Showing papers in "Journal of Materials Engineering and Performance in 2018"

Additive Manufacturing of Metallic Materials: A Review

Abstract: In this review article, the latest developments of the four most common additive manufacturing methods for metallic materials are reviewed, including powder bed fusion, direct energy deposition, binder jetting, and sheet lamination In addition to the process principles, the microstructures and mechanical properties of AM-fabricated parts are comprehensively compared and evaluated Finally, several future research directions are suggested

Additive Manufacturing of Ceramic Heat Exchanger: Opportunities and Limits of the Lithography-Based Ceramic Manufacturing (LCM)

Abstract: Additive manufacturing (AM) techniques allow the preparation of tailor-made structures for specific applications with a high flexibility in regard to shape and design. The lithography-based ceramic manufacturing (LCM) technology allows the AM of high-performance alumina and zirconia components. There are still some restrictions in regard to possible geometries. The opportunities and limits of the LCM technology are discussed in the following paper using the example of ceramic heat exchangers. Structures are presented which combine a large surface for heat exchange with a small component volume and low pressure drop. This paper concludes summarizing the essential remarks.

Processing Parameter Effects on Residual Stress and Mechanical Properties of Selective Laser Melted Ti6Al4V

Abstract: Selective laser melting (SLM) process is characterized by large temperature gradients resulting in high levels of residual stress within the additively manufactured metallic structure. SLM-processed Ti6Al4V yields a martensitic microstructure due to the rapid solidification and results in a ductility generally lower than a hot working equivalent. Post-process heat treatments can be applied to SLM components to remove in-built residual stress and improve ductility. Residual stress buildup and the mechanical properties of SLM parts can be controlled by varying the SLM process parameters. This investigation studies the effect of layer thickness on residual stress and mechanical properties of SLM Ti6Al4V parts. This is the first-of-its kind study on the effect of varying power and exposure in conjunction with keeping the energy density constant on residual stress and mechanical properties of SLM Ti6Al4V components. It was found that decreasing power and increasing exposure for the same energy density lowered the residual stress and improved the % elongation of SLM Ti6Al4V parts. Increasing layer thickness resulted in lowering the residual stress at the detriment of mechanical properties. The study is based on detailed experimental analysis along with finite element simulation of the process using ABAQUS to understand the underlying physics of the process.

Grain Boundary Wetting by a Second Solid Phase in Ti-Fe Alloys

Abstract: The microstructure of Ti-Fe polycrystals has been studied between 595 and 815 °C in the concentration interval between 1 and 9 wt.% Fe. In these conditions, two phases, namely hexagonal α(Ti, Fe) and cubic β(Ti, Fe), are in equilibrium. The α(Ti, Fe) phase forms either continuous or discontinuous layers in the β(Ti, Fe)/β(Ti, Fe) grain boundaries (GBs). Continuous layers correspond to the complete wetting of β(Ti, Fe)/β(Ti, Fe) GBs by a second solid phase α(Ti, Fe). Discontinuous layers correspond to the incomplete (or partial) GB wetting by a second solid phase. The temperature dependences of the portion of completely wetted GBs as well as that of the thickness of continuous GB layer of α(Ti, Fe) phase have been measured. Both values monotonously increase with increasing temperature.

The Atomic Structure of Ti 2 C and Ti 3 C 2 MXenes is Responsible for Their Antibacterial Activity Toward E. coli Bacteria

