As-received Condition Research Articles

Heat treatment effects on the shear performance and microstructure evolution of W-core SiC fibers

SiC fiber reinforced titanium alloy matrix composites employed in elevated temperature aeroengine components are subjected to complex loading conditions. Investigating the shear performance of SiC fibers after heat treatment can help ensure the load-carrying capability of composites at service temperatures. This study presents a novel double shear testing method for W-core SiC fibers. The shear strength and stiffness of the SiC fibers in as-received and heat-treated conditions were measured. The morphologies of SiC fibers’ shear fracture surfaces and C coatings were thoroughly analyzed. The evolution of the internal microstructure and the composition of reaction layers after heat treatments were investigated. The shear strength of W-core SiC fibers at 95% survival probability reached 588.64MPa after 200 h of heat treatment at 600°Celsius, representing a 55% improvement over both the as-received and 1100°Celsius heat-treated conditions. After heat treatment at 1100°Celsius, the reaction layer between the W core and the SiC sheath thickened exponentially due to extensive elemental diffusion, resulting in the formation of numerous Kirkendall voids. The voids facilitated crack initiation and propagation, leading to a deterioration in fiber shear performance. The insights gained in this study regarding the shear properties of SiC fibers can provide support for predicting the mechanical performance of composites under complex loading conditions.

The effect of cobalt alloying on the phase transformation kinetics of Ni-Ti alloys

This study investigates the influence of cobalt (Co) alloying addition and heat treatment temperature on the phase transformation behaviour controlling the superelasticity and shape memory effect (SME) of Nickel-Titanium (Ni-Ti) alloys, commonly known as nitinol. The microstructural evolution upon heat treatment conducted at a temperature ranging from 440 to 560 °C was thoroughly analyzed via Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), and Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS). Increase in heat treatment temperatures from 470 °C up to 530 °C led to the dissolution of particles present in as-received (cold-worked) condition. It was determined that Co addition into the Ni-Ti alloy system resulted in a change in the nucleation and growth kinetics of Ti-rich precipitates, leading to the formation of larger and fewer particles during processing. Both binary and ternary alloys showed a decrease in austenite finish temperature (Af) with increasing heat treatment temperatures, however, the rate of decrease was found to be higher for Co containing ternary alloys. This is linked with faster structural relaxation when Co is present and evidenced by lattice size variation during heat treatment. It is highlighted that heat treatment methodology needs to be tailored to the specific alloy composition for controlling superelasticity and SME via alloy design.

Machinability evaluation of inconel 600 by cryo-processed carbide inserts

ABSTRACT This work investigates the characterization of a cryo-processed AlTiN-coated tool and its turning characteristics for Inconel 600. The microhardness was enhanced by 3.68% under cryo-treatment when compared with the as-received condition of the inserts because of the wear-protective coating formed on the surfaces of the cutting tool. This was confirmed through EDS elemental analysis of carbon element growth and change in chemical composition, as well as XRD phase analysis. Next, this work studied the influence of cryo-treated inserts on roughness and mechanism of wear during turning Inconel 600 using varying cutting velocities (37, 60, and 100 m/min) under dry conditions. The output responses revealed that the use of cryo-treated tools reduced the roughness of the product by 11–27% and the rate of tool wear when compared with the untreated conditions. Due to these enhanced properties with cryo-treated conditions, it remains a suitable cutting tool for a significant contribution to sustainable machining toward dry cutting of aerospace alloys.

Effects of standard heat treatment on micro-to nanostructure heterogeneities in a Rene 65 Ni-based superalloy billet

