等温过程含Ti炉渣中钙钛矿相弥散颗粒长大研究

影响非平衡态含Ｔｉ炉渣中钙钛矿相长大因素有两个，一个是析出过程中自身长大，另一个是由大颗粒吞并小颗粒而产生的粗化。通过对非平衡态含Ｔｉ炉渣中钙钛矿相的析出长大研究，给出了描述非平衡态下由扩散控制弥散钙钛矿晶粒长大的动力学模型。     

高Ti炉渣中Ca—Ti矿相析出过程的计算机模拟

提出了模拟试样截面组织的方法，模拟了截面上Ca-Ti矿晶体的形貌和析出过程，模拟结果与实验结果基本一致，该方法将晶体在空间上的生长过程与试样截面上的组织联系起来，根据截面组织的模拟结果可以了解和研究空间上的晶体形貌和晶体生长过程。     

Kinetics of non-isothermal precipitation process of perovskite phase in oxidized Ti-bearing blast furnace slag

Kinetics of non-isothermal precipitation process and crystal growth of perovskite phase in oxidized Ti-bearing slag were investigated. The oxidized slag was obtained by blowing the air into the molten Ti-bearing blast furnace slag through a lance. The experimental results show that the cooling rate has important effect on precipitation and growth of perovskite phase in oxidized slag; the lower cooling rate is in favor of not only the increase of the volume fraction of perovskite phase, but also the growth of perovskite phase grain sizes. The particle coarsening in non-isothermal process has important effect on the crystal growth of perovskite phase. The relative volume fraction of perovskite phase could be approximately described by JMAK equation, and the experiential expression of the average crystal radius of perovskite phase was also obtained.     

等温变形0Cr14Mn21NiN无磁不锈钢的晶间腐蚀敏感性

通过Thermal-Calc热力学软件对0Cr14Mn21NiN无磁不锈钢中碳化物析出的平衡相区进行了计算,并通过时效处理试验进行了验证。通过不同参数的等温变形试验对实际的非平衡态碳化物析出行为进行了研究。通过双环电化学动电位再活化法(DL-EPR)对等温变形试样的晶间腐蚀敏感性进行了测试和对比。结果表明:热力学计算的平衡态Cr₂₃C₆碳化物析出温度范围为512~847 ℃,而通过时效试验验证的实际析出温度范围为720~940 ℃,表明二者之间存在约200 ℃的误差。当总变形量不超过20%时,等温变形非平衡态Cr₂₃C₆碳化物析出下限温度进一步降低至625 ℃,等温变形过程对晶界Cr₂₃C₆碳化物形核和长大过程均有加速作用。DL-EPR电化学方法结果表明等温变形后由于碳化物析出速度的加快,0Cr14Mn21NiN无磁不锈钢的晶间腐蚀敏感性显著增加。     

Modeling the overall solidification kinetics for undercooled single-phase solid-solution alloys. I. Model derivation

Departing from the volume-averaging method, the equiaxed solidification model was extended to describe the overall solidification kinetics of undercooled single-phase solid-solution alloys. In this model, a single grain, whose size is given assuming site saturation, is divided into three phases, i.e. the solid dendrite, the inter-dendritic liquid and the extra-dendritic liquid. The non-equilibrium solute diffusion in the inter-dendritic liquid and the extra-dendritic liquid, as well as the heat diffusion in the extra-dendritic liquid, is considered. The growth kinetics of the solid/liquid interface is given by the solute or heat balance, where a maximal growth velocity criterion is applied to determine the transition from thermal-controlled growth to solutal-controlled growth. A dendrite growth model, in which the nonlinear liquidus and solidus, the non-equilibrium interface kinetics, and the non-equilibrium solute diffusion in liquid are considered, is applied to describe the growth kinetics of the grain envelope. On this basis, the solidification path is described.     

