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Considering commonly employed carbide particles, titanium carbide (TiC) is regarded as an excellent reinforcement material due to its superior physical and mechanical characteristics ...and particularly appropriate interfacial bonding (wetting) ability with aluminum. In this study, 5 wt.% nanoparticle titanium carbide (TiCNP) reinforced AA7075 alloy composites were produced by ball milling and hot pressing. The effects of milling time (15 min, 1 h, 1.5 h, 2 h, 10 h) on the morphologic and crystallographic properties of powders were characterized by scanning electron microscopy, particle size analysis, X-ray diffraction, and high-resolution transmission electron microscopy. It was observed that particle size and morphology varied with milling time. The results indicated that the TiCNP were gradually dispersed into the matrix as ball-milling time increased and achieved a uniform dispersion after 2 h of milling. Consolidation of the milled powders was performed via hot pressing under 400 MPa and 430 °C for 30 min. The effect of milling time on the microstructural and mechanical properties of the bulk TiCNP/AA7075 composites was evaluated in terms of grain formation behavior, hardness, tensile strength, and relative density results. The results revealed that three times enhanced hardness value (277.55 HB) was achieved in a 10 h milled and hot-pressed sample than initial AA7075 alloy (94.43 HB) because of the hardened nanoparticles' homogeneous distribution within the matrix along with the increment in milling time. Tensile tests showed that the 1 h milled TiCNP/AA7075 composite's ultimate tensile strength (284.46 MPa) was increased by 40 % compared with the initial AA7075 alloy (210.24 MPa). Considering test results, it was determined that the hardness values increased as a function of the milling time, but the optimum milling time, which means achieving the highest tensile strength value, was determined as 1 h. This continuous increase in hardness is attributed to the homogeneous distribution of nanoparticles within the matrix, and increased hardness of particles originated from the severe plastic deformation due to advancing milling time. However, the incoherent variation of tensile strength values with milling time suggests that the increased hardness of particles and the changes in particle morphology after 1 h of milling deteriorates the sinterability and packing properties of the powders.
The main objective of this research is to prove the viability of obtaining magnesium (Mg) filled polylactic acid (PLA) biocomposites as filament feedstock for material extrusion-based additive ...manufacturing (AM). These materials can be used for medical applications, thus benefiting of all the advantages offered by AM technology in terms of design freedom and product customization. Filaments were produced from two PLA + magnesium + vitamin E (α-tocopherol) compositions and then used for manufacturing test samples and ACL (anterior cruciate ligament) screws on a low-cost 3D printer. Filaments and implant screws were characterized using SEM (scanning electron microscopy), FTIR (fourier transform infrared spectrometry), and DSC (differential scanning calorimetry) analysis. Although the filament manufacturing process could not ensure a uniform distribution of Mg particles within the PLA matrix, a good integration was noticed, probably due to the use of vitamin E as a precursor. The results also show that the composite biomaterials can ensure and maintain implant screws structural integrity during the additive manufacturing process.
A novel underwater directed energy deposition (UDED) technique was developed for the on-site repair of marine equipment in an underwater environment. A special drainage nozzle was integrated with a ...laser cladding head to form the underwater manufacturing tool which ensured the successful repair of the damage zone on an HSLA-100 steel plate. The influence mechanisms of inherently complex heat-treatment cycles and kinetics involved in the UDED process on the microstructural formation/evolution process were systematically investigated using both experimental and numerical approaches. The mechanical properties, including microhardness, nanohardness, tensile strength and Charpy impact toughness of the UDED repaired samples were investigated and the results were compared with those repaired by in-air directed energy deposition (DED). The experimental results show that the rapid cooling rate accelerated by the water quenching effect promoted the formation of columnar austenite and the subsequent fine martensite. Compared with the DED samples, the activation energy values for the nucleation and growth of the precipitates in UDED samples were much lower due to the existence of high-density crystal defects and large internal residual stresses. The numerical results indicate that compared with DED, the cooling rate significantly increased and the peak temperature decreased during UDED. The average microhardness of the samples prepared by UDED (315–334 HV) was higher than that prepared by DED (307 HV). The tensile properties and impact toughness of the as-repaired samples by UDED were equal or even better than those obtained by DED owing to the formation of fine martensite and high dislocation densities in the UDED samples. This work clarifies the difference in metallurgical processes in air and underwater environments, which can provide guidance for future structural manipulation of materials additively manufactured in underwater environments.
