掺碲InSb单晶的垂直温度梯度凝固生长法研究

本工作成功地建立一套垂直温度梯度凝固晶体生长设备，并在无氢气的气氛下生长了掺碲ＩｎＳｂ体单晶。通过霍尔效应、原子吸收谱和腐蚀等方法对掺碲ＩｎＳｂ晶体中的缺陷在宏观、微尺度上的分布进行分析。研究结果表明，在宏观尺度上碲杂质沿生长方向的分布与准静态生长的溶质分布接近，在微尺度上缺陷分布均匀，无观察到生长条纹。

反向凝固法制备复合不锈钢带时复合层凝固生长规律

试验用反向凝固工艺制备复合不锈钢带。讨论了复合层厚度与反向凝固工艺参数之间关系。研究结果表明 ,随母带厚度增加 ,复合层的初始增长速率、复合层的最大厚度增加 ,但增长幅度随之降低。在相同的过热度下不同钢种的复合层凝固生长规律也不同。

基于格子波尔兹曼法的热障陶瓷涂层凝固生长过程模拟

热障涂层(TBCs)在使用过程中表面陶瓷层的脱落是影响其使用寿命的关键,针对以上问题,建立了凝固生长过程流动及传热传质模型,用格子波尔兹曼法(LBM)研究了涂层凝固生长过程。结果显示:不考虑对流影响时,晶体生长的形貌呈现对称十字枝晶形状;在考虑对流的情况下,迎流部分生长快,背流部分生长受到抑制。在大的过冷度影响下,晶界出现波动,出现二次枝晶生长。等离子喷涂涂层在温度梯度下朝向正温度梯度方向呈柱状晶生长。枝晶生长受到对流的影响和侧向温度梯度的影响。迎流方向和大温度梯度方向枝晶形貌发达,背流方向和小温度梯度处枝晶生长受到抑制。

反向凝固连铸碳素钢铸带中新相层的凝固生长规律

在实验室条件下，采用碳素钢板为母带，以08Al低碳钢为新相层材料，对反向凝固连铸薄带工艺过程中新相层在母带表面上凝固生长的规律进行了详细研究。研究表明，母带在钢液中的浸渍时间、母带厚度、钢液过热度对新相层厚度有显著影响，各个工艺参数间存在交互作用；新相层的变化经历“快速生长”、“平衡相持”和“迅速回熔”三个阶段，这三个阶段在新相层厚度－浸渍时间图上显示出“∩”形特征曲线；较低的钢液温度和较厚的母带可促使新相层厚度增加。

定向凝固生长对Ni-Mn-Ga-RE(RE=Tb,Sm)合金磁感生应变的影响

采用定向凝固技术制备多晶合金 ,使合金获得择优取向 ,并研究这种择优取向对磁感生应变的影响 .研究结果表明 ,多晶Ni Mn Ga RE(RE =Tb ,Sm)合金定向凝固生长以后 ,在一定晶体学方向上发生择优取向 ,可以显著提高合金的磁感生应变值 .在同等大小的磁场下 ,定向凝固试样的磁感生应变值比铸态试样的应变值高出很多 ,特别是在高磁场下 (>0 5T) ,定向凝固试样的磁感生应变值约为相同成分的铸态试样的 2倍 .所以 ,定向凝固工艺是制备具有择优取向晶体并获得大磁感生应变的一种有效方法 .

反向凝固薄带的凝固层生长规律与焊合状况的研究

研究了母带厚度、钢液过热度、浸渍时间等工艺参数对薄带凝固层厚度的影响规律。认为母带与凝固层之间良好焊合的前提是母带表面产生部分熔化，并获得了焊合的最佳工艺条件。

课程思政在《晶体生长与凝固技术》中的实践与探索

该文反思了以往《晶体生长与凝固技术》的授课方式,结合习近平总书记在全国高校思想政治工作会议和学校思想政治理论课教师座谈会上的重要讲话,对该课程思政建设进行了教学探讨。以立德树人为总目标,探讨了晶体生长与祖国发展、民族命运相联系的教学模式,实现"润思政"于无声,在传授相关专业知识的同时,与思想政治理论课同向同行,形成协同效应,培养社会主义事业的合格建设者和可靠接班人。

