Mechanical behavior of borides formed on borided cold work tool steel

In this study, some mechanical properties of borided cold work low-alloy tool steels were investigated. Boronizing was performed in a solid medium consisting of Ekabor-I powders at 1000°C for 2, 4 and 6 h. The substrate used in this study was high-carbon, low-alloy tool steel essentially containing 1.18 wt.% C, 0.70 wt.% Cr, 0.30 wt.% Mn, 0.10 wt.% V and 0.25 wt.% Si. The presence of borides (FeB+Fe₂B) formed on the surface of steel substrate was confirmed by optical microscope and X-ray diffraction (XRD) analysis. The hardness of the boride layer formed on the surface of the steel substrate and unborided steel substrate were 1854 and 290 kg/mm², respectively. Experimental results revealed that longer boronizing time resulted in thicker boride layers. Optical microscope cross-sectional observation of the borided layers revealed denticular morphology. The fracture toughness of the boride layers measured by means of a Vickers indenter with a load of 3 N was in the range of 2.52–3.07 MPa m^1/2.     

Tensile Properties of Boronized N80 Steel Tube Cooled by Different Methods

The microstructures and tensile properties of boronized N80 steel pipes by pack boriding under four different cooling conditions were investigated. The boride layer was composed of FeB and Fe₂B phases with a hardness range of 1200-1600 HV. Fan cooling and fan cooling with a graphite bar in the center of the boriding agent were employed to improve the tensile properties. As cooling velocity was increased, the thickness of boride layer and grain size of the steel substrate were consequently reduced, whereas the pearlite volume in steel substrate was increased, resulting in improvement of tensile properties. Boronized N80 steel pipe which was fan cooled with a graphite bar inside possessed the highest ultimate tensile strength and yield strength, in accordance with the mechanical properties required by API SPEC 5L. Fracture surface analysis revealed that the boronized N80 steel showed ductile fracture at room temperature.     

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.     

Influence of nickel silicides presence on hardness,elastic modulus and fracture toughness of gas-borided layer produced on Nisil-alloy

The two-stage gas boriding in N₂?H₂?BCl₃ atmosphere was applied to producing a two-zoned borided layer on Nisil-alloy. The process was carried out at 910 °C for 2 h. The microstructure consisted of two zones differing in their phase composition. The outer layer contained only a mixture of nickel borides (Ni₂B, Ni₃B) only. The inner zone contained additionally nickel silicides (Ni₂Si, Ni₃Si) occurring together with nickel borides. The aim of this study was to determine the presence of nickel silicides on the mechanical properties of the borided layer produced on Ni-based alloy. The hardness and elastic modulus were measured using the nanoindenter with a Berkovich diamond tip under a load of 50 mN. The average values of indentation hardness (H_I) and indentation elastic modulus (E_I) obtained in the outer zone were respectively (16.32±1.03) GPa and (232±16.15) GPa. The presence of nickel silicides in the inner zone reduced the indentation hardness (6.8?12.54 GPa) and elastic modulus (111.79?153.99 GPa). The fracture toughness of the boride layers was investigated using a Vickers microindentation under a load of 0.981 N. It was confirmed that the presence of nickel silicides caused an increase in brittleness (by about 40%) of the gas-borided layer.     

Effect of boronizing temperature and time on microstructure and abrasion wear resistance of Cr12Mn2V2 high chromium cast iron

In this study, Cr12Mn2V2 high chromium cast iron (HCCI) was boronized at 900 °C and 950 °C for 2, 4, 6, and 8 h, respectively. The borided samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness tester and ring-on-block wear tester in terms of the phase composition, microstructure and worn surface morphology, microhardness, fracture toughness and abrasive wear resistance. The boride layer thickness ranges from 8 to 33 µm. XRD studies show the boride layer formed at 950 °C/8 h consists of the phases FeB, Fe₂B and CrB, while for the layer formed at 900 °C/8 h, consists of mainly the Fe₂B phase. Abrasive wear test results show that the relative wear resistance of the borided HCCIs increases with increasing surface microhardness.     

Boroaluminide coatings on ferritic-martensitic steel deposited by low-temperature pack cementation

In this study, new boroaluminide protective coatings were deposited on ferritic-martensitic steel substrates (P91) using the pack cementation technique, at moderate temperatures in order not to influence the substrates' mechanical properties. Extensive thermodynamic calculations were performed initially, using the Thermocalc Computer program, so as to optimize the process parameters. The most important gas-precursors for successful deposition of the coatings were identified. The effect of pack composition on the formation and growth of boroaluminides at 715 °C, using pack powders containing Al and B as element depositing sources, two halide salts as activators, and Al₂O₃ as inert filler, was investigated. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al, B and Fe and an inner layer containing mostly B, Cr and Fe. The layers were characterized by means of optical and Scanning Electron Microscopy (SEM) in terms of coating morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coatings due to the boroaluminizing process.     

