L1_(2)-strengthened high-entropy alloys(HEAs)are promising materials for advanced structural applications in harsh environments due to their outstanding mechanical properties.However,the Cr-depleted L1_(2)par-ticles u...L1_(2)-strengthened high-entropy alloys(HEAs)are promising materials for advanced structural applications in harsh environments due to their outstanding mechanical properties.However,the Cr-depleted L1_(2)par-ticles usually increase the alloy’s galvanic corrosion susceptibility,thus resulting in a decrease in pit-ting resistance.In this work,the corrosion behavior and associated passive film characteristics of a novel Co_(40)Cr_(20)Ni_(30)Al_(5)Ti_(5)HEA(at.%)additively manufactured by selective laser melting(SLM)were systemat-ically characterized and investigated.It was found that the precipitation of coherent nano-lamellar L1_(2)phase significantly refined the grain structure of the aged alloy,which leads to an anomalously improved corrosion resistance compared to the as-printed single-phase counterpart.Such excellent corrosion resis-tance of the aged alloy originated from the thin amorphous passive film with Cr_(2)O_(3),Al_(2)O_(3),and TiO_(2)as the main constituents that were firmly adhered to the alloy matrix.Moreover,the corrosion morphologies revealed that the dense and large-sized pits on the as-printed alloy were in sharp contrast to the sparse and irregularly-shaped pits on the aged alloy,which can be attributed to the potential difference and/or the refined grain structure.These findings will effectively advance the development of corrosion-resistant additively manufactured alloys and provide new insights into the innovative design of high-performance damage-tolerant L1_(2)-strengthened HEAs.展开更多
In order to investigate the response of cellular spacing to the variation of growth velocity under near-rapid directional solidification condition, Al-0.53wt%Zn alloy is directionally solidified with Bridgman apparatu...In order to investigate the response of cellular spacing to the variation of growth velocity under near-rapid directional solidification condition, Al-0.53wt%Zn alloy is directionally solidified with Bridgman apparatus. The results show that at the given temperature gradient the obtained microstrvctures are all cells and there exists a wide distribution range of cellular spacing. The maximum, λmax, minimum, λmin, and average cellular spacing, λ, as functions of growth rate, V, can be given by λmax=948.51V-0.4961, λmin= 661.16V-0.5015 and λ=412.41V-0.5049, respectively. The experimental results are compared with that predicted by KGT model, and a good agreement is found. Moreover,it is found that the average cellular spacing is also remarkably history-dependent.展开更多
Electromagnetic separation of non-metallic inclusions from Al-Si melt is studied by theoretical analysis and experiments on self-designed electromagnetic separation apparatus. Metallographs and LECO Image Analysis Sy...Electromagnetic separation of non-metallic inclusions from Al-Si melt is studied by theoretical analysis and experiments on self-designed electromagnetic separation apparatus. Metallographs and LECO Image Analysis System were used to analyze the content of alumina in aluminum alloy before and after electromagnetic separation. It is seen that removal effciency increases with the increase of electromagnetic force (EMF) and diameter of inclusion particles while decreases with the increase of melt velocity and height of separator. All alumina particles with diamete of 14μm have been removed successfully from the melt.展开更多
The solidification behavior of bulk undercooled Ni50Cu50 alloy was systematically investigated. Double recalescences were discovered for the first time in a single phase Ni-Cd alloy, in which there is no solid phase t...The solidification behavior of bulk undercooled Ni50Cu50 alloy was systematically investigated. Double recalescences were discovered for the first time in a single phase Ni-Cd alloy, in which there is no solid phase transition at elevated temperature. When the alloy melt was undercoolcd below the solidus temperature, the effect of nonequilibrium solidification could make the solid with the norminal composition C0 of the alloy nucleate and grow till tempemture approached To (the temperuture at which the free enengies of solid and liquid with C0 are equal). Following it, the nucleation and growth of the solid with more high melting point component were required, so the secondary recalescence took place. The concentration distribution in crystals was also analysed.展开更多
基金financial support from the Na-tional Natural Science Foundation of China(Grant Nos.52222112 and 52101135)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2024A1515011220)+2 种基金the Research Grants Council of the Hong Kong Special Administrative Region,China(Grant No.CityU 11208823)the International Cooperation and Innovation Fund(Grant No.KZ8F231907)The APT research was conducted at the Inter-University 3D APT Unit of City University of Hong Kong(CityU),which is supported by the CityU grant 9360161.
