渗硼层形成机理的探讨

渗硼层的形成机理,一直是渗硼研究的重要课题。本文主要采用X射线法对用气体法在工业纯铁上形成渗硼层的过程进行了研究。结果表明,在渗硼时,依次形成硼的固济体,Fe_2B、FeB。即渗硼层形成过程完全符合相图和相律。     

Surface layers on cobalt base alloys by boron diffusion

Boronizing is used to improve the wear resistance of the surface of metals and alloys. Various powder mixtures containing boron compounds or amorphous boron were tested at different treatment temperatures. The boronizing time was varied also. The diffusion was observed by metallography and microhardness testing of sloping cuts of the alloys; sloping cuts were necessary because of the thin boronized surface layers with different boride compositions. Borides are formed by reactions with the diffusing boron. Their structures were determined by X-ray diffraction. Separate layers containing different borides were found and the composition of some of these borides was studied. Cast cobalt base alloys and cemented carbides contain different amounts of cobalt. Since boronizing leads to the formation of mainly cobalt borides, the boronized layers of these types of alloys are different.Some examples of applications and results will be given.     

Pack-boriding of Fe–Mn binary alloys: Characterization and kinetics of the boride layers

In this work, the boronizing of Fe–Mn binary alloys at 0.42, 0.76 and 0.94 wt.% Mn was carried out in a solid medium using the powder pack method. In this method, commercial Ekabor-II boron source and activator (ferro-silicon) were thoroughly mixed to form the boriding medium. The samples were boronized in an electrical resistance furnace for exposure times of 2, 4, 6 and 8 h at 1173 K under atmospheric pressure and a series of boronized samples in the temperature range 1073–1373 K for 3 h. After the furnace process, boronized samples were removed from the furnace and cooled in air. Afterwards, the boride layers generated by the pack-boronizing process were characterized by optical microscopy, scanning electron microscopy, XRD analysis, Vickers microhardness and tensile testing. The generated boride layers, showing a saw-tooth morphology, had a surface microhardness in the range 1400–1270 HV0.1. It was shown that the values of yield stresses and ultimate tensile stresses were increased as the Mn content increases in the boronized Fe–Mn binary alloys. In contrast, the values of elongations determined from the stress–strain curves were decreased. Furthermore, it was found that the calculated mean value of the activation energy of boron diffusion was close to 119 J/mol.     

Investigation of the effect of boronizing on cast irons

Gray iron, ductile iron and compacted graphite iron were boronized with solid boron-yielding substances by box-boronizing method. Commercial EKabor^® 3 powder is used as the boronizing agent and the treatments are carried out at 850, 900 and 950°C for 2, 3, 4, 5 and 6 h. Thickness and microhardness of the boride layer, and the microstructure of the boronized specimens are reported.     

Production of ferroboron powders by solid boronizing method

Ferroboron is an iron-boron alloy containing 10–20% of boron by weight. Commercial ferroboron production is made by two main processes: carbothermic reaction and aluminothermic reaction. Ferroboron also occurs in steel surfaces due to boronizing, which is applied to increase surface hardness in steel. Boronizing is a thermo-chemical surface hardening treatment. The ferroboron phases like Fe₂B, FeB form by diffusing of boron element into iron. These phases are very hard, wear strengths are high, and friction coefficients are low.In this study, ferroboron powder was obtained by boronizing ASC 100.29 iron powder that was used widely in powder metallurgy area. Solid boronizing method was preferred due to its advantages in applications and Ekabor-HM powder was used as the boronizing agent. The 80% ASC 100.29 and 20% Ekabor HM were mixed homogeneously and subjected to boronizing at 850–950 °C for 1–6 h. Formation and development of ferroboron phase on the samples was determined by metallographic studies depending on various treatment conditions. The X-ray diffraction analysis revealed that the Fe₂B phase did form but FeB phase did not. Micro hardness distributions were measured on the powder grains. Eighteen GPa hardness was measured at Fe₂B phase obtained by boronizing while hardness of non-boronized iron powders was 1.06 GPa. The thickness of ferroboron layer formed by boronizing changed with boronizing conditions. The thickness of ferroboron layer increased with boronizing temperature or boronizing time. Depending upon processing parameters, ferroboron layers was formed partially or throughout ferrous powder structure. Since boronizing can be applied to iron powders having any size or shape, ferroboron production with required shape and size is possible.Finally, a new method, namely solid boronizing method, was developed in ferroboron powder production.     

