Recrystallization of molybdenum wire doped with potassium-silicate

The doping effect of the bubble formation oxide on the recrystallization of Mo wire was investigated. Five different wires of 1 mm in diameter were prepared through sintering, swaging, and drawing processes. Each wire was doped with various amounts of potassium (K) plus silicon (Si), i.e., 0, 0.028, 0.14, 0.28, and 0.49 by weight percent, and annealed for 30 minutes at given temperatures. To understand the overall recrystallization phenomena, changes in hardness and in optical microstructures were examined. Transmission electron micrographs were taken for the specimens in the as-drawn state and at the beginning of the decrease in hardness. And also, the relative excess resistivity was measured as a function of heating temperature to confirm the occurrence of the abnormal grain growth. During the grain growth, bubble dispersion was evaluated through fractography by scanning electron microscopy (SEM). Primary re-crystallization started at 750 °C regardless of the amount of dopants. For the specimens doped with 0.14 and 0.28 (K + Si), large elongated and interwoven grain structures indicating ab-normal grain growth developed over 1400 °C and 1600 °C, respectively. For the specimens doped with 0.028 and 0.49 (K + Si), however, small equiaxial grain structure developed similar to pure molybdenum wire. Such a difference was understood through the relationship between grain structures and bubble dispersion parameters (the average bubble diameter, the bubble row density, the columnar bubble spacing, and the bubble row distance). It was concluded that two of the most important parameters to develop a grain structure of high aspect ratio were bubble row density and bubble row distance. At a high bubble row density, irregularity in bubble row distance induced the higher aspect ratio (length/width (L/W)) of grain.     

柱状晶组织高硅电工钢二次再结晶的形成机理

  二次再结晶的发生会显著改变电工钢带材的组织和织构，进而影响其磁性能。以柱状晶组织高硅电工钢冷轧带材为研究对象，研究了不同退火方法对试样组织和织构的影响，明确了二次再结晶的发生条件、形成机理和控制方法。研究结果表明，柱状晶组织高硅电工钢冷轧试样发生二次再结晶的温度区间为850～1 000 ℃，在900 ℃退火可获得最大的晶粒尺寸。二次再结晶的形成是由于初次再结晶后试样的组织形成了织构抑制作用，小角度晶界抑制晶粒正常长大，大角度高能晶界迁移率高，具有大角度晶界的晶粒以取向长大方式发生二次再结晶。当退火温度高于1 000 ℃时，升温和冷却速率大于5 ℃/min可以有效抑制二次再结晶的发生。     

中温含铜取向硅钢的形变和再结晶织构特征

通过对比中温含铜取向硅钢与普通取向硅钢和高磁感取向硅钢的组织和织构特征,分析中温含铜取向硅钢独特的织构演变规律及其对二次再结晶行为的影响.结果表明,为了获得有利于高斯晶粒长大的强γ取向线织构,中温含铜钢需经过回复退火处理和高温退火阶段慢速升温.回复过程中γ取向线晶粒储能降低,同时慢速升温有利于γ取向线晶粒的形核和再结晶.中温含铜钢的二次再结晶开始温度超过1000℃,由于初次再结晶晶粒组织以γ织构为主且非γ取向线晶粒较少,导致最终二次晶粒尺寸超大且晶界圆滑,二次再结晶机理以择优长大为主导,超大的二次晶粒尺寸导致最终成品的铁损升高,但通过激光刻痕处理后,整体铁损的降低效果比二次晶粒较小的高磁感取向硅钢更加显著.      

Secondary recrystallization of pure molybdenum wires

The secondary recrystallization of drawn pure Mo wires has been studied; a particular attention has been paid on the effect of temperature gradients in the annealing process. The secondary recrystallized grains being very elongated along the wire axis have been obtained by annealing in a moderate temperature gradient furnace at about 2000°C. Orientations of the wire axis of the secondary recrystallized grains are mainly 〈023〉 or 〈135〉, while 〈011〉 oriented grains are less frequently observed. In contrast, the primary recrystallized texture consists of the 〈011〉 main component and 〈023〉-〈012〉 sub-component; many 〈011〉 oriented grains have large grain sizes. The observed discrepancy in orientation between the primary and secondary recrystallized grains is explained in terms of the difference in grain boundary mobilities which depend on the character of grain boundaries.     

