简介概要

Deformation twins and twinning at ambient temperature in cryomilled Al-Zn-Mg-Cu alloy powders

来源期刊:中国有色金属学报(英文版)2007年第5期

论文作者:陈汉宾 程军胜 杨滨 张济山 田晓风 樊建中

文章页码:898 - 898

Key words:cryomilling; Al-Zn-Mg-Cu alloy; twins; mechanism

Abstract: The nanocrystalline Al-Zn-Mg-Cu alloy powders were synthesized using cryomilling. Deformation twins and twinning at ambient temperature were observed in Al-Zn-Mg-Cu powders. Experimental results indicate that high strain rate at low temperature during cryomilling induces the formation of deformation twins by the climbing of the restricted dislocations in nano-scale grains, and the cryomilled powders at high energies and nonequilibrium state reduce the grain boundary energies by twinning.

基金信息:the Hi-tech Research and Development Program of China



详情信息展示

Deformation twins and twinning at ambient temperature in cryomilled Al-Zn-Mg-Cu alloy powders

CHEN Han-bin(陈汉宾)1, CHENG Jun-sheng(程军胜)2, YANG Bin(杨 滨)1, 3,

ZHANG Ji-shan(张济山)1, TIAN Xiao-feng(田晓风)4, FAN Jian-zhong(樊建中)4

1. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing,Beijing 100083, China;

2. Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100080, China;

3. International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016, China;

4. Beijing General Research Institute for Nonferrous Metals, Beijing 100088, China

Received 25 December 2006; accepted 18 April 2007

                                                                                                 

Abstract: The nanocrystalline Al-Zn-Mg-Cu alloy powders were synthesized using cryomilling. Deformation twins and twinning at ambient temperature were observed in Al-Zn-Mg-Cu powders. Experimental results indicate that high strain rate at low temperature during cryomilling induces the formation of deformation twins by the climbing of the restricted dislocations in nano-scale grains, and the cryomilled powders at high energies and nonequilibrium state reduce the grain boundary energies by twinning.

Key words: cryomilling; Al-Zn-Mg-Cu alloy; twins; mechanism

                                                                                                           

1 Introduction

Twins are generally classified into deformation twins and annealing twins. It is known that no deformation twins have been observed in coarse-grained Al and its alloy due to their high stacking fault energies(SFEs). However, based on the study of FCC polycrystal metals, EL-DANAF[1] suggested that the twinning stress instead of the critical value of the SFEs directly influences the production of deformation twins. The analytical model[2] indicates further that the stress of twin growth is much smaller than that for its nucleation. Deformation twins in FCC metal powders produced by cryomilling, such as Inconel 625[3] and Al[4-9], have been observed recently. As for annealing twins, it has been observed in variety of low SFE FCC metals deformed and subsequently annealed at recrystallized temperature. But the microscopic model proposed by MAHAJAN[10] indicated that annealing twins could not form in high stacking fault energy metals because Shockley partial loops are not stable. However, a number of twins were found in Al-Zn-Mg-Cu powder samples prepared by cryomilling for 2 and 10 h and then dwelling in a silica gel desiccator at ambient temperature for nearly two years. The present study was undertaken to elucidate the mechanism of twinning in cryomilling and the microstructural evolvement at ambient temperature.

2 Experimental

Al-Zn-Mg-Cu (10.0 Zn, 3.0 Mg, 1.8 Cu, balance Al, mass fraction, %) alloy powders with a particle size of about 75 ?m were fabricated by cryomilling. Details of processing method can be found in Ref.[11]. The temperature in vial was -140 ℃. The milling was performed in an attritor with a stainless steel vial at a rate of 200 r/min. The stainless steel balls with a diameter of 6.4 mm were used as the grinding media and the ball-to-powder mass ratio was 25?1.

Transmission electron microscopy was performed using a HITACHI H-800 microscope operated at 100 kV. The samples for TEM observations were prepared by carbon grid method. In this approach[12], powders were first immersed in methanol in a small container and agitated using a supersonic instrument for a few minutes. Then, a standard copper grid with a carbon film was used to collect some small fragment of powder particles from the methanol suspension. Finally, after being dried at ambient temperature, the sample was ion-milled at low temperature. The thermal analysis was carried out in a differential scanning calorimeter (NETZSCH STA 449C) employing a heating rate of 10 ℃/min under flowing argon.

3 Results

3.1 Transmission electron microscopy

有色金属在线官网  |   会议  |   在线投稿  |   购买纸书  |   科技图书馆

中南大学出版社 主办 版权声明   电话:0731-88830515 88830516   传真:0731-88710482   Email:administrator@cnnmol.com

互联网出版许可证:新出网证(湘)字005号   湘ICP备09001153号