Effects of the Cooling Rate on the Plasticity of Pd40.5Ni40.5P19 Bulk Metallic Glasses

• 来源期刊: 中国物理快报（英文版）
• 年，卷（期）: 2011,（11）
• 页码范围: 182-185
• 页数: 4页
• 语种: 英文
• DOI: 10.1088/0256-307X/28/11/116104

摘要

We prepare Pd40.5Ni40.5P19 glassy samples with purified ingots by copper mold casting at a high cooling rate and by water quenching at a low cooling rate.Both of them exhibit different supercooled liquid regions and multiple glass transition characteristics in their differential scanning calorimetric curves.The plasticity of the glassy sample prepared by copper mold casting is about 5％ while that prepared by water quenching is almost zero (0.2％),indicating that cooling rate has influenced the plasticity of glassy alloys.By using high resolution TEM image analysis,it is revealed that there exist characteristic regions with different contrasts in the full glassy samples.The characteristic size is about 20-40nm for the glassy sample prepared by water quenching and 2-4nm for the one prepared by copper mold casting.The large difference in the plasticity of the glassy samples prepared by different cooling rates is believed to be related to the difference in the size of the characteristic nanoscale structures.The results indicate that adjusting cooling rate in preparation of glassy samples could modify the thermal and mechanical properties of the glassy alloys.Bulk metallic glass (BMG) is a kind of new structural and functional material developed in recent years.Because of many excellent demonstrated properties such as high strength,corrosion resistance,elastic deformability and magnetic properties,BMGs have become a hot research topic in the materials field.A large number of BMG alloy systems have been developed and some breakthroughs have been achieved in their mechanical and functional properties.[1-5] The first reported bulk metallic glass with a critical size over one centimeter is the Pd40Ni40P20 glassy alloy,which nowadays can be obtained to be as large as 25mm in diameter.[6] Although Pd40Ni40P20 glassy alloy shows a large glass forming ability,it is very brittle with barely global plasticity.Recently,it was found that the bulk glassy alloy system containing precious metal will exhibit large plasticity such as Pd-Si,Pd-Cu-Si and Pt-Cu-Ni-P BMG.[7-11] It has also been found that all of these BMGs with large plasticity possess large Poisson's ratio (γ),[11] which is believed to contribute to the large plasticity of the glassy alloys.Pd40.5Ni40.5P19 BMG also exhibits large Poisson's ratio (0.41),[6] suggesting that there might be a way to enhance the plasticity of Pd40.5Ni40.5P19 BMG.