As the substrate for nucleation of primary austenite in hardfacing metals, the effectiveness of RE inclusions and the most common inclusions such as Al2O3, SiO2 and MnO in hardfacing metals of medium-high carbon steel...As the substrate for nucleation of primary austenite in hardfacing metals, the effectiveness of RE inclusions and the most common inclusions such as Al2O3, SiO2 and MnO in hardfacing metals of medium-high carbon steels was analyzed and calculated in detail. The calculation based on the theory of planar lattice misfit shows that Ce2O3, La2O3 and Ce2O2S, instead of SiO2, Al2O3, MnO and CeS, are effective as the heterogeneous nuclei of primary austenite in medium-high carbon steels.展开更多
The dendrite segregation in cast H13 steel was weakened with RE modification treatment. Grain boundary carbide during quenching was also under control and impact toughness was improved greatly. By thermodynamic calcul...The dendrite segregation in cast H13 steel was weakened with RE modification treatment. Grain boundary carbide during quenching was also under control and impact toughness was improved greatly. By thermodynamic calculation, analysis of two-dimensional lattice misfitting and electron probe analysis, it is found that Ce2O3 may act as the heterogeneous nuclei of modified cast H13 steel.展开更多
The effective heterogeneous nuclei in Mg-7.92 Zn-1.70 Y alloy during solidification process under high pressure was investigated by EBSD. It is found that the orientation relationship between Mg matrix and MgY phase, ...The effective heterogeneous nuclei in Mg-7.92 Zn-1.70 Y alloy during solidification process under high pressure was investigated by EBSD. It is found that the orientation relationship between Mg matrix and MgY phase, [111]_（MgY）//[1210]_（α-Mg） and（101）_（MgY）//（0001）_（α-Mg）, exists between Mg matrix and MgY phase.The MgY phase is the potential heterogeneous nuclei substrate for a-Mg solidified under high pressure. It is calculated by Bramfitt mode that the mismatch between Mg matrix and MgY phase is greater than 12% under atmospheric pressure. When solidified under high pressure of 4 GPa, the solidification pressure can increase the number of the α-Mg nucleus by reducing the size of the nucleus, decreasing interfacial energy of MgY/a-Mg, and changing the wettability between MgY phase and α-Mg from non-wetting under atmospheric pressure to wetting under high pressure. The MgY phase becomes a powerful heterogeneous nuclei for α-Mg crystal. Increasing the number of valid heterogeneous nuclei substrate increases nucleus number and refines the grain of the alloy.展开更多
The influence of Hf and B on the solidification structure of cast Ti-46Al alloys was investigated. The results show that the coupling effect of Hf and B changes the solidification structure morphology and strongly ref...The influence of Hf and B on the solidification structure of cast Ti-46Al alloys was investigated. The results show that the coupling effect of Hf and B changes the solidification structure morphology and strongly refines the grain size. When the Hf＋B contents were increased from 0 ＋ 0.0 to 3 ＋ 0.2, 5 ＋ 0.6 and 7 ＋ 1.0 （in at. %）, the solidification structure morphology changed from coarse columnar dendrite to fine columnar dendrite, then to equiaxed dendrite, and further to fine near granular grain whilst the average grain size decreased to 20 μm. It is concluded that the columnar dendrite refinement is due to the effect of Hf and B on the decrease of AI diffusion coefficient in the melt. The fine near granular grain formation is attributed to the combined constitutional supercooling formed by AI and B segregation that is strengthened by Hf and B additions at the solid/liquid interface during solidification, and the TiB2 precipitates acting as heterogeneous nuclei.展开更多
The influences of minor amounts of scandium on the microstructure and mechanical properties of as-cast ZA27 alloy have been experimentally investigated. The experimental results show that as far as the Sc addition is ...The influences of minor amounts of scandium on the microstructure and mechanical properties of as-cast ZA27 alloy have been experimentally investigated. The experimental results show that as far as the Sc addition is individually concerned, the refinement result of the as-cast ZA27 alloy with 0.5wt.%Sc addition is comparatively better. After alloying with minor amounts of Sc, the coarse dendrites of the ZA27 alloy are refined and transformed into the uniform and small equiaxed grain microstructure; also the eutectics among the grain boundaries become finer. The test results of mechanical properties show that the tensile strength and hardness of the as-cast ZA27 alloy containing 0.5wt.%Sc approach 495 MPa and 120.2 HB, increase by 28.5% and 33.1%, respectively, compared with those of the ZA27 alloy with no addition of Sc element, while the elongation of the alloy is improved to 7.6% from 2.7%. The SEM, EDAX and XRD analyses show that in the ZA27 alloy, the trace element Sc combines with AI to form the square AI3Sc phase particles, which serve as heterogeneous nuclei, facilitating the refinement of the microstructure and the improvement of the mechanical properties of the alloy.展开更多