Boronizing for erosion resistance

Boronizing is a diffusion process analogous to carburizing and nitriding. It is achieved by heating parts in a pack. One layer or two may be formed, depending on the boron potential of the pack. A single layer is generally better for wear resistance than a duplex layer. Other methods such as salt bath or gas phase boronizing are available.The layer is very hard and confers great resistance both to sliding wear and to abrasive wear. With mild steel, sliding wear can be reduced by up to three orders of magnitude. Boronizing prevents the transition to adhesive or severe wear.Sintered carbide wire-drawing dies wear by a mixture of corrosion and adhesion. The life of a die will depend on the material being drawn. In this respect, stainless steel is particularly difficult. Boronized dies can lead to a life increase of 10 times.In abrasive wear, boronizing is more cost effective than any other material for such items as agricultural machinery.Molten zinc is very corrosive to mild steel. In jobbing galvanizers' works boronized mild steel is cheaper and longer lasting than titanium for carrying ware into the zinc bath.Resistance to acids, in particular to hydrochloric acid, is increased by boronizing.     

Characterization of borided Incoloy 825 alloy

Incoloy 825 alloy is an alloy with high corrosion resistance but it has low strength and hardness. Increasing of hardness of the alloy is important for its wear resistance. In this study, Incoloy 825 alloy was boronized to increase its hardness. The boronizing process was carried out using the box boronizing method at 900 and 950 °C for 2, 4 and 6 h. The coating thickness that occurred by boronizing increased with the increase in temperature and time. The thickness of boride layers depending on temperature and process time was ranged from 35 to 170 μm. The presence of borides (e.g., FeB, Fe₂B, CrB, NiB) was confirmed by X-ray diffraction (XRD) analysis technique. The boron compounds have shown the random distribution. The microhardness has decreased along the coating thickness (towards to the matrix).     

气体渗硼工件的表面形貌及其与渗硼层孔洞的关系

利用扫描电子显微镜观察了经不同气体渗硼工艺处理的工件表面,研究了影响工件表面形貌的因素及表面形貌与渗层孔洞的关系。研究表明:恰当的工艺参数使工件表面由规则,细小,均匀的硼化物颗粒构成,否则,工件表面的硼化物颗粒将会粗化,甚至产生一种针状颗粒。本文重点研究了这种针状硼化物的形成机理及其影响因素。此外,表面较光滑的工件往往具有较致密的渗硼层,而粗糙的表面,尤其是表面产生针状硼化物的工件则对应孔洞较多的渗硼层。     

L415/IN825复合板焊接接头渗硼处理工艺及渗层的组织与性能

目前对双金属复合板焊接接头的渗硼处理鲜有研究报道。为了提高双金属复合板焊接接头的耐蚀和耐磨性能,对其表面进行渗硼处理。采用光学显微镜(OM)、扫描电镜(SEM)、X射线衍射仪(XRD)及显微硬度计分别对L415/IN825复合板复层焊接接头渗层的微观组织、物相组成及显微硬度进行了分析,并研究了复合板焊接接头及其渗层电化学腐蚀性能。结果表明:复合板焊接接头复层渗层分为硼化物层(Ni_2B、Cr_5B_3、Cr_2B和CrB)和硅化物层(Ni_2Si、Cr_3Ni_2Si和Cr_(13)Ni_5Si_2),全渗层的厚度随着加热温度和保温时间的增加而增加;不同区域渗层表面的显微硬度值均高于基体;复合板焊接接头基体耐蚀性能优于焊接接头表面渗层。     

Plasma paste boronizing of AISI 8620, 52100 and 440C steels

In the present study, AISI 8620, 52100 and 440C steels were plasma paste boronized (PPB) by using 100% borax paste. PPB process was carried out in a dc plasma system at temperature of 700 and 800 °C for 3 and 5 h in a gas mixture of 70%H₂–30%Ar under a constant pressure of 4 mbar. The properties of boride layer were evaluated by optical microscopy, X-ray diffraction and Vickers micro-hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed FeB and Fe₂B phases for 52100 and 8620 steels and FeB, Fe₂B, CrB and Cr₂B borides for 440C steel. PPB process showed that since the plasma activated the chemical reaction more, a thicker boride layer was formed than conventional boronizing methods at similar temperatures. It was possible to establish boride layer with the same thickness at lower temperatures in plasma environment by using borax paste.     

