The Athermal Strengthening of Discontinuous Reinforced NiAl Composites

1994 ◽  
Vol 350 ◽  
Author(s):  
L. Wang ◽  
K. Xu ◽  
R. J. Arsenault
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Grain Boundaries ◽  
Yield Stress ◽  
Low Temperatures ◽  
Particulate Composites ◽  
Matrix Composites ◽  
Size Refinement ◽  
Athermal Component ◽  
Nial Matrix

AbstractAn increase in the athermal component of the yield stress at low temperatures is the caused of the high temperature strengthening of discontinuously reinforced NiAl matrix composites. The reinforcements stabilize the microstructure. The strengthening in the temperature range of 300–1273K, is believed to be related to the grain size refinement and effective pinning of grain boundaries. This conclusion was obtained from analysis of data from AlN, TiB2 and Al2O3/NiAl particulate composites.

The Effect of Annealing on the Cu Distribution and AI2Cu Precipitation in Ai(Cu) Thin Films

1993 ◽  
Vol 309 ◽  
Author(s):  
E.G. Colgan ◽  
K.P. Rodbell ◽  
D.R. Vigliotti
Keyword(s):  
Thin Films ◽  
Grain Size ◽  
Grain Boundaries ◽  
Low Temperatures ◽  
Room Temperature ◽  
Annealing Temperature ◽  
Precipitate Morphology ◽  
Electromigration Lifetime ◽  
Bamboo Structure ◽  
Anneal Temperature

AbstractThe Cu distribution in AI(Cu) thin films has been examined in blanket and patterned samples as a function of annealing. The Cu concentration in the Al grains, measured at room temperature, closely follows the solubility at the anneal temperature when a high cooling rate is used (-100 or -200°C/min) from the annealing temperature. With fine lines, the room temperature Cu concentration follows the solubility at the anneal temperature only at low anneal temperatures, ≤350°C. With higher temperatureannealing, >400°C, the room temperature Cu concentration in the Al grains was substantially less than the solubility at the anneal temperature. These differences are attributed to the smaller grain size in fine lines, which reduces the distance to grain boundaries. With blanket films, the Θ-phase (Al2Cu) precipitate morphology depends on the Al grain size and annealing temperature. With small Al grains (100-300 nm), the Θ particles are small (100-200 nm) and round whereas with large Al grains (0.5-2μm), the precipitates are long and irregularly shaped. The morphology of the Θ precipitates is constrained by the Al grain size. With fine lines, having a bamboo structure, the Θ precipitates are “wedge” shaped along grain boundaries or span the width of the line. The electromigration lifetime was found to depend strongly on the heat treatment used, an increase of 3X in lifetime was obtained for samples rapidly cooled from a temperature above the solvus curve as compared with samples subjected to additional aging at low temperatures. This is believed to be dueto the different concentrations of Cu in solution and to the size and distribution of Θparticles in the patterned lines.

Engineered Nanocrystallites for Enhanced Performance of Ceramic Coatings by Ion Beam Assisted Deposition

1996 ◽  
Vol 438 ◽  
Author(s):  
F. Namavar ◽  
J. Haupt ◽  
E. Tobin ◽  
H. Karimy ◽  
J. Trogolo ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Grain Size ◽  
High Temperature ◽  
Low Temperatures ◽  
Ion Beam ◽  
Film Deposition ◽  
Tin Films ◽  
Grain Sizes ◽  
Ion Beam Assisted Deposition

AbstractTypical high-temperature thin-film deposition techniques are not suitable for certain substrates such as polymers and thermally-sensitive steels. In this work, ion beam assisted deposition (IBAD) was used to deposit ceramic and metallic films at temperatures below 150°C with nanocrystalline (< 100Å diameter) grain size. Nanoindentation studies of these films have shown hardnesses 50 to 100% greater than larger-grained films and, in some cases, fracture toughness approaching that of Si3N4.By combining chromium evaporation with nitrogen beam bombardment, hard, adherent CrN films without any porosity have been produced at low temperatures with a N/Cr arrival ratio of about 1. The grain size is typically smaller than 100Å and hardness is typically higher than 25 GPa. For a N/Cr arrival ratio slightly less than 1, we observed possible grain boundary porosity. However, even with porosity, hardness is typically 20 to 24 GPa for grain sizes smaller than 100Å. For a N/Cr arrival ratio of 1/4 we deposited elemental Cr with a grain size of 300 to 500Å and a hardness greater than that of silicon (12 GPa). Using Ar ions and a N backfill, we produced elemental Cr containing a mixture of coarse (120 to 150Å) and fine (25 to 30Å) grains. For high-temperature deposition of CrN, the grain size increases (200 to 600Å) with a noticeable decrease in hardness. Mechanical properties of CrN are greatly influenced by impurities, as well as by surface conditioning of the substrate.TiN films having gold color and grain sizes from 50 to 1000Å have been produced at low temperatures. Nanoindentation measurements of hardness and fracture toughness indicate that impurity-free TiN (with grains smaller than 100Å) has a hardness higher than 25 GPa and a fracture toughness close to that of Si3N4, but with higher wear resistance. Mechanical properties of our TiN films are greatly influenced by impurities, particularly oxygen, although it does not influence the gold color of TiN.

