| 摘要 |
A coated carbide tap comprises a substrate consisting of tungsten carbide cemented with 12 to 16% by weight cobalt with additions of small amounts of transition metal carbides added to restrain grain growth, and may also contain low levels of impurities that might be picked up during processing. The substrate is coated with a layer of metal nitrides, carbides, carbonitrides, borides and/or oxides, the metal being chosen from one or more of the following: aluminum, silicon and the transition metals from Groups IVa, Va, and VIa of the Periodic Chart. The coating may comprise a monolayer and/or alternating layers optionally with varying chemical composition. To reduce friction, a top outer layer comprised of molybdenum disulphide; molybdenum disulphide and transition metals, or any combination thereof; carbon; carbon and transition metal carbides, or any combination thereof; carbon and a transition metal, or any combination thereof; and/or carbon nitride may be either co-deposited as a single layer or deposited in multiple or alternating layers to the coating. The coated carbide tap of the invention can be used at cutting speeds at least three times faster than conventional taps without chipping or breaking the tap.
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