Advancements in the manufacturing of aeroengine components with superior mechanical properties rely on the microstructure homogeneity of industrially forged Ni-based superalloys. Billets often contain microstructural heterogeneities that can persist throughout the process, potentially compromising the integrity of the final product. Rene 65 is a relatively new superalloy with high-temperature mechanical properties superior to those of Alloy 718. However, systematic studies on its microstructure-property relationships are scarce. Here, we correlate the microstructural evolution with the hardness of a Rene 65 billet subjected to industrial processing and standard heat treatments. Multiscale microstructural heterogeneities, including grain size, geometrically necessary dislocations, twin boundary density, and the multimodal distribution of γʹ precipitates, are characterised. Grain growth occurs near the billet centre. Precipitation varies with radial position, showing up to a two-fold change in primary and secondary γʹ fractions. Tertiary γʹ precipitates exhibit variations in morphology and chemical composition, with Cr and Co enrichment near the billet surface. These heterogeneities arise from varying strain distributions and cooling rates during radial forging. Sub-solvus annealing and ageing are shown to mitigate these heterogeneities by promoting recrystallisation, recovery, and homogeneous precipitation of tertiary γʹ. A strengthening model elucidates the active mechanisms in as-received and heat-tread conditions, predicting hardness with a deviation of <8 %. Analyses of grain boundaries and γ/γʹ interfaces reveal strong segregation of Mo, W, Nb, C and B before and after heat treatment, with Mo and B showing the highest interfacial excess values. Insights into the microstructural evolution and its impact on properties could guide the development of next-generation aerospace parts.

Comparison of the physico-chemical behavior of two prepregs used for body armor

The development of ultra-high molecular weight polyethylene fibers has resulted in continued improvement in ballistic protection, along with reduced weight in body armors. Prepregs from newly developed fibers are constantly available, although prepregs from older brands still remain on the market. In this work, the physicochemical properties of two successive generations of pre-impregnated materials are characterized to compare the two materials in the as-received condition and also after be consolidated in a ballistic plate. The results showed that fibers from the newer brand have a smaller diameter and greater tensile strength. This is an important result because the tensile strength of fibers is one of the variables that influence the ballistic performance of body armors. The smaller diameter of these fibers was associated with a greater degree of stretching during their manufacture, as revealed by the presence of two melting peaks in the DSC analysis.

Effect of Cold-Rolling Deformation on the Microstructural and Mechanical Properties of a Biocompatible Ti-Nb-Zr-Ta-Sn-Fe Alloy.

The primary focus of the current paper centers on the microstructures and mechanical properties exhibited by a Ti-30Nb-12Zr-5Ta-2Sn-1.25Fe (wt. %) (TNZTSF) alloy that has been produced through an intricate synthesis process comprising cold-crucible induction in levitation, carried out in an atmosphere controlled by argon, and cold-rolling deformation (CR), applying systematic adjustments in the total deformation degree (total applied thickness reduction), spanning from 10% to 60%. The microstructural characteristics of the processed specimens were investigated by SEM and XRD techniques, and the mechanical properties by tensile and microhardness testing. The collected data indicate that the TNZTSF alloy's microstructure, in the as-received condition, consists of a β-Ti phase, which shows polyhedral equiaxed grains with an average grain size close to 82.5 µm. During the cold-deformation processing, the microstructure accommodates the increased applied deformation degree by increasing crystal defects such as sub-grain boundaries, dislocation cells, dislocation lines, and other crystal defects, powerfully affecting the morphological characteristics. The as-received TNZTSF alloy showed both high strength (i.e., ultimate tensile strength close to σUTS = 705.6 MPa) and high ductility (i.e., elongation to fracture close to εf = 11.1%) properties, and the computed β-Ti phase had the lattice parameter a = 3.304(7) Å and the average lattice microstrain ε = 0.101(3)%, which are drastically influenced by the applied cold deformation, increasing the strength properties and decreasing the ductility properties due to the increased crystal defects density. Applying a deformation degree close to 60% leads to an ultimate tensile strength close to σUTS = 1192.1 MPa, an elongation to fracture close to εf = 7.9%, and an elastic modulus close to 54.9 GPa, while the computed β-Ti phase lattice parameter becomes a = 3.302(1) Å.

