The plastic anisotropy of sheet metal is usually caused by preferred orientation of grains, developed by mechanical deformation and thermal treatment. In the present study, a Taylor-like polycrystal model suggested by...The plastic anisotropy of sheet metal is usually caused by preferred orientation of grains, developed by mechanical deformation and thermal treatment. In the present study, a Taylor-like polycrystal model suggested by Asaro and Needleman is applied to investigate the evolution of the anisotropic behavior of a face centered cubic (FCC) polycrystalline metal, which is considered having {111} 110 slip systems, by stretching it along an arbitrary direction after it has undergone a plane-strain compression that rationally simulates the cold rolling process of FCC polycrystalline pure aluminium. By using the Taylor-like polycrystal model, pole fgures are obtained to describe the texture development of polycrystalline aggregate after plane-strain compression, and then the plastic anisotropy of polycrystalline aggregate is evaluated by stretch- ing the polycrystalline aggregate in different direction in term of yield stress. According to the results, the contours of longitudinal fow stress in three-dimensional orientation space are given and analyzed. Experiment results similar to the prediction of planar anisotropy can be found in the literature written by Takahashi et al. that indirectly show the correctness of the prediction of non-planar plastic anisotropy by this analysis.展开更多
The effects of microstructure and its evolution on the macroscopic superelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)are studied by a microstructure-based constitutive model developed in th...The effects of microstructure and its evolution on the macroscopic superelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)are studied by a microstructure-based constitutive model developed in this paper.The model is established on the following basis:(1)the transformation conditions of the unconstrained single crystal SMA microdomain(to be distinguished from the bulk single crystal),which serve as the local criterion for the derivation of overall transfor- mation yield conditions of the polycrystal;(2)the micro-to macro-transition scheme by which the connection between the polycrystal aggregates and the single crystal microdomain is established and the macroscopic transformation conditions of the polycrystal SMA are derived;(3)the quantitative incorporation of three microstruc- ture factors(i.e.,nucleation,growth and orientation distribution of martensite)into the modeling.These microstructural factors are intrinsic of specific polycrystal SMA systems and the role of each factor in the macroscopic constitutive response is quan- titatively modeled.It is demonstrated that the interplay of these factors will result in different macroscopic transformation kinematics and kinetics which are responsible for the observed macroscopic stress-strain hardening or softening response,the latter will lead to the localization and propagation of transformation bands in TiNi SMA.展开更多
Based on the microstructure-based constitutive model established in Part Ⅰ,a detailed numerical investigation on the role of each microstructure pa- rameter in the kinematical and kinetic evolution of polycrystalline...Based on the microstructure-based constitutive model established in Part Ⅰ,a detailed numerical investigation on the role of each microstructure pa- rameter in the kinematical and kinetic evolution of polycrystalline SMA under ax- isymmetrical tension loading is performed.Some macroscopic constitutive features of stress-induced martensite transformation are discussed.展开更多
A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and...A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and the sensitivity of the various cohesive zone parameters in predicting the overall mechanical response are investigated.The overall strength is predominantly determined by the weak grain interfaces;both the grain aggregate morphology and the weak grain interfaces control the crack configuration;the different normal and tangential strengths of grain interfaces result in different intergranular cracking behaviors and play a critical role in determining the macroscopic mechanical response of the system.展开更多
