The modifying effect of La addition on primary phase Mg2Si in Mg-5Si alloys was investigated. The results showed that a proper amount of La could effectively modify the primary phase Mg2Si, Based on the present experi...The modifying effect of La addition on primary phase Mg2Si in Mg-5Si alloys was investigated. The results showed that a proper amount of La could effectively modify the primary phase Mg2Si, Based on the present experiment, the optimal modification effect was obtained with an addition of about 0.5 wt.% La. The size of the primary phase MgzSi was considerably reduced to 25μm or less and the morphology was modified from a coarse dendritic shape to a polyhedral shape. However, when the addition of La increased to 0.8 wt.% or higher, the primary Mg2Si grew into a coarse dendritic morphology again. Moreover, it was found that some LaSi2 compounds were formed during solidification and the amount of the compounds appeared to increase gradually with increasing La content.展开更多
Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb（mass fraction） alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of t...Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb（mass fraction） alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of the microstructure. Continuous temperature measurements were made during solidification at different positions along the length of the casting and these temperature data were used to determine solidification thermal parameters, including the growth rate（VL） and the cooling rate（TR）. High cooling rate cells and dendrites are shown to characterize the microstructure in different regions of the casting, with a reverse dendrite-to-cell transition occurring for TR5.0 K/s. Cellular（λc） and primary dendrite arm spacings（λ1） are determined along the length of the directionally-solidified casting. Experimental growth laws relating λc and λ1 to VL and TR are proposed, and a comparative analysis with results from a vertical upward directional solidification experiment is carried out. The influence of morphology and length scale of the microstructure on microhardness is also analyzed.展开更多
The significant role of ion beam flux during nitriding 304 austenitic stainless steel has been investigated by using a radio frequency inductively-coupled plasma reactor into which a sample with negative bias voltage ...The significant role of ion beam flux during nitriding 304 austenitic stainless steel has been investigated by using a radio frequency inductively-coupled plasma reactor into which a sample with negative bias voltage was inserted. A milliammeter is used to detect tile current of ions which collide with the sample and optical emission spectroscopy is used to discern the reactive species included in the nitrogen plasma. The nitriding efficiency is indicated by X-ray diffraction and the microhardness test. The reported data reveal that the ion beam flux density as well as the deposition pressure, bias voltage and time can strongly affect the nitriding of stainless steel via tile expanded multiphase microstructure inside the nitrided layer. The increase in the density of ion flux results in an ascent in the intensity of the expanded peak and a simultaneous decline in the intensity of the 3＇ austenite peak. The evolution trend of ion beam flux density is described as a function of tile operating pressure and the bias voltage. The maxinmm ion flux density has been achieved at 10 Pa pressure and 500 V bias voltage. A reasonable nitriding region has been, consequently, suggested after comparing this work with previously reported results.展开更多
基金Project supported by the Science and Technology of Heilongjiang Province (GC05A209)the Science and Technology of Harbin (2005AA5CG046)
文摘The modifying effect of La addition on primary phase Mg2Si in Mg-5Si alloys was investigated. The results showed that a proper amount of La could effectively modify the primary phase Mg2Si, Based on the present experiment, the optimal modification effect was obtained with an addition of about 0.5 wt.% La. The size of the primary phase MgzSi was considerably reduced to 25μm or less and the morphology was modified from a coarse dendritic shape to a polyhedral shape. However, when the addition of La increased to 0.8 wt.% or higher, the primary Mg2Si grew into a coarse dendritic morphology again. Moreover, it was found that some LaSi2 compounds were formed during solidification and the amount of the compounds appeared to increase gradually with increasing La content.
基金the financial support provided by IFPA, Federal Institute of Education, Science and Technology of Para, FAPESP-Sao Paulo Research Foundation,Brazil (grants 2016/18186-1 and 2017/15158-0)CNPq,The Brazilian Research Council (grants 301600/2015-5 472745/2013-1 and 308784/2014-6)
文摘Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb（mass fraction） alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of the microstructure. Continuous temperature measurements were made during solidification at different positions along the length of the casting and these temperature data were used to determine solidification thermal parameters, including the growth rate（VL） and the cooling rate（TR）. High cooling rate cells and dendrites are shown to characterize the microstructure in different regions of the casting, with a reverse dendrite-to-cell transition occurring for TR5.0 K/s. Cellular（λc） and primary dendrite arm spacings（λ1） are determined along the length of the directionally-solidified casting. Experimental growth laws relating λc and λ1 to VL and TR are proposed, and a comparative analysis with results from a vertical upward directional solidification experiment is carried out. The influence of morphology and length scale of the microstructure on microhardness is also analyzed.
基金supported by Shenyang Science and Technology Plan of China(No.F12028200)
文摘The significant role of ion beam flux during nitriding 304 austenitic stainless steel has been investigated by using a radio frequency inductively-coupled plasma reactor into which a sample with negative bias voltage was inserted. A milliammeter is used to detect tile current of ions which collide with the sample and optical emission spectroscopy is used to discern the reactive species included in the nitrogen plasma. The nitriding efficiency is indicated by X-ray diffraction and the microhardness test. The reported data reveal that the ion beam flux density as well as the deposition pressure, bias voltage and time can strongly affect the nitriding of stainless steel via tile expanded multiphase microstructure inside the nitrided layer. The increase in the density of ion flux results in an ascent in the intensity of the expanded peak and a simultaneous decline in the intensity of the 3＇ austenite peak. The evolution trend of ion beam flux density is described as a function of tile operating pressure and the bias voltage. The maxinmm ion flux density has been achieved at 10 Pa pressure and 500 V bias voltage. A reasonable nitriding region has been, consequently, suggested after comparing this work with previously reported results.
