Microstructure And Tribological Behavior Of Thermally Damaged Polycrystalline Cubic Boron Nitride

Polycrystalline cubic boron nitride is another new high-tech superhard material that emerged after the advent of synthetic diamond.As the main tool material for cutting hard materials,in its processing applications,high-speed,ultra-high-speed,heavy-load conditions,etc.,cause a large amount of cutting heat to be generated during cutting.Higher cutting heat generation not only causes structural changes and heat of the cutting tool.Damage causes unpredictable wear of the cutting tool during machining and also affects the surface integrity and dimensional accuracy of the workpiece being machined.This paper aims to simulate the cutting heat generated by polycrystalline cubic boron nitride in processing applications through heat treatment process,revealing the influence of high temperature heat treatment on the microstructure and tribological behavior of polycrystalline cubic boron nitride composite sheet materials,and analyzing the microstructure of materials.The relationship between physical properties,friction coefficient,wear rate and heat treatment temperature results in the following experimental results:?1?After the polycrystalline cubic boron nitride is heat treated at 600?to 800?,the annealing treatment causes thermal stress at the interface between the binder and the cBN due to the difference in thermal expansion coefficient between the binder phase and the cBN.This causes the binder to precipitate from around the cBN particles.At the same time,the precipitated binder phase slightly changed the microstructure of the surface of the PcBN composite sheet and changed its surface roughness to some extent.Since the binder has a lower hardness than the cBN particles,the precipitation of the binder also lowers the hardness of the polycrystalline cubic boron nitride.?2?After annealing at 900?,the chemical thermal damage mechanism appears.In the high temperature environment above 900?,the binder phase TiB₂ obtains the activation energy required for the reaction,and reacts with oxygen in the atmosphere to form new phase TiO₂,which causes the microstructure of the polycrystalline cubic boron nitride to change.And the production of new phase TiO₂ leads to a further decrease in the hardness of the polycrystalline cubic boron nitride.?3?The wear mechanism of the non-heat treated polycrystalline cubic boron nitride on the grinding of the GCr15 ball is mainly the adhesion phenomenon,and the adhesion layer protects the wear of the polycrystalline cubic boron nitride.After heat treatment at 600?and 700?,the hardness of the sample decreased,and the adhesion layer was not completely maintained,resulting in slight wear of the polycrystalline cubic boron nitride,and the friction coefficient was slightly lower than that of the untreated sample.After 800?,the adhesion layer continued to accumulate,but the form of wear was a combination of wear and adhesion.The heat treatment at 900?results in a phase change of the polycrystalline cubic boron nitride,a decrease in hardness,a large amount of wear on the grinding balls and the sample,and a sharp increase in the friction coefficient.?4?The maximum wear scar wear occurred when the Si₃N₄ sphere and the unheated polycrystalline cubic boron nitride were worn,and no sticking occurred.The friction coefficient between 600?and 800?is similar to each other.Due to the decrease of the hardness of the sample,the wear rate of the grinding ball also decreases.At 800?,slight sticking occurred at the wear scar boundary.After heat treatment at900?,the phase change of the sample causes the adhesion layer to accumulate in the wear marks,and the wear scar amount is low.Heat treatment at 1000?,wear scar wear mechanism by adhesion and wear together.