Nickel-silicon-copper alloys have been used in the art for over fifty years to produce cast articles especially suited for use in wet corrosion conditions.
U.S. Pat. Nos. 1,258,227, 1,753,904, 1,769,229 and 3,311,470; also British Pat. Nos. 1,114,398 and 1,161,914 are prior art patents that relate to alloys of this general composition. German Auslegeschift No. 1,243,397 also relates to a somewhat similar alloy. Table 1 presents the overall scope of these patents.
The earliest patent in this art appears to be U.S. Pat. No. 1,076,438 which discloses a nickel-silicon binary with optional contents of manganese or aluminum to remove "shortness" in the alloy. The silicon content is preferred at 3% to 5% because alloys with silicon contents about 7% or over cannot be produced in wrought form. The alloy is defined solely for use as a thermoelectric element.
U.S. Pat. Nos. 1,258,227 and 1,278,304 disclose articles for use as cutting tools containing 86 Ni-6 Al-6 Si-1.5 Zr and 81 Ni-8.4 Al-3.8 Si-6.8 Zr respectively.
TABLE 1 __________________________________________________________________________ COMPOSITION OF PRIOR ART ALLOYS, IN WEIGHT PERCENT, WT % U.S. PAT. NOS. BRITISH PATENTS GERMANY 1,076,438 1,769,229 3,311,470 1,114,398 1,161,914 1,243,397 __________________________________________________________________________ SILICON 3-7 up to 10 7-16 about 8.3 5-8.5 7-16 COPPER -- AVOID 0-5 -- -- 1-4 + MO TITANIUM -- PRESENT* 1-5 about 2.9 1-5* 1-5 ALUMINUM PRESENT PRESENT* -- -- -- -- TUNGSTEN -- PRESENT* 0-5 -- -- MANGANESE PRESENT PRESENT* 0-1 -- MOLYBDENUM -- -- 0-5 -- 3-10* 1-4 + CU CHROMIUM -- PRESENT* -- -- 6-10* -- IRON -- AVOID 0-3 -- 20-30* -- COBALT -- PRESENT* 0-10 -- 25-30* -- VANADIUM -- PRESENT* -- -- -- -- ZIRCONIUM -- PRESENT -- -- -- -- NICKEL BALANCE BALANCE BALANCE BALANCE BALANCE BALANCE __________________________________________________________________________ *AT LEAST ONE MUST BE PRESENT
In the present art, only one major alloy is produced under the registered trademark HASTELLOY.RTM. alloy D. The alloy normally contains about 9% silicon, 3.0% copper and the balance nickel. It is available generally only in the form of castings and proposed recently as coatings and articles made from the alloy powder as disclosed in U.S. Pat. No. 4,561,892. The alloy is especially useful in chemical processing plumbing and the like because of its resistance to sulfuric acid in high concentrations.
In the present art, alloy D is produced in cast form with a two-phase structure containing an FCC solid solution phase known as "alpha" and an intermetallic ordered phase, Ni.sub.3 Si also known at "beta". Present also may be the Ni.sub.5 Si.sub.2 phase which contributes to the unsatisfactory mechanical properties of the alloy, ie low ductility and poor to nil working characteristics. The alloy is notoriously weak at room temperatures and up to 600.degree. C.
Because of these limitations, the nickel-silicon alloys could not be used more extensively in the art.