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Shanghai Jiaotong University Offers New Train of Thought for Nano Material

Recently, Professor Sunhong Shanghai Jiaotong University published a thesis that has offered a new train of thought for nano materials harder than diamond.

From: iAbrasive.comDate: 2014-10-16 07:27:02Views: 334

Recently, Professor Sunhong from Department of Physics and Astronomy of Shanghai Jiaotong University, along with his research group, published a thesis titled Large Indentation Strain Stiffening in Nanotwinned Cubic Boron Nitride on the Nature Communication. The thesis has offered a new train of thought for nano materials harder than diamond.

Diamond is the hardest material known in the world. Its Vickers hardness reaches about 10Gpa. However, a domestic research group published an article on Nature, reporting that synthetic nano material that are harder than diamond has been developed. The new material's hardness is said to reach 108Gpa. It is called nanotwinned CBN, which is made by a combination of twin plane and ordinary CBN materials. Its Vickers hardness is twice the hardness of single crystal CBN (60Gpa). It is generally believed that twin plane is similar to ordinary crystal boundary surface that can strengthen material intensity and hardness. (The Hall-Petch effect). Actually, nanotwined CBN twin-plane boundary space is far shorter than critical distance. As a result, the Hall-Petch effect didn't appear, and the nanotwined CBN's hardness has strengthened. The experiment has bewildered many colleagues both in China and abroad.

Materials have different crystallographic planes and directions, along which the material's resistance to deformation vary. The material hardness abides by the Buckets effect. Namely, the direction that has the lowest resistance to deformation decides the material's hardness. The research group led by Sunhong has been engaged in the first-principles calculation research of superhard materials, taking advantage of the first-principles calculation method to establish a calculating software that can predict materials' Vickers hardness. Based on long-term research, they discovered that the weakest direction that decides material hardness of single crystal CBN is 62Gpa, the opposite direction being the strongest 130GPa. Thus the material intensity and hardness are highly improved. The process is similar to rubber sand drawing process. With drawing shape change, the rubber sand will become tense. (The strain stiffening effect). The following pictures show the restructuring process of atomic linkage on twin plane's surface, and the strengthening Vickers hardness with the material's shape change.

The system has given a good explanation to the physical process of nanotwined CBN material is harder than diamond and solved the Hall-Petch puzzle. The research has received help from national science funds.

Author: Liwei Chu 
Copyright: iAbrasive.com--Abrasives & Diamond Tools Market

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