熔体过热处理技术及其在镍基高温合金中的应用研究进展

镍基高温合金是先进航空发动机高温叶片不可或缺的关键核心材料,目前通过合金化来提高其承温能力已趋于极限。研究表明,材料熔体结构对合金凝固过程、凝固组织、性能以及成形质量具有重要的影响。熔体结构的变化能够直接导致熔体特性发生改变,进而对性能产生影响,然而在实际合金的制备过程中,熔体结构的作用通常被忽略。熔体过热处理技术通过利用合金熔体的遗传效应,将高温熔体的结构保留到低温熔体,从而大幅提高合金性能。系统介绍了熔体过热的原理、主要处理技术以及如何通过X射线衍射和物性参数测量来确定熔体过热处理参数,重点介绍了熔体过热处理技术在优化高温合金凝固组织和提升性能方面的应用,最后提出了熔体过热处理技术发展的方向和面临的挑战。     

过热处理细化亚共晶Al-7%Si合金的定量研究

在实验的基础上,运用定量金相和数理统计的方法,定量研究了过热处理细化亚共晶Al-7%Si合金的规律.通过对这些规律进行回归分析,得到相应的回归方程.方程分析表明,仅通过熔体过热处理这一因素,理论上能细化晶粒最小到20.0944μm.这一数据对熔体处理的工艺制定和熔体结构的研究有重要的意义.     

熔体过热对镍基高温合金凝固组织及性能的影响研究

基于对镍基高温合金熔体结构的认识,选择合适的熔体过热温度、过热时间和浇注温度,熔体过热处理可有效改善镍基高温合金的凝固组织并提高合金的力学性能.本文介绍了国内外熔体过热对镍基高温合金凝固组织及力学性能的研究进展.     

过热合金熔体的几种物性滞后效应

过热处理的合金熔体会使熔体结构状态发生不可逆变化。这种不可逆变化与合金熔体中结构不均匀性有关 ,即熔体过热处理引起非均匀形核中心数量的不可逆变化 ,导致熔体粘滞性 η和溶质扩散系数DL 出现滞后效应     

过热合金熔体的几种物性滞后效应

过热处理的合金熔体会使熔体结构状态发生不可逆变化，。这种不可逆变化与合金熔体中的结构不均匀性有关，即熔体过热处理引起非均匀形核中心数量的不可逆变化，导致熔体粘滞性η和熔质扩散系数DL出现滞后效应。     

铌-硅基超高温合金定向凝固及相组成的热力学研究进展

铌-硅基超高温合金作为有望在1200℃以上温度使用的结构材料而受到广泛研究。综述了铌-硅基超高温合金中合金化元素的作用以及熔体过热处理技术在该合金定向凝固中的应用,并评述了对铌-硅基多元合金相组成等的热力学研究进展。     

熔铸工艺对DZ417G合金组织性能的影响

为了分析熔铸工艺对DZ417G合金组织性能的影响,通过对DZ417G合金采取常规浇注(1 560℃高温精炼5~7 s普通定向凝固)、炉前经不同温度高温熔体过热处理后,以不同的拉晶速率定向凝固等7种不同工艺方案对其化学成分、组织及力学性能进行了研究.结果表明:合金经1 600~1 620℃高温熔体过热处理后,以6.0~7.0 mm/min不同的拉晶速率定向凝固,碳化物、硼化物明显变小,在晶内、晶界上呈弥散状态分布;晶界上的低熔点(!+!’)共晶组织有所减少甚至消失,晶内!’强化相进一步弥散、方形化,柱状晶生长状态、枝晶间咬合好,从而能获得良好的力学性能.     

立式离心场下钛合金熔体充填过程数值模拟

本文通过数值模拟方式研究了不同铸造工艺参数对立式离心场下钛合金熔体充填过程的影响,数值模拟结果显示铸型旋转方向直接影响合金熔体的充填顺序,进而影响其凝固顺序及缺陷形成.在给定的转速范围内,钛合金熔体的充填时间随铸型转速的增加而减小,因此,转速的增加有利于加快合金熔体充填速度,使合金熔体在较短的时间内迅速充填型腔.同时熔体的过热度及铸型温度的增加有利于合金熔体的快速充填.     

