Study On The Breakage Characteristics Of Diamond Particles Under Quasi-static And Impact Loads

In this paper,the quasi-static load is provided by the super-hard abrasive compressive strength tester.The compressive strength of different grades and crystal-form diamond particles is tested.The diamond particles before and after heat treatment are gradually pressurized to simulate the crack formation and expansion process.Optical microscopy and scanning electron microscopy were used to observe and analyze the evolution process of diamond surface cracks and the formation mechanism of various fracture morphology after fracture.The artificial diamond impact toughness tester was used to provide cyclic impact load,and different particle size,grade and impact times were tested.The fracture rate of diamond particles was measured by particle image analyzer and scanning electron microscopy image.The particle size distribution and morphology of the broken particles were tested.The fracture mode of diamond particles under cyclic loading was analyzed.The high-speed hedging flow to diamond particles was provided byjet mill.The fracture was tested and the morphology of the different particle size samples of the crushed product was tested.The main conclusions drawn in this paper are as follows.(1)Breaking characteristics of diamond particles under quasi-static loading:The average compressive strengths of the three grades of high,medium and low diamond particles were 478.25N,223.26N and 101.08N,respectively.The standard deviations were 195.41,92.43 and 61.04,respectively.High-grade particles were more prone to comminuted fracture.Low-grade particles are mainly localized fractures of the particles.The crack on the surface of the diamond particle(111)is mainly in the nucleation of the triangular pyramid pit,and the microcracks after the nucleation are combined to form a pit strip,and the pit strip develops to form a large crack to the crystal edge and finally leads to the fracture of the diamond particle.A large number of triangular pits with a side length of about 20 ?m appear on the surface of the heat-treated diamond particles.The original surface defects are no longer the main source of crack nucleation.and the crack propagation mode is more diverse.The fracture morphology of the diamond cleavage plane is characterized by river patterns,that is,a series of steps arranged along the crack propagation direction are merged layer by layer to form a larger step,which is formed by the spiral dislocation,the torsion grain boundary and the intersection of the cracks.With different topographical features,the nucleation point of the crack and its extension direction can be judged according to the details of the pattern.Samples with higher boron content in diamond have denser steps.(2)Breaking characteristics of diamond particles under impact load:Under the cyclic impact load,the diamond particle crushing method is mainly based on surface crushing,and there is volume crushing.The larger the particle size,the lower the grade of the diamond particles tends to cause surface fracture;the diamond particles mainly undergo volumetric fracture under high-speed airflow impact,and the diamond particle morphology of each grain level after fracture classification has similarity.Under the impact load,the diamond particles generate more cracks due to multiple loading or multi-angle loading,and a plurality of fracture surfaces are formed.Under the quasi-static load,the diamond particles are mainly cracking along the cleavage plane to form large cracks,resulting in fractures,less.After the cyclic impact,the residual crack on the surface of the diamond particles is more than the residual crack on the surface of the diamond particles after the impact of the high-speed airflow.The innovation of this article:(1)Innovation of research methods:On the one hand,the single particles are gradually pressurized and the surface topography changes of the force surface are observed.On the other hand,the particles which are not crushed and slightly broken after the compressive strength test are observed.Cracks in different degrees of fracture may exist in the particles,and the nucleation and expansion process of the crack on the diamond surface are derived by combining the two experimental results.(2)Innovation of research content:The river pattern image of diamond particle fracture was observed and analyzed in detail,and the formation mechanism of various steps was analyzed.The morphology of particles under quasi-static load,cyclic impact load and high-speed airflow impact load were compared.It provides a theoretical basis for identifying the type of diamond particle fracture,understanding the stress condition when it fails,and guiding its application.