Horizontal Tensile Research Articles

Effect of Different Welding Modes on Morphology and Property of SS316L Stainless Steel Deposition by Robotic Metal-Inert Gas Welding.

The widespread adoption of arc additive manufacturing techniques across various industries has advanced the field of SS316L stainless steel manufacturing. It is crucial to acknowledge that different welding modes exert distinct influences on the forming and mechanical performance. This study analyzed the thermal input associated with four specific welding modes in LORCH MIG welding, clarifying the transition dynamics of molten droplets through waveform analysis and examining the resultant effects on microstructure and performance characteristics. The Pulse, Speed-Pulse-XT, and Twin-Pulse modes were found to induce spatter during the manufacturing process, consequently reducing molding efficiency in comparison to the SA-XT mode. Notably, the Twin-Pulse mode, characterized by double-pulse agitation, generated fish scale patterns along the lateral surfaces of the fabricated parts, promoting anisotropic grain growth. This microstructural refinement, compared to single-pulse samples with equivalent thermal input, resulted in enhanced mechanical properties. Nevertheless, the horizontal tensile strength of the three pulse modes was lower than the industrial standard for SA-XT mode and forging. In contrast, the SA-XT mode with an average hardness of 168.1 ± 6.9 HV and a tensile strength of 443.58 ± 5.7 MPa. Therefore, while three pulse modes offer certain microstructural advantages, the SA-XT mode demonstrates superior overall performance.

Analytical solution of conductor tensile force in asymmetrical spans used in overhead power lines and substations with influence of tension insulators

Introduction. Designing electrical substations involves analyzing the horizontal tensile force in flexible tension conductors under varying temperatures. These temperature changes affect the conductor’s length and forces. Problem. Existing methods for calculating horizontal tensile force in conductors often focus on symmetric spans or require complex finite element modeling (FEM), which is impractical for routine substation design. Asymmetric spans with tension insulators present a more complex challenge that current solutions do not adequately address. Purpose. Universal analytical solution and algorithm for calculating the horizontal tensile forces in conductors in asymmetric spans with tension insulators used in power substations or short overhead power line spans. The solution is designed to be easily implementable in software without requiring complex tools or extensive FEM. Methodology. The methodology involves deriving an analytical solution based on the catenary curve formed by the conductor between attachment points at different heights. The analysis includes calculating the conductor’s length for a given tensile force and using a state change equation to determine forces under new temperature conditions. Validation is performed using FEM calculations. Results. The proposed solution was validated against FEM models with varying height differences (5 m and 15 m) and conductor temperatures (–30 °C, –5 °C, +80 °C). The results showed a minimal error (less than 0.15 %) between the analytical solution and FEM results, demonstrating high accuracy. Originality. This paper presents a novel analytical solution to the problem of calculating tensile forces in asymmetric spans with tension insulators. Unlike existing methods, our solution is straightforward and easily implementable in any programming language. Practical value. The solution is practical for routine design tasks in electrical substations or short overhead power lines. Especially in power substations, accurate tensile forces are needed not only for mechanical design and sag calculations but also for calculating the dynamic effects of short-circuit currents. References 23, tables 4, figures 3.

Comparative analysis of seismic isolation effects under three-way seismic actions for suspension core-tube structure and frame core-tube structure

In this paper, the suspension core-tube structure and frame core-tube structure are taken as the research objects, and the modal analysis of them and their basic seismic isolation structures are carried out firstly to explore the self-vibration characteristics and seismic isolation effect of the structures. Secondly, the nonlinear time-history analysis of the four structures under the action of rare earthquakes in the X, Y, and Z directions is carried out, and their inter-story drift angles, inter-story shear forces, base shear forces, maximum accelerations at the apex of the core-tube, and cantilever beam stresses are analyzed comparatively. Finally, the displacements and loads of the energy dissipators, the maximum horizontal displacements and tensile and compressive stresses of the seismic isolation bearings are analyzed to evaluate the performance of both of them under rare earthquakes. The results show that the suspension core-tube structure and the frame core-tube structure with base seismic isolation bearings can provide good control of their inter-story drift angles and internal forces, etc. The suspension core-tube structure is superior to the frame core-tube structure in controlling the maximum acceleration at the apex of the core tube response.