Abstract: The expanded Ti2C and Ti3C2 MXene phases were synthesized from their parent Ti2AlC and Ti3AlC2 MAX phases using the same conditions of the classical acidic aluminum extraction method. The assumption for the study was that the expanded Ti2C and Ti3C2 MXenes are composed of the same atoms and if are synthesized from MAX phases using the same conditions of the classical acidic aluminum extraction method, the observed bio-effects can be related only to the changes in their structures. The scanning electron microscope investigations indicated that the expanded Ti2C and Ti3C2 sheets formed the specific network of slit-shaped nano-pores. The x-ray photoelectron spectroscopy for chemical analysis (ESCA-XPS) showed almost no difference in surface chemistry of Ti2C and Ti3C2 MXenes. The high-resolution transmission electron microscope investigations revealed, however, differences in atomic structure of the individual Ti2C and Ti3C2 sheets. Measured distance between Ti-C atomic layers in Ti2C was 9.76 A and was larger by 0.53 A in comparison with Ti3C2 (9.23 A). Our investigations of bioactive properties toward model gram-negative Escherichia coli bacterial strain showed that the Ti2C MXene did not influence the viability of bacteria. Contrarily, the Ti3C2 MXene showed antibacterial properties. The results of the study indicate that the structure at the atomic scale may play a key role in the bioactivity of MXenes of the same chemical composition, but different stoichiometry, just like in case of Ti2C and Ti3C2.

Corrosion Behavior of 316L Stainless Steel Fabricated by Selective Laser Melting Under Different Scanning Speeds

Abstract: This work discussed the effects of different scanning speeds (800, 1083, 1200 and 1400 mm/s) on the microstructure of 316L stainless steel manufactured by selective laser melting (SLM) and the related corrosion behavior. Results showed that there were more voids with faster scanning speeds, and there were oxide powder and non-melt silicon inside the defects. The SLM 316L exhibited a full gamma austenite phase filled with sub-grains, and the average grain size of SLM-1083 mm/s 316L was approximately 42 μm, three times larger than that of the quenched 316L. The pitting potentials for the SLM 316L were all approximately 300 mV higher than that of the quenched due to the modification of inclusions in SLM, but the corrosion rate for the SLM 316L was faster, which was attributed to the voids and unstable passive film. The number of pitting sites increased with the scanning speed, and the pits occurred preferentially at the voids in SLM 316L.

The Temperature Effect on the Compressive Behavior of Closed-Cell Aluminum-Alloy Foams

Abstract: In this research, the mechanical behavior of closed-cell aluminum (Al)-alloy foams was investigated at different temperatures in the range of 25-450 °C. The main mechanical properties of porous Al-alloy foams are affected by the testing temperature, and they decrease with the increase in the temperature during uniaxial compression. From both the constant/serrated character of stress–strain curves and macro/microstructural morphology of deformed cellular structure, it was found that Al foams present a transition temperature from brittle to ductile behavior around 192 °C. Due to the softening of the cellular structure at higher temperatures, linear correlations of the stress amplitude and that of the absorbed energy with the temperature were proposed. Also, it was observed that the presence of inherent defects like micropores in the foam cell walls induced further local stress concentration which weakens the cellular structure’s strength and crack propagation and cell-wall plastic deformation are the dominant collapse mechanisms. Finally, an energy absorption study was performed and an optimum temperature was proposed.

Modeling of Powder Bed Manufacturing Defects

Abstract: Powder bed additive manufacturing offers unmatched capabilities. The deposition resolution achieved is extremely high enabling the production of innovative functional products and materials. Achieving the desired final quality is, however, hampered by many potential defects that have to be managed in due course of the manufacturing process. Defects observed in products manufactured via powder bed fusion have been studied experimentally. In this effort we have relied on experiments reported in the literature and—when experimental data were not sufficient—we have performed additional experiments providing an extended foundation for defect analysis. There is large interest in reducing the effort and cost of additive manufacturing process qualification and certification using integrated computational material engineering. A prerequisite is, however, that numerical methods can indeed capture defects. A multiscale multiphysics platform is developed and applied to predict and explain the origin of several defects that have been observed experimentally during laser-based powder bed fusion processes. The models utilized are briefly introduced. The ability of the models to capture the observed defects is verified. The root cause of the defects is explained by analyzing the numerical results thus confirming the ability of numerical methods to provide a foundation for rapid process qualification.

