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•TiOxNy/α-Ti composite coatings were deposited using laser surface engineering.•TiOxNy formed as a result of the atmospheric nitriding of titanium oxide.•The concentrations of O and N ...in TiOxNy varied with the laser power.•The composite coatings exhibited high hardness and superior wear resistance.
TiOxNy/Ti composite coatings were deposited on Ti-6Al-4V via laser surface engineering. This process was conducted in the air using TiO2 powder as the starting material. The effect of laser power on the defect, microstructure, chemical composition and mechanical properties of the coatings were systematically investigated. The use of a low laser power resulted in the formation of numerous cracks and pores in the coatings, which reduced considerably with the increased laser power. The predominant phase in the coatings was TiOxNy, a product of the nitridation of titanium oxide in air. The concentrations of O and N in TiOxNy varied with laser power. Ti alloy from the partially melted base metal mixed into the ceramic melt, leading to the formation of α-Ti grains between TiOxNy dendrites. The microhardness and wear resistance of the composite coatings were significantly improved by factors up to 4.7 and 3.9 respectively, compared to the base metal.
Understanding the densification behaviours and formation mechanisms of defects are essential to fabricate high quality and high strength aluminium components using selective laser melting (SLM) ...technology. In this work, the effects of laser power and scanning speed on the densification, defects evolution and their formation mechanisms in a SLMed 2024 aluminium (Al) alloy were investigated in consideration of the corresponding laser energy input, melting mode transition and microstructural evolution. The results showed that optimizing the processing parameters effectively reduced the porosity level below 1% by avoiding the lack of fusion and keyhole melting mode, and minimizing the gas pores. However, optimization of the processing parameters could not eliminate the columnar structure associated with the SLMed 2024 Al alloy, which contributed to the hot-tearing cracks in the SLMed parts. It was found that the dependence of porosity formation on SLM processing parameters was contrary to the crack density. Hence, to further improve the SLM-processability of the 2024 Al alloy it is necessary to develop SLM methods in order avoid the hot-cracking within the optimized processing parameter window associated with the minimum porosity formation.
Yttria stabilized zirconia (YSZ) thin wall components were fabricated using laser engineered net shaping (LENS) technique. It was found that after LENS processing, the monoclinic (m) phase in ...as-received YSZ powders transformed to tetragonal (t) and cubic (c) phases with the lenticular shaped t-ZrO
2
embedded in the c-ZrO
2
matrix. The relative density of the parts reached up to 98.7%. Our investigation showed that micro cracks within the wall structure were reduced by judiciously choosing laser power parameter. The fabricated parts have surface roughness values that ranged from 20 to 40 μm. The maximum hardness and elastic modulus achieved from the LENSed YSZ parts were 19.8 GPa and 236.1 GPa, respectively. We also demonstrated that dark brown color of the LENSed parts could be removed via heat treatment.
Abstract Ceramic oxides, renowned for their exceptional combination of mechanical, thermal, and chemical properties, are indispensable in numerous crucial applications across diverse engineering ...fields. However, conventional manufacturing methods frequently grapple with limitations, such as challenges in shaping intricate geometries, extended processing durations, elevated porosity, and substantial shrinkage deformations. Direct additive manufacturing (dAM) technology stands out as a state-of-the-art solution for ceramic oxides production. It facilitates the one-step fabrication of high-performance, intricately designed components characterized by dense structures. Importantly, dAM eliminates the necessity for post-heat treatments, streamlining the manufacturing process and enhancing overall efficiency. This study undertakes a comprehensive review of recent developments in dAM for ceramic oxides, with a specific emphasis on the laser powder bed fusion and laser directed energy deposition techniques. A thorough investigation is conducted into the shaping quality, microstructure, and properties of diverse ceramic oxides produced through dAM. Critical examination is given to key aspects including feedstock preparation, laser-material coupling, formation and control of defects, in-situ monitoring and simulation. This paper concludes by outlining future trends and potential breakthrough directions, taking into account current gaps in this rapidly evolving field.
Highlights Recent advances in shaping quality, microstructure, and mechanical performance of dAM processed ceramic oxides are reviewed. The research progress on critical issues within dAM of ceramic oxides is thoroughly examined. Future trends and potential breakthrough directions for dAM of ceramic oxides are outlined.
The purpose of this study was to evaluate the efficacy of ultrasonography-guided percutaneous A1 pulley release with the needle knife for trigger finger.
The prospective study included 21 patients ...(21 fingers) who underwent blind release with the needle knife and 20 patients (20 fingers) who underwent ultrasonography-guided release with the needle knife. The thickness and width of A1 pulley, clinical grade before and after release, complications, and operation time were compared between the groups.
The results showed that the ultrasonography-guided group had significantly better grade postoperatively and reached to 100% complete release in one time compared to the blind group (
< 0.05). Moreover, no any complications had been happened in the ultrasonography-guided group. A relatively longer operation time of the ultrasonography-guided group was observed compared to the time of the blind group.
The needle knife is a very good tool for release of triggering fingers. Ultrasound provides a direct and precise visualization of the thickness, width and location of A1 pulley lesion. The combined use of ultrasound and the needle knife can achieve the best result for trigger finger. Moreover, the combination changes the traditional opinion and operator-dependent mode that were once widely adopted in the hospital of Chinese Medicine.
