Characterization of plasma sprayed Fe-17Cr-38Mo-4C amorphous coatings crystallizing at extremely high temperature

A Fe-17Cr-38Mo-4C alloy powder was plasma sprayed by three processes: an 80 kW low-pressure plasma spray (LPPS), a 250 kW high-energy plasma spray (HPS), and a 40 kW conventional plasma spray (APS). The as-sprayed coating obtained by the LPPS process is composed of only amorphous phase. As-sprayed coatings obtained by the HPS and APS processes are a mixture of amorphous and crystalline phases. The three as-sprayed coatings exhibit a high hardness of 1000 to 1100 DPN. The amorphous phase in these coatings crystallizes at a high temperature of about 920 K. A very fine structure composed of hard ϰ-phase and carbides is formed after crystallization. The hardness of the coating obtained by LPPS reaches a maximum of 1450 DPN just after crystallization on tempering and retains a high hardness more than 1300 DPN after tempering at high temperatures of 1173 or 1273 K. The corrosion potential of the amorphous coating is the highest among the three coatings and higher than that of a SUS316L stainless steel coating. The anodic polarization measurements infer that the corrosion resistance of the amorphous coating is superior or comparable to SUS316L stainless steel coating in H₂SO₄ solution.     

Thermal-sprayed Fe-10CM3P-7C amorphous coatings possessing excellent corrosion resistance

An alloy of Fe-10Cr-13P-7C was thermally sprayed by three different processes: (1) 80 kW low-pressure plasma spraying (LPPS), (2) high-velocity oxyfuel (HVOF) spraying, and (3) 250 kW high-energy plasma spraying (HPS). The as-sprayed coating obtained by the LPPS process was composed of an amorphous phase. In contrast, the as-sprayed coatings obtained by the HVOF and HPS processes were a mixture of amorphous and crystalline phases. The as-sprayed coatings showed a high hardness of 700 DPN. A very fine structure composed of ferrite, carbide, and phosphide was formed, producing a maximum hardness of greater than 1000 DPN in the LPPS coating just after crystallization on tempering. The corrosion re-sistance of the amorphous coating was superior to a SUS316L stainless steel coating in 1N H₂SO₄ solution and 1N HC1 solution. Furthermore, the amorphous coating underwent neither general nor pitting corro sion in1NUCI solution and 6% FeCl₃ 6H₂O solution containing 0.05N HCl, whereas the SUS316L stain less steel coating was attacked aggressively.     

Formation of amorphous Fe-Cr-Mo-8P-2C coatings by the high velocity oxy-fuel process

Alloy powders of Fe-10%Cr-8%P-2%C(10Cr), Fe-20%Cr-8%P-2%C(20Cr), and Fe-10%Cr-10%Mo-8%P-2%C(10Mo) compositions (in mass%) were sprayed by the high velocity oxy-fuel (HVOF) process under different conditions. The as-sprayed coatings of 10Mo alloy were composed of only an amorphous phase under all the spray conditions, while the as-sprayed coatings of the 10Cr and 20Cr alloys consisted of an amorphous phase with a small amount of crystalline material. The volume fraction of the crystalline material increased slightly with the rise of the flame temperature. The hardnesses of the as-sprayed coatings of the 10Cr and 20Cr alloys were 600 to 700 DPN, respectively, while the 10Mo coating composed of an amorphous phase revealed 560 DPN. The corrosion resistance of the as-sprayed coating of the 10Mo alloy was the best among three amorphous coatings and also superior to the nickel-base self-fluxing alloy and SUS316L stainless steel coatings in 1N H₂SO₄ and 1N HCl solutions.     

Erosion-resistance of plasma sprayed coatings

Cr₃C₂/NiCr, ZrO₂/NiCr, WTiC₂/NiCr, and X40 were plasma sprayed on the substrate 1Cr18Ni9Ti in order to solve the erosion wear at high temperature encountered in the oil-refining industry. A series of properties of the coatings, including their microstructure, hardness, and erosion-behavior, have been tested. The test results show that the properties of the coatings have a significant effect on their erosionresistant performance. Good erosion-resistant materials need to be hard and tough. Both Cr₃C₂/NiCr and X40 have good erosion resistance at elevated temperature.     

