Mechanism for phase boundary sliding and its relevance to diffusion-solution zone in SPD

The diffusion behavior of Zn/Al interfaces in their powders sintering was investigated with SEM. The results show that Zn-Al eutectoid microstructure can be achieved through their powders sintering, and the diffusion characteristic between Zn and Al is just a demonstration of Kirkendall effect, by which Zn can dissolve into Al and contrarily Al cannot dissolve into Zn. During sintering, a diffusion-solution zone α′ has formed and subsequently transforms into eutectoid microstructure in cooling process. The superplastic deformation mechanism of Zn-Al eutectic alloy is phase boundary sliding which is controlled by diffusion-solution zone α′. If diffusion-solution zone α′ is unsaturated, it will have much more crystal defects and the combination between α′ and β phase is weak, thus the process of phase boundary sliding becomes easily; on the contrary, if the diffusion-solution zone α′ becomes thick and saturated, the sliding will be difficult.

Inter-granular liquid phase aiding grain boundary sliding in superplastic deformation of fine-grained ZK60 Mg alloy

For 7475 Al alloy,there were micrographs showing filaments or whiskers formation during the separation stage of superplastic elongation.This indicates the presence of liquid phase which accommodates grain boundary sliding to reach superplasticity.On the other hand,there is no such phenomenon reported regarding Mg alloy in literatures.Scanning electron microscopic(SEM)fractography exceptionally exhibits a mark of grain boundary sliding and its accommodating mechanism of inter-granular liquid phase.Under the testing conditions of 350℃ and 1×10- 4s -1,the initially fine-grained structure(3.7μm)yields 642%superplastic elongation and exhibits fluffy appearance on the fractured surface.For other specimens showing less superplasticity,their fractured surfaces exhibit partial fluffy appearance.

Sn含量对PbSnO3-Pb(Mg1/3Nb2/3)O3-PbTiO3三元系压电陶瓷相结构和电性能的影响

采用两步钶铁矿前驱体工艺制备了PbSnO3-Pb（Mg1/3Nb2/3）O3-PbTiO3（PSn-PMN-PT） 三元系压电陶瓷, 研究了Sn含量的变化对PSn-PMN-PT 三元系压电陶瓷结构和性能的影响。XRD结果表明, 所选成分均处于三方相和四方相共存的准同型相界上, 当Sn含量减少时, PSn-PMN-PT的XRD图谱基本没有发生变化, 而当Sn含量增加时, 在XRD图谱中逐渐出现烧绿石相。电性能研究表明, 缺失少量Sn可以提高PSn-PMN-PT的压电、介电和铁电性能, 减小损耗; 而添加过量Sn明显损害其压电和铁电性能, 增加损耗。缺失0.2mol%Sn的PSn-PMN-PT具有最佳的压电和铁电性能, d33： -530 pC/N, kp： -56.4%, Qm： -570, εr： -3070, tanδ： -0.32%, Pr： -28.9 μC/cm2, EC： -8 kV/cm。

Effects of Thermal Conditions in the Phase Formation of Undoped and Doped Pb(Zr_1-xTi_x)O₃Solid Solutions

The purpose of this research is to study the effect of thermal conditions such as temperature ramp rate and isothermal times in the phase formation of Pb(Zr1-xTix)O3 solid solutions with composition near the morphotropic phase boundary (MPB) by using the conventional ceramic method. The perovskite phase formation and morphology of undoped Pb(Zr0.52Ti0.48)O3 (abbreviated PZT) and doped new material Pb0.98Gd0.02[(Zr0.52Ti0.48)0.98(Mg1/3Nb2/3)0.01(Ni1/3Sb2/3)0.01]O3 (abbreviated PZT-PGMNNS) specimens calcined between 700°C and 900°C have been examined by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) while the thermal evolution of the initial precursor was followed by TG-DTA. So the results of these studies have been discussed.

