The world runs on rock · Story 9 of 12

The Engine the jet engine's hottest metals

A jet engine's turbine blades work at metal temperatures above 1,000°C. They manage it with nickel, cobalt, chromium and a pinch of rhenium, one of the rarest metals mined. The fan in front is titanium.

Scroll to take an engine apart

Black and white photo of a long jet engine mounted in a wind tunnel test section — Rolls-Royce Avon in NASA's Altitude Wind Tunnel, 1956. NASA (public domain).

A turbofan engine on a test stand inside a large round test chamber, with engineers kneeling beside it — A Pratt & Whitney JT8D turbofan in NASA's Propulsion Systems Laboratory, 1974. NASA (public domain).

An engineer holds a turbine blade beside a test rig lined with blade shapes — A transonic turbine blade cascade at NASA Glenn, 2020. NASA/Bridget Caswell (public domain).

Seventy years of testing

The same problem, hotter every decade

NASA and its predecessor have tested jet engines since the 1940s. Each generation burns hotter to get more thrust from less fuel, and each needs metal that can take it.

Take it apart

Cold at the front, white-hot in the middle

Air enters through the fan, is squeezed by the compressors, burns with fuel in the combustor, then spins the turbines that drive everything in front.

The fan

Hollow titanium

Every large Rolls-Royce turbofan since the RB211-22 has used hollow, wide-chord titanium fan blades, made by inflating bonded titanium sheets at high temperature.¹

Where the metal changes

Titanium is used where the engine stays below about 400°C; above that it risks catching fire in rare conditions, so the hotter stages switch to nickel superalloys.²

TiNiCoCrReAlWTa

The hottest part

Single-crystal blades

The first turbine blades are each cast as one single crystal of nickel superalloy, with no grain boundaries, because boundaries are where a hot blade slowly stretches, or creeps.²

A metal stator blade glowing in front of the orange flame of a hot gas test rig — A coated stator blade in a hot gas rig at NASA's Lewis Research Center, 1975. NASA (public domain).

Over 1,000°C

Ceramic coats, metal core

NASA tested ceramic thermal-barrier coatings like this one in the 1970s to lower the temperature the metal sees.³ Blade alloys themselves work at metal temperatures above 1,000°C.²

Inside the blade

Cubes in a mortar

Under a microscope a blade alloy is mostly tiny cubes of gamma-prime, an ordered compound of nickel and aluminium, Ni₃Al. In blades that run above 1,000°C they fill more than 60% of the volume.² Between them run thin channels of gamma: nickel with chromium, cobalt, tungsten and molybdenum dissolved in it.

The pinch of rhenium

3% to 6%

Second-generation single-crystal alloys contain about 3% rhenium by weight, third-generation about 6%. Rhenium sits in the gamma channels and is the slowest-moving element in nickel, which slows the creep.²⁴

The ordered cell

Gamma-prime's crystal is a cube with aluminium at its corners and nickel at the centre of each face.²

Follow the supply

1 · Rhenium

Rhenium is a by-product of the molybdenum in copper ores. About 81,000 kg was mined in 2025, Chile 30,000 kg of it. Superalloys take about 80% of US use, and the price of rhenium metal rose from $1,360 to $2,600 a kilogram between 2024 and 2025.⁵

2 · Nickel

Indonesia mined 67% of the world's nickel in 2025.⁶

3 · Cobalt

DR Congo mined 74% of the world's cobalt in 2025.⁷

4 · Titanium sponge

Titanium metal starts as porous "sponge". China made 260,000 of the world's 370,000 tonnes in 2025, Japan 53,000, Russia 25,000 and Kazakhstan 16,000. The last US sponge plant closed in 2024; US imports came mostly from Japan.⁸

7 March 2022

Boeing stops buying Russian titanium

After Russia invaded Ukraine, Boeing suspended purchases from Russia, home of VSMPO-Avisma, the world's largest titanium supplier, saying its stocks and other sources were enough. Russia had supplied about a third of Boeing's titanium. Airbus kept buying, within sanctions rules.⁹

Why "critical"

A few kilograms that decide the engine

Rhenium is a few percent of a blade, and the whole world mined about 81 tonnes of it in 2025.⁵ Titanium sponge comes almost entirely from six countries.⁸ There is little slack in either.

TiTitaniumsponge: China 70% NiNickelIndonesia 67% CoCobaltDR Congo 74% CrChromiumSouth Africa 45% ReRheniumfrom molybdenum WTungstenChina 79% TaTantalumDR Congo 52% AlAluminiumin Ni₃Al

Next in the series: The Grid, copper, the metal of electricity. Before this: The Body, The Shield, The Signal, The Rocket, The Magnet, The Battery, The Mind and The Chip.

Sources

Shares of world output are from USGS Mineral Commodity Summaries 2026 via our minerals data; rhenium and titanium sponge figures are from the USGS chapters below. The 3D models are illustrations, not engineering drawings or any one engine. Photos: NASA, public domain.