Corrosion and wear resistance of AZ31 Mg alloy treated by duplex process of magnetron sputtering and plasma electrolytic oxidation

In order to improve the wear and corrosion resistance of AZ31 magnesium alloy, a magnetron-sputtered Al layer with a thickness of 11 μm was firstly applied on the alloy, and then treated by plasma electrolytic oxidation (PEO) in an aluminate and silicate electrolytes, respectively. The performance of PEO coatings was investigated by dry sliding wear and electrochemical corrosion tests. The aluminate coating exhibits excellent wear resistance under both 10 and 20 N loads. The silicate coating only shows low wear rate under 10 N, but it was destroyed under 20 N. Corrosion tests show that the Al layer after magnetron sputtering treatment alone cannot afford good protection to the Mg substrate. However, the duplex layer of PEO/Al can significantly improve the corrosion resistance of AZ31 alloy. Electrochemical tests show that the aluminate and silicate coatings have corrosion current densities of ∼1.6×10⁻⁶ and ∼1.1×10⁻⁶ A/cm², respectively, which are two orders lower than that of the un-coated AZ31 alloy. However, immersion tests and electrochemical impedance spectroscopy (EIS) show that the aluminate coating exhibits better long-term corrosion protection than silicate coating.     

纳米金刚石粒径对Ni-P化学复合镀层耐磨性和耐腐蚀性的影响

为提高化学镀镀层的耐磨性和耐腐蚀性,采用化学镀制备含不同粒径的纳米金刚石Ni-P-D复合镀层,通过SEM、XRD、摩擦磨损试验、磨粒磨损试验和电化学试验,探究纳米金刚石粒径对Ni-P镀层微观形貌、力学性能、摩擦磨损性能、磨粒磨损性能和耐腐蚀性能的影响。经化学复合镀可以得到与基体结合良好,厚度约为30 μm,含纳米金刚石的Ni-P-D复合镀层;含50 nm 金刚石的Ni-P-D复合镀层的硬度最高,抗摩擦磨损和磨粒磨损性能最好;随着纳米金刚石粒径减小,Ni-P-D复合镀层的摩擦系数和抗腐蚀能力提高,含5 nm金刚石的Ni-P-D复合镀层的摩擦系数最小,抗腐蚀能力最强。      

Microstructure and Wear Performance of Arc Sprayed Fe-FeB-WC Coatings

Two Fe-FeB-WC coatings were deposited on the Q235 steel substrate by arc spraying. The microstructure and the abrasive wear performance of the coatings were characterized by x-ray diffraction (XRD) and scanning electron microscope (SEM). The wear mechanisms of the coatings were examined. It was found that Fe-Cr alloy and Fe₂B are present in the coating as the main phases. The results showed that adding hard particle powders could obviously increase the hardness and wear resistance of the coatings. The average microhardness of the coatings was about 870 to 920 HV_0.1. The coatings exhibited excellent abrasive wear resistance, being 3.3 to 4.8 times higher than that of arc sprayed 3Cr13 coating.     

The use of Al-Al2O3 cold spray coatings to improve the surface properties of magnesium alloys

Pure Al and 6061 aluminium alloy based Al₂O₃ particle-reinforced composite coatings were produced on AZ91E substrates using cold spray. The strength of the coating/substrate interface in tension was found to be stronger than the coating itself. The coatings have corrosion resistance similar to that of bulk pure aluminium in both salt spray and electrochemical tests. The wear resistance of the coatings is significantly better than that of the AZ91 Mg substrate, but the significant result is that the wear rate of the coatings is several decades lower than that of various bulk Al alloys tested for comparison. The effect of post-spray heat treatment, the volume fraction of Al₂O₃ within the coating and of the type of Al powder used in the coatings on the corrosion and wear resistance was also discussed.     

Surface characterization of plasma sprayed pure and reinforced hydroxyapatite coating on Ti6Al4V alloy

Hydroxyapatite coatings suffer from poor mechanical properties like fretting fatigue, toughness and abrasive wear resistance. These properties can be enhanced by incorporation of secondary ceramic and metallic reinforcements in HA. An attempt has been made to deposit HA and HA reinforced with 10 wt.% (80Al₂O₃-20TiO₂) by plasma spray process on Ti6Al4V substrate. These coatings have been characterized using SEM/EDAX, XRD and FTIR spectroscopy. Corrosion studies have been done in SBF solution. Bio compatibility study is not included in this work. Reinforcement has enhanced the tensile strength. There is marginal improvement in microhardness and surface roughness with reinforcement. Both pure and reinforced coatings show superior resistance against corrosion in simulated body fluid.     

