Characterisation and oxidation of LVOF sprayed Al2O3–40%TiO2 coating on superni 601 and superni 718 superalloys at 800 and 900°C

Failure of components due to high temperature oxidation is the major degradation mechanism in boiler and gas turbine industries. Superalloys having superior mechanical properties and creep resistance are used in these applications but lack resistance to oxidation under aggressive environments. Protective coatings are used to improve their oxidation resistance in such applications. In the present investigation, Al₂O₃–40%TiO₂ coating was deposited on superni 718 and superni 601 superalloys by low velocity oxy fuel process. The as sprayed coating was characterised for microhardness, surface roughness, scanning electron microscopy and X-ray diffraction analysis. High temperature oxidation behaviour of Al₂O₃–40%TiO₂ coated and uncoated superni 718 and superni 601 superalloys has been evaluated at the elevated temperatures of 800 and 900°C for total duration of 50 cycles under cyclic conditions. Each cycle consisted of keeping the samples for 1 h at the elevated temperature followed by 20 min cooling in ambient air. Al₂O₃–40TiO₂ coating in the as sprayed condition showed the presence of Al₂O₃–TiO₂, α-Al₂O₃, TiO₂ as the main phases. Al₂O₃–40%TiO₂ coating on superni 718 and superni 601 superalloys has shown a lower oxidation rate as compared to those of uncoated superalloys. However, the oxidation rate of the coating was not steady due to the occurrence of spallation/sputtering at various stages. The coating was found adherent on the substrate superalloys throughout the study.     

等离子熔覆-注射B4C铁基熔覆层组织耐磨性研究

目的采用等离子熔覆-注射工艺在Q235基体上制备B4C铁基熔覆层并研究其耐磨性。方法通过OM,SEM,EDS等分析熔覆层及界面的组织特征,并进行耐磨性测试。结果当B4C质量占主体熔覆材料质量的18%时,注射熔覆层表面比较平整,无裂纹。注射熔覆层组织致密,界面呈现平直的亮白色过渡层,稀释率小,与基体形成了良好的冶金结合。B4C陶瓷颗粒表面溶解会形成Fe,Cr等元素的硼化物。等离子熔覆-注射B4C熔覆层的耐磨性是42CrMo的22倍,是16Mn钢的41倍。结论等离子熔覆-注射B4C工艺能够增强B4C与熔覆层之间的结合力,提高熔覆层的硬度和耐磨性。     

添加CeO_2对MoS_2基复合涂层摩擦学性能的影响

针对MoS_2基复合涂层耐磨性差和承载能力低的问题,以不同含量(质量分数)的CeO_2作为添加剂,采用喷涂法在GCr15钢表面制备MoS_2基复合涂层。利用摩擦磨损试验机和划痕仪分别研究涂层摩擦磨损性能和结合强度,并借助金相显微镜对涂层磨损形貌进行表征。结果表明:添加适量CeO_2可以改善涂层的摩擦磨损性能,其最佳含量为2%,此时摩擦因数和磨损量均最小,分别为0.232和0.011 3 mm~3;同时结合强度从22 N提高到28.29 N。涂层磨损量随载荷的增大而增大;而载荷小于8 N时,涂层的摩擦因数随载荷的增大而减小,当载荷大于8 N时,摩擦因数又有回升趋势。添加稀土后涂层的承载能力有明显提高。未添加稀土时,涂层产生严重剥离,并发生磨粒磨损;添加2%CeO_2后,涂层发生轻微磨粒磨损,耐磨性得到显著提高。     

Y2O3对原位自生TiC增强Ni基涂层组织和性能影响

采用氩弧熔覆的方法，以Ni60A自熔性合金粉末为粘结相，添加Ti粉、C粉和不同含量的稀土氧化物Y₂O₃，在16Mn钢基体上制备出TiC陶瓷颗粒增强金属基熔覆涂层. 运用XRD, SEM等手段对复合涂层的显微组织进行表征和分析，并对熔覆涂层的硬度及耐磨性进行了测试. 结果表明，适量添加Y₂O₃可以使涂层组织中枝晶的方向性减弱、同时细化涂层组织，使涂层组织更加均匀，涂层的硬度和耐磨性有显著提高. 添加2% Y₂O₃熔覆涂层的组织为最细，涂层具有较高的显微硬度和良好的耐磨性能.     

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.     