Growth mechanism of primary silicon in cast hypoeutectic Al-Si alloys

The microstructural features of hypoeutectic AI-10%Si alloy were observed using optical microscopy and electron backscatter diffraction. The results show that primary silicon particles are frequently found in hypoeutectic alloys. Hence, the nucleation and growth mechanisms of the precipitation of primary silicon of hypoeutectic Al-10%Si alloy melts were investigated. It was discovered that Si atoms are easy to segregate and form Si-Si clusters, which results in the formation of primary silicon even in eutectic or hypoeutectic Al-Si alloys. In addition, solute redistribution caused by chemical driving force and large pile-ups or micro-segregation of the solute play an important role in the formation of the primary silicon, and the solute redistribution equations were derived from Jackson-Chalmers equations. Once Si solute concentration exceeds eutectic composition, primary silicon precipitates are formed at the front of solid/liquid interface.

Effect of growth rate and diameter on microstructure and hardness of directionally solidified Ti-46Al-8Nb alloy

Bridgman-type directional solidification experiments were conducted for Ti-46Al-8Nb （mole fraction, %） alloy. The effects of the growth rate and the diameter on the microstructure, phase transition and hardness of the alloy were investigated. The results show that with the increase of the growth rate and the decrease of the diameter, the fullyβphase solidification changes to the peritectic solidification, and the final microstructure is composed of theα2/γlamellar structure and a multiphase microstructure （B2 phase,α2/γlamellar structure） respectively, which can be attributed to the solute enrichment resulting from the decreasing diffusion and convection ability. The occurrence of peritectic reaction at high growth rate promotes the solute segregation heavily and the coarse lamellar spacing in Al-and Nb-rich region, which greatly decreases the hardness values and leads to the discontinuity of the hardness curves with the increase of the growth rate. Comparatively, the Ti-46Al-8Nb alloy has lower hardness values than the other applied TiAl-based alloys in previous studies.

Microstructure and crystal growth direction of Al-Cu alloy

The microstructures and crystal growth directions of permanent mould casting（PMC） and directionally solidified（DS） Al-Cu alloys with different contents of Cu were investigated. Simultaneously, the effects of pouring temperature on the microstructure and crystal growth direction of permanent mould casting pure Al were also discussed. The results indicate that the α（Al） crystals in the pure Al do not always keep common columnar grains, but change from the columnar grains to columnar dendrites with developed arms as the pouring temperature rises. The growth direction also varies with the change of pouring temperature. Cu element has similar effects on the microstructures of the PMC and DS casting Al-Cu alloys and the α（Al） crystals gradually change from columnar crystals in turn to columnar dendrites and developed equiaxed dendrites as the Cu content increases. The crystal growth direction in the PMC alloys gradually approaches （110） orientation with increasing Cu content. But the resulting crystals with growth direction of （110） do not belong to feathery grains. There are also no feathery grains to form in all of the DS Al-Cu alloys.

Phase-field simulations of forced flow effect on dendritic growth perpendicular to flow

The effect of supercooled melt forced laminar flow at low Reynolds Number on dendritic growth perpendicular to melt flow direction was investigated with the phase-field method by incorporating melt convection and thermal noise under non-isothermal condition. By taking the dendritic growth of high pure succinonitrile （SCN） supercooled melt as an example, side-branching shape difference of melts with flow and without flow was analyzed. Relationships among supercooled melt inflow velocity, deflexion angle of dendritic arm and dendritic tip growth velocity were studied. Results show that the melt inflow velocity has few effects on the dendritic tip growth velocity. A formula of relationship between the velocity of the melt in front of primary dendritic tip and the dendritic growth time was deduced, and the calculated result was in quantitative agreement with the simulation result.