With the advantages of high deposition rate and large deposition area, polycrystalline diamond films prepared by direct current (DC) arc jet chemical vapor deposition (CVD) are considered to be one of the most pro...With the advantages of high deposition rate and large deposition area, polycrystalline diamond films prepared by direct current (DC) arc jet chemical vapor deposition (CVD) are considered to be one of the most promising materials for high-frequency and high-power electronic devices. In this paper, high-quality self-standing polycrystalline diamond films with the diameter of 100 mm were prepared by DC arc jet CVD, and then, the p-type surface conductive layer with the sheet carrier density of 10^11-10^13 cm-2 on the H-terminated diamond film was obtained by micro-wave hydrogen plasma treatment for 40 min. Ti/Au and Au films were deposited on the H-terminated diamond surface as the ohmic contact electrode, respectively, afterwards, they were treated by rapid vacuum annealing at different temperatures. The properties of these two types of ohmic contacts were investigated by measuring the specific contact resistance using the transmission line method (TLM). Due to the formation of Ti-related carbide at high temperature, the specific contact resistance of Ti/Au contact gradually decreases to 9.95 × 10^-5 Ω-cm2 as the temperature increases to 820℃. However, when the annealing temperature reaches 850℃, the ohmic contact for Ti/Au is degraded significantly due to the strong diffusion and reaction between Ti and Au. As for the as-deposited Au contact, it shows an ohmic contact. After annealing treatment at 550℃, low specific contact resistance was detected for Au contact, which is derived from the enhancement of interdiffusion between Au and diamond films.展开更多
Aluminum-induced crystallized silicon films were prepared on glass substrates by magnetron sputtering. Aluminum was added in the silicon films intermittently by the regular pulse sputtering of an aluminum target. The ...Aluminum-induced crystallized silicon films were prepared on glass substrates by magnetron sputtering. Aluminum was added in the silicon films intermittently by the regular pulse sputtering of an aluminum target. The amount of aluminum in the silicon films can be controlled by regulating the aluminum sputtering power and the sputtering time of the undoped silicon layer; thus, the Seebeck coefficient and electrical resistivity of the polyerystaUine silicon films can be adjusted. It is found that, when the sputtering power ratio of aluminum to silicon is 16%, both the Seebeck coefficient and the electrical resistivity decrease with the increasing amount of aluminum as expected; the Seebeck coefficient and the electrical resistivity at room temperature are 0.185-0.285 mV/K and 0.30-2.4 Ω.cm, respectively. By reducing the sputtering power ratio to 7%, however, the Seebeck coefficient does not change much, though the electrical resistivity still decreases with the amount of aluminum increasing; the Seebeck coefficient and electrical resistivity at room temperature are 0.219-0.263 mV/K and 0.26-0.80 Ω·cm, respectively.展开更多
During heat treatment or mechanical processing,most polycrystalline materials experience grain growth,which significantly affects their mechanical properties.Microstructure simulation on a mesoscopic scale is an impor...During heat treatment or mechanical processing,most polycrystalline materials experience grain growth,which significantly affects their mechanical properties.Microstructure simulation on a mesoscopic scale is an important way of studying grain growth.A key research focus of this type of method has long been how to efficiently and accurately simulate the grain growth caused by a non-uniform temperature field with temperature gradients.In this work,we propose an improved 3D Monte Carlo Potts(MCP)method to quantitatively study the relationship between non-uniform temperature fields and final grain morphologies.Properties of the aluminum alloy AA6061-T6 are used to establish a trial calculation model and to verify the algorithms with existing experimental results in literature.The detailed grain growth process of the 6061-T6 aluminum alloy under different temperature fields is then obtained,and grain morphologies at various positions are analyzed.Results indicate that while absolute temperature and duration time are the primary factors determining the final grain size,the temperature gradient also has strong influence on the grain morphologies.The relationships between temperatures,temperature gradients and grain growth process have been established.The proposed MCP algorithm can be applied to different types of materials when the proper parameters are used.展开更多