基于预警边界的线控转向主动安全控制研究

为提高传统线控转向车辆转向稳定性,提出一种基于相平面预警边界的主动安全控制策略。首先,建立质心侧偏角与质心侧偏角速度β-β相平面图;其次,针对传统相平面稳定区域划分所用双线法在低路面附着系数时存在不足,提出“平行四边形”边界法改善相平面稳定区域的划分,并以稳定域边界建立预警边界模型。然后基于预警边界设计线控转向主动安全控制器,设计预警度PID控制器和横摆角速度滑模控制器联合决策横摆力矩,以保持车辆稳定行驶,避免失稳状态从而起到主动安全作用;最后,结合Simulink和CarSim联合仿真结果表明,控制器能够有效避免线控转向车辆失稳,提高了主动安全性。

永磁同步电机改进型全阶滑模观测器无传感控制

针对传统全阶滑模观测器在运行过程中系统抖振大及观测精度低的问题,提出了一种可控边界层的全阶滑模控制策略。引入归一化锁相环进行转速估计,避免参数变化对估计值的影响,使转子位置识别更加精确。利用Lyapunov方程证明了算法的稳定性。最后通过仿真和试验验证了改进型全阶滑模观测器无传感控制策略的可靠性和准确性。

Phase boundary sliding model controlled by diffusion-solution zone in superplastic deformation

With scanning electron microscope (SEM), the surface morphology of phase boundary sliding (PBS) in superplastic deformation (SPD) of Zn-Al alloy and the diffusion behavior of Zn, Al interfaces in their powers’ sintering have been investigated. The results show that Zn-Al eutec-toid microstructure can be achieved through their powders’ sintering, and the diffusion characteristic between Zn and Al is just a demonstration of Kirkendall effect, in which Zn can dissolve into Al whereas Al can hardly dissolve into Zn. During sintering, a diffusion-solution zone a’ has formed and subsequently transformed into a eutectoid microstructure in the cooling process. The superplastic deformation mechanism of Zn-Al eutectic alloy is phase boundary sliding which is controlled by the diffusion-solution zone α’. If the diffusion-solution zone α’ is unsaturated, it will have much more crystal defects and the combination between α’ and phase P is weak, thus the process of phase boundary sliding becomes easily; on the

一种改进的PWM整流器滑模控制方法

传统的三相两电平脉宽调制(PWM)整流器在PI控制下的启动运行瞬间会产生较大冲击电流,易损坏电路器件,影响系统的动、稳态性能,为此,提出了一种利用指数趋近律的改进滑模变结构双闭环控制策略。首先建立PWM整流器交流侧的离散化数学模型公式,分析影响启动冲击电流的参数变量关系。对PWM整流器进行预充电,以降低启动冲击电流。同时进行电流前馈补偿,以加快系统动态响应。其次通过采用可变边界层进行滑模控制的改进,削弱系统抖动影响。通过仿真实验,验证了改进滑模控制启动比传统PI控制输出波形更平滑;当负载改变时其动态响应时间也减少。改进后的滑模变结构输出波形的抖振得到了抑制,稳定状态时期望参数变量在滑模面上的波动幅值降低,避免了控制器的高频切换。系统的动、稳态性能更好。

Stress-induced phase transformation and phase boundary sliding in Ti: An atomically resolved in-situ analysis

In-situ tensile experiments on pure Ti were performed in a transmission electron microscope at room temperature.The dynamic process of stress-induced hexagonal closed-packed(hcp)to face-centered cu-bic(fcc)structural transformation ahead of a crack tip was captured at the atomic level.Intriguingly,a sliding behavior of the ensuing(0001)hcp/(1¯11)_(fcc) phase boundary was observed to further accommodate the plastic deformation until crack initiation.The sliding was accomplished via the successive conserva-tive glide of extended dislocations along the(0001)hcp/(1¯11)_(fcc) phase boundary.A molecular dynamics simulation was carried out to corroborate the experiments and the results confirm the new dislocation-mediated sliding mechanism.

三相三线制并联型有源电力滤波器的准滑模变结构控制

提出一种基于准滑模变结构控制(QSMC)的有源电力滤波器的控制策略,用于减小常规滑模控制中存在的抖动问题。使用的方法是将系统的运动轨迹限制在理想滑动模态的某一领域Δ内,从而实现对滑模控制非线性部分进行处理,保证了在减小了系统的抖动的同时系统又具有较好的鲁棒性。同时分析了该装置的原理及控制方法,并对控制器的存在性,可达性及稳定性进行了分析。仿真结果证明了该控制算法简单,响应速度快,对外界噪声干扰和参数摄动具有鲁棒性等特点,对抖动也具有较好的抑制作用。