The Effects of Grain Refinement and Rare Earth Intermetallics on Mechanical Properties of As-Cast and Wrought Magnesium Alloys

Abstract: The effects of rare earth intermetallics and grain refinement by alloying and hot extrusion on the mechanical properties of Mg-Gd-Al-Zn alloys have been studied to elucidate some useful ways to enhance the mechanical properties of magnesium alloys. It was revealed that aluminum as an alloying element is a much better grain refining agent compared with gadolinium, but the simultaneous presence of Al and Gd can refine the as-cast grain size more efficiently. The presence of fine and widely dispersed rare earth intermetallics was found to be favorable to achieve finer recrystallized grains during hot deformation by extrusion. The presence of coarse dendritic structure in the GZ61 alloy, grain boundary eutectic containing Mg17Al12 phase in the AZ61 alloy, and rare earth intermetallics with unfavorable morphology in the Mg-4Gd-2Al-1Zn alloy was found to be detrimental to mechanical properties of the alloy in the as-cast condition. As a result, the microstructural refinement induced by hot extrusion process resulted in a significant enhancement in strength and ductility of the alloys. The presence of intermetallic compounds in the extruded Mg-4Gd-2Al-1Zn and Mg-2Gd-4Al-1Zn alloys deteriorated tensile properties, which was related to the fact that such intermetallic compounds act as stress risers and microvoid initiation sites.

Mechanical Properties and Wear Behavior of AA5182/WC Nanocomposite Fabricated by Friction Stir Welding at Different Tool Traverse Speeds

Abstract: Grain growth inhibition at the heat-affected zone, improved weld strength and superior tribological properties of welds are desirable attributes of modern manufacturing. With the focused on these attributes, tungsten carbide (WC) nanoparticles were employed as reinforcements for the friction stir welding of 5-mm-thick AA5182 aluminum alloy by varying tool traverse speeds. The microstructure, microhardness, ultimate tensile strength, fracture and wear behavior of the resultant WC-reinforced welds were investigated, while unreinforced AA5182 welds were employed as controls for the study. The result shows that the addition of WC nanoparticles causes substantial grain refinement within the weld nugget. A decrease in traverse speed caused additional particle fragmentation, improved hardness value and enhanced weld strength in the reinforced welds. Improved wear rate and friction coefficient of welds were attained at a reduced traverse speed of 100 mm/min in the WC-reinforced welds. This improvement is attributed to the effects of reduced grain size/grain fragmentation and homogeneous dispersion of WC nanoparticles within the WC-reinforced weld nugget.

The Effect of Heat Treatment Process Parameters on Mechanical Properties, Precipitation, Fatigue Life, and Fracture Mode of an Austenitic Mn Hadfield Steel

Abstract: In this study, the effect of cooling rate after heat treatment on mechanical properties, fatigue life, precipitation and fracture mode of an austenitic Mn Hadfield steel was investigated Cast samples of the Hadfield steel were heat treated at 1100 C for 2 h The samples were subsequently quenched in pure water and also in 3 wt% NaCl salt bath Optical microscope (OM) and scanning electron microscope (SEM) were used to analyze microstructure and fracture surfaces Transmission electron microscope (TEM) was used to assess the precipitates X-ray diffraction (XRD) was used to determine the phases formed Mechanical properties and fatigue life were determined by uniaxial tensile test, bending fatigue and hardness measurements Results showed that the sample quenched in salt bath had lower Mn3C precipitates, hardness, yield and tensile strengths Instead, this situation resulted in a more ductile fracture mode and higher formability Finally, the fatigue life of the sample quenched in salt bath was longer than the one quenched in pure water

Tensile, Creep, and Fatigue Behaviors of 3D-Printed Acrylonitrile Butadiene Styrene