Underwater additive manufacturing of 10CrNi3MoV high-strength low-alloy steel by wire-feed laser melting deposition: Effect of microstructure evolution on mechanical properties

The underwater 10CrNi3MoV high-strength low-alloy steel thin-walled part with forming quality up to in-air laser deposition quality was successfully manufactured for the first time. The influencing mechanisms of complicated thermal history and water environment on microstructure evolution and mechanical properties of thin-walled part were researched. Due to austenitization and interlocking effect, the microstructure in the bottom, middle and top (below the 56th layer) areas of underwater sample and the middle area of in-air sample were composed of fine grain ferrite and granular bainite. With the increase of building height, the heat accumulation effect of underwater sample enhanced, resulting in small grain size (GS), high dislocation density, strong solution strengthening effect and low maximum texture strength at the bottom area, while the high proportion of high-angle grain boundaries (HAGBs) at the top area. These resulted in the greatest tensile strength (714 MPa) and microhardness (232 HV) at the bottom area and the highest elongation (11%) at the top area. Due to the cooling effect of water environment, the proportion of HAGBs reduced and there were oxides in fracture. As a result, the horizontal elongation of underwater sample was about 90.9% of in-air sample. Additionally, the GS reduced, and the dislocation density and solution strengthening effect increased, so the microhardness of underwater sample was slightly higher than that of in-air sample. However, due to some microscopic defects, the horizontal and vertical tensile strength of underwater sample were about 97.6% and 90.7% of in-air sample.

Thermal and structural evaluation of an asphalt pavement with an embedded inductive power transfer pad for stationary charging of EVs

A key strategy for increasing sustainability in transportation is to increase the use of Electric Vehicles (EVs) worldwide. Charging EVs wirelessly utilizing Inductive Power Transfer (IPT) pads eliminates most of the current limitations of EVs, such as range anxiety. In this study, the effect of an IPT pad on the temperature and strain response of an asphalt mixture was evaluated. A scaled IPT pad was placed into an experimental asphalt slab and the IPT-asphalt temperature, while energizing the IPT pad, was determined by a thermal camera, Fibre Bragg Grating (FBG) sensors, and thermistors. Moreover, a static wheel load was applied on the surface of the asphalt slab, with and without an IPT pad, and the horizontal tensile strain adjacent to the bottom of the asphalt slab was measured using an FBG sensor. ANSYS simulations were conducted and were validated using the experimental results. The results showed that embedding an energized IPT pad into the asphalt slab at 20 °C increased the asphalt’s surface temperature (approximately 32 mm offset from the pad) by 8.3 °C in the experiment. Raising the ambient temperature from 20 to 50 °C resulted in an elevation of the asphalt surface temperature from 28.3 to 56.7 °C in the experimental analysis. Placement of the IPT pad into the asphalt slab was seen to decrease the asphalt strain by 41 % in the experiment. Placing the static wheel load on the edge of the pad increases the maximum tensile strain by 16 % and moving the load 66.4 mm from the edge increases the maximum tensile strain by 54 %. Significantly, applying both the thermal load and the static wheel load increased the maximum tensile strain by 53 % compared to the asphalt slab without an IPT pad.

Effects of laser power on microstructure and mechanical properties of titanium alloy fabricated by laser-arc hybrid additive manufacturing

Laser-arc hybrid additive manufacturing (LAHAM) based on the synergistic interaction of laser and arc has vast potential applications due to the advantages of high precision and fast manufacturing speed. Titanium alloy is a kind of indispensable material in the aerospace and marine industries because of its superior performance. This study primarily investigates the effect of laser power on formability, microstructure evolution, and mechanical properties of Ti-6Al-4V, a titanium alloy fabricated by LAHAM. The results indicate that the material utilization of the Ti-6Al-4V wire first increases and then decreases with the increasing laser power, reaching a maximum value of 95.48% at a power of 1500 W. As laser power increases, the acicular martensite α′ content in the LAHAM samples decreases, while the α phase increases and exhibits a coarsening phenomenon. Tensile strength increases with the rise in laser power, reaching a maximum horizontal tensile strength of 1080 MPa and a maximum vertical tensile strength of 1100 MPa. However, elongation decreases with increasing laser power. Microhardness decreases with the rise in laser power. The increase in laser power enhances the bonding between deposition layers, significantly improving the tensile strength of the specimens.

