High-temperature alloys are a type of alloy materials with excellent properties at high temperatures and are widely used in aviation, aerospace, energy and other fields. Adding an appropriate amount of Hf to cast and deformed high-temperature alloys can strengthen and toughen the alloy by producing curved grain boundaries and removing the harmful effects of sulfur on grain boundaries. This is because Hf can dissolve into the g¢ phase and strengthen it. At the same time, for cast high-temperature alloys, it can increase the number of g/g¢ eutectics and change the morphology of the g¢ phase from cubic to dendritic. Increasing the number of bulk g¢ phases at grain boundaries promotes the development of Hf-rich dendritic g¢ phases near the grain boundaries and the existence of granular M23C6, changing the grain boundaries from straight to curved. This curved grain boundary can delay the initiation, connection and expansion of cracks, and improve the high-temperature strength and plasticity of the alloy.
For straight grain boundaries, the intragranular deformation is always less than the total deformation, indicating that the grain boundary deformation accounts for a certain proportion. For curved grain boundaries, the intragranular deformation is basically equal to the total creep deformation, indicating that the grain boundaries are strengthened and the grain boundary deformation is very small. Therefore, the creep rupture life and plasticity of the alloy can be improved by bending the grain boundaries. For example, when 1.55% Hf is added to B-1900 alloy, under the conditions of 760°C and 660MPa, its durability life is increased from 19 hours without Hf to 86 hours, and the endurance elongation is increased from 1.6% to 4.8%.
In addition, the Hf added to the alloy also has the effect of purifying grain boundaries. Hf has a high affinity for S and can generate high melting point sulfide and be removed, thereby preventing grain boundary embrittlement caused by S.
In addition to entering the g¢ phase to enhance its strengthening effect and causing bent grain boundaries to strengthen grain boundaries, Hf added to high-temperature alloys can also reduce the sensitivity of hot cracking in welds and heat-affected zones. This is because Hf expands the solid-liquidus temperature range and maintains the connected state of microliquid pools between dendrites over a wide temperature range in the late solidification stage. The remaining liquid in the later stage of solidification contains more than 15wt% hafnium. This Hf-rich multi-element eutectic liquid has a good self-welding effect and can “heal” the cracks.
Therefore, the role of Hf in high-temperature alloys is multi-faceted. It can improve the high-temperature strength, plasticity and creep rupture life of the alloy, purify grain boundaries, and reduce the sensitivity of hot cracking in welds and heat-affected zones. In the production and application of high-temperature alloys, the reasonable addition of Hf elements can improve their properties and play an important role in improving the technical level of aviation, aerospace, energy and other fields.
Tianjin Anton Metal Manufacture Co., Ltd. is a company specializing in the production of various nickel-based alloys, Hastelloy alloys and high-temperature alloy materials. The company was established in 1989 with a registered capital of 10.0 million, specializing in the production and sales of alloy materials. Anton Metal’s products are widely used in aerospace, chemical industry, electric power, automobile, nuclear energy and other fields, and can also provide customized alloy material solutions according to customer needs. If you need to know the price consultation of alloy materials or provide customized alloy material solutions, please feel free to contact the sales staff.
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Post time: Oct-21-2023
