H. Cross Company is the leading specialty metal rolling manufacturer of precision ribbons, sheets, foils and strips of molybdenum and molybdenum-base alloys. We also supply wire, rod and a comprehensive line of custom and lamp industry products. These include elliptically etched foil, platinum clad wire and ribbon. Our Lamp Seal Products section covers these products.
History of Molybdenum and Molybdenum Alloys
C.W. Scheele discovered molybdenum in 1778 in a substance that he called molybdic acid. P.H. Hjelm isolated it as an element in 1790. Between two-thirds and three-fourths of the world supply of molybdenum comes from mines where its recovery is the primary objective of the operation. The remainder is recovered as a by-product of certain copper mining operations, largely in the United States and Chile.
Fabrication and Applications
Molybdenum has a high melting temperature and it is impractical to transform it into ingot forms by conventional furnace melting techniques. Its manufacture by powder metallurgy consists of three distinct phases: the decomposition of the ore and its reduction to pure metal powder, the pressing of this powder into bars and the sintering of these bars into solid ingots and the swaging, rolling or drawing of these ingots into desired forms and sizes. Some products are fabricated from arc-cast ingots. Prefabricated or continuously compacted and sintered electrodes made from metal powder are arc-melted in a water-cooled copper mold. The process is usually carried out in a vacuum, although in some instances inert-atmosphere melting is employed.
After drawing or rolling operations have been completed, the material may be cleaned by exposure to elevated temperatures in a reducing atmosphere. Treating the surface chemically or electrolytically could also clean molybdenum.
The material may be further reduced after processing by electrolytic etching. The cleaned material can be electroplated with such elements as gold, silver, nickel and copper, for use primarily in electronic tubes. Platinum-clad wires are also available.
Each H. Cross Company product is delivered in packaging specifically designed for the product’s application. As an example, wire is furnished on returnable plastic reels, each containing a single length of wire measuring 50 meters (197 feet) minimum. If required, H. Cross Company can adapt standard packaging methods or develop new ones for your special needs.
In addition to pure molybdenum H. Cross Company also produces materials from 50/50 Molybdenum Rhenium Alloy and TZM Molybdenum Alloy:
50/50 Moly Rhenium
This alloy offers the strength of molybdenum with the ductility and weldability of rhenium. It is a more expensive alloy and it is available in a limited size ranges. It offers significant advantages in thin foil applications for high temperature delicate parts, especially those that must be welded. Note that, although this alloy is nominally 48% rhenium, it is customarily referred to 50/50 moly/rhenium. In addition to foil this material can also be made in wire and rod form from .005″ to .250″.
TZM Alloy (titanium, zirconium, molybdenum)
Molybdenum’s prime alloy is TZM. This alloy contains 99% Mo, 0.5% Ti and 0.08% Zr. TZM offers twice the strength of pure molybdenum at temperatures over 1300° C. The recrystallization temperature of TZM is approximately 250°C higher than molybdenum and it offers better weldability than pure molybdenum.
TZM’s finer grain structure and the formation of TiC and ZrC in the grain boundaries inhibit grain growth and the related failure of the base metal as a result of fracturing along grain boundaries. This characteristic also gives it better properties for welding. TZM generally costs around 25% more than pure molybdenum but in high heat and strength applications it can be well worth the cost differential.
TZM is generally available in sheet and foil in the same size ranges as pure moly with the exception of very thin foil. Contact Us for more specific information.