A suitable model is developed through the revision of the maximum entropy method (MEM) for the orientation distribution function (ODF) determination from one complete pole figure in the case of cubic materials. Its re...A suitable model is developed through the revision of the maximum entropy method (MEM) for the orientation distribution function (ODF) determination from one complete pole figure in the case of cubic materials. Its relevant software is demonstrated by a group of coefficients of the ODF and an experimental test of an Al-Li alloy. The results confirm that the model proposed in this study is accurate and reliable展开更多
A crystal-plasticity cyclic constitutive model of polycrystalline material considering intra-granular heterogeneous dislocation substructures,in terms of three dislocation categories:mobile dislocations,immobile dislo...A crystal-plasticity cyclic constitutive model of polycrystalline material considering intra-granular heterogeneous dislocation substructures,in terms of three dislocation categories:mobile dislocations,immobile dislocations in the cell interiors and in the cell walls,is proposed based on the existing microscopic and macroscopic experimental results.The multiplication,annihilation,rearrangement and immobilization of dislocations on each slip system are taken as the basic evolutionary mechanism of the three dislocation categories,and the cross-slip of screw dislocations is viewed as the dynamic recovery mechanism at room temperature.The slip resistance associated with the isotropic hardening rule results from the interactions of dislocations on the slip systems.Meanwhile,a modified nonlinear kinematic hardening rule and a rate-dependent flow rule at the slip system level are employed to improve the predictive capability of the model for ratchetting deformation.The predictive ability of the developed model to uniaxial and mul-tiaxial ratchetting in macroscopic scale is verified by comparing with the experimental results of polycrystalline 316L stainless steel.The ratchetting in intra-granular scale which is obviously dependent on the crystallographic orientation and stress levels can be reasonably predicted by the proposed model.展开更多
In this Letter, ceramic Nd:YAG is charactrizeby electron spin resonance (ESR) measurements. The ESR results indicate that the polycrystalline ceramic Nd:YAG has barely native defects and impurity ions localization...In this Letter, ceramic Nd:YAG is charactrizeby electron spin resonance (ESR) measurements. The ESR results indicate that the polycrystalline ceramic Nd:YAG has barely native defects and impurity ions localization defects, compared to an Nd:YAG crystal with the same Nd doping concentration, due to its density structure by sintering in a vacuum pure raw material and additives during the fabrication. It may conclude that the high quality ceramic Nd:YAG may have greater ability on optical characteristic, mechanical performance, and laser damage than that of the crystals, which is a promising candidate to use on laser diode-pumped solid-state lasers.展开更多
Predicting rolling bearing fatigue life requires knowledge of the three-dimensional(3D)stress fields in the roller and raceway near the lubricated contact.Owing to the increasingly severe operating conditions,the effe...Predicting rolling bearing fatigue life requires knowledge of the three-dimensional(3D)stress fields in the roller and raceway near the lubricated contact.Owing to the increasingly severe operating conditions,the effect of localized features such as surface roughness,subsurface inclusions,and even the crystallographic structure of the material becomes important.Achieving such detail requires(locally)extremely dense gridding in simulations,which in 3D is a major challenge.Multigrid techniques have been demonstrated to be capable of solving such problems.In this study,multigrid techniques are shown to further increase the efficiency of the solution by exploiting local grid refinement while maintaining the simplicity of a uniform discretization.This is achieved by employing increasingly finer grids only locally,where the highest resolution is required.Results are presented for dry contact and elastohydrodynamically lubricated contact cases,circular as well as elliptic,with varying crystallographic structure,and with surface roughness.The results show that the developed algorithm is very well suited for detailed analysis,with also excellent prospects for computational diagnostics involving actual material crystallographic structure from electron backscatter diffraction measurements.展开更多
