Reinforcement Of Iron-based Matrix Materials For Impregnated Diamond Drill Bits By Carbon Nanotubes Addition

The reinforcement of impregnated diamond bit iron-base matrix material plays an important role in improving the service life of the geological drill bit and the drilling efficiency.In this study,a carbon nanotubes?CNTs?-reinforced iron-base composite matrix material was fabricated by hot press-sintering using an intensified method of incorporating carbon nanotubes in an iron-base matrix.Firstly,the dispersion of carbon nanotubes by manual stirring,mechanical milling and active agent methods was studied.Then,the effect of different carbon nanotube concentrations on the properties of the matrix,such as density,hardness,bending strength,porosity,and wear ratio,was studied.Furthermore,on the basis of the optimized carbon nanotube concentration,the effect of the drilling of the carbon nanotube-iron-base matrix diamond micro drill was evaluated.In order to expand the application potential of the carbon nanotube-iron-base composite matrix material,the feasibility of laser surface remelting and even the effect of laser high-energy beam irradiation on carbon nanotubes and iron-base composite materials were further studied.The study of carbon nanotube-iron-base composite matrix material shows that the surfactant dispersion method can effectively disperse the carbon nanotubes,thereby significantly reducing the concentration of the incorporated carbon nanotubes,but at the same time obviously improving the performance of the composite material.In the range of 0.01-0.15 wt.%,the hardness and bending strength of carbon nanotubes increase first and then decrease with increasing concentration of carbon nanotubes.The content of 0.05 wt.%carbon nanotubes has the best toughening effect on the iron-base matrix.Compared to the primary iron-base material without carbon nanotubes,the Rockwell hardness increases by 10%and the bending strength increases by 220%.The effective dispersion of carbon nanotubes and good bonding with matrix tissue are important factors in the toughening effect caused by the effects of bridging,pulling out and crack deflection.The higher content of carbon nanotubes will cause the carbon nanotubes in the grain boundaries to aggregate and affect the bonding of the structure,which is the main reason for the decrease in bending strength.Compared with the original iron-based matrix,the wear ratio of the non-diamond composite matrix of 0.05%carbon nanotube-iron-base composite matrix increased by31%,while the wear ratio of the diamond-containing composite matrix increased by110%.Studies have also shown that under the experimental conditions,the effect of carbon nanotubes on the density,porosity and grain size of iron-base matrix materials is not significant.The high hardness of the iron-base matrix material is mainly related to the fine Fe₂B intermetallic particles dispersed in??Fe,Ni?+??Fe,Cr?structure.The micro drill test showes that the impregnated diamond drill with 0.05 wt.%carbon nanotubes have less wear in the inner and outer working layers of the carcass.The toughening effect of carbon nanotubes on the bit matrix is further demonstrated.Laser remelting studies show that 0.05%of carbon nanotubes-iron-base matrix materials of laser remelting area for the dendrite??Fe,Ni?and dendrite??Fe,Cr?between compacted remelting layer microstructure and partial melting zone.The 800W laser power generated not only thicker remelted layer and partially melted zone,coarser dendritic structure and a harder remelted microstructure,but also a transition of carbon nanotubes-matrix joining from mechanical doping to metallurgical bonding characteristic of carbon nanotubes'enwrapping with interdendritic constituents.The collateral coarsening and disintegration of carbon nanotubes are ascribed to the conjoint effect of laser irradiation and thermal annealing during the remelting.The harder interdendritic structure relative to the dendrite is also attributed to the therein dispersed carbon nanotubes and relevant constituents.The lower hardness in coarser partially meleted zone and the ascent hardness in finer partially meleted zone are mainly owing to the size effect of“granular”dendrites.The hardness level of the 800W-remelted layer comparable to the sintered composite substrate is accredited to the comprehensive effect from the reinforcing carbon nanotubes,alloying constituents,dendrite size in the dense remelted microstructure.