Ceramic is an important material with outstanding physical properties whereas impurities and porosities generated by traditional manufacturing methods limits its further industrial applications. In order to solve this...Ceramic is an important material with outstanding physical properties whereas impurities and porosities generated by traditional manufacturing methods limits its further industrial applications. In order to solve this problem, direct fabrication of Al2O3 ceramic structures is conducted by laser engineered net shaping system and pure ceramic powders. Grain refinement strengthening method by doping Zr O2 and dispersion strengthening method by doping Si C are proposed to suppress cracks in fabricating Al2O3 structure. Phase compositions, microstructures as well as mechanical properties of fabricated specimens are then analyzed. The results show that the proposed two methods are effective in suppressing cracks and structures of single-bead wall, arc and cylinder ring are successfully deposited. Stable phase of α-Al2O3 and t-Zr O2 are obtained in the fabricated specimens. Micro-hardness higher than 1700 HV are also achieved for both Al2O3 and Al2O3/Zr O2, which are resulted from fine directional crystals generated by the melting-solidification process. Results presented indicate that additive manufacturing is a very attractive technique for the production of high-performance ceramic structures in a single step.展开更多
Al7075 alloy is a typical aviation aluminum with good mechanical properties and anodic oxidation effect.Laser engineered net shaping technology has unique advantages in the integrated forming of high-performance large...Al7075 alloy is a typical aviation aluminum with good mechanical properties and anodic oxidation effect.Laser engineered net shaping technology has unique advantages in the integrated forming of high-performance large aircraft structural parts.The manufacturing of 7075 aluminum alloy structural parts by laser engineered net shaping technology has become an important development direction in the future aerospace field.Electrochemical corrosion resistance of aluminum alloys is of vital importance to improve reliability and life-span of lightweight components.A comparative study on microstructure and anti-corrosion performance of Al7075 alloy prepared by laser additive manufacturing and forging technology was conducted.There are hole defects in LENS-fabricated Al7075 alloy with uniformly distributedηphase.No defects are observed in Al7075 forgings.The large S phase particles and small ellipsoidalηphase particles are found in Al matrix.The corrosion mechanisms were revealed according to the analysis of polarization curves and corrosion morphology.It was found that compared with that prepared by forgings,the additive manufactured samples have lower corrosion tendency and higher corrosion rate.Corrosion occurred preferentially at the hole defects.The incomplete passivation film at the defects leads to the formation of a local cell composed of the internal Al,corrosion solution and the surrounding passive film,which further aggravates the corrosion.展开更多
In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process i...In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made.Then,the establishment process of the multi-physical field model of the melt pool is introduced in detail.It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile,space temperature gradient,and time temperature gradient.Meanwhile,some parameters,such as the 3D morphology and surface fluid field of the melt pool,which are not obtained in the online measurement experiment,are analyzed.Finally,the influence of changing the scanning speed on the profile,peak temperature,and temperature gradient of the single-line melt pool is also analyzed,and the following conclusions are obtained:With the increase in scanning speed,the profile of the melt pool gradually becomes slender;The relationship between peak temperature and scanning speed is approximately linear in a certain speed range;The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed,and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.展开更多
The present study describes the experiments on the application of geopolymer paste for groutless in situ casting or flooring. The paste was synthesized from fly ash and sodium silicate solution and cured at room tempe...The present study describes the experiments on the application of geopolymer paste for groutless in situ casting or flooring. The paste was synthesized from fly ash and sodium silicate solution and cured at room temperature, 60 and 80℃ for 24 hours. To simulate flooring application, the geopolymer paste was casted on Portland cement cubes which have been fully hydrated for 28 days. Silica fume was added to reduce cracks but at the same time compressive strength decreased. Averaged compressive strength decreased from 53 MPa to 37 MPa for paste cured at 60℃. Curing at higher temperatures produced stronger geopolymer, with compressive strength of 12 MPa, 53 MPa and 67 MPa for geopolymer cured at room temperature, 60℃ and 80℃ respectively, however, higher curing temperature resulted in more cracking when the geopolymer paste was applied on the Portland cement substrate. Averaged hardness values were 65 and 43 Brinnel scale （BHN）, and wear rate, measured using Ogoshi machine, were 0.66 and 1.80 mm3/min for samples cured at 60 and 80℃ respectively. Unless surface hardening was applied, the material is not suitable for flooring but do so for decorative masonry.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51175061,51402037)Science Fund for Creative Research Groups(Grant No.51321004)+1 种基金National Basic Research Program of China(973 Program,Grant No.2015CB057305)China Postdoctoral Science Foundation Funded Project(Grant No.2014M551072)
文摘Ceramic is an important material with outstanding physical properties whereas impurities and porosities generated by traditional manufacturing methods limits its further industrial applications. In order to solve this problem, direct fabrication of Al2O3 ceramic structures is conducted by laser engineered net shaping system and pure ceramic powders. Grain refinement strengthening method by doping Zr O2 and dispersion strengthening method by doping Si C are proposed to suppress cracks in fabricating Al2O3 structure. Phase compositions, microstructures as well as mechanical properties of fabricated specimens are then analyzed. The results show that the proposed two methods are effective in suppressing cracks and structures of single-bead wall, arc and cylinder ring are successfully deposited. Stable phase of α-Al2O3 and t-Zr O2 are obtained in the fabricated specimens. Micro-hardness higher than 1700 HV are also achieved for both Al2O3 and Al2O3/Zr O2, which are resulted from fine directional crystals generated by the melting-solidification process. Results presented indicate that additive manufacturing is a very attractive technique for the production of high-performance ceramic structures in a single step.