ZrO2 thin films were prepared in electron beam thermal evaporation method. And the deposition rate changed from 1.3 to 6.3 nm/s in our study. X-ray diffractometer and spectrophotometer were employed to characterize th...ZrO2 thin films were prepared in electron beam thermal evaporation method. And the deposition rate changed from 1.3 to 6.3 nm/s in our study. X-ray diffractometer and spectrophotometer were employed to characterize the films. X-ray diffraction (XRD) spectra pattern shows that films structure changed from amorphous to polycrystalline with deposition rate increasing. The results indicate that internal stresses of the films are compressive in most case. Thin films deposited in our study are inhomogeneous, and the inhomogeneity is enhanced with the deposition rate increasing.展开更多
Using LiF and YF3 as starting materials,we prepare feed material from fluorides according to the molar ratio of LiF:YF3=51.5:48.5.The anhydrous LiYF4 polycrystalline material is synthesized via the fluoridation proc...Using LiF and YF3 as starting materials,we prepare feed material from fluorides according to the molar ratio of LiF:YF3=51.5:48.5.The anhydrous LiYF4 polycrystalline material is synthesized via the fluoridation process with a dried HF flow at elevated temperature.By charging the feed material and adding a small amount of active carbon powder in a sealed platinum crucible,the crystal can be grown via the vertical Bridgman method in a nonvacuum atmosphere.This is possible because the oxidization and volatilization of the melt is avoided.Using optimum conditions,that is,a growth rate of 0.5-0.6 mm/h and a temperature gradient of 25-30℃/cm across the solid-liquid interface under a furnace temperature of 920-930℃,the colorless crystal LiYF 4 with the size of φ25 × 50 (mm) is successfully grown.The optical transmittance of the crystal is as high as 85% above the absorption edge at 190 nm.The induced absorption bands are observed below 700 nm in the transmission spectrum after the crystal is subjected to a high dose of γ-ray irradiation.展开更多
The optical property, structure, surface properties (roughness and defect density) and laser-induced damage threshold (LIDT) of TiO2 films deposited by electronic beam (EB) evaporation of TiO2 (rutile), TiO2 ...The optical property, structure, surface properties (roughness and defect density) and laser-induced damage threshold (LIDT) of TiO2 films deposited by electronic beam (EB) evaporation of TiO2 (rutile), TiO2 (anatase) and TiO2 + Ta205 composite materials are comparatively studied. All films show the polycrystalline anatase TiO2 structure. The loose sintering state and phase transformation during evaporating TiO2 anatase slice lead to the high surface defect density, roughness and extinction coefficient, and low LIDT of films. The TiO2 + Ta205 composite films have the lowest extinction coefficient and the highest LIDT among all samples investigated. Guidance of selecting materials for high LIDT laser mirrors is given.展开更多
基金Project supported by the National Natural Science Foundation of China(No.50371070),the Aviation Science Foun-dation of China(No.01C53015)and the Doctoral Foundation of Northwestern Polytechnical University.
文摘The plastic anisotropy of sheet metal is usually caused by preferred orientation of grains, developed by mechanical deformation and thermal treatment. In the present study, a Taylor-like polycrystal model suggested by Asaro and Needleman is applied to investigate the evolution of the anisotropic behavior of a face centered cubic (FCC) polycrystalline metal, which is considered having {111} 110 slip systems, by stretching it along an arbitrary direction after it has undergone a plane-strain compression that rationally simulates the cold rolling process of FCC polycrystalline pure aluminium. By using the Taylor-like polycrystal model, pole fgures are obtained to describe the texture development of polycrystalline aggregate after plane-strain compression, and then the plastic anisotropy of polycrystalline aggregate is evaluated by stretch- ing the polycrystalline aggregate in different direction in term of yield stress. According to the results, the contours of longitudinal fow stress in three-dimensional orientation space are given and analyzed. Experiment results similar to the prediction of planar anisotropy can be found in the literature written by Takahashi et al. that indirectly show the correctness of the prediction of non-planar plastic anisotropy by this analysis.