Microstructure and sliding wear behavior of nanostructured Ni60-TiB2 composite coating sprayed by HVOF technique

A nanostructured Ni60-TiB₂ composite coating (Ni60 is a brand of Ni-based self-fluxing alloy with a hardness of HRC60) was sprayed on steel substrate by high velocity oxy-fuel (HVOF) process using high energy ball milled powders. Its sliding wear resistance at room-temperature was evaluated by ball-on-disc testing. For comparison, conventional Ni60-TiB₂ composite coating was prepared by HVOF using mechanically mixed Ni60 and TiB₂ powders and tested under the same conditions. The results show that the nanostructured composite coating has excellent mechanical properties and sliding wear resistance due to the microstructural homogenization and the well preserved nanostructure characteristic of the ball milled powders. Adhesive and abrasive wears are found to be responsible for the wear down mechanisms of the nanostructured Ni60-TiB₂ composite coating.     

Ce(SO4)2浓度对电喷镀Ni-W-Ce合金镀层性能影响

为了研究Ce(SO4)2浓度与合金镀层表面性能的关系，采用喷射电沉积法制备了一系列Ni-W-Ce合金镀层工件。用扫描电镜(SEM)观察了镀层的表面结构，并用能谱仪(EDS)检测镀层中的元素组成。XRD分析表明，镀层存在晶格畸变。LEXT4100激光共焦显微镜观察磨损痕迹，发现磨损机理发生了变化。结果表明，添加Ce(SO4)2改善了涂层的表面微观形貌，当浓度为0.5g/L时，涂层的表面质量最佳。同时，显微硬度、耐磨性和耐腐蚀性随浓度的增加呈现先好后坏的规律。当Ce(SO4)2浓度为0.5g/L时，显微硬度达到峰值519.69HV0.1。此时，镀层耐磨性最好，其耐磨性表征参数均取得最小值。且镀层的耐蚀性也最好，腐蚀电位为-0.5537V，电弧电抗半径最小。     

Use of microhardness as a simple means of estimating relative wear resistance of carbide thermal spray coatings: Part 2. wear resistance of cemented carbide coatings

A selection of WC-Co and Cr₃C₂-25%NiCr coatings produced by plasma spray and high velocity oxygen fuel (HVOF) deposition techniques were subjected to various wear tests designed to simulate abrasion, cavitation, sliding, and particle erosion type wear mechanisms. All of the coatings were at least 200 μm thick and were deposited onto stainless steel substrates. In Part 1 of this contribution, the microstructures of the coatings were characterized and their mechanical properties were assessed using microindentation procedures. In this second part of the article, the behavior of the coatings when subjected to the various wear tests is reported and the utility of microhardness testing as an indication of relative wear resistance is discussed. It is shown that correctly performed, appropriate microhardness measurements are a good indication of abrasion resistance and sliding wear resistance, and also correlate well with cavitation resistance in Cr₃C₂-NiCr. The measurements were less useful for predicting erosion resistance for both Cr₃C₂-NiCr and WC-Co, however, and for abrasion resistance when WC-Co was ground against SiC. Here the contribution of micromechanisms involving fracturing and brittle failure is greater than that indicated by the coating microhardness, which is essentially a measurement of resistance to plastic deformation under equilibrium conditions.     

原位合成ZrO2/MgO膜层及自修复裂纹研究

微弧氧化熔融冷却成膜过程出现的裂纹将影响膜层的强韧性和磨损性能。本文利用ZrO₂自身的强韧性,采用原位合成制备具有自修复裂纹作用的ZrO₂/MgO膜层,研究原位合成的ZrO₂对膜层磨损性能的影响。研究发现,微弧氧化原位合成ZrO₂在高温放电通道发生相变产生体积膨胀氧化锆界面萌生微裂纹,抑制了成膜过程裂纹扩展从而实现自修复膜层裂纹的作用。通过控制锆源含量可以实现了对膜层中ZrO₂含量的调控,膜层中原位ZrO₂含量为32%,ZrO₂/MgO膜层裂纹呈现细小分散化,裂纹密度较传统膜层下降63.4%,摩擦系数减小53.4%,磨损量降低66.7%。研究认为,原位合成的ZrO₂在膜层制备过程的自修复裂纹和耐磨性的提高,可以降低摩擦系数和磨损量,改善ZrO₂/MgO膜层表面磨损性能。     

钛合金表面氩弧熔覆原位合成TiB2-TiN涂层组织及耐磨性能

以BN和Ni60A合金粉末为熔覆材料,采用氩弧熔覆技术在TCA合金表面原位合成TiB2-TiN增强颗粒耐磨涂层．利用x射线衍射仪、扫描电子显微镜和摩擦磨损试验机对熔覆层的组织和性能进行分析测试．结果表明,复合涂层的显微组织沿层深方向分为熔覆区、结合区和热影响区;熔覆层与基体呈良好冶金结合,TiB2-TiN颗粒弥散分布,...     

