High-temperature alloys are a class of metal materials based on iron, nickel, and cobalt that can operate for extended periods at temperatures exceeding 600°C and under certain stresses. They exhibit a combination of high-temperature strength, excellent oxidation and hot corrosion resistance, good fatigue performance, and fracture toughness. These materials are known in Europe and the United States as superalloys. They are typically used in components subject to long-term operation at high temperatures (600-1200°C) and complex stress conditions.
Nickel-based alloys are currently the most widely used high-temperature alloys, primarily used in high-temperature environments, strong acids or bases, and strong oxidizing environments. Their development and use began in the late 1930s, driven by the emergence of jet aircraft, which placed higher demands on the performance of high-temperature alloys.
By performance, they are classified as follows:
Nickel-based corrosion-resistant alloys: The main alloying elements are copper, chromium, and molybdenum. They offer excellent overall properties and are resistant to various acid corrosion and stress corrosion. Major nickel-based corrosion-resistant alloys include nickel-copper (Ni-Cu) alloys (Monel), nickel-chromium (Ni-Cr) alloys (nickel-based heat-resistant alloys, including the Incoloy and Inconel series), nickel-molybdenum (Ni-Mo) alloys (Hastelloy B series), and nickel-chromium-molybdenum (Ni-Cr-Mo) alloys (primarily the Hastelloy C series). Pure nickel is also a typical representative of nickel-based corrosion-resistant alloys.
Nickel-based wear-resistant alloys: The main alloying elements are chromium, molybdenum, and tungsten, with small amounts of niobium, tantalum, and indium. In addition to wear resistance, they also offer excellent oxidation resistance, corrosion resistance, and weldability.
Nickel-based precision alloys: These include nickel-based soft magnetic alloys, nickel-based precision resistance alloys, and nickel-based electric heating alloys. The most commonly used soft magnetic alloy is Permalloy, which contains approximately 80% nickel. It has high maximum and initial permeabilities and low coercivity, making it an important core material in the electronics industry. Nickel-based precision resistance alloys, primarily composed of chromium, aluminum, and copper, offer high resistivity, a low temperature coefficient of resistivity, and excellent corrosion resistance, making them ideal for resistors. Nickel-based electric heating alloys are nickel alloys containing 20% chromium. They exhibit excellent oxidation and corrosion resistance and can operate for extended periods at temperatures between 1000°C and 1100°C.
Nickel-based shape memory alloys: Nickel alloys containing 50% titanium (at%) have a recovery temperature of 70°C and exhibit excellent shape memory properties. By slightly varying the nickel-titanium ratio, the recovery temperature can be adjusted within a range of 30°C to 100°C.