Abstract: Acrylonitrile butadiene styrene (ABS) is a widely used thermoplastics in 3D printing. However, there is a lack of thorough investigation of the mechanical properties of 3D-printed ABS components, including orientation-dependent tensile strength and creep fatigue properties. In this work, a systematic characterization is conducted on the mechanical properties of 3D-printed ABS components. Specifically, the effect of printing orientation on the tensile and creep properties is investigated. The results show that, in tensile tests, the 0° printing orientation has the highest Young’s modulus of 1.81 GPa, and ultimate strength of 224 MPa. In the creep test, the 90° printing orientation has the lowest k value of 0.2 in the plastics creep model, suggesting 90° is the most creep resistant direction. In the fatigue test, the average cycle number under load of 30 N is 3796 cycles. The average cycle number decreases to 128 cycles when the load is 60 N. Using the Paris law, with an estimated crack size of 0.75 mm, and stress intensity factor is varied from 352 to 700 $$N\sqrt m$$ , the derived fatigue crack growth rate is 0.0341 mm/cycle. This study provides important mechanical property data that is useful for applying 3D-printed ABS in engineering applications.

High Chromium Cast Irons: Destabilized-Subcritical Secondary Carbide Precipitation and Its Effect on Hardness and Wear Properties

Abstract: This work evaluates the effect of a destabilization treatment combined with a subcritical diffusion (SCD) and a subsequent quenching (Q) steps on precipitation of secondary carbides and their influence on the wear properties of HCCI (16%Cr). The destabilization of the austenite at high temperature leads to a final microstructure composed of eutectic and secondary carbides, with an M7C3 nature, embedded in a martensitic matrix. An improved wear resistance was observed in the SCD + Q samples in comparison with the Q one, which was attributed to the size of secondary carbides.

Tribological Behavior of Pulsed Electrodeposited Ni-W/SiC Nanocomposites

Abstract: Ni-14 at.% W/SiC nanocomposite coatings containing 0-6 vol.% of submicron size (0.35 μm) SiC particles were obtained using pulsed electrodeposition technique on mild steel substrate. The coatings were subsequently characterized for uniformity of SiC distribution, grain size and mechanical properties (hardness and elastic modulus) using SEM, XRD and nanoindentation techniques, respectively. It was observed that the SiC particulates were uniformly distributed within the coating. The coating matrix (Ni-W) also exhibited nanograin size. Tribological behavior of Ni-14 W/SiC nanocomposite was analyzed under dry sliding wear test conditions using pin on disk method. The interrelationship between SiC content, interparticle spacing, mechanical properties and wear behavior was analyzed. The results suggest that whereas hardness and modulus of nanocomposite coatings varied with SiC content as per Rule of Mixtures, wear mechanism can be best explained on the basis of Inverse Rule of Mixtures.

Additive Manufacturing of PLA and CF/PLA Binding Layer Specimens via Fused Deposition Modeling

Abstract: As one of the most popular additive manufacturing techniques, fused deposition modeling (FDM) is successfully applied in aerospace, automotive, architecture, and other fields to fabricate thermoplastic parts. Unfortunately, as a result of the limited nature of the mechanical properties and mass in raw materials, there is a pressing need to improve mechanical properties and reduce weight for FDM parts. Therefore, this paper presents an experiment of a special polylactic acid (PLA) and carbon fiber (CF)/PLA-laminated experimental specimen fabricated using the FDM process. The mechanical properties and mass analysis of the new composites for the PLA and CF/PLA binding layer specimen are investigated experimentally. Through the experimental analysis, one can conclude that the mass of laminated specimen is lighter than the CF/PLA specimen, and the tensile and flexural mechanical properties are higher than the pure PLA specimen.

Effect of the Heat Treatment on the Corrosion Resistance of Duplex Stainless Steels

Abstract: Duplex stainless steels (DSS) are biphasic austenitic-ferritic steels in which the best combination of mechanical and corrosion resistance properties is achieved for an almost equal volume fraction of the phases. In this work, the effect of secondary phases precipitation on the corrosion resistance of four DSS grades (2101, 2304, 2205 and 2507), after isothermal aging in the critical temperature range 750-900 °C, was studied. The corrosion resistance was investigated by potentiodynamic polarization tests in both 0.6 M NaCl solution (pH 7) and in an acid chlorinated solution (pH 3) at room temperature. Moreover, the critical pitting temperature was determined according to ASTM G150. The results showed that secondary phases precipitation mainly influenced the resistance to corrosion of the lean duplex grades.

