Characterization of Tribological and Mechanical Properties of the Si3N4 Coating Fabricated by Duplex Surface Treatment of Pack Siliconizing and Plasma Nitriding on AISI D2 Tool Steel

Silicon nitride (Si₃N₄) coating was deposited on AISI D2 tool steel through employing duplex surface treatments—pack siliconizing followed by plasma nitriding. Pack cementation was performed at 650 °C, 800 °C, and 950 °C for 2 and 3 hours by using various mixtures to realize the silicon coating. X-ray diffraction analyses and scanning electron microscopy observations were employed for demonstrating the optimal process conditions leading to high coating adhesion, uniform thickness, and composition. The optimized conditions belonging to siliconizing were employed to produce samples to be further processed via plasma nitriding. This treatment was performed with a gas mixture of 75 pct H₂-25 pct N₂, at the temperature of 550 °C for 7 hours. The results showed that different nitride phases such as Si₃N₄-β, Si₃N₄-γ, Fe₄N, and Fe₃N can be recognized as coatings reinforcements. It was demonstrated that the described composite coating procedure allowed to obtain a remarkable increase in hardness (80 pct higher with respect to the substrate) and wear resistance (30 pct decrease of weight loss) of the tool steel.

     

High-Temperature Behavior of a High-Velocity Oxy-Fuel Sprayed Cr3C2-NiCr Coating

High-velocity oxy-fuel (HVOF) sprayed coatings have the potential to enhance the high-temperature oxidation, corrosion, and erosion-corrosion resistance of boiler steels. In the current work, 75?pct chromium carbide-25?pct (nickel-20?pct chromium) [Cr₃C₂-NiCr] coating was deposited on ASTM SA213-T22 boiler steel using the HVOF thermal spray process. High-temperature oxidation, hot corrosion, and erosion-corrosion behavior of the coated and bare steel was evaluated in the air, molten salt [Na₂SO₄-82?pct Fe₂(SO₄)₃], and actual boiler environments under cyclic conditions. Weight-change measurements were taken at the end of each cycle. Efforts were made to formulate the kinetics of the oxidation, corrosion, and erosion-corrosion. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM)/energy dispersive spectroscopy (EDS) techniques were used to analyze the oxidation products. The coating was found to be intact and spallation free in all the environments of the study in general, whereas the bare steel suffered extensive spallation and a relatively higher rate of degradation. The coating was found to be useful to enhance the high-temperature resistance of the steel in all the three environments in this study.     

Effects of Phosphorus and Carbon Contents on Amorphous Forming Ability in Fe-based Amorphous Alloys Used for Thermal Spray Coatings

Cost-effective Fe-based amorphous alloys used for thermal spray coatings were developed by varying contents of P and C, and their microstructure, hardness, and corrosion resistance were analyzed. In order to achieve chemical compositions having high amorphous forming ability, thermodynamically calculated phase diagrams of Fe-Al-P-C-B five-component system were used, from which compositions of super-cooled liquid having the lowest driving force of formation of crystalline phases were obtained. The thermodynamic calculation results showed that only phases of Fe₃P and Fe₃C were formed in the Fe₇₈Al₂P_(18.3?x)C _x B_1.7 alloy system. Considering driving force curves of Fe₃P and Fe₃C, the carbon contents were selected to be 6.90 and 7.47 at. pct, when the thermodynamic calculation temperatures were 697 K (414 °C) and 715 K (442 °C), respectively. According to the microstructural analysis of suction-cast alloys, the Fe₇₈Al₂P_10.83C_7.47B_1.7 alloy showed a fully amorphous microstructure, whereas the Fe₇₈Al₂P_11.40C_6.9B_1.7 and Fe₇₈Al₂P_10.3C_8.0B_1.7 alloys contained Fe₃P and Fe₃C phases. This Fe₇₈Al₂P_10.83C_7.47B_1.7 alloy showed the better hardness and corrosion resistance than those of conventional thermal spray coating alloys, and its production cost could be lowered using cheaper alloying elements, thereby leading to the practical application to amorphous thermal spray coatings.     

