**Sergei Zenkin \*, Aleksandr Gaydaychuk, Vitaly Okhotnikov and Stepan Linnik**

Research School of High-Energy Physics, Tomsk Polytechnic University, Savinyh str. 2a, Tomsk 634050, Russia; gaydaychuk@tpu.ru (A.G.); ohotnikov@tpu.ru (V.O.); linniksa@tpu.ru (S.L.)

**\*** Correspondence: zen@tpu.ru

Received: 8 November 2018; Accepted: 5 December 2018; Published: 10 December 2018

**Abstract:** Chemical vapor deposition (CVD) diamond is a prospective thin film material for cutting tools applications due to the extreme combination of hardness, chemical inertness, and thermal conductivity. However, the CVD diamond cutting ability of ferrous materials is strongly limited due to its extreme affinity to iron, cobalt, or nickel. The diamond–iron interaction and the diffusion behavior in this system are not well studied and are believed to be similar to the graphite–iron mechanism. In this article, we focus on the medium-temperature working range of 400–800 ◦C of a CVD diamond–Fe system and show that for these temperatures etching of diamond by Fe is not as strong as is generally accepted. The starting point of the diamond graphitization in contact with iron was found around 400 ◦C. Our results show that CVD diamond is applicable for the cutting of ferrous materials under medium-temperature conditions.

**Keywords:** CVD diamond; diffusion; Fe–C interaction