基于可变边界层的永磁同步电机滑模观测器

为了提高 SPMSM转子位置和速度的观测性能,提出一种基于准滑动模态的可变边界层 S型开关函数与锁相环模块相结合的滑模观测器系统。首先,基于隐极式 PMSM的数学模型,建立电流信号的滑模面;其次,为提高电机转速与转子位置估算精度,采用可变边界层的设计思想,通过一种边界层随转速变化的 S型开关函数代替传统符号函数,达到减弱抖振并提高跟踪精度的目的;再次,利用锁相环得到转子位置及转速信号,并针对锁相环在动态阶段跟踪精度较低的缺点,设计一个信号抑制器以削弱动态误差并提高响应速度;最后,搭建 Matlab/Simulink仿真平台对此方法进行验证,结果表明提出的方法可行并拥有良好的跟踪能力。

Zn-Al合金超塑变形的相界滑移与表面效应研究

用扫描电镜 (SEM )对Zn Al合金超塑变形时的晶界 (或相界 )滑移特性进行了研究。结果表明 ,Zn Al合金的超塑变形机制是晶界 (或相界 )滑移 ,且α/β相界面滑移容易进行并可实现长程滑移 ,同时合金试样的表面特性对相界滑移有很大的影响。表面镀层对Zn 5Al合金超塑变形中的相界滑移有阻碍作用 ,而当试样在电场中进行超塑变形时 ,由于表面感应电荷的作用 ,导致试样表面产生大量的空洞 ,提高了超塑变形抗力 ,使应变速率和伸长率降低 ,表现为一种负的电塑性效应。

高性能无铅压电材料Ba(Ti_(0.8)Zr_(0.2))O_(3-x)-(Ba_(0.7)Ca_(0.3))TiO_3单晶和薄膜的制备

具有三相点准同型相界附近成分的Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3无铅压电材料,具有优异的铁电、压电性能,作为一种具有潜在应用前景的无铅压电材料得到广泛关注。利用溶胶-凝胶法制备了该成分的薄膜以及尝试了利用浮区单晶炉的单晶生长工艺。利用XRD对薄膜和生长的晶体样品进行了物相鉴定;用AFM表征了薄膜的表面形貌;用TFAnalyz-er2000HS铁电测试系统测试了其电滞回线;还分析了气氛对晶体生长和紫外-可见透过光谱的影响。

α、β相分布形态对TC11钛合金高温低周疲劳寿命的影响

对TC1 1钛合金施行了不同的热处理制度 ,得到 6种α、β相分布组织形态 ,研究不同的组织形态的高温低周疲劳。结果表明 ,等轴组织具有最高的疲劳寿命 ,而晶间 β组织的疲劳寿命较低 ,分析认为。高温循环形变时 。

Critical review of superplastic magnesium alloys with emphasis on tensile elongation behavior and deformation mechanisms

The tensile elongation behavior and deformation mechanisms of superplastic Mg alloys and Mg composites were examined by extensively reviewing the literature published from the time of the first report on the superplasticity of Mg alloys to the present day.Studies on the superplasticity of Mg alloys have been conducted mainly on Mg-Al-Zn(AZ)series alloys,Mg-Zn-Zr(ZK),Mg-Li and Mg-RE(rare earth)alloys,and in recent years,Mg-RE alloys have attracted the greatest attention.The effect of grain size and the type and amount of secondary phase particles on the superplasticity of Mg alloys was systematically examined and reviewed.The alloys processed by severe plastic deformation(SPD)and powder-metallurgy methods have smaller grain sizes and exhibit superior superplasticity compared to conventionally processed(by extrusion and rolling)Mg alloys.For the AZ alloys,as the volume fraction of the Mg17Al12phase increases,smaller grains are obtained,and the low-temperature superplasticity(LTS)and high-strain-rate superplasticity(HSRS)characteristics become enhanced.The ZK60 alloy with finely dispersed Mg Zn2particles exhibits excellent LTS,while the Mg-RE alloys with a high fraction of thermally stable particles exhibit excellent HSRS.Mg-Li alloys can exhibit LTS even at room temperature due to the presence of a high-volume fraction of the body centered cubic(BCC)phase where atomic diffusivity is high.Grain boundary diffusion-and lattice diffusion-controlled grain boundary sliding are found to operate as the dominant deformation mechanisms below~473 K and above~673 K,respectively,at small grain sizes.Deformation mechanism maps were constructed based on the analysis of the deformation behavior of superplastic Mg alloys,and from the maps,the critical conditions for achieving LTS,HSRS and simultaneous achievement of LTS and HRSR were calculated and proposed,and their importance was discussed.

