Effect of Annealing Temperature on Tribological Properties and Material Transfer Phenomena of CrN and CrAlN Coatings

This study evaluates the effects of annealing temperature and of the oxides produced during annealing processes on the tribological properties and material transfer behavior between the PVD CrN and CrAlN coatings and various counterface materials, i.e., ceramic alumina, steel, and aluminum. CrAlN coating has better thermal stability than CrN coating in terms of hardness degradation and oxidation resistance. When sliding against ceramic Al₂O₃ counterface, both CrN and CrAlN coatings present excellent wear resistance, even after annealing at 800 °C. The Cr-O compounds on the coating surface could serve as a lubricious layer and decrease the coefficient of friction of annealed coatings. When sliding against steel balls, severe material transfer and adhesive wear occurred on the CrN and CrAlN coatings annealed at 500 and 700 °C. However, for the CrAlN coating annealed at 800 °C, much less material sticking and only small amount of adhesive wear occurred, which is possibly due to the formation of a continuous Al-O layer on the coating outer layer. The sliding tests against aluminum balls indicate that both coatings are not suitable as the tool coatings for dry machining of aluminum alloys.     

Morphology,Structure, Microhardness and Corrosion Resistance of Ni-W Coating Annealed in Hydrogen and Argon Atmosphere

In this paper, an amorphous Ni-W coating was electrodeposited on the low-carbon steel and then annealed in hydrogen and argon atmosphere. Their characterization was carried out using scanning electron microscopy and x-ray diffraction. The corrosion characterization was carried out using the potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy. The results show that microcracks inevitably exist on the surface of Ni-W coating when annealed at 750 °C or higher temperature. After annealing treatment, amorphous structure transforms to crystalline and some new phases are precipitated, which is significantly affected by the annealing temperature and atmosphere. The microhardness of annealed Ni-W coatings is much higher than that of as-deposited coating, while an adverse corrosion performance is observed for the annealed Ni-W coatings. The coating annealed in hydrogen at 500 °C shows a huge improvement in hardness and a fairly acceptable corrosion resistance compared with the as-deposited Ni-W coating.     

Electrochemical evaluation of the corrosion protectiveness and porosity of vacuum annealed CrAlN and TiAlN cathodic arc physical vapor deposited coatings

The corrosion behavior of cathodic arc physical vapor deposited CrAlN and TiAlN coatings were examined in 1 M HCl solution before and after vacuum annealing at 700, 800, 900, and 1000 °C. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods were used to study the corrosion behavior and porosity of the coatings in comparison with the bare steel substrate (304SS). Structural and mechanical characterization of the coatings were also conducted. It is found that with increasing annealing temperature, the mechanical properties of TiAlN increased due to age hardening caused by spinodal decomposition while the hardness of CrAlN decreased as result of relaxation. Similarly, EIS and PDP results revealed that the as‐deposited and annealed coatings offer higher corrosion resistance as compared to the bare 304SS substrate. The coatings susceptibility to corrosion is reduced after annealing as indicated by the increasing nobility of E_corr. Both PDP and EIS tests revealed that CrAlN coating annealed at 1000°C exhibited superior corrosion resistance properties. It is found that the reduced current density for CrAlN coating annealed at 1000°C was due to the reduction in the porosity. Annealed TiAlN coating follows similar behavior until an optimum annealing temperature of 800°C. Beyond this temperature, porosity enlargement and an increase in the number of pores subsequent to structural changes deteriorated the corrosion resistance of TiAlN coating.     

Microstructure,Mechanical Properties,and Two-Body Abrasive Wear Behavior of Cold-Sprayed 20 vol.% Cubic BN-NiCrAl Nanocomposite Coating

