The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures...The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures were compared under mold electromagnetic stirring （MEMS） conditions （current of 300 A and frequency of 3 Hz）. Thereafter, the solidification structures of the large round billet were investigated under different superheats, casting speeds, and secondary cooling intensities. Finally, the effect of the MEMS current on the solidification structures was obtained under fixed superheat, casting speed, secondary cooling intensity, and MEMS frequency. The model accurately simulated the actual solidification structures of any steel, regardless of its size and the parameters used in the continuous casting process. The ratio of the central equiaxed grain zone was found to increase with decreasing superheat, increasing casting speed, decreasing secondary cooling intensity, and increasing MEMS current. The grain size obviously decreased with decreasing superheat and increasing MEMS current but was less sensitive to the casting speed and secondary cooling intensity.展开更多
Hot deformation behavior and microstructure evolution of TC11（Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） alloy with equiaxed structure were investigated in the two-phase field at temperatures in the range of 980-800 ℃ and at stra...Hot deformation behavior and microstructure evolution of TC11（Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） alloy with equiaxed structure were investigated in the two-phase field at temperatures in the range of 980-800 ℃ and at strain rates of 0.001 s-1,0.01 s-1,0.1 s-1.Effects of thermo-mechanical parameters on both of the stress—strain curves and microstructure evolution were analyzed.Grain boundary characteristics of deformation microstructures were tested by electron backscattered diffraction（EBSD）.The results reveal that β-phase dominates the deformation and presents discontinuous dynamic recrystallization at 980 ℃;meanwhile,α-phase coarsens at lower strain rates and dissolves at higher strain rates,and α-phase volume fraction and grain size decrease with increasing strain rate.Super-plastic deformation occurs at 950-900 ℃ and strain rate of 0.001 s-1.And the deformation is dominated by soft β-phase,phase interfaces and grain boundaries.Microstructural mechanism operated at 850 ℃ is continuous dynamic recrystallization of α-phase that dominates the deformation,and β-phase deforms to match the deformation of α-phase.展开更多
As the raw materials in the post process of rolling and heat treatment, ingots have great effects on the properties of the final products. Inclusions and solidification structures are the most important aspects of the...As the raw materials in the post process of rolling and heat treatment, ingots have great effects on the properties of the final products. Inclusions and solidification structures are the most important aspects of the quality of ingots. Niobium and titanium are usually used to react with carbon and nitrogen to improve the properties of ferritic stainless steels. In this research, combined with thermodynamic calculation, effects of niobium and titanium on the inclusions and solidification structures in three kinds of high pure ferritic stainless steels with different titanium additions were investigated by optical microscope（OM）, scanning electron microscope（SEM）, transmission electron microscope（TEM）, and energy disperse spectrometer（EDS）. Results show that Al2O3 and a few（Nb,Ti）N particles form when titanium addition is 0.01 %.Furthermore, inclusions are mainly Ti N and Al2O3–Ti Ox–Ti N duplex inclusions when titanium addition is more than0.10 %. Those two types of inclusions are in well distribution, and can afford nuclei to the solidification process.Therefore, the ratio of equiaxed zone increases with the increase of titanium addition. The ratio increases from42.1 % to 64.0 % with the titanium addition increasing from 0.01 % to 0.10 %, and it increases to 85.7 % when the titanium addition reaches 0.34 %.展开更多
To investigate the superplastic deformation behavior of cryorolled Ti-6Al-4V titanium alloy,tensile tests were carried out at760℃and 830℃with different strain rate.The evolution of grain and micro structure has been...To investigate the superplastic deformation behavior of cryorolled Ti-6Al-4V titanium alloy,tensile tests were carried out at760℃and 830℃with different strain rate.The evolution of grain and micro structure has been studied using transmission electron microscopy and electron backscatter diffraction.When the tensile temperature was 760℃(<0.5T_(m),T_(m)is absolute melting point of alloy.)and the strain rate was 5×10^(-4)s^(-1),the fracture elongation of the sample reached 385%,showing good low-temperature superplasticity.Compared with the tensile temperature of 760℃,the fracture elongation of the s ample at 830℃was lower due to grain coarsening and oxidation.The strain rate sensitivity value m of all samples was larger than0.3,which confirmed that the cryorolled Ti-6A1-4V titanium alloy with a non-equiaxed grains structure can achieve high superplasticity at a temperature lower than 0.5T_(m),and indicated that the main deformation mechanisms in the tensile test at760-830℃were grain rotation and grain boundary sliding.After the tensile test,the average grain size of all samples was less than 5μm,in which significant dynamic recrystallization and recovery occurred.展开更多