文摘L1_(2)-strengthened high-entropy alloys(HEAs)are promising materials for advanced structural applications in harsh environments due to their outstanding mechanical properties.However,the Cr-depleted L1_(2)par-ticles usually increase the alloy’s galvanic corrosion susceptibility,thus resulting in a decrease in pit-ting resistance.In this work,the corrosion behavior and associated passive film characteristics of a novel Co_(40)Cr_(20)Ni_(30)Al_(5)Ti_(5)HEA(at.%)additively manufactured by selective laser melting(SLM)were systemat-ically characterized and investigated.It was found that the precipitation of coherent nano-lamellar L1_(2)phase significantly refined the grain structure of the aged alloy,which leads to an anomalously improved corrosion resistance compared to the as-printed single-phase counterpart.Such excellent corrosion resis-tance of the aged alloy originated from the thin amorphous passive film with Cr_(2)O_(3),Al_(2)O_(3),and TiO_(2)as the main constituents that were firmly adhered to the alloy matrix.Moreover,the corrosion morphologies revealed that the dense and large-sized pits on the as-printed alloy were in sharp contrast to the sparse and irregularly-shaped pits on the aged alloy,which can be attributed to the potential difference and/or the refined grain structure.These findings will effectively advance the development of corrosion-resistant additively manufactured alloys and provide new insights into the innovative design of high-performance damage-tolerant L1_(2)-strengthened HEAs.
文摘In order to investigate the response of cellular spacing to the variation of growth velocity under near-rapid directional solidification condition, Al-0.53wt%Zn alloy is directionally solidified with Bridgman apparatus. The results show that at the given temperature gradient the obtained microstrvctures are all cells and there exists a wide distribution range of cellular spacing. The maximum, λmax, minimum, λmin, and average cellular spacing, λ, as functions of growth rate, V, can be given by λmax=948.51V-0.4961, λmin= 661.16V-0.5015 and λ=412.41V-0.5049, respectively. The experimental results are compared with that predicted by KGT model, and a good agreement is found. Moreover,it is found that the average cellular spacing is also remarkably history-dependent.
基金This work supported by the National Natural Science Foundation of China(Grant,No.59871029)the National Key Fundamental Research Project(973)(No.G1999064900)
文摘Electromagnetic separation of non-metallic inclusions from Al-Si melt is studied by theoretical analysis and experiments on self-designed electromagnetic separation apparatus. Metallographs and LECO Image Analysis System were used to analyze the content of alumina in aluminum alloy before and after electromagnetic separation. It is seen that removal effciency increases with the increase of electromagnetic force (EMF) and diameter of inclusion particles while decreases with the increase of melt velocity and height of separator. All alumina particles with diamete of 14μm have been removed successfully from the melt.
文摘The solidification behavior of bulk undercooled Ni50Cu50 alloy was systematically investigated. Double recalescences were discovered for the first time in a single phase Ni-Cd alloy, in which there is no solid phase transition at elevated temperature. When the alloy melt was undercoolcd below the solidus temperature, the effect of nonequilibrium solidification could make the solid with the norminal composition C0 of the alloy nucleate and grow till tempemture approached To (the temperuture at which the free enengies of solid and liquid with C0 are equal). Following it, the nucleation and growth of the solid with more high melting point component were required, so the secondary recalescence took place. The concentration distribution in crystals was also analysed.
