The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed ...The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed nano powders(~50 nm average particle size), we are able to sinter W-10Re alloy to 98.4% density below 1200 ℃ while maintaining a fine grain size of 260 nm, and sinter molybdenum to 98.3% density below 1120 ℃ while maintaining a fine grain size of 290 nm. Compared to normal sintering,two-step sintering offers record-fine grain sizes and better microstructural uniformity, which translates to better mechanical properties with higher hardness(6.3 GPa for tungsten-rhenium and 4.0 GPa for molybdenum, both being the highest in all pressurelessly sintered samples of the respective material system)and larger Weibull modulus. Together with our previous demonstration in tungsten, we believe that twostep sintering is a general effective method to produce high-quality fine-grained refractory metals and alloys, and the lessons learned here are transferable to other materials for powder metallurgy.展开更多
Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However...Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However,the sintering concurrently becomes increasingly more difficult with increasing Re contents.Here we proposed that the sintering conundrum is caused by the lowered crystal symmetry and the wider dihedral angle distribution when body-center-cubic(BCC)W is alloyed with more hexagonal-close-packed(HCP)Re,which results in inefficient pore removal in the final stage sintering.We showed that the conundrum can be resolved by pressureless two-step sintering(TSS)which suppresses acceler-ating final-stage grain growth,and our proposal is supported by the data of the critical densityρc that is required to start the second step for successful TSS at different W-Re compositions.Dense ultrafine-grained W-Re alloys with∼300 nm average grain size and up to 25 wt%Re were successfully produced.Our work demonstrates the unique opportunities offered by two-step sintering to advance the scientific understanding and technological practices in powder metallurgy and related fields.展开更多
Three-photon microscopy(3PM)enables high-resolution three-dimensional(3D)imaging in deeply situated and highly scattering biological specimens,facilitating precise characterization of biological morphology and cellula...Three-photon microscopy(3PM)enables high-resolution three-dimensional(3D)imaging in deeply situated and highly scattering biological specimens,facilitating precise characterization of biological morphology and cellular-level physiology in vivo.However,the use of fluorescent probes with relatively low three-photon absorption cross-sections necessitates high-peak-power lasers for excitation,which poses inherent risks of light-induced damage.Additionally,the low repetition frequency of these lasers prolongs scanning time per pixel,hampering imaging speed and exacerbating the potential for photodamage.Such limitations hinder the application of 3PM in studying vulnerable tissues,including muscle regeneration.To address this critical issue,we developed the Multi-Scale Attention Denoising Network(MSAD-Net),a precise and versatile denoising network suitable for diverse structures and varying noise levels.Our network enables the use of lower excitation power(1/4–1/2 of the common power:1.0–1.5 mW vs 4–6 mW)and shorter scanning time(1/6–1/4 of the common time:2–3μs/pixel vs 12μs/pixel)in 3PM while preserving image quality and tissue integrity.It achieves a structural similarity index(SSIM)of with an average of 0.9932 and a fast inference time of just 80 ms per frame which ensured both high fidelity and practicality for downstream applications.By utilizing MSAD-Net-assisted imaging,we characterize the biological morphology and functionality of muscle regeneration processes through deep in vivo five-channel imaging under low excitation power and short scanning time,while maintaining a high signal-to-noise ratio(SNR)and excellent axial spatial resolution.Furthermore,we conducted high axial-resolution dynamic imaging of vascular microcirculation,macrophages,and ghost fibers.Our findings provide a deeper understanding of the mechanisms underlying muscle regeneration at the cellular and tissue levels.展开更多
基金supports by the Natural Science Foundation of China(52074032,51974029,52131307,52071013)and“111”Project(No.B170003).Y.D.and J.L.acknowledge the support by Eni S.p.A.through the MIT Energy Initiative.
