Microindentation and tribological study of nitrogen implanted martensitic steels

Ion implantation is an established technique for the modification of the surface characteristics of materials by bombardment with high energy ions to improve properties such as wear resistance, hardness, fatigue, and friction behaviour. The low treatment temperatures involved in this technique ensure the avoidance of distortion and are ideal for components and tools finished to a high precision. Results obtained in the present work illustrate that wear resistance and surface hardness of AISI M2, D2, and 420 steels can be improved by nitrogen implantation at doses >10¹⁷ ions C^-2. Lubricated Falex wear tests carried out using high loads showed an enhancement in wear resistance and a significant decrease in the coefficient of friction, especially for 420 and D2 steels. Use of an ultramicrohardness technique has shown that the true hardness of implanted surface layers is greater than the values obtained by conventional microhardness methods that result in penetration below the implanted depth. Other mechanical property data, such as elastic recovery and elastic modulus, can also be obtained from the shallow implanted layer. The results indicate that implantation of nitrogen can bring about a significant change of the near surface region of steels, promoting a change in the dominant wear mechanism and thus improving tribological behaviour of the surface.