oxidation. These hard particles spread between surfaces, causing three-body fretting wear. Fretting wear surface width increases with increasing load and number of cycles.Originality/valueThe useful life of many tribological joints is limited by wear or deterioration of the fretting components due to fretting by oscillating relative displacements of the friction surfaces. Such displacements are caused by vibrations, reciprocating motion, periodic bending or twisting of the mating component, etc. Fretting also tangibly reduces the surface layer quality and produces increased surface roughness, micropits, subsurface microphone.

Wear resistance of surfaced modified CoCr alloy with stellite alloys and boron carbide coating via laser alloying

Resistance in joint prostheses remains widely studied in terms of wear due to the loose debris that causes the implant loosening failure. The present work aims to explore the tribological behavior of surface-modified CoCr alloy using Stellite 6 and Stellite 12 coatings with and without B4C additions created via laser surface alloying. The microstructural analysis of the laser surface alloying coatings was performed using metallographic techniques, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), and nanoindentation tests. The tribological performance of coatings was evaluated using a pin-on-disc tribometer under dry sliding wear conditions. The experimental results showed that the Stellite 6, Stellite 12, and B4C particles were uniformly distributed in the coatings produced with the circular spot of the laser. The microstructure after laser surface alloying generates different intermetallic secondary phases as M23C6, WC, and B4C carbides, modifying the mechanical and tribological response. Tribological results of Stellite 12 with B4C additions and B4C laser surface alloying coatings showed better performance by reducing the coefficient of friction and increasing the wear resistance.