工艺参数对超音速火焰喷涂Fe基非晶涂层性能的影响

Fe基非晶涂层具有优异的耐磨、耐蚀性能,以及较高的性价比,适合在表面防护涂层领域广泛应用。本文通过正交试验研究了煤油流量、氧气流量、送粉速率、喷涂距离对超音速火焰喷涂制备的Fe基非晶涂层的孔隙率、硬度、耐磨性能的影响。采用图像法、显微硬度计和摩擦磨损试验机分别对Fe基非晶涂层的孔隙率、硬度、耐磨性能进行了表征。采用X射线衍射仪和扫描电镜分别对涂层的相组成和显微结构进行了表征。通过极差分析法分析得出以涂层孔隙率最低为目标的优化制备工艺,最佳喷涂工艺参数为:煤油流量0.41 L/min,氧气流量830 L/min,喷涂距离430 mm,送粉速率40 g/min。结果表明:送粉速率和氧气流量对涂层孔隙率影响较大,进而影响涂层的硬度及耐磨性能。孔隙率随着氧气流量和送粉速率的增加而增加,随着煤油流量和喷涂距离的增加而降低。制备的Fe基非晶涂层硬度达到1158.9HV0.2,孔隙率为1.22%,磨损实验的质量损失量只有316L不锈钢的一半。     

Preparation of Al-based amorphous coatings and their properties

Al₈₆Ni₈Co₁La₁Y₂Gd₂ amorphous coatings were prepared using cold gas kinetic spray technology.The results show that Al₈₆Ni₈Co₁La₁Y₂Gd₂ amorphous coatings are achieved with the porosity about 3.2%,thickness about 893 μm,the amount of amorphous phase about 82.5%,the hardness about 300 HV0.2.The corrosion potential and anti-corrosion life of 7075 T6 alloy aluminum are about-0.78 V and 72 h,respectively.The electrochemical analysis and neutral salt spray are about-0.69 V corrosion potential and 274 h anti-corrosion life for amorphous Al-based coatings,respectively.Therefore,the life of the Albased amorphous coatings is about 3.8 times that of 7075 T6 aluminum alloy.Besides,the failure mechanism was analyzed using TEM in this investigation.In a word,Al₈₆Ni₈Co₁La₁Y₂Gd₂ coatings keep dense structure,high amorphous content,favorable amorphous phase stabilizing ability and longer anticorrosion life.That is,Al₈₆Ni₈Co₁La₁Y₂Gd₂ coatings have better comprehensive properties.Therefore,these findings indicate that the present Al₈₆Ni₈Co₁La₁Y₂Gd₂ amorphous coatings prepared using cold gas kinetic spray technique can protect aluminum alloy very well and they can be considered to be used in aviation field.     

Magnetron Sputtered TiN Coatings Modified by Chromium,Nickel and Electroless Nickel (EN) Interlayers on Mild Steel

Abstract

TiN films were deposited by reactive d.c. magnetron sputtering on mild steel substrate. Because of presence of inherent porosity and internal stresses, TiN coatings cannot be relied to give corrosion protection; also TiN coatings need a good load support. Electroplated chromium and nickel and electroless nickel (EN) were deposited by plating as interlayers below the TiN coatings to study comparatively the effect of these interlayers. Chromium was electrodeposited from conventional sulfate catalysed chromic acid bath and nickel using Watt's bath while EN by electroless deposition process using acidic hypophosphite bath. Three different thicknesses viz. 2. 4 and 10 μm of interlayers were employed to study their influence on TiN coatings. The corrosion behaviour of TiN coated mild steel samples with and without the interlayers was studied using potemiodynamic measurement technique in deaerated IN H₂SO₄ electrolyte. It was observed that TiN coatings on mild steel without any interlayer almost mimic the behaviour of the substrate, while the presence of any of the three interlayers showed a considerable improvement in the corrosion resistance.