20 vol.% cubic boron nitride (cBN) dispersoid reinforced NiCrAl matrix nanocomposite coating was prepared by cold spray using mechanically alloyed nanostructured composite powders. The as-sprayed nanocomposite coating was annealed at a temperature of 750 °C to enhance the inter-particle bonding. Microstructure of spray powders and coatings was characterized. Vickers microhardness of the coatings was measured. Two-body abrasive wear behavior of the coatings was examined on a pin-on-disk test. It was found that, in mechanically alloyed composite powders, nano-sized and submicro-sized cBN particles are uniformly distributed in nanocrystalline NiCrAl matrix. Dense coating was deposited by cold spray at a gas temperature of 650 °C with the same phases and grain size as those of the starting powder. Vickers hardness test yielded a hardness of 1063 HV for the as-sprayed 20 vol.% cBN-NiCrAl coating. After annealed at 750 °C for 5 h, unbonded inter-particle boundaries were partially healed and evident grain growth of nanocrystalline NiCrAl was avoided. Wear resistance of the as-sprayed 20 vol.% cBN-NiCrAl nanocomposite coating was comparable to the HVOF-sprayed WC-12Co coating. Annealing of the nanocomposite coating resulted in the improvement of wear resistance by a factor of ~33% owing to the enhanced inter-particle bonding. Main material removal mechanisms during the abrasive wear are also discussed.     

The Influence of Temperature on Frictional Behavior of Plasma-Sprayed NiAl-Cr2O3 Based Self-Adaptive Nanocomposite Coatings

Frictional behavior of nano and hybrid-structured NiAl-Cr₂O₃-Ag-CNT-WS₂ adaptive self-lubricant coatings was evaluated at a range of temperatures, from room temperature to 700 °C. For this purpose, hybrid structured (HS) and nanostructured (NS) composite powders with the same nominal compositions were prepared by spray drying and heat treatment techniques. A series of HS and NS coating samples were deposited on steel substrate by an atmospheric plasma spraying process. The tribological behavior of both coatings was studied from room temperature to 700 °C at 100° intervals using a custom designed high temperature wear test machine. Scanning electron microscopy was employed for the evaluation of the composite coatings and worn surfaces. Experimental results indicated that the hybrid coating had inferior tribological properties when compared to the nanostructured coating, showing the attractive frictional behavior on the basis of low friction and high wear resistance; the NS coating possessed a more stable friction coefficient in the temperature range of 25-700 °C against alumina counterface. Microstructural examinations revealed more uniformity in NS plasma-sprayed coatings.     

Mechanical Properties and Oxidation Behavior of a Graded (Ti,Al)N Coating Deposited by Arc-Ion Plating

A graded (Ti,Al)N coating was deposited on 1Cr–11Ni–2W–2Mo–V stainless steel for aero-engine compressor blades by arc-ion plating(AIP). The microstructure and the morphology of the graded coating were investigated using electron-probe microanalysis (EPMA), X-ray diffraction and scanning-electron microscopy. The mechanical properties of the graded coating were investigated and it was found that the microhardness and the wear resistance were similar to those of the monolithic (Ti,Al)N coating, but much better than those of a homogenous TiN coating. In addition, the adhesive strength and the thermal-shock resistance of the graded (Ti,Al)N coating were much better than those of the monolithic TiN and (Ti,Al)N coatings. The oxidation tests were performed at 600 and 700°C in air for 500 hr, and corrosion tests were carried out at 600°C under the synergistic effect of water vapor and NaCl for 20 hr. Compared to pure TiN, it was found that due to the incorporation of aluminum, a protective layer rich in alumina was formed on top of the graded (Ti,Al)N coating, which greatly improved the oxidation resistance and corrosion resistance of the coating.     

Production of Annealed Cold-Sprayed 316L Stainless Steel Coatings for Biomedical Applications and Their in-vitro Corrosion Response

316L powders were successfully deposited onto Al5052 aluminium substrates by cold spray method. Annealing was treated on the coated samples at 250–1000°C temperatures under Ar atmosphere. The in vitro performances of the coatings have been compared with using electrochemical corrosion test technique in the simulated body fluid (SBF) at body temperature (37°C). A scanning electron microscope (SEM-EDS) and X-ray diffraction (XRD) have been used for microstructural characterization and phases identifications of the coatings, respectively. The results were shown that there are high adhesions at particle and substrate interfaces and between the particles deposited as well. Also, the increasing annealing temperature increases corrosion resistance of the cold sprayed 316L stainless steel coatings. The corrosion susceptibility of the coating annealed at 1000°C was similar that of standard 316L stainless steel implant material in Ringer’s solution. The microstructural observations revealed that corrosion starts between the inter-splat powders and continues throughout the surface not in-depth.     

