Characterization of borided pure molybdenum under controlled atmosphere

In this study, the structural characterization and boriding kinetics of the molybdenum borides formed on the surface of borided pure molybdenum (Mo) have been investigated. Boronizing was carried out in solid medium with boron component forming Ekabor ® 2 (90% SiC, 5% KBF₄, 5%B₄C) powders at 1273 K, 1373 K for 2, 4, 6, 8 hours under a controlled atmosphere containing argon gas flow. The boride layer was characterized by the scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Energy dispersive spectroscopy (EDS) and Vickers microhardness tester. X-ray diffraction analysis showed that the boride layers on molybdenum consisted of MoB and Mo₂B phases. However, the MoB phase was observed at certain boriding temperature and boriding times. The thickness of boronized layers almost ranged from 12 to 42.5 μm with boriding time. A parabolic relationship was observed between boride layer thickness and boriding time. The growth rate constant and activation energy for the boride layer were calculated. The hardness of borides compounds formed on the surface of molybdenum ranged from 925 to 1150 HV_0.05, whereas the hardness of the untreated molybdenum sample was 258 HV_0.05.     

渗硼对Ti(C,N)基金属陶瓷组织和性能的影响

采用粉末冶金法制备了纳米改性Ti(C,N)基金属陶瓷,并用固体粉末法对其进行了渗硼处理。研究了渗硼处理对Ti(C,N)基金属陶瓷微观组织以及抗弯强度和硬度的影响。结果表明:渗硼处理使Ti(C,N)基金属陶瓷中生成了CoB、TiB2、MoB2和石墨相。金属陶瓷的渗硼层由硼化物层、扩散层和基体区组成,厚度为100～140μm。硼化物层主要由CoB组成,扩散层含有较多孔隙,基体区存在富硼的渗硼影响区,影响区具有与Ti(C,N)基金属陶瓷近似的微观组织,但金属相含量较少。渗硼处理使Ti(C,N)基金属陶瓷的抗弯强度降低,主要是由材料中产生的热应力、组织应力以及组织变化引起的。Ti(C,N)基金属陶瓷的表面硬度提高48.7%。在由渗硼层表面向内部100～140μm范围内,硬度呈下降趋势。     

Role of RE Element Nd on Boronizing Kinetics of Steels

Boronizing of AISI 1045 and ASTM W1-111/2 steels was carried out by pack boriding using Nd₂O₃-containing agent in the temperature range of 1053 to 1213?K. The effect of RE element Nd on boronizing kinetics was analyzed in terms of possible chemical reactions in boriding agent, surface elemental distribution and morphology evolution of the steels boronized at different temperatures. The results showed that the RE element Nd has two opposite effects on boronizing process, i.e., promoting effect at high temperatures and hindering effect at low temperatures. Boronizing using Nd₂O₃-containing agent can remarkably reduce the diffusion activation energy at higher temperatures. Empirical equations relating the boride layer thickness with processing time and temperature are established. Based on these equations, the contour diagrams of boride layer thickness for the studied steels boronized with addition of 5% Nd₂O₃ are presented.     

Experiment and modeling of TiB2/TiB boride layer of Ti−6Al−2Zr−1Mo−1V alloy

The influence of the boriding conditions on the boride layers was examined by boriding Ti−6Al−2Zr− 1Mo−1V alloy in the temperature range of 920−1120°C. The experimental results show that the boride layers were composed of a continuous thin outer layer of TiB₂ and a thick inner layer of TiB with whiskers or needle-like morphologies that extended into the substrate. Thick and compact boride layers were obtained when the boriding temperatures were 1000−1080 °C, and the treatment time exceeded 8 h. The boride layer depth increased with the boriding temperature and time, and the growth kinetics of the boride layers was characterized by a parabolic curve. The growth kinetics of the boride layers, including both TiB₂ and TiB layers, were predicted by establishing a diffusion model, which presented satisfactory consistency with the experimental data. As a result, the activation energies of boron in the TiB₂ and TiB layers were estimated to be 223.1 and 246.9 kJ/mol, respectively.     