CrN/CrAlSiN涂层海水环境下的摩擦学性能

为提高海洋装备摩擦零部件的摩擦学性能,采用多弧离子镀技术在316L不锈钢上制备了CrN/CrAlSiN涂层。通过XRD、XPS表征涂层的物相及成分,SEM和TEM表征涂层的形貌和微观结构,并用纳米压痕仪测试其硬度,采用摩擦磨损试验机对涂层在大气和海水环境中的摩擦磨损性能进行测试。结果表明:CrN/CrAlSiN涂层的微观结构主要有CrN相、AlN相以及非晶态Si_3N_4包裹CrN、AlN相,(111)择优取向最为明显;基于微观结构与CrN过渡层的设计,CrAlSiN涂层硬度高达35.5 GPa;较之于316L基底,涂层致密的结构使其在海水环境下表现出更好的耐腐蚀性能;在大气和海水环境下,CrN/CrAlSiN涂层的摩擦因数及磨损率均明显降低,在海水环境下达到最优。     

Effect of nanostructuring and Al alloying on friction and wear behaviour of thermal sprayed WC–Co coatings

Nanostructured WC–Co and WC–Co–Al coatings, with about 300-μm as-deposited coating thickness, were deposited by high velocity oxy-fuel (HVOF) spraying. Agglomerated nanostructured cermet powders produced by the Mechanomade® process was used for HVOF spraying. Dense and well-adherent coatings with crystal sizes below 30 nm were deposited on stainless steel 304 substrate. Porosity was less than 5% and the bond strength with the substrate was around 60 MPa. Experimental data on friction, wear, and abrasion resistance revealed that nanostructured WC–Co based coatings containing some Al as alloying element, exhibit improved tribological characteristics in comparison to nanostructured and micron-sized WC–Co coatings. This was attributed to a carbide particle distribution within the coating revealed by SEM, the absence of brittle W₂C-like phases revealed by XRD, and the presence of Al at particle/matrix boundaries revealed by TEM.     

碳化铬基金属陶瓷电火花沉积涂层的微观组织与性能

采用电火花沉积分别制备了碳化铬基金属陶瓷单涂层和碳化铬基金属陶瓷/Ni复合涂层。采用X射线衍射仪(XRD)、扫描电镜(SEM)、显微硬度计和摩擦磨损试验机对比研究了单涂层和复合涂层的物相、微观组织结构、显微硬度和摩擦磨损性能。结果表明,两种涂层组织结构致密,与基体呈良好的冶金结合,并在涂层内形成了纳米晶的微观组织。复合涂层中FeCr_0.29Ni_0.16C_0.06韧性相含量增加,在涂层界面处存在过渡层Ni,并以塑性变形的方式释放了更多沉积时产生的热应力,因而涂层裂纹明显减少。复合涂层的峰值硬度(1186HV_0.05)虽略低于单涂层,但该涂层具有最小的摩擦系数(0.2462),1h磨损量仅为单涂层的1/3,因此表现出更好的耐磨性能,其主要磨损机制为磨粒磨损和疲劳磨损。     

Enhanced Wear Resistant Nickel-based Alloy Coatings Produced by High Velocity Oxy-Fuel Spraying

Three Ni-Cr based powders (Meteo 700, Armacor C and PSI-1) have been thermally sprayed using the HVOF process. The resultant deposits were then characterised using SEM, TEM and XRD. Microhardness surveys were carried out on the coatings together with abrasive wear tests. Coatings 250 μm thick, were produced with low oxides and porosity levels. The most consistent coatings were prepared from powder sources with a minimum particle size of 25 μm. Coating microstructures were either nano-crystalline or mixtures of amorphous and microcrystalline phases. Boron additions to the powder encouraged the formation of amorphous coatings and higher microhardness values i.e. > 675 Hv. The formation of boride precipitates in the coatings does not appear to raise their hardness as the precipitates were either of larger diameter > 500 nm or present in tow volume fractions. Limited amounts of oxides were produced in the coatings, e.g. as α-Cr₂O₃ or spinel oxide NiCr₂O₄ particularly at intersplat boundaries. Abrasive wear resistance of the PSI-1 coating was superior to the other two coatings because it contains more amorphous material. The combination of wear and corrosion resistance associated with these coatings may prove to be attractive in many applications where both these properties are needed, carbides and borides.     

