The deformation behaviour of intermetallic superlattice compounds

Combining in an additive or synergetic manner the most potent strengthening mechanisms available in an alloy is the art of the metallurgist. The various models proposed in the literature in order to interpret the Hall-Petch relation are critically reviewed by comparison with experimental data. The pile-up models and the work hardening theories must include the inner structure of the grain in the case of alloys hardened by a second phase. Similarly, the properties and structure of the grain boundaries are influenced by impurities or the presence of particles. Ultra-fine grain sizes can provide ductility to high strength materials when surface preparation eliminates microcracks. In steady-state creep equations, introducing the influence of grain size in complex alloys by incorporating the Hall-Petch stress as one component of the internal stress helps in rationalizing the existence of an optimal grain size where creep resistance is maximized. Slower crack growth rates can be obtained by controlling the grain boundary structure as well as grain size. Fatigue tests at room temperature clearly point out the interest of small grain sizes for reducing crack initiation, usually associated, however, with lower propagation threshold and somewhat faster growth rates.

Influence of grain size on the mechanical behaviour of some high strength materials

The physical and mechanical metallurgy of Ni3Al and its alloys is reviewed Emphasis is on developments within the past five years, a period of extremely rapid growth in research on the behaviour of this unusually interesting intermetallic compound This review is particularly concerned with solute effects on properties such as diffusion rates, ductility, fatigue resistance, and environmental stability, subjects that only recently have received much attention Novel processing techniques, including rapid solidification and powder processing, are shown to have played a key role in providing Ni3Al-base alloys with improved properties An assessment of needed areas of research to hasten commercial applications of Ni3Al alloys concludes the review

Physical and mechanical metallurgy of Ni3Al and its alloys

Many ordered intermetallic alloys have attractive high-temperature properties; however, low ductility and brittle fracture limit their use for structural applications. The embrittlement in these alloys is mainly caused by an insufficient number of slip systems (bulk brittleness) and poor grain-boundary cohesion. Recent studies have shown that the ductility and fabricability of ordered intermetallics can be substantially improved by alloying processes and control of microstructural features through rapid solidification and thermomechanical treatments. These results demonstrate that the brittleness problem associated with ordered intermetallics can be overcome by using physical metallurgical principles. Application of these principles will be illustrated by results on Ni(3)Al and Ni(3)V-Co(3)V-Fe(3)V. The potential for developing these alloys as a new class of high-temperature structural materials is discussed.

https://science.sciencemag.org/content/sci/226/4675/636.full.pdf

Ductile ordered intermetallic alloys

Environmental embrittlement in boron-free and boron-doped FeAl (40 at. % Al) alloys

IMPROVED STRENGTH AND DUCTILITY OF Ni3Al BY BORON MODIFICATION AND RAPID SOLIDIFICATION.

A study of the effect of Cr additions (5, 10, and 12.5 at. pct) on the microstructure of melt-spun Ni3Al-base alloys has been carried out using analytical electron microscopy. The analyses showed that the formation of the β-NiAl phase could not be totally avoided at all three levels of Cr additions studied. However, its volume fraction, morphology, and distribution were affected by the Cr concentration as well as by changes in the rapid solidification conditions. The ordering structure of the matrix γ contains anisotropic antiphase boundaries or cube-plane-oriented thin layers of disordered γ, depending on the local chemistry. A series of microchemistry measurements along the radius of a grain was used to trace the route of Al and Cr segregation, and an unexpected reverse segregation with a partition coefficient greater than 1 was observed for Cr. The bend ductility and tensile properties of the melt-spun ribbons were also studied. It was shown that the Cr additions substantially increased the ribbon strength and modified the mode of failure toward transgranular fracture. The improved tensile properties were partially attributed to the fine matrix γdomains which had mixed interfaces of antiphase boundaries and y thin layers.

L12-type Ni-Al-Cr alloys processed by rapid solidification

Polycrystalline Ni/sub 3/Al-based intermetallic alloys have overcome their room temperature brittleness problem with a small amount or boron addition. Because of their unique strength-temperature relationship and good oxidation resistance at high temperatures, research efforts have been concentrated extensively on structural applications at elevated temperatures. In this paper the authors show that ductile Ni/sub 3/Al-B alloys also exhibit remarkable mechanical properties at cryogenic temperatures.

/pdf/cryogenic-properties-of-a-p-m-ni3al-b-alloy-zn5gmjyogo.pdf

K. M. Chang

Papers

IMPROVED STRENGTH AND DUCTILITY OF Ni3Al BY BORON MODIFICATION AND RAPID SOLIDIFICATION.

L12-type Ni-Al-Cr alloys processed by rapid solidification

Cryogenic properties of a P/M Ni3Al-B alloy