Microhardness measurements have shown that the surface hardness values of TiN coatings on mild steel increased to 1907 HK₂₅ from about 1000 HK₂₅ when employed with chromium interlayer. and to 1484 HK₂₅ with EN interlayer, while electroplated nickel as an interlayer increased the hardness to a lesser extent (1289 HK₂₅).

X-ray diffraction analysis has shown that the phases present in the TiN coatings were mainly TiN (200) and TiN (111). Chromium coated samples were found to show the broadening of Fe (110) peak, which also corresponds to Cr (110) peak. Interlayer nickel showed the presence of mainly Ni (200) and Ni (111) phases while EN was amorphous in structure. The crystalline phases Ni₃P and Ni were evident when TiN top-coat was given by d.c. magnetron sputtering on EN plated mild steel samples.     

Investigation of Corrosion Behavior of Borided Gear Steels

In this study, corrosion behaviors of GS18NiMoCr36 (GS 18) and GS32NiCrMo6.4 (GS 32) gear steels borided in Ekabor-II powder at the temperature of 950 °C for 2 and 6 h were investigated in a 6 % M HCI acid solution. The boride layer was characterized by optical microscopy, X-ray diffraction technique and the Micro-Vickers hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe₂B, CrB and Cr₂B compounds. The thickness of the boride layer increases by increasing boriding time for gear steels. The hardness of the boride compounds formed on the surface of the steels GS 18 and GS 32 ranged from 1,728 to 1,905 HV_0,05 and 1,815 to 2,034 HV_0,05 respectively, whereas Vickers hardness values of the untreated steels GS 18 and GS 32 were 335 HV_0,05 and 411 HV_0,05, respectively. The corrosion resistance of borided gear steels is higher compared with that of unborided steels. The boride layer increased the corrosion resistances of gear steels 4–6-fold.     

The effect of metallic elements on the crystallization behavior of amorphous Fe-Si-B alloys

The crystallization behavior of amorphous Fe_84-X Si₆B₁₀M_X (M=Nb, Zr, V, or Cu) alloys was examined using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) with the aim of clarifying the effect of additional M elements. The compositional dependence of the first crystallization temperatureT _x1 increased in the order of Zr > Nb > V; however, the addition of 1 at. pct Cu caused a decrease inT _x1. Such an effect of the M elements on the thermal stability of an amorphous phase was interpreted in terms of the difference in the atomic size. These alloys were composed of a mixed structure ofα-Fe and amorphous phases after aging for 3.6 ks in the first exothermic temperature range. The addition of more than 3 at. pct Nb or Zr significantly affected the morphology and grain size of theα-Fe phase. However, their particles possessed dendritic morphology with a grain size of 0.1 to 0.3 μm, when the Nb or Zr content was less than 2 at. pct. Further addition of these elements brought about the formation of sphericalα-Fe particles. The average grain size, for instance, was as small as 20 nm in the aged alloy containing 6 at. pct Nb, which shows that a remarkable grain refinement occurs with increasing Nb content.     

Effects of zinc coatings on the stress corrosion cracking and hydrogen embrittlement of low-alloy steel

The effects of electroplated and hot-dip zinc coatings on the fracture of low-alloy steel AISI 4140 bars tempered to hardnesses in the range Rc 33 to 49 were studied. Either electroplated or hot-dip zinc coatings decrease resistance to stress corrosion cracking,i.e., they reduceK _sc, the threshold stress intensity for stress corrosion cracking in 3.5 wt pct NaCl solution. AboveK _scelectroplated-zinc coatings do not appear to affect the crack-growth rate, although the incubation period prior to the onset of crack growth is reduced. Hot-dip zinc coatings increase stress corrosion crack growth rates slightly because of the additive effect of internal dissolved hydrogen. Hot-dip zinc coatings reduce the critical stress intensity for fracture in the absence of a corrosive environment because of embrittlement by internal hydrogen which is released from traps during hot-dip coating and confined by the inter metallic coatings which form on the steel surface in the hot dip bath. A simple fracture mechanics analysis indicates that either increasing diameter or the presence of a zinc coating lowers the critical hardness at which the stress corrosion cracking of structural bolts can occur.     

