Research On Stripping Coating Of Scrap Coated Carbide Tools

Coated carbide tool is one of major cutting tools in the world, because it exists big ingredient differences between coating layers and cemented carbide matrixes, scrap coated carbides need strip for their coatings in recycling process. Different mark scrap coated carbides are used as experimental materials in the paper, stripping of their coatings have been researched with various methords. By means of 3D digital microscope, scanning electron microscopy, EDS, EDX, XRD, microhardness texter and so on, the surface morphology, chemical ingredient, structure composition and performance of the samples were discussed, The results show that:1) The TiN coating on scrap coated carbides can be effectively removed by alkaline solution consisted of potassium oxalate and hydrogen peroxide, the optimized matching of the solution is K2C2O4(0.5mol/L), H2O2(3mol/L) and PH=13. It’s obvious that TiN coating strip preferential phenomenon, three corrosion styles appear, including spot corrosion, crevice corrosion and uniform corrosion. The reason why spot corrosion and crevice corrosion come out is that there exist defects like etch pits and crevices in TiN coating and form blocking areas. Uniform corrosion is dominant in the TiN coating stripping process, when TiN coating is stripped, nitrogen exists in form of ammonia or ammonia water, however titanium is dissolved in the solution in form of TiO(C2O4)222-.2) The TiN/α-Al2O3/TiCN coating can be removed effectively using mixed solution of NaOH and Na2CO3, the best removal coating efficiency can be obtained in condition of 700℃ and 40 min by molten-salt growth method, but do harm to matrix heavily. Mass loss rate of sample reaches 3.32%. α-Al2O3 coating is removed mainly reacting with NaOH solution.3)The Multi-constituent coating on different types scrap coated carbide tools can be effectively removed by means of physical pretreatment and then using self-research stripping solution. In the process of stripping coating by dissolution method, preprocessing methods have important effects on coating stripping rate, stripping efficiency and morphology of cemented carbide matrixes after stipping. In the high-temperature processing process, TiN and Ti(C, N) coating crack at low oxidizing temperature, lead to a large number of latticed microcracks, loose oxide layer render hardness descend rapidly, reduce the bonding strength of coating and matrix; sand blasting may break coating structure, which lead to embossments, small cracks and cavities in the coating, reduce the binding force between coating and matrix, speed up coating stripping rate. The best physical pretreatment mode is processing 90min at high-temperature of 450℃, and then air cooling, the Multi-constituent coating can be removed completely in self-research stripping solution when the reaction time is more than 24 h, mass loss rate is about 1%.