Directional solidification and characterization of NiAl-9Mo eutectic alloy

Ni-45.5Al-9Mo （mole fraction,%） alloy was directionally solidified with a constant temperature gradient （GL=334 K/cm） and growth rates ranging from 2 to 300 μm/s using a Bridgman type crystal growing facility with liquid metal cooling （LMC） technique. The effect of growth rate （v） on the solidified microstructures such as rod spacing （λ）, rod size （d） and rod volume fraction was experimentally investigated. Two types of the solidified interfaces, planar and cellular, were identified. On the condition of both planar and cellular eutectic microstructures, the relationships between λ, d and v were given as： λv1/2=5.90 μm·μm1/2·s1/2 and dv1/2=2.18μm·μm1/2·s1/2, respectively. It was observed that the volume fraction of Mo phase could be adjusted in a certain range. The variation of phase volume fraction was attributed to undercooling increase and the growth characteristics of the individual constituent phases during the eutectic growth.

重轨钢大方坯连铸过程中凝固传热和坯壳生长的数值模拟

采用有限元方法,对某钢厂的大方坯连铸机的凝固传热情况以及坯壳凝固生长进行了数值模拟,并通过现场数据对模型进行了验证。以此为依据,对该钢厂新建的重轨钢大方坯在不同的拉速和过热度条件下的凝固过程温度场分布情况、坯壳生长规律和凝固分率进行了预测性的模拟研究,从而为新建的重轨钢大方坯连铸机的结晶器和二冷区冷却制度的制定提供理论依据。

Simulation and experimental validation of three-dimensional dendrite growth

A three-dimensional （3-D） modified cellular automaton （MCA） method was developed for simulating the dendrite morphology of cubic system alloys. Two-dimensional （2-D） equations of growth velocities of the dendrite tip, interface curvature and anisotropy of the surface energy were extended to 3-D system in the model. Therefore, the model was able to describe the morphology evolution of 3-D dendrites. Then, the model was applied to simulate the mechanism of spacing adjustment for 3-D columnar dendrite growth, and the competitive growth of columnar dendrites with different preferred growth orientations under constant temperature gradient and pulling velocity. Directional solidification experiments of NH4Cl-H2O transparent alloy were performed. It was found that the simulated results compared well with the experimental results. Therefore, the model was reliable for simulating the 3-D dendrite growth of cubic system alloys.

Phase-field simulation of forced flow effect on random preferred growth direction of multiple grains

The random distribution problem of dendrite preferred growth direction was settled by random grid method.This method was used to study the influence of forced laminar flow effect on multiple grains during solidification.Taking high pure succinonitrile （SCN） undercooled melt as an example,the forced laminar flow effect on multiple grains was studied by phase-field model of single grain which coupled with flow equations at non-isothermal condition.The simulation results show that the random grid method can reasonably settle the problem of random distribution and is more effective.When the solid fraction is relatively low,melt particles flow around the downstream side of dendrite,and the flow velocity between two dendrite arms becomes high.At the stage of solidification time less than 1800Δt,every dendrite grows freely;the upstream dendrites are stronger than the downstream ones.The higher the melt flow rate,the higher the solid fraction.However,when the solid fraction is relatively high,the dendrite arm intertwins and only a little residual melt which is not encapsulated can flow;the solid fraction will gradually tend to equal to solid fraction of melt without flow.

Effect of growth rate on microstructure and solute distribution of Al-Zn-Mg alloy

An Al-5.3%Zn-5.3%Mg alloy was unidirectionally solidified to determine morphological transition and solute distribution by a modification of the Bridgman technique for crystal growth with growth rates ranging from 4-500 μm/s and a temperature gradient of 25 K/cm. It was determined that growth rates from 6.5-9.5 μm/s generated a cell morphology, where the lower limit corresponds to the plane front to cellular transition and the upper limit indicates the cellular to columnar dendrite transition. The microstructures of the alloys solidified from 30 μm/s to growth rates less than 500 μm/s were mainly composed of columnar dendrites, while the microstructures solidified at growth rates greater than 500 μm/s were equiaxed. Regarding experimental results on solute distribution, a prediction of the model developed by Rappaz and Boettinger for dendrite solidification of multicomponent alloys was applied with excellent agreement. Results of solute distribution were employed to derive the precipitation fraction of τ-phase needed to increase the electrochemical properties of the alloy to be used as an Al-sacrificial anode.

