Accident tolerant fuel(ATF) for the light water reactor has gained wide attentions after the Fukushima accident. To enhance the accident-tolerance of the nuclear system, one strategy is to modify the Zr-based alloy cl...Accident tolerant fuel(ATF) for the light water reactor has gained wide attentions after the Fukushima accident. To enhance the accident-tolerance of the nuclear system, one strategy is to modify the Zr-based alloy cladding surface with advanced ceramic coating. In this work, monolithic and dense Cr_2AlC coating has been synthesized by magnetron sputtering. The as-grown Cr_2AlC coating exhibits good chemical compatibility with Zr-based alloy substrate as well as mechanical integrity under both pull-off and scratch tests. The coating system also presents moderate thermochemical compatibility at 800℃ but degrades above 1000℃ under simulated loss-of-coolant accident(LOCA) conditions.展开更多
Cr_(2)AlC,a representative MAX phase,gains increasing attention for the excellent oxidation tolerance and corrosion resistance used in harsh high temperature and strong radiation environments.However,the lack of the p...Cr_(2)AlC,a representative MAX phase,gains increasing attention for the excellent oxidation tolerance and corrosion resistance used in harsh high temperature and strong radiation environments.However,the lack of the phase formation mechanism has become the key bottleneck to the practical applications for Cr_(2)AlC synthesis with high purity at low temperatures.In this work,we fabricated the amorphous Cr-Al-C coating by a hybrid magnetron sputtering/cathodic arc deposition technique,in which the in-situ heating transmission electron microscopy(TEM)was conducted in a temperature range of 25-650℃ to address the real-time phase transformation for Cr_(2)AlC coating.The results demonstrated that increas-ing the temperature from 25 to 370℃ led to the structural transformation from amorphous Cr-Al-C to the crystalline Cr_(2)Al interphases.However,the high-purity Cr_(2)AlC MAX phase was distinctly formed at 500℃,accompanied by the diminished amorphous feature.With the further increase of temperature to 650℃,the decomposition of Cr_(2)AlC to Cr_(7)C_(3)impurities was observed.Similar phase evolution was also evidenced by the Ab-initio molecular dynamics calculations,where the bond energy of Cr-Cr,Cr-Al,and Cr-C played the key role in the formed crystalline stability during the heating process.The observa-tions not only provide fundamental insight into the phase formation mechanism for high-purity Cr_(2)AlC coatings but also offer a promising strategy to manipulate the advanced MAX phase materials with high tolerance to high-temperature oxidation and heavy ion radiations.展开更多
Ternary layered MAX phase materials have excellent corrosion and oxidation resistance.However,their applications are limited by low hardness yet poor crack resistance,due to weak M–A metallic bonding and poor crack r...Ternary layered MAX phase materials have excellent corrosion and oxidation resistance.However,their applications are limited by low hardness yet poor crack resistance,due to weak M–A metallic bonding and poor crack resistance stemming from their extremely high plastic anisotropy with ultrahigh c/a ratio(>4).In this work,we demonstrate significant improvements in both hardness and crack resistance when the grain size of MAX phases is reduced to nanoscale.Nanocrystalline Cr_(2)AlC MAX coatings with grain size ranging from 0 to 100 nm were successfully fabricated using a controllable PVD-based twostep bottom-up strategy.Remarkable improvements are achieved in both hardness and toughness,with hardness(15.5 GPa)/record-high strength(8.53 GPa)and toughness/plasticity peaking at a grain size of 15.8 nm near the critical value.Such unusual hardening-toughening effect at nanoscale stems from homogeneous deformation mode transitions with synchronous Hall–Petch hardening.Transmission electron microscopic observations proved that both pyramidal and prismatic slip,which are unlikely to operate at microcrystalline regime at room temperature,are completely active at nanocrystalline regime,unlocking the key c-axial plasticity.As grain size further decreases approaching the critical value,a dynamic grain refinement-induced secondary sub-shear banding mechanism is triggered,which further extends the homogeneous deformation stage.These findings provide a simple route to fabricate advanced MAX phase corrosion-protection coatings with superior mechanical properties for extreme condition applications.展开更多
In this study,novel high-quality Cr_(2)AlC coating was fabricated on Ti65 alloy substrate as its protective oxidation resistance coating.Isothermal oxidation tests were performed at 650 and 750℃ for up to 400 h in ai...In this study,novel high-quality Cr_(2)AlC coating was fabricated on Ti65 alloy substrate as its protective oxidation resistance coating.Isothermal oxidation tests were performed at 650 and 750℃ for up to 400 h in air.The results indicated that Ti65 alloy underwent severe oxidation at 750℃,accompanied by the presence of the cracking and exfoliating of the oxide scale during oxidation.Compared to the bare Ti65 substrate,the coated samples revealed more excellent oxidation resistance,meeting the parabolic law with low oxidation rate constants of 8.70×10^(-13)kg^(2)·m^(-4)·s^(-1) at 650℃ and 2.80×10^(-13)kg^(2)·m^(-4)·s^(-1) at 750℃.At the surface,Al preferentially oxidized to form the protective Al_(2)O_(3) layer and synchronously Cr_(7)C_(3) sublayer,retarding the inward diffusion of oxygen and presenting excellent oxidation resistance.Besides,at the coating/substrate interface,Al diffused from Cr_(2)AlC coating into the substrate to form an Al-rich layer in substrate adjacent to the coating/substrate interface.Due to the Al consumption,Cr-carbide and nitride,as well as TiN,were thereby formed at the interface reaction layer,which could act as a barrier for the interdiffusion process.展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos. 51402311 and 51772302the National Key R&D Program of China under Grant No. 2017YFB0703201
文摘Accident tolerant fuel(ATF) for the light water reactor has gained wide attentions after the Fukushima accident. To enhance the accident-tolerance of the nuclear system, one strategy is to modify the Zr-based alloy cladding surface with advanced ceramic coating. In this work, monolithic and dense Cr_2AlC coating has been synthesized by magnetron sputtering. The as-grown Cr_2AlC coating exhibits good chemical compatibility with Zr-based alloy substrate as well as mechanical integrity under both pull-off and scratch tests. The coating system also presents moderate thermochemical compatibility at 800℃ but degrades above 1000℃ under simulated loss-of-coolant accident(LOCA) conditions.