Residual stresses in high-velocity oxy-fuel metallic coatings

X-ray based residual stress measurements were made on type 316 stainless steel and Fe₃Al coatings that were high-velocity oxy-fuel (HVOF) sprayed onto low-carbon and stainless steel substrates. Nominal coating thicknesses varied from 250 to 1500 μm. The effect of HVOF spray particle velocity on residual stress and deposition efficiency was assessed by preparing coatings at three different torch chamber pressures. The effect of substrate thickness on residual stress was determined by spraying coatings onto thick (6.4 mm) and thin (1.4 mm) substrates. Residual stresses were compressive for both coating materials and increased in magnitude with spray velocity. For coatings applied to thick substrates, near-surface residual stresses were essentially constant with increasing coating thickness. Differences in thermal expansion coefficient between low-carbon and stainless steels led to a 180 MPa difference in residual stress for Fe₃Al coatings. Deposition efficiency for both materials is maximized at an intermediate (∼600 m/s) velocity. Considerations for X-ray measurement of residual stresses in HVOF coatings are also presented.     

Influence of Fracture Toughness and Microhardness on the Erosive Wear of Cermet Coatings Deposited by Thermal Spray

An evaluation of the relationship between the microhardness and fracture toughness with resistance to erosive wear of WC10Co4Cr, WC-12Co, and Cr3C2-25NiCr coatings was conducted. Powder and flexible cored wire feedstock materials were applied by high-velocity oxygen fuel (HVOF) and flame spray (FS), respectively. The erosive wear mechanism prevailing in the coatings was found to be brittle, which also explains the higher erosion rate for the experimental condition using the particle impact angle of 90 deg and impact velocity of 9.33 m/s. The best wear performance was for the coatings applied by HVOF that attains 1.83 mm³/kg for the 90 deg/3.61 m/s test condition. The coating obtained with the WC-10Co4Cr material using the FSFC method showed tungsten carbide decarburization, justifying its poor mechanical properties and poor performance in the erosive wear test. Flame-sprayed flexicords proved to be a promising alternative to HVOF in obtaining coatings with low porosity and acceptable mechanical properties, especially in applications where the use of the HVOF technique is inadequate because of inaccessibility or excessively high cost. Values of K _c for the coatings obtained by HVOF (7.35 to 10.83 MPa.m^1/2) were between two and three times greater than the values obtained for the coatings resulting from FSFC (2.39 to 3.59 MPa.m^1/2), in a similar manner as with the microhardness.

     

Microstructural Characterization and Properties Evaluation of Ni-Based Hardfaced Coating on AISI 304 Stainless Steel by High Velocity Oxyfuel Coating Technique

The present study concerns a detailed investigation of microstructural evolution of nickel based hardfaced coating on AISI 304 stainless steel by high velocity oxy-fuel (HVOF) deposition technique. The work has also been extended to study the effect of coating on microhardness, wear resistance and corrosion resistance of the surface. Deposition has been conducted on sand blasted AISI 304 stainless steel by HVOF spraying technique using nickel (Ni)-based alloy [Ni: 68.4 wt pct, chromium (Cr): 17 wt pct, boron (B): 3.9 wt pct, silicon (Si): 4.9 wt pct and iron (Fe): 5.8 wt pct] of particle size 45 to 60 ??m as precursor powder. Under the optimum process parameters, deposition leads to development of nano-borides (of chromium, Cr₂B and nickel, Ni₃B) dispersion in metastable and partly amorphous gamma nickel (??-Ni) matrix. The microhardness of the coating was significantly enhanced to 935 VHN as compared to 215 VHN of as-received substrate due to dispersion of nano-borides in grain refined and partly amorphous nickel matrix. Wear resistance property under fretting wear condition against WC indenter was improved in as-deposited layer (wear rate of 4.65 × 10^?7 mm³/mm) as compared to as-received substrate (wear rate of 20.81 × 10^?7 mm³/mm). The corrosion resistance property in a 3.56 wt pct NaCl solution was also improved.     

