Effect of melt spinning on grain size and texture in Ni-Mo alloys

Chill block melt spun ribbons of nickel molybdenum alloys with molybdenum contents of 8 to 41.8 wt pct Mo have been examined for their microstructure and texture dependence on processing conditions. Linear features observed in grains solidified with a planar liquid-solid interface at the quench side of the ribbons have been identified to be due to the twins on (111),, plane formed during solidification. Grain size variation with the wheel surface speed and the alloy composition has been studied. Crystallographic texture on quench side and free surface side of the ribbons has been investigated.     

The relationship between grain size and the surface roughening behavior of Al-Mg alloys

The inhomogeneous surface deformation generated during metal forming presents significant challenges to the use of high-strength, lightweight alloys in automotive applications through the initiation of strain localizations that produce both tearing during metal forming and increased friction between mating die surfaces. Thus, a generic understanding of the relationships between plastic strain, grain size, and deformation-induced roughness at the free surface is needed before forming models can be fully developed to accurately predict the behavior and, ultimately, the changes in the friction within the dies. This research examines the roughening behavior of a solid solution strengthened, commercial Al-Mg alloy. The results of this evaluation indicate that the standard roughness measures increase with uniaxial plastic strain in a manner that can be represented by a simple linear estimate. The results also demonstrate that the roughening rate (dR _a/dɛ _pl) is dependent on the grain size in this alloy, and the relationship between the roughening rate and grain size also appears to be linear for the range of grain sizes included in this evaluation. However, examinations of the roughened surfaces reflect that the roughening process is a highly complex combination of mechanisms and it is strongly influenced by grain size. As a result, representing the complex changes that occur during roughening of a free surface by plastic deformation with a single number calculated from profilometry scans may be too coarse of a measure to fully describe these changes when modeling roughness-dependent behavior or properties.     

The effect of penultimate grain size on rolling texture in cu-Sn alloys

The effect of penultimate grain size on the texture of Cu-Sn alloys has been investigated using the modulus method. It was observed that in alloys which exhibited the brass-type texture, the large grained specimens yielded a smaller proportion of textured material than those which were fine grained. In alloys which exhibited transition textures, however, the larger grain size specimens exhibited a greater amount of material residing in the brass-type components. As might be expected, increasing the rolling reduction diminished the effect of penultimate grain size upon rolling. The 50:50 texture transition for 971/2 pct reduction occurred at 0.55 at. pct Sn. Unlike Cu-Zn and Cu-Al alloys, the percentage of brass-type texture reached a maximum at 1.8 at. pct Sn and then decreased for tin contents up to 5.06 at. pct. A self-consistent explanation, based on the “dislocation interaction” hypothesis, has been offered to account for the experimental observations. The present results indicate that the twinning processper se, can actually be detrimental to, rather than promote the formation of the brass-type texture in Cu-Sn alloys.     

The role of grain size and selected microstructural parameters in strengthening fully lamellar TiAl alloys

More than 5 years ago, wrought processing was first used to produce fully lamellar (FL) microstructures in TiAl alloys having grain sizes less than ≈400 μm. These alloys exhibit an improvement in overall balance of properties, especially at high temperatures. More recently, such microstructural forms led to exceptional yield strengths (500 to 1000 MPa at low temperatures) while maintaining attractive high-temperature properties. The improvements appeared to be related to an unusually high apparent sensitivity of strength to grain size. Studies reported an apparent value for the slope of the Hall-Petch (HP) plot approaching 5 MPa√m for FL gamma alloys, while that for single-phase or duplex microstructures is near unity. The present investigations examine the slope of the HP plot for FL microstructures, paying particular attention to the lamellar microstructural variables. Results show that the α ₂ lamellar thickness and spacing and the γ lamellar thickness can vary over more than two orders of magnitude with typical process methods. These spacings influence the value of k _y in the HP (grain size) relationship. Since they often change concomitantly with grain size in processing, they can give rise to a large scatter in the HP plot. The investigations also examine the flow behavior, glide barriers, and slip multiplicity for polysynthetically twinned (PST) crystals (the single-grain analogue of FL material), and then map this behavior into an explanation of the yield behavior of high-strength FL gamma alloys. This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations Committees.     

On the relation between grain size and grain topology

Experimental studies of the topology of grains in polycrystals have indicated that the topological complexity of a grain is related to its diameter, as opposed to its surface area or volume. This paper presents additional experimental documentation of this correlation and a theoretical derivation of the empirically observed relationship.     

Complex grain structure of metals and alloys

An algorithm is derived for the identification of parameters characterizing the complex grain structure of metals and alloys. The analysis of photographs of sample sections confirms the applicability of the algorithm.     

