不同脉冲电压对45钢凝固组织的影响

选择45钢作为研究对象,考察了不同脉冲电压对其宏观凝固组织、微观凝固组织以及成分偏析的影响.实验发现,经过不同脉冲电压处理后,45钢的宏观凝固组织得到明显改善,等轴晶增加,柱状晶减少,随脉冲电压升高,效果越明显;并发现经过电脉冲处理后,45钢的显微组织也发生了显著改变,魏氏组织减少,珠光体增加,且珠光体片层间距变薄;同时,脉冲电压对45钢的成分偏析具有一定的影响,使易偏析元素C、S、P的偏析均有一定程度的改善.C的偏析指数由未处理的1.257降低为1.125,S的偏析指数由来处理的1.502降低为1.063,P的偏析指数由未处理的1.384降低为1.237.     

电脉冲处理对45钢凝固组织的影响

采用不同的脉冲电压对45钢在凝固前进行电脉冲处理.实验结果表明,经过电脉冲处理后,45钢的宏观凝同组织得到明显改善,树枝晶减少,等轴晶增加;45钢的显微组织也发生了显著改变,魏氏组织减少,珠光体增加,且珠光体片层间距变薄.     

物理外场对合金组织及力学性能影响研究现状及进展

施加物理外场可以对液态金属凝固过程进行调控,改善凝固组织进而获得高性能的优质铸件。阐述了不同物理外场（电脉冲、电磁场、重力场、超声波等）对纯金属和合金凝固组织影响及其作用机理,总结了物理外场对合金凝固过程的影响及其在金属材料中的应用,并介绍了各外场的创新应用以及发展趋势。     

物理场对金属凝固组织的影响

综述了国内外关于电流、磁场和超声波处理对金属凝固过程与凝固组织影响的研究概况 ,根据电磁学、声学及金属凝固原理分析了物理场细化和改善凝固组织的主要机制 ,提出了外加物理场凝固细晶技术在工业中应用尚需研究解决的技术与理论问题 ,特别强调了脉冲物理场处理技术的优越性及应用前景。     

断面尺寸对电脉冲处理45钢凝固组织的影响

对不同断面尺寸的45钢在凝固过程进行电脉冲处理的试验发现,在相同的电脉冲参数条件下,试样断面尺寸对电脉冲处理效果产生明显的影响。在试样断面较小时,试样整个断面均为细小的等轴晶,随试样断面尺寸的增加,细化效果降低。同时,试样断面尺寸对电脉冲处理的45钢微观组织也有明显影响,在小断面条件下,珠光体明显变薄,并呈现出不连续现象,而随断面尺寸增加,珠光体片层间距逐渐增加。     

不同超声波处理方式对高碳钢液凝固组织的影响

主要研究了超声处理对高碳钢凝固组织的作用,分析了不同处理方式对其凝固组织的影响。试验结果表明:高碳钢液凝固前进行超声处理,其凝固组织没有发生明显的变化;对加稀土铈的高碳钢液在凝固前进行超声处理,凝固组织细化明显;在钢液凝固过程中引入超声波,初生树枝晶被击碎形成均匀细小的等轴晶,高碳钢凝固组织显著细化。     

超声波对GCr15钢凝固组织与性能的影响

GCr15轴承钢凝固过程中在钢锭模侧部引入不同功率超声波,研究其对组织性能的影响。结果表明,未加入超声波时,钢中柱状晶较粗大,组织不均匀;在合适的功率范围内,超声波可以细化钢中晶粒,使组织均匀。在0~500 W功率范围内,随着功率的增加,钢中合金元素的偏析逐步降低,在500 W时,C、Si的最大偏析度分别降低至1.129、1.196,统计偏析度分别降低到0.0693、0.1075。超声处理可以细化钢中碳化物,均匀碳化物分布,处理功率300 W时,细化后的碳化物平均尺寸为2.96μm,同时钢的抗拉强度、屈服强度、断面收缩率、伸长率分别提升至653 MPa、370 MPa、58%、27%。     

电脉冲时间对铸造ZA12合金凝固组织和性能的影响

以ZA12合金为实验材料，在合金的凝固过程中进行了脉冲电流处理，研究电脉冲时间对作用结果的影响。实验结果表明，就细化合金的凝固组织、改善力学性能而言，在合金凝固的整个过程都进行脉冲电流处理比仅在合金凝固的前半段进行处理的效果要好。结合ZA12合金的凝固特性和电流对金属熔体的作用机制进行分析。认为在合金凝固后半段施加的脉冲电流处理促进了枝晶之间液体的流动。增强了枝晶间液体的补缩能力，并且导致部分小的枝晶熔断。从而进一步抑制了枝晶的生长．得到更均匀细小的凝固组织。从而对合金力学性能的改善效果也更为显著。     

稳恒磁场及直流电场对铝硅合金凝固组织及性能的影响

采用砂型浇注,通过加入电极产生直流电场,利用永磁装置产生稳恒磁场,研究ZL114合金在不同电场、磁场组合条件下的凝固组织和力学性能.结果表明,在大磁场与小电场组合下凝固组织细化的比较好,其综合力学性能较高.     