Optimization of process parameters of boro-carburized low carbon steel for tensile strength by Taquchi method with grey relational analysis

The results of study on the boro-carburizing and boronizing of AISI 1015 steel on tensile strength was carried out by Taquchi-grey relational method. The orthogonal array L₉(3⁴) was used to conduct the experiment. The thickness of boride layer increased with increase in process temperature and time. The thickness of boride layers for boronized AISI 1015 steel was more than the pre-carburized and boronized AISI 1015 steel. The microhardness decreased with increase in distance from the surface to the core. However, the hardness gradient reduced gradually from the surface to the core in case of boro-carburized treatments compared to boronized treatments. The optimal process parameters and their levels for pre-carburized AISI 1015 steel are carbon content 0.45% at 950 °C temperature and 4 h process duration. The results revealed that process time, case carbon content and process temperature influenced the yield strength and % elongation. The ultimate strength is influenced by the process temperature, process time and carbon content. The process temperature was the most influential control factor that affects the tensile strength properties.     

Some properties of boronized layers on steels with direct diode laser

Boronized layer on steel is known to be formed by thermal diffusion of boron into the surface of steel improving corrosion-erosion resistant properties. Boronizing is carried out at temperatures ranging from 800 °C to 1050 °C and takes from one to several hours. There is one problem in this process, however, that the structure and properties of the base material are influenced considerably by the high temperature and long time of treatment. In order to avoid the aforementioned drawbacks of pack boronizing and laser-assisted boronizing, a better way is to activate the pack boronizing media and the workpiece with a high density power. The laser boronizing processes do not change the properties of the base material. In this study, the effect of laser characteristics was examined on the laser boronizing of carbon steel. After laser boronizing, the microstructure of the boride layer was analysed with an optical microscope and X-ray diffractometer (XRD). The mechanical properties of borided layer are evaluated using Vickers hardness tester and sand erosion tester. Results showed that the boride layer was composed of FeB and Fe₂B with thickness ranging 200-300 μm. The laser boronizing process did not change the properties of the base material.     

Mössbauer and metallographic analysis of borided surface layers on Armco iron

Armco iron samples boronized at 850 and 1000° C in crystalline boron powder have been studied. Scattering and transmission Mössbauer measurements, supported by optical and electron scanning metallography and by X-ray diffraction analysis, enabled the surface phases to be identified, the multi-layer structure of the coatings to be defined and the average thickness of each layer to be measured. In addition to an inner Fe₂B layer and to an intermediate FeB layer, the presence of an outer layer of a third phase richer in boron that FeB has been ascertained in the boride coatings. The morphology of the reaction products and their mechanical consistency have also been examined and discussed.     

Effects of boronizing on mechanical and dry-sliding wear properties of CoCrMo alloy

In this study, CoCrMo alloy was boronized at 950 °C for 2, 4, 6 and 8 h, respectively. The boronized samples were characterized by scanning electron microscopy, X-ray diffraction, microhardness tester and ring-on-block wear tester. X-ray diffraction studies showed the boride layer formed at 950 °C for 2–8 h consisted of the phases Co₂B and CrB. A large number of pores formed in diffusion zone were probably attributed to the Kirkendall effect. Depending on boronizing time, the thickness of boride layer ranged from 4 to 11 μm. The excellent wear resistance of the boronized CoCrMo alloy was attributed to the high surface hardness of the Co₂B and CrB under dry-sliding conditions when compared to the as-received state.     

