Lightweight, high-strength, and heat-resistant aluminum alloys are increasingly crucial foundational materials in fields such as aerospace, transportation, and beyond. Oxide dispersion strengthened (ODS) alloys exhibit high thermal stability and high-temperature mechanical performance. Introducing finely dispersed oxide nanoparticles into aluminum alloys holds the promise of significantly enhancing their heat resistance. However, current methods for producing such alloys, mainly through internal oxidation or chemical reduction of the metal matrix, are not suitable for lightweight metals like aluminum, titanium, and magnesium that cannot undergo chemical reduction.
In response, Professor He Chunnian's team from the School of Materials Science and Engineering at Tianjin University has innovatively proposed a "interface replacement" dispersion strategy. They successfully achieved the uniform distribution of oxide particles of around 5 nanometers at the single-particle level in aluminum alloys. This breakthrough allows the prepared oxide dispersion strengthened aluminum alloy to maintain unprecedented tensile strength (approximately 200 megapascals) and high-temperature creep resistance at temperatures as high as 500 degrees Celsius. The process is simple, cost-effective, and easily scalable for production, thus holding significant industrial application value.
The research findings have recently been published in the journal "Nature Materials."
The pressing demand in aerospace, transportation, and other fields for accelerated weight reduction places higher requirements on the heat resistance of lightweight metal materials. Traditional aluminum alloys experience a sharp decline in mechanical performance due to phase coarsening at high temperatures, with service performance above 300 degrees Celsius reaching a bottleneck. Tensile strength is less than 200 megapascals at 300 degrees Celsius and less than 50 megapascals at 500 degrees Celsius. The rapid deterioration of mechanical properties of aluminum alloys in the critical temperature range of 300 to 500 degrees Celsius poses a key limitation for structural design under high-power conditions in aerospace and other industries, impacting operational safety.
Currently, there are two main approaches to enhance the heat resistance of aluminum alloys: improving the thermal stability of precipitates and introducing high-stability ceramic phase nanoparticles. Compared to the former, ceramic particles typically have higher melting points (>1000 degrees Celsius) and elastic moduli, thus offering greater thermal and deformation stability. Among these, oxide ceramic particles are favored by researchers for their excellent strength, thermal conductivity, high-temperature resistance, oxidation resistance, corrosion resistance, and low cost. Researchers have achieved outstanding high-temperature mechanical performance in various metal systems (such as iron, copper, nickel, molybdenum, etc.) by in-situ synthesizing oxide nanoparticles. However, the principle of achieving dispersed distribution is based on the dissolution-precipitation of oxide particles in the matrix or the reduction of metal precursors to the metal matrix after liquid-phase mixing. These methods are not applicable to lightweight metal materials like aluminum, magnesium, and titanium, which exhibit high reactivity with oxygen and cannot undergo chemical reduction. Thus, the challenge of achieving oxide nanoparticle dispersion strengthening in aluminum alloys to improve their high-temperature mechanical performance remains an international scientific and technological hurdle in aluminum and even lightweight alloy systems.
To address this challenge, Professor He Chunnian's team proposed and implemented a "interface replacement" dispersion strategy to prepare 5-nanometer oxide dispersion strengthened aluminum alloys. Initially, they utilized the self-assembly effect during the decomposition of metal salt precursors to produce ultrafine oxide particles coated with a few layers of graphite. By replacing the strong chemical bonds between nano-particles with the weaker van der Waals forces between graphite coating layers, the adhesion force between nano-particles decreased by 2 to 3 orders of magnitude. Building upon this, through a simple mechanical ball milling-powder metallurgy process, they achieved the uniform dispersion of high-volume fraction (8% volume fraction) single-particle level ultrafine oxide particles in the aluminum matrix. This resulted in the aluminum alloy exhibiting outstanding high-temperature mechanical performance and high-temperature creep resistance, with tensile strengths of 420 megapascals at 300 degrees Celsius and 200 megapascals at 500 degrees Celsius. Under creep conditions of 500 degrees Celsius and 80 megapascals, the steady-state creep rate is 10^-7 per second, significantly surpassing the best levels reported internationally for aluminum-based materials.
Related paper link: https://doi.org/10.1038/s41563-024-01884-2