Effects of Tungsten Addition on the Microstructure and Mechanical Properties of Near-Eutectic AlCoCrFeNi 2 High-Entropy Alloy

Abstract: The effects of tungsten addition on the microstructure and mechanical properties of near-eutectic AlCoCrFeNi2 high-entropy alloy were investigated in this paper. The AlCoCrFeNi2W x alloys comprised the primary BCC phase plus eutectic FCC/BCC phases. It was found that W element can both promote the formation of the primary BCC phase and act as a solid solution strengthening element. The hardness of the AlCoCrFeNi2W x alloys increased from HV 293 to HV 356.2 with the increase in W content. The addition of W element improved the strength of alloys but reduced ductility. Thereinto, the AlCoCrFeNi2W0.2 alloy showed the most excellent compressive properties with the fracture strength of 2785.9 MPa and the plastic strain of 0.42, respectively, which implied the potential industrial application values.

Static and Dynamic Mechanical Properties of Graphene Oxide-Incorporated Woven Carbon Fiber/Epoxy Composite

Abstract: This study investigates the synergistic effects of graphene oxide (GO) on the woven carbon fiber (CF)-reinforced epoxy composites. The GO nanofiller was incorporated into the epoxy resin with variations in the content, and the CF/epoxy composites were manufactured using a vacuum-assisted resin transfer molding process and then cured at 70 and 120 °C. An analysis of the mechanical properties of the GO (0.2 wt.%)/CF/epoxy composites showed an improvement in the tensile strength, Young’s modulus, toughness, flexural strength and flexural modulus by ~ 34, 20, 83, 55 and 31%, respectively, when compared to the CF/epoxy composite. The dynamic mechanical analysis of the composites exhibited an enhancement of ~ 56, 114 and 22% in the storage modulus, loss modulus and damping capacity (tanδ), respectively, at its glass transition temperature. The fiber–matrix interaction was studied using a Cole–Cole plot analysis.

Metallization of Carbon Fiber Reinforced Polymers for Lightning Strike Protection

Abstract: Carbon fiber reinforced polymers (CFRPs) are increasingly used in the latest generations of aircraft, but their low electrical conductivity is a concern for lightning strike protection During the past few years, development of lightning strike protection solutions for CFRP has attracted increasing interest, and cold spray is one coating approach to achieving this In this work, pure tin coatings and tin–copper composite coatings were cold sprayed on CFRP as possible lightning strike protection materials The coatings were subjected to various mechanical and electrical characterizations The effect of annealing on electrical conductivity was also examined Furthermore, continuous current injection tests, which duplicated component C of a lightning waveform, were performed on the coatings The results showed that the cold-sprayed coatings can provide effective protection to the CFRP underneath when subjected to currents up to 200 A with 1-s duration

Influence of Particle Size on the Basic and Time-Dependent Rheological Behaviors of Cemented Paste Backfill

Abstract: The rheological properties of cemented paste backfill (CPB) significantly influence the material’s transportability, and these properties are strongly affected by the material’s particle size. This paper mainly focuses on the influence of particles size on the basic and time-dependent rheological behaviors of CPB. The rheology tests and microstructure analysis were conducted using multiple CPB samples with different solid contents, cement contents, and particle sizes. Results show that the CPB samples with finer particle sizes have a lower apparent maximum packing density compared to the CPB samples with larger particle sizes. Fresh CPB mixture samples exhibit shear thinning characteristics which are more pronounced in samples with larger particle sizes and higher volume fraction to apparent maximum packing density ( $$\phi /\phi_{\text{m}}$$ ) ratios. When the $$\phi /\phi_{\text{m}}$$ ratio is lower than 0.875, the samples with finer particle sizes display a higher yield stress but less time-dependent rheological behavior than coarser samples. In all CPB samples that contained cement, the shear stress decreases first and then increases over the shearing time when samples are sheared at a constant shear rate. In the CPB samples without cement, samples with finer particle sizes show lower apparent viscosities, and it is observed in the sample with the finest particles that the shear stress only decreases over the shearing time. Moreover, it is found that the number of hydration products and the rate of particle sedimentation are both higher in samples with larger particle sizes, which result in these samples having higher apparent viscosities.

