Preparation Of Vitrified Bond Porous Diamond Grinding Tools And Their Application In The Field Of Single Crystal Silicon Grinding

There are still problems with low efficiency,deep damage layers,high residual stress and low precision in single crystal silicon grinding,which makes subsequent polishing time long and economically costly.Diamond abrasives are widely used in precision machining of hard and brittle materials,but ordinary diamond has a smooth surface that does not easily bond firmly with the bond,a small and coarse cutting edge,and problems such as easy dislodgement,low utilisation rate,low grinding efficiency and stress concentration that easily scratches the workpiece during grinding.In response to the above situation,the thesis uses Fe/Fe₂O₃to thermochemically etch diamond micropowder to obtain diamond micropowder with a porous structure,which enables the bond to improve its holding power and makes the abrasive less likely to fall off the surface of the abrasive as a whole during the grinding process;the finely structured abrasive can form new cutting edges by breaking micro-edges on the surface,which greatly increases the self-sharpening of the diamond and improves the grinding efficiency;the surface of the abrasive The large number of tiny cutting edges can disperse the grinding heat and stress,making the grinding pattern fine,thus maintaining the high quality and high efficiency of grinding tools.The article is based on a systematic study of the preparation and application of porous diamond,the main research contents and results are as follows:（1）The effects of the corrosion conditions on the morphology,structure and properties of diamond micropowder after corrosion were systematically investigated by using Fe,Fe₂O₃and Fe/Fe₂O₃respectively.The results show that Fe corrodes diamond mainly in the longitudinal direction,and the mechanism is that Fe catalyzes the transformation of diamond into graphite at high temperature;Fe₂O₃corrodes diamond mainly in the transverse direction,and the mechanism is that Fe₂O₃oxidizes diamond at high temperature,and both Fe or Fe₂O₃only corrodes pits on the diamond surface,and neither can corrode diamond into porous structure alone.Using the synergistic differential corrosion effect of Fe and Fe₂O₃,diamond with a porous structure was corroded using Fe/Fe₂O₃as a corrosive agent,with a pore volume of 0.141 ml/g.The mechanism of diamond porosity is:differential corrosion of the diamond in contact with Fe and in contact with Fe₂O₃.（2）According to the structural characteristics of porous diamond,a R₂O-Si O₂-Al₂O₃-B₂O₃series vitrified bond suitable for porous diamond was designed and developed by smelting method.The influences of Li₂O addition and sintering temperature on the structure and property of the vitrified bond were analysed,the sintering mass transfer model was established,and activation energy of sintering was calculated.The results indicate that as the Li₂O content increases,the glass transition temperature,crystallization temperature,refractoriness and sintering activation energy of vitrified binder all decrease,and the fluidity increases.The change of Li₂O content and sintering temperature changes the type and quantity of the precipitated crystals in the binder.When the Li₂O addition amount is 13 mol%,the refractoriness is530°C,and the thermal expansion coefficient of the binder prepared at the sintering temperature of 670°C and the diamond is relatively matched,the fluidity reaches 171%,the bending strength is 93 MPa,and the organizational structure and element distribution are relatively uniform,which is suitable for the preparation of porous diamond bonded abrasives.（3）The wettability of vitrified bond to ordinary diamond and porous diamond was compared and analyzed,and mechanism of the increase of wettability of vitrified bond to porous diamond was investigated.The results show that for porous diamond,the etchant causes a lattice distortion of C on the diamond surface,resulting in the formation of a thin layer of diamond-like carbon containing SP²structural C,which increases the zeta potential of the diamond surface and in turn enhances the chemisorption of positively charged ions from the bonding agent.In addition,the pore structure also increases the physical embedding of the bonding agent into the porous diamond.The chemisorption and physical embedding increase the wetting of the bonding agent to the diamond,resulting in a higher holding power of the bonding agent to the diamond.（4）The molecular dynamics method is used to simulate the process of precision grinding of single crystal silicon wafers with ordinary and porous diamond abrasive particles.The surface morphology change,force analysis,temperature change and potential energy change of the workpiece are used as evaluation indicators to systematically compare the ordinary diamond and porous diamond.The wear mechanism of porous diamond grinding was discussed and verified by grinding experiments.The results show that ordinary diamond abrasive grains have large single-edged edges,mainly brittle cutting,and the abrasive grains achieve self-sharpening by disorderly crushing or detachment from the binder;while the porous diamond abrasive grains have a large number of tiny cutting edges,mainly plastic cutting,the cutting depth is small,and the grinding heat and stress are dispersed,which can effectively reduce the cutting damage of the workpiece and improve the surface processing quality.（5）Porous diamond and vitrified bond were prepared into bonded abrasive tools and used in the grinding process of single-crystal silicon.The results show that the TTV of the wafer after grinding with the W40 porous diamond bonded grinding disc can be controlled within 2.5μm,the surface roughness Ra within 0.25μm and the thickness of the damage layer within 3μm,and all the performance indicators are better than those of the conventional process.The residual stress value on the wafer surface after grinding（30μm de-thickening）and polishing（10μm de-thickening）by a porous diamond grinding disc with a grain size of W40 is less than 5 MPa,and the thickness of the residual stress layer on the wafer is less than 5 nm,indicating that the use of a porous diamond grinding disc to grind and thin single crystal silicon wafer and then directly polished can obtain a high-quality machined surface,the porous diamond bonded grinding disc grinding process can greatly reduce the time and cost of acid corrosion and polishing in the traditional process.