Mechanical alloying (MA) of Ni50Al45Ti5 (atomic per cent) is studied by in situ thermal analyses, XRD and metallography. The results showed that the alloying process of Ni50Al45Ti5 is similar to that of Ni50Al50. The ...Mechanical alloying (MA) of Ni50Al45Ti5 (atomic per cent) is studied by in situ thermal analyses, XRD and metallography. The results showed that the alloying process of Ni50Al45Ti5 is similar to that of Ni50Al50. The addition of 5 at.%Ti prolongs the milling time of alloy prior to the explosive reaction in the alloy. The final product is nanocrystalline β-phase NiAl(Ti) (B2 structure). The addition of 5 at.% Ti shows little effect on the lattice parameter of β-phase.展开更多
Positron lifetime results showed that there are two kinds of interfacial defects in the nanocrystalline alloys obtained by crystallization of the amorphous alloy, namely free-volume-sized and nanovoid-sized defects. T...Positron lifetime results showed that there are two kinds of interfacial defects in the nanocrystalline alloys obtained by crystallization of the amorphous alloy, namely free-volume-sized and nanovoid-sized defects. The former is smaller than a monovacancy; the latter is of the size of several monovacancies and is usually situated at the intersections of several interfaces. In comparison with the nanovoid-sized defect, though the free-volume-sized defect is a shallow trapping potential, the quantity can be as much as 90% of all defects. It should be noted that nanovoids can change remarkably in both size and concentration with grain growth. So it is imaginable that this type of defect will exert a great influence on the interfacial structure and properties of nanocrystalline materials. So far, reports in this aspect are still meager.展开更多
文摘Mechanical alloying (MA) of Ni50Al45Ti5 (atomic per cent) is studied by in situ thermal analyses, XRD and metallography. The results showed that the alloying process of Ni50Al45Ti5 is similar to that of Ni50Al50. The addition of 5 at.%Ti prolongs the milling time of alloy prior to the explosive reaction in the alloy. The final product is nanocrystalline β-phase NiAl(Ti) (B2 structure). The addition of 5 at.% Ti shows little effect on the lattice parameter of β-phase.
文摘Positron lifetime results showed that there are two kinds of interfacial defects in the nanocrystalline alloys obtained by crystallization of the amorphous alloy, namely free-volume-sized and nanovoid-sized defects. The former is smaller than a monovacancy; the latter is of the size of several monovacancies and is usually situated at the intersections of several interfaces. In comparison with the nanovoid-sized defect, though the free-volume-sized defect is a shallow trapping potential, the quantity can be as much as 90% of all defects. It should be noted that nanovoids can change remarkably in both size and concentration with grain growth. So it is imaginable that this type of defect will exert a great influence on the interfacial structure and properties of nanocrystalline materials. So far, reports in this aspect are still meager.
