The Experts below are selected from a list of 22425 Experts worldwide ranked by ideXlab platform
Hui Xiao - One of the best experts on this subject based on the ideXlab platform.
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Enhancing Hardness and Wear Performance of Laser Additive Manufactured Ti6Al4V Alloy Through Achieving Ultrafine Microstructure.
Materials, 2020Co-Authors: Yanqin Li, Lijun Song, Cheng Manping, Hui XiaoAbstract:Refining microstructure is an important issue for laser additive manufacturing (LAM) of titanium alloy. In the present work, the microstructures of LAM-fabricated Ti6Al4V alloy were refined using a low energy density with the combination of a small spot diameter, a low laser power, and a High Scanning Speed. The microstructure, hardness, wear performance, and molten pool thermal behavior of LAM-fabricated Ti6Al4V coatings were studied. The results show that the grain sizes of both prior β and α phases are strongly dependent on the cooling rate of the molten pool. The fine prior β grains and submicron-scale acicular α phases were obtained under a low energy density of 75 J mm−2 due to the High cooling rate of the molten pool. In addition, the as-fabricated Ti6Al4V sample with submicron-scale acicular α phase showed a very High hardness of 7.43 GPa, a High elastic modulus of 133.6 GPa, and a low coefficient of friction of 0.48. This work provides a good method for improving the microstructure and mechanical performance of LAM-fabricated Ti6Al4V alloy.
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Direct laser cladding of layer-band-free ultrafine Ti6Al4V alloy
Surface and Coatings Technology, 2016Co-Authors: Lijun Song, Hui XiaoAbstract:Abstract Ti6Al4V alloy was fabricated on pure titanium substrate using laser cladding. The effect of Scanning Speed on microstructure, hardness and wear performance of the Ti6Al4V cladding was investigated. The layer-band-like zone, which consists of coarse basket-weave microstructure with short-lamellar α phase and β phase, decreases with the increase of Scanning Speed. Layer-band-free cladding is obtained at a High Scanning Speed. With the increase of the Scanning Speed, the microstructure of the cladding evolves from lamellar or lath-like α/α′ phase to refined acicular α/α′ phase. The ultra-fine microstructure with submicron scaled acicular α/α′ phases (60–400 nm in width) and β phase is obtained under the Scanning Speed of 600 mm min − 1 . The clad exhibits a High hardness of 7.6 GPa, a High elastic modulus of 136.4 GPa, a reduced friction coefficient of 0.46 and a low wear loss of 0.5 mg in dry sliding wear tests. The main worn mechanisms are fatigue and abrasive wear. A rational High Scanning Speed is beneficial to the enhancement of wear performance of the Ti6Al4V cladding, due to the obtained ultra-fine microstructure, High residual stress, High hardness and fatigue strength.
Jan Van Humbeeck - One of the best experts on this subject based on the ideXlab platform.
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Influence of SLM on shape memory and compression behaviour of NiTi scaffolds
CIRP Annals - Manufacturing Technology, 2015Co-Authors: Sasan Dadbakhsh, Jean‐pierre Kruth, Mathew Speirs, Jan Van HumbeeckAbstract:Octahedron-shaped porous scaffolds made from shape memory nickel–titanium (NiTi) were manufactured with different solid volume fractions using selective laser melting (SLM). Various SLM parameters were selected to affect the mechanical behaviour and shape memory response. It was shown that High laser power with High Scanning Speed (HP) parameters reduced the martensitic transformation temperatures as compared to low laser power low Scanning Speed (LP) parameters, resulting in an increased pseudoelastic behaviour (due to presence of austenite at room temperature). HP parameters, however, led to a larger geometrical mismatch with the original design and a Higher solid volume fraction. The compression behaviours were also analysed and exhibited in correlation with the volume fractions.