The electrodes for hardfacing medium carbon steel with six additions of rare earth oxide were developed in this work. By means of optical microscopy and scanning electron microscopy, the microstructure, inclusion and ...The electrodes for hardfacing medium carbon steel with six additions of rare earth oxide were developed in this work. By means of optical microscopy and scanning electron microscopy, the microstructure, inclusion and the fractograph of the hardfacing metal were observed. Then, the effects of rare earth oxide on microstructure and inclusions in hardfacing metal were analyzed. The effectiveness of rare earth oxide as heterogeneous nuclei of δ-Fe was calculated with the misfit theory. The results showed that, the microstructure of hardfacing metal was composed of ferrite and small amount of pearlite. The microstructure was refined at first and then coarsened with the increase of rare earth oxide addition. The fractograph was changed from brittle to equiaxed dimples, then became quasi-cleavage and cleavage gradually. The calculated results showed that, the ferrite grain size could be refined because that LaAlO3 as heterogeneous nuclei of δ-Fe was moderately effective, and the ferrite grain size was coarsened because the misfits between Ce2O3 and δ-Fe, Ce2O2S and δ-Fe were increased with futher increase of rare earth oxide addition.展开更多
The purpose of this work was to investigate the effect of La2O3 on the granular bainite microstructure and wear resistance of hardfacing layer metal. The hardfacing layer metals with different contents of La2O3 were p...The purpose of this work was to investigate the effect of La2O3 on the granular bainite microstructure and wear resistance of hardfacing layer metal. The hardfacing layer metals with different contents of La2O3 were prepared. The microstructures of the hardfacing layer metals were observed by field emission scanning electron microscopy （FESEM） and transmission electron micros-copy （TEM）. The hardness and wear resistance of the hardfacing layer metals were measured respectively. The results indicated that with the increasing content of La2O3, the amount of granular bainite increased, while that of martensite decreased and that of retained austenite did not change obviously. When the content of La2O3 was 2.55 wt.%, the volume fraction of the granular bainite in the hardfacing layer metal was 73.2%. Meanwhile, the wear resistance of the hardfacing layer metal was the largest, which was 12100 min/g. The mismatch between the face （100） of LaAlO3 and the face （100） ofδ-Fe was 7.1%. Therefore, LaAlO3 could act as moder-ate effective heterogeneous nuclei ofδ-Fe and the granular bainite could be refined.展开更多
文摘As the substrate for nucleation of primary austenite in hardfacing metals, the effectiveness of RE inclusions and the most common inclusions such as Al2O3, SiO2 and MnO in hardfacing metals of medium-high carbon steels was analyzed and calculated in detail. The calculation based on the theory of planar lattice misfit shows that Ce2O3, La2O3 and Ce2O2S, instead of SiO2, Al2O3, MnO and CeS, are effective as the heterogeneous nuclei of primary austenite in medium-high carbon steels.
文摘The dendrite segregation in cast H13 steel was weakened with RE modification treatment. Grain boundary carbide during quenching was also under control and impact toughness was improved greatly. By thermodynamic calculation, analysis of two-dimensional lattice misfitting and electron probe analysis, it is found that Ce2O3 may act as the heterogeneous nuclei of modified cast H13 steel.
基金Project supported by National Natural Science Foundation of China(51675092,51775099)
文摘The effective heterogeneous nuclei in Mg-7.92 Zn-1.70 Y alloy during solidification process under high pressure was investigated by EBSD. It is found that the orientation relationship between Mg matrix and MgY phase, [111]_（MgY）//[1210]_（α-Mg） and（101）_（MgY）//（0001）_（α-Mg）, exists between Mg matrix and MgY phase.The MgY phase is the potential heterogeneous nuclei substrate for a-Mg solidified under high pressure. It is calculated by Bramfitt mode that the mismatch between Mg matrix and MgY phase is greater than 12% under atmospheric pressure. When solidified under high pressure of 4 GPa, the solidification pressure can increase the number of the α-Mg nucleus by reducing the size of the nucleus, decreasing interfacial energy of MgY/a-Mg, and changing the wettability between MgY phase and α-Mg from non-wetting under atmospheric pressure to wetting under high pressure. The MgY phase becomes a powerful heterogeneous nuclei for α-Mg crystal. Increasing the number of valid heterogeneous nuclei substrate increases nucleus number and refines the grain of the alloy.
