Investigation of cryo-treatment on hardness and XRD profile of WC and AlTiN coated inserts

The recent trend in the machining industry is moving towards dry cutting by considering cost and environmental factors. But the dry cutting of advanced materials results in a higher cutting zone temperature, which causes poor finish, excessive tool wear, and higher power consumption. To overcome these drawbacks, the machining industry expects cutting tools with higher hardness and wear resistance. In order to satisfy the required criteria for a cutting tool, a supplementary process such as cryogenic treatment of the cutting tool is carried out to enhance its mechanical properties and cutting performance.

In this deep cryogenic treatment, tungsten carbide (WC) and AlTiN-coated carbide inserts were processed at −196 °C for 24 hours of soaking periods with a cooling/heating rate of 0.25 °C/min and then oil tempering was carried out at 140 °C for 2 hours. The impact of cryo-treatment on the microhardness (HV 1) and X-ray diffraction (XRD) profiles of cutting inserts were evaluated. The micro Vicker hardness of WC and AlTiN-coated inserts was increased by 3.16 % and 5.13 % with cryo-treated over untreated conditions, respectively. From XRD profiles, a small, sharp peak was observed in the 20–30° region with cryo-treated conditions of WC and AlTiN-coated carbide inserts over untreated ones. Hence, a new existence peak of AlTiN₂ (Ti_0.44 Al_0.56) N at 37° and 63° with a cryo-treated AlTiN insert over an untreated one. In addition, a peak of WC; AlTiN₂ (Ti_0.44 Al_0.56) N was observed at 76°. Finally, it was confirmed that there was an increase in hardness with cryo-treatment by the formation of small, sharp peaks, i.e., η-phase carbides, and hard surface coating over untreated conditions.