Self-propagating High-temperature Synthesis of Ti5Si3/TiAl3 Intermetallics

Abstract

The products with designed volume ratio of Ti 5 Si 3 : TiAl 3 ϭ1 : 0, 3 : 1, 1 : 1, 1 : 3 and 0 : 1 prepared by selfpropagating high-temperature synthesis (SHS) were investigated in the present study. The differential thermal analysis (DTA) results suggested that the Si in reactants had a significant influence not only on the melting of Al, but also on the subsequently exothermic reaction between Ti and Al. Also, the presence of Al altered the reaction process of Ti 5 Si 3 . The phase composition of SHS reaction product agreed well with the designed volume ratio of Ti 5 Si 3 : TiAl 3 . Compared with those apparently coarse ones in monolithic Ti 5 Si 3 or TiAl 3 , the grains were considerably refined and microcracks gradually disappeared in products with coexistence of Ti 5 Si 3 and TiAl 3 .KEY WORDS: intermetallics; combustion synthesis (CS); microstructure; differential thermal analysis. 453© 2009 ISIJ microstructures and improved properties, especially, both the reactions for the reinforcement and matrix formations are exothermic in the preparation of IMCs. 4,10,12,13) Therefore, we conduct an investigation on Ti 5 Si 3 -TiAl 3 system with changing volume ratio of Ti 5 Si 3 : TiAl 3 by SHS process. The study aims to investigate the reaction mechanism, also the phase composition and morphology of final products with changing volume ratio of Ti 5 Si 3 : TiAl 3 . It is expected that the preliminary work could lay a foundation and make a significant promotion in the development of high-temperature structure materials. Experimental ProcedureFive different mixtures of Al, Ti, and Si powders were prepared in order to produce Ti 5 Si 3 -TiAl 3 with varying volume fractions of each phase. The intended final products were designed to contain Ti 5 Si 3 and TiAl 3 with a volume ratio corresponding to 1 : 0, 3 : 1, 1 : 1, 1 : 3 and 0 : 1, respectively. The powders used in the present work were commercial powders of Al (98.0 % purity, ϳ29 mm), Ti (99.5 % purity, ϳ15 mm), and Si (99.5 % purity, ϳ15 mm), respectively. Powder blends with different starting compositions were mixed sufficiently by a ball milling for 6 h with the weight ratio of ball to powder of 2 : 1, and then were cold-isostatically pressed at pressures ranging from 55 to 60 MPa to form cylindrical preforms (22 mm in diameter and 11Ϯ0.5 mm in length) with 70Ϯ9 % theoretical density.The combustion synthesis experiments were carried out under a protective atmosphere of industrial argon (99.9 %). The combustion reaction of the preforms was ignited by heating its bottom surface. The preforms were placed on the graphite-flat which was fixed above a tungsten electrode and ignited by the arc heat. Experiments were performed with preforms without any preheating.Prior to various measurements and characterization, all samples were carefully polished to remove a thin surface layer in order to eliminate the possible oxidation products which might form during combustion synthesis process. The as-combusted compacts were hand-ground with pestle and mortar into fine powders, ...

Study on Wear Resistance of Ti-6Al-4V Alloy Composite Coating Prepared by Laser Alloying

“…Moreover, the X-ray diffraction pattern in Figure 3 shows that the coating mainly contains TiN and a small amount of TiB, Ti 5 Si 3 . In the composite of Ni60A, B elements account for 3.0% to 4.5%, so Ni60A is almost completely decomposed under the action of higher laser energy [24,25]. Although the chemical bond between Ti and N is strong, TiN is partially decomposed.…”