Unveiling the microstructure evolution and mechanical properties in a gas tungsten arc-welded Fe–Mn–Si–Cr–Ni shape memory alloy

Fe–Mn–Si–Cr–Ni shape memory alloys (SMAs) are unique low-cost materials with shape memory properties that grant them the ability to be used in both functional and structural applications. Such SMAs are especially sought in the construction sector for the creation of new components and/or the reinforcement of damaged ones. In this study, a Fe–17Mn–5Si–10Cr–4Ni–1(V, C) wt% SMA was gas tungsten arc welded, with the objective to investigate the microstructure and mechanical performance changes occurring after welding. A comprehensive assessment of processing, microstructure and properties relationships was established combining microscopy (optical and electron), synchrotron X-ray diffraction, microhardness mapping and tensile testing including cycling assessment of the joint’s functional performance. It is shown that the present SMA has good weldability, with the joints reaching nearly 883 MPa at fracture strain of 23.6 ± 2.1%. Alongside this, several microstructure differences were encountered between the as-received and as-welded condition, including the formation of ferrite and Fe5Ni3Si2 P213 cubic precipitates amidst the fusion zone in the latter region.Graphical abstract

Enhanced Microhardness and Corrosion Performance of Additively Manufactured Inconel 718 Specimens through Nanostructuring by Severe Plastic Deformation

Severe plastic deformation (SPD) processes, particularly high-pressure torsion (HPT) have been increasingly applied to metallic specimens fabricated by laser powder bed fusion (L-PBF) additive manufacturing (AM) for enhancing their mechanical and functional properties through nanoscale grain refinement (≤ 100 nm). In this study. L-PBF AM-fabricated Inconel 718 (IN 718) specimens are initially subjected to 10 HPT revolutions to produce nanosized grains. Subsequently, microstructural characterisation, as well as hardness and electrochemical tests are conducted to evaluate the evolution of microstructures, hardness, and corrosion performance of the as-received and HPT-processed specimens by using various microscopy, Vickers microhardness (HV) measurements, and corrosion performance, respectively. The results reveal an average grain size of ~ 46 nm, dense dislocation networks, and nanotwins after 10 HPT processing, which contribute to the two-fold hardness increase compared to the as-received condition. Such microstructures also contributed to the overall improved corrosion performance after 10 HPT processing, as quantified by the 83% and 73% reduction in corrosion rate and pitting potential, respectively.

Corrosion of an Additively Manufactured Ti6Al4V Alloy in Saline and Acidic Media.

The present work aims to provide corrosion performance data for an additively manufactured Ti6Al4V alloy in saline and polluted environments. The as-received additively manufactured material underwent heat treatment at 850 °C for 3 h to transform the acicular α' microstructure into a lamellar α microstructure. Comparative corrosion assessments were conducted between the heat-treated substrates, the as-received condition, and a conventionally mill-annealed alloy. Potentiodynamic polarization experiments were carried out in saline (3.5 wt.% NaCl) and acid aqueous media ((NH4)2SO4 containing Harrison's solution). The corrosion performance of additively manufactured substrates matched or surpassed that of the conventional alloy in Harrison's solutions while remaining inferior in saline medium, despite forming a thicker passive film. Overall, the XY plane showed better corrosion performance, particularly after the elimination of the acicular α' martensite by the applied heat treatment. The results also suggested that the presence of the coarse β phase was beneficial in 3.5 wt.% NaCl solution and detrimental in Harrison's solutions, more so in acidified and fluorinated conditions.

Influence of heat treatment on the microstructure, wettability, and corrosion resistance of a Ti–30Nb–7Zr alloy used in biomedical applications

Commercially pure titanium (cp Ti ASTM F67) and the Ti–6Al–4V ELI (Extra Low Interstitial) alloy (ASTM F136) are commonly used as biomaterials due to their biocompatibility, mechanical strength, and corrosion resistance. The low mechanical resistance of cp Ti reduces its applications. The F136 alloy may release toxic ions (Al and V). Moreover, the fact that the elastic modulus of the F136 is larger than the bone leads to stress shielding and induces bone loss. These factors drive research towards the development of new biomedical metal alloys with more suitable mechanical properties. β titanium and β-metastable alloys have special attention as potential alternatives to the F136 alloy applications. This work aimed to analyze the microstructure, wettability, and corrosion resistance of the β Ti–30Nb–7Zr alloy before and after heat treatment, and compare the results with those for the F136 alloy. The β Ti–30Nb–7Zr is an alloy based on non-toxic elements and with a smaller elastic module than F136. The techniques of open circuit potential, potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy were used. The results of this work showed that the Ti–30Nb–7Zr alloy in the as-received condition had a β matrix with precipitates, and after recrystallization heat treatments, the precipitates were eliminated. The Ti–30Nb–7Zr alloy heat treated at 500 °C for 30 min had α phase precipitates, which increased the surface energy and decreased the corrosion resistance. The best corrosion resistance was observed in Ti–30Nb–7Zr after heat treatment at 900 °C for 1 h. The conclusion is that after adequate heat treatment, the Ti–30Nb–7Zr alloy is an alternative to Ti–6Al–4V for biomedical applications.

