锭坯双喷嘴扫描喷射成形雾化锥沉积轨迹及其耦合研究

双喷嘴扫描喷射成形是提高生产效率和制备大直径锭坯的主要工艺方式.研究了双喷嘴扫描喷射成形工艺雾化锥扫描沉积轨迹及其耦合产生条件.建立了雾化锥沉积轨迹坐标及扫描沉积区域数学模型,分析了工艺参数对沉积轨迹的影响规律,从理论上推导了沉积轨迹耦合条件.对沉积轨迹模型和耦合特性进行了图形仿真.研究表明:沉积轨迹呈"花瓣"形状,由喷嘴偏心距、初始倾斜角、扫描范围角、喷射高度、扫描频率、沉积盘旋转速度确定.通过喷射成形试验对建立的理论模型和研究结论进行了验证,表明了其正确性.     

喷射成形工艺的理论研究进展

喷射成形是人为地控制凝固条件,经过金属熔体的分散、飞行快速冷却、半固态凝固及锭坯进一步冷却等阶段,得到特殊的锭坯组织的成形过程。沉积锭坯组织是上述四个阶段金属熔体凝固的综合结果。近终形成形是喷射成形技术的另一特点,喷嘴形式、喷嘴数量、沉积器的形状与运动方式影响和决定沉积锭坯的外形。材料的凝固与成形受众多因素影响,很多工艺参数的作用规律尚不明确,因此喷射成形过程的模拟研究十分必要。笔者介绍了目前喷射成形工艺中所涉及的理论问题与相关模型。     

喷射成形过程中圆锭坯外形生长的数值模拟

通过多次试验后得出雾化喷嘴的雾化特性公式,在此基础上建立了一种模拟喷射成形过程中圆锭坯外形生长的数学模型.该数学模型考虑了喷射成形过程中各种工艺参数,如喷嘴的雾化参数、偏心距离、沉积盘的旋转速度和下拉速度等参数的影响.经过模拟计算,得到了锭坯生长的三维外形尺寸,与实际喷射成形制备的锭坯外形对比,二者吻合很好;采用该模型分析了不同时间下锭坯的轮廓形状、偏心距离以及下拉速度变化后的锭坯轮廓形状.综合分析得出,此数学模型可以预测在不同工艺参数下喷射成形锭坯的外形生长过程.     

喷射成型锭坯形状的数值模拟研究

建立了描述喷射成型过程中沉积坯外轮廓动态生长的三维数学模型,该模型考虑了喷射成型过程中各种工艺参数的影响,这些工艺参数包括喷嘴的雾化特性值、偏心距离、沉积盘的旋转速度和下拉速度,在计算后进行数据处理得出了锭坯生长的三维外形轮廓,通过与实际喷射成型设备成形的锭坯对比,两种结果符合较好,并可用此模型来预测不同工艺条件下锭坯的外形生长轮廓。     

喷射成形过共晶AlSi合金锭坯的渐变组织研究

喷射成形是通过控制凝固条件,使金属熔体经过雾化分散、飞行快速冷却、半固态凝固及形成锭坯后进一步冷却等阶段,得到特殊的喷射成形锭坯组织的成形过程.沉积锭坯组织是上述四个阶段金属熔体凝固的综合结果.由于散热条件的不同,沉积锭坯组织形态随沉积位置而变化.本文分析了喷射成形锭坯组织的变化情况和形成原因.     

热挤压对喷射沉积7055铝合金显微组织和力学性能的影响

采用全自动控制往复喷射成形工艺制备工业规格7055铝合金锭坯,研究热挤压工艺对喷射成形7055铝合金的显微组织和力学性能的影响。采用电子背散射衍射技术对经不同热挤压后7055铝合金的织构进行研究。结果表明,喷射沉积锭坯组织为等轴状晶粒,均匀细小(30~50μm),基体中不存在枝晶型偏析。由于喷射沉积工艺本身的特点,在合金中存在大量的显微疏松缺陷。沉积锭坯经过热挤压致密化后,合金力学性能显著提高,抗拉强度σb为390 MPa,伸长率δ为13.3%,表明热挤压工艺可有效消除疏松缺陷,从而充分发挥出喷射沉积工艺的优越性。EBSD分析表明,挤压后沿着挤压轴方向形成丝织构,主要为?001?与?111?两种织构。     

喷射成形Cu-15Ni-8Sn合金的显微组织和性能研究

采用喷射成形技术制备了Cu-15Ni-8Sn(%,质量分数)合金坯锭,利用光学显微镜和扫描电子显微镜观察分析了合金坯锭的微观组织和成分分布;利用拉伸实验测量了坯锭试样的力学性能。结果表明,喷射成形工艺制备的Cu-15Ni-8Sn合金沉积坯底部和中部位置的微观组织存在较大差异,底部微观组织由多相组成,其余部位基本为单相α固溶体;合金中的大量孔洞降低了喷射成形Cu-15Ni-8Sn合金的致密度和力学性能。     

