高温溶液结晶过程的光学研究法(一)——饱和温度和自发成核温度的测定

本文介绍了一套自行设计和组装的、高温热台显微镜实验装置,建立了一套高温溶液饱和点及自发成核温度测定法,测定了 KTP一磷酸盐熔液溶解度曲线和过冷度曲线。饱和温度测定精度在1℃左右。本装置及所介绍的方法,适于某些高温溶液晶体生长的定量实验研究。     

氯化镁电解时液镁阴极析出相过程的研究

在750℃下,研究了MgCl_2-NaCl-KCl三元系熔体电解时液镁阴极析出相过程的机理,即液镁析出的相过程为三维瞬时成核过程,并导出了成核速度及新核生长速度表达式。     

汽－液相变中成核的热力学理论

对现有汽－液相变过程有关文献中关于汽泡形成过程的分析提出了不同看法，并利用热力学理论从亚稳平衡态的特性出发对汽泡形成的热力学机制作出了分析，对系统从液态转变到汽－液共存状态的各阶段作出了说明。     

某些添加剂对镍在玻璃碳上电结晶的影响

用阶跃电位法研究了光亮镍Watts镀液中添加剂:糖精、丁炔二醇和香豆素,对镍在玻璃碳上沉积初始阶段的影响.结果表明,在不含添加剂的该电解液,镍电结晶的初始阶段按连续成核的三维生长机理进行;分别或同时含有糖精和丁炔二醇时,则按瞬时成核的三维生长机理进行.糖精或丁炔二醇促进成核过程而阻化晶核的生长,这两种添加剂同时存在时则对成核和三维生长都起促进作用;添加香豆素或者同时添加三种添加剂不改变成核和生长的方式,但香豆素对成核过程和晶核生长都起着促进作用,而三种添加剂混用则对成核和生长过程起着阻化作用.本文采用Fleischmann等人郝二建模型.     

成核改性对聚乳酸结晶行为的影响

选用PPA-Zn、TMC-328和TMP-3000为成核剂(NA),分别与聚乳酸(PLA)熔融共混,改性制备成PLA/NA复合材料,通过差示扫描量热分析、偏光显微观察、X射线衍射、动态热力学分析和热变形温度测试研究PLA/NA材料的结晶行为、动态热力学性能和耐热性能。结果表明,3种成核剂中,PPA-Zn和TMC-328更能提高PLA结晶度、储能模量和热变形温度,PLA/PPA-Zn和PLA/TMC-328半结晶时间分别为0.27min和0.28min,晶体形貌分别为针状晶和枝状晶,为α晶型,初始储能模量分别为3.921GPa和4.486GPa,110℃退火60s结晶后的热变形温度分为127.1℃和121.1℃。     

Kinetics and formation mechanisms of intragranular ferrite in V-N microalloyed 600 MPa high strength rebar steel

To systematically investigate the kinetics and formation mechanisms of intragranular ferrite (IGF), isothermal heat treatment in the temperature range of 450℃ to 600℃ with holding for 30 s to 300 s, analysis of the corresponding microstructures, and observation of the precipitated particles were conducted in V-N microalloyed 600 MPa high strength rebar steel. The potency of V(C,N) for IGF nucleation was also analyzed statistically. The results show that the dominant microstructure transforms from bainite (B) and acicular ferrite (AF) to grain boundary ferrite (GBF), intragranular polygonal ferrite (IPF), and pearlite (P) as the isothermal temperature increases from 450℃ to 600℃. When the holding time at 600℃ is extended from 30 s to 60 s, 120 s, and 300 s, the GBF content ranges from 6.0vol% to 6.5vol% and the IPF content increases from 0.5vol% to 2.8vol%, 13.1vol%, and 13.5vol%, respectively, because the ferrite transformation preferentially occurs at the grain boundaries and then occurs at the austenite grains. Notably, V(C,N) particles are the most effective nucleation site for the formation of IPF, accounting for 51% of the said formation.     

Peritectic solidification under high undercooling conditions

The solidification characteristics of highly undercooled Cu-7.77%Co peritectic alloy has been examined by glass fluxing technique. The obtained undercoolings vary from 93 to 203 K(0.14 TL). It is found that the α(Co) phase always nucleates and grows preferentially, which is followed by peritectic transformation. This means that the peritectic phase cannot form directly, even though the alloy melt is undercooled to a temperature far below its peritectic point. The maximum recalescence temperature measured experimentally decreases as undercooling increases , which is lower than the thermodynamic calculation result owing to the actual non-adia-batic nature of recalescence process. The dendritic fragmentation of primary α(Co) phase induced by high undercooling is found to enhance the completion of peritectic transformation. In addition, the LKT/BCT dendrite growth model is modified in order to make it applicable to those binary alloy systems with seriously curved liquidus and solidus lines. The dendrite growth velocities of primary α(Co) phase are subsequently calculated as a function of undercooling on the basis of this model.     

410S铁素体不锈钢的静态再结晶行为

通过不同温度-时间的再结晶实验,研究热轧态铁素体不锈钢410S的再结晶行为.结果表明,对于竹节状铁素体+马氏体(质量分数约30%)的410S热轧态变形组织,为防止马氏体的再度出现以及加快再结晶过程的综合考虑,其最佳再结晶退火温度为780~800℃.在此温度下所发生的再结晶,均有一个2~5 h的孕育期,当再结晶体积分数达到50%时,结晶速度达到最大.与试样内部相比,热轧态410S板材的再结晶晶粒更易于在表面形成.经过再结晶的410S硬度从初始的86.5 HRB下降到66.5 HRB,硬度降低25%.     

Microstructure, crystallography and nucleation mechanism of NANOBAIN steel

The microstructure of bainite ferrite in NANOBAIN steel transformed at different temperatures was investigated by scanning electron microscopy, transmission electron microscopy, electron back-scattered diffraction, and vickers hardness tester in detail. It is found that the average width of bainitic ferrite (BF) plates can be refined to be thinner with the reduction of temperature (473–573 K), and the bainitic ferrite plates can reach up to 20–74 nm at 473 K. Crystallographic analysis reveals that the bainitic ferrite laths are close to the Nishiyama-Wasserman orientation relationship with their parent austenite. Temperature shows a significant effect on the variant selection, and a decrease in temperature generally weakens the variant selection. Thermodynamic analyses indicates that the Lacher, Fowler and Guggenheim (LFG) model is more suitable than the Kaufman, Radcliffe and Cohen (KRC) model dealing with NANOBAIN steel at a low temperature range. The free energy change ΔGγ→BF is about ?1500 J·mol?1 at 473 K, which indicates that nucleation in NANOBAIN steel is the shear mechanism. Finally, the formation of carbon poor regions is thermodynamically possible, and the existence of carbon poor regions can greatly increase the possibility of the shear mechanism.