Influence of process duration on structure and chemistry of borided low carbon steel

In this study, we employed an ultra-fast boriding technique to grow hard boride layers on low carbon steel substrates using an induction furnace at 900 °C. The technique utilizes an electrochemical cell in which it is possible to achieve very thick (i.e., about 90 μm thick) boride layers in about 30 min. The effects of process duration on boride layer thickness, composition, and structural morphology were investigated using microscopic and X-ray diffraction (XRD) methods. We also developed an empirical equation for the growth rate of boride layers. XRD results revealed two principal boride phases: FeB and Fe₂B thickness of which was very dependent on the process duration. For example, Fe₂B phase was more dominant during shorter boriding times (i.e., up to 15 min.) but FeB became much more pronounced at much longer durations. The growth rate of total boride layer was nearly linear up to 30 min of treatment. However during much longer process duration, the growth rate assumed a somewhat parabolic character that could be expressed as d = 1.4904 (t)^0.5 + 11.712), where d (in μm) is the growth rate, t (in s) is duration. The mechanical characterization of the borided surfaces in plane and in cross-sections has confirmed hardness values as high 19 GPa at or near the borided surface (where FeB phase is present). However, the hardness gradually decreased to 14 to 16 GPa levels in the region where Fe₂B phase was found.     

Investigation of the diffusion kinetics of borided stainless steels

In this study, the kinetics of borides formed on AISI 420, AISI 304 and AISI 304L stainless steels was investigated. Boronizing treatment was carried out using Ekabor-II powders at the processing temperatures of 1123, 1173 and 1223 K for 2, 4 and 6 h. The phases of the boride layers of borided AISI 420, AISI 304 and AISI 304L stainless steels were FeB, Fe₂B, CrB and NiB, respectively. The thickness of the boride layer formed on the borided steels ranged from 4.6 to 64 μm depending on the boriding temperature, boriding time and alloying elements of the stainless steels. Depending on the chemical composition, temperature and layer thickness, the activation energies of boron in AISI 420, AISI 304 and AISI 304L stainless steels were found to be 206.161, 234.641 and 222.818 kJ/mol, respectively. The kinetics of growth of the boride layers formed on the AISI 420, AISI 304 and AISI 304L stainless steels and the thickness of the boride layers were investigated.     

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.     

Fracture Toughness of Thick Boride Layers Estimated by the Cross-Sectioned Scratch Test

New results about the fracture toughness (K_c) of thick boride layers estimated by the cross-sectioned scratch test are presented in this study. The FeB-Fe₂B layers developed at the surface of borided AISI 1018 and AISI 1045 steels and the Fe₂B layer formed on the borided AISI 1045 steel exposed to a diffusion annealing process (DAP) were used for this purpose. The cross-sectioned scratch tests were performed with a Vickers diamond stylus drawn across the thick boride layer under a constant load to produce a half-cone-shaped fracture near to the top surface of the borided steels. The height of the half-cone-shaped fracture as a function of the cross-sectioned scratch loads was used to determine the fracture toughness of the FeB and Fe₂B layers. The results showed a fracture resistance of \(\sim2.8\,{\text{MPa}}\sqrt m\) for the FeB layer formed at the surface of borided AISI 1045 steel. Likewise, the effect of the DAP on the surface of the borided AISI 1045 steel promoted the formation of an exclusively Fe₂B layer, with an increase in the fracture toughness of the whole boride layer around \(5\,{\text{MPa}}\sqrt m\). Finally, the principle of the technique can be used to minimize the influence of the anisotropic properties on the fracture toughness along the depth of boride layers.     

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.     

硼对等离子熔覆高硼铁基合金组织和性能的影响

采用等离子弧熔覆技术在20g钢表面堆焊Fe-Cr-B-C系的铁基复合材料,利用X射线衍射（XRD）,光学显微镜（OM）,扫描电镜（SEM）,洛氏硬度计及湿砂磨损试验机等试验设备进行检测、试验,研究不同硼加入量对熔覆层显微组织与性能的影响规律.结果表明,熔覆层显微组织由过饱和α-Fe枝晶固溶体、枝晶间硼化物共晶组织以及碳化物等组成;熔覆层中硬质相主要有Cr2B,CrB2,Fe2B,Cr7C3,B4C等;随着硼含量的增加,硼化物明显增多,当硼添加量为5%时熔覆层的硬度及耐磨性达到最佳,其硬度值为66.1 HRC,磨损量仅为0.383 g;继续增加硼的添加量,熔覆层的耐磨性能降低.     

