Durable metal carbide layers on steels formed by ion implantation at high temperatures

Abstract

High-power beams (4–10 W/cm2) of Ti ions have been used to heat Fe and steel substrates to 600–800 °C during high fluence (5×1017/cm2) implantation. Auger sputter depth profiles find a stoichiometric TiC surface layer, about 100 nm deep, graded continuously into both Fe and steel substrates. Secondary ion mass spectrometry of Fe and steels implanted in 13CO atmospheres indicate that the carbon originates from the bulk in carbon steels but from the atmosphere in Fe foils. Transmission electron microscopy reveals a continuous layer of fine-grained (50–100 nm) TiC crystallites in a preferred Baker–Nutting orientation relationship with respect to underlying Fe grains. Abrasive-wear measurements performed with diamond paste (1–5 μm) show the TiC layer on hardened M2 steel is 3–10 times more wear resistant than the substrate. Sliding-wear studies find an extremely durable layer that reduces friction by up to 60%, and increases by 50% the contact-stress threshold of M2 tool steel to boundary lubrication. The metallurgical processes responsible for the TiC layer will be discussed, and the advantages of this high-temperature treatment will be presented.