Structural Uses for Ductile Ordered Alloys (1984) / Chapter Skim
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'CONSTITUTION, PROPERTIES, AND CURRENT STRUCTURAL USES'
'CONSTITUTION, PROPERTIES, AND CURRENT STRUCTURAL USES'
Pages 7-40
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From page 7... ...
For example, at low temperatures CuZn and Cu•jAu have the ordered structures shown in Figure l, but above a critical temperature (Tc) , the atoms become randomly mixed on the different atomic sites and become random solid solutions.
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From page 8... ...
FIGURE 1 (a) At low temperatures: CuZn has the cesium chloride B2 long-range-ordered structure and (b)
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From page 9... ...
However, the use of single crystals in high-temperature applications such as gas turbines was not seriously considered until about 1970, by which time little additional research on ordered alloys was being carried out in this country. Rather than attempting to use ordered alloys in structural applications, metallurgists identified other uses for them in which brittleness was not a problem or, at least, could be minimized.
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From page 10... ...
Soviet publications on ordered alloys have been voluminous, but there is little visible evidence to date of Soviet progress in developing such alloys for structural applications; rather, Soviet research has emphasized alloy theory, yielding and strain-hardening phenomena, and the use of various imaging techniques to aid in the study of crystal structure and crystal defects. The characteristics that render ordered alloys so interesting as bases for alloy development will be discussed below as will their current status and applications.
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From page 11... ...
11 io O •O 41 V4 0l M O 0)
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From page 12... ...
Rather, the principal effects of ordering on mechanical properties arise from changes in dislocation configurations due to the added constraints that ordering places on the nucleation and motion of dislocations. One of the attractive features of aluminides such as TiAl and Fe3Al in structural applications is the high specific modulus.
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From page 13... ...
. Therefore, the stacking fault energy of the alloy plays a role in determining the dislocation fine structure.
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From page 14... ...
However, an exception to this behavior is noted in Ni^Mo, which rarely exhibits superlattice dislocations at room temperature. When superlattice dislocations are observed in Ni^Mo, they consist of five identical unit dislocations (Nesbit and Laughlin 1980)
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From page 15... ...
Departures from Stoichiometry Departures from perfect order cause strengthening through means not directly connected with the AP8. Deviations in stoichiometry from the ideal AB or AgB composition often lead to strengthening at low test temperatures, and, for this reason, slowly cooled alloys of the Fe-Co, Ni-Al, Ni-Ga, Mg-Cd, or Cu-Au systems reveal minima in room-temperature hardness at stoichiometric compositions.
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From page 16... ...
300 .£ 200 CN S 100 O • N 1 1 23 24 25 26 CONCENTRAT1ON OF Al OR Ga (at%) 27 FIGURE 4 Effect of composition on the temperature dependence of yielding of binary Ni3Al alloys (Noguchi et al.
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From page 17... ...
alloys contain large volume fractions of Ni3Al, the yield and ultimate tensile strengths of these alloys often rise or remain nearly constant with increasing temperature to at least 700°C. Increases in flow stress with temperature also have been noted in long range ordered alloys of other cubic or hexagonal crystal structures.
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From page 18... ...
18 cd .0 CO .0 00 00 00 00 ON ON ON ON OO r-l r-l r-l r-l ON CO co 4J 4J CO CO 4J 4J r- 1 4•1 4J CO CO 4J 4J CO CO CO U rl rl •^ •^ JC •r*
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From page 19... ...
In the case of alloys such as FeCo-2% V, where the flow stress peak occurs at the order-disorder transition temperature, and Fe3Al, where the flow stress peak occurs just under the temperature for a transition between two ordered structures, the anomaly has been attributed to a transition from plastic deformation by superlattice dislocations at temperatures below that of the peak to deformation by unit dislocations at temperatures above that of the peak (Stoloff and Davies 1964a)
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From page 20... ...