外加电场对合金凝固组织的影响

综述了外加电场对合金凝固组织影响的研究现状,分析总结了外加电场对合金凝固过程和凝固组织的影响机理。在此基础上,讨论了目前外加电场影响合金凝固研究中存在的问题,初步探讨了这一方法的研究方向和应用前景。     

Refinement mechanism of low voltage pulsed magnetic field on solidification structure of silicon steel

The grain refinement of a silicon steel solidified with a low voltage pulsed magnetic field (LVPMF) was investigated by experiments and modeling. The experiment results show that complete fine equiaxed grains are acquired by applying the LVPMF. The effects of process parameters, such as the melt cooling rate and superheating on the solidification structure, were also studied. Complete fine equiaxed grains can be obtained under a larger range of cooling rate or superheating when the LVPMF is applied. The magnetic force and the melt flow during solidification were modeled and simulated to reveal the grain refinement mechanism. The simulation results show that the LVPMF has a double role in electromagnetic convection and electromagnetic vibration on the alloy melt. We propose the refining mechanism: The melt vibration and convection can promote nucleus multiplication, which contributes to heterogeneous nucleation enhancement and leads to a high nucleation rate and grain refinement.     

不锈钢板坯连铸过程中温度场及凝固的研究

采用有限元法计算了不锈钢板坯在连铸凝固过程中温度场及坯壳的生长随时间的变化.讨论了拉速、过热度、二冷区水量对温度场及凝固末端位置的影响.结果表明,影响铸坯温度场和凝固末端位置的主要因素是拉速,而过热度的影响较小.     

ULCB钢焊接熔池凝固过程数值模拟

采用元胞自动机法建立ULCB钢焊接熔池凝固过程的宏微观耦合模型,模拟非均匀温度场下焊接熔池凝固过程的组织形貌演变和溶质场分布,分析不同形核参数和合金成分对焊接熔池枝晶形貌的影响。结果表明,熔池边缘形成柱状晶,熔池中心形成等轴晶,柱状晶和等轴晶相互抑制长大;枝晶生长过程中始终存在着枝晶偏析现象;形核密度和合金成分影响枝晶的形核和生长,随着形核密度和合金成分的增加,焊缝中等轴晶区域增加,晶粒细化。     

Electronic structure and physical property of TiAl

lINTRODUCTIONInrecentyearslthePau1ing'svaIenceb0nd(VB)the0ryhasmadeagreatprogressinChi-m.First,YtidevelopedthePauling'svalencebondtheoryandestablishedtheEETtheory[']landthenbasedontheenergy-b0ndthe0ryandEETtheory,Xieproducedtheone-atom-statetheory['1(OAtheory)ofpuremetalswiththeunityof"shape"and"energy"andthendevel-opedthecentralat0msmodelinthestatisticthermodynamicsandbuiltthecharacteristiccrys-talthe0ry(CCtheory)[31.NowtheOAtheoryhasmadeanewprogressandcanbeappliedto-intermetallic…     

各向异性对焊接凝固裂纹影响规律的相场法模拟

Effects of anisotropy on the solidification cracking susceptibility in the molten pool of an Al-Cu alloy are investigated using phase field modeling. The results show that the tip of dendrites becomes stable, side-branches and bridges are difficult to form, and the longer liquid channel is easily formed between dendrites with the increase of anisotropic strength. In the case of large anisotropic strength, welding tensile stresses are difficult to transfer and release through bridging, and the metal melt is also difficult to supply the tensile position through the long liquid channel, so it is easy to form cracks. Based on the simulation results, the solidification cracking susceptibility index |dT/d(f_s)1/2| is calculated. It is found that the index is higher when the anisotropic strength is larger. In conclusion, the solidification crack sensitivity is higher when the anisotropy strength is larger.     

45钢直流电场增强粉末法渗硼层相结构与性能

在粉末渗剂和45钢试样上施加4 A电流的直流电场,于800℃进行直流电场增强渗硼。以X射线衍射、光学显微观察和显微硬度测试等手段,分析位于电场不同位置试样渗硼层的相结构、显微组织、厚度与及显微硬度分布。结果表明:电场渗硼的渗层组织形态基本与常规渗硼的一致,以锯齿状楔入基体,但其相结构、显微硬度分布、厚度等与试样位置有关;朝正极面的渗层一般由Fe B和Fe2B两相组成,渗层较厚且较硬;朝负极面的渗层主要由Fe2B组成,随渗硼时间延长Fe B先增加,后减少至消失;渗硼时间等于及超过2 h,渗层下出现明显的过渡区;渗层厚度与保温时间关系曲线呈抛物线特征。从直流电场对渗剂化学反应、含硼活性基团在气氛中的扩散及硼在试样内扩散的影响等方面进行了分析。     

脉冲磁场下铝合金定向凝固磁场分布数值模拟

采用ANSYS 8.0有限元分析软件对铝合金脉冲磁场定向凝固磁场分布作了数值模拟,得到了凝固过程中的磁场分布状态.结果表明:在试样中心附近磁感应强度较强,而在端部较弱.模拟结果和实验测得结果相符合.通过数值模拟,不仅可以初步了解凝固过程中的磁场分布状态,而且有助于进一步研究凝固组织细化的原因.     

Heat transfer and solidification microstructure evolution of continuously cast steel by non-steady physical simulation

The heat transfer and solidification microstructure evolution during continuous casting were experimentally studied in this work. A new approach to physically simulate the steel solidification behavior during continuous casting was developed. Six steel grades with different solidification mode were introduced to elucidate the carbon equivalent dependent mold heat flux, prior austenite grain size and secondary dendrite arm spacing. It is found that the non-steady mold heat fluxes in the experiment against time for all steel grades are comparative to that versus distance in practical continuous casting. Due to the occurrence of L→L+δ→δ+γ→γ transformation with the largest amount of volume contraction in hypo-peritectic steel, it shows the lowest mold heat flux among these six steel grades. It is also demonstrated from the solidification microstructure results that the prior austenite grain size and secondary dendrite arm spacing in the physical simulation are in good agreement with those in continuously cast strand. In addition, the steel with a higher temperature for the onset of δ→γ transformation reveals the larger prior austenite grains resulted from the higher grains growth rate in the post solidification process.