渗硼对Ti(C,N)基金属陶瓷抗热震性能的影响

采用粉末冶金法制备了Ti(C,N)基金属陶瓷,并对其进行了固体渗硼。研究了渗硼后金属陶瓷的显微组织和力学性能以及渗硼对抗热震性能的影响。结果表明,Ti(C,N)基金属陶瓷的渗硼层由硼化物层、扩散层和基体区组成;渗硼使金属陶瓷的表面硬度提高,抗弯强度降低,使导致金属陶瓷热震残留强度急剧下降的临界热震温差降低约100℃;渗硼使Ti(C,N)基金属陶瓷热震后的残留强度降低,主要是分布不均和形状不规则的孔洞所致;当热震温差较小时,渗硼使金属陶瓷表面萌生热震裂纹的孕育期延长,从而推迟了主裂纹的形成;而热震温差较大时,经渗硼的金属陶瓷热震裂纹扩展较快,易形成龟裂。     

The growth of single Fe2B phase on low carbon steel via phase homogenization in electrochemical boriding (PHEB)

In this study, we introduce a new electrochemical boriding method that results in the formation of a single-phase Fe₂B layer on low carbon steel substrates. Although FeB phase is much harder and more common than Fe₂B in all types of boriding operations, it has very poor fracture toughness; hence, it can fracture or delaminate easily from the surface under high normal or tangential loading. We call the new method “phase homogenization in electrochemical boriding” (PHEB), in which carbon steel samples undergo electrochemical boriding for about 15 min at 950 °C in a molten electrolyte consisting of 90% borax and 10% sodium carbonate, then after the electrical power to the electrodes is stopped, the samples are left in the bath for an additional 45 min without any polarization. The typical current density during the electrochemical boriding is about 200 mA/cm². The total original thickness of the resultant boride layer after 15 min boriding was about 60 μm (consisting of 20 μm FeB layer and 40 μm Fe₂B layer); however, during the additional phase homogenization period of 45 min, the thickness of the boride layer increased to 75 μm and consisted of only Fe₂B phase, as confirmed by glancing-angle x-ray diffraction and scanning electron microscopy in backscattering mode. The microscopic characterization of the boride layers revealed a dense, homogeneous, thick boride layer with microhardness of about 16 GPa. The fracture behavior and adhesion of the boride layer were evaluated by the Daimler-Benz Rockwell C test and found to be excellent, i.e., consistent with an HF1 rating.     

Indentation size effect on the Fe2B/substrate interface

This study evaluated the indentation size effect on the Fe₂B/substrate interface using the Berkovich nanoindentation technique. First, the Fe₂B layers were obtained at the surface of AISI 1018 borided steels by the powder-pack boriding method. The treatment was conducted at temperatures of 1193, 1243 and 1273 K for 4, 6 and 8 h at each temperature. The boriding of AISI 1018 steel resulted in the formation of saw-toothed Fe₂B surface layers. The formation of a jagged boride coating interface can be attributed to the enhanced growth at the tips of the coating fingers, due to locally high stress fields and lattice distortions. Thus, the mechanical properties achieved at the tips of the boride layer are of great importance in the behavior of borided steel.Applied loads in the range of 10 to 500 mN were employed to characterize the hardness in the tips of the Fe₂B/substrate interface for the different conditions of the boriding process. The results showed that the measured hardness depended critically on the applied load, which indicated the influence of the indentation size effect (ISE). The load-dependence of the hardness was analyzed with the classical power-law approach and the elastic recovery model. The true hardness in the tips of the Fe₂B/substrate interface was obtained and compared with the boriding parameters. Finally, the nanoindentation technique was used to estimate the state of residual stresses in this critical zone of the Fe₂B/substrate interface.     