Effect of Ni–P and Phosphate Intermediate Layers on Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating Developed by Sol-Gel Method

Sol–gel method was used for applying of alumina coating on carbon steel substrate. Alumina sol was prepared with Al-isopropoxide as a precursor material. Specimens were coated with prepared alumina sol by dip coating technique. Either a film of Ni–P or phosphated intermediate layer has been pre-deposited on the carbon steel substrate by electroless plating to improve the adherence of alumina coating. The corrosion resistance of coatings in the presence of intermediate layers was evaluated by electrochemical measurement in 3.5% NaCl solution by open-circuit potential measurement at room temperature. The abrasive wear behavior of sol–gel coated specimens was measured in high stress conditions. The results indicate that, after applying an intermediate layer of phosphate or Ni–P by electroless plating technique, the wear and corrosion resistance of alumina coating have been improved. Moreover, the phosphate intermediate layer has been associated with a higher corrosion resistance, while the intermediate layer of Ni–P is more effective to improve the hardness and wear resistance of alumina 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.     

Characterization of High-Temperature Abrasive Wear of Cold-Sprayed FeAl Intermetallic Compound Coating

FeAl intermetallic compound coating was prepared by cold spraying using a mechanically alloyed Fe(Al) alloy powder followed by post-spray annealing at 950 °C. The high-temperature abrasive wear test was carried out for the FeAl coating at a temperature range from room temperature to 800 °C. The high-temperature abrasive wear of a heat-resistant stainless steel 2520 was performed for comparison. It was observed that the abrasive wear weight loss of FeAl coating was proportional to wear cycles in terms of sample revolutions at the tested temperatures. It was found that with the increase of the test temperature higher than 400 °C, the wear rate of cold-sprayed FeAl coating decreased with the increase of test temperature, while the wear rate of the heat-resistant steel increased significantly. The results indicate that the high-temperature abrasive wear resistance of the cold-sprayed FeAl intermetallic coating increased with the increase of the wear temperature in a temperature range from 400 to 800 °C. The wear resistance of cold-sprayed FeAl coating was higher than that of heat-resistant 2520 stainless steel under 800 °C by a factor of 3.     

Influence of Pulse Electrodeposition and Heat Treatment on Microstructure,Tribological, and Corrosion Behavior of Nano-Grain Size Co-W Coatings

In the present study, Co-W nano-structured alloy coatings are produced on low-carbon steel substrate by means of pulse electrodeposition from a citrate-based bath under different average current densities and duty cycles. The results indicate that the coating deposited under 60% of duty cycle and 1 A/dm² of average current density exhibit optimum pulse plating conditions with 44.38 wt.% W, 37 nm grain size, and 758 HV microhardness. The effect of heat treatment temperature on microstructure, composition, corrosion behavior, and morphology of amorphous deposited Co-W alloy with 44 wt.% W was investigated. The microhardness of the coating increased to 1052 HV after heat treatment at 600 °C, which is due to the formation of Co₃W and CoWO₄ phases in the deposit. Furthermore, the coatings heat-treated at 600 °C had lower friction coefficients and better wear resistance under various loads than before heating.     

The Effects of Heat Treatment on Microstructure and Mechanical Properties of Tribaloy 400 Coatings Deposited by Laser Cladding

The effects of heat treatment on the microstructure, microhardness, nanohardness and wear resistance of Tribaloy 400 coatings prepared by laser cladding on 304 stainless steel were studied in this paper. The results show that the microstructures of Tribaloy 400 laser cladding layer are cobalt matrix dendrites and eutectic structure. After the heat treatment at 1250 °C for 1 h, the eutectic structure disappears and the strip-like Laves phase is formed on the Co matrix. Meanwhile, the hardness is obviously improved. After the heat treatment at 1250 °C for 1 h and then 900 °C for 4 h, a small amount of ε-Co appears, the strip-like Laves phases become coarser and blunter, and some of the strip structures combine together to form blocky structures, and the hardness is decreased. The wear resistance of the samples at 600 °C is better than that at RT since the hardness of the Laves phase increases with the rise in temperature.     