基金supported by the National Natural Science Foundation of China(50771041)NCET05-0350,the program of excellent team in Harbin Institute of Technology
文摘The influence of Hf and B on the solidification structure of cast Ti-46Al alloys was investigated. The results show that the coupling effect of Hf and B changes the solidification structure morphology and strongly refines the grain size. When the Hf＋B contents were increased from 0 ＋ 0.0 to 3 ＋ 0.2, 5 ＋ 0.6 and 7 ＋ 1.0 （in at. %）, the solidification structure morphology changed from coarse columnar dendrite to fine columnar dendrite, then to equiaxed dendrite, and further to fine near granular grain whilst the average grain size decreased to 20 μm. It is concluded that the columnar dendrite refinement is due to the effect of Hf and B on the decrease of AI diffusion coefficient in the melt. The fine near granular grain formation is attributed to the combined constitutional supercooling formed by AI and B segregation that is strengthened by Hf and B additions at the solid/liquid interface during solidification, and the TiB2 precipitates acting as heterogeneous nuclei.
基金financially supported by the Natural Science Foundation of Liaoning Province(No:20072043)
文摘The influences of minor amounts of scandium on the microstructure and mechanical properties of as-cast ZA27 alloy have been experimentally investigated. The experimental results show that as far as the Sc addition is individually concerned, the refinement result of the as-cast ZA27 alloy with 0.5wt.%Sc addition is comparatively better. After alloying with minor amounts of Sc, the coarse dendrites of the ZA27 alloy are refined and transformed into the uniform and small equiaxed grain microstructure; also the eutectics among the grain boundaries become finer. The test results of mechanical properties show that the tensile strength and hardness of the as-cast ZA27 alloy containing 0.5wt.%Sc approach 495 MPa and 120.2 HB, increase by 28.5% and 33.1%, respectively, compared with those of the ZA27 alloy with no addition of Sc element, while the elongation of the alloy is improved to 7.6% from 2.7%. The SEM, EDAX and XRD analyses show that in the ZA27 alloy, the trace element Sc combines with AI to form the square AI3Sc phase particles, which serve as heterogeneous nuclei, facilitating the refinement of the microstructure and the improvement of the mechanical properties of the alloy.
基金Project supported by One Hundred Excellent Talents of Hebei Province of China (SPRC021)Key Project of Science and Technology of Hebei Province (09215106D)
文摘The electrodes for hardfacing medium carbon steel with six additions of rare earth oxide were developed in this work. By means of optical microscopy and scanning electron microscopy, the microstructure, inclusion and the fractograph of the hardfacing metal were observed. Then, the effects of rare earth oxide on microstructure and inclusions in hardfacing metal were analyzed. The effectiveness of rare earth oxide as heterogeneous nuclei of δ-Fe was calculated with the misfit theory. The results showed that, the microstructure of hardfacing metal was composed of ferrite and small amount of pearlite. The microstructure was refined at first and then coarsened with the increase of rare earth oxide addition. The fractograph was changed from brittle to equiaxed dimples, then became quasi-cleavage and cleavage gradually. The calculated results showed that, the ferrite grain size could be refined because that LaAlO3 as heterogeneous nuclei of δ-Fe was moderately effective, and the ferrite grain size was coarsened because the misfits between Ce2O3 and δ-Fe, Ce2O2S and δ-Fe were increased with futher increase of rare earth oxide addition.
基金Project supported by National Natural Science Foundation of China(51271163)the Key Project of Science and Technology of Hebei Province(09215106D)
文摘The purpose of this work was to investigate the effect of La2O3 on the granular bainite microstructure and wear resistance of hardfacing layer metal. The hardfacing layer metals with different contents of La2O3 were prepared. The microstructures of the hardfacing layer metals were observed by field emission scanning electron microscopy （FESEM） and transmission electron micros-copy （TEM）. The hardness and wear resistance of the hardfacing layer metals were measured respectively. The results indicated that with the increasing content of La2O3, the amount of granular bainite increased, while that of martensite decreased and that of retained austenite did not change obviously. When the content of La2O3 was 2.55 wt.%, the volume fraction of the granular bainite in the hardfacing layer metal was 73.2%. Meanwhile, the wear resistance of the hardfacing layer metal was the largest, which was 12100 min/g. The mismatch between the face （100） of LaAlO3 and the face （100） ofδ-Fe was 7.1%. Therefore, LaAlO3 could act as moder-ate effective heterogeneous nuclei ofδ-Fe and the granular bainite could be refined.
