Research On Catalytic Etching Of Synthetic Diamond By Iron Group Metals

Diamond has a series of excellent performance such as high hardness, high strength, high wear resistance and high thermal conductivity, etc., which makes it have been widely applied in many fields. However, duo to high surface energy and smooth surface of diamond, the interface bonding strength between the diamond and the binder materials is so weak, which seriously limit the service life of diamond tools. In this paper, it was the first time to catalytic etching of diamond crystal by iron group metals under the high temperature conditions. The corrosion pits were obtained on diamonds' smooth surface, which increased the surface roughness of diamond and improved the holding strength of bond to diamond in abrasive tools. The main research contents and results were as follows:First, Respectively, Fe, Co and Ni powders were used as catalytic etching agent. The influences of heat treatment temperature and holding time on the corrosion microstructure morphology and corrosion depth of diamond crystal surface were studied. The results showed that: the corrosion depth increased with the raise of temperature and holding time, but promoting heat treatment temperatures was more effective.Second, it was found that the {100} plane was etched more severely than the {111} plane in the same etching conditions. The reversed pyramid-like etching pits were observed on etched {100} plane, while the triangular or hexagonal etching pits with a smooth flat bottom were observed on etched {111} plane. Moreover, the etched diamond crystal also retained the original particle morphology. Raman spectroscopy analysis showed that the corrosion pits caused by the graphitization of diamond.Third, after being etched, the diamond structure has been preserved, and its strength decreased slightly with the increase corrosion temperature. Compared with the untreated diamond, the TI values and TTI values of diamond etched by iron at 960 ?only decreased by 3.17% and 1.88%. The TI values and TTI values of diamond etched by cobalt at 930?reduced by 3.96% and 2.18% and the single particle compressive strength merely cut down by 5.6%.Fourth, for the temperature of obtaining obvious corrosion effect, the lowest temperature were got when cobalt were used as etching agent, while the highest temperature were got when iron were used. When the heat treatment temperature was 870?, the corrosion rates of {100} plane and {111} plane of diamond etched by iron were 0.939% and 0.785%. When the processing temperature was 810?, the corrosion rates of {100} plane by cobalt or nickel were 51.631% and 13.278%, respectively. The corrosion rates of {111} plane were 34.062% and 4.158%, respectively. The corrosion uniformity and corrosion rates of cobalt etched diamond was better than nickel, while iron was the weakest.Five, the mechanisms of iron group metals etched diamond crystals were proposed. The solid metal gradually melted into liquid phase with the increase of temperature and holding time, which made the point contact gradually transform into surface contact between the metal powders and diamond particles. Then the molten metals could promote the carbon atoms from the diamond phase transform into the graphite phase, and graphite carbon diffused away from the diamond-metal interface in molten metals.