掺杂复合稀土氧化物的钼的组织与性能

对掺杂一种（以下简称：单元）或一种以上（以下简称：复合）稀土氧化物的钼粉、坯条及不同温度退火丝材的性能及组织结构进行了系统研究。结果表明：复合稀土同单元稀土一样,都能提高钼丝的再结晶温度,复合稀土钼丝表现出优异的高温退火强度,并具有比同含量的单元稀土钼丝更高的延伸率,具有更好的成型性和加工性。     

低温加热渗氮型取向硅钢二次晶粒取向度下降成因分析

低温加热渗氮型取向硅钢二次再结晶完全、磁性能却不高是一种常见的现场质量问题,其成因的判断及问题的解决对降低生产成本至关重要。本文对两组企业生产中存在上述现象的低温渗氮钢的一次再结晶板进行高温退火中断实验,确定其二次再结晶温度及基体晶粒和二次晶粒的取向分布特征,探索其成因。结果表明,磁性能下降的原因是二次晶粒取向度偏差大,主要向{110}<227>取向偏转;其本质是一次晶粒尺寸偏小,二次再结晶温度提前了约50 ℃;高斯晶粒以外的偏高斯取向晶粒优先形成。两组样品的差异不在于其二次再结晶温度不同,而是二次晶粒的偏差度不同。这种差异又反映出两组样品微小的一次退火组织织构和抑制剂的差异或成分波动性。     

热阴极用稀土钼丝材的组织和性能的研究

研究了在钼中添加稀土氧化物对几种钼丝的组织及性能的影响。结果表明，添加适量稀土能够获得细小均匀的还原钼粉，烧结后的钼坯条的晶粒细小均匀，掺杂提高了钼丝材的室温强度和再结晶温度，这种稀土钼丝材经1700℃高温退火后具有良好的延伸率，有利于热阴极用的定型加工。     

The recrystallization of commercially pure and doped tungsten wire drawn to high strain

The recrystallization processes in both undoped and doped tungsten wire after drawing to a true strain of 7.7 were examined by light microscopy and transmission electron microscopy. High angle grain boundary migration commenced at approximately the same temperature in both materials, but proceeded much more rapidly in the undoped wire, where the absence of a potassium bubble dispersion allowed a coarser, more equiaxed grain structure to form. No change from the (110) deformation texture was observed in either case. Recrystallization in the undoped wire was dominated at lower temperatures (1100 to 1200°C) by the growth of large grains into a much finer structure. As the annealing temperature was increased, this process was replaced by a general grain coarsening which eventually produced a relatively equiaxed recrystallized grain structure. It appeared probable that it was the second phase dispersion inhibition alone that prevented similar structural changes in the doped wire. This paper is based on a presentation made at a symposium on “Recovery Recrystallization and Grain Growth in Materials” held at the Chicago meeting of The Metallurgical Society of AIME, October 1977, under the sponsorship of the Physical Metallurgy Committee.     

Recrystallization of W-1 wt pct ThO2 wire

The recrystallization behavior of W-l wt pct ThO₂ wires of two sizes, 0.457 and 0.178 mm (18 and 7 mil), was studied using optical microscopy, transmission electron microscopy, hardness, and resistivity ratio techniques. For the 0.178 mm wire the effects of heating rate were also analyzed. Recrystallization of the 18 mil wire is characterized by rather gradual changes in hardness, resistivity ratio, and microstructure leading to a small recrystallized grain size. The 0.178 mm wire, on the other hand, exhibits more abrupt changes in resistivity ratio and hardness which coincide with the development of a recrystallized structure having a large grain-size range. Variation of heating rates between about 150,000°C/min and 500°C/min did not significantly affect the grain structure or hardness achieved for annealing temperatures of 2000°, 2500°, and 2700°C. However, very slow heating rates, less than 10°C/min, were shown to prevent the formation of large grains in the 0.178 mm wire. These results are explained on the basis of differences in the effectiveness of ThO₂ particles in hindering grain boundary motion.     