基金The project supported by the Research Grant Committee(RGC)of Hong Kong SARthe National Natural Science Foundation of China and the Provincial Natural Foundation of Jiangxi Province of China
文摘The effects of microstructure and its evolution on the macroscopic superelastic stress-strain response of polycrystalline Shape Memory Alloy(SMA)are studied by a microstructure-based constitutive model developed in this paper.The model is established on the following basis:(1)the transformation conditions of the unconstrained single crystal SMA microdomain(to be distinguished from the bulk single crystal),which serve as the local criterion for the derivation of overall transfor- mation yield conditions of the polycrystal;(2)the micro-to macro-transition scheme by which the connection between the polycrystal aggregates and the single crystal microdomain is established and the macroscopic transformation conditions of the polycrystal SMA are derived;(3)the quantitative incorporation of three microstruc- ture factors(i.e.,nucleation,growth and orientation distribution of martensite)into the modeling.These microstructural factors are intrinsic of specific polycrystal SMA systems and the role of each factor in the macroscopic constitutive response is quan- titatively modeled.It is demonstrated that the interplay of these factors will result in different macroscopic transformation kinematics and kinetics which are responsible for the observed macroscopic stress-strain hardening or softening response,the latter will lead to the localization and propagation of transformation bands in TiNi SMA.
基金The subject supported by the Research Grant Committee(RGC)of Hong Kong SARthe National Natural Science Foundation of China and the Provincial Natural Science Foundation of Jiangxi Province of China
文摘Based on the microstructure-based constitutive model established in Part Ⅰ,a detailed numerical investigation on the role of each microstructure pa- rameter in the kinematical and kinetic evolution of polycrystalline SMA under ax- isymmetrical tension loading is performed.Some macroscopic constitutive features of stress-induced martensite transformation are discussed.
基金supported by the NationalNatural Science Foundation of China (NSFC) under Grant 11872078,and Beijing Natural Science Foundation No.3222005.
文摘A micromechanical model is presented to study the initiation and propagation of microcracks of intermetallic compounds(IMCs)in solder joints.The effects of the grain aggregate morphology,the grain boundary defects and the sensitivity of the various cohesive zone parameters in predicting the overall mechanical response are investigated.The overall strength is predominantly determined by the weak grain interfaces;both the grain aggregate morphology and the weak grain interfaces control the crack configuration;the different normal and tangential strengths of grain interfaces result in different intergranular cracking behaviors and play a critical role in determining the macroscopic mechanical response of the system.
基金financially supported by the National Natural Science Foundation of China (No. 51272024)the Ph.D. Programs Foundation of the Ministry of Education of China (No. 20110006110011)the Fundamental Research Funds for Central Universities (No. FRF-TP-13-035A)
文摘With the advantages of high deposition rate and large deposition area, polycrystalline diamond films prepared by direct current (DC) arc jet chemical vapor deposition (CVD) are considered to be one of the most promising materials for high-frequency and high-power electronic devices. In this paper, high-quality self-standing polycrystalline diamond films with the diameter of 100 mm were prepared by DC arc jet CVD, and then, the p-type surface conductive layer with the sheet carrier density of 10^11-10^13 cm-2 on the H-terminated diamond film was obtained by micro-wave hydrogen plasma treatment for 40 min. Ti/Au and Au films were deposited on the H-terminated diamond surface as the ohmic contact electrode, respectively, afterwards, they were treated by rapid vacuum annealing at different temperatures. The properties of these two types of ohmic contacts were investigated by measuring the specific contact resistance using the transmission line method (TLM). Due to the formation of Ti-related carbide at high temperature, the specific contact resistance of Ti/Au contact gradually decreases to 9.95 × 10^-5 Ω-cm2 as the temperature increases to 820℃. However, when the annealing temperature reaches 850℃, the ohmic contact for Ti/Au is degraded significantly due to the strong diffusion and reaction between Ti and Au. As for the as-deposited Au contact, it shows an ohmic contact. After annealing treatment at 550℃, low specific contact resistance was detected for Au contact, which is derived from the enhancement of interdiffusion between Au and diamond films.
