EFFECT OF CARBON AND BORON ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A SINGLE CRYSTAL SUPERALLOY RR 2072

Carbon and boron have been considered to strengthen grain boundaries that might form during single crystal casting. In this study the effect of boron on solidification behavior and creep properties of the carbon doped single crystal RR 2072 has been investigated. In order to understand solidification behavior with boron addition, the solid/liquid interface morphology and solidification microstructare were examined with solidification rate. The relationship between microstructaral evolution and creep properties of the carbon and boron modified single crystal has been also investigated.     

The mechanism of grain refinement in TiAl alloys by boron addition — an alternative hypothesis

The as-cast microstructures of a series of TiAl-based alloys with and without boron additions have been studied and the observations have been used to infer the mechanism by which boron induces grain refinement in these alloys. It has been shown that the minimum level of boron required to achieve grain refinement is different for alloys with different ternary or quaternary alloying elements and that alloying with strong boride formers, such as Ta, Nb, etc., can increase the minimum level required. It has also been found that when less than the critical level of boron is used, the dendritic structure becomes more pronounced with reduced dendritic arm spacings. However, when the levels of boron added are higher than the critical level, dendritic structures become less obvious. In one case where the level of boron added was only slightly less than the critical level, the alloy was refined in the region adjacent to the mould but became coarse towards the centre of the ingot. These microstructural observations are not consistent with the mechanisms proposed previously for grain refinement in such alloys. As a result, an alternative hypothesis has been put forward which is based on renucleation in the constitutionally supercooled zone ahead of the solidification front.     

Effect of Boron Content on Hot Ductility and Hot Cracking Susceptibility in 316L Austenitic Stainless Steel for Welding Components

Liquation cracking may occur in the heat-affected zone during welding. Two factors influence this phenomenon: the tensile stresses generated during welding and the potential loss of ductility due to the presence of a liquid film at grain boundaries depending on their chemical composition. Gleeble hot ductility tests have been used to study the combined effect of boron content and holding time on ductility drop in the liquation temperature range of a 316L type austenitic stainless steel. It is shown that high boron contents and short holding times promote the loss of ductility in this temperature range. Secondary ion mass spectrometry has been used to correlate mechanical results to boron distribution either at grain boundaries or in the bulk. Other welding tests have been performed to confirm the influence of boron content on hot cracking sensitivity of AISI 316L stainless steels. Results indicate that cracks appear on all specimens but at different strain levels. The higher the boron content is, the more the specimen exhibits tendency to hot cracking.     

Effect of iron on the wetting,sintering ability,and the physical and mechanical properties of boron carbide composites: A review

Due to its favorable physical, mechanical and chemical properties, boron carbide (B₄C) is one of the most important ceramics used in various industries. After diamond and boron nitride with a cubical structure, this material is the third hardest substance known; and due to its low density, large cross-sectional surface area for neutron absorption, excellent chemical stability, and other desired properties, it is considered as a strategic material. The sintering of boron carbide ceramics is very difficult due to the existence of strong covalent bonds in pure boron carbide and its low self-diffusion, high resistance against grain boundary slipping, and low surface energy. For these reasons, many additives have been added to boron carbide, as sintering aids. These additives, in addition to facilitating the sintering of boron carbide, do not have an adverse effect on its properties, and they improve the characteristics of the resulting product. Iron is one of the additives that reduces the sintering temperature and improves the mechanical properties of boron carbide by producing a liquid phase and thus preventing the growth of B₄C particles. In this paper, the role of iron additive in the wetting, sintering ability, and the physical and mechanical properties of boron carbide composites has been investigated.     

Study on Mn-Si-B system hardfacing electrode

ＳｔｕｄｙｏｎＭｎ－Ｓｉ－ＢｓｙｓｔｅｍｈａｒｄｆａｃｉｎｇｅｌｅｃｔｒｏｄｅＷａｎｇＬｉａｎｆａｎｇ；ＣｈｅｎＢｏｌｔａｎｄＪｉｎＸｉｌｏｎｇ（ＴｓｉｎｇｈｕａＵｎｉｖｅｒｓｉｔｙ，Ｂｅｉｊｉｎｇ）Ａｂｓｔｒａｃｔ：Ｍｎ－Ｓｉ－Ｂｓｙｓｔｅｍｍｅｄ...     