Microstructure analysis of boronized pure nickel using boronizing powders with SiC as diluent

In this study, boronizing of 99.9% pure nickel was performed by means of a powder-pack method using Commercial LSB-II powders (that contained SiC) at 850, 900 and 950 °C for 2, 4, 6 and 8 h, respectively. The coated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and hardness tests. The presence of boride (Ni₂B) and silicide (Ni₅Si₂, Ni₂Si) phases, formed on the surface of boronized pure nickel, were confirmed by X-ray diffraction analysis. The Ni₃Si phase was found when pure nickel was boronized at 850 °C for 2 h. Depending on boronizing time and temperature, the thickness of coating layer ranged from 36 to 237 μm. The hardness values were 832 HV_0.01 for the silicide layer, 984 HV_0.01 for boride layer, and 139 HV_0.01 for the Ni substrate.     

Formation and properties of diffusion coatings applied to steels by boronizing in melts

We propose the optimum modes for the formation of diffusion boride coatings on steels of various classes from liquid-metal melts. The microstructure and physical properties of boronized steels 20, 30, 45, R18, DI22, and U10 are analyzed. The advantages of boronizing from lithium-based melts, which enables one to combine the process of deposition with heat treatment, over the familiar methods of creation of a coating from powder mixtures are established. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 2, pp. 86–91, March–April, 1999.     

固体深层渗硼中元素的分布

本文介绍用自行研制的固体粉末深层渗硼剂对45钢进行渗硼,研究了元素的分布特点,且与45钢浅层渗硼作了比较。     

一种用于制备大厚度MEMS结构层的浓硼掺杂方法(英文)

在MEMS器件中,浓硼掺杂层通常为器件的结构层.但由于受表面固溶度及浓度梯度影响,该掺杂层(硼原子浓度≥5×1019cm-3)厚度越大所需的扩散时间越长.为了能在同等扩散工艺条件下,制备出更厚的浓硼掺杂层以满足器件要求,提出了多步扩散法.即在保证总的累计扩散时间不变的前提下,将传统的扩散过程分为两个相对短的扩散周期.并且这两个周期连续进行,每个周期各包含一次预扩散和再分布.与传统的两步扩散相比,多步扩散法可为硅基底引入更大量的硼杂质,并且具有一定能力使硼杂质留在一定深度范围内.因此该方法可以获得更大的有效节深.实验中采用该方法成功制备出21μm厚的浓硼掺杂层.然而在文献中提到的采用传统两步法在同样条件下得到的厚度则小于15μm.从而验证了该方法可在同等扩散工艺条件下,可以制备出更厚的浓硼掺杂层.     

Synthesis of indium tin oxide powder by solid-phase reaction with microwave heating

Indium tin oxide (ITO) powder was synthesized from indium oxide and tin oxide powders by a solid-phase method using microwave heating and conventional heating methods. Microwave heating could reduce the treatment time necessary for the completion of the solid-phase reaction by 1/30. This decrease was attributed to an increase in the diffusion rate of Sn at the local heat spot in the indium oxide formed by microwave irradiation. However, microwave heating also decreased the amount of ITO produced, since the powder layer of the raw material was heated unevenly and had an uneven temperature distribution.Therefore, a microwave heating method including a mixing process was proposed in order to diminish the uneven progress of the ITO synthesis reaction in the powder layer. This revised method could increase the conversion to ITO, which is higher than that obtained by using the conventional heating method. Hence, the electric conductivity of the powder layer obtained by the proposed method was higher than that of the commercially supplied ITO powder layer.     

The Effect of Precarburizing Treatment on Morphology of the Boride Layer

Structural steel samples were boronized with a newly introduced boronizing pack containing boric acid (H₃BO₄), cryolite (Na₃B₄O₇), aluminum and aluminum oxide (Al₂O₃). In this research, the effect of precarburizing treatment on the morphology of the boride layer was studied and compared with unprecarburized specimens. The treated specimens were characterized using SEM, x-ray diffractometry, ED AX and microhardness tester. The results indicate that the boride layers are constituted by Fe₂B in either case. It has also been found that with precarburized specimens, the thickness of boride layer has been reduced and its morphology changed to a more flat structure.