Surface Etching Of Diamond And Preparation And Performance Of Ferrochromium Composite Coating

Owing to merits of strong strength,high hardness,and low coefficient of thermal expansion,diamond has been widely used in many fields.In view of the inherent size drawbacks of diamond,bonding agents?e.g.a iron-based bonding agent?were needed to be a substrate to prepare tools with various shapes.However,the smooth and poor wettability characteristics of diamond give rise to weak interface bonding and bonding strength between metal substrates and diamond,which restricts the performance of its mechanical properties.To this end,in this paper,the adhesion between diamond and the bonding agent was boosted through two strategies?i.e.,surface etching and surface depositing a chromium-iron composite coating?.The details are as follows:?1?With iron powder as catalyst and iron sulfate as etching additive,a two-step strategy of material ratio-vacuum sintering was proposed to accelerate the diamond etching process.With the help of the corresponding characterization technology,the process parameters in the material ratioing and vacuum sintering process were optimized.The five factors of raw material ratio,etching additives,iron powder particle size,sintering temperature and holding time were systematically explored;and the influences on the surface morphology and performance of diamond before and after etching as well as the optimal solution of diamond etching process were obtained.The results display that temperature has the most significant effect during diamond etching.With the increase of temperature,the etch pits on{111}face tend to spread laterally and their shapes are polygonal;while the etch pits on{100}face change from circular/elliptical shape to regular quadrilateral shape.After 900?etching,compared with the original diamond,the quality of diamond,single particle compressive strength and impact toughness were only reduced by 1.18wt.%,4.80%and4.59%,respectively.The final etching mechanism analysis shows that diamond graphitization is the main reason for etching.?2?Based on the vacuum micro-evaporation plating technology,the content of diamond,chromium and iron in the mixing process was first optimized,and then the effects of plating temperature and time on surface morphology,structure,thickness,composition,and mechanical properties of diamond with Cr-Fe composite coating were discussed under the optimal ratio,and the optimal solution was obtained.The research shows that the best plating process is:plating temperature 875?,holding time 120min,under this process,a dense and uniform ternary composite coating with a thickness of 843 nm and the main components of Cr₇C₃ and FeCr was obtained.Compared with the original diamond,the diamond weight,compressive strength and impact toughness of the single-grain diamond after plating increased by 2.96wt.%,11.37%and 2.72%,respectively.