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Effect of SLM parameters on transformation temperatures of shape memory nickel titanium parts
Advanced Engineering Materials, 2014Co-Authors: Sasan Dadbakhsh, Jean‐pierre Kruth, Mathew Speirs, Jan Luyten, Jan Schrooten, Jan Van HumbeeckAbstract:Selective laser melting (SLM) is used to manufacture dense nickel titanium (NiTi) parts. The reversible martensitic transformation of the NiTi parts is investigated with various SLM parameters. The parameters are in the same energy density range, composed of High laser parameters (HP: High laser power adjusted to High Scanning Speed) and low laser parameters (LP: low laser power adjusted to low Scanning Speed). The results are linked to the mechanical behavior and shape memory response achieved from compression and dilatometry tests. It is shown that the products may exhibit distinct transformation temperatures depending on the used SLM parameters. The atomized powders and the HP SLM parts with dominant pseudoelastic properties contain austenite at room temperature (due to their lower transformation temperatures), in contrast to the large thermal memory of the LP parts originating from martensitic phases (corresponding to Higher transformation temperatures). The post-annealed samples undergo transformations in a comparable temperature range, implying no significant effect of SLM on composition of the originally used powder. The possible origin of the above findings is postulated and discussed.
Lijun Song - One of the best experts on this subject based on the ideXlab platform.
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Enhancing Hardness and Wear Performance of Laser Additive Manufactured Ti6Al4V Alloy Through Achieving Ultrafine Microstructure.
Materials, 2020Co-Authors: Yanqin Li, Lijun Song, Cheng Manping, Hui XiaoAbstract:Refining microstructure is an important issue for laser additive manufacturing (LAM) of titanium alloy. In the present work, the microstructures of LAM-fabricated Ti6Al4V alloy were refined using a low energy density with the combination of a small spot diameter, a low laser power, and a High Scanning Speed. The microstructure, hardness, wear performance, and molten pool thermal behavior of LAM-fabricated Ti6Al4V coatings were studied. The results show that the grain sizes of both prior β and α phases are strongly dependent on the cooling rate of the molten pool. The fine prior β grains and submicron-scale acicular α phases were obtained under a low energy density of 75 J mm−2 due to the High cooling rate of the molten pool. In addition, the as-fabricated Ti6Al4V sample with submicron-scale acicular α phase showed a very High hardness of 7.43 GPa, a High elastic modulus of 133.6 GPa, and a low coefficient of friction of 0.48. This work provides a good method for improving the microstructure and mechanical performance of LAM-fabricated Ti6Al4V alloy.
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Direct laser cladding of layer-band-free ultrafine Ti6Al4V alloy
Surface and Coatings Technology, 2016Co-Authors: Lijun Song, Hui XiaoAbstract:Abstract Ti6Al4V alloy was fabricated on pure titanium substrate using laser cladding. The effect of Scanning Speed on microstructure, hardness and wear performance of the Ti6Al4V cladding was investigated. The layer-band-like zone, which consists of coarse basket-weave microstructure with short-lamellar α phase and β phase, decreases with the increase of Scanning Speed. Layer-band-free cladding is obtained at a High Scanning Speed. With the increase of the Scanning Speed, the microstructure of the cladding evolves from lamellar or lath-like α/α′ phase to refined acicular α/α′ phase. The ultra-fine microstructure with submicron scaled acicular α/α′ phases (60–400 nm in width) and β phase is obtained under the Scanning Speed of 600 mm min − 1 . The clad exhibits a High hardness of 7.6 GPa, a High elastic modulus of 136.4 GPa, a reduced friction coefficient of 0.46 and a low wear loss of 0.5 mg in dry sliding wear tests. The main worn mechanisms are fatigue and abrasive wear. A rational High Scanning Speed is beneficial to the enhancement of wear performance of the Ti6Al4V cladding, due to the obtained ultra-fine microstructure, High residual stress, High hardness and fatigue strength.
Jiangtao Xu - One of the best experts on this subject based on the ideXlab platform.
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a global shutter High Speed tdi cmos image sensor with pipelined charge transfer pixel
IEEE Sensors Journal, 2018Co-Authors: Jiangtao XuAbstract:In this paper, a $120\,\times \, 45$ global shutter High Speed time delay integration (TDI) CMOS image sensor with pipelined charge transfer pixel (PCT-pixel) is presented. Offset free and low noise pipelined signal accumulation are achieved by the PCT-pixel, and a novel layout is also proposed to increase the equivalent photosensitive area’s fill factor of the proposed pixel. Due to the parallelism of the proposed PCT-pixel, global shutter exposure method is applied in this sensor, which can eliminate nonsynchronous signal capturing problem. The proposed TDI sensor is implemented in a 0.11- $\mu \text{m}$ one-poly three-metal CMOS image sensor technology with a line rate of 100 KHz, a PCT-pixel size of $30\,\times \, 15 \,\,\mu \text{m}^{2}$ , and a fill factor of 43.5%. Measurement results show that the sensor can achieve a maximum sensitivity of 95 V/lux $\,\times \, $ sec and an energy consumption of 0.12 nJ/pixel. Measured signal-to-noise ratio boost value follows theoretical value well. The proposed sensor has the potential to achieve High Scanning Speed and High TDI stage while costing less power and silicon area.