喷射沉积Al-Fe-V-Si系耐热铝合金制备工艺的研究

采用两种不同喷嘴喷射沉积制备了Al-Fe-V-Si系耐热铝合金，并对沉积坯件的热挤压工艺进行了优化，对材料的组织和性能进行了比较。结果表明：采用做扫描运动的非约束式复合喷嘴和G／M为4．3米喷射沉积。沉积坯件具有良好的成形性和高达93％的致密度，通过随后的热挤压可使材料十分接近全致密，其室温下的挤压棒材σb达538MPa。     

喷射成形高钒高速钢环坯制备技术研究

采用喷射成形技术制备高钒高速钢环坯,阐述了喷射成形制备过程方法及工艺参数,制备得到的沉积坯收得率为83.5%。对比观察沉积坯不同位置组织及碳化物形貌,发现:组织均匀细小,碳化物颗粒细小、形状较为规则、分布均匀,合金元素无宏观偏析;孔隙及缺陷主要位于沉积坯与基体的结合界面附近,产生于喷射沉积未完全稳定的试验初期。对热处理后的沉积坯试样进行硬度测试,喷射成形高钒钢淬火硬度为63HRC,高于粉末冶金高钒钢;经过3次回火,硬度逐渐下降,未出现二次硬化现象。     

喷射成形GH742y合金的组织和性能

研究了喷射成形GH742y合金沉积坯的组织和性能以及热变形特性.研究结果表明,氮气雾化喷射成形GH742y合金沉积坯整体致密、成分均匀、无宏观偏析、组织细化、氧含量低,而且具有较好的力学性能,其主要力学性能超过技术指标的要求.同时,由于晶粒细小均匀,所以该合金具有较好的热变形性能.     

喷雾阀嘴多步成形有限元分析

喷雾阀嘴是喷雾罐的关键部件,其成形过程复杂、难度较大。采用三维光学扫描仪检测喷雾阀嘴各步成形件的三维尺寸,推导模具方案进行逆向建模。同时采用有限元技术分析喷雾阀嘴成形过程特点,探索材料性能对其成形质量的影响。结果表明,模型实现了精确分析喷雾阀嘴复杂的多步成形过程,可分析喷雾阀嘴任一时刻、任一位置的成形状态和成形质量状况。同时得出,MR T3-BA材料或比其屈服强度更高的材料容易出现成形质量问题。     

Spray Forming of Bulk Ultrafine-Grained Al-Fe-Cr-Ti

An Al-2.7Fe-1.9Cr-1.8Ti alloy has been spray formed in bulk and the microstructure and properties compared with those of similar alloys produced by casting, powder aomization (PA), and mechanical alloying (MA) routes. In PA and MA routes, a nanoscale metastable icosahedral phase is usually formed and is known to confer high tensile strength. Unlike previous studies of the spray forming of similar Al-based metastable phase containing alloys that were restricted to small billets with high porosity, standard spray forming conditions were used here to produce a ~98 pct dense 19-kg billet that was hot isostatically pressed (“HIPed”), forged, and/or extruded. The microstructure has been investigated at all stages of processing using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and synchrotron X-ray diffraction (XRD) at the Diamond Light Source. Consistent with the relatively low cooling rate in spray forming under standard conditions, the microstructure showed no compelling evidence for the formation of metastable icosahedral phases. Nonetheless, after downstream processing, the spray-formed mechanical properties as a function of temperature were very similar to both PA rapid solidification (RS) materials and those made by MA. These aspects have been rationalized in terms of the typical phases, defects, and residual strains produced in each process route.     

喷射成形高合金工具钢的组织与力学性能

采用喷射成形工艺制备了高合金工模具钢,对沉积坯进行了热锻致密化处理和淬火+回火热处理.对比分析了喷射沉积态合金和电渣重熔态合金的组织形态和力学性能.结果表明:喷射成形材料晶粒组织为均匀细小的等轴晶,碳化物细小且弥散分布,有效解决熔铸态合金热锻后仍无法完全消除的成份偏析和粗大网状碳化物的问题.由于喷射沉积态材料具有良好的组织形态,使得喷射沉积态的强度和冲击韧性比电渣重熔态分别提高了40%和18%.由于喷射沉积态材料中非金属夹杂物的影响,使得材料的冲击韧性值偏低,有待进一步优化工艺,减少夹杂物的含量,提高材料的力学性能.     

Control of Equiaxed Crystal Ratio of High Carbon Steel Billets by Circular Seam Cooling Nozzle

 A circular seam cooling nozzle and its online control system have been developed to reduce the center segregation in high carbon steel billets by decreasing the superheat of the molten steel and improving the equiaxed crystal ratio based on the numerical results. An industrial experiment has been carried out on a 150 mm×150 mm caster to investigate the effect of the circular seam cooling nozzle on the superheat removal of the molten steel. The results show that the circular seam cooling nozzle can be used to control the casting temperature in a closed loop control system. The online control system can be effectively adapted to the variation of operating parameters. The casting lasts about 4 h and about 400 t steel is successfully produced in a continuous operation. The removal of about 14 ℃ superheat and the improvement of approximate 10% equiaxed crystal ratio can be achieved by the newly developed circular seam cooling nozzle.     