新型奥氏体─贝氏体双相钢滑动磨损特性的研究

本文研究了在边界润滑、滑动磨损条件下，新型奥氏体─贝氏体双相钢的磨损规律，磨面及磨屑形貌，磨损表层微观组织及硬度变化，动态摩擦系数及表面氧化膜与微观磨损机制的关系，并首次建立了“载荷─滑动速度─滑动时间”三维磨损机制图。

基于新型滑模观测器的永磁同步电机无传感器控制

滑模观测器(SMO)的高鲁棒性使其在永磁同步电机(PMSM)无传感器控制系统中成为了研究热点之一。针对传统SMO的计算量大及自身存在的高频抖振现象,主要研究了PMSM无传感器中高速控制过程,设计了一种新型SMO,将边界层和锁相环(PLL)技术共同应用于SMO中,理论分析并建立PMSM的SMO数学模型后,对PLL的设计进行了严格的推导,验证其获得转子位置的精确性。最后,对整体设计方案进行了全面的仿真和试验,结果表明新型SMO对高频抖振的抑制效果显著,且具有更高的精确性和更强的鲁棒性。

铌锆合金高温力学性能及变形机制研究

测试了铌锆合金在1 000~1 800℃下的抗拉强度、屈服强度、延伸率和断面收缩率,并对单向拉伸后的断口形貌进行了观察。结果表明:随着温度升高,铌锆合金在高温下的抗拉强度和屈服强度的下降速度由快转慢,且二者逐渐接近;延伸率在1 000~1 200℃温度区间的变化不大,但在1 200℃以上随温度增加而快速增大;断面收缩率在试验温度范围内变化不大;铌锆合金在1 000~1 200℃温度区间内的主要变形机制为位错滑移,在1 400~1 800℃温度区间内的主要变形机制为晶界滑动;铌锆合金组织中有两种第二相粒子,其中氧化锆颗粒主要起弥散强化作用,而碳化锆颗粒主要起沉淀强化作用。

Creep resistance of Mg-4%Al-2%RE-2%Ca alloy

The creep resistance of the alloy Mg-4Al-2RE-2Ca（AEC422） and the base alloy AE42 was studied. The results reveal that the precipitated phases of AEC422 consist of Al2La and Al2Ca by contrast with the precipitated phase Al11La3 in AE42, which is instable and decomposes to Al2La and Al at high temperature. Creep resistance of AEC422 is significantly improved compared with that of AE42. The microstructure of AEC422 has no obvious changes after creep test at 175℃ and 70MPa, as compared to that before creep test, indicating that Al2La and Al2Ca have high thermal stability. Especially Al2Ca phase largely increases the strength of the grain boundaries in AEC422, which accounts for the creep resistance improvement.

In-situ study of damage mechanisms in Mg-6Li dual-phase alloy

Interfaces play a crucial role in influencing the mechanical properties of Mg alloys.For Mg-Li dual-phase alloy,the type of interfaces is complex,which includes both grain boundary and phase boundary,and the influence of such interfaces on the damage nucleation is yet to be explored.In this paper,in-situ scanning electron microscopy(SEM)based measurements were carried out to investigate the meso-scale damage nucleation mechanisms of the Mg-6Li dual-phase alloy.Results show that 94.8%of cracks are nucleated at the α-Mg grain boundary in the post-uniform elongation stage,while 5.2%are at phase boundary and almost no crack at the β-Li grain boundary.The initiation of α-Mg grain boundary cracks is attributed to strain incompatibility,which induces micro-strain localization,and then causes grain boundary sliding(GBS)and crack nucleation.Deformation compatibility analysis reveals that the geometric compatibility factor(Mk)can be used to predict the nucleation of α-Mg grain boundary crack.When Mk is lower than 0.075,α-Mg grain boundary cracks tend to form.Few cracks are generated at the phase boundary is due to the mild strain partitioning between α-Mg phase and β-Li phase and may also be partly attributed to multiple slip systems in body-centered cubic(BCC)-structured β-Li phase,which can accommodate well with the deformation of adjacent α-Mg phase.