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•Underwater directed energy deposition is firstly carried out on HSLA-100 steel.•The repair quality by UDED is equal or even better than that repaired by in-air DED.•Difference of metallurgical processes in underwater and air environments is clarified.•Unique microstructural evolution mechanisms are related with UDED thermal process.•UDED can be employed to repair and restore the damaged parts in marine engineering.
The double‐crystal ultra‐small‐angle neutron scattering (USANS) diffractometer KOOKABURRA at ANSTO was made available for user experiments in 2014. KOOKABURRA allows the characterization of ...microstructures covering length scales in the range of 0.1–10 µm. Use of the first‐ and second‐order reflections coming off a doubly curved highly oriented mosaic pyrolytic graphite premonochromator at a fixed Bragg angle, in conjunction with two interchangeable pairs of Si(111) and Si(311) quintuple‐reflection channel‐cut crystals, permits operation of the instrument at two individual wavelengths, 4.74 and 2.37 Å. This unique feature among reactor‐based USANS instruments allows optimal accommodation of a broad range of samples, both weakly and strongly scattering, in one sample setup. The versatility and capabilities of KOOKABURRA have already resulted in a number of research papers, clearly demonstrating that this instrument has a major impact in the field of large‐scale structure determination.
The concept, design and performance of the variable‐wavelength Bonse–Hart ultra‐small‐angle neutron scattering diffractometer KOOKABURRA at ANSTO are described.
An anti-ablation composite coating with the major phases of cubic YSZ and ZrC was prepared by reaction-introduced plasma spraying. The as-prepared coating demonstrated promising ablation-resistant ...property within 45 s under the plasma torch ablation and then showed a last-ply failure when the ablation time reached 135 s. The ablation property of the in-situ YSZ-ZrC composite coating was evaluated qualitatively and quantitatively. Phase transition behaviors of YSZ, ZrC, and amorphous AlO during the ablation process were revealed by XRD and Raman spectra. The coating lamellae composed of YSZ and nanosized ZrC phase showed good integrity under long-time ablation process. Dense and continuous Zr-Al-Si-O oxidation layer with good compatibility between the oxide phases was formed on the after-ablation coating surface. The anti-ablation mechanism was explored based on the microstructure analysis of the as-prepared YSZ-ZrC coating before and after the ablation process by SEM and TEM.
•Dense YSZ-ZrC anti-ablation coating was reactively synthesized.•YSZ and in-situ ZrC shown good compatibility in the lamella after ablation.•Ablation behavior of amorphous AlO was revealed.•Dense Zr-Al-Si-O oxide layer was formed after ablation.
Laser solid forming (LSF) is a newly developed additive manufacturing which offers a less material waste and reduction in lead-time for fabricating aerospace titanium alloys components. In this ...paper, two types of block with different build dimension (section geometries) were fabricated by LSF with same processing parameters. The corresponding microstructure, texture, and tensile properties were investigated systematically. The results show that the samples exhibits similar columnar β grains morphology and 〈100〉 fiber texture, but very different α variant characterizations (morphology and texture) due to the different thermal history they experienced respectively. The fine basket-weave microstructure with weak texture can be obtained under the fast cooling conditions, while the colony microstructure shows a strong transformation texture as a result of variant selection in the relative slow cooling rate. The α characterizations depend strongly on the competition growth mechanism between the αWGB (grin boundary Widmanstatten structure) and αI (intragranular α nuclei) during cooling process. The presence of αGB (grain boundary α layers) enhances the nucleation of certain variants in β→α phase transformation. Tensile results reveal that fine basket-weave microstructure has relative high strength and ductility with dimple fracture mode. The colony microstructure shows a feature of dominant brittle fracture appearance and results in low tensile ductility.
