Akademik Veri Yönetim Sistemi
7th International Symposium on Processing and Fabrication of Advanced Materials VII, Illinois, Amerika Birleşik Devletleri, 11 - 15 Ekim 1998, ss.235-245
Pure powders of TiH2 and elemental Al were mixed to have Ti-53 at % Al powder mixture before mechanical milling. TiAl(gamma) powder produced by are-melting of pure Al and Ti is also mechanically milled before pressing. These mechanically milled powder samples, i.e., TiH2 powder, Ti-53 at %Al powder mix and TiAl (gamma) compound powder were pressed to obtain compressed pellets. Afterwards, these pellets were not only vacuum annealed up to 720 degrees C but also reactively sintered at 1020, 1070, and 1135 degrees C under vacuum. As-received, as-mixed, mechanically milled, pressed, annealed, and reactively sintered samples of experimental materials were characterized by XRD and SEM investigation. In addition, elevated temperature micro-hardness measurements were also carried out. It was observed that reactive sintering between solid Al and Ti in the 600-660 degrees C temperature range results in incomplete synthesis in TiH2-53 at %Al powder mix (MM'ed, pressed and sintered) due to the presence of unreacted Ti in the structure after reactive sintering process thereby leading to the formation of a multiphase, porous compact of TiAl (gamma)-Ti IMC material. Using titanium hydride in the powder mixture with Al significantly accelerates diffusion processes and therefore makes possible processing of Titanium alumide (TiAl) by thermal exposure at reasonable time-temperature conditions. This is mostly owing to the refinement of powder mixture of TiH2-53 at % Al by mechanical milling, work hardening of Al and Ti during mechanical milling, and possibly reduction of Al2O3 film by atomic hydrogen which is a by-product of TiH2 decomposition at around 420 degrees C. Owing to an intensive reaction of freshly surfaced Al (due to surface Al-oxide film reduction by atomic hydrogen) with Ti (formed after TiH2 decomposition) at temperature ranges between 600 degrees C and melting temperature of Al, the whole of the Al reacts in the solid state. This results in a formation of an intermetallic matrix composite of TiAl (gamma)-Ti product out of mechanical milling, pressing, and reactive sintering cycle. Elevated temperature hardness values of TiH2-53 at % Al sintered compacts were lower than those of 100% TiAl (gamma) compound compacts regardless of the sintering temperatures used indicating the presence of unreacted Ti thereby causing observed lower values of high temperature hardness values. This brings in the possibility of workability of TiAl (gamma)-Ti IMC material. However, as sintering temperature is increased, hardness increases due to the further formation of TiAl compound by reactive sintering and therefore ductility and workability of this IMC material becomes difficult. Since lower sintering temperatures result in less TiAl (gamma) formation due to incomplete synthesis reactions, these temperatures are advantageous in terms of room temperature ductility of the IMC material investigated in the present work.