Effects of electrochemical boriding process parameters on the formation of titanium borides

In this study, the boriding of titanium via molten salt electrolysis was investigated in borax based electrolyte at various current densities (50–700 mA/cm²), temperatures (900–1200°C) and process durations (1 min-4 h). Thin film XRD results revealed that two main titanium boride phases TiB₂ and TiB was formed even after 1 minute of process time. Scanning electron microscopy (SEM) images conducted on the cross-sections demonstrated a bilayer boride structure composed of a continuous uniform TiB₂ phase and TiB whiskers that grew below the TiB₂ layer toward the substrate. Dependence of boride layer thickness and morphology on the process parameters was evaluated. The results of the study showed that temperature of boriding was the most critical parameter both on boriding rate and morphology of the boride layer. It was possible to grow 8 μm thick TiB₂ layer on titanium in 30 minutes of boriding at 1200°C.     

A Kinetic Model for the Boriding Kinetics of AISI D2 Steel During the Diffusion Annealing Process

In this work, a diffusion model was proposed to estimate the boron activation energies for FeB and Fe₂B layers during the pack-boriding of AISI D2 steel at temperatures of 1223, 1253 and 1273 K for a treatment time varying between 2 and 10 h. This model considers the effect of boride incubation times during the formation of the FeB and Fe₂B phases. To study the influence of diffusion annealing process on the boriding kinetics of AISI D2 steel, the mass balance equations were modified in order to follow the evolution of boride layers as a function of annealing time for the specified boriding parameters. Finally, the kinetic model was validated by a comparison of the experimental thicknesses of boride layers with the predicted ones at a temperature of 1243 K for 2, 4 and 6 h. A simple equation was then obtained for estimating the total time necessary to get a single boride layer (Fe₂B) that depends on the boriding parameters and on the thickness of each boride layer prior to the diffusion annealing process.     

渗硼对Ti(C,N)基金属陶瓷刀具性能的影响

采用粉末冶金法制备了Ti(C,N)基金属陶瓷,并用固体渗硼法对其进行了渗硼处理。研究了渗硼后金属陶瓷的微观组织和力学性能以及渗硼对切削性能的影响。结果表明:Ti(C,N)基金属陶瓷的渗硼层组织由硼化物层、扩散层和基体区组成。渗硼使金属陶瓷的表面硬度提高,抗弯强度降低。渗硼使金属陶瓷刀具在切削速度为200 m/min时的使用寿命提高约1倍;在300 m/min切削速度下,渗硼对延长金属陶瓷刀具的使用寿命没有明显作用;切削速度增至400 m/min时,渗硼使金属陶瓷刀具的使用寿命变短。强烈的热冲击是导致高速切削条件下渗硼层耐磨性降低的主要原因。渗硼层有效地减轻了金属陶瓷刀具表面发生的粘结,并抑制了刀具的扩散磨损和氧化磨损。     

Kinetics of plasma paste boronized AISI 8620 steel in borax paste mixtures

In the present study, AISI 8620 steel was plasma paste boronized by using various borax paste mixtures. The plasma paste boronizing process was carried out in a dc plasma system at a temperature of 973, 1023 and 1073 K for 2, 5 and 7 h respectively in a gas mixture of 70% H₂-30% Ar under a constant pressure of 10 mbar. The properties of the boride layer were evaluated by optical microscopy, X-ray diffraction, the micro-Vickers hardness tester and the growth kinetics of the boride layers. The thickness of the boride layers varied from 14 to 91 μm depending on the boronizing time and temperature. X-ray diffraction analysis of boride layers on the surface of the steel revealed the formation of FeB and Fe₂B phases. Depending on the temperature and layer thickness, the activation energies of boron in steel were found to be 99.773 kJ/mol for 100% borax paste.     