基金financially supported by the Ministry of Science and Technology of China under a Joint Research Program of China-Japan-Korea(No.2010DFA62170)the National Natural Science Foundation of China(No.51172123)
文摘Aluminum-induced crystallized silicon films were prepared on glass substrates by magnetron sputtering. Aluminum was added in the silicon films intermittently by the regular pulse sputtering of an aluminum target. The amount of aluminum in the silicon films can be controlled by regulating the aluminum sputtering power and the sputtering time of the undoped silicon layer; thus, the Seebeck coefficient and electrical resistivity of the polyerystaUine silicon films can be adjusted. It is found that, when the sputtering power ratio of aluminum to silicon is 16%, both the Seebeck coefficient and the electrical resistivity decrease with the increasing amount of aluminum as expected; the Seebeck coefficient and the electrical resistivity at room temperature are 0.185-0.285 mV/K and 0.30-2.4 Ω.cm, respectively. By reducing the sputtering power ratio to 7%, however, the Seebeck coefficient does not change much, though the electrical resistivity still decreases with the amount of aluminum increasing; the Seebeck coefficient and electrical resistivity at room temperature are 0.219-0.263 mV/K and 0.26-0.80 Ω·cm, respectively.
基金The authors would like to acknowledge the financial support from China Postdoctoral Science Foundation Project(2018M641128)the National Key Research and Development Program of China(2018YFB0703500).
文摘During heat treatment or mechanical processing,most polycrystalline materials experience grain growth,which significantly affects their mechanical properties.Microstructure simulation on a mesoscopic scale is an important way of studying grain growth.A key research focus of this type of method has long been how to efficiently and accurately simulate the grain growth caused by a non-uniform temperature field with temperature gradients.In this work,we propose an improved 3D Monte Carlo Potts(MCP)method to quantitatively study the relationship between non-uniform temperature fields and final grain morphologies.Properties of the aluminum alloy AA6061-T6 are used to establish a trial calculation model and to verify the algorithms with existing experimental results in literature.The detailed grain growth process of the 6061-T6 aluminum alloy under different temperature fields is then obtained,and grain morphologies at various positions are analyzed.Results indicate that while absolute temperature and duration time are the primary factors determining the final grain size,the temperature gradient also has strong influence on the grain morphologies.The relationships between temperatures,temperature gradients and grain growth process have been established.The proposed MCP algorithm can be applied to different types of materials when the proper parameters are used.
文摘A suitable model is developed through the revision of the maximum entropy method (MEM) for the orientation distribution function (ODF) determination from one complete pole figure in the case of cubic materials. Its relevant software is demonstrated by a group of coefficients of the ODF and an experimental test of an Al-Li alloy. The results confirm that the model proposed in this study is accurate and reliable
基金This research is supported by the National Natural Science Foundation of China(11790282,U1534204,11472179)the Natural Science Foundation of Hebei Province(A2016210099).
文摘A crystal-plasticity cyclic constitutive model of polycrystalline material considering intra-granular heterogeneous dislocation substructures,in terms of three dislocation categories:mobile dislocations,immobile dislocations in the cell interiors and in the cell walls,is proposed based on the existing microscopic and macroscopic experimental results.The multiplication,annihilation,rearrangement and immobilization of dislocations on each slip system are taken as the basic evolutionary mechanism of the three dislocation categories,and the cross-slip of screw dislocations is viewed as the dynamic recovery mechanism at room temperature.The slip resistance associated with the isotropic hardening rule results from the interactions of dislocations on the slip systems.Meanwhile,a modified nonlinear kinematic hardening rule and a rate-dependent flow rule at the slip system level are employed to improve the predictive capability of the model for ratchetting deformation.The predictive ability of the developed model to uniaxial and mul-tiaxial ratchetting in macroscopic scale is verified by comparing with the experimental results of polycrystalline 316L stainless steel.The ratchetting in intra-granular scale which is obviously dependent on the crystallographic orientation and stress levels can be reasonably predicted by the proposed model.
文摘In this Letter, ceramic Nd:YAG is charactrizeby electron spin resonance (ESR) measurements. The ESR results indicate that the polycrystalline ceramic Nd:YAG has barely native defects and impurity ions localization defects, compared to an Nd:YAG crystal with the same Nd doping concentration, due to its density structure by sintering in a vacuum pure raw material and additives during the fabrication. It may conclude that the high quality ceramic Nd:YAG may have greater ability on optical characteristic, mechanical performance, and laser damage than that of the crystals, which is a promising candidate to use on laser diode-pumped solid-state lasers.