•We develop a hybrid approach for fault diagnosis of planetary bearings.•Accelerometer is mounted internally on the planet carrier for better detection.•Detection algorism is developed by using ...several advanced DSP techniques.•Optimized spectral kurtosis is used for demodulation band selection.•Both inner race and outer race faults of the planetary bearings can be detected.
Planetary gearboxes exhibit unique challenges in bearing fault detection. This paper presents a hybrid approach for fault diagnosis of planetary bearings using an internal vibration sensor and novel signal processing strategies. An accelerometer is mounted internally on the planet carrier to address the issues of variable transmission path. An effective bearing faults detection algorism is developed by employing several advanced signal processing techniques, including Cepstrum whitening, minimum entropy deconvolution (MED), spectral kurtosis (SK) and envelope analysis. The adverse effect of the electromagnetic interference in the signal due to the use of a slip ring is tackled by optimizing the SK technique for demodulation band selection. The proposed method is assessed by analyzing experimental data from a planetary gearbox test rig with seeded bearing faults. The result shows that the new method can effectively detect both inner race and outer race faults of the planetary bearing.
Ceramics-based additive manufacturing is a complex process and the solidification mechanism and microstructural evolution are currently not fully understood. In this work, Al2O3 single tracks were ...formed using a customised selective laser melting (SLM) system equipped with a high power diode laser. The effects of laser energy density (LED) on geometry, microstructure and micro-mechanical properties of Al2O3 tracks were investigated. To better understand the solidification mechanism, a transient three-dimensional thermal model was developed for predicting the thermal behaviour of the melt pool. The results indicated the use of high LED gave rise to decreased viscosity and surface tension of the molten alumina and led to localized melting of the substrate. Both, in turn, enabled the formation of a continuous solidified track. The solidified tracks were primarily composed of columnar dendrite. When relatively high LED (≥ 25.7 kJ/m) was applied, equiaxed dendrite appeared along the central line near the track surface. The size of dendritic grains decreased with the decreased LED, attributed to the increased cooling rate at solidification interface. The micro-hardness of the solidified track was found to be inversely proportional to the grain size owning to grain boundary strengthening effect.
The metastable dual-phase non-equiatomic Fe50Mn30Co10Cr10 high entropy alloy (HEA) was successfully prepared via laser melting deposition (LMD) technique. The phase composition, microstructure and ...mechanical performance were systematically characterized at different sections of LMDed HEA samples. The as-printed HEA specimens were dominated by FCC γ phase, plate and needle-like HCP ε phase, and high density stacking faults and dislocations were observed at high magnification. The as-printed samples exhibited anisotropic mechanical properties, together with the maximum ultimate tensile strength of 760 MPa and maximum elongation of 28%. The fracture surface along X and Z directions exhibit smooth curve shape, while the fracture surface along Y direction shows saw tooth shape, indicating the boundary of melt pool is weakly bounded. After deformation, the deformation bands were observed in the FCC matrix, showing that the plastic strain was controlled by FCC γ phase. In addition, stacking faults, dislocation increase significantly owing to the formation of stacking fault is caused by sliding of Shockeley partial dislocation, and the stacking fault is the core of HCP martensite nucleation.
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•The brittle-to-ductile transition (BDT) during nanoscratching of brittle single crystals is significantly influenced by the tip shape and crystallite structure.•Sharp-tip scratching ...results in a higher BDT critical depth in GaAs compared to Si due to higher bond-breaking energy required.•Using a blunt tip, GaAs exhibits a smaller BDT critical depth than Si due to its higher brittleness and increased crystallite defect density.•Scratch-induced defects in GaAs cause strain hardening, reducing its ductility, while amorphization in Si enhances ductility.
Determining the brittle-to-ductile transition (BDT) threshold is crucial for developing efficient machining processes for brittle materials. In this study, nanoscratch tests were performed on the (001) face of single-crystal silicon (Si) and gallium arsenide (GaAs) using a sharp Berkovich and a blunt Conical tip. The aim was to understand the effects of tip shape and microstructural variation on their BDT behaviour. The result showed that the critical cutting depth for BDT (dc) was affected by not only material microstructure but also tip shape. The stress distribution within the deformed sublayer varied with tip shape, ultimately impacting the microstructure evolution and thus deformation/removal mechanism. Using the sharp tip, Si had a slightly smaller dc than GaAs due to the ease of cracking along the {111} plane. In contrast, with the blunt tip GaAs had a smaller dc than Si, attributed to its relatively high brittleness index and higher density of crystallite defects. The defects in GaAs caused strain hardening and hence reduced ductility, while the amorphization of Si enhanced its ductility.
Grain refinement of additively manufactured titanium and titanium alloys can be promoted via adding foreign elements or particles, but it may lead to a reduction in ductility due to the formation of ...brittle intermetallic compounds. The present study shows that in-situ grain refinement of commercially pure titanium (CP-Ti) can be achieved through properly controlling the selective laser melting (SLM) parameters. It was found that higher input energy density worked in favour of grain refinement. Detailed microstructural characterization coupled with multi-physics simulation were performed to reveal the grain refinement mechanism. This was attributed to the intrinsic heat treatment (IHT) effect which resulted from the cyclic reheating inherent to the SLM process. As a result, the refined CP-Ti exhibited an exceptionally high ductility of 34.3 ± 0.5% without notable mechanical anisotropy. This work demonstrates the feasibility of utilizing thermal cycling of additive manufacturing (AM) to refine grains of metals without changing the composition.
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