A preliminary study of the influence of separate and combined aluminum and nickel additions on the properties of a secon
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Complete solid solubility of the additive in tungsten
A Preliminary Study of the Influence of Separate and Combined Aluminum and Nickel Additions on the Properties of a Secondary Hardening Steel W. M. GARRISON, Jr. and R. STRYCHOR
A
W (a)
High solubility of additive in Ni and/or Fe
Ni/Fe
A (b)
Fig. 3--Ideal binary phase diagrams involving the body-centered cubic additive A that will induce grain refinement and solid solution strengthenmg for tungsten heavy alloys.
strengths. The strengthening effect comes from both the solid solution alloying and microstructure control aspects associated with these additions.
This research was supported by the United States Army Research Office. REFERENCES 1. R.M. German: Liquid Phase Sintering, Plenum Press, New York, NY, 1985. pp. 228-29. METALLURGICALTRANSACTIONS A
With the exception of some maraging steels, t~l the only steels which can be precipitation hardened to hardnesses of Rc 60 and higher are various types of secondary hardening steels. 121These secondary hardening steels have extremely low impact and fracture toughnesses and after conventional treatment they contain large volume fractions of primary carbides.[3'4'5~ Efforts to improve the toughness of ultra high strength secondary hardening steels have concentrated on determining compositions which minimize the volume fraction of primary carbides without impairing the secondary hardening response. Secondary hardening steels containing the smallest volume fraction of primary carbides consistent with a reasonably fine grain size and the concentrations of carbon (C -> 0.5 wt pct) and carbide forming elements needed to achieve hardnesses of R e 57 to 60 have been designed. I6~However, the impact and fracture toughnesses of even these steels are undesirably low. Evl An alternative to these steels is a medium carbon steel combining the precipitation of alloy carbides and of an intermetallic compound. Introducing strengthening by intermetallic precipitation will decrease strengthening required of the precipitation of alloy carbides. This will permit a reduction in the carbon level, the amounts of carbon forming elements and, as a result, the volume fraction of primary carbides. One possible choice for the intermetallic is the nickelaluminum compound/3-NiA1, an ordered bod~-centered cubic structure with a lattice constant of 2.886. cJ Strengthening by the precipitation of/3-NiA1 has been utilized in both martensitic stainless steels t91and in ferritic steels ~~ and in these materials/3-NiA1 precipitates as ordered particles coherent to the matrix. While the precipitation hardened martensitic stainless steels contained about 7 wt pet nickel and 1 wt pct aluminum, studies of age hardening by/3NiA1 in ferritic steels indicate that substantial strengthening can be achieved at nickel and aluminum levels of about 4 and 1.5 wt pet, respectively, after aging for reasonable
W. M GARRISON, Jr., Associate Professor, and R. STRYCHOR, Research Associate, are with the Department of Metallurgical Engineering and Materials Science,
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