A Study On Sintering Of High Property Polycrystalline Cubic Boron Nitride

Cubic Boron Nitride (cBN) is a second hardest material known ,after diamond ,and is superior to diamond in several respects :a higher oxidation resistance ,greater chemical resistance to ferrous alloys such as steels and nickel-based superalloys. Developed countries developing cBN tools as a important material, because it is economy ,energy saving , efficient and precision, And it indicate the technology of a country. But the development of cBN tool is not perfect in our country .We drop behind developed countries not only in variety ,but also in quality.The sintering of Polycrystalline Cubic Boron Nitride(PcBN) from cBN is investigate in this paper.cBN powder is sintered by infiltrated molten Co from WC-Co substrate into cBN layer during high pressure and high-temperature sintering.. Both assembly of direct heating and assembly indirect heating are used in our experiment.. The sinter of cBN power was investigated on several temperature and pressure. From the analysis of our product by SEM ,EDS and Knoop hardness tester, some conclusion can be draw : (1)The reaction of sinter are completed in a short time (less than 40 seconds) when assembly of direct heating is used,.. There is not change clearly when prolong the heating time. (2)The assembly of direct heating is not steadily. It is very difficultto gain PcBN with excellent properties. (3)It is very difficult for cobalt to substrate into cBN layer while the size of starting cBN powder less than 10(x.The cobalt line will appear on the surface of PcBN. The Co line will debase the quality of PcBN. PcBN's hardness is low also if the size of starting is more than 40u.(4) The highest Knoop hardness of 3134 was achieved for the 50 wt.% lOucBN power- 50 wt.% 40ncBN power composition specimen sintered at. 1500°C and 6.0GPa for 30 min.Considering the result of our experiment, The factors influencing the quality stability of PcBN are analysised. We consider that the Co line appear on PcBN surface is the result that Co is concentrated among the grains of cBN and leak out on the surface of PcBN. The fact of cBN layer separating from WC-Co layer is mainly caused by the impurity of starting cBN power ,or the temperature and pressure of sintering is not enough.Studies on sintering PcBN will play an important role in both the theoretical guide and practical value for the application in industry.