Evaluation of mechanical properties of hybridised coir-carbon-basalt reinforced epoxy composites

ABSTRACT The present work focuses on the evaluation of the mechanical properties of epoxy composites reinforced with coir/carbon/basalt fibres. Reinforcements were used in as-received condition without any surface modifications. Composites were subjected to tensile, flexural and impact tests as per ASTM standards. Water absorption analysis was performed on the prepared composites using normal, salt and distilled water. The highest void fraction of 0.57% was obtained for the composite reinforced with carbon and basalt fibres. Highest tensile strength and modulus of 280 and 2500 MPa were achieved for composites reinforced only with carbon fibres. Hybrid composites fabricated using carbon fibres as outer layers and basalt as inner layers exhibited the highest flexural strength of 55 MPa. Composites reinforced only with basalt fibres displayed maximum impact strength of 22.64 kJ/m2 among the tested laminates. Inclusion of coir fibres significantly reduces tensile strength and modulus by 92.86% and 90%; flexural strength and modulus by 90.91% and 82%; impact strength by 71.74%, respectively. Composites reinforced only with basalt fibres absorbed more water than other combinations under all testing conditions. Scanning electron micrographs showed better interfacial bonding between synthetic fibres and the matrix as compared to natural fibre-reinforced composites.

Effects of Heat Treatment and Erosion Particle Size on Erosion Resistance of a Hypereutectic High-Chromium Cast Iron

This research addresses the erosive resistance of a hypereutectic high-chromium cast iron subjected to solid particle erosion. The study stems from a specific application of high-chromium cast iron, i.e., the critical surfaces of large industrial fans operating in a cement clinker grinding plant where such damage is a limiting factor for the components’ lifespan. A dedicated experimental investigation on the impact of substrate microstructure and erodent particle size on erosion resistance was set. The experimental campaign, conducted on a dedicated test bench per the ASTM G76 standard, comprised the analysis of the as-received, tempered, and destabilized conditions for the cast iron. From a preliminary image analysis of the microstructural features, two diameters of the erodent powder for the erosion tests were defined. The observed erosion rate decreased with the increase in the mean particle diameter of the erodent, indicating more severe erosive conditions for smaller particles. From the analysis of the worn surfaces, it was possible to highlight the involved mechanisms concerning the considered test combinations. For the as-received condition, the erosion rate with the larger mean particle diameter of the erodent decreased three times compared to the smaller one. For the heat-treated conditions, the erosion rate was halved with the larger mean particle diameter of the erodent. The proposed analysis, intended to acquire more insight into the limiting factor for the components’ lifespan for erosive wear damage, proved that erosion resistance is not dependent on the material’s hardness. The contribution of the mean particle diameter of the erodent is predominant compared to the substrate conditions.

Effect of Temperature and Ageing on Fracture Toughness of Alloy 617M

In recent years, Advanced Ultra Super Critical (AUSC) plants have used Ni-Cr-Co-Mo based alloy 617M for high-temperature components like steam piping and rotors, where material resistance against fracture after prolonged exposure in a hostile environment is a matter of concern to the designers. To this end, fracture toughness characterization of the material in as-received and aged conditions using an elastic-plastic fracture mechanics (J-R curves) approach can provide a significant input towards the component integrity assessments at service conditions. In this study, J-R curves of the alloy 617M have been determined for the as-received and differently aged (up to 20000 h at 710 °C) conditions using compact tension (CT) specimens following ASTM E 1820-13. Repeated tests have been carried out at temperatures 27 °C, 650 °C, 710 °C and 750 °C. The fracture toughness (JIC) thus determined, has shown a declining trend with test temperatures. This attributes to the ease of the crack initiation process owing to the γ′ induced matrix hardening and subsequent ageing-inducing precipitations of M23C6 carbides at the grain boundaries.