Effects of strontium and boron interactions in Al-7Si alloys

Effects of boron and strontium combined treatment on the microstructure of hypoeutectic Al-7Si alloy have been studied.Experimental results show that strontium has no significant effect on the grain refinement efficiency of boron and the eutectic silicon modification efficiency is not only related to the strontium content but also related to the boron content in the Al-7Si alloy melt.There is a negative interaction between boron and strontium that results in the formation of a strontium-boron-aluminum containing compound,which reduces the effective strontium level and decreases the eutectic silicon modification efficiency substantially.The refinement and modification mechanisms remain unchanged after the combined addition of strontium and boron,Based on the experimental results,a model for assessing the modification level in the Al-Si alloy melts after combined addition of boron and strontium was presented.     

Structural state and fracture strength upon friction of boron-containing alloys and coatings with an amorphous structure

The structural condition and wear resistance of electrochemical Co-B and Ni-B coatings with different amounts of boron, as well as Ni-Co-Fe-Cr-Mo-Si-B and Ni-Fe-Si-B amorphous alloys obtained by rapid solidification from the melt have been studied. It has been found that in Co-B and Ni-B coatings with a boron concentration less than 8 at %, there is formed a solid solution of boron in the matrix phase, and the coatings are characterized by a high fracture strength upon friction. At a boron concentration from 8 to 15 at %, there is formed in the coatings a metastable amorphous structure with a decreased wear resistance. An increase in the B concentration to 20 at % stabilizes the amorphous structure of coatings, which leads to an increase in their fracture strength. A conclusion is made that during friction interaction at the surface of amorphous layers there are formed crystalline layers, which are subject to tensile stresses and are characterized by a decreased fracture strength. The difference in the wear resistance of the alloys studied is explained by a different deformation and thermal stability of the amorphous structure of the material.     

THE NON-EQUILIBRIUM SEGREGATION OF BORON TO AUSTENITE GRAIN BOUNDARIES

采用高分辨率的径迹显微照相技术,研究了淬火硼钢中硼向奥氏体晶界偏聚的规律,定量地测定出跨过奥氏体晶界的硼的成分剖面图以及非平衡晶界偏聚的特征参量(晶界贫硼区宽度、晶界富集程度和富集带宽度)。试验表明,这种偏聚具有如下特征: 在偏聚晶界的两侧存在有一定宽度的贫硼区,晶界偏聚的硼是在冷却过程中由该区富集而来;这种偏聚对冷却速度很敏感,急速冷却可以抑制这种偏聚。冷却速度降低,晶界偏聚由连续的偏聚带,逐步发展为不连续的聚集直至明显地析出硼相,贫硼区宽度与冷却速度的平方根成反比;它的温度关系与晶界平衡偏聚预言相反,随淬火温度升高,晶界偏聚程度与贫硼区宽度增加。 通过试验,论证了淬火钢中硼向奥氏体晶界的偏聚,是在冷却过程中发生的一种非平衡的晶界偏聚现象。     

Laser cladding of continuous caster lateral rolls: Microstructure,wear and corrosion characterisation and on-field performance evaluation

Laser cladding has been used to improve the service life of lateral rolls which experience high temperature wear and corrosion in the zero segment zone of continuous slab caster. Three different compositions of nickel base powders with varying chromium, molybdenum, boron and niobium content with different wear and corrosion resistance properties have been used as cladding consumables. The microstructure of the clad layers shows a two phase cellular dendritic structure, with nickel–chrome dendrites surrounded by hard phases rich in chromium and boron or niobium. Hard precipitates contribute to wear resistance whereas the presence of chromium along with molybdenum in nickel-rich matrix improves resistance to corrosion. Actual performance results suggest that the powder material with higher wear resistance property gives the maximum life when the corrosion conditions are less hostile. In rolls cladded with highest boron and nickel containing powders, the layers were intact, whereas fine cracks and de-lamination was observed in the other rolls.     