Ti-Al-N 涂层的组织结构与摩擦学性能

目的采用多元等离子体注入与沉积(MPIIID)技术制备Ti-Al-N涂层,系统研究涂层的微观组织结构、力学性能与摩擦学特性。方法借助XRD,XPS,SEM和TEM等,观察分析Ti-Al-N涂层的微观组织结构与物相组成,采用纳米压入试验仪、布氏硬度试验仪、摩擦磨损试验仪和激光共聚焦显微镜等测试分析Ti-Al-N涂层的力学性能、膜基结合力和摩擦磨损性能。结果 Ti-Al-N涂层表现出较高的膜-基结合强度。Al元素掺杂诱发Ti-Al-N涂层发生严重晶格畸变。当Al原子数分数为6.18%时,Ti-Al-N涂层以c-TiAlN相结构为主,表现出超高硬度(达到39.83 GPa);随着Al元素含量增加,涂层中的软质h-TiAlN相结构增多,硬度随之下降。摩擦试验结果表明,低Al含量Ti-Al-N涂层的抗磨损能力良好,其主要磨损机制为磨粒磨损;高Al含量Ti-Al-N涂层的抗磨损能力较差,其主要磨损机制倾向粘着磨损。结论 MPIIID技术成功实现了Ti-Al-N涂层的低温制备与成分调控,低Al含量的Ti-Al-N涂层具有优良的力学性能和优异的抗磨损能力。     

沉积气氛对电火花沉积Mo2FeB2基金属陶瓷涂层组织与性能的影响

采用电火花沉积分别在空气和氩气中制备了Mo_2FeB_2基金属陶瓷涂层,通过扫描电镜(SEM)、X射线衍射(XRD)、显微硬度计和摩擦磨损试验机研究了沉积气氛对涂层形貌、相组成、硬度和摩擦磨损性能的影响。结果表明,2种气氛中沉积所得涂层的组织结构都致密,涂层与基体间无分层,呈冶金结合的特征,但空气中沉积涂层的表面较粗糙,并发生了严重的氧化,涂层均匀性也较差。它们都主要由非晶相和马氏体相组成,但氩气中沉积的涂层含有更多的非晶相。氩气和空气中沉积涂层的最大显微硬度(HV_(0.05))分别为12 862和10 129 MPa,相差2733 MPa,前者涂层2 h的磨损量几乎仅为后者涂层的1/7,表现出更好的耐磨性。2种涂层的主要磨损机制都是疲劳磨损和磨粒磨损,但氩气中沉积涂层以疲劳磨损为主,空气中沉积涂层则以磨粒磨损为主。     

Studies on the Sliding Wear Performance of Plasma Spray Ni-20Cr and Ni3Al Coatings

Two metallic powders namely Ni-20Cr and Ni₃Al were coated on AISI 309 SS steel by shrouded plasma spray process. The wear behavior of the bare, Ni-20Cr and Ni₃Al-coated AISI 309 SS steel was investigated according to ASTM Standard G99-03 on a Pin-on-Disc Wear Test Rig. The wear tests were carried out at normal loads of 30 and 50 N with a sliding velocity of 1 m/s. Cumulative wear rate and coefficient of friction (μ) were calculated for all the cases. The worn-out surfaces were then examined by scanning electron microscopy analysis. Both the as-sprayed coatings exhibited typical splat morphology. The XRD analysis indicated the formation of Ni phase for the Ni-20Cr coating and Ni₃Al phase for the Ni₃Al coating. It has been concluded that the plasma-sprayed Ni-20Cr and Ni₃Al coatings can be useful to reduce the wear rate of AISI 309 SS steel. The coatings were found to be adherent to the substrate steel during the wear tests. The plasma-sprayed Ni₃Al coating has been recommended as a better choice to reduce the wear of AISI 309 SS steel, in comparison with the Ni-20Cr coating.     

Electroless Ni-P and Ni-P-Al2O3 Nanocomposite Coatings and Their Corrosion and Wear Resistance

In an effort to utilize beneficial aspects of nanoparticles in providing corrosion and wear resistance, electroless Ni-P and Ni-P-Al₂O₃ nanocomposite coatings were produced. Alumina particles with various contents from 5 to 20 g/L in bath were co-deposited within Ni-P deposits on mild steel (ms) substrate. Coatings were characterized by scanning electron microscopy (SEM) for morphology, energy dispersive analysis of x-ray EDAX for analyzing elemental composition and x-ray diffractometry for investigating the structural changes of their components. Electrochemical and immersion measurements were used to analyze corrosion behavior of the coatings in 3.5% NaCl solution. Wear resistance of the coating was measured by pin-on-disc method. The results indicated that the Ni-P-Al₂O₃ coatings provide the high hardness as compare to the Ni-P coating. Corrosion and wear resistance of coatings is observed to be superior to that of ms. Corrosion protection properties of the coatings are found to be affected with continuous exposure to the electrolyte. Coating with high concentration of alumina is exhibiting high wear resistance than Ni-P coating. Wear mechanism in case of Ni-P coating appears to be adhesive type and seems to change to abrasive type on introduction of alumina.     