Weibull尺寸分布晶粒组织演变的仿真研究

采用一种改进的Potts模型Monte Carlo算法,对具有Weibull尺寸分布(参数β=3.47)的晶粒组织进行了3D正常晶粒长大过程的仿真研究.仿真结果表明:整个晶粒长大过程遵循抛物线长大规律,晶粒生长指数为0.501,非常接近理论值0.5.晶粒长大过程可分为过渡阶段与准稳态长大两个阶段.Weibull尺寸分布参数β由过渡阶段的3.47逐渐演变为准稳态阶段的2.76,准稳态阶段晶粒尺寸分布参数保持β=2.76不变.晶粒的平均面数〈f〉随仿真时间的增加而增大,在准稳态阶段后期趋近于稳定数值.晶粒面数分布为Lognormal分布,最高频率面数f为10,个体晶粒面数范围为3~43.     

The density and surface tension of dilute liquid Na-In alloys and comparison with liquid Na-Cd alloys

The density and surface tension of five liquid Na-ln alloys, containing between 0.5 and 7 at. pct In, have been measured in the temperature range 170° to 400°C using a maximum bubble pressure technique which incorporates an automatic pressure measuring and recording device. The results are compared with corresponding data reported previously for Na-Cd alloys. The gram-atomic volumes of the Na-ln alloys, calculated from the densities, indicate a substantial contraction on alloying which is, on average, about double that for the Na-Cd alloys and qualitatively consistent with thermodynamic data for the two systems. The surface tension of liquid sodium is increased slightly on adding indium, indicating a lower indium concentration in the surface than in the bulk, in contrast to the marked surface active behavior of cadmium. The surface excess concentrations of indium and cadmium are calculated using Gibbs’ adsorption equation. The surface excess entropy, estimated from the temperature dependence of the surface tension, is compared and briefly discussed for the two systems.     

Automatic grain size determination and classification of iron carbides with neural nets

Under the aspect of quality assurance material testing is getting more and more important. As a consequence there is a strong demand for automation and objective procedures. This article concentrates on the inspection of polished steel specimens using image processing and intelligent software techniques. Nowadays computer aided image processing of microstructures is widely used, but final analysis and quality grading are based on the experience of the testing personnel. Using intelligent software techniques (soft computing), especially neural nets, allows complex decision processes to be done on a computer in a reproducible manner. Of course there are certain premises: suitable restriction of the application domain, careful image preprocessing and feature extraction, critical surveillance of the training process. The article focuses on two neural net applications: grain size determination and classification of iron carbides. To learn the ability to do complex decisions in a reproducible manner from a suitable example data set – at least in a restricted domain – is the main advantage of a neural net solution.     

高饱和磁化强度铁基非晶纳米晶软磁合金发展概况

概括了铁基非晶软磁合金和纳米晶合金的发展历史和现状,分别详述了高饱和磁化强度(B_s)铁基块体和薄带非晶以及纳米晶合金近年来的研究成果.主要内容包括:高饱和磁化强度块体铁基非晶软磁合金成分和性能,高饱和磁化强度铁基非晶薄带软磁合金的成分和性能,高饱和磁化强度铁基纳米晶合金的组织、结构和性能,各类元素对合金磁性能的影响.为进一步研究高饱和磁化强度的铁基软磁材料提供了有价值的参考.     

An analysis of the relationship between grain size,solute content,and the potency and number density of nucleant particles

To be able to determine the grain size obtained from the addition of a grain refining master alloy, the relationship between grain size (d), solute content (defined by the growth restriction factor Q), and the potency and number density of nucleant particles needs to be understood. A study was undertaken on aluminium alloys where additions of TiB₂ and Ti were made to eight wrought aluminum alloys covering a range of alloying elements and compositions. It was found from analysis of the data that . From consideration of the experimental data and from further analysis of previously published data, it is shown that the coefficients a and b relate to characteristics of the nucleant particles added by a grain refiner. The term a is related to the maximum density of active TiB₂ nucleant particles within the melt, while b is related to their potency. By using the analysis methodology presented in this article, the performance characteristics of different master alloys were defined and the effects of Zr and Si on the poisoning of grain refinement were illustrated.     

Preparation of ceria with large particle size and high appearance density

Cerium is one of the most abundant rare earth elements in both bastnasite and monazite. Ceria has been widely used in optical, catalytic, electrolyte, and sensor materials, with unique performances. With the development of functional materials, great interest has been focused on the synthesis and characterization of specific fine/mesoporous ceria powder. In this study, the modified precipitation and recrystallization processes combined with a controlled calcination process for fabricating the ceria with large particle size and high appearance density was reported. During precipitation, a certain amount of mineral acid such as nitric acid served as an additive, to adjust the precipitation and crystallization processes of cerium oxalates. An appropriate acidic condition could lead the process into the Oswald ripening stage and made the particles become bigger. Thus, the appearance density of powder was increased. The optimized conditions, such as the temperature, feeding speed, type and concentration of mineral acids, and the concentration of cerium-contained stock solution, were investigated and evaluated.