Effect of Isothermal Heat Treatment on Mechanical Properties of WC-17Co Coatings

利用超音速火焰喷涂技术在Ni718合金表面制备WC-17Co涂层,然后进行150℃/10 h,300℃/10 h和450℃/10 h恒温热处理。利用纳米压痕和显微压痕的方法研究热处理过程对涂层显微硬度、弹性模量和断裂韧性的影响,利用Almen试片曲率法计算试片中残余应力的变化。结果表明,150,300和450℃的热处理过程未对WC-17Co涂层的组织和结构特征造成显著地影响;涂层的显微硬度、弹性模量和断裂韧性随热处理温度的升高而降低;涂层机械性能随温度升高而降低的变化趋势是由涂层残余压应力的变化特征引起的。     

Effect of substrate on the 3 body abrasion wear of HVOF WC-17 wt.% Co coatings

WC-17 wt.% Co coatings were deposited using high velocity oxy-fuel (HVOF) spraying onto four different substrate materials, namely aluminium, brass, 304 stainless steel and super-invar. These substrates have different coefficients of thermal expansion which have been shown to influence the final coating microstructural properties. The abrasive wear properties of the coatings were characterised using an ASTM-G65 three body abrasive wear machine with silica sand as the abrasive. The highest mass loss was recorded for the coating on the aluminium substrate whilst the coated 304 stainless steel showed the lowest mass loss. The coatings on brass and super invar experienced similar mass losses. SEM studies of the worn surfaces showed preferential removal of the Co binder phase as well as cracking and rounding of the carbide grains. The differences in wear behaviour may be attributed to the presence of residual stresses where the highest compressive residual stress led to the highest wear rate. The coatings deposited onto brass showed compressive stresses whilst those deposited onto super-invar had tensile stresses, yet these two coatings had similar wear rates. Thus further study is required to provide conclusive evidence of the role of residual stresses on the abrasion resistance of these coatings.     

磷酸铝铬封孔处理对热喷涂WC-12Co涂层耐蚀性的影响

以磷酸铝铬溶液和Cr_2O_3粉末为原料制备了一种封孔剂,并对WC-12Co热喷涂涂层进行封孔处理。利用XRD、SEM、EDS以及TG-DSC分别对磷酸铝铬的物相、封孔前后涂层表面形貌、固化特性和耐热性能进行检测分析。利用动电位极化电化学测试和热震试验分别对封孔前后涂层的抗腐蚀性和固化后的磷酸铝铬层的抗热震性能进行研究。结果表明:磷酸铝铬的固化温度在250℃左右,在700℃内体系无任何热效应发生,材料具有良好的耐热性能。固化后涂层表面致密,磷酸铝铬对涂层孔隙具有良好的填充作用,明显降低了涂层的孔隙率。封孔后的涂层具有较高的自腐蚀电位和较小的腐蚀电流密度,涂层耐蚀性显著提高。在450℃下进行热震试验,当热震次数一定时(热循环100次),添加填料的磷酸铝铬层的剥落面积低于未添加填料的磷酸铝铬层,表现出较高的抗热震性能。     

300M钢基体上高速火焰喷涂WC-17Co和WC-10Co4Cr涂层的疲劳和抗盐雾腐蚀性能

以涂层在飞机起落架的应用作为研究背景,在300M超高强钢基体上对替代电镀硬铬的两种高速火焰喷涂WC-17Co和WC-10Co4Cr涂层的疲劳和抗中性盐雾腐蚀性能进行了研究.结果表明,两种有涂层的300M钢的疲劳寿命均高于无涂层300M钢,如考虑扣除涂层承受载荷,有涂层的300M钢与无涂层300M钢的疲劳寿命相当.喷砂镶嵌在基体表面的刚玉砂粒导致有WC-10Co4Cr涂层的疲劳寿命低于有WC-17Co涂层的300M钢.两种涂层对基体的疲劳性能都没有负面影响;两种涂层都提高了300M钢的抗盐雾腐蚀性能,但有WC-10Co4Cr涂层的300M钢表现出更好的抗盐雾腐蚀性能.综合比较两种涂层的性能,高速火焰喷涂WC-10Co4Cr涂层是更好的电镀铬替代涂层.     