Influence of Base Layer Thickness and Property on Flexible Pavement Behavior

When designing the pavement layers, a suitable thickness must be chosen to protect the pavement from environmental conditions and traffic loads and ensure the structure's durability up to the design life. To investigate the behavior of flexible pavement, the characteristics and thickness of each layer are programmed into the finite element method (FEM). The Abaqus program is one of the infinite-element analysis programs. The use of the Abaqus program leads to a reduction in cost and time compared to laboratory tests. In this study, the Abaqus program analyzed a three-dimensional model of a multi-layered road section, and all materials have elastic behavior. The model comprises five layers (wearing, binder, base, subbase, and subgrade). The model was looked at with different base layer thicknesses (15, 25, and 30 cm) and elasticity moduli (1655, 2070, and 3000 MPa). Critical parameters were looked at in the present research: vertical displacement at the wearing layer's top, horizontal tensile strain in the asphalt layer's lowest point, and vertical compressive strain at the subgrade's surface. The outcomes indicated that the pavement is more susceptible to rutting than fatigue as a result of static load. An increase in thickness and modulus of elasticity for the base layer leads to a reduction in rutting risks.

Development of prediction model for structural behavior and gradation of porous asphalt pavement

This study is aimed at developing prediction model for structural behavior of Porous Asphalt Pavement (PAP) using ABAQUS software and also developing ANN (Artificial Neural Network) model to predict void percentages in Porous Asphalt mix gradations. Data from the past literatures were used to analyze various mixing parameters affecting the properties of Porous Asphalt gradation mixes. The study analyzed PAPs using KENPAVE software. The findings indicated that fewer allowable repetitions to fatigue and rutting failures were observed for thinner Porous Asphalt Concrete (PAC) layer thicknesses. This suggests that thicker PAC layers may offer better resistance to fatigue and rutting failures in pavement systems. The study found that the nature of subgrade material significantly influenced the rutting performance of PAP systems. Specifically, clayey soils exhibited a 77.74% reduction in the design life of the pavement compared to gravelly soil subgrades. This highlights the importance of considering subgrade characteristics in pavement design and construction to optimize pavement performance and longevity. Higher contact pressures resulted in higher tensile stresses at the bottom of PAC layer which in turn reduced the fatigue life of PAP. The findings from ABAQUS analysis indicated that an increase in the void percentage in Porous Asphalt Concrete (PAC) mixes led to a significant increase in horizontal tensile strain at the bottom of the PAC layer, with a 12.3% increase observed. Additionally, there was a noticeable increase in tensile strain for a PAC mix with 28% voids compared to a mix with 16% voids. This suggests that higher void percentages in the PAC mixes can potentially enhance the flexibility and deformation resistance of the pavement structure, which may contribute to improved performance under various loading conditions, hence leading to 92.8% reduction in allowable load repetitions to fatigue failure.The study further revealed that an increased void percentage in Porous Asphalt Concrete (PAC) mixes resulted in a decrease in vertical stress and deflection in the PAP system. However, no significant effect on the allowable repetitions to rutting failure was observed. This suggests that higher void percentages may lead to better load distribution and reduced vertical stresses within the pavement structure, contributing to improved performance in terms of stress and deflection.Moreover, Asphalt Pavement mixes were compiled to develop an Artificial Neural Network (ANN) prediction model. The results demonstrated good conformity between predicted and actual data, with a mean square error of 0.109 and a coefficient of correlation of 0.994. This indicates that the ANN model accurately predicts pavement performance based on the compiled asphalt pavement mixes, providing a valuable tool for pavement design and analysis.

