返回学校首页

图片新闻

more

师资队伍

more
李占勇
李占勇
张峻霞
张峻霞
李建宇
李建宇
吴中华
吴中华
您现在的位置:首页 >> 正文

学术讲座——Hybrid CO2 laser/waterjet (CO2-LWJ) Processing of polycrystalline Boron Nitride (pCBN)

  人:Pranav Shrotriya教授

    间:201771日(周二)下午2:00

    点:河西校区21号楼304会议室

欢迎广大师生踊跃参加! 

机械工程学院

                       天津市轻工与食品工程机械装备

集成设计与在线监控重点实验室

        2017710

 

AbstractI will present results from non-traditional hybrid CO2 laser/waterjet (CO2-LWJ) cutting and surface treatment of poly-crystalline cubic boron nitride (pCBN) material.   Cubic Boron Nitride (CBN) is the second hardest material on earth, inferior only to diamond. It is not found in nature but can be synthesized by application of high temperature and pressure. Since its discovery, PCBN has been used in industry as a substitute for diamond due to the superior thermal and chemical stability. The advantages that PCBN does not react with ferrous metals and has a high resistance to oxidation make it ideal tool material for machining but complicate its machining.  The hybrid CO2-LWJ machining system was used for cutting experiments on different thicknesses of pCBN blanks and results indicate a “score and snap” cutting mechanism for material separation.  Laser irradiation of the sample surface leads to scoring and phase transformation of the pCBN from sp3 to sp2 hybridized BN phases along the cutting direction.  Constrained volumetric expansion of transformed material leads to development of tensile stresses in the surrounding material and propagation of laser-scored cracks along the thickness. Finite element modeling of the transformation induced surface deformation and energy release rates for cracks is utilized to validate the “score and snap” mechanism for pCBN cutting. In the second part of the talk, we will present results from the surface treatment of a dual-phase BN material that has the same level of hardness as polycrystalline diamond.  The dual phase BN material was initially synthesized from high pressure and high temperature consolidation of powder materials and subsequently, the CO2 laser/waterjet heat treatment (LWH) was applied to the material surface.  The indentation hardness of the as-synthesized material was measured to be nominally 37 GPa. After the heat treatment the indentation hardness increased to nominal values of 75 GPa reaching the hardness of polycrystalline diamond 65-80 GPa.  Comparison of the as-synthesized and heat treated material microstructure revealed that heat treatment resulted in microstructure that consists of large grains; surrounded with regions of nano-grains between larger grains and; formation of solid interlayer along the grain boundaries.  A combination of amorphous phase formation at the grain boundaries and grain size refinement are suggested as the mechanisms responsible for the LWH processing induced hardness increase. 

主讲人简介Pranav Shrotriya is a Professor of Mechanical Engineering at Iowa State University, Ames, Iowa.  Before joining Iowa State University in fall 2003, he was a post-doctoral research associate in Division of Engineering at Brown University from July 2002 to August 2003 and in Mechanical and Aerospace Engineering at Princeton University from December 2001 to June 2002.  He received B.Tech degree in Mechanical engineering from IIT Bombay and his PhD and MS degrees in Theoretical and Applied Mechanics from the University of Illinois at Urbana-Champaign.  His research interests are in describing how materials deform and fail under interacting mechanical and environmental stimuli such as thermal, chemical and electrical fields.