热轧变形量对MGH754合金板材组织和性能的影响

在相同的轧制温度下,通过组织分析和显微硬度分析的方法,研究了热轧工艺中不同的最后一火变形量对MGH754合金热轧态板材组织、退火态板材组织以及板材高温持久强度的影响。研究结果表明:最后一火变形量越高,热轧态板材组织能充分地进行动态再结晶,其晶粒越细小均匀;最后一火变形量越高,更有利于退火中二次再结晶的发生,生成粗大的盘状晶组织;板材的高温持久强度随着最后一火变形量的增大而升高。     

退火工艺对冷轧高强IF钢组织及织构的影响

为了观察高强IF钢退火处理后的显微组织和再结晶织构的变化规律,采用两种不同退火工艺对高强IF钢进行热处理。结果表明,IF钢在两种退火方式下均形成了γ-{111}纤维织构,快速升温(350℃/min)退火时,再结晶新核呈等轴状,由变形带内的亚晶合并形成,与冷轧变形基体保持相同取向。慢速升温(2℃/min)退火时,新核在晶界弓出形成,且沿轧制方向呈饼形分布,与基体没有明显取向关系。慢速升温退火样品的γ-{111}取向密度强于快速升温的。对进一步改善薄板钢深冲性能具有指导作用。     

The influence of microstructure on fracture of drawn tungsten wire

The microstructures and longitudinal fracture resistances of 0.635 mm diam lamp-doped and undoped tungsten wire were examined in the as-drawn condition and after anealing at temperatures between 600 and 1500°C. A variety of experimental techniques were employed, including Auger Electron Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy and a newly developed mechanical testing technique. The longitudinal fracture mode was intergranular for all wires and a second phase was observed on the grain boundaries of all doped wires. High concentrations of the dopant element potassium were present on the fracture surfaces of doped wires and experimental evidence was obtained which suggests they may be due to postfracture surface diffusion. Doped wires demonstrated increasing amounts of structure coarsening up to 1500°C whereas large equiaxed grains were formed in undoped wires annealed at 1300 and 1500°C. The longitudinal fracture resistance of undoped wire was unaltered by annealing at 1050°C and below, but decreased dramatically after annealing at 1300 and 1500°C. In contrast the fracture resistance of doped wire decreased after annealing at 1050 and 1300°C, but increased after annealing at 1500°C. Fracture resistance is discussed in terms of microstructure and fracture surface chemistry. A. W. FUNKENBUSCH, formerly Research Metallurgist with General Electric Refractory Metals Product Department     

A Model for the formation of the non-sag structure of potassium-doped tungsten wire

During recrystallization, potassium-doped tungsten wire develops a favorable stable structure of elongated grains. This is caused by a special bubble structure which is produced by the doping agent, potassium. The paper aims at a coherent semiquantitative model describing the formation of sinter pores, of potassium bands during deformation, of the bubble structure, and of driving and dragging forces during recrystallization.     

Formation of AlN Nano Particles Precipitated in St-14 Low Carbon Steel by Micro and Nanoscopic Observations

In low carbon steels, dissolution and precipitation of the second phases such as carbides and nitrides during annealing cycles can affect the final structure and properties of the materials. The interaction of above processes depends on parameters such as reheating temperature, heating rate, annealing temperature, soaking time and finishing temperature in hot rolling stage before cold rolling. The effects of heating rate and annealing temperature on the microstructure and hardness were investigated. Two heating rates for annealing temperatures of 550, 610 and 720℃ were applied on cold-rolled specimens and St-14 low carbon steel, which were immediately quenched after isothermal annealing. The intercept method was used tO measure average grain sizes. However, resulted microstructures are dif- ferent for the two heating rates. While pancaked structures were observed in specimens annealed with low heating rate, in samples annealed with high heating rate, equiaxed microstructures were observed. Vickers micro-hardness values decreased at all temperatures, which were more significant at higher temperatures. At longer annealing time, signs of increase of hardness values were detected. All results and observations consistently suggest that a precipitati- on process has occurred concurrently with restoration processes during annealing. In addition, the energy dispersive spectroscopy analysis resulted from transmission electron microscopic micrographs have proved that the nano particles precipitated in grain boundaries are AlN.     