Insight into the shear failure mechanism of Wound FRP reinforced concrete beams through numerical simulations considering interface damage and material anisotropy

Utilizing the inherent flexibility of high-strength fibres, Fibre-Reinforced Polymers (FRP) can be engineered as optimized reinforcing cages for concrete structures through the application of advanced digital fabrication techniques. However, existing codified design methods and numerical investigations found in the literature fall short in providing an accurate characterization of the actual performance of FRP reinforcement in concrete structures. This work presents a novel Finite Element (FE) modelling approach for concrete beams reinforced with FRP in non-traditional arrangements, accounting for reinforcement-concrete interface behaviour and FRP material anisotropy. Validation against experimental tests of flexible Wound-FRP (W-FRP) reinforced beams demonstrates accurate predictions of load-displacement curves, crack propagation, and load-strain curves. The study delves into shear failure mechanisms, emphasizing FRP reinforcement behaviour and damage evolution at reinforcement-concrete interfaces. Further parametric analysis explores the impact of W-FRP inclination angle and spacing, revealing their significant influence on beam stiffness and ultimate capacity. Specifically, the horizontal tensile force component in inclined links and increased modulus of links with reduced spacing enhance stiffness. Altered crack propagation due to W-FRP patterns, coupled with resulting damage development at concrete-stirrup interfaces and stress evolution in W-FRP stirrups, are key contributors to varied ultimate capacity. Moreover, higher performance of W-FRP stirrups with smaller spacing and reduced cross-section area further bolsters ultimate capacity. This research advances the modelling of FRP-reinforced concrete, offering potential solutions for optimizing FRP material utilization in concrete structures.

Flame retardancy and mechanical properties of polypropylene composites containing intumescent flame retardants, preceramic polymers, and other additives

AbstractThis study aims to investigate the flame retardancy and mechanical properties of polypropylene (PP)‐based intumescent flame retardants (IFRs) consisting of melamine phosphate (MP) and pentaerythritol (PER), and different additives; boron phosphate (BP), antimony oxide (AO), and preceramic polymers, namely poly(dimethylsilane) (PDMS) and poly(methylsilsesquioxane) (PMSQ). The composites were produced by twin‐screw extrusion, and then molded by injection molding. Their characterizations were performed with limiting oxygen index (LOI), horizontal burning tests, thermogravimetric analysis (TGA), tensile and impact tests. The total amount of IFRs and the additives in polypropylene was kept constant at 20 wt%. The additive concentration was varied as 1, 3, and 5 wt% in the composites. The highest LOI value of 29% was obtained for PP/MP/PER composite with MP/PER ratio of 3/1. PP/IFR‐based composites with 1 wt% additive exhibited higher LOI and horizontal burning performance than the other composites with 3 and 5 wt% additives. It is revealed that tensile modulus and impact strength of neat PP were improved with the addition of IFRs, and for each type and amount of the additives used in the study.Highlights Usage of IFRs, preceramic polymers, BP and AO in PP improved flame retardancy. Lower amount of additives (1%) in PP/IFR composites led to higher LOI values. Additive incorporation enhanced tensile modulus and impact strength of neat PP.

Stress Evaluation Through the Layers of a Fibre-Metal Hybrid Composite by IHD: An Experimental Study

BackgroundIncremental hole-drilling (IHD) has shown its importance in the measurement of the residual stress distribution within the layers of composite laminates. However, validation of these results is still an open issue, especially near the interfaces between plies. ObjectivesIn this context, this study is focused on experimentally verifying its applicability to fibre metal laminates.MethodsTensile loads are applied to cross-ply GFRP-steel [0/90/steel]s samples. Due to the difference in the mechanical properties of each ply, Classical Lamination Theory (CLT) predicts a distribution of the uniform stress within each layer, with pulse gradients between them. The interfaces act as discontinuous regions between the plies. The experimental determination of such stress variation is challenging and is the focus of this research. A horizontal tensile test device was designed and built for this purpose. A differential method is used to eliminate the effect of the existing residual stresses in the samples, providing a procedure to evaluate the ability of the IHD technique to determine the distribution of stress due to the applied tensile loads only. The experimentally measured strain-depth relaxation curves are compared with those determined numerically using the finite element method (FEM) to simulate the hole-drilling. Both are used as input for the IHD stress calculation method (unit pulse integral method). The distribution of stress through the composite laminate, determined by classical lamination theory (CLT), is used as a reference.ResultsUnit pulse integral method results, using the experimental and numerical strain-depth relaxation curves, compare reasonably well with those predicted by CLT, provided that there is no material damage due to high applied loads.ConclusionsIHD seems to be an important measurement technique to determine the distribution of residual stresses in fibre metal laminates and should be further developed for a better assessment of the residual stresses at the interfaces between plies.

