There are two kinds of common tool coating methods: chemical vapor deposition (cvd) and physical vapor deposition (pvd) at present. In recent years, some new coating processes have appeared, which has a good application prospect.
CVD method, which belongs to atomic deposition, is a method of forming solid deposition layer on the surface of heating matrix by using vapor, hydrogen and other chemical components of metal halide at high temperature of 950~1050℃. The process includes three stages: vaporization of material, transport to the vicinity of matrix and formation of overlay on matrix.
Among all kinds of cvd methods, vacuum ion bombardment and magnetron ion reaction spraying are the most used. cvd technology is mainly used for the surface coating of cemented carbide cutting tools, which is suitable for high speed roughing and semi-finishing of medium and heavy cutting.
Compared with other coating methods, cvd method not only has the advantages of simple equipment, mature process, but also has the following advantages:
There are many kinds of sediments, which can be coated with metals, alloys, carbides, nitrides, borides, oxides, carbon nitrides, oxygen nitrides, hydro-carbon nitrides, etc: With high permeability and uniformity, multilayer coatings with different tissues can be obtained, and the coating thickness is uniform. The deposition rate is high and easy to control. The coating has high purity and fine and dense grains. Strong adhesion can obtain thicker coating. Low process cost, suitable for mass production.
PVD method is to remove materials from target sources by physical forms such as evaporation or sputtering, and then deposit these energetic vapor ions onto the substrate or part surface to form a film layer through vacuum or semi-vacuum space. The vapor reaction of evaporated or sputtered metal atoms leads to the deposition of the required compounds on the tool surface. pvd coating can be coated with titanium nitride, titanium carbon nitride, aluminum titanium nitrogen compounds, as well as various refractory metals of carbides and nitrides.
PVD technology is mainly used in the surface treatment of integral cemented carbide tools and high speed tool steel tools. It has been widely used in coating treatment of cemented carbide bit, milling cutter, reamer, tap, special-shaped tool, welding tool and so on.
The tcn coating with dense fibrous crystalline morphology can be obtained by medium temperature chemical vapor deposition (MT-CVD) at 700~900℃. The coating thickness can reach 8~10μm, and can be a2o3、tin on the surface layer by cvd technology.
MT-CVD coating blade is suitable for high speed, high temperature, large load, dry cutting conditions, its life is about twice as high as that of ordinary coating blade. cvd main drawback of the method is that the deposition temperature is high, and the tool annealing and deformation will occur when the high speed tool steel tool is coated. So the deposited tool must be quenched.
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