Novel Ti6Al4V particles-reinforced AZ91 Mg matrix composites were successfully fabricated by stir casting method. The stirring time in semisolid condition directly affected the particle distribution and the quality of...Novel Ti6Al4V particles-reinforced AZ91 Mg matrix composites were successfully fabricated by stir casting method. The stirring time in semisolid condition directly affected the particle distribution and the quality of the ingots. Furthermore, the optimal speed of the heating and the liquid stirring could overcome particle settlement caused by the density difference between the matrix and the particles. Ti6Al4V particles distributed uniformly in the composites with different particle contents. The average grain size decreased with the increase in the particle contents. The Ti6A14V particles bonded pretty well with the alloy matrix. In addition, there were some interfacial reactions in the composites. There were rod-like A13Ti phases at the interface. The precipitates extended from the particle surface to the matrix, and they might improve the interfacial bonding strength. The ultimate tensile strength, yield strength and elastic modulus were enhanced as the particle contents increased, and the elongation was much better than that of the same matrix material reinforced with SiC particles. Thus, the novel composites exhibit better comprehensive mechanical properties.展开更多
Gradient boosting decision tree(GBDT)machine learning(ML)method was adopted for the first time to automatically recognize and conduct quantitative statistical analysis of boundaries in bainitic microstructure using el...Gradient boosting decision tree(GBDT)machine learning(ML)method was adopted for the first time to automatically recognize and conduct quantitative statistical analysis of boundaries in bainitic microstructure using electron back-scatter diffraction(EBSD)data.In spite of lack of large sets of EBSD data,we were successful in achieving the desired accuracy and accomplishing the objective of recognizing the boundaries.Compared with a low model accuracy of<50%as using Euler angles or axis-angle pair as characteristic features,the accuracy of the model was significantly enhanced to about 88%when the Euler angle was converted to overall misorientation angle(OMA)and specific misorientation angle(SMA)and considered as important features.In this model,the recall score of prior austenite grain(PAG)boundary was~93%,high angle packet boundary(OMA>40°)was~97%,and block boundary was~96%.The derived outcomes of ML were used to obtain insights into the ductile-to-brittle transition(DBTT)behavior.Interestingly,ML modeling approach suggested that DBTT was not determined by the density of high angle grain boundaries,but significantly influenced by the density of PAG and packet boundaries.The study underscores that ML has a great potential in detailed recognition of complex multi-hierarchical microstructure such as bainite and martensite and relates to material performance.展开更多
Relativistic electron beams driven by laser wakefield acceleration were utilized to produce ultrashort neutron sources.The experiment was carried out on the 38 fs,~0.5 J,800 nm Ti:Sapphire laser in the 10 TW UT 3 lase...Relativistic electron beams driven by laser wakefield acceleration were utilized to produce ultrashort neutron sources.The experiment was carried out on the 38 fs,~0.5 J,800 nm Ti:Sapphire laser in the 10 TW UT 3 laser lab at University of Texas at Austin.The target gas was a high density pulsed gas jet composed of 90%He and 10%N 2.The laser pulse with a peak intensity of 1.5×10^(18) W/cm^(2) interacted with the target to create a cylindrical plasma channel of 60 mm radius(FWHM)and 1.5 mm length(FWHM).Electron beams of~80 pC with the Gaussian energy distribution centered at 37 MeV and a width of 30 MeV(FWHM)were produced via laser wakefield acceleration.Neutron fluences of~2.4×10^(6) per shot with hundreds of ps temporal length were generated through bremsstrahlung and subsequent photoneutron reactions in a 26.6 mm thick tungsten converter.Results were compared with those of simulations using EPOCH and GEANT4,showing agreement in electron spectrum,neutron fluence,neutron angular distribution and conversion rate.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 51471059)the China Postdoctoral Science Foundation (Grant No. 2014T70328)
文摘Novel Ti6Al4V particles-reinforced AZ91 Mg matrix composites were successfully fabricated by stir casting method. The stirring time in semisolid condition directly affected the particle distribution and the quality of the ingots. Furthermore, the optimal speed of the heating and the liquid stirring could overcome particle settlement caused by the density difference between the matrix and the particles. Ti6Al4V particles distributed uniformly in the composites with different particle contents. The average grain size decreased with the increase in the particle contents. The Ti6A14V particles bonded pretty well with the alloy matrix. In addition, there were some interfacial reactions in the composites. There were rod-like A13Ti phases at the interface. The precipitates extended from the particle surface to the matrix, and they might improve the interfacial bonding strength. The ultimate tensile strength, yield strength and elastic modulus were enhanced as the particle contents increased, and the elongation was much better than that of the same matrix material reinforced with SiC particles. Thus, the novel composites exhibit better comprehensive mechanical properties.
基金financially supported by the National Key Research and Development Program of China(No.2017YFB0304900)。
文摘Gradient boosting decision tree(GBDT)machine learning(ML)method was adopted for the first time to automatically recognize and conduct quantitative statistical analysis of boundaries in bainitic microstructure using electron back-scatter diffraction(EBSD)data.In spite of lack of large sets of EBSD data,we were successful in achieving the desired accuracy and accomplishing the objective of recognizing the boundaries.Compared with a low model accuracy of<50%as using Euler angles or axis-angle pair as characteristic features,the accuracy of the model was significantly enhanced to about 88%when the Euler angle was converted to overall misorientation angle(OMA)and specific misorientation angle(SMA)and considered as important features.In this model,the recall score of prior austenite grain(PAG)boundary was~93%,high angle packet boundary(OMA>40°)was~97%,and block boundary was~96%.The derived outcomes of ML were used to obtain insights into the ductile-to-brittle transition(DBTT)behavior.Interestingly,ML modeling approach suggested that DBTT was not determined by the density of high angle grain boundaries,but significantly influenced by the density of PAG and packet boundaries.The study underscores that ML has a great potential in detailed recognition of complex multi-hierarchical microstructure such as bainite and martensite and relates to material performance.
基金This paper is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-14-1-0045The project was also supported by the NNSA coop-erative agreement DE-NA0002008the Defense Advanced Research Projects Agency's PULSE program(12-63-PULSE-FP014).
文摘Relativistic electron beams driven by laser wakefield acceleration were utilized to produce ultrashort neutron sources.The experiment was carried out on the 38 fs,~0.5 J,800 nm Ti:Sapphire laser in the 10 TW UT 3 laser lab at University of Texas at Austin.The target gas was a high density pulsed gas jet composed of 90%He and 10%N 2.The laser pulse with a peak intensity of 1.5×10^(18) W/cm^(2) interacted with the target to create a cylindrical plasma channel of 60 mm radius(FWHM)and 1.5 mm length(FWHM).Electron beams of~80 pC with the Gaussian energy distribution centered at 37 MeV and a width of 30 MeV(FWHM)were produced via laser wakefield acceleration.Neutron fluences of~2.4×10^(6) per shot with hundreds of ps temporal length were generated through bremsstrahlung and subsequent photoneutron reactions in a 26.6 mm thick tungsten converter.Results were compared with those of simulations using EPOCH and GEANT4,showing agreement in electron spectrum,neutron fluence,neutron angular distribution and conversion rate.