Fatigue Cracking Behaviour and Characteristics of Flexible Pavement Subjected to Freight Coal-Truck Loading

Fatigue cracking is one of the varieties of flexible pavement distress caused by frequent traffic loads, and it is also a sign of structural collapse. Using finite element methods, numerical simulations were conducted to evaluate the strain changes that occur throughout the process of flexible pavement cracking. Several flexible pavement configurations with various thickness and different material properties of AC layer were developed, and several loading conditions in terms of the axle load, the speed, and the loading cycles of the freight truck were modelled. The numerical modelling showed that the greatest horizontal tensile strain in the 1stAC layer (surface course) is at the surface-centre of the pavement structure, which is predicted to be prone to top-down cracks. In other side, the greatest horizontal tensile strain in the 2ndAC layer (base course) is at the bottom-below of the tire tread, which is predicted to be vulnerable to bottom-up cracks. The outcomes of this study added to the knowledge gathered from previous studies, especially regarding the critical locations within the AC layer with the greatest magnitude of horizontal tensilestrain and their potency to experience either the top-down cracking or bottom-up cracking, as well as related to the effect of slowing the truck speed and increasing both the truck’s hauling load and loading cycles on the fatigue life of asphalt concrete layer. Future research needs to be done to evaluate the balance between both permanent deformation behaviour of the AC layer and to determine the optimum flexible pavement configurations.

Effect of carbonation of soil-slag mixtures on the resilient behaviour and structural response of an asphalt pavement

In the face of rapid population growth and industrialisation, mitigating the harmful effects of CO2 emissions becomes an important issue to be studied. The objective of this study was to perform a structural analysis evaluating the influence of carbonation of soil-electric arc furnace slag (EAFS) mixtures used in the subgrade layer of an asphalt pavement. Resilient modulus tests (RM) were performed on the soil-EAFS mixtures subjected to two curing processes. The structural analysis was performed using the AEMC software, being evaluated: (i) the deflection at the top of the asphalt layer, (ii) the horizontal tensile strain at the bottom of the same layer, and (iii) the vertical strain at the top of the subgrade layer. Carbonation increased the values of RM due to the formation of calcium carbonate, which led to a reduction in the analysed deflection and strains, resulting in a more durable asphalt pavement.

On the orientation-dependent mechanical properties of interstitial solute-strengthened Fe49.5Mn30Co10Cr10C0.5 high entropy alloy produced by directed energy deposition

Interstitial solute-strengthened Fe49.5Mn30Cr10Co10C0.5 (at%) high entropy alloy was additively manufactured by directed energy deposition (DED) process in this work. While the as-deposited material exhibits an excellent combination of strength and ductility, the effect of anisotropy on the mechanical performance of the DED processed component was studied in detail. The ultimate tensile strength (UTS) of the horizontal tensile sample with a main fiber texture of <111> // tensile direction (TD) went up to 1 GPa while maintaining a superb failure elongation of 36%. The vertical tensile sample, with a dominant <001> // TD texture, failed at an UTS of 750 MPa with an enhanced failure elongation of 52%. Microstructural analysis of the deformed samples showed that the horizontal samples were mainly deformed via the formation of mechanical twins, whereas the twining activity was less profound in the vertical samples. Single crystal micro-pillar compression testing revealed that the deformation mechanism complies well with the Schmid’s factor. In addition, a higher critical resolved shear stress for twining compared to slip was also confirmed in the micro-pillar compression testing.