文摘Predicting rolling bearing fatigue life requires knowledge of the three-dimensional(3D)stress fields in the roller and raceway near the lubricated contact.Owing to the increasingly severe operating conditions,the effect of localized features such as surface roughness,subsurface inclusions,and even the crystallographic structure of the material becomes important.Achieving such detail requires(locally)extremely dense gridding in simulations,which in 3D is a major challenge.Multigrid techniques have been demonstrated to be capable of solving such problems.In this study,multigrid techniques are shown to further increase the efficiency of the solution by exploiting local grid refinement while maintaining the simplicity of a uniform discretization.This is achieved by employing increasingly finer grids only locally,where the highest resolution is required.Results are presented for dry contact and elastohydrodynamically lubricated contact cases,circular as well as elliptic,with varying crystallographic structure,and with surface roughness.The results show that the developed algorithm is very well suited for detailed analysis,with also excellent prospects for computational diagnostics involving actual material crystallographic structure from electron backscatter diffraction measurements.
文摘ZrO2 thin films were prepared in electron beam thermal evaporation method. And the deposition rate changed from 1.3 to 6.3 nm/s in our study. X-ray diffractometer and spectrophotometer were employed to characterize the films. X-ray diffraction (XRD) spectra pattern shows that films structure changed from amorphous to polycrystalline with deposition rate increasing. The results indicate that internal stresses of the films are compressive in most case. Thin films deposited in our study are inhomogeneous, and the inhomogeneity is enhanced with the deposition rate increasing.
基金supported by the Natural Science Foundation of Zhejiang Province(No. Y4090057)the Natural Science Foundation of Ningbo City(No.2009610016)+1 种基金the support extended by the Personnel Training Project of the Zhejiang Education Departmentsponsored by the K. C. Wong Magna Fund of Ningbo University
文摘Using LiF and YF3 as starting materials,we prepare feed material from fluorides according to the molar ratio of LiF:YF3=51.5:48.5.The anhydrous LiYF4 polycrystalline material is synthesized via the fluoridation process with a dried HF flow at elevated temperature.By charging the feed material and adding a small amount of active carbon powder in a sealed platinum crucible,the crystal can be grown via the vertical Bridgman method in a nonvacuum atmosphere.This is possible because the oxidization and volatilization of the melt is avoided.Using optimum conditions,that is,a growth rate of 0.5-0.6 mm/h and a temperature gradient of 25-30℃/cm across the solid-liquid interface under a furnace temperature of 920-930℃,the colorless crystal LiYF 4 with the size of φ25 × 50 (mm) is successfully grown.The optical transmittance of the crystal is as high as 85% above the absorption edge at 190 nm.The induced absorption bands are observed below 700 nm in the transmission spectrum after the crystal is subjected to a high dose of γ-ray irradiation.
基金the National Natural Science Foundation of China under Grant No.60608020.
文摘The optical property, structure, surface properties (roughness and defect density) and laser-induced damage threshold (LIDT) of TiO2 films deposited by electronic beam (EB) evaporation of TiO2 (rutile), TiO2 (anatase) and TiO2 + Ta205 composite materials are comparatively studied. All films show the polycrystalline anatase TiO2 structure. The loose sintering state and phase transformation during evaporating TiO2 anatase slice lead to the high surface defect density, roughness and extinction coefficient, and low LIDT of films. The TiO2 + Ta205 composite films have the lowest extinction coefficient and the highest LIDT among all samples investigated. Guidance of selecting materials for high LIDT laser mirrors is given.
基金support from the National Natural Science Foundation of China, the Basic Science Center for “Multiscale Problems in Nonlinear Mechanics” (11988102 and 11790291)。