Boridic surfaces and edge layers for hot forming applications

Introduction/Purpose: Hot forging operations with high thermo-mechanical and -chemical cyclic loads require durable surfaces and edge layers of the tools to enable an efficient production. Boridic materials therefore offer properties fitting into the requirement profile concerning the necessary chemical and thermal resistance with additional outstanding mechanical characteristics. Methods: Two different treatment approaches generate the presented boridic material systems: application of coatings and boriding of the tools. Results: PECVD deposition enables the development of multi-element coating systems with the transient metal titanium and boron, nitrogen, carbon and silicon. Due to structural properties, excellent wear resistance against various wear mechanisms even under extreme conditions with high pressures, adhesive contacts and thermal loads are detectable. The internal composition of the coatings consists of nm-size grains embedded in an amorphous matrix. In-situ phase analyses under thermal load up to 750°C revealed the capability to optimize the mechanical properties due to changes in the structural composition. Additional tribological investigations under high-temperature conditions showed improved wear resistance, especially of newly developed Si-containing systems. Other recent developments in diffusion processes used boron as the diffusing element for the generation of hard and good adherent compound layers. The technological goal is to obtain high temperature resistant boride layers with a hardness beyond 1,500 HV at the focused hot-working steel (AISI H11). The high process temperatures above 730 °C enable the diffusion process but soften the base material. Supplementary heat treatments after the boriding process restores the mechanical properties of the base material. This also changes the phase composition of the borides and provides a higher hardness. SEM-analysis shows a nonporous top layer with a thickness of 10 μm up to 25 μm with good layer adhesion between diffusion zone and the base material. Conclusions: The presented boridic systems show a high potential of wear reduction in the application field of hot forming