通过引入梯度结构可以提升双相不锈钢的力学性能,然而其高度异质性结构会导致更为复杂多变的应力应变分配行为。为了深入研究梯度结构对双相不锈钢变形行为的影响,通过超声表面滚压处理(ultrasonic surface rolling processing,USRP)技...通过引入梯度结构可以提升双相不锈钢的力学性能,然而其高度异质性结构会导致更为复杂多变的应力应变分配行为。为了深入研究梯度结构对双相不锈钢变形行为的影响,通过超声表面滚压处理(ultrasonic surface rolling processing,USRP)技术制备了具有梯度结构的双相不锈钢,并采用晶体塑性有限元方法研究梯度结构中奥氏体和铁素体相的应力分配及相间协调变形机制。研究结果表明,经过USRP后材料表层的晶粒显著细化,且小角度晶界比例增加,铁素体晶粒中形成位错壁和位错胞结构,而奥氏体晶粒中形成层错和孪晶。另外,双相梯度结构中显著的异质变形诱导(heterogeneous deformation-induced,HDI)硬化效应,使试样屈服强度由581.34 MPa提升至690.98 MPa,表现出良好的强塑性组合。模拟结果显示,梯度双相结构中的相界和晶界处产生较大的应力集中,而细晶区的HDI硬化效应有效降低了铁素体与奥氏体之间的应变失配,缓解了局部应力集中。此外,在相同晶粒尺寸条件下,奥氏体与铁素体也会表现出不同的变形序列特征。在拉伸变形过程中,晶粒尺寸越小的区域微观异质性越低,高密度几何必须位错逐渐从表层向芯部扩展,使微观结构的异质性逐渐降低。揭示了梯度双相不锈钢在变形过程中的应变协同演化机制,为优化双相不锈钢的材料设计及综合性能提供了理论依据和试验支持。展开更多
Super duplex stainless steels(SDSS) show complex precipitation and transformation behavior during heat treatment processes,which affects both mechanical and corrosion properties. This report presents some data on the ...Super duplex stainless steels(SDSS) show complex precipitation and transformation behavior during heat treatment processes,which affects both mechanical and corrosion properties. This report presents some data on the microstructures that develop after folding and subsequent precipitation during heat treatment of UNS S32750 SDSS sheet samples.The microstructural and textural changes have been followed using SEM/EBSD techniques.Upon folding,both a texture and strain gradient form in the folded/bent region,subsequent heat treatment at 845℃results in the ferrite phase to transform to sigma,austenite and chi phases.Transformation was found to be accelerated by strain.Complete transformation of the ferrite phase occurred within half the annealing time required in the unstrained regions.The local mis-orientations in the ferrite and austenite phases reduced during annealing,however,the reduction in the austenite was not very high and a significant amount remained even after the longest annealing time.The texture components that developed during the folding process remained unchanged even after one hour annealing at 845℃.The implication of these findings could have a bearing on the formation of sigma phase during welding of SDSS that may have residual stresses introduced during final processing.展开更多
核磁共振(NMR)显微镜是在高分辨率的核磁共振波谱仪的磁头外部施加一线性梯度场(line-ar magnetic field gradient G),由于磁场梯度G是空间座标的线性函数,因此垂直于G方向的每一层面都有各自的磁场强度。当被观察样品处于这种环境中,...核磁共振(NMR)显微镜是在高分辨率的核磁共振波谱仪的磁头外部施加一线性梯度场(line-ar magnetic field gradient G),由于磁场梯度G是空间座标的线性函数,因此垂直于G方向的每一层面都有各自的磁场强度。当被观察样品处于这种环境中,如同时又受到射频场的作用,根据Larmor公式ω=γB,则沿G方向的每一垂直层面都有相对应的共振频率。由于核磁共振信号的强度与这一层面的样品中参与共振的元素(如氢核)的数目成正比,因此通过连续波扫频法可以确定样品中沿G方向的质子分布,得到质子密度的一维投影,改变G的方向(或改变样品的方位)。展开更多
全双工系统能实现在同一时隙与同一频率传输数据,相比于半双工系统能大大地提升数据吞吐量和频谱效率。为了进一步提高全双工多输入多输出(Multi-input and multi-output,MIMO)中继系统传输速率,本文基于放大转发(Amplify-and-forward,...全双工系统能实现在同一时隙与同一频率传输数据,相比于半双工系统能大大地提升数据吞吐量和频谱效率。为了进一步提高全双工多输入多输出(Multi-input and multi-output,MIMO)中继系统传输速率,本文基于放大转发(Amplify-and-forward,AF)传输模式,在全双工双向中继系统中引入梯度下降算法,将用户发送端、接收端波束成形与中继端波束成形矩阵相结合设计一种最大化速率的交替迭代算法,并构造出一种最小均方误差(Minimum mean square error,MMSE)迭代算法作为初始条件,在此基础上推导出中继接收端与发射端的波束成形矩阵表达式。仿真结果表明,本文构造的交替迭代算法收敛速度快,而且相比于迫零、最小均方误差以及最大泄信噪比算法,和速率有显著提高。展开更多
文摘Super duplex stainless steels(SDSS) show complex precipitation and transformation behavior during heat treatment processes,which affects both mechanical and corrosion properties. This report presents some data on the microstructures that develop after folding and subsequent precipitation during heat treatment of UNS S32750 SDSS sheet samples.The microstructural and textural changes have been followed using SEM/EBSD techniques.Upon folding,both a texture and strain gradient form in the folded/bent region,subsequent heat treatment at 845℃results in the ferrite phase to transform to sigma,austenite and chi phases.Transformation was found to be accelerated by strain.Complete transformation of the ferrite phase occurred within half the annealing time required in the unstrained regions.The local mis-orientations in the ferrite and austenite phases reduced during annealing,however,the reduction in the austenite was not very high and a significant amount remained even after the longest annealing time.The texture components that developed during the folding process remained unchanged even after one hour annealing at 845℃.The implication of these findings could have a bearing on the formation of sigma phase during welding of SDSS that may have residual stresses introduced during final processing.
文摘核磁共振(NMR)显微镜是在高分辨率的核磁共振波谱仪的磁头外部施加一线性梯度场(line-ar magnetic field gradient G),由于磁场梯度G是空间座标的线性函数,因此垂直于G方向的每一层面都有各自的磁场强度。当被观察样品处于这种环境中,如同时又受到射频场的作用,根据Larmor公式ω=γB,则沿G方向的每一垂直层面都有相对应的共振频率。由于核磁共振信号的强度与这一层面的样品中参与共振的元素(如氢核)的数目成正比,因此通过连续波扫频法可以确定样品中沿G方向的质子分布,得到质子密度的一维投影,改变G的方向(或改变样品的方位)。
文摘全双工系统能实现在同一时隙与同一频率传输数据,相比于半双工系统能大大地提升数据吞吐量和频谱效率。为了进一步提高全双工多输入多输出(Multi-input and multi-output,MIMO)中继系统传输速率,本文基于放大转发(Amplify-and-forward,AF)传输模式,在全双工双向中继系统中引入梯度下降算法,将用户发送端、接收端波束成形与中继端波束成形矩阵相结合设计一种最大化速率的交替迭代算法,并构造出一种最小均方误差(Minimum mean square error,MMSE)迭代算法作为初始条件,在此基础上推导出中继接收端与发射端的波束成形矩阵表达式。仿真结果表明,本文构造的交替迭代算法收敛速度快,而且相比于迫零、最小均方误差以及最大泄信噪比算法,和速率有显著提高。
