F. H.(Sam) Froes
,
C. Suryanarayana
,
and D. Mukhopadhyay (Institute for Materials and Advanced Processes (IMAP)
,
University of Idaho
,
Moscow
,
ID 83844-3026
,
USA)C-G. Li(BlM
,
P.O. Box 81
,
Beijing
,
100095
,
P.R. CHINA)K. Brand(On leave from Institut fur Werkstoffwissenshaft
,
Technische Universitst Dresden
,
07062 Dresden
,
Germany
,
at IMAP)
金属学报(英文版)
Mechanical alloying (MA), a solid-state powder processing method, is a "far from equilibrium" synthesis technique which allows development of novel crystal structures and microstructures, leading to enhanced physical and mechanical properties. The ability to synthesize a variety of alloy phases including supersaturated solid solutions, nanocrystalline structures, amorphous phases and intermetallic compounds themselves is discussed. No extension of solubility using MA has been observed in the intermetallics studied. Nanostructured grains were observed in all compositions. Long time milling generally resulted in amorphous phase formation in large part because of the increase in grain boundary energy/mole with reduced grain size; good agreement with the Miedema model for amorphization was obtained in the Al-Fe system. Generally an anneal was required to form the intermetallic after MA; however,intermetallics with a large negative enthalpy of formation were detected in the MA condition. A study of the hot isostatic pressing of γ-TiAl powders produced by MA demonstrated that full density can be achieved at least 400℃ below the normal temperature required for conventional powder, that is 725℃ or below. Nanometered sized grains (≤100nm)were observed after HIP'ing up to 850℃.
关键词:
: Intermetallics
,
null
,
null
ZHU Ziyong V.A.Marichev Institute of Physical Chemistry of the Academy of Sciences of the USSR
,
Moscow
,
117171
,
USSR.
材料科学技术（英文）
The ambiguous effect of cathodic polarization on SCC of two high strength steels in 0.1 M Na_2HPO_4 and 0.1 M NaNO_3 has been investigated by means of meas- uring electric resistance(R)and recording acoustic emis- sion(AE)signals simultaneously.Results showed that AE sensitivity strongly depends on K value in different solu- tions.Both anodic and cathodic polarization can acceler- ate crack growth rate at high K values,but it appears that there are only subtle differences in their AE characteristics.AE signals only reflect the macroprocesses of crack growth rather than the elementary ones and can not be used for identification of the micro-mechanisms of SCC.
关键词:
acoustic emission
,
null
,
null
,
null