Investigation of corrosion behaviors at different solutions of boronized AISI 316L stainless steel

In this study, corrosion behaviors of boronized and non-boronized AISI 316L stainless steel (AISI 316L SS) were investigated with Tafel extrapolation and linear polarization methods in different solutions (1 mol dm^?3 HCl, 1 mol dm^?3 NaOH and 0.9% NaCl) and in different immersion times. AISI 316L SS were boronized by using pack boronizing method for 2 and 6 hours at 800 and 900°C within commercial Ekabor®-2 powder. Surface morphologies and phase analyses of boride layers on the surface of AISI 316L SS were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis. SEM-EDS analyses show that boride layer on AISI 316L SS surface had a flat and smooth morphology. It was detected by XRD analyses that boride layer contained FeB, Fe₂B, CrB, Cr₂B, NiB and Ni₂B phases. Boride layer thickness increases with increased boronizing temperature and time. The corrosion experiments show that boride layer significantly increased the corrosion resistance of the AISI 316L SS in 1 mol dm^?3 HCl solution. While no positive effect of the boride layer was observed in the other solutions the corrosion resistance of the borid layer on AISI 316L SS was increased in all solution with the increase of the waiting periods.     

Diffusion Boronizing of H11 Hot Work Tool Steel

The H11 hot work tool steel was boronized at various processing parameters, austenitized, quenched, and tempered to a core hardness of 47-48 HRC. Microstructure, phase constitution, and microhardness of boronized layers were investigated. Effect of boronized region on the bulk properties was determined by the Charpy impact test. Structure of boronized regions is formed by the compound layers and diffusion inter-layer. The compound layers consisted of only (Fe,Cr)₂B phase, but in the case of longer processing time, they contained also of the (Fe,Cr)B-phase. The inter-layer contained enhanced portion of carbides, formed due to carbon diffusion from the boride compounds toward the substrate. Microhardness of boronized layers exceeded considerably 2000 HV 0.1. However, boronizing led to a substantial lowering of the Charpy impact toughness of the material.     

渗硼对45钢耐液态金属腐蚀性能影响的研究

对经过渗硼处理的45钢在液态Zn、Al和Zn-Al合金中的耐蚀性进行研究。结果表明：渗硼处理后45钢在液态Zn、Al和Zn—Al中的耐蚀性大为提高；硼化物层对Zn、Zn—Al合金具有良好的耐蚀性，在Al液中的耐蚀性略低。表明钢的渗硼处理在耐液态金属腐蚀上有较好的应用前景。硼化物在液态Zn、Al和Zn—Al液中的腐蚀是硼化物的均匀溶解过程，没有出现择优腐蚀。     

B（C2H5）3等离子辅助渗硼的研究

对新型渗硼剂Ｂ（Ｃ２Ｈ５）３的渗硼工艺进行了研究。结果表明：在正常渗硼工艺条件下,基体表面没有形成连续致密的渗硼层,而是形成了一层数μｍ厚的硼碳层;在间歇渗硼工艺条件下,基体表面形成了一层致密的渗硼层,这是因为通过溅射消除了在渗硼过程中沉积在基体表面的硼碳层,使硼原子在渗硼时能无阻碍地向基体内部扩散的缘故     

钢复合渗硼层的组织结构及显微硬度

分析并系统研究了合金元素对复合渗硼层宏观组织,相成分及显微硬度的影响,结果表明,合金元素使Ｆｅ－Ｂ相图上的共晶点移动,从而改变复合渗硼层中高硬度硼化物和低硬度共晶体的相对含量。复合渗硼层的显微硬度比渗硼层的高０．５－１倍。     

The Study on Plasma Boriding of H13 Steel at Low Temperature Assisted by Surface Nanocrystallization Technology