Effect of Feedstock Size and its Distribution on the Properties of Detonation Sprayed Coatings

The detonation spraying is one of the most promising thermal spray variants for depositing wear and corrosion resistant coatings. The ceramic (Al₂O₃), metallic (Ni-20 wt%Cr) , and cermets (WC-12 wt%Co) powders that are commercially available were separated into coarser and finer size ranges with relatively narrow size distribution by employing centrifugal air classifier. The coatings were deposited using detonation spray technique. The effect of particle size and its distribution on the coating properties were examined. The surface roughness and porosity increased with increasing powder particle size for all the coatings consistently. The feedstock size was also found to influence the phase composition of Al₂O₃ and WC-Co coatings; however does not influence the phase composition of Ni-Cr coatings. The associated phase change and %porosity of the coatings imparted considerable variation in the coating hardness, fracture toughness, and wear properties. The fine and narrow size range WC-Co coating exhibited superior wear resistance. The coarse and narrow size distribution Al₂O₃ coating exhibited better performance under abrasion and sliding wear modes however under erosion wear mode the as-received Al₂O₃ coating exhibited better performance. In the case of metallic (Ni-Cr) coatings, the coatings deposited using coarser powder exhibited marginally lower-wear rate under abrasion and sliding wear modes. However, under erosion wear mode, the coating deposited using finer particle size exhibited considerably lower-wear rate.     

原位生成 WC-B4C 增强镍基激光熔覆层及其性能研究

目的通过激光熔覆技术,在Q235钢表面原位生成WC-B4C增强镍基熔覆层。方法以WO3,B2O3,C和Ni60混合粉末为预涂原料,采用激光熔覆技术原位生成WC-B4C增强镍基熔覆层,对熔覆层的显微组织和物相构成进行分析,研究其摩擦磨损性能。结果采用合适的工艺参数,通过原位生成WC-B4C形成的增强镍基涂层形貌良好,与基材呈现较好的冶金结合。熔覆层平均硬度1200HV0.3,摩擦磨损失重仅为纯Ni60熔覆层的1/3。结论熔覆层硬度较高,耐磨性很好。大量原位生成的WC-B4C增强相及其均匀分布是熔覆层硬度和耐磨性提高的原因。     

激光原位合成TiB2-TiC颗粒增强铁基涂层

采用B4C,TiO2,石墨以及铁基粉末为激光熔覆材料,利用激光多道搭接熔覆技术在碳钢基体上制备TiB2-TiC颗粒增强铁基复合涂层．利用XRD,SEM对涂层的相结构和显微组织进行了研究．采用显微硬度计和滑动磨损试验机分别测试了涂层的硬度和耐磨性能．结果表明,激光熔覆过程B4C,TiO2和石墨反应生成了TiB2和TiC颗粒,并均匀分布在基体中．随着激光功率密度增加,涂层中TiC含量减少,甚至出现FeB脆性相．TiB2-TiC颗粒增强的涂层其硬度和耐磨性能优于基材45钢．     

Oxidation resistance of refractory γ-TiAlW coatings

The resistance to oxidation of the W-alloyed magnetron sputtered γ-TiAl fine-crystalline 4 μm thick coatings have were investigated in this work. The oxidation tests were performed in an atmosphere of pure oxygen or in the air at a temperature of 1173 K for 120 h. The resistance to high-temperature oxidation was investigated by means of micro-thermogravimetric analysis with continuous or stepwise control of the substrate weight. Before and after the oxidation the morphology of the coatings as well as their chemical and phase composition were investigated by SEM, EDS and EBSD, respectively. The results have been compared with those obtained for the uncoated γ-TiAl substrate.It was found that: (1) the W-alloyed γ-TiAl coatings have a considerably higher oxidation resistance (about four orders of magnitude) than the uncoated γ-TiAl substrates and that their resistance to oxidation increases with the concentration of alloying element in the range of the concentrations investigated in the work; (2) the high resistance to oxidation of the coatings is a result of the thin α-Al₂O₃ layer formation on the surface of the substrate during oxidation; (3) the formation of dense and uniform α-Al₂O₃ layer on the coating surface is due to a fine-crystalline structure of the magnetron deposited γ-TiAlW coating.     

纳米稀土CeO2掺杂对Ni-Fe-Co-P合金镀层性能的影响

利用喷射电沉积技术制备了Ni-Fe-Co-P-CeO_2复合镀层。通过SEM、XRD、EDS等测试了复合镀层的表面形貌、截面形貌、物相结构和组成成分,同时,表征了复合镀层的硬度、耐磨和耐蚀性能,探究和分析了纳米稀土CeO_2颗粒浓度对镀层性能的影响。结果表明:该多元复合镀层为非晶态结构;随着镀液中CeO_2颗粒浓度的增加,复合镀层的显微硬度、耐磨性和耐蚀性均呈先增强后减弱的趋势;镀液中CeO_2颗粒浓度为1 g/L时,复合镀层的表面均匀致密,其HV_(0.1)显微硬度达到最大值5982 MPa,且具有最优的耐磨和耐蚀性能。     