Structural and Mechanical Properties of Zr-Si-N Coatings Deposited by Arc Evaporation at Different Substrate Bias Voltages

Abstract: ZrN and Zr-Si-N coatings were formed using vacuum-arc plasma fluxes deposition system at the substrate bias voltage (UB) ranged from − 50 to − 220 V on HS6-5-2 steel substrates. The structural, mechanical and tribological properties were characterized using x-ray diffraction, atomic force microscopy, scanning electron microscopy, optical microscopy, nanoindentation and ball-on-disk test. The surface roughness parameter Ra of ZrN coatings is lower than Zr-Si-N coatings. Both roughness Ra of Zr-Si-N coatings and the number of surface defects with mainly small dimensions to 1 µm decrease with increasing negative substrate bias voltage. The addition of silicon to ZrN significantly reduces the crystallite size, from about 18.3 nm for ZrN coating to 6.4 nm for Zr-Si-N coating both deposited at the same UB = − 100 V and 7.8 nm for UB = − 150 V. The hardness of Zr-Si-N coatings increases to about 30 GPa with the increase in negative substrate bias voltage (UB = − 220 V). Adhesion of the coatings tested is high, and critical load is above 80 N and reduces with UB increase. Coefficient of friction determined using AFM shows similar trend as surface roughness in microscale.

Effects of Disodium Phosphate Concentration (Na 2 HPO 4 ·2H 2 O) on Microstructure and Corrosion Resistance of Plasma Electrolytic Oxidation (PEO) Coatings on 2024 Al Alloy

Abstract: Since the electrolyte composition plays a pivotal role in the microstructure and corrosion behavior of plasma electrolytic oxidation (PEO) coatings, the effects of disodium phosphate (Na2HPO4·2H2O) concentration on the microstructure and corrosion resistance of PEO coatings fabricated on 2024 Al alloy were studied in this investigation. Accordingly, electrolyte with four different concentrations of phosphate ion (5, 10, 15 and 20 g/L) was used. All PEO processes were conducted at constant current density of 15 A/dm2 for 15 min. The surface and cross-sectional morphologies of the coatings indicated that the coating formed in the electrolyte with 10 g/L Na2HPO4·2H2O (with 9.14 µm thickness) had the most compact and uniform structure with the lowest and smallest micropores. Furthermore, studying the corrosion behavior of samples in 3.5 wt.% NaCl solutions by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests revealed that the sample coated in the electrolyte with 10 g/L Na2HPO4·2H2O had the highest corrosion potential, the lowest corrosion current density and, accordingly, the best corrosion resistance. The corrosion resistance of this coating was 4.574 × 105 Ω cm2, which could increase the corrosion resistance of uncoated 2024 Al alloy substrate 48 times. The x-ray diffraction pattern of this coating proved that the coating was composed of α-Al2O3 and γ-Al2O3 phases.