Plasma boriding treatment was carried out at low temperature for the hot work die steel H13 assisted by surface nanocrystallization technology in this paper.At the same time,the thermal fatigue property of it was investigated through thermal fatigue testing with 3000 continuous cycles from room temperature to 700℃.The changes of structure and grain size in surface layer were characterized by high-resolution transmission electron microscopy(HRTEM).After plasma boriding at 580℃ for 4 h,the phase composition,morphology and in-situ nanomechanical property of boride layer were investigated by X-ray diffraction spectroscopy(XRD),scanning electron microscope(SEM),nanoindentation test,respectively.The results show that the boride layer with about thickness of 5μm is composed with two phases of Fe2B and FeB.The nanohardness of boride layer is as high as 21 GPa.Furthermore,thermal fatigue testing shows that the boride layer with excellent oxidation resistance and mechanical strength at elevated temperatures could effectively delay the crack initiation and impede the crack propagation.Therefore,the thermal fatigue property of H13 can be remarkably improved.     

Electrochemical boriding of titanium for improved mechanical properties

In this study, we introduce a rapid boriding technique that can produce very thick titanium diboride (TiB₂) layers on titanium substrates. We also discuss the effects of process duration on boride layer thickness, chemistry and, morphology. In our experiments, the boriding of commercial purity titanium (CP-Ti) substrates was carried out in an electrochemical cell in which we used a mixture of sodium tetraborate and sodium carbonate as the base ingredients of molten electrolyte at 950 °C and at current density of 300 mA/cm². The titanium test pieces were attached to the cathode holder of the electrochemical cell while a graphite crucible served as the anode. Both TiB and TiB₂ phases were detected by X-ray diffraction method even after 5 min of treatment. Scanning electron microscopy (SEM) images verified that the production of 4.5 µm thick TiB₂ layers was feasible after boriding for an hour. The boride layers consisted of a homogeneous TiB₂ phase on the top and TiB whiskers toward the substrate. The micro-indentation studies indicated that the layer on top has hardness values as high as 40 GPa. The main advantages of this technique are its ability to produce very thick and hard TiB₂ quickly and to create no gaseous emissions or solid wastes during or after the treatment.     

The effect of boron-pack refreshment on the boriding of mild steel by the spark plasma sintering (SPS) process

Mild steel samples were borided with and without boron pack refreshment using the spark plasma sintering (SPS) process. Results show that the borided samples with boron pack refreshment developed a thicker boride layer compared to that without boron pack refreshment for the same boriding duration. When boriding duration is t < 120 min, the boriding growth in the samples borided with boron pack refreshment followed a parabolic growth pattern. In contrast, the boride growth in samples processed without boron-pack refreshment deviates from parabolic at t = 60 min. Computer simulation shows that the boron concentration change in the boriding media during the boriding process is an important factor affecting the composition and final thickness of the boride layer.     

2205双相不锈钢包埋粉末渗硼性能研究

目的 提高2205双相不锈钢的硬度和耐蚀性能.方法 2205双相不锈钢采用固体包埋粉末渗硼,于马沸炉中分别在830、860、890℃下保温5 h;在860℃下保温3、5、7 h,随炉冷却到室温.用金相显微镜、扫描电镜观察渗硼层的形貌和测定渗硼层的厚度,用维氏硬度计测定渗硼层的硬度,用纳米压痕仪测定渗硼层不同深度的硬度,用X射线衍射仪分析渗硼层的物相组成,评定渗硼层与基体的结合力,做不同介质下耐蚀性对比试验.结果 渗硼层与基体结合牢固,破坏等级评为一级,渗硼层主要由Fe2 B单相组成.在860℃下保温不同时间,渗硼层的厚度及硬度均随时间的增长而逐渐增大;在不同温度下保温5 h时,渗硼层的厚度及硬度随温度的升高而逐渐增大.渗硼后试样在质量分数都为10%的HCl和NaCl溶液中耐蚀性提高,在质量分数均为10%的H2 SO4、NaOH和HNO3溶液中耐蚀性变差.结论 固体粉末包埋法渗硼工艺改善了2205双相不锈钢的表面组织和性能,有效提高了其硬度及耐蚀性.