In the context of global carbon neutrality, the application of lightweight magnesium alloys is becoming increasingly attractive. In this study, selective laser melting(SLM) was employed to achieve nearly full dense an...In the context of global carbon neutrality, the application of lightweight magnesium alloys is becoming increasingly attractive. In this study, selective laser melting(SLM) was employed to achieve nearly full dense and crack-free AZ91D components with fine equiaxed grain structure. The formation mechanism of typical pore defects(gas pore, lack-of-fusion pore and keyhole pore) and melting modes(keyhole mode and conduction mode) were systematically studied by varying the laser power and scanning speed. The morphology and volume fraction of the pores under different processing conditions were characterized. A criterion based on the depth-to-width ratio of the melt pool was established to identify different melting modes. The strength and ductility(tensile strength up to 340 MPa and uniform elongation of 8.9%)of the as deposited AZ91D are far superior to those of the casting components and are comparable to those of its wrought counterparts.The superior balance of strength and ductility of SLMed AZ91D, as well as the negligible anisotropic properties are mainly ascribed to the extremely fine equiaxed grain structure(with average grain size of ~1.2 μm), as well as the discontinuous distribution of β-Al_(12)Mg_(17) phases. It thus provides an alternative way to fabricate high-strength magnesium alloys with complex geometry.展开更多
The TiB2 thin films were deposited on steel substrates using RF magnetron sputtering technique with the low normalized substrate temperature （0.1〈Ts/Tm〈0.2）. Microstructure of these films was obtained by field emi...The TiB2 thin films were deposited on steel substrates using RF magnetron sputtering technique with the low normalized substrate temperature （0.1〈Ts/Tm〈0.2）. Microstructure of these films was obtained by field emission scanning electron microscope （FESEM） and the grazing incidence X-ray diffraction （GIXRD） characterization, while the composition of films was obtained using Auger emission spectroscopy （AES） analysis. It was found that the TiB2 thin films were overstoichiometric with the B/Ti ratio at 2.33 and the diffusion of Ti and B atoms on the substrate surface was greatly improved at 350 ℃. Moreover, a new dense structure, named ＂equiaxed＂ grain structure was observed by FESEM at this substrate temperature, Combined with FESEM and AES analysis, it was suggested that the ＂equiaxed＂ grain structure was located in Zone 2 at the normalized substrate temperature as low as 0.18.展开更多
By the solidification experiment of a medium carbon steel with refrigerant added.the effect of refrigerant on solidification structure of steel was studied.The results clearly show that refrigerant can increase the ra...By the solidification experiment of a medium carbon steel with refrigerant added.the effect of refrigerant on solidification structure of steel was studied.The results clearly show that refrigerant can increase the ratio of equiaxed crystal,fine grains and decrease central porosity and segregation.展开更多
文摘The solidification structure of a continuous casting large round billet was analyzed by a cellular-automaton-finite-element coupling model using the ProCAST software. The actual and simulated solidification structures were compared under mold electromagnetic stirring （MEMS） conditions （current of 300 A and frequency of 3 Hz）. Thereafter, the solidification structures of the large round billet were investigated under different superheats, casting speeds, and secondary cooling intensities. Finally, the effect of the MEMS current on the solidification structures was obtained under fixed superheat, casting speed, secondary cooling intensity, and MEMS frequency. The model accurately simulated the actual solidification structures of any steel, regardless of its size and the parameters used in the continuous casting process. The ratio of the central equiaxed grain zone was found to increase with decreasing superheat, increasing casting speed, decreasing secondary cooling intensity, and increasing MEMS current. The grain size obviously decreased with decreasing superheat and increasing MEMS current but was less sensitive to the casting speed and secondary cooling intensity.
基金Project(2008011045) supported by the Natural Science Foundation of Shanxi Province,China
文摘Hot deformation behavior and microstructure evolution of TC11（Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） alloy with equiaxed structure were investigated in the two-phase field at temperatures in the range of 980-800 ℃ and at strain rates of 0.001 s-1,0.01 s-1,0.1 s-1.Effects of thermo-mechanical parameters on both of the stress—strain curves and microstructure evolution were analyzed.Grain boundary characteristics of deformation microstructures were tested by electron backscattered diffraction（EBSD）.The results reveal that β-phase dominates the deformation and presents discontinuous dynamic recrystallization at 980 ℃;meanwhile,α-phase coarsens at lower strain rates and dissolves at higher strain rates,and α-phase volume fraction and grain size decrease with increasing strain rate.Super-plastic deformation occurs at 950-900 ℃ and strain rate of 0.001 s-1.And the deformation is dominated by soft β-phase,phase interfaces and grain boundaries.Microstructural mechanism operated at 850 ℃ is continuous dynamic recrystallization of α-phase that dominates the deformation,and β-phase deforms to match the deformation of α-phase.