Impurity characterization of zinc-recycled WC-6 wt.% Co cemented carbides

The impurity levels of three WC-6 wt.% Co grades produced using new and zinc recycled powders, were characterized using several analytical techniques. One of the grades was produced from 70% mining scrap material which was subjected to the zinc reclamation process, while a second grade was produced from 100% zinc recycled powder of a new, un-used alloy. The spray dried granules and the sintered alloys were characterized using ICP–OES (inductively coupled plasma/optical emission spectrometry), XRD (X-ray diffraction), SEM/EDS (scanning electron microscopy/energy dispersive X-ray spectrometry), and micro-PIXE (proton induced X-ray emission). All grades had high purity levels of approximately 99%. Iron was found to be the main impurity in all the grades and was predominantly concentrated in the Co binder phase. The main source of the impurities was found to be the production processes and not the zinc reclamation process. The 70% mining scrap zinc recycled grade had the most homogeneous Co binder distribution, while the grade produced from new powders had the least homogeneous Co distribution. This difference is due to the additional levels of crushing and milling which the mining scrap grade underwent. The micro-PIXE analysis clearly demonstrated that powder production conditions, powder homogeneity, and recycling directly impact the microstructures of the sintered materials, and that production process contamination can be detected, quantified, and mapped within the microstructures to a depth approaching 30 μm.     

喷涂距离对等离子喷涂WC-12Co涂层抗冲蚀磨损性能的影响

为提高WC-12Co涂层抗冲蚀磨损性能,在Q235钢基体上采用大气等离子喷涂(APS)方法制备WC-12Co涂层,研究了喷涂距离对粒子温度与速度、涂层组织结构、力学性能及抗冲蚀磨损性能的影响。结果表明:喷涂距离对涂层质量影响较为明显,喷涂距离为130 mm时涂层质量较好,粒子速度与温度达到较好的配合,涂层抗冲蚀磨损能力较强。喷涂距离为120 mm与140 mm时涂层抗冲蚀磨损能力较差。550μm(30目)沙粒直径对涂层冲蚀磨损量大,沙粒速度为15.68 m/s比13.33 m/s沙粒速度冲蚀磨损量大;冲蚀角为60°时冲蚀磨损量最大,30°冲蚀磨损量最小。     

热处理工艺对WC-10%Co粗晶硬质合金性能及微观结构的影响

本文采用淬回火及深冷两种热处理工艺,对WC-10%Co粗晶硬质合金进行烧结后的处理,分析了合金热处理前后的物理机械性能、WC平均晶粒度及分布、钴相分布离差系数、钴相平均自由程的变化以及钴相中钨、碳的固溶度,并对烧结态、淬回火态、深冷态合金进行花岗岩冲击磨损实验,研究了热处理对合金的微观结构及物理机械性能的影响。实验表明:通过淬回火、深冷处理的粗晶合金的密度、磁力、硬度、WC平均晶粒度及分布变化较小;淬回火处理的合金钴磁降低比较明显,深冷处理对合金钴磁几乎无影响;淬回火、深冷处理后的合金钴相离差系数较烧结态有略微增大,淬回火、深冷处理的合金钴相平均自由程较烧结态的合金均有所增加;淬回火处理使钨在钴相中的固溶度提高,深冷处理使钴相中钨的固溶度降低。冲击磨损实验证明,淬回火态的WC-10%Co粗晶合金具备最佳的耐冲击磨损性能,而深冷态的合金最差。     

等离子喷涂WC-12Co涂层抗冲刷磨损行为

目的探索WC-12Co复合涂层抗冲刷磨损的能力。方法采用大气等离子喷涂(APS)方法在Q235钢基体上制备WC-12Co复合涂层。用扫描电镜(SEM)、X射线衍射仪(XRD)和能谱仪(EDS),对涂层微观形貌和相组成及成分进行分析。采用维氏显微硬度计表征了涂层的力学性能。采用自制的干砂型常温冲刷磨损试验机对涂层进行冲刷磨损实验。结果所制备的涂层主要由WC以及少量的W2C、Co3W3C和Co6W6C相组成。涂层以机械结合方式为主,同时伴有微冶金结合。截面显微硬度高于粘结层,其截面平均显微硬度为1169HV0.05。WC-12Co涂层厚度为300μm,粘结层厚度为50μm。在冲刷角为60°时涂层失重率最大,为0.4788 mg/g;在30°时涂层失重率最小,为0.3696 mg/g。结论在小角度30°冲刷时,具有较好的抗塑性冲刷磨损能力;在冲刷角为60°时出现最大的冲刷失重率,抗冲刷磨损效果较差;在大角度90°时,有一定的抗脆性冲刷磨损性能。     