A three-dimensional model of the spray forming method

A three-dimensional model has been formulated to calculate the shape of the general preform, using vector calculus. The shape of a rod, tube, plate, or irregular preform can be calculated at given spray forming conditions. The shape of a spray-formed rod was analyzed at various spray forming conditions using the three-dimensional model. The effects of spray forming parameters, such as spray distribution parameters, angular velocity of rotation, withdrawal velocity, spray angle, and eccentric distance on rod shape, were analyzed. The most important parameters affecting the shape of rods are the spray distribution parameters and the withdrawal velocity. The dynamic evolution of rod shape with a stepwise variation of the withdrawal velocity during spray forming was investigated. The effect of a stepwise change of the withdrawal velocity was the same as that of the scanning atomizer. The calculated surface profiles were compared with those of spray-formed 7075 aluminum alloy rods prepared on a pilot scale. The calculated results for the surface profiles were in agreement with those of the spray-formed rods.     

直流等离子喷枪的研究现状及发展趋势

直流等离子喷枪是等离子喷涂系统中最为核心的部件,决定了粒子的熔融软化沉积效果和涂层性能。总结 了阴极、阳极 ( 喷嘴 ) 和气体分配环等关键部件的结构特征对等离子射流的影响。进一步介绍了直流等离子喷枪 的结构优化发展,重点从等离子体射流稳定性和涂层沉积效率提升等角度进行阐述,介绍了级联等离子喷枪对射 流稳定性的优化,以及送粉方式对涂层沉积效率的提升,并展望了未来的发展趋势。     

The selection of the spray deposition rate during the spray rolling process

This article presents a detailed theoretical analysis of the selection of the maximum and minimum spray deposition rates under steady-state conditions during the spray-rolling process. The following predictions are made on the basis of the preceding theoretical analysis. First, the key factor that may control the minimum spray deposition rate is either the removal of porosity or the removal of prior droplet boundaries. With an increase in initial liquid fraction at the deposit/roll interfaces, the mechanism changes from the former to the latter. Second, the mechanism that controls the maximum spray deposition rate is related to either the drag-in angle or the distance between the nozzle and the deposited material’s surface. With an increase in roll diameter or a decrease in distance between the nozzle and the roll-axis plane, the controlling mechanism is changed from the former to the latter. Third, both the calculated maximum and minimum spray deposition rates markedly increase with an increase in roll diameter and roll rotational frequency. In addition, the present theoretical analysis suggests that spray rolling can be optimized to manufacture strips with a high production rate.     

Microstructural features and heat flow analysis of atomized and spray-formed Al-Fe-V-Si alloy

Microstructural features of rapidly solidified powders and preforms of Al₈₀Fe₁₀V₄Si₆ alloy produced by spray forming process have been studied. The atomization and spray deposition were carried out using a confined gas atomization process and the microstructural features were characterized using scanning electron microscopy and transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The microstructure of a wide size range of atomized powders invariably revealed cellular and dendritic morphology. The extent of dendritic region and the dendritic arm spacing were observed to increase with powder particle size. The TEM investigations indicated the presence of ultrafine second-phase particles in the intercellular or interdendritic regions. In contrast, the spray deposits of the alloy showed considerable variation in microstructure and size and dispersion of the second-phase particles at specific distances from the deposit-substrate interface and the exterior regions of the deposit. Nevertheless, considerable homogeneity was observed in the microstructure toward the center of the spray deposit. The formation and distribution of a cubic phase α-Al(Fe,V)Si has been characterized in both atomized powders and spray deposits. A one-dimensional heat flow model has been used to analyze the evolution of microstructure during atomization and also during spray deposition processing of this alloy. The results indicate that thermal history of droplets in the spray on deposition surface and their solidification behavior considerably influence the micro-structural features of the spray deposits.     

Modeling and Simulation of Spray Forming of Clad Deposits with Graded Interface Using Two Scanning Gas Atomizers

A three-dimensional shape model based on a surface coordinate tracking method has been developed for clad deposits with graded interface which are spray formed using two scanning gas atomizers. The calculation of element distributions in the deposits has been incorporated into the shape model. On this basis, the deposit shape and the element distributions in the deposit have been simulated. It shows that the scanning mode of the atomizers and the degree of overlapping of the two sprays play important roles in the spray forming of clad deposits. A concentration gradient of chemical elements in the deposits can be achieved under proper processing conditions. Finally, the modeling and simulation of the spray forming of clad deposits have been validated by experimental investigations.