Wear-resistance also should be enhanced by rapid strain hardening, permitting possible replacement of cobalt-base alloys for such applications. Fracture Polycrystalline ordered alloys often are brittle when tested in tension although considerable plasticity may be displayed by single crystals or by polycrystals tested in compression.
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From page 21... ...
. In this alloy, slip occurs on more slip systems in the ordered than in the disordered state whereas in all other alloys studied to date, ordering either reduces the number of available slip systems or restricts cross slip of screw dislocations from one slip plane to another.
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From page 22... ...
22 2 < Q OJ IE 8 12 16 20 24 ATOM1C PERCENT ALUM1NUM FIGURE 6 Ductility of Fe-Al alloys slowly cooled to 477°K and fractured in tension at that temperature (Harcinkowski et al.
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From page 23... ...
. The change was attributed to an increased degree of long-range order and segregation of solutes to grain boundaries.
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From page 24... ...
A summary of all rapid solidification processing efforts reported to date appears in Table 4. TABLE 4 Rapid Solidification of Aluminides Alloys Method Remarks Reference Ni-Al-X Ni3Al-B FeAl-borides Fe-35 at% Al Fe-50 at% Al Ni3Al-B Fe3Al-TiB2 Melt spin Arc hammer Melt spin & PM RSR RSR Melt spin RSR Ductile at 25°C, unstable at 1000°C Ductile Brittle to 540°C TG at 25°C, IG at 600°C Inoue et al.
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From page 25... ...
Both the aluminide alloys and the LRO alloys show a substantial strength increase between room temperature and elevated temperatures, as is usually noted with Ll2-type superlattices.
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26 THE YIELD STRENGTH OF ORDERED INTERMETALLIC ALLOYS INCREASES WITH TEMPERATURE UJ a: UJ >• 900 800 700 600 5OO 400 300 200 100 "ADVANCED LRO ALLOY 316 STA1NLESS STEELj I 1 l 130 120 HO 100 90 80 70 g |
From page 27... ...
In the case of LRO alloys, however, formation of long range order causes only a small increase in AH, even though the creep rate is decreased by two orders of magnitude (Liu 1984)
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From page 28... ...
. Fatigue The suppression of cross slip or reduction in number of available slip systems with long-range order that occurs in most alloys suggests a diminished probability of crack nucleation under cyclic loading.
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From page 29... ...
Environmental Cracking The previously described changes in slip character caused by long-range order, most notably reduced cross slip in alloys with high anisotropy in APB energy, suggest that there should be a significant effect of LRO on resistance to environmental cracking since increased susceptibility to stress corrosion cracking of some austenitic steels deforming by planar glide has been noted (Barnartt 1962) [although this association has been disputed (Saxena and Dodd 1966)
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From page 30... ...
30 1U • LR060- 600 C A Aitroloy, 575° C He 1nconel X •750, 650° C 10~5 -- A Rene 95, 650° C D Nimonic901,550°C • Udimet 718, 550°C ID'6 O A288, 550° C Ti 1 10'7 !
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From page 31... ...
31 CD LL o CM O Cl 1 O O O< CU OS
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From page 32... ...
. Although directionally solidified eutectic alloys have not been commercially manufactured, some have been engine tested successfully under relatively short time conditions and may in the future be selected for turbine applications, especially if production costs can be reduced.
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From page 33... ...
1967. The effect of composition and ordering on adhesion in some binary solids solution alloy systems.
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From page 34... ...
1975. The effect of order on the low cycle fatigue response of ru ^Au single crystals.
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1965. Slip character and the ductile to brittle transition of single phase solids.
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1952. Mechanical properties of intermetallic compounds at elevated temperatures.
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From page 37... ...
1974. Plastic deformation of polycrystalline binary and ternary beta brass alloys.
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From page 38... ...
475. In Ordered Alloys: Structural Applications and Physical Metallurgy, Proceedings of the 3rd Bolton Landing Conference, Lake George, N.Y., September 1969.
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From page 39... ...
1983. Influence of thermomechanical processing on elevated temperature slow plastic flow properties of B2 aluminide Fe-39.8a%Al.
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