Preparation Of Copper-based Superhard Honing Stone And Its Mechanical Properties

Honing is a machining process for inner hole reaming and polishing with high requirements on production accuracy,and thus the high properties oilstones are required to guarantee the accuracy in machining process.Therefore,it is necessary to raise the machining efficiency of honing oilstones by improving the properties of honing oilstone.The honing oilstone is mainly fabricated by the hot-pressed sintering with the abrasive material embedded in the metal matrix materials,where the role of the hard abrasive material is mainly grinding in the machining process.At present,the CBN and diamond are considered to be the most promising abrasive materials due to their high hardness,excellent chemically inertness and oxidation resistance at high temperature.However,a main technological challenge for the diamond or CBN honing oilstone is the interfacial compatibility between the hard abrasive material and metal matrix during the machining process,resulting in the relatively low grinding efficiency.In this paper,the diamond or CBN honing oilstone samples were prepared by hot-pressed sintering in the air.Effects of Cu-based alloys composition,volume fraction of the abrasive material and sintering temperature on the density,bending strength,Rockwell hardness,microstructure and phase composition were investigated.And then wearing test was utilized to judge their mechanical properties.The experiment results show that the density,bending strength and Rockwell hardness of metal matrix increase with the sintering temperatures and the content of Co increasing.A Co-rich solid solution containing Cu and Sn can be observed in the microstructure of the metal matrix.Additionally,the agglomeration of Ti can be regarded as a second phase and deteriorate the mechanical properties of the oilstone as Ti is added in the metal matrix.The added Ag in the metal matrix can aggregate together to form a large scale of Ag particle at a relatively low sintering temperature.The increase of sintering temperature can weak the degree of the Ag aggregation with some Ag atoms dissolving in the Cu-Sn phase,which can raise the properties of the metal matrix.The Rockwell hardness of the honing stones increase with the volume fraction of abrasive(diamond or CBN)increasing,while the density and bending strength corresponding decrease.In addition,the density and bending strength corresponding increase after the abrasive material(diamond and CBN)subjected to the surface coating,especially for the W-coated diamond samples.However,the Rockwell hardness of the honing stones decreases after the W-coated diamond is applied into the honing stones.From the fracture SEM images of different oilstone samples,it can be seen that the fracture paths are mainly along with the interface of abrasive material and metal matrix,suggesting that the main fracture mode is brittle rupture as the low sintering temperature;however,the main fracture mode become ductile fracture as the sintering temperature increasing due to the obviously increasing adhesion between matrix and abrasive.According to the results of the abrasive wear test of the diamond honing oilstone,the grinding ratio(G)is 0.732 as the diamond is W-coated with 15% W-coated diamond fraction.Furthermore,when the diamond,CBN and Ti-coated CBN are respectively used as the abrasive material with 10 vol.%,the grinding ratio(G)is 0.825,0.813,and 0.796,respectively.From the microstructure of the honing oilstone after abrasive wear test,most of diamond grains are still embedded in metal matrix and a small quantity of diamond grains are ruptured due to the plowing action,showing high machinability of diamond honing oilstone.For the CBN or Ti-coated CBN as the abrasive material,a large amount of abrasive materials are ruptured and removed out from the metal matrix.