玻璃Cr2O3陶瓷涂层表面液态重金属润湿角的测量与表征

金属材料的腐蚀性能与其表面润湿特性有着密切的关系。采用亚音速火焰喷涂技术制备了玻璃-Cr2O3陶瓷涂层,设计了一套运行在高温环境中且密封的专用试验平台,研究经过不同保温时间后,重金属在45钢与喷有玻璃-Cr2O3陶瓷涂层的45钢表面的润湿角及相关现象的变化。结果表明:相同质量的重金属液滴在45钢表面的润湿角为18°,在玻璃-Cr2O3陶瓷涂层表面的润湿角为114°,玻璃-Cr2O3陶瓷涂层抗液态重金属润湿性能较好。固化后重金属颗粒与试样之间的接触面积及剪切强度均有所不同,304不锈钢与颗粒剪切强度为1.42MPa,而涂层与颗粒剪切强度为0.21MPa。     

Preparation and wear performance of NiCr/Cr3C2-NiCr/hBN plasma sprayed composite coating

NiCr clad hexagonal BN powder (NiCr/hBN) was added to NiCr/Cr₃C₂ feedstock to improve the tribological properties of chromium carbide nichrome coating. The microstructure, flowability and apparent density of the composite powder, as well as the structure and mechanical properties of the plasma sprayed coating were characterized. The friction and wear behavior of the NiCr/Cr₃C₂-NiCr/hBN coating from ambient temperature up to 800 °C was evaluated on a ball-on-disk wear tester and compared with that of NiCr/Cr₃C₂ coating and NiCr/Cr₃C₂-NiCr/BaF₂·CaF₂ coating. The results show that NiCr cladding can reduce the decarburization of Cr₃C₂ and oxidation of hBN during the thermal spray. The main wear mechanisms of the NiCr/Cr₃C₂-NiCr/hBN composite coating are ploughing and adhesive wear. Layered hexagonal BN particle reduce the direct contact and severe adhesion between friction pairs, thus decreasing the friction coefficient. The NiCr/Cr₃C₂-NiCr/hBN composite coating shows a promising application in the high temperature environment with the request of both wear resistance and friction reduction.     

Improving the surface hardness and wear resistance of Ti3SiC2 by boronizing treatment

In order to modify surface properties of Ti₃SiC₂, boronizing was carried out through powder pack cementation in the 1100-1400 °C temperature range. After boronizing treatment, one mixture layer, composed of TiB₂ and β-SiC, forms on the surface of Ti₃SiC₂. The growth of the coating is processed by inward diffusion of boron and obeys a linear rule. The boronizing increases the hardness of Ti₃SiC₂ from 3.7 GPa to a maximal 9.3 GPa and also significantly improves its wear resistance.     

Microhardness as a simple means of estimating relative wear resistance of carbide thermal spray coatings: Part 1. characterization of cemented carbide coatings

A selection of WC-Co and Cr₃C₂-25%NiCr coatings deposited by plasma spraying and high velocity oxygen fuel (HVOF) were tested. The microstructures of the coatings were characterized, and their mechanical properties were assessed using Knoop microindentation procedures. The coatings were also subjected to various wear tests. All of the coatings were at least 200 μm thick and were deposited onto stainless steel substrates. The wear tests simulated abrasion, cavitation wear, sliding wear, and particle erosion wear. In this first part of a two-part contribution, the microstructures of the coatings are characterized and a discussion on the evaluation of mechanical properties from the microindentation response is presented. The nature of microhardness testing as applied to thermal spray coatings is evaluated as a means of assessing resistance to plastic flow, elasticity, and brittleness. In Part 2, the results of the various wear simulations are reported, and the utility of microhardness as an indicator of wear resistance is examined.     

Development and performance of new hard and wear-resistant engineering materials

Wear is a major problem in many industrial applications, and the development of wear-resistant materials is therefore both a technical and an economic advantage. Iron-base composites bring new possibilities into the production of wear-resistant materials because of their high hardness and sufficient fracture toughness. They are suitable replacements for the conventional WC/Co cermets owing to their lower fabrication cost, better machinability, weldability, and corrosion resistance. In this study, hot-work steel/Cr₃C₂ composites and reference wear-resistant materials were produced by hot isostatic pressing. It was found that the matrix powder size used during processing did not affect the resultant wear properties of the composite. On the other hand, the impact toughness increased when fine matrix powders were used. The increasing reinforcement volume fraction increased significantly the hardness and wear resistance of the composite; however, the impact resistance decreased. The newly proposed hot-work steel/30 vol% Cr₃C₂ composite demonstrated a better combination of properties than some of the most abrasion-resistant materials available today.