Study on the Friction and Wear Behavior of a TA15 Alloy and Its Ni-SiC Composite Coating

Ni-SiC composite coatings were prepared on TA15 alloy by composite electroplating technology. The friction and wear behavior of TA15 alloy, and the coating were comparatively studied at both room temperature and 600 °C using GCr15 as the counterparts. The results show that the obtained coating is relatively dense and compact, and possesses higher micro-hardness than TA15 alloy. The coating has significant friction reduction effect sliding at 600 °C, but has no obvious friction reduction effect sliding at room temperature. The coating possesses superior wear resistance than TA15 alloy, evidenced by its much lower mass losses than those of TA15 alloy sliding at both room temperature and 600 °C. The TA15 alloy and the coating showed different wear mechanisms under the given sliding conditions.     

Tribological and electrochemical characteristics of DLC coatings with bias voltage

Diamond-like carbon (DLC) coatings were deposited on a STS 316L substrate by means of R.F plasma-assisted chemical vapor deposition (R.F PACVD) technique using benzene (C₆H₆) as a reaction gas. The tribological and electrochemical characteristics of the DLC coatings were investigated by a tribological technique (wear test) and by electrochemical techniques (potentiodynamic polarization test and electrochemical impedance spectroscopy). Surface analyses of the DLC coatings were conducted by means of scanning electron microscopy and atomic force microscopy. This study provides reliable and quantitative data for an assessment of the effect of bias voltage on tribological and electrochemical characteristics in a simulated body fluid environment (0.89 wt.% NaCl of pH 7.4 at 37°C). From the results of the tribological and electrochemical techniques, wear and corrosion resistance of the DLC coatings were improved owing to the low surface roughness, low porosity and good adhesion strength. Among all DLC coatings in this experiment, the DLC coating with a bias voltage of −800 V showed better wear and corrosion resistance than did other coatings     

Nanoscratching deformation and fracture toughness of electroless Ni-P coatings

In the present investigation electroless Ni-P coatings were prepared. Structural characterizations indicated that the as-deposited coating had an amorphous structure with a P content of 23 at.%. The deformation behavior of an electrolessly amorphous Ni-P coating was investigated by using the Vickers indentation and the Tribo-indenter instrumented nano-indentation technique. The hardness of the Ni-P coating is remarkably improved after proper heat-treatment and the hardness is as high as 12.7 GPa for the coating annealed at 400 °C for 1 h. However, the cracks were observed during the indentation of the Ni-P coatings annealed at 400 °C and 500 °C for 1 h. The corresponding fracture toughness was evaluated as 2.58 MPa m^0.5 and 1.33 MPa m^0.5, respectively. Nanoscratching tests indicated that the wear resistance of the Ni-P coatings was improved significantly with an increasing ratio of hardness (H) to elastic modulus (E). It was observed that the friction coefficient increased from 0.083 ± 0.006 for the Ni-P coating annealed at 300 °C up to 1.337 ± 0.009 for the IF steel substrate, while the H/E simultaneously decreased from 0.084 (10.7/128) to 0.009 (1.85/200). The study revealed that the electrolessly amorphous Ni-P coating had offered better corrosion resistance than the Ni-P coatings after heat-treatment. An annealing temperature of 300 °C is preferentially suggested for the trade-off between the wear resistance property and anti-corrosion property of the Ni-P coating.     

对磨材料对TC11合金高温磨损行为的影响

采用高温磨损试验机对TC11合金在400、500、600℃进行磨损试验,研究对磨材料GCr15和M2钢对TC11合金的磨损行为的影响。结果表明,TC11合金无论与GCr15还是M2钢对磨,磨损率均随温度的升高而降低,TC11合金表现出优异的高温耐磨性。在大多数情况下,TC11合金磨损率随载荷增加均处于较低值且波动较小,但在400℃、超过200 N(与GCr15钢对磨)时和在400、500℃,大于200 N(与M2钢对磨)时磨损率显著增加。与M2钢对磨比与GCr15钢对磨使TC11合金磨损率升高。TC11合金的高耐磨性归因于摩擦氧化物层的保护作用。硬的对磨材料(M2钢)比软的对磨材料(GCr15钢)易于破坏TC11合金表面摩擦氧化物层而损害其保护作用。     

Poly(3‐octylthiophene) thermally treated as coating for corrosion protection of SS304 in sulfuric acid media