Mechanical property of Fe-base metallic glass coating formed by gas tunnel type plasma spraying

Metallic glass has excellent functions such as high toughness and corrosion resistance. Therefore it is one of the most attractive materials, and many researchers have conducted various developmental research works. However, the metallic glass material is expensive and a composite material is preferred for the industrial application. Thermal spraying method is one of potential candidates to produce metallic glass composites. The gas tunnel type plasma system, which has high energy density and efficiency, is useful for smart plasma processing to obtain high quality ceramic coatings such as alumina (Al₂O₃) and zirconia (ZrO₂) coatings. Also, the gas tunnel type plasma spraying can produce metallic glass coatings. In this study, the Fe-base metallic glass coatings were formed on the stainless-steel substrate by the gas tunnel type plasma spraying, and the microstructure and mechanical property were investigated. The Fe-base metallic glass coatings of about 200 μm in thickness were dense with a Vickers hardness of about Hv = 1100 at plasma current of 300 A. The abrasive wear resistance of Fe-base metallic glass coating was higher than the SUS substrate.     

冷喷涂辅助原位合成FeCoxCrAlCu高熵合金涂层组织性能研究

利用冷喷涂辅助原位合成高熵合金涂层的方法,在45_^#钢基体表面成功制备出不同Co含量的FeCo_xCrAlCu(x=0,0.5,1,1.5,2)高熵合金涂层。通过XRD、SEM、EDS、TEM、显微硬度计、磨料磨损试验机、电化学工作站等设备,检测分析了Co含量的变化对合金涂层相结构、显微组织,硬度、耐磨性及耐腐蚀性的影响。结果表明：合金涂层是由简单的FCC+BCC双相混合结构组成,Co含量的改变对涂层相组织的数量影响不大;随着Co含量的增加,合金涂层中显微组织的枝晶数目增加,并且得到明显粗化,通过面扫得显微组织中枝晶内富集Fe,Cr,Co元素,枝晶间富集Cu元素,Al均匀的分布在整个涂层中;随着Co含量的增加,硬度先增加后减小,在Co=1时合金涂层硬度达到最大为555.6HV;合金涂层中最小的摩擦系数为0.361;在3.5wt.%NaCl腐蚀介质中,合金涂层相比与45_^#钢基体具有较正的自腐蚀电位(E_corr=-0.325V),说明涂层耐腐蚀性比基体好。     

铝基非晶纳米晶复合涂层研究

采用自动化高速电弧喷涂系统,用自行研制的粉芯丝材,在AZ91镁合金基体表面上制备出Al-Ni-Y-Co非晶纳米晶复合涂层.采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、透射电子显微镜(TEM)分析了Al-Ni-Y-Co非晶纳米晶复合涂层的微观形貌和组织结构,结果表明Al-Ni-Y-Co非晶纳米晶复合涂层是由非晶相和纳米晶化相共同组成的,涂层结构致密,孔隙率约为1.8%.Al-Ni-Y-Co非晶纳米晶复合涂层的平均显微Vickers硬度值为311.7 HV0 1,结合强度为26.8 MPa.涂层的抗磨损耐腐蚀性能优于Al涂层和AZ91镁合金基体;其相对耐磨性约为Al涂层的10倍,为AZ91镁合金的6倍;其自腐蚀电位值正于Al涂层及AZ91镁合金,自腐蚀电流密度值约为Al涂层的1/2,AZ91镁合金的1/5;其腐蚀后的表面形貌比Al涂层和AZ91镁合金平整,点蚀较少.Al-Ni-Y-Co非晶纳米晶复合涂层的耐磨防腐综合性能优异.     