Contact Pressure Evolution in Heat-Treated Iron-Based Shape Memory Joints

This paper presents an experimental investigation into the behavior of open-ended Fe-based Shape Memory Alloy (Fe-SMA) tubes under biaxial pre-straining conditions, focusing on development of interface contact pressure as a result of the shape memory effect (SME). During the pre-straining process of Fe-SMA tubes, the cross-section undergoes complete inelastic deformation with a non-uniform distribution. Consequently, non-uniform biaxial pre-strain emerges across the cross-section, leading to the formation of stress-induced martensite in both the radial and circumferential directions. This results in the alteration of the SME due to the direction and interaction of biaxial martensite. Consequently, the material experiences a complex pre-strain state, posing challenges in assessing the SME in Fe-SMA tubes. Nevertheless, it is possible to interpret the complex overall SME performance on the basis of measurements of the resultant pressure exerted by the Fe-SMA tube on a substance, thereby limiting its free recovery. This study explores the development of the interface contact pressure highlighting the impact of heat-treatment on the gripping capacity in Fe-SMA tubes. Via coupling of analytical models with results extracted from an experimental campaign, the resultant pressure at the interface throughout the course of activation is quantified aiding to assess the SME performance. The experimental setup involves Fe-SMA and steel tubes enabling the quantification of interface contact pressure through principal strain measurements at the inner diameter of the steel tube, allowing for differentiation of SME performance under as-received and heat-treated conditions.

High-cycle fatigue testing on AM60 magnesium alloy samples for as-received and pre-corroded conditions in simulated body fluid

In this present work, the pure fatigue (PF) behaviors of AM60 magnesium alloys were investigated for the as-received samples, compared to the pre-corroded specimens in simulated body fluid (SBF). The standard fatigue testing specimens were held for 28 days in the SBF, so-called corrosion fatigue (CF) samples, while their weights were recorded. Afterward, bending fatigue experiments were carried out under fully-reversed rotary conditions, within high-cycle fatigue regimes. Moreover, the fracture mechanism was also investigated using field-emission scanning electron microscopy (FE-SEM). The obtained results indicated that the weight of the samples first increased and then decreased with time. The CF lifetime was 71 % of the relative difference, shorter than PF under the lowest stress level (80 MPa) and 38 % of the relative difference, shorter than PF at the highest stress level (140 MPa). The CF lifetime was entirely behind the PF lifetime, and fracture mechanisms were mostly brittle.

Electrochemical Behavior of an Alpha-Phase Titanium Alloy in Oxidizing Nitric Acid Environments: Influence of an Oxygen-Enriched Layer

The study focuses on establishing the influence of an oxygen-enriched layer (OEL) on the electrochemical properties of an alpha-phase titanium alloy, Ti-Al-Zr, in oxidizing nitric acid environments. Heat treatment was given to the material at 760°C for 700 h in air which resulted in the formation of an OEL on the surface. The electrochemical properties were studied and compared with as-received (AR) conditions by techniques like open-circuit potential (OCP), potentiodynamic polarization, chronoamperometry, and electrochemical impedance spectroscopy measurement. It was established that the presence of an OEL on the surface reduced the cathodic activity of oxidizing species on the material’s surface. The OCP value did not depend on the presence/absence of the OEL on the surface. The presence of the OEL on the surface promoted the formation of a protective passive film. The material with an OEL on the surface had a lower donor density as compared to the AR condition.