Poly(3‐octylthiophene) (P3OT) was synthesized by direct oxidation of the 3‐octylthiophene monomer using ferric chloride (FeCl₃) as an oxidant. Using the drop‐casting technique, P3OT coatings were deposited onto 304 type stainless steel electrodes. For the purpose of determining the effect of thermal annealing on the corrosion protection of stainless steel with P3OT coatings, the coated electrodes were thermally annealed for 30 h at two different temperatures, 55 and 100 °C. The corrosion behavior of P3OT coated stainless steel was investigated in 0.5 M sulfuric acid (H₂SO₄) at room temperature using potentiodynamic polarization curves (PPC), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). The results indicated that the thermally treated P3OT coatings improved the corrosion resistance of the stainless steel in 0.5 M H₂SO₄. The best corrosion protection was obtained by the P3OT coating annealed at 100 °C. In order to study the temperature effect on the morphology of the coatings before and after the corrosive environment and compare it with corrosion protection, atomic force microscopy (AFM) and scanning electronic microscopy (SEM) were used.     

H13钢的铁基和钴基熔覆层组织与耐磨性

采用激光熔覆技术在AISI H13 热作模具钢表面分别制备了铁基熔覆层、钴基熔覆层. 借助金相显微镜、扫描电镜、洛氏硬度计和高温摩擦磨损试验机,对比分析了两种熔覆层的组织形貌、硬度和耐磨性. 采用马弗炉进行加热600 ℃,保温1 h,反复4 次,并测得红硬性硬度. 结果表明,基材、铁基、钴基熔覆层硬度分别为HRC 47,HRC 52,HRC 48. 基材和铁基熔覆层的红硬性硬度有所下降,而钴基熔覆层的红硬性硬度提升. 钴基熔覆层磨损失重量和摩擦系数皆最小. 基材、铁基熔覆层、钴基熔覆层的磨损机理分别是以磨粒磨损、粘着磨损以及粘着磨损和磨粒磨损为主.     

TC4钛合金表面化学镀Ni-P合金耐磨层研究

利用化学镀方法在TC4钛合金表面成功制备结合力良好的Ni-P合金耐磨层,研究了提高镀层结合力的方法,结合SEM、XRD、EDS等现代物理分析方法分析了不同温度热处理后镀层的组织结构,从而建立不同热处理温度、镀层结构与镀层硬度和耐磨性能的关系。结果表明:二次浸锌活化方法和热处理能显著提高镀层与基体的结合强度,经600℃热处理后镀层结合力达到35N。基材的硬度HV为3780MPa,磨损量为9.6mg,镀态镀层的硬度HV为5760MPa、磨损量为7.7mg。随着热处理温度升高Ni3P相增多,该相的弥散分布使镀层硬度增加,最高硬度HV达到9790MPa,但400℃后硬度降低,这是由于Ni3P相随着热处理温度的继续升高而发生偏聚,使弥散强化程度下降;镀层的磨损量随着热处理温度的升高而减小,说明耐磨性能随着热处理温度的升高而增强,600℃热处理后,虽然镀层晶粒长大、粗化及镀层硬度降低,但此时镀层晶格的完整性最佳,镀层塑性和韧性提高,所以耐磨性能最好。     

Investigation of Wear and Corrosion Protection of AlSi20 Coatings Produced by Plasma Spraying and Laser Cladding on AZ31B

Magnesium and magnesium alloys are the lightest structural materials with an approximate density of 1.7 g/cm² (density of aluminum ~2.7 g/cm²). Due to poor corrosion and wear resistance properties, they need to be coated for usage in service conditions under corrosive and tribological loads. AlSi20 was found to be a suitable coating material to improve the wear and corrosion protection properties of magnesium alloys. Within this work, AlSi20 coatings were applied by plasma spraying, laser cladding, and a combination of both processes. First, the coatings are characterized by their microhardness and residual stresses formed within the coating during the different coating processes. Then, these coatings were investigated regarding corrosion resistance in 3.5% sodium chloride solution in a three-electrode setup to obtain electrochemical corrosion characteristics. Abrasive wear was investigated using a pin-on-disk tribometer and the abrasion rate was calculated. Resistance against shock loads was tested by applying a cyclic load at 50 Hz to investigate the resistance against impact stresses.