Corrosion inhibition of aluminum alloy AA6063-T5 by vanadates (NaVO3) in 0.05 M NaCl solution has been investigated by electrochemical and weight loss measurements, and associated with microstructure ...and Volta potential data. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy analyses confirmed the presence of micrometer-sized Fe-rich Al4.01MnSi0.74, Al1.69Mg4Zn2.31, and FeAl3 intermetallic phases (IMPs) and nanometer-sized CuAl2, ZnAl2, and Mg2Si precipitates in the microstructure. Scanning Kelvin probe force microscopy measurements showed Volta potential differences of up to 600 mV between the microstructure constituents indicating a high susceptibility to micro-galvanic corrosion, with interphase boundary regions exhibiting the highest propensity to corrosion. Most IMPs had cathodic character whereas some nanometer-sized Mg-rich particles exhibited anodic nature, with large Volta potential gradients within interphase regions of large cathodic particles. Electrochemical potentiodynamic polarization measurements indicated that the vanadates provided mixed corrosion inhibition effects, mitigating both oxygen reduction, occurring on cathodic IMPs, and anodic metal dissolution reaction, occurring on anodic sites, such as Mg2Si and interphase boundary regions. Electrochemical measurements indicated that the sodium metavanadate inhibitor blocks active metal dissolution, giving high inhibition efficiency (>95%) during the initial exposure, whereas long-term weight loss measurements showed that the efficacy decreases after prolonged exposure.
Directed energy deposition (DED) of Inconel 718 is a promising process for the reconstruction of aerospace components, but a large number of Laves phases precipitated in inter-dendrites can impair ...the mechanical properties of the reconstructed parts. This paper puts forward a gradient laser power (GLP) deposition method to tailor the morphology and content of the Laves phase effectively, thereby enhancing the mechanical properties. The deposited Inconel 718 parts with the same volume as the Inconel 718 substrate were fabricated by different laser powers to simulate the practical thin-wall repair. An infrared camera was utilized to capture the thermal information during the DED process. The thermal-history-dependent microstructure, residual stress, microhardness and tensile properties were comprehensively investigated. The results indicate that the GLP method not only alleviates heat accumulation but also increases cooling rates and lateral heat dissipation. For GLP samples, the discrete and fine Laves phases tailored with a uniform distribution are featured by fine columnar dendrites with random growth direction, in sharp contrast to their long-chain interconnected configurations obtained by the conventional constant laser power (CLP) deposition method. Compared with CLP samples, GLP samples show compressive residual stress, high hardness and excellent ductility of elongation 30.09 % with comparable strength.
Large repositories of microstructure realizations lie at the centre of developing effective structure–property correlations in materials. It is, however important that the microstructure generation ...procedures not only reconstruct a large number of microstructures in a computationally inexpensive manner but also hold awareness regarding the physical significance of the underlying microstructure. While machine learning techniques are used for computationally efficient microstructure generation, the similarity and physical awareness of the generated microstructures with the ground truth are rarely quantified. In this work, we use a variant of generative adversarial network (GAN) i.e. StyleGAN2, to generate microstructures with varied morphologies from a small dataset of Dual Phase (DP) steels. The similarity between the generated and the original microstructures is quantified using various metrics such as structure similarity index (SSIM), peak signal to noise ratio (PSNR) and signal to noise ratio (SNR). The physical awareness is quantified by comparing the predictions of macroscopic mechanical properties of the GAN generated and original microstructures using a reduced order model. We also qualitatively estimate the learning of the GAN latent space in terms of microstructure morphology. It is observed that there exists a relationship between the microstructure morphological information and the similarity assessment metrics.
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•StyleGAN2 with ADA is used to generate similar microstructures from a small dataset.•Latent Space studies show that the GAN is learning morphological parity of data.•Similarity studies show a relationship between the metrics and data morphology.•Awareness studies show that the ROM can assess damage in generated microstructures.•This work can be appended to a prediction framework for its rigorous validation.
The microstructure of Ti-6.5Al-2Zr-1Mo-1 V (TA15) alloy fabricated by laser powder bed fusion (LPBF) is characterized by the ultrafine α′ martensite with a high density of dislocations and twins, ...which is distinct to that of conventionally forged TA15 alloy. The α′ martensite in the as-built alloy transforms to stable α phase when annealing below the β transus, and meanwhile the dislocation density decreases and the α lamellae coarsen with increasing of annealing temperature. An excellent synergy of strength and ductility was achieved in the sample after designated heat treatments, which is better than that of the forged counterpart at both room temperature and 500 °C. In-situ tensile test at 500 °C demonstrated that the plasticity of as-built TA15 alloy was dominated by the formation of microscale shear bands (MSBs) between the α′ lamellae, which results in pronounced strain localization and limited tensile ductility. In the sample with coarsened α lamellae, it was found that the activation of pyramidal < c + a > slip system at 500 °C effectively alleviated the strain localization and cracking tendency during mechanical loading, which is essential to achieve a desired balance of strength and ductility. These findings are helpful to promote the practical applications of LPBF near-α titanium alloys.
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