Effect of Ti and TiC coating on the thermal stability of diamond

Abstract

The metallization of diamond surface is one of the important methods to improve the properties of diamond products. The quality of the coating has an important influence on the thermal stability of diamond and its products. Ti and TiC layers were successfully coated on the diamond surface by high temperature molten salt method. The composition and morphology of the coated layers were characterized by XRD and SEM, and the thermal stability of the coated diamond particles was studied. The results showed that the colour of the diamond changed from yellow to gray black, and the optical transmittance was greatly reduced after coating. After coating at 800～900 ℃, Ti-TiC composite layer was formed on the diamond surface. The coating layer was thin and sparse, and some areas were even uncoated at 800 ℃. While after coating at 900 ℃, the coating layer became uniform and dense. Increasing temperature to 1 100 ℃, the coating was conveyed to be TiC layer. However, this TiC layer was so thick that delamination and cracking are observed in some areas. Due to the protective effect of the coating layer, the oxidation temperature was increased while the weight loss rate was decreased greatly for diamond particles. Especially for the diamond sample coated at 900 ℃, its the weight loss rate was decreased from original 91.3% to 9.3% up to 1 100 ℃, showing its thermal stability was significantly improved after coating. Finally, the formation process of the coating layer was discussed, and the effect of temperature on the composition and thermal stability of the coating layer was revealed.

Keywords

• diamond
• molten salt
• ti
• tic
• thermogravimetric analysis