Surface Hardening of Titanium by Mixed-Interstitial Compounds and Mixed-Interstitial Solid Solutions Using Gaseous Carbo-Oxidizing and Nitriding

Abstract The present study investigates the response of CP titanium grade 2 on gaseous carbo-oxidizing in CO atmospheres. The treatments were carried out at 1000 and 1080 °C for different durations, which resulted in formation of mixed interstitial compounds, consisting of carbo-oxides and mixed interstitial solid solutions based on carbon and oxygen. The hardened surfaces were characterized by light optical microscopy, hardness indentation and X-ray diffraction. The case depth exceeded 0.5 mm and the formed carbo-oxides exhibited hardness values that range from 2500 to more than 3000 HV, depending on the carbon and oxygen content. Combination of carbo-oxidizing and nitriding resulted in augmented interstitial solubility, which is reflected in a higher hardness. In metallic alpha titanium, solid solution strengthening resulted in hardness values above 1700 HV.