基于减小热处理畸变的20CrMnMoH高性能齿轮预先热处理工艺

采用理论分析和实验研究相结合的方法,对20CrMnMoH齿轮钢在预先热处理过程中产生贝氏体非平衡组织的现象进行了分析研究。结果表明:20CrMnMoH齿轮钢在常规预先热处理过程中的冷却速度无法控制,过冷奥氏体进行非平衡组织转变,容易得到贝氏体等非平衡组织。根据贝氏体等非平衡组织的组织遗传效应,结合过冷奥氏体等温转变的原理和机制,设计了两次等温正火预先热处理工艺,首次等温正火预先热处理完成了非平衡组织到平衡组织的转变,二次等温正火预先热处理实现了晶粒的细化和均匀化。通过工艺优化控制实现了齿轮锻件的金相组织为1~2级、同批次不同齿轮锻件硬度差≤5 HB的技术指标。成品齿轮的精度可以达到6级,验证了预先热处理对减小齿轮热处理畸变、提高齿轮精度的有效性。     

超超临界转子钢X12CrMoWVNbN10-1-1的等温转变动力学

通过膨胀试验测定了X12CrMoWVNbN10-1-1铁素体耐热钢连续加热过程相变动力学曲线(CHT),根据等温转变动力学与连续转变动力学之间的关系将CHT曲线转换为等温加热相变动力学曲线(IHT);采用定量金相法测定X12CrMoWVNbN10-1-1铁素体耐热钢以30℃/h加热至1070℃保温12h的过冷奥氏体经过不同温度等温转变的转变量与等温时间的关系,根据试验结果求解出修正的Avrami方程中的系数,并绘制出这种奥氏体化条件下的过冷奥氏体等温转变动力学曲线(TTT)。     

18CrNiMo7-6齿轮钢温锻后余热等温正火工艺

对18CrNiMo7-6齿轮钢进行了温锻余热等温正火工艺研究。结果表明:在温锻余热等温正火工艺中,冷却速度、等温温度、等温时间为关键的工艺参数。较低冷却速度和较高的等温温度,可在有限等温时间内有效提高珠光体的转变量,减少残留奥氏体含量及室温马氏体和贝氏体等非平衡组织,获得理想的组织及性能。以0.1 ℃/s和1 ℃/s冷却速度降至等温正火温度650 ℃保温1 h 后冷却可获得硬度163~164 HBS,F晶粒度10~11.5级,带状组织1.5级,组织及性能均符合技术要求,可具有良好的切削加工性能,并为后续热处理工艺提供理想组织。     

时效温度对非平衡凝固K424合金析出相及硬度的影响

采用铜模喷铸与等温时效相结合的方法,研究了快冷K424高温合金的非平衡凝固组织及其沉淀相析出行为。结果表明,铜模喷铸合金组织发生了显著细化,二次枝晶间距相比铸态大幅降低,溶质偏析的减弱有利于抑制粗大碳化物及共晶组织形成。随铜模内径下降,枝晶形貌由无方向性等轴晶逐渐转变为择优生长的定向枝晶。经800~1000℃等温时效30min后,快冷合金的过饱和固溶体组织中开始析出γ′相。随时效温度提高,沉淀相尺寸及体积分数同时增加。900℃×30min时效后可获得大量细小均匀的球形γ′相,快冷合金的显微硬度(HV)高达478,相比原始非平衡态合金提高了13%。     

Zr_(55)Cu_(30)Ni_5Al_(10)大块金属玻璃的等时和等温晶化(英文)

采用差示扫描量热仪(DSC)和X射线衍射仪(XRD)研究Zr55Cu30Ni5Al10大块金属玻璃的非等温晶化转变动力学和在过冷液相区的等温晶化动力学行为。在非等温过程中,采用不同方法(Kissinger,Flynn-Wall-Ozawa和Augis-Bennett)得到的Zr55Cu30Ni5Al10大块金属玻璃平均激活能彼此之间吻合很好。此外,采用Johnson-Mehl-Avrami(JMA)模型描述Zr55Cu30Ni5Al10大块金属玻璃的等温转变动力学。研究结果表明:Zr55Cu30Ni5Al10大块金属玻璃的Avrami指数n介于2.2和2.9之间,表明其晶化机制主要是扩散控制过程。在等温晶化的过程中,晶核长大主要是三维的长程有序扩散控制的过程,平均激活能为469kJ/mol。     