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a 128 stage cmos tdi image sensor with on chip digital accumulator
IEEE Sensors Journal, 2016Co-Authors: Jiangtao XuAbstract:A 128-stage CMOS time delay integration (TDI) image sensor with on-chip digital accumulator was presented in this paper. By using two sets of sampling capacitors and an optimized timing, the on-chip column parallel cyclic analog-to-digital converter (ADC) in the sensor conducts the correlated double sampling, digital program gain amplifying, and A/D conversion all altogether in one ADC’s conversion time simultaneously. An on-chip digital accumulator suitable for this sensor is also proposed. A prototype $1024 \times 128$ CMOS TDI image sensor is fabricated in the 0.18- $\mu \text{m}$ CMOS technology, and the measurement results proof that the pixels and readout circuits in the sensor work properly. With a line rate of 3875 lines/s, the sensor costs a power consumption of 290 mW and a silicon area of $18.2~\textrm {mm}\times 18.9$ mm. The estimated maximum sensitivity of the fabricated sensor is 2010 $\textrm {V}/\textrm {lux}\cdot \textrm {sec}$ . This paper is suitable for applications in low-illumination, High Scanning Speed, and remote sensing systems.
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thirty two stage cmos tdi image sensor with on chip analog accumulator
IEEE Transactions on Very Large Scale Integration Systems, 2014Co-Authors: Jiangtao XuAbstract:This brief presents a 32-stage CMOS time delay integration image sensor with on-chip column parallel analog accumulator. Temporal oversampling technique is applied in the sensor to realize synchronous signal capturing. A column parallel analog accumulator with layout size of 0.09 mm2 is integrated at both sides of pixel array. Through adopting input-offset storing technique, a column fixed pattern noise because of the amplifier's offset variations is reduced by the accumulator. The accumulator also acts as a pixel noise canceller. The fabricated chip in 0.18- μm one-poly four-metal 1.8/3.3-V CMOS technology achieves the maximum line rate of 3875 lines/s. The measured signal-to-noise ratio of the fabricated sensor is improved on average by 11.9 dB at 16 stages and 14.2 dB at 32 stages. The presented sensor is suitable for application in low illumination, High Scanning Speed, and remote sensing systems.
Jie Sun - One of the best experts on this subject based on the ideXlab platform.
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Effect of Scanning Speed on the microstructure and mechanical behavior of 316L stainless steel fabricated by selective laser melting
Materials & Design, 2020Co-Authors: Jiangwei Liu, Ya'nan Song, Chaoyue Chen, Xiebin Wang, Chang'an Zhou, Jiang Wang, Kai Guo, Jie SunAbstract:Abstract In this work, the tensile behavior and microhardness of 316L stainless steel fabricated by selective laser melting under different process parameters were investigated. The ultimate tensile strength decreased slightly with increasing energy input, while the opposite tendency was observed for the elongation to failure. Microstructure characterizations were performed to relate the pore morphology, melting pool geometry, solidification cell structure, and grain sizes to the mechanical performance of as-built samples. Fine grains with High fraction of low-angle grain boundaries and fine cellular structures with nano-inclusions are observed in the sample fabricated with a High Scanning Speed (1000 mm/s). As a result, the sample shows High ultimate tensile strength of up to 707 MPa, while maintaining a total elongation of 30%. The sample fabricated with a low Scanning Speed (800 mm/s) shows High ductility with total elongation to failure of 55%. The improved ductility is mainly attributed to the elimination of residual pores and melting pool boundaries, which result in brittle features in the as-built samples. The results indicate that selective laser melting may act as a physical metallurgy method to modify the microstructure, and thus improve the mechanical performance of metallic materials.