等离子弧喷涂法制备铁基非晶合金的研究

非晶态合金具有强度、韧性以及耐磨性能优于普通晶态金属材料,耐蚀性好,磁抗小等优点,倍受材料科学和工程技术人员的关注,但是非晶态材料只有在非平衡条件下才能形成,加工难度大,阻碍了非晶态材料的发展和应用.对此,采用等离子弧喷涂方法制备铁基非晶合金,制备了Fe79Si10B11非晶态合金.对制备的非晶合金进行了XRD和TEM分析,并研究了喷涂过程中粒子的飞行温度和速度,通过传热学方法计算了喷涂过程中的粉末冷却速度.结果表明,所制备的非晶合金组织均匀,喷涂过程冷却速度达4.16×107 K/s.     

医用镁合金等离子喷涂羟基磷灰石涂层研究

为了提高医用镁合金的表面耐蚀性和生物相容性,采用等离子喷涂技术在镁合金表面制备羟基磷灰石(HA)涂层.研究结果表明,镁合金表面所制备的HA涂层与基体结合牢固,界面无裂纹、气孔等缺陷.相组成为生物相容性较好的HA和少量的Ca3(PO4)2(TCP),显微组织具有层状特征,涂层表面存在一些有利于骨长人的孔隙.涂层的弹性模量约为19.825 GPa,接近骨的弹性模量,涂层表面硬度为300～350 HV.腐蚀试验和钙磷沉积试验结果表明HA涂层具有较好的耐蚀性和骨诱导性.     

Wear and corrosion resistance of laser remelted and plasma sprayed Ni and Cr coatings on copper

Nickel and chromium coatings were produced on the copper sheet using plasma spraying and laser remelting. The sliding wear test was achieved on a block-on-ring tester and the corrosion test was carried out in an acidic atmosphere. The corrosive behaviors of both coatings and original copper samples were investigated by using an impedance comparison method. The experimental results show that the nickel and chromium coatings display better wear resistance and corrosion resistance relative to the original pure copper sample. The wear resistance of the coatings is 8 - 12 times as large as original samples, and the wear resistance of laser remelted samples is better than that of plasma sprayed ones. The corrosion resistance of laser remelted nickel and chromium samples is better than that of plasma sprayed samples respectively. The corrosion rate of chromium coatings is less than that of nickel coatings, and the laser remelted Cr coating exhibits the least corrosion rate.     

等离子喷涂制备铁基非晶涂层及其耐磨性

采用等离子喷涂的方法制备铁基非晶涂层,并对不同喷涂功率制备涂层的组织和耐磨性进行了分析。结果表明,3种功率制备涂层表面致密、孔隙率低,且具有较高的热稳定性、硬度和耐磨性。当喷涂功率为30 k W时,涂层非晶程度高;喷涂功率为35和40 k W时,涂层中有Fe2B和Mo6Co6C晶相出现,随喷涂功率增加,涂层硬度和摩擦因数升高,35 k W制备涂层的耐磨性最好。     

Fe基非晶合金的晶化及其在NaCl溶液中的电化学腐蚀行为

采用单辊甩带法制备出完全非晶态的Fe_(78)Si_(13)B_9和Fe_(73.5)Si_(13.5)B_9Nb_3Cu_1薄带,并利用非晶晶化退火法制备非晶和纳米晶双相合金Fe_(73.5)Si_(13.5)B_9Nb_3Cu_1薄带.利用X射线衍射仪和示差扫描量热计对该非晶薄带的非晶特性及其晶化过程进行研究,并用电化学极化曲线的方法和电化学阻抗技术对比研究非晶Fe_(78)Si_(13)B_9和双相合金Fe_(73.5)Si_(13.5)B_9Nb_3Cu_1在1 mol/L NaCl溶液里的电化学腐蚀行为,用SEM对极化测试后的试样形貌进行观察;同时还研究不同的热处理温度对材料的结构及在1 mol/L NaCl溶液里耐腐蚀性能的影响.结果表明:该非晶薄带的晶化过程分为两步;双相合金比非晶合金的耐腐蚀性要好;随着热处理温度升高,非晶合金和双相合金的耐腐蚀性能都得到提高.     