热喷涂Fe基非晶合金涂层的研究现状

综述了超音速火焰喷涂(HVOF),等离子喷涂(PS)技术的性能特征,以及运用热喷涂技术制备Fe基非晶涂层的发展历史与现状。从非晶合金涂层的高硬度、耐磨性及腐蚀性能等方面阐述了非晶合金涂层的优越性,对新型Fe基非晶涂层的形成机理进行研究,探讨采用超音速火焰喷涂技术制备高质量非晶合金涂层的关键因素。并展望了采用热喷涂技术制备非晶合金涂层的未来发展趋势。     

热喷涂Fe基非晶合金涂层的微观结构与摩擦磨损行为

分别采用超音速火焰喷涂工艺和爆炸喷涂工艺,在Q235不锈钢基体上制备Fe基非晶合金涂层,对比研究这2种非晶合金涂层在室温下的干摩擦磨损特性,并探讨摩擦磨损机理.结果表明,与超音速火焰喷涂工艺制备的Fe基非晶合金涂层相比,采用爆炸喷涂工艺制备的涂层更致密,孔隙率为2.1％,显微硬度更高,平均硬度高达1 095.6 HV,且耐磨性更好;并且涂层摩擦因数增至稳定值的时间较短,具有更稳定的摩擦磨损行为.超音速火焰喷涂涂层的磨损形式主要以疲劳磨损为主,而爆炸喷涂涂层的磨损形式为粘着磨损和磨粒磨损的综合作用,并以粘着磨损为主.     

On the Prospects of Using Nanoindentation and Wear Test to Study the Mechanical Behavior of Fe-Based Metallic Glass Coating Reinforced by B4C Nanoparticles

In this study, Fe-based metallic glass was served as the matrix in which various ratios of hard B₄C nanoparticles as reinforcing agents were prepared using a high-energy mechanical milling. The feedstock nanocomposite powders were transferred to the coatings using a high-velocity oxygen fuel process. The results showed that the microstructure of the nanocomposite coating was divided into two regions, namely a full amorphous phase region and homogeneous dispersion of B₄C nanoparticles with a scale of 10 to 50 nm in a residual amorphous matrix. As the B₄C content is increased, the hardness of the composite coatings is increased too, but the fracture toughness begins to be decreased at the B₄C content higher than 20 vol pct. The optimal mechanical properties are obtained with 15 vol pct B₄C due to the suitable content and uniform distribution of nanoparticles. The addition of 15 vol pct B₄C to the Fe-based metallic glass matrix reduced the friction coefficient from 0.49 to 0.28. The average specific wear rate of the nanocomposite coating (0.48 × 10⁻⁵ mm³ Nm⁻¹) was much less than that for the single-phase amorphous coating (1.23 × 10⁻⁵ mm³Nm⁻¹). Consequently, the changes in wear resistance between both coatings were attributed to the changes in the brittle to ductile transition by adding B₄C reinforcing nanoparticles.

     

Effects of Duty Cycle,Current Frequency,and Current Density on Corrosion Behavior of the Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy in Artificial Seawater

