Hafnium Alloys: Part Two

Hafnium, with a melting point of 2,233°C is a key member of the superalloy family with key usage in a range of extreme high temperature uses.
Possessing excellent mechanical and corrosion resistance properties, in combination with the ability to absorb neutrons, hafnium is a key constituent of nuclear reactor control rods.

Hafnium forms refractory compounds with carbon, nitrogen, boron, and oxygen. Hafnium oxide, or hafnia, HfO2, is a better refractory ceramic than zirconia, but is costly.

Uses of Hafnium

Currently, hafnium has three important uses: superalloys (in both aerospace and nonaerospace), refractory metal alloys and nuclear applications.

Alloys

In high-temperature alloys and polycrystalline nickel-based superalloys, hafnium's high melting point - 2,233°C (4,051°F) - helps strengthen grain boundaries, thus considerably improving both high-temperature creep and tensile strength. In addition, with its high affinity for carbon, nitrogen and oxygen, the metal also provides strengthening through second-phase particle dispersion.

One of the most common uses of hafnium is as one of the alloys in the superalloy group used in the turbine blades and vanes found in the "hot end" of jet engines, i.e., in environments with very high temperatures and pressure and high stress. Such superalloys can contain 1-2 percent hafnium. For example, MAR-M 247-a polycrystalline nickel-based alloy developed by Martin-Marietta Corp. and used by Siemens in land-based turbines that operated at temperatures up to 1,038°C - contains 1.5 percent hafnium.

Hafnium can also to be found in a number of other alloys, such as tantalum-based T111 (Ta-8%W-2%Hf); tantalum/tungsten-based T222 (Ta-10%W-2.5%Hf-0.01%C) and molybdenum-based MHC, or molybdenum-hafnium-carbide, which breaks into 1.2%Hf-0.1%C (the rest moly). In addition, it can be found in a number of niobium-based alloys: C-103 (10% Hf-1%Ti-1%Zr); C-129Y (10%W-10%Hf-0.7%Y) and WC-3015 (30%Hf-15%W-1.5%Zr).

Among other applications, niobium-based alloys containing hafnium have been used as coatings for cutting tools, while C-103 and hafnium-tantalum-carbide have been used in the fabrication of rocket engine thruster nozzles.

In both alloys containing tantalum and molybdenum, as well as in binary compounds, hafnium is also an excellent refractory material. With a melting point of over 3,890°C, hafnium carbide (HfC) makes one of the most refractory binary materials around. And with a melting point of some 3,310°C, hafnium nitride is the most refractory of all known metal nitrides.

Hafnium is used for nuclear reactor control rods because of its ability to absorb neutrons and its good mechanical and corrosion resistance qualities. It is also used in gas filled and incandescent lights. Hafnium alloys with several other metals, such as iron, niobium, tantalum and titanium. Hafnium-niobium alloys, for example, are heat resistant and are used in aerospace applications, such as space rocket engines.

Al C Cr Cu Fe H Mo N Nb Ni O Si Sn Ta Ti U V W
100 150 100 100 500 25 20 100 100 50 400 100 50 200 100 10 50 150

Bright finish Hafnium wire and rod according to ASTM B737 Grade R1
Hf+Zr≥99.7%; Zr≤4.5%; Impurities (ppm, max)

Applications of hafnium:

Plasma Cutting Electrodes, Vacuum Plating and Welding Consumables

October, 2012
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