高耐腐蚀Fe-(Cr,Ni)-Mo-P-C-B块体非晶合金

Fe-Mo-P-C-B铁基块体非晶合金具有高强度、高塑性和良好的软磁性,作为结构和功能材料具有较好的应用前景。本研究通过Cr、Ni合金化制备了耐腐蚀Fe-(Cr,Ni)-Mo-P-C-B块体非晶合金,其非晶形成临界直径达5mm。Cr、Ni合金化显著提高了Fe-Mo-P-C-B块体非晶合金在HCl、H2SO4、NaCl溶液中的耐腐蚀性能,使钝化电流密度降低、腐蚀速度降低、电化学反应电阻增大。     

Characterization of mechanical properties of suspension plasma sprayed TiO2 coatings using scratch test

The study aimed at characterizing mechanical properties of TiO₂ coatings obtained by the use of aqueous suspensions of fine rutile and anatase particles onto metal substrates. Thickness of the coatings was found with the use of optical microscope observations of metallographical cross-sections. The coatings morphology was found with scanning electron microscope (SEM) and their phase composition was determined by X-ray diffraction method. The mechanical properties were characterized using scratch test. The test enabled to characterize the adhesion of coatings by determination of critical force necessary to peel off the coatings from the substrate and, on the other hand, to estimate their cohesion by the measurement of the scratch hardness. The hardness was calculated using the width of the scratch and the value of force applied. The design of experiments (DOE) of spraying with the use of a 2³ full factorial plan was applied to rutile powder. The coatings were sprayed onto aluminium substrate. The DOE enabled to find the effects of three principal parameters, i.e. electric power input to plasma, spray distance and suspension feed rate onto coating adhesion expressed by critical force. A preliminary data for anatase powder sprayed with one set of operational parameters onto stainless steel substrate are also shown.     

铬锆铜表面等离子喷涂Cr3C2p/NiCr涂层的组织与性能

采用等离子喷涂技术在铬锆铜(CrZrCu)基体表面制备了Cr3C2 p/NiCr涂层。利用X射线衍射仪(XRD)、扫描电镜(SEM)等仪器研究了涂层的显微组织及结构,采用磨粒磨损试验机对Cr3C2 p/NiCr涂层与电镀NiCo层的磨损性能进行了测试比较。结果表明:涂层组织呈片层状结构,在NiCr合金片层上分布着未熔的Cr3C2和Cr7C3、Cr2Ni3、CrNi析出相。与电镀Ni-Co镀层相比,Cr3C2 p/NiCr涂层具有较高的硬度和耐磨粒磨损性能,其磨损量仅为电镀层的35%。     

The corrosion behavior and microstructure of high-velocity oxy-fuel sprayed nickel-base amorphous/nanocrystalline coatings

The corrosion characteristics of two Ni-Cr-Mo-B alloy powders sprayed by the high-velocity oxy-fuel (HVOF) process have been studied using potentiodynamic and potentiostatic corrosion analysis in 0.5 M H₂SO₄. The deposits were also microstructurally characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM) (utilizing both secondary electron and backscattered electron modes), and transmission electron microscopy (TEM). Results from the microstructural examination of the two alloys have revealed a predominantly amorphous/nanocrystalline face centered cubic (fcc) matrix containing submicron boride precipitates as well as regions of martensitically transformed laths. Apparent recrystallization of the amorphous matrix has also been observed in the form of cellular crystals with a fcc structure. The oxide stringers observed at splat boundaries were found to be columnar grained α-Cr₂O₃, though regions of the spinel oxide NiCr₂O₄ with a globular morphology were also observed. The coatings of the two alloys exhibited comparable resistance to corrosion in 0.5 M H₂SO₄, as revealed by potentiodynamic tests. They both had rest potentials approximately equal to −300 mV saturated calomel electrode (SCE) and passive region current densities of ∼1 mA/cm². Microstructural examination of samples tested potentiostatically revealed the prevalence of degradation at splat boundaries, especially those where significant oxidation of the deposit occurred. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

Advanced microstructural study of suspension plasma sprayed titanium oxide coatings

Suspension plasma sprayed titanium oxide coatings were analyzed using transmission electron microscope (TEM) and using Raman spectroscopy. The suspensions used to spray were formulated using fine rutile pigment, water, alcohol or their mixtures, and a small quantity of dispersant. TEM study realized using a “face-to-face” preparation technique enabled to visualize a lamellar shape of grains and their columnar growth. The Raman spectroscopy was made for the samples prepared using different operational spray parameters. The investigations showed the presence of rutile and anatase phase in coatings sprayed using rutile fine powder.     

