Applied Research, Co-precipitation - To Restore The Preparation Of Ni-co Alloy Powder In The Thin-walled Diamond Bits

In diamond industry, cobalt is always considered as the best metalmatrix. However, cobalt is rare and the reserve is quite finite. So it's verydear and the price is rising year by year. Because cobalt resource is poorin our country and the production of cobalt is unsufficient to demand.International market quotation constrains purchasing from abroad. So theapplication of cobalt bears great restriction. Therefore it is valuable toseek substitution of cobalt. Because nickel and cobalt both are iron groupmetal, their physical properties, such as density, melting point, atomicradius and so on, are almost the same. So are the chemical properties.Both nickel and cobalt can wet diamond well. Thus it is theoreticallypossible to displace cobalt by nickein. Nickel resourse is richer thancobalt, reserves of the former is as 15 times as that of the latter in theworld. So nickel is cheaper than cobalt. It will greatly decrease cost toproduct diamond tools in which matrix material is composed by part orfull nickel. Therefore it has broad market outlook and outstandingsocioeconomic benefit. In this papper Ni-Co alloyed powder is preparedby coprecipitation method. The preparation technology, sinteringtechnology and mechanical properties have been systematicallyresearched. Working conditions of thin-walled diamond bit separatelyusing Ni-Co alloy powder and pure cobalt powder as matrix metarialhave been studied comparely. The conclusions are as follows:1. Precursor is preparaed by coprecipitation method, usingNiCl₂·6H₂O and COCl₂·6H₂O as raw materials, oxalic acid as precipitant,ammonia solution adjusting pH value of reactive solution. Precursor issimple solid solution phase. Then after calcination and reduction, Ni-Coalloyed powder is gained. The size, morphology and content ofcomponents of Ni-Co alloyed powder can all be accurately controlled.Ni-Co alloyed powder is solid solution with cobalt as solute. Crystalstructure of the powder is face-centered cubic lattice.2. The pH value of solution has great effect on gain qutiety andmorphology of alloyed powder. In chosen pH value range in our experiment, the best one is 6.0～6.5, and in this condition, the powder isnear spherical. Reaction temperature and concentration of salt solutionhas some effect on size of alloyed powder. In chosen range ofconcentration of salt solution in the experiment, the optimal reactiontempeature is 70℃and the optimal concentration of salt solution is [Ni²⁺]+[Co²⁺]=0.8mol/L. The feeding order has considerable effect on thedispersivity of the alloyed powder, using parallel flow method conld gainthe best dispersivity.3. Precursor is calcined and reduced in pusher furnace. Whencalcing time and reducing time are both one hour, optimal calcining andreducing temperature of precursor is separately 400℃and 550℃.4. Among the experimental hot pressing temperatures, as hotpressing temperature rises, mechanical properties of Ni-Co alloy decrease.When being hot pressed at 700℃, the best mechanical properties get.Ni-Co alloyed powder is fit for being hot pressed at low temperature andthe ideal temperature should be lower than 800℃.5. As cobalt content increases, range from 10% to 50%, mechanicalproperties of Ni-Co alloy are growing stronger and stronger. After cobaltcontent reaches 30%, the improving trends of mechanical propertiesbecome weak. When hot pressing temperaure is 700℃, flexural strengthsof Ni-Co alloys with cobalt content of 30%, 40% and 50% are seperately1188.7 Mpa, 1220.5 Mpa and 1227.1 Mpa, which are equivalent to purecobalt.6. Among hot pressing temperature range of the experiment, whenhot pressing temperature is 750℃, bond strength of the interface between70Ni30Co alloy and diamond is the best. When drilling reinforcedconcrete with steel ratio of 3.3%, average drilling speed of Ni-Co alloydiamond bit is equivalent to pure cobalt diamond bit, and speed ofdrilling cement is obviously higher than pure cobalt diamond bit.