Analysis of Spacecraft Materials Discrimination Using Color Indices for Remote Sensing for Space Situational Awareness

The increasing number of space missions have resulted in an augmented density of artificial objects positioned in orbital domains near Earth. Knowing the material composition of the resident space object can be of value in object identification and risk assessment using remote sensing techniques. To perform this task, it is increasingly imperative to optically characterize spacecraft materials to identify unique material-specific spectroscopic markers. In this work, a variety of materials frequently utilized by the aerospace industry in spacecraft design and construction were analyzed using reflectance spectroscopy. The collected data provide a spectral characterization baseline for modern-day and historical spacecraft materials. The color index was computed for standard astronomical and suggested theoretical filter passbands and compared to each other in their capability to discriminate materials belonging to different classes. The color index was calculated from reflectance spectra of common spacecraft materials in their pristine, as-received conditions that fell under different family groupings. Different color-index combinations were studied using color-color diagrams. Visual and quantitative analysis of the color-color diagrams were used to evaluate the possibility of discriminating materials from one another by means of optical measurements. Results of the analysis show that polyimide and photovoltaic materials are most easy to discriminate from all other materials via color indices using different filter passbands evaluated in this study.

Enhancing durability of ASTM A416 prestressed steel wires against hydrogen embrittlement

In the face of aggressive environment, cathodic protection shows promise as a solution to reducing the risk associated with corrosion initiation and propagation of prestressed concrete structures. This can be achieved by applying an impressed current to the system that brings the electrical potential of steel members to such a level where localized corrosion does not occur. However, atomic hydrogen that evolves at negative potential can cause hydrogen embrittlement of ASTM A416 steel wires used in prestressed concrete, leading to system failure without warning. To reduce the risks of brittle failures, nickel–cobalt alloy was applied to steel wires. The corrosion properties of the coated specimens were studied in simulated concrete and corrosive environments. The steel wires were also placed in an aggressive environment to predict the time to failure of the samples due to hydrogen embrittlement. A brittle crack developed in wires tested in the as-received condition, but samples coated with the proposed coating passed the embrittlement test. Nickel–cobalt coated specimens not only showed corrosion properties similar to as-received samples, but also did not fail the embrittlement test.

Sulfide Stress Cracking of column overhead pipe to flange fitting joints in a petroleum industry

The light hydrocarbon containment leakage in a petroleum industry overhead piping have caused severe fire explosion. This paper reports Sulfide Stress Cracking (SSC) in an overhead piping of splitter unit which separates out lighter components from heavier hydrocarbon. The failed overhead piping has been analyzed to determine the root cause of fire incident. The piping metallurgy was SS316L and chemistry of failed fitting components & its weld have been complied with NACE specification. Initially fittings were evaluated for intergranular corrosion to determine as-received material condition and confirmed defect free material. However, metallographic evaluation clearly evidenced transgranular brittle mode of cracking while hardness was higher than NACE specification (22HRC). Furthermore, virgin pipe joint was compared with damaged pipe joint for microstructural assessment. Moreover, actual service conditions were evaluated to obtain pH and H2S concentration in overhead condensed boot water. Microstructural factors have been discussed in detail as well. The results revealed that cold deformed austenitic structure attributed to SSC and undesired manufacturing steps were employed. Further, the root cause of an accident investigation also revealed failed components were not according to NACE specified metallurgy for sour service conditions.

Accelerated corrosion of Ni-based alloys in molten chloride salts, due to Ni2Cr phase formation

To understand how the precipitation of long-range ordering (LRO) in alloys affects molten salt corrosion, two Ni-Cr model alloys—one in as-received (AR) condition, the other isothermally aged to contain MoPt2-type Ni2Cr-ordered precipitates, and both featuring the same Ni-33at%Cr composition—were tested for 500 hours in molten NaCl–MgCl2 salt at 550°C. Post-corrosion weight loss analysis and advanced microstructural characterization of the corroded alloys revealed (through comparison with the AR specimens) that the ordered phase significantly accelerated the corrosion process. This suggests that the loss of Cr atoms in the corroded Ni2Cr-ordered superlattice structure, which creates extra weakness for molten salt corrosion. In terms of high-temperature corrosion resistance, the results of this study emphasize the importance of phase stability when designing alloys for molten-salt applications.