Thin film coatings are widely applied to extend the service life of hot metal forming dies by improving wear resistance, reducing friction, and mitigating thermal and chemical damage. Nitride coatings deposited by Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) methods have demonstrated potential to deal with critical challenges at the die-workpiece interface. This paper reviews the designs and applications of nitride coatings to hot metal forming dies. The discussion begins with the fundamentals and characteristics of monolithic, binary, and laminated coatings, which aim to enhance tribological performance at the interface. It then explores the application of nitride coatings used in the hot forming processes of steels, aluminum alloys, and other metal alloys. Finally, the review concludes with key highlights and recommendations for coatings selection and future research to improve the tribological performance of hot metal forming dies.

Galling phenomena in metal forming not only affect the quality of the engineered surfaces but also the success or failure of the manufacturing operation itself. This paper reviews the different galling conditions in sheet and bulk metal forming processes along with their evolution and the effects of temperature on galling. A group of anti-galling methods employed to prevent galling defects are also presented in detail. The techniques for quantitatively measuring galling are introduced, and the related prediction models, including friction, wear, and galling growth models, are presented to better understand the underlying phenomena. Galling phenomena in other processes similar to those occurring in metal forming are also examined to suggest different ways of further studying galling in metal forming. Finally, future research directions for the study of galling in metal forming are suggested.

The tribo-characteristics of metal forming at high temperatures have not yet been well understood due to the complex nature of thermal, microstructural, interaction, and process parameters. This is a review paper on the effects of temperature, coating, and lubrication to the tribological characteristics in hot forming as well as the tribometers for different metal forming processes at elevated temperatures mainly based on the experimental work. The tribological behaviors of oxides in hot forming, such as rolling and stamping, were reviewed and presented. Some commonly used surface coatings and lubricants in hot forming were given. Many types of tribometer were selected and presented and some of them provided a great potential to characterize friction and wear at elevated temperatures. Nevertheless, more testing conditions should be further investigated by developing new tribometers. Eventually, experimental results obtained from reliable tribometers could be used in theory and model developments for different forming processes and materials at high temperatures. The review also showed the great potential in further investigations and innovation in tribology.