Low friction stainless steel coatings graphite doped elaborated by air plasma sprayed

A new process has been developed to incorporate graphite particles into a stainless steel coating during its formation. Four means have been tested to inject the graphite particles outside the plasma jet and its plume: graphite suspension, a graphite rod rubbed on the rotating sample, powder injection close to the substrate with an injector, or a specially designed guide. The last process has been shown to be the most versatile and the most easily controllable. It allows the incorporation of between 2 and 12 vol.% of graphite particles (2–15 μm) within the plasma sprayed stainless steel coatings. A volume fraction of 2% seems to give the best results with a slight decrease (6%) of the coating hardness. This volume fraction also gave the best results in dry friction on the pin-on-disk apparatus. Depending on the sliding velocity (0.1–0.5 m/s) and loads (3.7–28 N), the dry friction coefficient against a 100C6 pin is reduced by between 1.5 and 4 compared with that obtained with plasma sprayed stainless steel.     

Impedance spectroscopy of suspension plasma sprayed titania coatings

Two TiO₂ coatings were plasma sprayed, using an aqueous suspension as a feedstock onto initially prepared alumina substrates. Their thickness was about 7 and 15 μm. The coatings were tested using impedance spectroscopy (IS) in the frequency range from 100 Hz to 2 MHz at temperatures ranging from 320 to 1020 K. The measurements allowed to find the Nyquist plots and equivalent circuits of the tested samples. The IS results were interpreted by the microstructural features of the deposits such as chemical composition, atomic structural and phase analysis. The mechanism of electric current conduction in tested coatings was proposed.     

Stability of amorphous Al90TMxCe10—x（TM=Fe or Ni） alloys

X-ray diffraction(XRD) and differential scanning calorimetry(DSC) were used to investigate the crystallization process of amorphous Al90TMxCe10-x (atom fraction in%;TM=Fe or Ni;x=3,5)alloys,Aging effects were examined by X-ray diffraction,The structure corresponding to the prepeak for the amorphous Al90Fe5Ce5 alloy is more stble than the amorphous matrix,but it is not stable for amorphous Al90Ni5Ce5 alloy during the first crystallization stage and even decomposes at room temperature,Although both Al-Ni and Al-Fe have strong chemical bonding,the cyrstallization onset temperature of amorphous Al-Fe-Ce alloys is much higher than that of amorphous Al-Ni-Ce alloys,which is likely caused by the different stability of the structure corresponding to the prepeak.The crystallization onset temperature increases as Ce/Ni ratio increases in amporphous Al90NixCe10-x alloys,whereas it decreases as Ce/Fe ratio increases in amorphous Al90FexCe10-x alloys.A better atomic packing produces as Ce content increases because of the size mismatch in Al-Ni-Ce systems and as Fe content increases because of the increasing Fe central structural units.     

Antibacterial properties of vacuum plasma sprayed titanium coatings after chemical treatment

Implant-related infection is one of the common clinical complications that cause high rates of mortality and morbidity in orthopedic surgery. Endowing implant antibacterial properties is a useful method to reduce such infection. In this paper, vacuum plasma sprayed titanium coatings were treated by NaOH solution firstly, and then antimicrobial silver was introduced into the coatings by immersing in 0.02 mM (denoted as CA1), 0.06 mM (denoted as CA2) and 0.1 mM (denoted as CA3) Ag⁺ containing calcification solution. Antibacterial property of the treated titanium coatings was examined by employing three types of bacteria stains, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. X-Ray diffraction and scanning electron microscopy were used to observe the phase composition and surface morphology of the modified titanium coatings. Results showed that all of the three kinds of coatings exhibited more than 90.00% antibacterial ratio except CA1 to Staphylococcus aureus which is 63.30%. The release of silver in physiological environment was monitored and it was found that the excellent antibacterial property of the treated coatings was attributed to the release of silver.     

反应等离子喷涂TiN涂层热处理后的电化学腐蚀性能

研究了热处理后TiN涂层在模拟海水中的腐蚀行为,采用电化学阻抗谱(EIS)、动电位极化曲线、扫描电镜和能谱分析等技术研究了热处理后TiN涂层电化学腐蚀参数及组织的变化。结果表明:热处理后TiN涂层的耐蚀性明显提高,自腐蚀电流仅为热处理前的13.3%,极化电阻约是热处理前的20倍;电化学阻抗谱描绘了热处理后涂层的腐蚀过程及导致涂层腐蚀的主要因素,涂层局部的孔隙腐蚀是引起电化学腐蚀参数变化的主要因素,腐蚀初期孔隙电阻由大变小,后期又会由小变大,从而使涂层的腐蚀速率发生变化;热处理会使涂层的通孔率降低为87%,主要原因是在热处理过程,TiN与大气中的O2发生了氧化反应,生成密度较TiN小的TiO2相和Ti3O相,使涂层中的部分通孔被封闭,耐蚀性得以提高。