基金supported by the financial support of the National Science Fund for Distinguished Young Scholars of China(No.52025014)the National Natural Science Foundation of China(Nos.52101109 and 52171090)+1 种基金the Zhejiang Provincial Natural Science Foundation of China(No.LD24E010003 and LZJWY23E090001)the Natural Science Foundation of Ningbo(Nos.2023J410).
文摘Cr_(2)AlC,a representative MAX phase,gains increasing attention for the excellent oxidation tolerance and corrosion resistance used in harsh high temperature and strong radiation environments.However,the lack of the phase formation mechanism has become the key bottleneck to the practical applications for Cr_(2)AlC synthesis with high purity at low temperatures.In this work,we fabricated the amorphous Cr-Al-C coating by a hybrid magnetron sputtering/cathodic arc deposition technique,in which the in-situ heating transmission electron microscopy(TEM)was conducted in a temperature range of 25-650℃ to address the real-time phase transformation for Cr_(2)AlC coating.The results demonstrated that increas-ing the temperature from 25 to 370℃ led to the structural transformation from amorphous Cr-Al-C to the crystalline Cr_(2)Al interphases.However,the high-purity Cr_(2)AlC MAX phase was distinctly formed at 500℃,accompanied by the diminished amorphous feature.With the further increase of temperature to 650℃,the decomposition of Cr_(2)AlC to Cr_(7)C_(3)impurities was observed.Similar phase evolution was also evidenced by the Ab-initio molecular dynamics calculations,where the bond energy of Cr-Cr,Cr-Al,and Cr-C played the key role in the formed crystalline stability during the heating process.The observa-tions not only provide fundamental insight into the phase formation mechanism for high-purity Cr_(2)AlC coatings but also offer a promising strategy to manipulate the advanced MAX phase materials with high tolerance to high-temperature oxidation and heavy ion radiations.
基金supported by the National Sci-ence Fund for Distinguished Young Scholars of China(No.52025014)the National Natural Science Foundation of China(Nos.U22A20111 and 52171090)the Natural Science Foundation of Zhe-jiang Province(No.LD24E010003).
文摘Ternary layered MAX phase materials have excellent corrosion and oxidation resistance.However,their applications are limited by low hardness yet poor crack resistance,due to weak M–A metallic bonding and poor crack resistance stemming from their extremely high plastic anisotropy with ultrahigh c/a ratio(>4).In this work,we demonstrate significant improvements in both hardness and crack resistance when the grain size of MAX phases is reduced to nanoscale.Nanocrystalline Cr_(2)AlC MAX coatings with grain size ranging from 0 to 100 nm were successfully fabricated using a controllable PVD-based twostep bottom-up strategy.Remarkable improvements are achieved in both hardness and toughness,with hardness(15.5 GPa)/record-high strength(8.53 GPa)and toughness/plasticity peaking at a grain size of 15.8 nm near the critical value.Such unusual hardening-toughening effect at nanoscale stems from homogeneous deformation mode transitions with synchronous Hall–Petch hardening.Transmission electron microscopic observations proved that both pyramidal and prismatic slip,which are unlikely to operate at microcrystalline regime at room temperature,are completely active at nanocrystalline regime,unlocking the key c-axial plasticity.As grain size further decreases approaching the critical value,a dynamic grain refinement-induced secondary sub-shear banding mechanism is triggered,which further extends the homogeneous deformation stage.These findings provide a simple route to fabricate advanced MAX phase corrosion-protection coatings with superior mechanical properties for extreme condition applications.
文摘In this study,novel high-quality Cr_(2)AlC coating was fabricated on Ti65 alloy substrate as its protective oxidation resistance coating.Isothermal oxidation tests were performed at 650 and 750℃ for up to 400 h in air.The results indicated that Ti65 alloy underwent severe oxidation at 750℃,accompanied by the presence of the cracking and exfoliating of the oxide scale during oxidation.Compared to the bare Ti65 substrate,the coated samples revealed more excellent oxidation resistance,meeting the parabolic law with low oxidation rate constants of 8.70×10^(-13)kg^(2)·m^(-4)·s^(-1) at 650℃ and 2.80×10^(-13)kg^(2)·m^(-4)·s^(-1) at 750℃.At the surface,Al preferentially oxidized to form the protective Al_(2)O_(3) layer and synchronously Cr_(7)C_(3) sublayer,retarding the inward diffusion of oxygen and presenting excellent oxidation resistance.Besides,at the coating/substrate interface,Al diffused from Cr_(2)AlC coating into the substrate to form an Al-rich layer in substrate adjacent to the coating/substrate interface.Due to the Al consumption,Cr-carbide and nitride,as well as TiN,were thereby formed at the interface reaction layer,which could act as a barrier for the interdiffusion process.
