Journal of Manufacturing and Materials Processing

This study evaluates the effect of different precipitation-hardening regimes on the microstructure, hardness, and tribological behaviour of W720 maraging steel. Experimental specimens were aged at temperatures ranging from 460 to 490 °C for 3–16 h following solution annealing. Tribological tests were performed using the Ball-on-Flat method under dry sliding conditions against a G40 steel ball. The worn surfaces were analysed using LSCM, SEM, and EDS. Aging increased the hardness from 323 HV1 to 580–606 HV1 and reduced the coefficient of friction from approximately 0.75 to 0.63–0.71. The lowest nominal specimen wear volume was measured for the as-received, solution-annealed W720 condition (0.011 mm³), followed by HT490_6 (0.012 mm³); these values were compared descriptively without inferential statistical testing. However, the reference specimen produced a narrow, locally deepest wear track and caused the highest wear of the counter-body. The highest wear volume of the specimen was recorded for HT480_3 (0.027 mm³), while HT460_8x2 combined the highest hardness and the lowest coefficient of friction with a high wear volume. The dominant wear mechanism was a combination of abrasive grooving, adhesive damage, and tribo-oxidation. The results demonstrated that the tribological resistance of W720 is not governed by hardness alone, but rather by the interplay between microstructure, wear-track geometry, wear-product morphology, and the distribution of wear between the specimen and the counter-body.

In this paper, extraordinarily-high-speed (EHS) turning of Alloy 718 is investigated using a mixed alumina ceramic (Al₂O₃/TiC) tool. Although ceramic tools have been applied to high-speed turning of nickel-based alloys, previous studies have been limited to cutting speeds of 500 m/min or less. On the other hand, previous studies have suggested that cutting temperature saturation may occur in an extraordinarily-high-cutting-speed range. Therefore, cutting force, cutting temperature, and tool wear measurements are conducted over a wide cutting speed range from 100 to 1700 m/min to investigate the cutting temperature behavior and the corresponding tool wear characteristics in each speed range. As a result, the occurrence of cutting temperature saturation is confirmed for Alloy 718 in the EHS cutting regime. Furthermore, it is also found that the tool wear progression saturates in the temperature saturation region. Comprehensive analyses of cutting temperature, tool wear, cutting-edge profiles, and SEM/EDS observations clarify the speed-dependent tool wear mechanism. These findings suggest that the EHS turning can significantly improve cutting efficiency without sacrificing tool life.

The cutting temperature is an important aspect of the cutting process, and various methods have been devised to measure it. However, most previous studies have focused on the rake-face temperature since the highest temperature is generally observed near the cutting edge on the rake face. On the other hand, tool life and surface quality are strongly related to flank wear; therefore, the flank-face temperature is also of considerable practical importance. This study proposes a method that combines an electrically insulating layer with the tool–workpiece thermocouple method. By placing the insulating layer on the rake face or flank face, the flank-face or rake-face temperature can be measured directly and independently. The proposed method is first validated in the cutting of brass by comparing the rake-face, flank-face, and dual-face temperatures. The method is then applied to the cutting of medium carbon steel to investigate the evolution of the flank-face temperature during flank-wear progression. The results support the feasibility of directly and independently measuring the apparent average temperatures of the flank and rake faces and demonstrate that the measured flank-face temperature increases with flank wear.