熔体过热对Sb-Bi合金凝固组织的影响

以Sb-4.6%Bi合金为研究对象,在限定其它因素保持不变的情况下,考察了熔体过热温度对凝固过程的影响。,实验结果发现,随着熔体过热温度的提高,合金形过冷度增大,凝固组织显著细化,研究表明,熔体过冷倾向是熔体结构状态的一个必然反映,熔体结构状态随温度发生变化是导致合金结晶过冷度发生明显的变化的原因,随着过热温度的提高,Sb-4.6%Bi合金晶粒显著细化,其原因是经过热处理的合金熔体在较大的过冷度下凝固。     

定向凝固过程中温度参数对含Re镍基单晶高温合金铸态组织的影响

研究了一种含Re为4.0%～5.5%(质量分数)的实验型镍基单晶高温合金在不同定向凝固结晶条件下铸态的宏微观组织特征,分析了凝固结晶温度参数对单晶完整性、显微疏松与共晶含量、枝晶偏析等的影响。结果表明:高的熔体过热处理温度不仅促进合金元素分布的均匀化,同时降低了高Re和高难熔元素含量的单晶合金结晶缺陷的倾向性,提高了单晶完整性。合金熔体过热温度、铸型温度/浇注温度的适度提高有利于枝晶间的补缩,并减少显微疏松。     

Effect of Process Parameters on Porosity in Aluminum Lost Foam Process

1.IntroductionLost foam casting process is still a new technology,and is gaining confidence among manufacturers[1].It isexpected to dramatically improve the competitiveness ofthe foundry industry.Many advantages like eliminatingmachining steps,making complex casting without coresand reducing environmental loads can be offered by thisprocess,because molding binder is not added into themold of the lost foam process.Aluminum alloy castings are widely used in the auto-mobile and aerospace industri…     

补加合金成分对铝合金熔体直接氧化生长的影响

为了控制DIMOX工艺中复合材料的生长速度和体积,采用压差法补加合金,使剩余铝合金熔体的成分得到调整并与正在氧化生长的Al₂O₃/Al复合材料层保持连续接触。试验研究了补加合金成分对Al-3Mg-10Si合金氧化生长的影响作用。结果表明:补加纯Al或低Mg、Si含量的铝合金,能够降低合金熔体的含镁量,缩短材料生长前沿合金熔体成分到达Al₂O₃-(Al,Mg)两相区的时间,促进传质过程,加速材料生长,有利于获取较大体积的复合材料。     

Influence of boron on the microstructure and mechanical properties of Al-11.6Si-0.4Mg casting alloy modified with strontium

Abstract

The influence of the addition of Al-1B master alloy on the microstructure and mechanical properties of Al-11.6%Si-0.4%Mg alloy modified with 0.030%Sr has been investigated. The mechanical properties and fracture behaviour of the alloys as cast and after T6 heat treatment with three different melt treatments (no treatment; 0.030%Sr modifying treatment; and 0.030%Sr + 0.028%B combined melt treatment) were also compared. Al-1B master alloy has a strong action in refining the dendritic structure in near eutectic Al-Si casting alloys modified with Sr. The Sr+B combined melt treatment can improve considerably the mechanical properties of the alloys, both as cast and after T6 heat treatment. Fracture modes of the alloys with the Sr modifying treatment and the Sr+B combined melt treatment are typically ductile. However, fractographs indicate that the alloy with combined melt treatment suffered greater ductile deformation before fracture. The Sr+B combined melt treatment significantly improves the mechanical properties of near eutectic Al-Si casting alloys.     

Mathematic modeling of diffusion processes of the formation of rim-core structure at sintering TiC–Ni alloys with alloying carbide additions

Using mathematical modeling the kinetics of the rim-core structure formation of TiC grains in an isothermal liquid-phase sintering of TiC–Ni hard alloy, doped with a transition metal carbide has been investigated. The algorithm that has been used to study the nature of the concentration distribution of the diffusant in a TiC grain allows for the structural characteristics of the alloy; diffusion coefficients of alloying additives in the metal melt and a grain, boundary solubility of the diffusant in the binder, and its concentration in the alloy as well as the sintering temperature and time.     