硼含量对Ti-B-N纳米复合涂层显微结构与性能的影响

将硼加入Ti－N涂层,使用活化离子镀制备出了硼含量为（5～16）at％的Ti－B－N涂层,并着重研究了硼含量对Ti－B－N涂层结构与性能的影响。EPMA与AES分析表明,Ti－B－N涂层元素Ti、B、N在涂层内分布均匀,但在膜／基界面处有一界面扩散区。TEM显微分析表明,Ti－B－N涂层为致密微细的纳米晶多相复合结构,晶粒度不超过50nm。XRD与XPS综合分析表明,Ti－B－N涂层主要由面心立方TIN、简单正交TiB、立方BN与简单六方Ti－B－N相组成,且随着硼含量的增加,含硼相含量增加。Ti－B－N涂层的硬度、韧性与附着强度等力学性能比相应的Ti－N涂层要好得多,且其沉积温度更低。     

Properties of coatings on the basis of carbon,tungsten, boron,and titanium obtained by the pulsed vacuum-arc method

Results of an investigation of the properties of coatings on the basis of carbon, tungsten, boron, and titanium obtained by the pulsed vacuum-arc method are presented. It has been found that the adhesion characteristics of coatings based on boron and titanium may be improved using a composite carbon-based coating, doped with tungsten, boron, and titanium, which, moreover, has a microhardness greater than those of a coating based on titanium and boron.     

Notch toughness in hot-rolled low carbon steel wire rod

Charpy V-notch toughness has been investigated in four hot-rolled, low carbon steels with different grain sizes and carbon contents between 0.019 and 0.057%. The raw material was wire rod designed for drawing and possible subsequent cold heading operations and manufactured from continuous cast billets. In this study, the influence of microstructure, mechanical properties, and alloying elements on the ductile-brittle transition behavior has been assessed. A particular emphasis has been given to the influence of boron with contents up to 0.0097%. As a result, transition temperatures between −29 and +50°C explicated by the material properties have been obtained. The examination also shows that the transition temperature raises with circa 0.5°C for each added ppm boron most likely as a consequence of an enlargement of the ferrite grain size and the reduction of yield and tensile strength. The highest upper shelf energy and lowest transition temperature can be observed in a steel without boron additions and with maximum contents of carbon, silicon, and manganese.     

THE DISTRIBUTION OF BORON IN LOW ALLOY CAST STEELS

研究了Mn-Mo-B-RE系低合金铸钢中硼的偏析和在均匀化、正火、调质热处理过程中硼分布的变化,以及含硼量、稀土元素加入和钢中Mo等合金元素对硼分布的影响.硼在铸钢中有明显的偏析倾向,并随含硼量的增加而加剧;经通常的均匀化处理后,铸钢中硼分布的均匀性受Mo偏析的强烈影响.在特定的条件下,会产生沿奥氏体一定结晶学平面的硼相析出,或沿晶界形成粗大连续网状的硼相,导致脆断.试验还显示稀土元素有保护硼的良好作用.     

B和Sr同时存在的6201铝合金的金相组织与电性能

实验研究了含 B和 Sr的 62 0 1铝合金显微组织 ,发现 62 0 1铝合金在同时含有 B和 Sr的情况下 ,铸态组织中有明显的缩松出现。而在同样的凝固条件下 ,仅含有 B或 Sr的合金都不会出现缩松。通过电阻率测试 ,发现缩松对合金的电阻率的影响是显著的。     

