Synergistic improvement of strength and ductility via doping cerium into PH13-8Mo stainless steel by laser powder b e d fusion

In this study,the PH13-8Mo stainless steel parts doped without and with cerium(Ce)were fabricated via laser powder bed fusion followed by post-heat treatment,and systematically compared in terms of microstructure,phase constituent,and tensile properties.The comparative results show that doping Ce-modified grains with the equiaxed morphology and finer size,increased the mechanical stability of austenite,and enhanced the sphericity of oxide inclusion in the resultant PH13-8Mo.Additionally,the coherency between the newly-formed CeAlO 3 inclusion and matrix was effectively im proved after doping Ce,as compared to the original aluminum oxide inclusion without doping Ce.The resultant PH13-8Mo parts doped with Ce yielded an ultimate tensile strength of 1446±20 MPa with a fracture elongation of 16.0%±1.5%,for the first time meeting the AMS 5629E H1000 standard for the PH13-8Mo made by additive manufacturing(AM).The enhanced strength results from the strengthening effects of nanoscale precipitation(inclusion)and grain refining.Meanwhile,the ductilizing mechanism can be attributed to the enhanced inclusion sphericity and ameliorative coherency between the inclusion and matrix,and improved misorientation angle of grain boundary owing to the modification by Ce,which efficiently re-duced the stress concentration and enhanced cracking resistance during deformation.Therefore,doping rare earth elements presents a promising pathway to synergistically improve the strength and ductility of stainless steels by AM.

3D printed modular Bouligand dissipative structures with adjustable mechanical properties for gradient energy absorbing

Three-dimensional(3D)printing allows for the creation of complex,layered structures with precise micro and macro architectures that are not achievable through traditional methods.By designing 3D structures with geometric precision,it is possible to achieve selective regulation of mechanical properties,enabling efficient dissipation of mechanical energy.In this study,a series of modular samples inspired by the Bouligand structure were designed and produced using a direct ink writing system,along with a classical printable polydimethylsiloxane ink.By altering the angles of filaments in adjacent layers(from 30◦to 90◦)and the filament spacing during printing(from 0.8 mm to 2.4 mm),the mechanical properties of these modular samples can be adjusted.Compression mechanical testing revealed that the 3D printed modular Bouligand structures exhibit stress-strain responses that enable multiple adjustments of the elastic modulus from 0.06 MPa to over 0.8 MPa.The mechanical properties were adjusted more than 10 times in printed samples prepared using uniform materials.The gradient control mechanism of mechanical properties during this process was analyzed using finite element analysis.Finally,3D printed customized modular Bouligand structures can be assembled to create an array with Bouligand structures displaying various orientations and interlayer details tailored to specific requirements.By decomposing the original Bouligand structure and then assembling the modular samples into a specialized array,this research aims to provide parameters for achieving gradient energy absorption structures through modular 3D printing.

领导风格组合和演变的整合研究——基于历史和当代案例的比较分析

在实践中,领导风格存在着组合和演变的客观现象。本文通过对领导过程中多种领导风格组合和演变特征的整合,考察其动态变化情境下的多种风格可能出现的关系及组合和演变规律。基于尼希米重建城墙"项目"和中国当代企业项目的双案例研究,在历史案例和当代案例之间不断迭代发展相关理论。同时,研究过程还混合了叙事分析、社会历史方法和统计测量手段。研究发现:领导风格组合和演变的整合避免了各自研究的片面性,体现出优秀领导者的领导风格组合体内,各个领导风格既互相补充又有侧重的特征,对领导权变理论适当修正。领导过程中存在不演变且道德特征明显的领导风格。不演变的领导风格需要和其他多种领导风格相组合,有效地探析自我和外部环境,有效地影响下属的计划行为因素,适应动态变化情境,共同实现领导目标。领导过程中不演变的伦理型领导和精神型领导的重要作用需要得到学界和实践界的重视。管理实践的其他启示是领导风格组合和演变的整合可以使领导者达到遵守道德规范和实现领导目标的共赢结果。