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Due to rising worldwide industrial competitiveness the machining sector is compelled to improve day by day. In this way, CO2 cryogenic machining is presented as alternative to conventional hard turning. So, in the tests carried out in this research, dry and CO2 cryogenic hard turning with two types of inserts were compared. The variables measured were tool life, superficial roughness and the piece microstructure. The results show an increase of tool life over 60%, a similar superficial roughness and, when positive insert is used, the absence of the white layer. [ABSTRACT FROM AUTHOR]

In this study, diamond-like carbon (DLC) films are coated onto oxynitriding-treated ASP23 high-speed steel by DC-pulsed PECVD. The main research parameters of the DC-pulsed PECVD process are the various duty cycles (5%, 10%, 15% and 20%) used to examine the coating characteristics. In order to investigate the DLC film properties, a Raman spectroscopy analysis, wear test, adhesion, and hardness tests are performed. The experimental results show that the duplex coating layers have optimal properties when DLC films are treated with a low-pulse voltage (− 1.5 kV), a coating time of 90 min and duty cycles maintained at 10%. As a result, the DLC/oxynitriding duplex-treated specimens with the highest surface hardness (Hv 0.01 1931) and the lowest wear volume loss (3 × 10 − 3 mm 3 ) can be acquired. In addition, compared with non-treated (polarization resistance R p = 5 × 10 3 Ω cm 2 ) and oxynitriding-treated (R p = 8 × 10 3 Ω cm 2 ) specimens, the optimal DLC/oxynitriding duplex-treated ASP23 high-speed steel possesses the lowest corrosion current (I corr = 8 × 10 −6 A cm − 2 ) and highest polarization resistance (R p = 1 × 10 4 Ω cm 2 ) in 3.5 wt.% NaCl solutions. This result confirms that the DLC/oxynitriding duplex treatment enhances optimal wear and corrosion resistance. [ABSTRACT FROM AUTHOR]