Modelling dynamic breakage in rock blocks with different elongation and flatness ratios upon impact

AbstractThe two crucial shape factors (elongation ratio and flatness ratio) of brittle particles may influence the dynamic breakage of brittle particles upon impact. Hence, three‐dimensional discrete element method simulations of brittle rock blocks with different shapes upon normal impact were performed. The simulated results indicate that the elongation ratio, that is, ratio of width to length and flatness ratio, that is, ratio of thickness to width can significantly affect the breakage of brittle rock blocks. Three fracture mechanisms, that is, fragmentation, horizontal tensile fracture and vertical tensile fracture, were revealed, which determine the dynamic breakage of rock blocks. The fragmentation results in numerous single‐sphered fragments with velocities even larger than 2 times of the initial velocities. Fragmentation can provide a buffering effect at high impact velocities of larger than 4 m/s. With an increasing elongation ratio or flatness ratio, the phenomenon of fragmentation gradually disappears. The reflection of a compression stress wave results in horizontal tensile fracture. The expansion in the plane perpendicular to the impact velocity results in vertical tensile fracture.

Effect of truck and train loading on permanent deformation and fatigue cracking behavior of asphalt concrete in flexible pavement highway and asphaltic overlayment track

Abstract This research investigated the largest magnitude of displacement and horizontal tensile strain in several critical locations within the asphalt concrete (AC) layer in both the flexible pavement highway (FPH) and asphaltic overlayment track (AOT) structure using the numerical modeling method. The role of the hauling loads, speed, and loading cycles of freight truck’s dumps and freight train’s wagons on the mechanical behavior of FPH and AOT in terms of the permanent deformation and fatigue cracking was examined. Furthermore, the performance of the FPH and AOT in terms of permanent deformation and fatigue cracking characteristics due to various magnitudes of hauling loads, speed, and loading cycles of freight truck’s dumps and freight train’s wagons was compared to determine the optimum infrastructure for the freight coal transportation, based on the hauling capacity as well as the magnitude of permanent deformation and the horizontal tensile strain of the AC layer. According to the findings of this study, it is suggested to choose the AOT structure with fourth or sixth loading systems to run the freight coal transportation with the highest magnitude of the hauling capacity of 360,000 tons, since it produces the minimum magnitude of the permanent deformation and fatigue cracking of the AC layer. Future research should be conducted to examine the potential and the characteristics of fatigue cracking due to the contact between the edge of the sleeper and the surface of the AC layer in AOT.

Installation and Use of a Pavement Monitoring System Based on Fibre Bragg Grating Optical Sensors

The evolution of technological tools, namely affordable sensors for data collection, and the growing concerns about maintaining roads in adequate conditions have promoted the development of continuous pavement monitoring systems. This paper presents the installation and use of an innovative pavement monitoring system, which was developed to measure the effects of vehicle loads and temperature on the performance of a pavement structure. The sensors used are based on fibre Bragg grating optical technology, collecting data about the strains imposed in the pavement and the temperature at which those measurements are made. The site selection for the system’s installation and the essential installation details to ensure successful data collection are addressed. A calibration procedure was implemented by performing falling weight deflectometer tests and passing preweighed heavy vehicles over the sensors. In addition to validating the system installation, the results obtained in the calibration confirmed the importance of adequately choosing the distance between sensors. Differences of 50 mm in the position of the load may cause differences of about 20% to 25% in the resulting strains. These results confirmed the importance of increasing the sensor concentration in wheel paths. Furthermore, for loads between 25 kN and 65 kN, raising the temperature by 8 °C caused an increase of about 20% in the horizontal tensile strains measured in the pavement. In summary, it was possible to conclude that this innovative system is capable of capturing the effects of temperature and vehicle speed on the response of the pavement, which may be considered an advantage of this type of monitoring system when compared to those that are only used to determine the loads applied to the pavement or to characterise the type of vehicle.

