High Temperature Alloys for Furnace Applications

H.C. Starck Solutions’ fabricated product solutions cater to a myriad of industries, markets, and applications, including brazing, annealing, sintering, vacuum heat treating, and all high temperature furnace applications.

High temperature materials exhibiting superior physical and mechanical properties are required in applications such as annealing of aerospace and medical components to critical specifications, voluminous production of components for brazing with controlled atmosphere furnaces, and heat treatment of large aerospace components in vacuum furnaces.

Alloys of molybdenum, niobium, tantalum, and tungsten such as MoLa (molybdenum-lanthanum), MoW (molybdenum-tungsten), MHC, and TZM are ideally suited for the furnace and heat treating markets. The characteristics of these high temperature refractory metals include:

• High mechanical durability
• High ductility and toughness
• Superior thermal and electrical conductivity
• Low coefficient of thermal expansion
• Unprecedented strength and stability at temperatures up to 2000°C

H.C. Starck Solutions designs and supplies customer specific furnace components and fixtures, and fabricates components such as heat shields, furnace racks, hot zones, boats and trays, flat ribbed heating elements, and furnace assemblies from foils, sheets, plates, and rods.

Furnace Applications and Operations

H.C. Starck Solutions’ high temperature refractory metal materials and components are supplied to end users, OEMs, and aftermarket manufacturers, and are used in furnace applications, such as in heating elements and their auxiliary parts such as supports, feed-throughs, and hangers, and in heat shields and their own auxiliary parts such as separators, staples, and rivets.

H.C. Starck Solutions’ refractory materials are used in high temperature furnaces in vacuum, inert, or reducing atmospheres, and in chemical reaction furnaces in air, vacuum or other atmospheres. Industrial furnace operations served include annealing, brazing, heat treating, HIPing, melting, pre-heating for metalworking, powder processing, sintering, tempering, and MIM (sintering/debonding). Industries served include automotive, aerospace, defense, energy, medical, nuclear fuel, crystal growth, and waste treatment.

Powder Metallurgy and Vacuum Arc Cast Products

H.C. Starck Solutions employs powder metallurgy and vacuum arc cast processing to obtain products with superior quality. The company’s alloys are engineered for furnace applications with the highest temperature utilization capabilities.

Molybdenum Products - Powder Metallurgy (P/M)

The production of molybdenum (Figure 1) by this process involves compaction of less than 99.95% pure powder into billets, followed by sintering and making into finished wrought forms. The process uses only the highest commercially pure powders.

Figure 1. Molybdenum

Molybdenum mill products by powder metallurgy are given in the following table:

* Submit size required for H.C. Starck Solutions quotation
** Inquire for thickness x length x width combinations

Molybdenum Products - Vacuum Arc Cast

H.C. Starck Solutions exclusively offers products made by the vacuum arc cast process. Arc cast wrought products show high workability and weldability, and have good machining characteristics with fracture toughness, greater ductility, and lower oxygen when compared to powder metallurgy products.

The vacuum arc melting process involves compacting, sintering, arc melting, and casting of 99.95 % minimum pure molybdenum powder with or without required additions into an ingot of weight to one ton. All these processes are carried out under vacuum. Molybdenum mill products by vacuum arc cast are given in the following table:

Molybdenum Alloys

TZM Molybdenum Alloy

Either the PM or vacuum arc-casting process is used to fabricate TZM alloy (0.50 Ti, 0.08 Zr, balance Mo). The presence of titanium and zirconium carbides improves the strength and creep resistance at higher temperatures. TZM molybdenum alloy maintains toughness at higher service temperatures when compared to pure molybdenum. The abrasion resistance property of arc cast material makes it suitable for use in injection molding nozzles.

MoW Alloys

H.C. Starck Solutions offers the only commercially available arc cast molybdenum and tungsten alloy with 70wt% Mo and 30wt% W, demonstrating superior service life while handling high purity molten zinc (99.99% Zn). Using the P/M method, H.C. Starck manufactures Mo 75wt% and W 25wt% alloy to serve as heat shields in furnaces.

MHC Alloys

The P/M process is used to consolidate MHC (1.2% Hf, 0.1% C) alloys composed of hafnium carbide. MHC alloys exhibit high thermal conductivity, low thermal expansion, and high recrystallization temperature.

ODS MoLa Alloys

Molybdenum-lanthana (MoLa) alloys are a kind of oxide-dispersion strengthened (ODS) molybdenum composed of molybdenum and a very fine array of lanthanum trioxide particles, exhibiting exotic properties such as high-temperature warpage and resistance to recrystallization (. They are suitable for applications demanding strength and dimensional stability at temperatures beyond the capabilities of either pure molybdenum or molybdenum TZM alloy.

H.C. Starck Solutions produces MoLa alloys by doping with different levels of lanthanum trioxide: 0.3wt%, 0.6wt%, and 1.1wt%. The grain structure of the material is stabilized by the addition of trioxide particles, thus permitting high temperature performance. H.C. Starck Solutions’ unique doping process of adding the oxide particles to the molybdenum matrix provides the competitive edge to the company over other manufacturers of similar materials.