Co基非晶软磁合金的制备与晶化动力学行为研究

采用旋铸急冷工艺在大气环境中制备出Co6.85Fe4Si10B17.5非晶合金带材.XRD分析表明:样品为完全非晶.用DiamondTG/DTA差热分析仪在高纯氩气保护下测量了非晶薄带的等温晶化动力学曲线.采用JMA方程计算出了合金的晶化动力学参数,在不同的晶化温度下,Avrami指数的值在2.11～2.58之间,晶化激活能Ec为113.67 kJ/mol.Co6.85Fe4Si10B17.5非晶合金的晶化方式是初晶型(761、791、803 K)和共晶型晶化(813 K),合金的晶化百分比与退火时间的关系曲线均为S型曲线.     

Kinetics of nanoscale precipitation in Ni-Fe-Al alloys: A magnetic monitoring approach

In this study, time-temperature dependence and kinetic aspects of nanoscale precipitation responsible for strengthening of Ni₅₀Fe_xAl_50−x alloys with x = 20, 25 and 30 were investigated by temperature-scan and isothermal magnetic measurements in a vibrating sample magnetometer. Temperature-scan magnetization curves contained a magnetization rise for all studied alloys at temperatures above the Curie transition of the primary phase. These transient rises at relatively higher temperatures were associated with the formation of secondary ferromagnetic precipitates, identified as nano-sized body centered cubic α crystallites by microstructural observations under the transmission electron microscope. The isothermal kinetics of ferromagnetic α-phase precipitation was analyzed with the Johnson-Mehl-Avrami model. The Avrami exponent was determined to be close to unity and independent of the extent of precipitation, annealing temperature and alloy composition. It was concluded that α-phase precipitation was governed by a diffusion controlled growth process with decreasing growth rate, which closely resembles continuous precipitation kinetics. The activation energies, ranging between 75 and 83 kJ/mol, were utilized to construct magnetically assessed isothermal transformation diagrams of precipitation. Conforming to the kinetic analysis, annealing at an intermediate temperature ensures precipitation of fine second phase particles and brings about a significant hardening effect, whereas a higher annealing temperature yields coarser precipitates and a smaller extent of precipitation hardening.     

Non-Equilibrium Grain-Boundary Segregation of Phosphorus And the Effective Time in Step Cooling Process

The non-equilibrium grain-boundary segregation of phosphorus in step cooling process in an industrial steel,12CrlMoV, is studied based on the effective-time-method and compared with that in isothermal holding process. The non-equilibrium grain-boundary segregation concentration of phosphorus was measured with Auger Electron Spectroscopy (AES) and calculated based on the kinetic equations of non-equilibrium grain-boundary segregation. Results show that the calculated result is in good accordance with the experimental observation.     

Effects of quenching conditions on crystallization behavior of amorphous Al90Ni5Ce5 alloys

X-ray diffraction and DSC were used to investigate the crystallization behavior of amorphous Al90Ni5Ce5 alloys at different quenching temperatures.All the amorphous Al90Ni5Ce5 alloys quenched at different temperatures crystallize by two stages.The first stage corresponds to FCC Al phase precipitating from the amorphous matrix.The crystallization onset temperature increases with increasing quenching temperature.The quenching temperature also influences the isothermal behaviors.At low quenching temperatures,the FCC Al precipitation is only through grain growth.At high quenching temperatures,the FCC Al precipitation is through growth of quenched-in Al unclei and nucleation and growth of new crystallites.The reason that the crystallization onset temperature varies with quenching temperature is likely as that the quenched-in Al nuclei decreases with increasing temperature.     

