Nature of the strength of tungsten-nickel-iron alloys

Summary A study was made, by electron-microscope fractography of the effects of composition and conditions of cooling from the sintering temperature on the character of rupture of W-Ni-Fe heavy alloys. It has been established that the change in the mechanism of rupture from brittle to tough is due to structural changes in the alloy linked with the aging process.Translated from Poroshkovaya Metallurgiya, No. 6 (66), pp. 61–66, June, 1968.     

Creep strength of magnesium-based alloys

The high-temperature creep resistance of magnesium alloys was discussed, with special reference to Mg-Al and Mg-Y alloys. Mg-Al solid-solution alloys are superior to Al-Mg solid-solution alloys in terms of creep resistance. This is attributed to the high internal stress typical of an hcp structure having only two independent basal slip systems. Although magnesium has a smaller shear modulus than aluminum, the inherent creep resistance of Mg alloys is better than that of Al alloys. The creep resistance of Mg alloys is improved substantially by the addition of Y. Solid-solution hardening is the principal mechanism of the strengthening, but the details of the mechanism have not been elucidated yet. Forest dislocation hardening in concentrated alloys and dynamic precipitation in a Mg-2.4 pct Y alloy also contribute to the strengthening. An addition of a very small amount of Zn raises the dislocation density and significantly improves the creep resistance of Mg-Y alloys. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Creep strength of magnesium-based alloys

The high-temperature creep resistance of magnesium alloys was discussed, with special reference to Mg-Al and Mg-Y alloys. Mg-Al solid-solution alloys are superior to Al-Mg solid-solution alloys in terms of creep resistance. This is attributed to the high internal stress typical of an hcp structure having only two independent basal slip systems. Although magnesium has a smaller shear modulus than aluminum, the inherent creep resistance of Mg alloys is better than that of Al alloys. The creep resistance of Mg alloys is improved substantially by the addition of Y. Solid-solution hardening is the principal mechanism of the strengthening, but the details of the mechanism have not been elucidated yet. Forest dislocation hardening in concentrated alloys and dynamic precipitation in a Mg-2.4 pct Y alloy also contribute to the strengthening. An addition of a very small amount of Zn raises the dislocation density and significantly improves the creep resistance of Mg-Y alloys. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

High strength microduplex Cu-Ni-Zn alloys

High ambient temperature tensile and fatigue strengths have been obtained in two-phase α-β Cu-Ni-Zn alloys (nickel silvers) by controlled thermomechanical working. The thermomechanical working operation involves cold working of solution annealed stock, followed by annealing in the two-phase region. This results in simultaneous recrystallization and precipitation yielding a fine-grained two phase microstructure termed “microduplex”. The high mechanical properties obtained are attributed to the fine-grained two-phase microduplex microstructure. Compositional variations studied included 10 to 40 pct Ni, 35 to 40 pct Zn, balance Cu. On the basis of ease of processing and mechanical properties, a particularly attractive composition is Cu-15Ni-37.5Zn, designated IN-836. Typical room temperature properties of IN-836 in the microduplex condition include 100 ksi (690 MN/m²) yield strength with 25 pct elongation and 40 ksi (275 MN/m²) fatigue limit (10⁷ cycles). Finally, superplastic behavior has been observed in IN-836. F. J. ANSUINI was formerly with The International Nickel Company, Inc., Paul D. Merica Laboratory, Sterling Forest, Suffern, N. Y. 10901.     

Development of high strength zirconium alloys

Abstract

Assessment of the effects of various alloying elements and strengthening methods in zirconium alloys has indicated that alloys with adequate strengtl1 for use as pressure tube material at temperatures above 400°C can be developed. Ternary, quaternary and quinary alloys based on zirconium have been prepared and subjected to various thermal and deformation treatments. Their age-hardening behaviour and tensile properties are described and some information on their corrosion resistance and response to fast neutron irradiation at 300° and 450°C is presented. The target of UTS in the range 90–120 kpsi at 450°C can be achieved in alloys having an acceptable thermal neutron capture cross section. Adequate strength combined with the ductility necessary for pressure tube fabrication can be obtained by air cooling selected alloys from temperatures high in the (α + β) range.

Résumé

L'evaluation des effets de divers éléments d'alliage et des méthodes dc durcissement permet de croire que des alliagcs ayant une résistance adéquate peuvent être développés pour des tubes de force utilisés à des températures supérieures à 400°C. Des alliages ternaires, quaternaires et quénaires à base de zirconium ont été préparés et soumis à divers cycles thermiques et cycles de déformation. L'étude a porté sur leur vieillissement et leurs propriétés en traction; quelques observations sur leur tenue en corrosion et en irradiation par des neutrons rapides à 300° et 450°C sont présentées. Il est possible d'atteindre des résistances à la traction de 90 à 120 kpsi a 450°C pour des alliages ayant une faible section de capture des neutrons. Une résistance suffisante jointe à la ductilité nécessaire pour la fabrication des tubes peut être obtenue par refroidissement à l'air de certains alliages à partir d'une température élevée dans le domaine α + β.     

