报告题目：Engineering grain boundary structures of aluminium alloys and titanium by high strain/strain rate deformation

报告人：贾海龙 博士

主持人（邀请人）：王慧远教授

报告时间：2019年4月16日上午10:00-11:00

报告地点：南岭校区逸夫机械材料馆209报告厅

主办单位：材料科学与工程学院、汽车材料教育部重点实验室

摘要：A comprehensive study was carried out to clarify the effects of severe plastic deformation (SPD) and high strain rate deformation on various aluminium alloys and commercial purity titanium. Equal channel angular pressing (ECAP) was conducted on the Al-Cu, Al-Zn and Al-Bi-Zn alloys. Split Hopkinson pressure bar (SHPB) experiments were applied to a commercial purity titanium. Detailed analyses were made on the microstructures and mechanical properties, the relationships between which were established as well. By using ECAP, the Al-5Cu alloy with a bimodal grain structure composed of coarse micron-sized grains and submicron-sized ultrafine grains have been obtained, showing high strength and good ductility simultaneously. More importantly, it has been revealed that a short time aging at low temperatures can increase the ultimate tensile strength and uniform elongation without sacrificing the yield strength. Based on a quantitative evaluation of different supposed strengthening mechanisms, the grain boundary segregation strengthening has been firstly quantified. This work provides an important method for the industry to fabricate Al-Cu alloys with high strength and high ductility. Al-Bi alloys are of particular interest as potential bearing materials to replace the Pb containing alloys. By using ECAP, ultrafine grains have formed in the Al-6Bi-8Zn alloy. The yield strength of the as-deformed Al-6Bi-8Zn sample was more than three times as that of the as-cast sample. It is revealed that soft Bi particles have a strong influence on enhancing grain refinement during ECAP. After ECAP deformation, most of the Bi particles are deformed into flake shapes with higher surface area, which may be good for the lubrication. This work shows that ECAP can be used as a tool for adjusting the morphology of soft Bi particles, and thus fabricating high performance Al-Bi based bearing materials. By applying the high strain rate deformation on the commercial purity Ti alloy, large amounts of twin boundaries have been formed. Interestingly, a new {11 1} twin boundary formation mechanism has been found.

报告人简介：Dr. Hailong Jia, born in 1988, is working as a postdoctor at Norwegian University of Science and Technology (NTNU). He received the Master’s degree of materials and process engineering in June 2014 from Northeastern University, China. Then, he studied at Norwegian University of Science and Technology (NTNU) as a Ph.D candidate. His Ph.D research is mainly on Al and Ti alloys processed by severe plastic deformation (SPD) and high strain rate deformation. In 2018, he was awarded the “Innovation Scholarship from the President of Norwegian University of Science and Technology” (5 people from NTNU per year, 500000 NOK ≈ 60000 USD).