THE MECHANISM OF NON-EQUILIBRIUM SEGREGATION OF BORON TO AUSTENITE GRAIN BOUNDARIES

业已证实,淬火硼钢中硼向奥氏体晶界的偏聚,是在冷却过程中发生的一种非平衡的晶界偏聚。本文通过解变温扩散方程,导出了非平衡晶界偏聚的理论公式,建立了晶界贫硼区宽度与淬火加热温度、冷却速度以及非平衡晶界偏聚扩散激活能与扩散常数之间的关系,理论预言与实验结果较好地吻合。 根据实验结果和理论分析,提出这种非平衡晶界偏聚的机制,是在冷却过程中,过饱和空位或双空位带着硼原子向晶界(空位阱)迁移的结果。 基于这种非平衡晶界偏聚的新概念,可以较完满地说明影响硼钢淬透性的众多复杂因素。     

Electroless deposition and investigation of composite coatings based on nickel or cobalt matrix,including boron nitrides as dispersoids,on polyethylene terephthalate substrate

Composite coatings, based on nickel or cobalt matrix with incorporated boron nitride particles (BN) as dispersoid, have been chemically deposited and investigated. The mass, and relative thicknesses, of the obtained composite coatings, as well as the number of co-deposited particles, depending on the type (alpha boron nitride – BN(h) or cubic boron nitride – BN(c)) and particle size of the dispersoid, as a function of dispersoid concentration in the working electrolyte and the concentration of the reducing agent in the plating electrolyte have been determined. The morphology, structure and chemical composition of the deposited coatings have been characterised by means of SEM and EDS analysis.     

Positron annihilation in Ni-B and Ni-P alloys prepared by catalytic chemical reduction of nickel ions by borohydride, dimethylamino borane, and hypophosphite

Positron-annihilation technique was used to determine the Fermi energy and the concentration of trapping centers in nickel alloys (with various contents of phosphorus and boron) prepared by catalytic chemical reduction of nickel ions. It has been established that for Ni-B alloys there is observed a charge transfer from nickel to boron. In Ni-P alloys, the Fermi energy increases with increasing phosphorus concentration in the alloy. The introduction of phosphorus or boron into nickel increases the concentration of trapping centers for positrons.     

Corrosion synthesis of boron carbide with pore and hollow structure

In this study, corrosion synthesis of boron carbide particles with pore size ranging from hundreds of nanometers to several micrometers was reported. Firstly, the pristine boron carbide powders which contain free carbon have been synthesized at 350 °C in a steel autoclave. As the pristine boron carbide was refluxed by HClO₄ at 170 °C for 1–2 h, the boron carbide particles with macropores were produced. Similarly, the boron carbide nanocages can also be obtained. The corrosion of the embedded amorphous and/or low crystallinity carbon/boron carbide using HClO₄ was considered for the formation of boron carbide with macropores and hollow nanocages.     

Process diagnostics during the deposition of cubic boron nitride

Using spatially resolved optical emission spectroscopy and Langmuir double probe technique, the magnetron deposition process of cubic boron nitride thin films has been investigated. The ion current to the r.f-biased susbstrate electrode was estimated by means of Bohm's sheath criterion. In order to deposit the cubic boron nitride phase, a much higher ion energy is required in the d.c. magnetron in comparison to the r.f. sputtering magnetron mode at usually applied target power. Furthermore, there is a significant phase inhomogeneity across the substrate holder. Both facts have been explained in terms of the total momentum per deposited boron atom. The plasma excitation degree (vibrational and excitation temperatures) determined by emission spectroscopy was found to be higher in the r.f. sputtering mode. It has been shown that both in situ techniques applied can supply reliable information on the reactive magnetron deposition process.     

Deformation-induced dissolution of the Fe2B boride in nanocrystalline α-Fe

Structural-phase transformations in the α-Fe+Fe₂B composite with a total boron content of 15 at. % during mechanical grinding in a planetary ball mill have been studied using X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. It has been established that dissolution of the Fe₂B boride with the formation of an amorphous phase and segregations of boron atoms at grain boundaries occur after the grain size reaches 3 nm. In this work a comparative analysis of the deformation-induced dissolution of Fe₂B and Fe₃C in the Fe-B and Fe-C systems has been made and the possible mechanisms of the structural-phase transformations have been discussed.