Development of high strength wrought aluminum-base alloys

Work is reported on small-scale laboratory techniques described for development of high strength wrought aluminum alloys and on structure and properties of alloys produced. Alloy screening tests were on splat cooled samples and mechanical property measurements were from cast and rolled thin section cast plates. The highest tensile strengths obtained were in excess of 115,000 psi; highest yield strenghts were in excess of 110,000 psi. Four different alloys tested showed yield strengths in excess of 90,000 psi with elongations in excess of 5 pct.     

High strength copper alloys by thermomechanical treatments

A thermomechanical processing technique for in creasing the strength of copper alloys is described. Alloys studied include phosphor bronze (5 pct Sn), nickel silver (12 pct Ni-28 pct Zn), tin-modified cupronickel (9 pct Ni-2 pctSn), and Cu?Be (2 pct Be). In this technique, the material is cold-rolled to about 95 pct reduction in thickness followed by heat treatment below the recrystallization temperature. The severe cold work results in increased strenght through strain hardening and texture strengthening, but at the expense of decreased ductility. The terminal heat treatment recovers the ductility while maintaining or increasing the strength imparted by cold work alone. Preliminary results indicate that cold work-accelerated precipitation is chiefly responsible for the strength increase during heat treatment. As a result of the present processing, the copper alloys exhibit higher yield strengths for given amounts of ductility than have heretofore been attained.     

Creep and stress-rupture of high strength zirconium alloys

Abstract

Zirconium-based alloys with small additions of tin, molybdenum, niobium and aluminum are being developed as candidate materials for high-strength pressure tubes in advanced CANDU reactors. The out-reactor creep and stress-rupture properties of 12 alloys based on these elements have been determined and correlated with their metallographic structures and substructures and thermomechanical histories. An alloy of composition Zr-3 wt% Sn-1 wt% Mo-1 wt% Nb was the best for high creep strength, low neutron capture cross section and reasonable corrosion resistance.

Résumé

Des alliages à base de zirconium et con tenant de faibles additions d'étain, de molybdéne, de niobium et d'aluminium sont en voie de développement comme matériaux à haute résistance pour des tubes de force pour le réacteur CANDU. Les propriétés de 12 de ces alliages ont été évaluées hors réacteur quant au fluage et à la rupture; des corrélations ont été établies entre ces propriétés et la structure métallographique, et les traitements thermomécaniques subis. Le meilleur alliage pour sa résistance au fluage, sa faible section de caputre des neutrons et sa résistance à la corrosion, a une composition de: Zr-3% Sn-1% Nb (% pondéral).     

On the problem of the maximum strength of metals and alloys in crystalline,amorphous, and nanocrystalline states

The true breaking stresses and the ultimate tensile strengths of 11 metals with various structures are calculated. Moreover, the fracture strengths of these metals at 0 and 298 K are calculated in the amorphous (σ _{f, a}) and nanocrystalline (σ _f,nano^max) states formed upon severe plastic deformation. The temperature dependences of these properties are also determined. These properties are obtained for a number of alloys (TiNi, NiNb, Pd₈₀Si₂₀, Ni₆₀Nb₄₀). The values of σ _{f, a} are shown to correlate with yield strength σ_{y, nano} of nanocrystalline substances, and a hypothesis of a deviation from the Hall-Petch relation is advanced. This hypothesis is supported by the calculation of the properties and diffusion characteristics. The obtained numerical results agree satisfactorily with the experimental data and the results of other approaches to estimating these properties.     

Nature of the strength of tungsten - nickel - iron alloys

Conclusions A study was made of the structural changes taking place in W - Ni - Fe alloys during slow cooling from the sintering temperature. It is shown that aging occurs in the binder phase and in a layer of the refractory tungsten-base phase adjoining the low-melting-point constituent.A W - Ni - Fe alloy sintered in the presence of a liquid phase and slowly cooled from the sintering temperature has a complex multiphase structure of a dispersed-aggregate type. The results of the present investigation provide a foundation for subsequent research into the behavior of the phase constituents of these alloys during plastic deformation and into the nature of their strength.Translated from Poroshkovaya Metallurgiya, No. 5(65), pp. 73–78, May, 1968.     

Yield strength of overaged alloys containing coherent ordered precipitates

The existing models for yielding of overaged alloys do not account for the observed strain rate sensitivity of the yield stress and predict a sharper decrease in stress as a function of particle size than the experimental observations. A dynamic model has been presented here to account for the yield strength of overaged alloys containing coherent ordered precipitates which takes into consideration the intrinsic characteristics of the precipitates. Concentric glide loops are supposed to form around precipitate particles. Their sizes as a function of applied stress have been computed. The stress on the innermost loop rises with increasing applied stress and when it exceeds the opposing force due to antiphase boundary, the loops shrink. The rate of shrinkage of loops has been calculated for different values of applied stresses. The yielding occurs when the external stress is high enough to account for the applied strain rate. The model has been applied to calculate the yield strength of an austenitic stainless steel containingγ’ precipitates. The antiphase boundary energy of the precipitates was measured by dislocation pair spacing method. The mode of variation of calculated yield stress values with particle size is predicted more accurately than by earlier models. The model qualitatively accounts for the observed sensitivity of yield stress to strain rate and antiphase boundary energy of the precipitates. Formerly Manager Research & Development, Alloy Steels Plant, Durgapur