Effect of Heat Treatment on Borides Precipitation and Mechanical Properties of CoCrFeNiAl<Subscript>1.8</Subscript>Cu<Subscript>0.7</Subscript>B<Subscript>0.3</Subscript>Si<Subscript>0.1</Subscript> High-Entropy Alloy Prepared by Arc-Melting and Laser-Cladding

Effects of heat treatment on borides precipitation and mechanical properties of arc-melted and laser-cladded CoCrNiFeAl_1.8Cu_0.7B_0.3Si_0.1 high-entropy alloys were comparatively studied. The arc-melted alloy contains lots of long strip borides distributed in the body-centered cubic phase, with a hardness about 643 HV_0.5. Laser-cladding can effectively inhibit the boride precipitation and the laser-cladded alloy is mainly composed of a simple bcc solid solution, with a high hardness about 769 HV_0.5, indicating the strengthening effect by interstitial boron atoms is greater than the strengthening by borides precipitation. Heat treatments between 800°C and 1200°C can simultaneously improve the hardness and fracture toughness of arc-melted alloys, owing to the boride spheroidization, dissolution, re-precipitation, and hence the increased boron solubility and nano-precipitation in the bcc solid solution. By contrast, the hardness of laser-cladded alloys reduce after heat treatments in the same temperature range, due to the decreased boron solubility in the matrix.     

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.     

Preparation of Fe2B boride coating on low-carbon steel surfaces and its evaluation of hardness and corrosion resistance

Fe₂B coating was prepared on low-carbon steel by surface alloying. A series of experiments were carried out to examine some surface properties of boride coating. The surface heat treatment of coated low-carbon steel was performed at 700 °C, 800 °C and 900 °C for 2 h, 4 h, 6 h and 8 h under hydrogen atmosphere. The boride coating was revealed by XRD analysis and the microstructure of the boride coating was analyzed by scanning electron microscopy (SEM). Depending on the temperature and time of the process, the hardness of the borided low-carbon steel ranged from 99 to 1100 HV. The hardness showed a maximum (about 1100 HV) at 900 °C for 8 h. The corrosion resistance of the borided samples was evaluated by the Tafel polarization and electrochemical impedance spectroscopy (EIS). Shift in the corrosion potential (E_corr) towards the noble direction was observed, together with decrease in the corrosion current density (I_corr), increase in the charge transfer resistance (R_ct) and decrease in the capacitance (C_c), which indicated an improvement in corrosion resistance with increasing temperature and time of the treatment.     

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.     

WC/钢复合材料渗硼中WC颗粒对硼化物生长的影响

采用粉末渗硼法,对三种WC含量不同的WC/钢复合材料进行渗硼处理.利用SEM、XRD及自制的黑白图片伪彩色处理仪等方法对渗硼层的组织结构、硬度分布、渗硼层厚度及渗硼层内裂纹萌生进行研究,重点分析了WC含量及分布状况对硼化物生长的影响.结果表明：进行渗硼后,材料表面可获得高硬度FeB＋Fe2B的渗硼层,且随WC含量的增加,Fe2B含量相对增加.在渗硼过程中,WC颗粒对硼化物的生长起阻碍作用,而且含量愈多,阻碍作用愈大,渗硼层愈浅.当WC颗粒的分布方向与渗硼方向平行时,对硼化物生长的阻碍作用最小,渗硼层厚且致密,且在冷却时不易产生裂纹;当WC颗粒的分布方向与渗硼方向垂直时,对硼化物的生长阻碍作用最大,获得的渗硼层较浅,并且在渗层中出现明显的疏松区;当WC粒子呈无序分布,对硼化物的生长阻碍作用介于上面两者之间.硼化物生长时,遇到大颗粒WC其尖端变钝并停止生长;遇到小颗粒WC可以＂吞食＂.     

Korrosionseigenschaften dünner Schichten im System Ti?B?N

Corrosion properties of thin coatings in the Ti? B? N system Thin titanium nitride TiN, boride TiB₂ and boronitride Ti(B, N) hard coatings were deposited on titanium substrates by the PVD-process Magnetron-Sputter-Ion-Plating (MSIP). They were characterized by X-ray diffractometry, SEM and WDX-analysis. With increasing B-content the Vickers hardness of the coatings increases. Photoelectron spectroscopic measurements show that all coatings are covered in atmosphere by thin oxid layer. Titanium nitride is electrochemically in 1 N sulphuric acid stable up to 1.3 V (SHE), above 1.3 V it becomes oxidized to titanium oxide TiO₂ and nitrogen N₂. The oxidation products were detected with XPS. Corrosion tests in nitric acid HNO₃ show that the corrosion resistance of titanium nitride is lower than the resistance of titanium. The corrosion of titanium boride and titanium boronitride in sulphuric acid is more intensive compared to titanium nitride. The borides cannot be passivated, but dissolve completely by anodic polarization.     

Oxidation resistance of boronized CoCrMo alloy

Boronizing of CoCrMo alloy has been performed by means of a powder-pack method using commercial LSB powders at 850, 900 and 950 °C for 8 h, respectively. In this study, the boronized CoCrMo alloy before and after oxidation tests were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The distribution of alloy elements of boronized samples from surface to interior was determined using energy-dispersive X-ray spectroscopy (EDS). XRD study showed the boride layer formed at 950 °C/8 h consisted of the phases Co₂B and CrB. Depending on boronizing temperature, the thickness of boride layer ranged from 2 to 11 μm. Cyclic oxidation behavior of the boride layer has been investigated at an oxidation temperature of 950 °C with a total exposure time up to 50 h in air. The test results indicated that the boronized CoCrMo alloy had superior oxidation resistance compared to unboronized sample.