二元合金激光快速熔凝过程的非Fourier模型

基于非Fourier定律，建立了脉冲激光加热条件下单相二元合金表面快速重熔和凝固过程的非平衡传热传质模型，并根据碰撞理论和Aziz的连续生长模型处理固／液界面，以解释快速熔凝过程界面动力学的非平衡效应，快速熔凝问题是涉及热质传输的移动界面问题，通过二阶精度的Von Neumann隐式差分格式和界面跟踪方法进行过程模型的数值求解。应用该模型，分析了Al-Cu二元合金的激光表面熔凝过程，结果表明，激光的高能量密度和非平衡界面动力学所引起的熔化过程和凝固过冷对于快速熔凝过程的影响很大，在快速熔凝过程中，界面速度的变化很大，且因基底材料和热流大小而不同，通过计算获得了界面温度，速度、溶质浓度及非平衡分配系数随界面位置的变化，结果显示，在凝固过程中界面速度和界面溶质浓度都存在着很大的波动。     

钒、钛元素对Fe-C合金等温转变动力学和形成组织的影响

研究了含钒、钛元素的Ｆｅ－Ｃ合金等温转变动力学和组织转变。等温相变时,铁素体以激发形核方式成核,以扩散型的台阶侧向生长而长大,岛状组织（Ｍ＋Ａ）是中间相变产物,最终产物为铁素体与碳化物。分析了钒、钛元素的碳（氮）化物析出的相形貌、结构和化学组成的关系,提出了碳（氮）化物析出相的在奥氏呈立方形态析出,在铁素体中呈片状形态析出,延长等温转变时间、上两种碳（氮）化物发生球化。讨论了硅、锰元素对Ｆｅ－Ｃ合     

最大熵产生原理在非平衡凝固中应用

近年来,最大熵产生原理在物理、化学、生物等领域得到广泛应用,被认为是描述非平衡体系演化的普适性原理;其核心思想是孤立非平衡耗散体系演化总是选择最短路径,以使体系尽可能快地向平衡态演化。非平衡凝固技术在工业生产中应用日益广泛,凝固理论研究却仍集中于近平衡过程;最大熵产生率原理在非平衡凝固中的应用,可推动非平衡凝固理论的发展,进而促进凝固理论的工业应用。总结了近年来最大熵产生原理在非平衡凝固中的应用,包括二元合金非平衡凝固界面动力学模型及多相场模型、多元合金非平衡凝固界面动力学模型、平界面稳定性分析及自由枝晶生长模型。对建立这些模型的热力学过程和相应的数学方法进行了详尽的描述。最后对最大熵产生原理的研究前景进行了展望。     

加热工艺对AZ91D镁合金部分重熔组织的影响

提出半固态金属坯料先在液相线以上温度适当加热再降低温度至两相区温度继续等温保温的二次加热工艺。采用该工艺对晶粒细化AZ91D镁合金坯料进行部分重熔,研究了其组织演变规律,并与等温二次加热工艺进行比较。结果表明,与等温二次加热工艺相比,坯料先在液相线以上温度适当加热再降低温度至两相区温度继续保温,坯料重熔速度明显加快,相同加热时间时,晶粒更加细小和圆整。组织演变机理分析表明,加快液相形成速度可适当抑制晶粒的合并,降低晶粒长大速度,并促进晶粒球化。     

晶界非平衡偏聚研究的回顾与展望

溶质晶界非平衡偏聚现象已在大量合金系中发现,它对材料的性能,相转变、界面化学。界面结构及运动均有重要影响。本文综述了连续冷却与高速淬火等温过程静止晶界上溶质非平衡偏聚研究已获得的主要实验规律,分析评述了已有的主要理论模型,讨论了当前存在的问题。同时还评述了近年来移动界面溶质反常偏聚研究的实验研究和理论研究现状。     

Degradation kinetics at 650 °C and lifetime prediction of Ni2Al3/Ni hybrid coating for protection against high temperature oxidation of creep resistant ferritic steels

The degradation kinetics of the Ni₂Al₃/Ni hybrid coating formed on creep resistant ferritic steel is studied by prolonged isothermal annealing experiments at 650 °C. The sequence of formation and subsequent consumption of all the intermediate phase layers are determined by intermittent analysis of the specimen at various annealing intervals. It is shown that the Ni₅Al₃ phase layer starts to form only when the outer Ni₂Al₃ phase layer is completely consumed and the growth kinetics of each of the intermediate layers differs from that of its subsequent consumption. A model is subsequently formulated to predict the lifetime of the coating studied.