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
材料科学技术（英文）
A study was conducted to develop low-friction,wear-resistant surfaces on high temperature alloys for the temperature range from 26 degrees C to 900 degrees C. The approach investigated consists of modifying the naturally occurring oxide film in order to improve its tribological properties. improvement is needed at low temperatures where the oxide film, previously formed at high temperature, spalls due to stresses induced by sliding. Experiments with Ti, W and Ta additions show a beneficial effect when added to Ni and Ni-base alloys. Low friction can be maintained down to 100 degrees C from 900 degrees C. For unalloyed Ni friction and surface damage increases at 400 degrees C to 500 degrees C. Two new alloys were perpared based on the beneficial results of binary alloys and ZrO2 diffusion in Ni. Low friction at temperature above 500 degrees C and reasonable values (0.32 similar to 0.42) at low temperature are obtained.
关键词:
oxidation;behavior;alloys
Surface & Coatings Technology
The discontinuous and cyclic oxidation behavior of TiAlNb intermetallics with coatings such as NiCrAlY, TiAlCr and ultrafine enamel coatings at 800 C was studied. The results indicated that the three coatings could decrease the mass gains of TiAlNb alloys during discontinuous and cyclic oxidation at 800 C. However, heavy interdiffusion occurred at the interface of NiCrAIY/TiAlNb during oxidation. Some discontinuous Al2O3 scales formed at interface of NiCrAIY/TiAlNb, where interdiffusion might be depressed. A protective Al2O3 scale could form on TiAlCr coating during oxidation at 800 C; however, the outward diffusion of Nb and inward diffusion of Cr through the interface and the formation of Al-depletion zone at the subsurface might be detrimental to the long-term oxidation resistance of coating. Enamel coating kept intact during oxidation at 800 C. But the thermodynamic instability of enamel in contact with TiAl alloys resulted in the formation of an Al-depletion zone and TiSiO3 layer at the interface of enamel/TiAlNb, which would be harmful to the adherence of the enamel coating to the substrate. (c) 2004 Published by Elsevier B.V.
关键词:
TiAlNb intermetallics;discontinuous and cyclic oxidation;coatings;tial-based intermetallics;high-temperature air;titanium aluminides;nb;addition;ti60 alloy;resistance;corrosion
S.Q. Zhou
,
W. Zhao
,
W.H. Xiong
,
Y.N. Zhou
,
null
,
null
,
null
,
null
金属学报(英文版)
Effect of Mo and Mo2C on the microstructure
and properties of Ti(C,N)-based cermets was investigated in this
article. The results have indicated that the weight percentage of Mo
from 5 to 10 can reduce Ti(C,N) grain diameter and thickness of the
rim, and Ti(C,N) grain can be wetted by Ni-Cu-Mo liquid so as to get
small contiguity of Ti(C,N) grain. In that way, the transverse
rupture strength of Ti(C,N)-based cermets has reached
1800—1900 MPa; the fracture toughness has been due to
16—18 MPa m1/2. But 15wt pct Mo was not more effective
on Ti(C,N)-based cermets, because the thickness of the rim becomes
larger. In the circumstance of Mo 2 C, 5 wt pct Mo 2 C was
good for microstructure and properties of Ti(C,N)-based cermets, but
11 wt pct Mo 2 C has resulted in larger contiguity of Ti(C,N)
grain and big Ti(C,N) grain diameter so as to reduce transverse
rupture strength and fracture toughness. So that, the effect of Mo
on Ti(C,N)-based cermets is better than Mo 2 C.