微米WC增强Ni60合金高频感应熔覆涂层耐磨性能

采用高频感应熔覆方法在Q235低碳钢基体上制备了不同含量的微米WC增强Ni60A合金复合涂层.用MLS-225型湿砂橡胶轮磨粒磨损试验机评价了涂层的耐磨性能,利用SEM,XRD观察并分析了涂层的显微组织和磨损表面形貌.结果表明,在相同试验条件下,涂层的硬度和耐磨性随WC含量的增加而提高,当WC含量少于30%时,WC分布不均匀,主要集中于涂层的中部,涂层中Cr7C3相以粗大的六方状和长条状存在,不利于涂层耐磨性的提高;当WC含量达到50%时,Ni基合金中加入WC的含量达到了合适比例,耐磨性最佳,相对耐磨性为Ni60A涂层的6.5倍;当WC含量达到60%时,涂层的硬度最高,但出现了较多的孔洞,大量未熔的WC颗粒在磨粒的反复作用下剥落形成了大的剥落坑,导致耐磨性下降.涂层与基体实现了冶金结合,涂层的磨损机制主要为轻微的塑性切削和硬质相的脆性剥落.     

Abrasive wear resistance of electroless Ni-P coated aluminium after post treatment

Electroless nickel (EN) coatings are recognised for their hardness and wear resistance in automotive and aerospace industries. In this work, electroless Ni-P coatings were deposited on aluminium alloy substrate LM24 (Al-9 wt.% Si alloy) and the effect of post treatment on the wear resistance was studied. The post treatments included heat treatment and lapping with two different surface textures. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and micro-abrasion tester were used to analyse morphology, structure and abrasive wear resistance of the coatings. Post heat treatment significantly improved the coating density and structure, giving rise to enhanced hardness and wear resistance. Microhardness of electroless Ni-P coatings with thickness of about 15 μm increased due to the formation of Ni₃P after heat treatment.     

Effects of critical plasma spray parameter and spray distance on wear resistance of Al2O3-8 wt.%TiO2 coatings plasma-sprayed with nanopowders

Effects of plasma spraying conditions on wear resistance of nanostructured Al₂O₃-8 wt.%TiO₂ coatings plasma-sprayed with nanopowders were investigated in this study. Five kinds of nanostructured coatings were plasma-sprayed on a low-carbon steel substrate by varying critical plasma spray parameter (CPSP) and spray distance. The coatings consisted of fully melted region of γ-Al₂O₃ and partially melted region, and the fraction of the partially melted regions and pores decreased with increasing CPSP or decreasing spray distance. The hardness and wear test results revealed that the hardness of the coatings increased with increasing CPSP or decreasing spray distance, and that the hardness increase generally led to the increase in wear resistance, although the hardness and wear resistance were not correlated in the coating fabricated with the low CPSP. The main wear mechanism was a delamination one in the coatings, but an abrasive wear mode also appeared in the coating fabricated with the low CPSP. According to these wear mechanisms, the improvement of wear resistance in the coating fabricated with the low CPSP could be explained because the improved resistance to fracture due to the presence of partially melted regions might compensate a deleterious effect of the hardness decrease.     

Effect on Corrosion Resistance of Ce-Rich-Sealed Ni-P Coatings on Cf/Al Composite Surface

In this study, Ni-P coatings and sealing of the coatings by Ce-rich solution on Cf/Al composite surface for enhanced corrosion resistance are investigated. The corrosion resistance of uncoating sample in 3.5 wt.% NaCl solution was investigated and a comparison with Ni-P and Ce-sealed Ni-P coatings is given. Effect of Ce-sealing on Ni-P coating is discussed. The results of electrochemical measurements of corrosion performance of Cf/Al composites show that sealing of Ni-P coatings with Ce-rich solution can improve the corrosion resistance. The Ce-rich-sealed Ni-P coating has higher corrosion resistance than the coating without Ce, and the electroless plated Ni-P coating on composite surface has higher corrosion resistance than the bare sample, as evidenced by EIS and potentiodynamic polarization measurements. The microstructure of the Cf/Al composites and the two kinds of coatings (i.e., Ni-P coating and Ce-sealed Ni-P coating) were examined by scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. The Ce-sealed Ni-P coatings on Cf/Al composite surface have a total thickness of ~11 μm of which 10 μm is the thickness of the Ni-P coating and ~1 μm is the thickness of the Ce-rich sealing. It shows that the selected area electron diffraction ring pattern of Ce-rich sealing on Ni-P plated composite is consistent with Ce₆O₁₁ or CeO₂. X-ray photoelectron spectroscopy results show that Ce⁴⁺ was the dominant oxidation state for Ce-rich sealing on Ni-P plated composite. The Ce-sealing treatment on Ni-P coating has improved the corrosion resistance over and above the corrosion resistance offered by the Ni-P mono-coating to the bare substrate.