基金financially supported by the Fundamental Research Funds for the Central Universities (No. N100602011)the National Natural Science Foundation of China (No. 51104039)+4 种基金the National Key Basic Research Program of China (No. 2012CB626812)the Program for New Century Excellent Talents in University (No. NCET-11-0077)Liaoning Provincial Natural Science Foundation of China (No. 201102062)Liaoning Provincial Science and Technology Plan (No. 2012221013)the National Innovation Experiment Program for University Students
文摘As the raw materials in the post process of rolling and heat treatment, ingots have great effects on the properties of the final products. Inclusions and solidification structures are the most important aspects of the quality of ingots. Niobium and titanium are usually used to react with carbon and nitrogen to improve the properties of ferritic stainless steels. In this research, combined with thermodynamic calculation, effects of niobium and titanium on the inclusions and solidification structures in three kinds of high pure ferritic stainless steels with different titanium additions were investigated by optical microscope（OM）, scanning electron microscope（SEM）, transmission electron microscope（TEM）, and energy disperse spectrometer（EDS）. Results show that Al2O3 and a few（Nb,Ti）N particles form when titanium addition is 0.01 %.Furthermore, inclusions are mainly Ti N and Al2O3–Ti Ox–Ti N duplex inclusions when titanium addition is more than0.10 %. Those two types of inclusions are in well distribution, and can afford nuclei to the solidification process.Therefore, the ratio of equiaxed zone increases with the increase of titanium addition. The ratio increases from42.1 % to 64.0 % with the titanium addition increasing from 0.01 % to 0.10 %, and it increases to 85.7 % when the titanium addition reaches 0.34 %.
基金financial support from the High-tech Industry Technology Innovation Leading Plan of Hunan Province(Grant No.:2020GK2032)the Research Fund of the Key Laboratory of High-Performance Complex Manufacturing at Central South University。
文摘To investigate the superplastic deformation behavior of cryorolled Ti-6Al-4V titanium alloy,tensile tests were carried out at760℃and 830℃with different strain rate.The evolution of grain and micro structure has been studied using transmission electron microscopy and electron backscatter diffraction.When the tensile temperature was 760℃(<0.5T_(m),T_(m)is absolute melting point of alloy.)and the strain rate was 5×10^(-4)s^(-1),the fracture elongation of the sample reached 385%,showing good low-temperature superplasticity.Compared with the tensile temperature of 760℃,the fracture elongation of the s ample at 830℃was lower due to grain coarsening and oxidation.The strain rate sensitivity value m of all samples was larger than0.3,which confirmed that the cryorolled Ti-6A1-4V titanium alloy with a non-equiaxed grains structure can achieve high superplasticity at a temperature lower than 0.5T_(m),and indicated that the main deformation mechanisms in the tensile test at760-830℃were grain rotation and grain boundary sliding.After the tensile test,the average grain size of all samples was less than 5μm,in which significant dynamic recrystallization and recovery occurred.
基金the financial support from the National Natural Science Foundation of China [51805415,51922048]China Postdoctoral Science Foundation [2019M663682]+2 种基金China Postdoctoral Science Foundation [Grant number 2019M663682]Young Elite Scientists Sponsorship Program by CAST [Grant number 2021QNRC001]the fund of State Key Laboratory of Long-life High Temperature Materials (DECSKL202104)。
文摘In the context of global carbon neutrality, the application of lightweight magnesium alloys is becoming increasingly attractive. In this study, selective laser melting(SLM) was employed to achieve nearly full dense and crack-free AZ91D components with fine equiaxed grain structure. The formation mechanism of typical pore defects(gas pore, lack-of-fusion pore and keyhole pore) and melting modes(keyhole mode and conduction mode) were systematically studied by varying the laser power and scanning speed. The morphology and volume fraction of the pores under different processing conditions were characterized. A criterion based on the depth-to-width ratio of the melt pool was established to identify different melting modes. The strength and ductility(tensile strength up to 340 MPa and uniform elongation of 8.9%)of the as deposited AZ91D are far superior to those of the casting components and are comparable to those of its wrought counterparts.The superior balance of strength and ductility of SLMed AZ91D, as well as the negligible anisotropic properties are mainly ascribed to the extremely fine equiaxed grain structure(with average grain size of ~1.2 μm), as well as the discontinuous distribution of β-Al_(12)Mg_(17) phases. It thus provides an alternative way to fabricate high-strength magnesium alloys with complex geometry.
基金the Scientific Research-special Funds of Dongguan City in Guangdong Province (No. 2003D1011)
文摘The TiB2 thin films were deposited on steel substrates using RF magnetron sputtering technique with the low normalized substrate temperature （0.1〈Ts/Tm〈0.2）. Microstructure of these films was obtained by field emission scanning electron microscope （FESEM） and the grazing incidence X-ray diffraction （GIXRD） characterization, while the composition of films was obtained using Auger emission spectroscopy （AES） analysis. It was found that the TiB2 thin films were overstoichiometric with the B/Ti ratio at 2.33 and the diffusion of Ti and B atoms on the substrate surface was greatly improved at 350 ℃. Moreover, a new dense structure, named ＂equiaxed＂ grain structure was observed by FESEM at this substrate temperature, Combined with FESEM and AES analysis, it was suggested that the ＂equiaxed＂ grain structure was located in Zone 2 at the normalized substrate temperature as low as 0.18.
文摘By the solidification experiment of a medium carbon steel with refrigerant added.the effect of refrigerant on solidification structure of steel was studied.The results clearly show that refrigerant can increase the ratio of equiaxed crystal,fine grains and decrease central porosity and segregation.
