Abstract
A combined strengthening of cutting tools for finishing has been carried out in glow discharge plasma filling a process vacuum chamber. At the first stage, reamers rotating around the axis distanced from the magnetron targets at 8 cm were bombarded by fast argon atoms produced due to charge exchange collisions of ions accelerated in space charge sheathes between the plasma and a negatively biased to 3 kV grid with a 25 cm radius of its concave surface curvature. The reamer bombardment by fast neutral atoms led to a reduction of its cutting-edge radius from ~7 μm to ~2 μm. At the second stage, the reamer surface was nitrided within 1 h at a temperature of 500 °C stabilized by regulation of the negative bias voltage accelerating the nitrogen ions. At the third stage, a 3 μm thick TiN coating has been synthesized on the reamer bombarded by pulsed beams of 3 keV neutral atoms at a 50 Hz repetition rate of 50 μs wide pulses. After the combined strengthening, the cutting edge radius of the coated reamer amounted to ~5 μm and the roughness of the area machined by the reamer holes in blanks made of structural steel reduced by about 1.5 times.
Highlights
The useful life of tools, machine parts, and other products can be increased due to vacuum arc deposition [1,2,3,4,5] of wear-resistant TiN [6,7] and other coatings with a microhardness of ~25 GPa, whose manifold exceeds hardness of the product material
When the magnetron targets are disconnected from the power supply, the chamber is filled with quite uniform plasma (Figure 3)
The combined processing of cutting tools based on the vacuum arc, which includes the surface pre-nitriding and subsequent deposition of wear-resistant coatings [18,23,26], has two main drawbacks
Summary
The useful life of tools, machine parts, and other products can be increased due to vacuum arc deposition [1,2,3,4,5] of wear-resistant TiN [6,7] and other coatings with a microhardness of ~25 GPa, whose manifold exceeds hardness of the product material. Prior to the coating synthesis, tools are heated and etched by metal ions accelerated from the arc discharge plasma at the gas pressure of 0.001 Pa by a negative bias voltage of ~1000 V applied to the tools. Nitrogen is admitted to the process chamber and, at the gas pressure of 0.1–1 Pa, a hard nitride coating is synthesized on the tools under a negative bias voltage of ~100 V. A nitrided surface layer with a thickness by an order of magnitude exceeding the coating thickness exhibits a fatigue strength and high load-bearing capacity This prevents plastic and elastic deformations of the tool surface as well as brittle rupture of the deposited coating [8,9,10]. The tools are immersed in nitrogen plasma and heated up to an effective temperature of thermodiffusion 500–800 ◦ C by ions accelerated from the plasma by Machines 2018, 6, 58; doi:10.3390/machines6040058 www.mdpi.com/journal/machines
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