A low-alloyed Mg-1.2Zn-0.1Ca(wt.%)alloy was fabricated via low-temperature extrusion and annealing at 250℃for different times(10,30,and 90 min)to attain heterostructures with different fine-grained fractions,focusing...A low-alloyed Mg-1.2Zn-0.1Ca(wt.%)alloy was fabricated via low-temperature extrusion and annealing at 250℃for different times(10,30,and 90 min)to attain heterostructures with different fine-grained fractions,focusing on the effect of heterostructure on the mechanical properties.Partial dynamic recrystallization(RX)occurred during extrusion at 150℃,and a lamellar structure consisting of fine RX grains and coarse unRX grains was obtained.The subsequent annealing promoted static RX in the as-extruded alloy,leading to an increased fine-grained fraction from 67%to 95%.Meanwhile,the co-segregation of Zn and Ca atoms impeded the migration of grain boundaries,thus achieving a fine grain size of 0.8–1.6μm.The sample annealed for 10 min with a fine-grained fraction of 73%and an average RX grain size of 0.9μm exhibited a superior combination of high yield strength(305 MPa)and good ductility(20%).In comparison,an excellent elongation of 30%was achieved in the alloy with a nearly fully-RXed microstructure and an average grain size of 1.6μm after 90 min annealing,despite a lower yield strength of 228 MPa.In unRX grains,the hard orientation with(01–10)parallel to the extrusion direction and high-density dislocations made it more difficult to deform compared with the RX grains,thus producing hetero-deformation induced(HDI)strengthening.Besides fine grains and high-density dislocations,HDI strengthening is the key to achieving the superior mechanical properties of the low-alloyed Mg alloy.展开更多
As one of the most important forming technologies for industrial bulk metallic glass (BMG) parts withcomplex shapes, high-pressure die casting (HPDC) can fill a die cavity with a glass-forming metallic liquidin millis...As one of the most important forming technologies for industrial bulk metallic glass (BMG) parts withcomplex shapes, high-pressure die casting (HPDC) can fill a die cavity with a glass-forming metallic liquidin milliseconds. However, to our knowledge, the correlation between flow and crystallization behavior inthe HPDC process has never been established. In this study, we report on the solidification behavior ofZr_(55)Cu_(30)Ni_(5)Al_(10) glass forming liquid under various flow rates. Surprisingly, the resulting alloys display adecreasing content of amorphous phase with increase of flow rate, i.e. increase of cooling rate, suggestingthat crystallization kinetics of glass-forming metallic liquids in the HPDC process is strongly dependenton the flow field. Analysis reveals that the accelerated crystallization behavior is mainly ascribed to therapid increase in viscosity with a decreasing temperature as well as to the huge shear effect in the glassforming liquid at the end stage of the filling process when the temperature is close to the glass-transitionpoint;this results in a transition from diffusion- to advection-dominated transport. The current investigation suggests that flow-related crystallization must be considered to assess the intrinsic glass-formingability of BMGs produced via HPDC. The obtained results will not only improve the understanding ofcrystallization dynamics but also promote the high-quality production and large-scale application of BMGparts.展开更多
The filtered cathodic vacuum-arc (FCVA) technique is a supplementary and alterna tive technique with respect to convendtional physical and chemical vapour deposi tion which can remove macro-particles effectively and m...The filtered cathodic vacuum-arc (FCVA) technique is a supplementary and alterna tive technique with respect to convendtional physical and chemical vapour deposi tion which can remove macro-particles effectively and make the deposition proces s at ambient temperature. In this work, high quality TiN thin films were deposi ted on silicon substrates at low temperature using the improved filtered cathodi c arc plasma (FCAP) technique. AFM, XRD, TEM were employed to characterize the T iN thin films. The effects of the negative substrate bias on the grain size, pre ferred crystalline orientation, surface roughness of TiN thin films were discuss ed.展开更多
基金the Key-Area Research and Development Program of Guangdong Province(No.2020B010186002)the Natural Science Foundation of Guangdong for Research Team(No.2015A030312003)。