基金Project(2016YFB1100101)supported by the National Key Research and Development Program of China。
文摘Al7075 alloy is a typical aviation aluminum with good mechanical properties and anodic oxidation effect.Laser engineered net shaping technology has unique advantages in the integrated forming of high-performance large aircraft structural parts.The manufacturing of 7075 aluminum alloy structural parts by laser engineered net shaping technology has become an important development direction in the future aerospace field.Electrochemical corrosion resistance of aluminum alloys is of vital importance to improve reliability and life-span of lightweight components.A comparative study on microstructure and anti-corrosion performance of Al7075 alloy prepared by laser additive manufacturing and forging technology was conducted.There are hole defects in LENS-fabricated Al7075 alloy with uniformly distributedηphase.No defects are observed in Al7075 forgings.The large S phase particles and small ellipsoidalηphase particles are found in Al matrix.The corrosion mechanisms were revealed according to the analysis of polarization curves and corrosion morphology.It was found that compared with that prepared by forgings,the additive manufactured samples have lower corrosion tendency and higher corrosion rate.Corrosion occurred preferentially at the hole defects.The incomplete passivation film at the defects leads to the formation of a local cell composed of the internal Al,corrosion solution and the surrounding passive film,which further aggravates the corrosion.
基金This work was financially supported by the National Key R&D Program of China(Grant No.2017YFB1103900)National Natural Science Foundation of China(Grant No.11972084)+1 种基金National Science and Technology Major Project(2017-VI-0003-0073)Beijing National Science Foundation(1192014).
文摘In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made.Then,the establishment process of the multi-physical field model of the melt pool is introduced in detail.It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile,space temperature gradient,and time temperature gradient.Meanwhile,some parameters,such as the 3D morphology and surface fluid field of the melt pool,which are not obtained in the online measurement experiment,are analyzed.Finally,the influence of changing the scanning speed on the profile,peak temperature,and temperature gradient of the single-line melt pool is also analyzed,and the following conclusions are obtained:With the increase in scanning speed,the profile of the melt pool gradually becomes slender;The relationship between peak temperature and scanning speed is approximately linear in a certain speed range;The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed,and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.
文摘The present study describes the experiments on the application of geopolymer paste for groutless in situ casting or flooring. The paste was synthesized from fly ash and sodium silicate solution and cured at room temperature, 60 and 80℃ for 24 hours. To simulate flooring application, the geopolymer paste was casted on Portland cement cubes which have been fully hydrated for 28 days. Silica fume was added to reduce cracks but at the same time compressive strength decreased. Averaged compressive strength decreased from 53 MPa to 37 MPa for paste cured at 60℃. Curing at higher temperatures produced stronger geopolymer, with compressive strength of 12 MPa, 53 MPa and 67 MPa for geopolymer cured at room temperature, 60℃ and 80℃ respectively, however, higher curing temperature resulted in more cracking when the geopolymer paste was applied on the Portland cement substrate. Averaged hardness values were 65 and 43 Brinnel scale （BHN）, and wear rate, measured using Ogoshi machine, were 0.66 and 1.80 mm3/min for samples cured at 60 and 80℃ respectively. Unless surface hardening was applied, the material is not suitable for flooring but do so for decorative masonry.