Numerical simulation of dendrite growth in Ni-based superalloy casting during directional solidification process

An understanding of dendrite growth is required in order to improve the properties of castings. For this reason, cellular automaton-finite difference(CA-FD) method was used to investigate the dendrite growth during directional solidification(DS)process. The solute diffusion model combined with macro temperature field model was established for predicting the dendrite growth behavior. Model validation was performed by the DS experiment, and the cooling curves and grain structures obtained by the experiment presented a reasonable agreement with the simulation results. The competitive growth of dendrites was also simulated by the proposed model, and the competitive behavior of dendrites with different misalignment angles was also discussed in detail.Subsequently, 3D dendrites growth was also investigated by experiment and simulation, and both were in good accordance. The influence on dendrites growth of initial nucleus was investigated by three simulation cases, and the results showed that the initial nuclei just had an effect on the initial growth stage of columnar dendrites, but had little influence on the final dendritic morphology and the primary dendrite arm spacing.

Formation of twinned dendrites during unidirectional solidification of Al-32%Zn alloy

The present study focused on the formation and crystallographic orientation of twinned dendrites coexisting with equiaxed grains in unidirectional solidification of Al-32%Zn(mass fraction)alloy.The morphology was investigated by optical metallograph and electron back-scattered diffraction technique.Results showed that the macrostructure of the alloy exhibited a typical feathery and fan-like structure while the microstructures were elongated lamellas,which were separated by coherent and incoherent twin boundaries.Both the primary trunk and all lateral arms of twinned dendrites grew along〈110〉directions,unlike regular〈100〉α(Al)dendrites.The facet growth of crystals at solid/liquid interface was responsible for the origin of twinned dendrites during the weak local convection,and high thermal gradient and medium solidification velocity had significant contribution to the formation of twinned dendrites.The formation mechanism of twinned dendrites which consisted of three multiplication ways of new twin boundaries formation and one way of dendrite evolution in twin plane was shown schematically.

Liquid phase separation and subsequent dendritic solidification of ternary Fe_(35)Cu_(35)Si_(30) alloy

Liquid Fe35Cu35Si30alloy has achievedthemaximum undercooling of 328 K （0.24TL） with glass fluxing method, and it displayed triple solidification mechanisms. A critical undercooling of 24 K was determined for metastable liquid phase separation. At lower undercoolings,α-Fe phase was the primary phase and the solidification microstructure appeared as homogeneous well-defined dendrites. When the undercooling exceeded 24 K, the sample segregated into Fe-rich and Cu-rich zones. In the Fe-rich zone, FeSi intermetallic compound was the primary phase within the undercooling regime below 230 K, while Fe5Si3intermetallic compound replaced FeSi phase as the primary phase at larger undercoolings. The growth velocity of FeSi phase increased whereas that ofFe5Si3 phase decreased with increasing undercooling. For the Cu-rich zone, FeSi intermetallic compound was always the primary phase. Energy-dispersive spectrometry analyses showed that the average compositions of separated zones have deviated substantially from the original alloycomposition.

Advances of the Vertical Directional Solidification Technique for the Growth of High Quality GaSb Bulk Crystals

Advantages of the detached phenomena have influenced researchers to modify the conventional methods to promote it on the earth. Since 1994, the vertical directional solidification （VDS） technique has been employed for the growth of bulk crystals, without the seed, without contact to the ampoule wall, without coating and without external pressure. An automated furnace was designed and fabricated for the controlled temperature gradients, growth conditions and parameters. The typical ingots growths of GaSb have shown the gap of 20 μm-145 μm and mobility μn = 1125 cm^2/V.sec at 300 K. Mobility is highest and five times larger than the attached growths. Dislocation density is the order of 104/cm2 in the conical region, decreases in the direction of growth, and in many crystals reached less than 103/cm2. The spontaneous gap formation due to the meniscus depends on the pressure differences and thermal state. GaSb grown ingots have shown progress in the properties of crystal grown ever, and attributed to reduce thermal stress without contact to the ampoule wall.