Study on the Relationship between Process Parameters and theFormation of GTAW Additive Manufacturing of TC4 Titanium Alloy Using the Response Surface Method

The geometric parameters of the deposited layer include the width, height, and penetration depth of the deposited layer. The welding current, wire feeding speed, and torch travel speed during the additive manufacturing process of TC4 titanium alloy have the greatest impact on the geometric parameters of the deposited layer. In order to study how the deposition layer width, deposition layer height, and penetration depth are affected by the welding current, wire feeding speed, and torch travel speed, this article uses Design Expert 8.0.6 software for Box−Behnken design response surface experiments. During the experimental design, the welding current, wire feeding speed, and torch travel speed are used as input variables. The deposition layer width, deposition layer height, and penetration depth are selected as the responses. We designed 17 response surface experiments that were conducted using GTAW-AM. The results show that as the welding current increases, the penetration depth and width of deposition layer gradually increase, and the deposition layer height gradually decreases. As the wire feeding speed increases, the deposition layer height and penetration depth gradually increase, and the wire feeding speed has a minimal effect on the deposition layer width. As the torch travel speed increases, the penetration depth, width and height of deposition layer gradually decrease. The response surface method experimental design can also optimize the matching of three process parameters: welding current, wire feeding speed, and torch travel speed, thereby obtaining the optimal matching range of process parameters. Within the optimized matching range of process parameters, a welding current of 90 A, a wire feeding speed of 900 mm/min, and a torch travel speed of 200.18 mm/min were selected to prepare TC4 titanium alloy thin-walled part. The microstructure of the top, middle and bottom are all basketweave structure. The α phase gradually becomes coarse from the top to the bottom. The microhardness of the top, middle, and bottom of the thin-walled parts is 362.7 HV, 352.7 HV, and 340.5 HV, respectively. The horizontal tensile strength is 926.1 MPa, with an elongation of 12.22%, and the vertical tensile strength is 938.1 MPa, with an elongation of 14.41%.

Investigations of the mechanical and high-temperature tribological properties of the Inconel 718 alloy formed by selective laser melting

Selective laser melting (SLM) is a 3D printing technology suitable for manufacturing high-precision metal parts with complex geometries. At present, the research on SLM technology to produce high performance, complex structures made of superalloy parts has become the focus of aerospace and other fields. In this work, the microstructure, microhardness, and tensile strength of an Inconel 718 superalloy synthesized using SLM technology were first investigated. Then, the wear characteristics of the alloy at various temperatures were examined by multifunctional friction and wear testing equipment. Finally, a thorough analysis of the wear damage mechanisms of the materials over a wide temperature range was performed. The grains of the Inconel 718 superalloy formed by SLM developed as columnar grains that were more evenly and firmly dispersed along the horizontal axis. The material had a slightly greater microhardness in the vertical plane (HV1 =346) than in the horizontal plane (HV1 =324). A tensile test revealed that the horizontal tensile strength of SLM-formed Inconel 718 alloy was 50.1 MPa higher than that in the vertical direction, while the elongation was 0.14 % lower than the latter. The fracture mechanism of the material presented a fracture type dominated by microporous aggregation. A friction wear test showed that the friction wear coefficient of the SLM-formed Inconel 718 alloy gradually decreased with temperature. Abrasive wear, oxidative wear, and adhesive wear were the main wear mechanisms for the material during wear testing in the high temperature environments. The wear surface of the alloy material generated an oxide layer at 650 °C, which was effective in lowering friction and wear.

Microstructure, crack formation and improvement on Nickel-based superalloy fabricated by powder bed fusion

Nickel-based superalloy (Haynes 230) parts were fabricated by powder bed fusion using a laser - based system. Crack defects were unavoidable. In order to solve the cracking problem, it was necessary to understand the crack formation mechanism, and the hot isostatic pressing method was used to eliminate the crack defects. The results indicated that the microstructure displayed cellular crystal structure in XY direction and columnar crystal structure with {001} < 001 > cubic texture in XZ direction. Under the thermal stress and micro-segregation, M23C6 carbides and NiSi eutectic phases were precipitated at high angle grain boundaries, which promoted the formation of solidification and liquation cracks. Because the direction of the internal cracks in the horizontal tensile sample was perpendicular to the tensile direction and the microstructure was {001} < 001 > cubic texture, the tensile properties were anisotropic. After hot isostatic pressing treatment, the cracks were obviously eliminated, the ultimate tensile strength and elongation were significantly improved. The carbides transformed from Cr-rich M23C6 to W-rich M6C.