A new patent filed by superalloys producer Cannon-Muskegon shows that the rhenium content of single crystal superalloys for turbine blades and vane applications can be successfully lowered to 1.4–1.6% Re, while maintaining high-temperature creep resistance and other properties. Total refractory elements (tungsten, molybdenum, tantalum and rhenium) were balanced at 18–19% by weight to achieve good creep-rupture mechanical stability and acceptable alloy phase stability.
Rhenium has been a core component of single crystal superalloys since the 1980s, with typical nickel-base superalloys for single crystal castings containing 3–7% rhenium by weight. However, world supply of rhenium is relatively scarce, amounting to 75t in 2019, with all primary production sourced as a by-product of other metals. The majority of primary rhenium supply is recovered from flue gases generated during the roasting of molybdenite concentrates produced from porphyry copper-molybdenum deposits; it is also a by-product of smelting copper ore.
The by-product nature of rhenium production has contributed to periods of tightness in supply and the rapid growth of the aero-engine sector has previously led to concern over rhenium availability. As a result, prices for rhenium have witnessed substantial volatility over the last 15 years. During price peaks, rhenium has accounted for more than half the raw material costs incurred in turbine blade production. As a result, superalloy producers have aimed to reduce costs through the development of low- or zero-rhenium superalloys. Nickel-base superalloys provide by far the largest market for rhenium, accounting for nearly 80% of world demand in 2018/2019.
Roskill’s NEW Rhenium: Outlook to 2029 report was published in December 2019. Click here to download the brochure and sample pages for the report, or to access further information.