In this study, the effects of duty cycle, current frequency, and current density on corrosion behavior of the plasma electrolytic oxidation (PEO) coatings on 6061 Al alloy in artificial seawater (3.5 wt pct NaCl solution) were investigated. To serve this purpose, the electrical parameters of a unipolar pulsed current were applied during the PEO process on 6061 Al alloy in alkaline silicate electrolyte with and without Al₂O₃ nanoparticles. The coating morphology and microstructure were characterized by the scanning electron microscopy. The corrosion behavior and electrochemical response of the specimens treated by plasma electrolytic oxidation were analyzed by the electrochemical impedance spectroscopy and the potentiodynamic polarization in artificial seawater. It was found that PEO coatings formed in the presence of Al₂O₃ nanoparticle had lower porosity and exhibited better corrosion behavior compared with the coatings formed in the absence of Al₂O₃ nanoparticle in the structure. This can be attributed to the nanoparticles’ incorporation and penetration through the PEO coatings. On the other hand, the decrease in the current density and increases in the duty cycle and frequency lead to further reduction of the nanoparticles’ incorporation and distribution on the coating surface.

     

Effect of Alloying Additions on Microstructure,Mechanical and Magnetic Properties of Rapidly Cooled Bulk Fe-B-M-Cu (M = Ti,Mo and Mn) Alloys

The influence of alloying additions on the microstructure, mechanical, and magnetic properties of bulk Fe₇₉B₂₀Cu₁, Fe₇₉B₁₆Ti₄Cu₁, Fe₇₉B₁₆Mo₄Cu₁ and Fe₇₉B₁₆Mn₄Cu₁ (at. pct) alloys was investigated. Nanocrystalline samples in the form of 3 mm rods were prepared directly by suction casting without additional heat treatment. Mössbauer spectroscopy, transmission electron microscopy and scanning electron microscopy studies confirmed that the investigated alloys consist α-Fe and Fe₂B nanograins embedded in an amorphous matrix. The addition of alloying elements, such as Ti, Mo and Mn to Fe₇₉B₂₀Cu₁ alloy increases the amount of amorphous phase and decreases the presence of Fe₂B phase in all examined alloys. The mechanical properties of the samples, such as hardness, elastic modulus, and elastic energy ratio, were analysed by an instrumented indentation technique performed on a 12 × 12 nanoindentation grid. These tests allowed to characterise the mechanical properties of the regions observed in the same material. For the Fe₇₉B₂₀Cu₁ alloy, the hardness of 1508 and 1999 HV, as well as Young’s modulus of 287 and 308 GPa, were estimated for the amorphous- and nanocrystalline-rich phase, respectively. The addition of Ti, Mo, and Mn atoms leads to a decrease in both hardness and elastic modulus for all regions in the investigated samples. Investigations of thermomagnetic characteristics show the soft magnetic properties of the studied materials. More detailed studies of magnetisation versus magnetic field curves for the Fe₇₉B_20−xM_xCu₁ (where x = 0 or 4; M = Ti, Mo, Mn) alloy, recorded in a wide range of temperatures, followed by the law of approach to magnetic saturation revealed the relationship between microstructure and magneto-mechanical properties.

     

