Modification of Ti-Alloys Characteristics by Surface Engineering Methods

Titanium alloys find extensive application in aerospace industry due to their high strength to weight ratio, high elevated temperature properties and excellent corrosion resistance. Experiments have been undertaken to explore the possibility of creating an oxygen barrier layer, which is effective in preventing oxidation of several low-Al content Ti-base alloys during exposure to oxidizing environments at elevated temperatures. The fabrication process has involved three steps, namely co-deposition of Carbon sputtering onto a substrate material, followed by vacuum annealing and furnace air oxidizing. The first two steps produce an overlay and through thickness of TiC rich matrix, while the last step provides the necessary conditions for bringing about the blended oxide-carbide effect upon subsequent high-temperature oxidation. Analysis techniques such as X-ray spectroscopy (EDX), X-ray diffraction (XRD), and microhardness have been used to study the microstructure, phase formation and depth distribution of the elements in the substrate material. Following long time oxidation in air at 600 °C, specimens have been prepared for metallographic analysis, and their cross sections have been characterized by scanning electron microscopy (SEM) in combination with EDX, and colored etching. The results obtained show that during oxidation exposure the surface is capable of forming a mixed scale protective TiC-containing which serves as an oxygen barrier, thereby preventing oxygen embrittlement. In addition, since the only constituents of this layer are Ti and Al, it exhibits excellent chemical substrate compatibility.