| Due to strong bonding strength between Fe-based metal bond and diamond,long sevice life and low cost,Fe-based metal bond diamond wheels are used a lot in precision and ultra-precision grinding of metal and hard brittle nonmetal materials.However,high relative density and high toughness of Fe-based metal bond make the wheel poor self-sharpening.This paper was focused on the preparation of the self-sharpening metal-vitrified composite bond diamond wheels by adding Na2O-B2O3-SiO2-Al2O3-LI2O vitrified addition(weak grinding phase).It was a new way to preparation of high grinding performance Fe-based metal bond diamond wheels.Firstly,this paper discussed the effects of the content of FeNi alloy powders and TiO2 on the performance of metal and vitrified addition.Secondly,the effect of coefficient of thermal expansion of vitrified addition,sintering temperature and holding time on interface bonding strength of metal-vitrified samples were studied.Thirdly,the effect of sintering temperature and holding time on the performance of metal-vitrified composite bond were studied.Finally,the effect of sintering temperature,holding time and vitrified addition content on the mechanical property and performance of grinding molybdenum cast iron of metal-vitrified composite bond diamond wheels were investigated.This paper was first researched on the selection and optimization of the metal bond and vitrified addition.The effects of the contents of the FeNi alloy powders on the hardness,bend strength,expansion coefficient of Fe-based metal bond,interfacial thermal stress between diamond and metal bond and hoding force to diamond were studied.Through the experiments,it had firstly proved that the FeNi alloy powders would have great influence on the performance of the Fe-based metal bond and expounded the reason.With the increasing of FeNi alloy powders,the hardness,bend strength,expansion coefficient of metal bond and interfacial thermal stress were decreased due to the increasing of y-(Fe,Ni)with low hardness,strength and expansion coefficient.The holding force between diamond and metal bond diamond samples were first increased and then decreased with the increasing of FeNi alloy powders,the reason was that the decreasing of the interfacial thermal stress contributed to the increasing of holding force.However,excessive FeNi alloy powders decreased the density of metal bond,which was harm to the holding force.When the content of FeNi alloy powders was 9wt%,the hardness,bend strength,expansion coefficient of metal bond,interfacial thermal stress and holding force were HRB92,960MPa,11.45R10-6/K,815MPa and thehighest,respectively.For vitrified addition,the TiO2 were introduced to promote the performance of vitrified addition.When the TiO2 content was less than 3mol%,the Ti4+ would enter into glass network struction,which could mend and agglomerate glass network.With the increasing of TiO2,the vitrified addition's expansion coefficient were decreased,refractoriness and bend strength were increased.It was also found that the wetting angle between the vitrified addition and diamond change smaller because of the enrichment of Ti4+ on diamond and vitrified addition interface.When TiO2 content was no less than 3mol%,phase separation effect of TiO2 promoted the low expansion coefficient ?-spodumene precipitation.When TiO2 content was 3mol%,bend strength of vitrified addition reached the maximum value,93MPa.Secondly,in consideration of improving the interfacial bonding strength between the metal bond and the vitrified addition,the effect of the vitrified addition with different expansion coefficient and sintering temperature on the interface bonding strength of metal-vitrified samples were discussed.When the sintering temperature was 850?,the interface of metal-vitrified samples was composed of metal phase,transition layer FeSiO3 and vitrified phase.With the decreasing of vitrified addition's expansion coefficient,the transition layer reduced from about 50nm to 30nm.So the interfacial thermal stress and the wetting angle between vitrified addition and metal bond increased constantly.The interfacial bonding strength decreased constantly.When the expansion coefficient of vitrified addition reduced to 6.12×10-6/K,the interface bonding strength also reduced to 95MPa.The sintering temperature also had great influence on interface bonding strength.When the sintering temperature was 850?,the protoxide of Fe attracted the anionic group in vitrified addition.The metal and vitrified addition reacted on the interface and formed transition layer.With the increasing of sintering temperature,the transition layer increased from about 50nm to 80nm.So the interfacial thermal stress and the wetting angle between vitrified addition and metal bond decreased constantly.Finally,the interface bonding strength increased constantly.Thirdly,in consideration of improving the performence of the metal-vitrified composite bond,the effect of the sintering temperature and holding time on hardness,bend strength and densification process of metal-vitrified composite bond were discussed.With the increasing of sintering temperature and holding time,the shape of vitrified addition changed from sphere,ellipse,strip to lamellar.When the sintering temperature was 850 ?and holding time was 3min,the reaction between the metal and vitrified addition increased the interface bonding strength,and the transmutative vitrified addition increased the path of the crack propagation.So the the bend strength of metal-vitrified bond reached to the maximum value 827MPa,and the hardness reached to HRB95.When the sintering temperature was lower than softening point of vitrified addition,the vitrified addition were solid particles,which replaced the metal liquid phase,so the densification rate of composite bond was lower than metal bond.With the increasing of sintering temperature and holding time,the viscosity of vitrified addition rapidly decreased,the liquid phase of composite bond increased,which were benefit to rearrangement of metal solid particles and grain boundary diffusion.So the densification rate of composite bond rapidly increased.When the sintering temperature was 850 ? and holding time was 3min,the density of composite bond reached to the maximum value 95.76%.Finally,the self-sharpening metal-vitrified bond diamond wheels were fabricated by hot pressed sintering technique.The effect of the sintering temperature,holding time and vitrified addition content on mechanical property and grinding performence of metal-vitrified composite bond diamond wheels were discussed.With the increasing of sintering temperature and holding time,the hardness of composite bond diamond wheels sample had little increase,the bending strength firstly increased and then decreased.When the sintering temperature was 850? and holding time was 3min,the relative density of composite bond diamond wheels sample reached the maximum value,the B-C and C-O chemical bond were formed between vitrified addition and diamond,the holding force between diamond and composite bond reached thehighest.So the bending strength,abrasive ratio of composite bond diamond wheels reached the maximum value 698MPa and 43.77,and surface roughness of the workpiece reached to the minimum value 4.2?m.When the sintering temperature was 900 ? or holding time was 4min,the diamond occurred graphite transition,which decreased the interface bonding strength between diamond and composite bond and the grinding performance of composite bond diamond wheels.With the increasing of the vitrified addition content,due to the vitrified addition was brittle phase,the bending strength decreased.When the vitrified addition content was 3wt%,the abrasive resistance of composite bond decreased,and the grinding force and specific grinding energy of composite bond diamond wheels also decreased,so the sharpness of composite bond diamond wheels was increased.Comparing with the metal bond diamond wheels,the roundness and straightness of the molybdenum cast iron cylinders grinded by the metal-vitrified composite bond diamond wheels reduced to 2.7tm and 2.1?m. |
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