Besides creating MoLa alloys with excellent properties, the doping process optimizes the uniformity of the dispersion o f lanthanum oxide in the molybdenum matrix. H.C. Starck Solutions’ MoLa alloy products are utilized in high temperature furnace and heat treating applications:

• High pulse magnet research
• Nuclear fuel pellet production
• Aircraft and aerospace components
• Medical devices

The formability of MoLa alloys is better at all grade levels than pure molybdenum in the same condition. At roughly 1200°C, pure molybdenum becomes very brittle with below 1% elongation due to recrystallization, which affects its formability in this condition.

The plate and sheet forms of MoLa alloys show better performance than pure molybdenum and TZM in high temperature applications. Lanthana particle will be released from the surface at temperatures above 1900°C, which is thus the optimum maximum advisable temperature for MoLa alloys. The MoLa alloy comprising 0.6wt% lanthana has the best combination of properties (Figures 2). Its thin sheet form exhibits high malleability and its bendability is analogous irrespective of the bending direction, whether traverse or longitudinal (Figure 3).

Figure 2. Room temperature strength of thick gauge MoLa sheet remains almost unchanged over a wide range of thicknesses.

Elongation development in 0.6% MoLa alloy is summarized in the following table:

L = Longitudinal
T = Transverse

Figure 3. Microstructures of recrystallized 0.2 mm thick MoLa sheet

The material has to be recrystallized before being used at high temperatures in order to realize the of high lanthana MoLa such as high creep resistance. The MoLa alloy comprising 0.3wt % Lanthana is an alternative to pure molybdenum at 1100-1900°C, but with longer life owing to its superior creep resistance.

The MoLa alloy comprising 1.1wt % Lanthana exhibits strong warpage-resistance, high strength properties, and has the highest creep resistance of all grades offered by H.C. Starck Solutions. Its strength is five folds higher than pure molybdenum at 1500°C and higher than that of the TZM alloy above 1400°C. MoLa alloys deliver superior performance in applications requiring high-temperature dimensional stability and sag resistance such as furnace elements, sintering boats, and setter tiles.

H.C. Starck Solutions supplies MoLa alloys in a range of forms, including bars, rods, plates, sheets, and as complex assembled products:

¹ Dimensional tolerance is identical to our molybdenum and TZM mill products in the same forms.
² Trays are similar to boats, but less height and can be made by folding without riveting or deep drawing and stamping.
³ We recommend rectilinear heating elements due to their lower power consumption versus round.

Tungsten Mill Products

Tungsten mill products (Figure 4) are produced by the P/M method by pressing, sintering pure tungsten metal powder into an ingot for hot, and cold rolling. The material used is 99.95% minimum pure tungsten typically supplied as-rolled or cut to shape parts.

Figure 4. Tungsten

The different forms of tungsten mill products are listed in the following table:

Tantalum Mill Products

Electron Beam Melting

Tantalum (Figure 5) produced has stabilized grain structure and is engineered for high temperature applications. It exhibits creep resistance properties for vacuum furnaces.

Figure 5. Tantalum

The specifications of tantalum plates, sheets and foils are listed in the following table:

Rectangular Flat Product Tolerances for TA130 (SGS) and Embossed Material (Embossed Material available from 0.0050“ to 0.0150“ only) Tolerances are applied before the emboss process. 1 inch = 25.4 mm

The specifications of tantalum bars, wires and rods are listed in the following table:

1 inch = 25.4 mm

Product in Annealed Condition

• Longer lengths are supplied in the unannealed condition
• Straightness deviation of machined rod is 0.0625" per foot maximum
• Ends are saw cut at 0.375" and above
• Ends are sheared through 0.3749" diameter

Refractory Metal Production Processes

Molybdenum Process

The molybdenum process involves uniform gauge control, controlled flatness, precision machining (5 Axis), laser and water jet cutting, riveting, in-house expertise for extrusion and rotary forging, copper and nickel cladding of molybdenum (Figure 8).

Figure 8. The molybdenum process

Tungsten Process

The tungsten process involves fully integrated supply chain, controlled flatness, water jet cutting, in-house expertise in rolling operations, and uniform gauge control (Figure 9).

Figure 9. The tungsten process

Tantalum Process

The tantalum process involves competitive costs, cutting-edge R&D and technology, forging expertise – consistent grain size and texture control, electron beam (EB) melting – control purity to precise levels, and vacuum Arc Re-melting (VAR) (Figure 10).

Figure 10. The tantalum process

Niobium Process

The niobium process involves in-house expertise in forging, rolling, machining, cutting and fabrication, expertise in thermal processing, chemical, mechanical, and microstructure monitoring in-house, and consistent grain size and texture control (Figure 11).

Figure 11. The niobium process

This information has been sourced, reviewed and adapted from materials provided by H.C. Starck Solutions.

For more information on this source, please visit H.C. Starck Solutions.