文摘A low-alloyed Mg-1.2Zn-0.1Ca(wt.%)alloy was fabricated via low-temperature extrusion and annealing at 250℃for different times(10,30,and 90 min)to attain heterostructures with different fine-grained fractions,focusing on the effect of heterostructure on the mechanical properties.Partial dynamic recrystallization(RX)occurred during extrusion at 150℃,and a lamellar structure consisting of fine RX grains and coarse unRX grains was obtained.The subsequent annealing promoted static RX in the as-extruded alloy,leading to an increased fine-grained fraction from 67%to 95%.Meanwhile,the co-segregation of Zn and Ca atoms impeded the migration of grain boundaries,thus achieving a fine grain size of 0.8–1.6μm.The sample annealed for 10 min with a fine-grained fraction of 73%and an average RX grain size of 0.9μm exhibited a superior combination of high yield strength(305 MPa)and good ductility(20%).In comparison,an excellent elongation of 30%was achieved in the alloy with a nearly fully-RXed microstructure and an average grain size of 1.6μm after 90 min annealing,despite a lower yield strength of 228 MPa.In unRX grains,the hard orientation with(01–10)parallel to the extrusion direction and high-density dislocations made it more difficult to deform compared with the RX grains,thus producing hetero-deformation induced(HDI)strengthening.Besides fine grains and high-density dislocations,HDI strengthening is the key to achieving the superior mechanical properties of the low-alloyed Mg alloy.
基金L.H.Liu would like to thank the financial support from the National Natural Science Foundation of China(No.52001123)the China Postdoctoral Science Foundation(Nos.2019TQ0099 and 2019M662908)+5 种基金Guangdong Basic and the Applied Basic Research Foundation(No.2019A1515110215)the Foundation for Distinguished Young Talents in Higher Education of Guangdong(No.2019KQNCX003)the Fundamental Research Funds for the Central Universities(No.2020ZYGXZR030)the Open Fund of National Engineering Research Center of Near-net-shape Forming for Metallic Materials(No.2019003)C.Yang would like to thank the financial support from the Key Basic and Applied Research Program of Guangdong Province(No.2019B030302010)the National Natural Science Foundation of China(No.51971149).
文摘As one of the most important forming technologies for industrial bulk metallic glass (BMG) parts withcomplex shapes, high-pressure die casting (HPDC) can fill a die cavity with a glass-forming metallic liquidin milliseconds. However, to our knowledge, the correlation between flow and crystallization behavior inthe HPDC process has never been established. In this study, we report on the solidification behavior ofZr_(55)Cu_(30)Ni_(5)Al_(10) glass forming liquid under various flow rates. Surprisingly, the resulting alloys display adecreasing content of amorphous phase with increase of flow rate, i.e. increase of cooling rate, suggestingthat crystallization kinetics of glass-forming metallic liquids in the HPDC process is strongly dependenton the flow field. Analysis reveals that the accelerated crystallization behavior is mainly ascribed to therapid increase in viscosity with a decreasing temperature as well as to the huge shear effect in the glassforming liquid at the end stage of the filling process when the temperature is close to the glass-transitionpoint;this results in a transition from diffusion- to advection-dominated transport. The current investigation suggests that flow-related crystallization must be considered to assess the intrinsic glass-formingability of BMGs produced via HPDC. The obtained results will not only improve the understanding ofcrystallization dynamics but also promote the high-quality production and large-scale application of BMGparts.
基金This work was supported by the National Natural Science Foundation of China(No.10074022)the Excellent Young Teachers Prograom of MOE,China.
文摘The filtered cathodic vacuum-arc (FCVA) technique is a supplementary and alterna tive technique with respect to convendtional physical and chemical vapour deposi tion which can remove macro-particles effectively and make the deposition proces s at ambient temperature. In this work, high quality TiN thin films were deposi ted on silicon substrates at low temperature using the improved filtered cathodi c arc plasma (FCAP) technique. AFM, XRD, TEM were employed to characterize the T iN thin films. The effects of the negative substrate bias on the grain size, pre ferred crystalline orientation, surface roughness of TiN thin films were discuss ed.