Behavior of magnesium and silicon in the formation of MgO/AlN composite

MgO/AlN composites have been fabricated by directed metal nitridation of Al–Si alloy in flowing N₂ at 1473 K. A mixture of magnesia particles and chemically pure magnesium powder was placed on the surface of Al–Si alloy block as reinforcement materials. Mg powder initiates the infiltration and nitridation of Al alloy melt by eliminating protective Al₂O₃ film at the reaction frontier. New Mg vapor from the interface reaction between Al and MgO particles, keeps as continuous deoxidization agent as the added Mg powder. The spinel layer thickness due to the reaction of Al melt with MgO particles is controlled by Mg content. Si not only reduces the surface tension and viscosity of Al alloy melt, but also leads to increase in N₂ content.     

Dealloying by metallic melt

Dealloying, which commonly involves corrosion processes in aqueous solutions, is a promising technique for preparing functional nanoporous metals. While this technique is ideal for preparing nanoporous noble metals such as of Au, it is not readily applicable to less-noble metals. Here, we propose a novel dealloying method employing a metallic melt, instead of an aqueous solution, as the dealloying liquid for a preparing of nanoporous metals. An atomic interaction among alloy components and metallic melt causes specific component to dissolve out from the alloy solid into the melt with self-organizing nanoporous structure by the remaining component. The dealloying method can be applied for preparation of nanoporous less-noble metal such as of Ti for the development of functional materials such as fluid filters, gas absorption media, and biomaterials.     

Characterization of fold defects in AZ91D and AE42 magnesium alloy permanent mold castings

Casting premium-quality magnesium alloy components for aerospace and automotive applications poses unique challenges. Magnesium alloys are known to freeze rapidly prior to filling a casting cavity, resulting in misruns and cold shuts. In addition, melt oxidation, solute segregation and turbulent metal flow during casting contribute to the formation of fold defects. In this research, formation of fold defects in AZ91D and AE42 magnesium alloys cast via the permanent mold casting process was investigated. Computer simulations of the casting process predicted the development of a turbulent metal flow in a critical casting region with abrupt geometrical transitions. SEM and light optical microscopy examinations revealed the presence of folds in this region for both alloys. However, each alloy exhibited a unique mechanism responsible for fold formation. In the AZ91D alloy, melt oxidation and velocity gradients in the critical casting region prevented fusion of merging metal front streams. In the AE42 alloy, limited solubility of rare-earth intermetallic compounds in the α-Mg phase resulted in segregation of Al₂RE particles at the leading edge of a metal front and created microstructural inhomogeneity across the fold.     

Preparation and properties of cast aluminium alloy-granite particle composites

With a view to develop light weight, low cost and abrasion resistant material cast aluminium alloy composites dispersed with granite particles were prepared and their properties were evaluated. Natural mineral granite was crushed and treated prior to its incorporation in the aluminium alloy. Liquid metallurgy techniques was used to prepare composites involving the following steps: melting of aluminium alloy in graphite crucible, stirring of the melt, addition of granite particles and reactive metal in the melt and pouring the composite melt into permanent moulds. Physical, mechanical, tribological and metallographic properties of composites were studied. It was observed that there was reasonably uniform dispersion of granite particles in the matrix. Hardness and tribological (abrasive wear) properties of the base alloy improved considerably due to addition of the granite particles into it. This clearly indicates that these cast aluminium alloy based composites can be used as wear resistant materials.     

金属熔体结构及其控制技术的研究进展

综述了国内外在熔体结构研究方面的现状与进展,介绍了通过控制合金熔体的预结晶状态来改善合金组织和性能的相关技术及成果。可以得出:温度和压力可使金属熔体发生液/液结构转变,金属熔体结构随温度的变化存在滞后性,利用熔体结构随温度变化的滞后性可控制合金的凝固过程、明显细化合金的凝固组织、大大提高合金的力学性能。