A Ti-48Al (at. pet) alloy prepared by elemental powder metallurgy (EPM) has been heat treated under various conditions. Through optical and scanning electronic microscopy, EDAX, XRD analysis, and DTA, it was shown tha...A Ti-48Al (at. pet) alloy prepared by elemental powder metallurgy (EPM) has been heat treated under various conditions. Through optical and scanning electronic microscopy, EDAX, XRD analysis, and DTA, it was shown that the hot pressed microstructure consisted of alpha(2)-Ti3Al and TiAl phases. The alpha(2)-Ti3Al phase was island-like, and had a high stability and heredity in subsequent heat treatments. The supersaturation of Al in the island-like alpha-Ti3Al phase strongly influenced the transformation of alpha(or alpha(2)) to alpha(2)/gamma lamellar colonies. After a heat treatment at 1380 degrees C for 0.5 h and 1000 degrees C for 8 h, a fully lamellar microstructure with a colony size of 50 mu m was obtained. This result indicates that a homogeneous composition and an equilibrium microstructure in EPM TiAl-base alloys can only be obtained after heat treatment at temperatures above alpha transus temperature (T-alpha).展开更多
A simple analytic embedded atom method for bcc Fe and fee Al metals is used to calculate the thermodynamic properties of the disordered solid solution and ordered intermetallic alloys of Fe aluminides. The thermodynam...A simple analytic embedded atom method for bcc Fe and fee Al metals is used to calculate the thermodynamic properties of the disordered solid solution and ordered intermetallic alloys of Fe aluminides. The thermodynamic properties, such as the dilute-limit heats of solution, formation enthalpies of disordered solid solutions and intermetallic compounds (Fe3Al in the D0(3) structure type, FeAl in the B2 structure type, and Fe13Al3) are in good agreement with the experimental data, and with the results calculated using the first principles and Miedema theory.展开更多
The structure of Mo-15.16 Si, Mo-30 Si and Mo-36.3 Si (wt pct) elemental powder mixture during mechanical alloying was studied using electron microscopy and X-ray diffraction. It had been found that, in all the system...The structure of Mo-15.16 Si, Mo-30 Si and Mo-36.3 Si (wt pct) elemental powder mixture during mechanical alloying was studied using electron microscopy and X-ray diffraction. It had been found that, in all the systems under study, silicon disappeared initially during mechanical alloying (MA). In the Mo-Si systems all products were in form of amorphous state after long time milling, but there were different intermediate products. MoSi2 and Mo5Si3 intermetallic compounds in the Mo-30Si and Mo-36.3Si (wt pct) were directly synthesized from elements through inter-diffussion process. The high density of defects and interface of nano-crystal lines induced by ball milling would promote the reaction process. Only in the Mo-15.16Si (wt pct) system was Mo(Si) supersaturated solid solution formed as an intermediate product. Schematic free-energy diagram of Mo-Si system based on the thermodynamics was used to analyze the difference among the intermediate state products.展开更多
文摘A Ti-48Al (at. pet) alloy prepared by elemental powder metallurgy (EPM) has been heat treated under various conditions. Through optical and scanning electronic microscopy, EDAX, XRD analysis, and DTA, it was shown that the hot pressed microstructure consisted of alpha(2)-Ti3Al and TiAl phases. The alpha(2)-Ti3Al phase was island-like, and had a high stability and heredity in subsequent heat treatments. The supersaturation of Al in the island-like alpha-Ti3Al phase strongly influenced the transformation of alpha(or alpha(2)) to alpha(2)/gamma lamellar colonies. After a heat treatment at 1380 degrees C for 0.5 h and 1000 degrees C for 8 h, a fully lamellar microstructure with a colony size of 50 mu m was obtained. This result indicates that a homogeneous composition and an equilibrium microstructure in EPM TiAl-base alloys can only be obtained after heat treatment at temperatures above alpha transus temperature (T-alpha).
文摘A simple analytic embedded atom method for bcc Fe and fee Al metals is used to calculate the thermodynamic properties of the disordered solid solution and ordered intermetallic alloys of Fe aluminides. The thermodynamic properties, such as the dilute-limit heats of solution, formation enthalpies of disordered solid solutions and intermetallic compounds (Fe3Al in the D0(3) structure type, FeAl in the B2 structure type, and Fe13Al3) are in good agreement with the experimental data, and with the results calculated using the first principles and Miedema theory.
文摘The structure of Mo-15.16 Si, Mo-30 Si and Mo-36.3 Si (wt pct) elemental powder mixture during mechanical alloying was studied using electron microscopy and X-ray diffraction. It had been found that, in all the systems under study, silicon disappeared initially during mechanical alloying (MA). In the Mo-Si systems all products were in form of amorphous state after long time milling, but there were different intermediate products. MoSi2 and Mo5Si3 intermetallic compounds in the Mo-30Si and Mo-36.3Si (wt pct) were directly synthesized from elements through inter-diffussion process. The high density of defects and interface of nano-crystal lines induced by ball milling would promote the reaction process. Only in the Mo-15.16Si (wt pct) system was Mo(Si) supersaturated solid solution formed as an intermediate product. Schematic free-energy diagram of Mo-Si system based on the thermodynamics was used to analyze the difference among the intermediate state products.