低温取向硅钢常化工艺和渗氮工艺对组织、织构和磁性能的影响

利用电子背散射衍射技术(EBSD)、扫描电镜(SEM)分析了低温取向硅钢常化工艺、渗氮工艺对常化组织、再结晶组织与抑制剂的影响, 对比研究了常化冷却速率、渗氮温度和渗氮量对再结晶组织、织构和磁性能的影响规律.结果表明, 常化冷却速率越快, 一次再结晶晶粒尺寸越小.常化冷却速率较慢时, 高温渗氮的样品一次再结晶晶粒尺寸偏大, 使二次再结晶驱动力降低, 二次再结晶温度提高, 且渗氮量低, 追加抑制剂不足, 最终二次再结晶不完善.高温渗氮与低温渗氮导致脱碳板中抑制剂尺寸不同, 高温渗氮表层抑制剂与次表层抑制剂尺寸基本无差异, 低温渗氮表层抑制剂尺寸比次表层抑制剂尺寸大.低温渗氮且渗氮量低的样品虽然二次再结晶较完善, 但由于其常化温度低、常化冷却速率快, 一次再结晶晶粒尺寸小, 二次再结晶开始温度稍早, 黄铜取向晶粒出现, 最终磁性差.渗氮量较高的高温渗氮和低温渗氮样品虽都能基本完成二次再结晶, 但磁性存在差异, 磁性差的原因是高温渗氮样品的最终退火板中出现较多的偏{210} < 001>取向晶粒.      

Dopant particle characterization and bubble evolution in aluminum-potassium-silicon-doped molybdenum wire

The present article describes the creation of dopant inclusions in aluminum-potassium-silicon (AKS)-doped molybdenum powder and the generation of potassium bubbles in doped molybdenum wire. Molybdenum wire is used extensively in the incandescent lamp industry for coiling mandrels, filament support wires, and foil seals. The AKS-doped molybdenum wire is an important product, because it possesses greater high-temperature strength and a higher recrystallization temperature than undoped molybdenum; both of these properties are important for structural applications in lamps. The AKS-doped molybdenum wire is produced in a similar manner to AKS-doped tungsten wire, but lower processing temperatures are typically used for the production of molybdenum wire. Previous studies on AKS-doped tungsten wire have shown that the dispersion which provides the interlocking grain structure in recrystallized tungsten wire is bubbles of elemental potassium; these enhance incandescent lamp filament life. However, there is little previous work on the potassium-containing dispersion in AKS-doped molybdenum wire. In AKS-doped molybdenum, the dispersion can be either potassium bubbles, or solid oxide particles, depending on the processing method. This article will describe a series of analyses of doped molybdenum wire and its precursors, namely, doped powder and sintered ingots. The roles of high- and low-temperature sintering are also described.     

Study of grain boundary fracture surfaces in doped tungsten-rhenium alloys

The combination of Auger electron spectroscopy and scanning electron microscopy has identified the source of the unique interlocked elongated grains responsible for the high temperature sag resistance in doped tungsten and tungsten-rhenium alloys as due to bubbles which are formed by the volatilization of potassium during sintering. By pinning grain boundaries these bubbles raise the recrystallization temperature (from 1300†C to 2100†C) and their distribution within the material controls the recrystallized grain morphology. There is a thin layer of potassium remaining on the bubble surfaces. The size and distribution of the bubbles is related to the amount of material deformation during processing. Increasing rhenium content does not affect the concentration or distribution of residual potassium. It has no noticeable effect on bubble size, distribution or density. The presence of a thermal gradient during annealing does affect bubble density and recrystallization temperature. Formerly with the Air Force Materials Laboratory, Wright-Patterson AFB, Ohio Formerly with the Aerospace Research Laboratory, Wright-Patterson AFB, Ohio     

在动态热处理条件下对取向电工钢二次再结晶的研究

对应用动态加热进行短时温度退火的取向电工钢进行了二次再结晶研究。所进行研究的实验用取向电工钢是经过终冷轧和后续罩式退火后的一条工业化生产线生产的。研究结果表明,运用短时热处理条件可引起研究钢完全的异常晶粒长大。在实验室处理的材料的织构和金相组织与工业化生产的经过终退火而获得的相同的取向电工钢类似。但是,在实验室处理的取向电工钢的二次再结晶的矩阵中可观测到"寄生"晶粒。从磁性观点看,这些"寄生"晶粒含有不理想的{111}取向织构。     

Effect of a temperature gradient on bubble growth in tungsten

Bubble distributions in doped tungsten wires have been examined following high temperature anneals (2500° to 3000°C) both in the presence and absence of a thermal gradient. Electron and optical microscopy show that much more bubble growth occurs during gradient anneals, and the results suggest that the gradient is a driving force for bubble growth. This process takes place predominantly on the grain boundaries. Semiquantitative estimates of the bubble flux were made by measuring the change in aggregate bubble surface areas found at various positions in the gradient. Stress induced bubble growth was shown not to be a factor.