Gang Wang
,
Zbigniew H. Stachurski
金属学报(英文版)
doi:10.1007/s40195-016-0369-2
The homogeneous plastic flow in bulk metallic glasses (BMGs) must be elucidated by an appropriate atomistic mechanism. It is proposed that a so-called concordant shifting model, based on rearrangements of five-atom subclusters, can describe the plastic strain behaviour of BMGs in a temperature range from room temperature to the supercooled liquid region. To confirm the effectiveness of the atomic concordant shifting model, a comparative investigation between the vacancy/atom model and the concordant shifting model is carried out based on the estimation of the strain rate deduced from two models. Our findings suggest that the atomic concordant shifting model rather than the vacancy/atom exchange model can well predict the large strain rate in the superplasticity of BMGs.
关键词:
Bulk
,
metallic
,
glasses
,
Superplasticity
,
Vacancy/atom
,
exchange
,
model
,
Atomic
,
concordant
,
shifting
,
model
,
Strain
,
rate
Ying Yan
,
Wan-Peng Deng
,
Zhan-Feng Gao
,
Jing Zhu
,
Zhong-Jun Wang
,
Xiao-Wu Li
金属学报(英文版)
doi:10.1007/s40195-016-0373-6
To explore the coupled effect of temperature T and strain rate ε˙ε˙ on the deformation features of AZ31 Mg alloy, mechanical behaviors and microstructural evolutions as well as surface deformation and damage features were systematically examined under uniaxial tension at T spanning from 298 to 523 K and ε˙ε˙ from 10-4 to 10-2 s-1. The increase in T or the decrease in ε˙ε˙ leads to the marked decrease in flow stress, the appearance of a stress quasi-plateau after an initially rapid strain hardening, and even to the occurrence of successive strain softening. Correspondingly, the plastic deformation modes of AZ31 Mg alloy transform from the predominant twinning and a limited amount of dislocation slip into the enhanced non-basal slip and the dynamic recrystallization (DRX) together with the weakened twinning. Meanwhile, the cracking modes also change from along grain boundaries (GBs) and at twin boundaries (TBs) or the end of twins into nearby GBs where the DRX has occurred. The appearance of a stress quasi-plateau, the formation of large-sized cracks nearby GBs, and the occurrence of continuous strain softening, are intimately related to the enhancement of the non-basal slip and the DRX.
关键词:
AZ31
,
Mg
,
alloy
,
Uniaxial
,
tension
,
Temperature
,
Strain
,
rate
,
Deformation
,
Damage
,
Twinning
Ya-Qiang Wang
,
Zhao-Qi Hou
,
Jin-Yu Zhang
,
Xiao-Qing Liang
,
Gang Liu
,
Guo-Jun Zhang
,
Jun Sun
金属学报(英文版)
doi:10.1007/s40195-016-0372-7
Cu-Al/Al nanostructured metallic multilayers with Al layer thickness h Al varying from 5 to 100 nm were prepared, and their mechanical properties and deformation behaviors were studied by nanoindentation testing. The results showed that the hardness increased drastically with decreasing h Al down to about 20 nm, whereafter the hardness reached a plateau that approaches the hardness of the alloyed Cu-Al monolithic thin films. The strain rate sensitivity (SRS, m), however, decreased monotonically with reducing h Al. The layer thickness-dependent strengthening mechanisms were discussed, and it was revealed that the alloyed Cu-Al nanolayers dominated at h Al ≤ 20 nm, while the crystalline Al nanolayers dominated at h Al > 20 nm. The plastic deformation was mainly related to the ductile Al nanolayers, which was responsible for the monotonic evolution of SRS with h Al. In addition, the h Al-dependent hardness and SRS were quantitatively modeled in light of the strengthening mechanisms at different length scales.
关键词:
Nanostructured
,
films
,
Cu-Al/Al
,
multilayers
,
Hardness
,
Strain
,
rate
,
sensitivity
,
Layer
,
thickness
,
dependence
王峰
,
同秋燕
高分子材料科学与工程
利用微分扫描热分析（DSC）获得了聚对苯二甲酸乙二醇酯（PET）熔体等温结晶过程焓松弛速率曲线,并对结晶焓松弛速率曲线进行微分从而获得等温结晶焓松弛加速度曲线。文中通过定义相对结晶速率R和相对结晶加速度A,确定了相对结晶速率R和相对结晶加速度A与结晶焓松弛速率和结晶焓松弛加速度之间对应相差的一个常数值,然而其所对应的变化趋势却是相反的。根据结晶焓松弛速率和结晶焓松弛加速度的变化趋势,笔者认为PET熔体的等温结晶可以分为三个阶段,分别称之为阶段Ⅰ,阶段Ⅱ和阶段Ⅲ。其中结晶中间阶段（阶段Ⅱ）还可以分成两个＂亚阶段＂。利用结晶焓松弛速率和结晶焓松弛加速度的极值点确定了三个阶段及两个＂亚阶段＂的转化的临界时间点和相对结晶度。
关键词:
等温结晶
,
微分
,
焓松弛
,
速率
,
加速度
,
结晶阶段
刘新华
,
晏玉平
,
谢建新
中国有色金属学报
采用定向凝固法制备藕状多孔镁,采用GLEEBLE-1500材料模拟实验机和直撞式霍普金森压杆(SHPB)实验设备,在10-3～1650 S-1的应变速率范围内,沿平行于气孔方向进行压缩变形实验,研究应变速率对藕状多孔镁压缩变形行为和力学性能的影响及影响机理.结果表明:藕状多孔镁沿平行于气孔方向的压缩变形过程主要包含线弹性变形阶段、局部坍塌变形阶段、低应力平台变形阶段和密实化阶段4个阶段,其中平台变形阶段较宽(应变在0.2～0.7之间).平行于气孔方向压缩时,应变速率对藕状多孔镁的变形行为影响显著,在应变速率ε＜60 s-1条件下变形时,主要以孔壁首先发生局部剪切断裂,然后孔壁向孔隙内塌陷的方式变形,而在较高应变速率ε=450～1650 s-1条件下变形时,主要以孔壁首先发生整体偏转,然后产生弯曲折断的方式变形;应变速率对藕状多孔镁的坍塌应力和平台应力有较明显的影响,其影响机制主要是由于不同应变速率时孔壁的变形方式发生变化,而受冲击波效应的影响不明显.
关键词:
藕状多孔镁
,
应变速率
,
变形行为
,
力学性能
,
变形机制