Effect of Different Cooling Rates on the Corrosion Behavior of High-Carbon Pearlitic Steel

Abstract: The present work discusses the effect of pearlitic morphology on the corrosion behavior of high-carbon fully pearlitic steel in 3.5% NaCl solution. Four different types of pearlitic steels (furnace-cooled, as-received, air-cooled and forced-air-cooled) consisting of coarse, medium, fine and very fine microstructures, respectively, were tested. Electrochemical behavior of these steels was studied with the help of dynamic and linear polarization and AC impedance spectroscopic tests. The corrosion resistance improved with fineness of the microstructure in general. However, with further reduction in interlamellar spacing beyond a limit, the corrosion resistance reduced slightly. Formation of homogeneous distribution of microgalvanic cells between cementite and ferrite lamellae of fine pearlitic steel improved the corrosion resistance. However, entanglement of the lamellae of pearlite in very fine pearlitic structure as well as breaking of cementite lamellae due to finer pearlitic colonies was attributed to the higher corrosion of the forced-air-cooled steel as compared to the air-cooled steel.

Identification of Post-necking Tensile Stress–Strain Behavior of Steel Sheet: An Experimental Investigation Using Digital Image Correlation Technique

Abstract: The stress–strain behavior of sheet metal is commonly evaluated by tensile test. However, the true stress–strain curve is restricted up to uniform elongation of the material. Usually, after the uniform elongation of the material the true stress–strain is obtained by extrapolation. The present work demonstrates a procedure to find out the true tensile stress–strain curve of the steel sheet after necking using digital image correlation (DIC) technique. Hill’s normal anisotropic yield criteria and local strains measured by DIC technique are used to correct the local stress and strain states at the diffuse necked area. The proposed procedure is shown to successfully determine the true tensile stress–strain curve of ferritic and dual-phase steel sheets after necking/uniform elongation.

Plasma Electrolytic Oxidation Coatings on Pure Ti Substrate: Effects of Na 3 PO 4 Concentration on Morphology and Corrosion Behavior of Coatings in Ringer’s Physiological Solution

Abstract: Plasma electrolytic oxidation has been used as a relatively new method for applying ceramic coatings having different features. In the present study, commercially pure titanium is used as substrate, and effects of trisodium phosphate electrolyte concentration on the microstructure, as well as corrosion behavior of the coating in Ringer’s physiological solution are investigated. The morphology and phase compositions of coatings were analyzed by using scanning electron microscopy (SEM) and x-ray diffraction patterns. The study on the corrosion behavior of samples in a Ringer’s physiological solution was carried out using open-circuit potential potentiodynamic polarization and electrochemical impedance spectroscopy. The results of electrochemical analysis proved that higher concentration of phosphate electrolyte leads to increase in the corrosion resistance of applied coatings. Accordingly, obtained results revealed that the optimum electrolyte concentration for the best corrosion behavior was 20 g L−1. Furthermore, SEM images and reduction in the dielectric breakdown potential indicated that increase in the electrolyte concentration leads to morphological improvement and smoothening of the surface.

Low-Velocity Impact Behavior of Sandwich Structures with Additively Manufactured Polymer Lattice Cores

Abstract: Sandwich panel structures are widely used in aerospace, marine, and automotive applications because of their high flexural stiffness, strength-to-weight ratio, good vibration damping, and low through-thickness thermal conductivity. These structures consist of solid face sheets and low-density cellular core structures, which are traditionally based upon honeycomb folded-sheet topologies. The recent advances in additive manufacturing (AM) or 3D printing process allow lattice core configurations to be designed with improved mechanical properties. In this work, the sandwich core is comprised of lattice truss structures (LTS). Two different LTS designs are 3D-printed using acrylonitrile butadiene styrene (ABS) and are tested under low-velocity impact loads. The absorption energy and the failure mechanisms of lattice cells under such loads are investigated. The differences in energy-absorption capabilities are captured by integrating the load–displacement curve found from the impact response. It is observed that selective placement of vertical support struts in the unit-cell results in an increase in the absorption energy of the sandwich panels.

