Critical Assessment 4: Challenges in developing high temperature materials

Abstract

Materials are a key enabling feature for high efficiency engines for power generation or transportation. While significant research continues, progress in this century has certainly slowed compared to the previous century where modern materials science spawned a rapid advance in high temperature materials. One area that hampers new high temperature materials is a lack of inherent (i.e. uncoated) oxidation or environmental resistance, especially for the highest temperature applications such as Ni-base superalloys for turbomachinery. Thus, there appears to be more opportunity to develop materials for 600-1000uC applications than for higher temperatures. New materials requirements ranging from mechanical and environmental resistance to manufacturing and joining need to be clearly defined and experimental work focused on validating these properties for successful alloy development to proceed. For most applications the materials requirements have become so broad and complex that progress by single researchers is difficult. A teaming approach, especially among research institutions and industry, is needed to both define the critical needs and assemble experts in a range of disciplines to address these issues during the materials development process.

The microstructure and hardness of Ni-Co-Al-Ti-Cr quinary alloys

“…Currently available alloys are already working close to their temperature and strength limits, thereby necessitating the development of new materials capable of withstanding the inimical conditions that will be encountered in the hottest sections of future, more efficient, engines. However, despite significant research to develop alternative materials [4][5][6][7][8], the exceptional balance of properties offered by superalloys with fine scale dispersions of L1 2 γ′ precipitates in an A1 γ matrix, continues to make them the preferred solution for high temperature structural applications. Therefore, identifying alloying strategies that can extend the capabilities of A1 -L1 2 superalloys continues to be a key research activity in the aerospace industry.…”

Oxidation Protection of High-Temperature Coatings on the Surface of Mo-Based Alloys—A Review

“…With the rapid development of aerospace, national defense and the military industry, electronics, and so on, increasing attention has been paid to the research and application of refractory metals [1][2][3][4]. Molybdenum and molybdenum-based alloys have a high melting point (2620 • C), good high-temperature mechanical properties and high conductivity and thermal conductivity, and are widely used in high-temperature structures [5][6][7][8][9][10].…”

On precipitates in Fe–Ni base alloys used for USC boilers

“…This is confirmed by Chai's work, 67 which indicated that a sharp decrease in rupture strength existed when testing Sanicro 25 at 800°C. On the other hand, corrosion at elevated temperature affects rupture life greatly; 70–72 this requires the material to possess a high level of protective oxide scale forming elements such as aluminium and chromium. 73 Referring to the above discussion, the Fe–Ni base alloys strengthened by both Z phase and Cu rich phase cannot fulfil the strength requirement at higher temperatures.…”