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Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes

 

USTB’s new state key laboratory of metal materials, materials of genetic engineering in Beijing high-tech innovation centre Lv Zhaoping professor team to break the people's perception gap of traditional solid solution strengthening, found that interstitial add can not only improve the strength of the alloy, also can greatly improve the plasticity of alloy, and puts forward a design of high strength and high plasticity design of new alloy metal materials. Top international academic journals Nature published online on November 14, 2018. Lv Zhaoping professor team following the ultra-high strength steel last year after a breakthrough research progress, the Enhanced strength and ductility in a high - entropy alloy via ordered oxygen complexes ".

As the backbone material in the important fields of national economy, such as aerospace, transportation and national defense equipment, metal materials inevitably introduce impurities in the manufacturing process, especially the ubiquitous oxygen. Once too much oxygen is doped, the brittle oxide ceramic phase will greatly deteriorate the mechanical properties of the metal material, leading to catastrophic brittle fracture. Therefore, the generation of brittle oxide phase caused by oxygen doping is always avoided in metal smelting process. The other state of existence of oxygen in the alloy is in the form of interstitial atoms. In conventional metals and alloys, the addition of interstitial atoms can significantly improve the strength of alloys, but at the same time, the plasticity and toughness are greatly reduced. This is mainly due to the fact that interstitial atoms tend to deflect to the grain boundary, crack tip, dislocation and other internal stress sources, leading to significant distortion and stress concentration of the matrix in this region, resulting in the failure of local atomic bonding and highly concentrated local plastic deformation, and eventually leading to catastrophic brittle fracture.

Lv Zhaoping professor team to such as atomic ratio TiZrHfNb alloy of high entropy alloy model, add the right amount of oxygen, found another kind of interstitial atom in the alloy with new existence state, people have not yet been discovered and named it orderly interstitial complex (ordered interstitial complexes), it is a kind of between conventional random interstitial and ceramic phase of new interstitial existence state. This ordered interstitial atom complex structure can significantly improve the strength and plasticity of the alloy, breaking the curse that the strength and plasticity of metal materials cannot be achieved at the same time, and providing a new idea for researchers to re-understand the gap strengthening and ordered strengthening and design high-strength and high-toughness metal materials.

The strain hardening mechanism of the ordered interstitial atom complex proposed by professor Lv zhaoping's team does not involve the phase transition or twin deformation of the alloy, which is a new method for strengthening and toughening the alloy. This method provides a new way to improve the strength and plasticity of the alloy system which is difficult to be strengthened and toughened by adjusting the dislocation energy or the phase transition. Although the alloy system studied in this paper is a high-entropy alloy, this effect of abnormal gap toughening is not limited to high-entropy alloys, but also applicable to traditional alloys. For example, professor lu's team also found the same phenomenon in titanium alloys. At the same time, although only interstitial oxygen atoms are reported to be able to simultaneously improve the strength and plasticity of metal materials, other interstitial atoms also have similar toughening and toughening effects when suitable alloy systems or preparation processes are selected. This indicates that the ordered interstitial atom complex, which improves both the strength and plasticity of the alloy, is universal and can be widely used in the design of various high-strength and high-plasticity metal materials.

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