Dislocation Morphologies in TiB2/NiAl

1990 ◽  
Vol 194 ◽  
Author(s):  
L. Wang ◽  
R. J. Arsenault
Keyword(s):  
High Temperature ◽  
Dislocation Density ◽  
Nickel Aluminide ◽  
Volume Fraction ◽  
High Temperature Strength ◽  
Matrix Composites ◽  
Annealed Condition ◽  
Low Dislocation Density ◽  
Particulate Form ◽  
Nial Matrix

AbstractThe addition of 20 volume percent titanium diboride in particulate form (1-3 μm) to nickel aluminide (TiB2/NiAl) results in a twofold increase in the high temperature strength of NiAl. Theories that have been proposed to account for the high temperature strength of discontinuous reinforced metal matrix composites can not be adequately used as a basis to explain the observed strengthening.An investigation was undertaken of NiAl, 10 V% TiB2/NiAl and 20 V% TiB2/NiAl in the annealed condition and after deformation, allowed to cool slowly. There is a low dislocation density in the annealed samples and the dislocation density did increase slightly as a result of deformation. However, deformation did produce some intriguing dislocation arrangements; for example, it was found that there was a high dislocation density within the TiB2 in the deformed higher volume fraction composites and the dislocation density within NiAl matrix was not uniform.

High Temperature Lubricating Behavior of NiAl Matrix Composites With Addition of CuO

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Shengyu Zhu ◽  
Jun Cheng ◽  
Zhuhui Qiao ◽  
Yuan Tian ◽  
Jun Yang
Keyword(s):  
Wear Resistance ◽  
High Temperature ◽  
Powder Metallurgy ◽  
Friction Coefficient ◽  
High Temperatures ◽  
Room Temperature ◽  
Tribological Behavior ◽  
Matrix Composites ◽  
Powder Metallurgy Technique ◽  
Nial Matrix

High temperature self-lubricating NiAl matrix composites with addition of CuO (15, 20, and 25 wt.%) were fabricated by powder metallurgy technique, and the tribological behavior from room temperature to 1000 °C was investigated. It was found that Ni–Cu and Al2O3 phases formed during the fabrication process due to reaction of NiAl and CuO. The tribological results showed that the composite with addition of 25 wt.% CuO has a favorable friction coefficient of about 0.2 and excellent wear resistance with the magnitude of 10−6 mm3 N−1 m−1 at high temperatures (800 and 1000 °C).

Enhanced high-temperature electrical response of hydroxyapatite upon grain size refinement

2015 ◽  
Vol 61 ◽  
pp. 534-538 ◽  
Author(s):  
Miodrag J. Lukić ◽  
Čedomir Jovalekić ◽  
Smilja Marković ◽  
Dragan Uskoković
Keyword(s):  
Grain Size ◽  
High Temperature ◽  
Electrical Response ◽  
Size Refinement

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

Interfacial studies in Nb3Sn superconductors

1991 ◽  
Vol 49 ◽  
pp. 590-591
Author(s):  
Ernest L. Hall ◽  
Lee E. Rumaner ◽  
Mark G. Benz
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Flux Pinning ◽  
Size Control ◽  
High Magnetic Fields ◽  
Type Ii ◽  
Reaction Interface ◽  
Liquid Diffusion ◽  
Type Ii Superconductor ◽  
Grain Size Control

The intermetallic compound Nb3Sn is a type-II superconductor of interest because it has high values of critical current density Jc in high magnetic fields. One method of forming this compound involves diffusion of Sn into Nb foil containing small amounts of Zr and O. In order to maintain high values of Jc, it is important to keep the grain size in the Nb3Sn as small as possible, since the grain boundaries act as flux-pinning sites. It has been known for many years that Zr and O were essential to grain size control in this process. In previous work, we have shown that (a) the Sn is transported to the Nb3Sn/Nb interface by liquid diffusion along grain boundaries; (b) the Zr and O form small ZrO2 particles in the Nb3Sn grains; and (c) many very small Nb3Sn grains nucleate from a single Nb grain at the reaction interface. In this paper we report the results of detailed studies of the Nb3Sn/Nb3Sn, Nb3Sn/Nb, and Nb3Sn/ZrO2 interfaces.

Precipitation of NiHfsi phase in NiAl single crystals containing Hf

1995 ◽  
Vol 53 ◽  
pp. 532-533
Author(s):  
A. Garg ◽  
R. D. Noebe ◽  
R. Darolia
Keyword(s):  
High Temperature ◽  
Single Crystals ◽  
High Temperature Strength ◽  
Bridgman Technique ◽  
Shell Mold ◽  
Third Phase ◽  
Unknown Phase ◽  
Transmission Electron ◽  
Two Phases ◽  
Nial Matrix

Small additions of Hf to NiAl produce a significant increase in the high-temperature strength of single crystals. Hf has a very limited solubility in NiAl and in the presence of Si, results in a high density of G-phase (Ni16Hf6Si7) cuboidal precipitates and some G-platelets in a NiAl matrix. These precipitates have a F.C.C structure and nucleate on {100}NiAl planes with almost perfect coherency and a cube-on-cube orientation-relationship (O.R.). However, G-phase is metastable and after prolonged aging at high temperature dissolves at the expense of a more stable Heusler (β'-Ni2AlHf) phase. In addition to these two phases, a third phase was shown to be present in a NiAl-0.3at. % Hf alloy, but was not previously identified (Fig. 4 of ref. 2 ). In this work, we report the morphology, crystal-structure, O.R., and stability of this unknown phase, which were determined using conventional and analytical transmission electron microscopy (TEM).Single crystals of NiAl containing 0.5at. % Hf were grown by a Bridgman technique. Chemical analysis indicated that these crystals also contained Si, which was not an intentional alloying addition but was picked up from the shell mold during directional solidification.

Sign in / Sign up

Export Citation Format

Share Document