Effect of Heating Conditions on Surface Modification of Titanium with a Mixture of Iron, Graphite and Alumina Powders

We developed a new surface modification technique called "iron-powder pack (IPP) treatment". A layer of titanium carbonitride, Ti(C, N), was formed on the surface of a titanium sample embedded in a mixture of iron, graphite, and alumina powders and held around 1273 K in a nitrogen flow. In this work, IPP treatment using a 4:6:3 (volume ratio) mixture of iron, graphite, and alumina powders was applied to titanium plates, and the effects of the heating temperature and nitrogen gas flow rate on the microstructures near the titanium surface were investigated. The Ti(C, N) layer was observed on the titanium plate heat-treated at 1173 K for 3.6 ks at a nitrogen flow rate of 0.5 L/min. This layer became uniform and thick as the heating temperature increased. At 1373 K, a Ti(C, N) layer with a thickness of more than 30 μm that increased the hardness of the titanium surface to an HV value of about 1500 was obtained. In addition, an increase in the nitrogen flow rate increased the surface hardness further. Spherical titanium powder was treated at 1273 K to examine the growth of the Ti(C, N) layer. The layer thickness increased with the holding time. Because the average diameter of the spherical powder was unchanged after heating, the Ti(C, N) layer grew toward the inside of the titanium via the diffusion of carbon and nitrogen from the powder mixture and the atmosphere.