Heat Treatment of Thixo-Formed Hypereutectic X210CrW12 Tool Steel

Steel is a particularly challenging material to semisolid process because of the high temperatures involved and the potential for surface oxidation. Hot-rolled X210CrW12 tool steel was applied as a feedstock for thixoforming. The samples were heated up to 1525?K (1250?°C) to obtain 30?pct of the liquid phase. They were pressed in the semisolid state into a die preheated up to 473?K (200?°C) using a device based on a high-pressure die casting machine. As a result, a series of main bucket tooth thixo-casts for a mining combine was obtained. The microstructure of the thixo-cast consisted of austenite globular grains (average grain size 46 ??m) surrounded by a eutectic mixture (ferrite, austenite, and M₇C₃ carbides). The average hardness of primary austenite grains was 470?HV_0.02 and that of eutectic 551?HV_0.02. The X-ray analysis confirmed the presence of 11.8?pct ??-Fe, 82.4?pct ??-Fe, and 5.8?pct M₇C₃ carbides in the thixo-cast samples. Thermal and dilatometric effects were registered in the solid state, and the analysis of curves enabled the determination of characteristic temperatures of heat treatment: 503?K, 598?K, 693?K, 798?K, 828?K, 903?K, and 953?K (230?°C, 325?°C, 420?°C, 525?°C, 555?°C, 630?°C, 680?°C). The thixo-casts were annealed at these temperatures for 2?hours. During annealing in the temperature range 503?K to 693?K (230?°C to 420?°C), the hardness of primary globular grains continuously decreased down to 385HV_0.02. The X-ray diffraction showed a slight shift of peaks responsible for the tension release. Moreover, after the treatment at 693?K (420?°C), an additional peak from precipitated carbides was observed in the X-ray diffraction. Thin plates of perlite (average hardness 820?HV_0.02) with carbide precipitates appeared at the boundaries of globular grains at 798?K (525?°C). They occupied 17?pct of the grain area. Plates of martensite were found in the center of grains, while the retained austenite was observed among them (average hardness of center grains was 512?HV_0.02). A nearly complete decomposition of metastable austenite was achieved after tempering at 828?K (555?°C) due to prevailing lamellar pearlite structure starting at grain boundaries and the martensite located in the center of the grains. The X-ray analysis confirmed the presence of 3.4?pct ??-Fe, 84.6?pct ??-Fe, and 12?pct M₇C₃ carbides. The dilatometric analysis showed that the transformation of metastable austenite into martensite took place during cooling from 828?K (555?°C). The additional annealing at 523?K (250?°C) for 2?hours after heat treatment at 828?K (555?°C) caused the precipitation of carbides from the martensite. After tempering at 903?K (630?°C), the thixo-cast microstructure showed globular grains consisting mainly of thick lamellar perlite of the average hardness 555?HV_0.02.     

Mechanical properties of Fe-Si-B amorphous wires produced by in-rotating-water spinning method

Amorphous wires with high strength and good ductility have been produced in Fe-Si-B alloy system by the modified melt-spinning technique in which a melt stream is ejected into a rotating water layer. These wires have a circular cross section and smooth peripheral surface. The diameter is in the range of about 0.07 to 0.27 mm. Their Vickers hardness (H_v) and tensile strength (σ_f) increase with silicon and boron content and reach 1100 DPN and 3920 MPa, respectively, for Fe₇₀Si₁₀B₂₀, exceeding the values of heavily cold-drawn steel wires. Fracture elongation(ε _f ), including elastic elongation, is about 2.1 to 2.8 pct. An appropriate cold drawing results in the increase of σ_f and ε_f by about eight and 65 pct, respectively. This increase is interpreted to result from an interaction among crossing deformation bands introduced by cold drawing. The undrawn and drawn amorphous wires are so ductile that no cracks are observed, even after closely contacted bending. Further, it is demonstrated that the σ_f of the Fe₇₅Si₁₀B_l5 amorphous wire increases by the replacement of iron with a small amount of tantalum, niobium, tungsten, molybdenum, or chromium without detriment to the formation tendency of an amorphous wire. Such iron-based amorphous wires are attractive as fine gauge, high strength materials because of their uniform shape and superior mechanical qualities.     

Microstructural Evolution of the 55 Wt Pct Al-Zn Coating During Press Hardening

Press hardening is increasingly being used to produce ultra-high strength steel parts for passenger cars. Al-Si, Zn, and Zn-alloy coatings have been used to provide corrosion protection to press hardening steel grades. The use of coatings has drawbacks such as coating delamination or liquid metal-induced embrittlement. In the present work, the microstructural evolution of Al-Zn coating during press hardening was studied. The 55 wt pct Al-Zn coating can in principle provide both Al barrier protection and Zn cathodic protection to press hardened steel. During the heat treatment associated with the press hardening, the 55 wt pct Al-Zn alloy coating is converted to an intermetallic surface layer of Fe₂Al₅ and a FeAl intermetallic diffusion layer. The Zn is separated from both intermetallic compounds and accumulates at grain boundaries and at the surface. This Zn separation process is beneficial in terms of providing cathodic protection to Al-Zn coated press hardening steel.