关键词:
Transverse rupture strength (TRS)
,
null
,
null
Journal of Materials Processing Technology
The effects of brazing temperature on microstructure and bonding strength of vacuum brazed joints of Ti(C,N)-based cermet and 17-4 PH stainless steel, using filler metal BNi-2, were investigated. At a lower brazing temperature of 1050 C. the distribution of melting point depressants (MPD) concentrated on the diffusion affected zone (DAZ) and the brazing seam near the Ti(C,N)-based cermet, the generation of brittle phases in the brazing seam was unavoidable. The uniform distribution of the MPD and full solid solution of gamma-nickel occurred in the brazing seam at a higher brazing temperature of 1150 degrees C. A maximum shear strength of 690 MPa was achieved at a brazing temperature of 1150 degrees C. (C) 2011 Elsevier B.V. All rights reserved.
关键词:
Brazing;Ti(C,N)-based cermet;Steel;Microstructure;Mechanical;properties;isothermal solidification
Materials Science and Technology
The relationship between degeneration of the primary M7C3 carbide and precipitation of the secondary M23C6 carbide has been investigated in a cobalt base superalloy after 100 h aging at 850 degrees C. The results indicated that the primary M7C3 carbide could not transform in situ into the secondary M23C6 carbide. The M23C6 formed by a direct reaction between chromium and carbon atoms. The dissolution of M7C3 provided the precipitation of M23C6 with essential carbon, which acted as a carbon reservoir. Near M7C3, the chromium content is a controlling factor of M23C6 precipitation while away from it, the carbon content dominated the reaction. The precipitate free zone around M7C3 is attributed to chromium depletion which is inherited from the as cast condition. MST/4174
关键词:
Oxidation of Metals
The isothermal-oxidation behavior of a single-crystal (SC) Ni-base superalloy was studied over the temperature range from 900 to 1100 degrees C and analyzed by OM, TGA, XRD, EDX, SEM and EPMA. The alloy obeyed a subparabolic rate law during oxidation at 900 and 1000 degrees C, whereas the alloy showed parabolic behavior at 1100 degrees C exposure. The variations in the chemical composition due to segregation, which resulted from the solidi. cation process, led to the formation of different kinds of oxide scale on the dendritic and interdendritic areas during oxidation at 900 and 1000 degrees C, while the alloy exhibited relatively uniform oxidation at 1100 degrees C. The growth mechanism of the scale is discussed.
关键词:
Ni-base single-crystal;superalloy;oxidation;microstructure;kinetics;cr-al alloys;internal nitridation;coatings
Tribology Letters
The isothermal oxidation behavior of a single-crystal (SC) Ni-base superalloy was studied over the temperature range from 900 to 1100 degrees C and analyzed by OM, TGA, XRD, EDX, SEM and EPMA. The alloy obeyed subparabolic rate law during oxidation at 900 and 1000 degrees C, whereas the alloy showed parabolic rate law at 1100 degrees C exposure. The variations in the chemical composition due to segregations, which resulted from the solidification process, led to the formation of different kinds of oxide scale on the dendritic and interdendritic area during oxidation at 900 and 1000 degrees C, while the alloy exhibited relatively uniform oxidation at 1100 degrees C. The growth mechanism of the scale was discussed.
关键词:
Ni-base single-crystal;superalloy;oxidation;microstructure;kinetics;cr-al alloys;internal nitridation;coatings
Oxidation of Metals
The oxidation of Ti-48Al-8Cr-2Ag (at.%) was studied for 50 h at 900 and 1000 degrees C. The microstructure of the oxide scales was characterized by means of scanning-electron microscopy (SEM) and high-resolution electron microscopy (HREM). The results showed that the mass gain of the alloy at 1000 degrees C was lower than that at 900 degrees C. At 1000 degrees C, a continuous and dense scale of quite pure Al2O3 formed, but at 900 degrees C, a complex scale with an outer layer of Al2O3 + TiO2 and an layer of inner Al2O3. A Laves phase and a Z-phase were found at the scale/substrate interface, which might be a factor beneficial to the formation of Al2O3.
关键词:
Ti-Al-Cr-Ag alloy;oxide scale;HREM;al-cr alloys;temperature oxidation behavior;tial-intermetallic-compound;resistance;alumina;chromium;oxygen;film