文摘The challenge of sintering ultrafine-grained refractory metals and alloys to full density is hereby addressed by pressureless two-step sintering in tungsten-rhenium alloy and pure molybdenum. Using properly processed nano powders(~50 nm average particle size), we are able to sinter W-10Re alloy to 98.4% density below 1200 ℃ while maintaining a fine grain size of 260 nm, and sinter molybdenum to 98.3% density below 1120 ℃ while maintaining a fine grain size of 290 nm. Compared to normal sintering,two-step sintering offers record-fine grain sizes and better microstructural uniformity, which translates to better mechanical properties with higher hardness(6.3 GPa for tungsten-rhenium and 4.0 GPa for molybdenum, both being the highest in all pressurelessly sintered samples of the respective material system)and larger Weibull modulus. Together with our previous demonstration in tungsten, we believe that twostep sintering is a general effective method to produce high-quality fine-grained refractory metals and alloys, and the lessons learned here are transferable to other materials for powder metallurgy.
基金This work is financially supported by National Key R&D Pro-gram of China(no.2022YFB3700075)Natural Science Foundation of China(nos.52074032,51974029,52071013,52130407)+3 种基金Beijing Natural Science Foundation(no.2232084)Guangdong Basic and Applied Basic Research Foundation(no.2021B1515120033)Basic and Applied Basic Research Fund of Guangdong Province(no.BK20BE015)111 Project(no.B170003).
文摘Tungsten-rhenium(W-Re)alloys with high-Re contents are the preferred refractory metal materials in many applications because of the improved ductility and processability over pure W and low-Re tung-sten alloys.However,the sintering concurrently becomes increasingly more difficult with increasing Re contents.Here we proposed that the sintering conundrum is caused by the lowered crystal symmetry and the wider dihedral angle distribution when body-center-cubic(BCC)W is alloyed with more hexagonal-close-packed(HCP)Re,which results in inefficient pore removal in the final stage sintering.We showed that the conundrum can be resolved by pressureless two-step sintering(TSS)which suppresses acceler-ating final-stage grain growth,and our proposal is supported by the data of the critical densityρc that is required to start the second step for successful TSS at different W-Re compositions.Dense ultrafine-grained W-Re alloys with∼300 nm average grain size and up to 25 wt%Re were successfully produced.Our work demonstrates the unique opportunities offered by two-step sintering to advance the scientific understanding and technological practices in powder metallurgy and related fields.
基金supported by the National Key R&D Program of China(2022YFB3206000)Dr.Li Dak Sum&Yip Yio Chin Development Fund for Regenerative Medicine,Zhejiang University,National Natural Science Foundation of China(61975172)Postdoctoral Fellowship Program of CPSF under Grant Number GZB20240646.
文摘Three-photon microscopy(3PM)enables high-resolution three-dimensional(3D)imaging in deeply situated and highly scattering biological specimens,facilitating precise characterization of biological morphology and cellular-level physiology in vivo.However,the use of fluorescent probes with relatively low three-photon absorption cross-sections necessitates high-peak-power lasers for excitation,which poses inherent risks of light-induced damage.Additionally,the low repetition frequency of these lasers prolongs scanning time per pixel,hampering imaging speed and exacerbating the potential for photodamage.Such limitations hinder the application of 3PM in studying vulnerable tissues,including muscle regeneration.To address this critical issue,we developed the Multi-Scale Attention Denoising Network(MSAD-Net),a precise and versatile denoising network suitable for diverse structures and varying noise levels.Our network enables the use of lower excitation power(1/4–1/2 of the common power:1.0–1.5 mW vs 4–6 mW)and shorter scanning time(1/6–1/4 of the common time:2–3μs/pixel vs 12μs/pixel)in 3PM while preserving image quality and tissue integrity.It achieves a structural similarity index(SSIM)of with an average of 0.9932 and a fast inference time of just 80 ms per frame which ensured both high fidelity and practicality for downstream applications.By utilizing MSAD-Net-assisted imaging,we characterize the biological morphology and functionality of muscle regeneration processes through deep in vivo five-channel imaging under low excitation power and short scanning time,while maintaining a high signal-to-noise ratio(SNR)and excellent axial spatial resolution.Furthermore,we conducted high axial-resolution dynamic imaging of vascular microcirculation,macrophages,and ghost fibers.Our findings provide a deeper understanding of the mechanisms underlying muscle regeneration at the cellular and tissue levels.