High Cycle Fatigue Performance in Laser Shock Peened TC4 Titanium Alloys Subjected to Foreign Object Damage

Abstract: During their service, titanium alloys are likely to suffer from the foreign object damage (FOD), resulting in a decrease in their fatigue strength Laser shock peening (LSP) has been proved to effectively increase the damage tolerance of military engine components by introducing a magnitude compressive residual stress in the near-surface layer of alloys In this paper, smooth specimens of a TC4 titanium alloy were used and treated by LSP and subsequently exposed to FOD, which was simulated by firing a steel sphere with a nominal velocity of 300 m/s, at 90° with the leading edge of the LSP-treated region using a light gas gun All impacted specimens were then subjected to fatigue loading The results showed that LSP could effectively improve the fatigue strength of the damaged specimens The effect of LSP on the fatigue strength was assessed through fracture observations, microhardness tests and residual stress analyses The residual stresses due to the plastic deformation caused by LSP and the FOD impact, which were found to play a crucial role on the fatigue strength, were determined using the commercial software ABAQUS

Friction Stir Welding of Al-B 4 C Composite Fabricated by Accumulative Roll Bonding: Evaluation of Microstructure and Mechanical Behavior

Abstract: In this investigation, friction stir welding (FSW) of Al-B4C composite fabricated by 10 cycles accumulative roll bonding was conducted. In order to investigate the influences of pin geometry on microstructure and mechanical properties, four different pin geometries (cylindrical, square, triangular and hexagonal) were selected. It was found that FSW parameters had a major effect on the fragmentation and distribution of reinforcement particles in stir zone. When the tool travel speed was increased, the distribution of B4C particles was become gradually uniform in the aluminum matrix. The effect of tool rotational speed on the peak temperature was determined to be greater than the tool travel speed. The attained data of tensile properties and microhardness tests showed that the tool travel speed had bilateral effect on the tensile strength. The maximum tensile joint efficiency was obtained as 238% for FSWed of Al-2%B4C composite to annealed base Al sheet.

Phase Evolution and Mechanical Properties of AlCoCrFeNiSi x High-Entropy Alloys Synthesized by Mechanical Alloying and Spark Plasma Sintering

Abstract: In the current investigation, AlCoCrFeNiSix (x = 0, 0.3, 0.6 and 0.9 in atomic ratio) high-entropy alloy systems are prepared by mechanical alloying and subsequently consolidated by spark plasma sintering. The microstructural and mechanical properties were analyzed to understand the effect of Si addition in AlCoCrFeNi alloy. The x-ray diffraction analysis reveals the supersaturated solid solution of the body-centered cubic structure after 20 h of ball milling. However, the consolidation promotes the transformation of body-centered phases partially into the face-centered cubic structure and sigma phases. A recently proposed geometric model based on the atomic stress theory has been extended for the first time to classify single phase and multi-phases on the high-entropy alloys prepared by mechanical alloying and spark plasma sintering process. Improved microhardness and better wear resistance were achieved as the Si content increased from 0 to 0.9 in the present high-entropy alloy.

An Analysis on the Constitutive Models for Forging of Ti6Al4V Alloy Considering the Softening Behavior

Abstract: This paper developed high-temperature deformation constitutive models for a Ti6Al4V alloy using an empirical-based Arrhenius equation and an enhanced version of the authors’ physical-based EM + Avrami equations. The initial microstructure was a partially equiaxed α + β grain structure. A wide range of experimental data was obtained from hot compression of the Ti6Al4 V alloy at deformation temperatures ranging from 720 to 970 °C, and at strain rates varying from 0.01 to 10 s−1. The friction- and adiabatic-corrected flow curves were used to identify the parameter values of the constitutive models. Both models provided good overall accuracy of the flow stress. The generalized modified Arrhenius model was better at predicting the flow stress at lower strain rates. However, the model was inaccurate in predicting the peak strain. In contrast, the enhanced physical-based EM + Avrami model revealed very good accuracy at intermediate and high strain rates, but it was also better at predicting the peak strain. Blind sample tests revealed that the EM + Avrami maintained good predictions on new (unseen) data. Thus, the enhanced EM + Avrami model may be preferred over the Arrhenius model to predict the flow behavior of Ti6Al4V alloy during industrial forgings, when the initial microstructure is partially equiaxed.