Influence of Powder Porous Structure on the Deposition Behavior of Cold-Sprayed WC-12Co Coatings

The limited deformation of hard cermet particles and impacted coating makes it difficult for conventional thermal spray powders to continuously build up on impact in cold spraying. In this study, three nanostructured WC-12Co powders with different porous structure and apparent hardness were employed to deposit WC-Co coatings on stainless steel substrate by cold spraying. The deposition characteristics of three powders of porosity from 44 to 5% were investigated. It was found that WC-Co coating is easily built-up using porous powders with WC particles bonded loosely and a low hardness. The microhardness of WC-12Co coatings varied from 400 to 1790 Hv with powders and spray conditions, which depends on the densification effects by impacting particles. With porous WC-Co powders, the fracture of particles on impact may occur and low deposition efficiency during cold spraying. The successful building up of coating at high deposition efficiency depends on the design of powder porous structure.     

镍基高温合金上Co改性铝化物涂层的组织结构与耐蚀性能

为研究Co改性铝化物涂层在室温环境中的耐蚀性,利用包埋法渗Co和气相沉积渗Al(两步法)制备出两种不同Co含量的Co改性铝化物涂层,采用XRD、SEM、EDS分析涂层的组织结构。结果表明:850℃和1 000℃渗Co涂层外层和内层均为γ-(Ni,Co)相,内层有氮化物/碳化物相析出。Co改性铝化物涂层与简单NiAl涂层结构一致,外层为β-(Co,Ni)Al相,内层为互扩散区含有大量的富Cr(W)相。简单NiAl涂层的自腐蚀电流为0.04μA/cm2,约为Co改性铝化物涂层的十分之一。这说明在涂层中添加Co降低涂层的耐蚀性,一方面因为Co的腐蚀电位(-0.28V)低于Ni的腐蚀电位(-0.25V),另一方面因为渗Co过程中产生的夹杂物与涂层电位不一致,容易成为微阴极区,加速涂层的腐蚀。     

热处理对超音速火焰喷涂FeAl-Al涂层组织结构的影响

目的通过超音速火焰喷涂(High Velocity Oxygen Fuel,HVOF)的粉末喂料设计,获取结构致密的铁铝金属间化合物涂层,并详细考察热处理对所制备涂层组织结构的影响。方法在铁铝合金粉末喂料中添加质量分数为5%的铝粉,改善喷涂效果,在316L不锈钢表面制备致密的FeAl-Al涂层,并进行真空热处理。采用X射线衍射仪(XRD)、场发射扫描电子显微镜(SEM)、能谱仪(EDS)及维氏显微硬度计,详细分析了涂层在不同热处理温度下的微观组织、成分、结构与显微硬度的变化。结果喷涂态FeAl-Al涂层厚度约为150μm,物相为Fe2Al5,未检测到单质Al。随着热处理温度升高,Fe2Al5相的衍射峰逐渐增强。500℃热处理后,喷涂态涂层中扁平粒子间存在的细微孔隙大量消失,涂层致密性明显提高。但是800℃热处理后,涂层中产生了与界面平行的裂纹。喷涂态FeAl-Al涂层的硬度为465.06HV0.1,500℃热处理2 h后增加至472.06HV0.1,继续提高热处理温度,涂层的显微硬度则明显下降。结论在粉末喂料中引入质量分数为5%的Al粉,可明显改善超音速火焰喷涂效果,获得结构致密、与基体结合牢固的FeAl-Al涂层。合适的热处理能进一步消除喷涂缺陷,使涂层显微硬度增加,微观结构更加致密。     

Vacuum sintering of WC-8 wt.% Co hardmetals from WC powders with different dispersity

The effect of sintering temperature and particle size of tungsten carbide WC on phase composition, density and microstructure of hardmetals WC-8 wt.% Co has been studied using X-ray diffraction, scanning electron microscopy and density measurements. The sintering temperature has been varied in the range from 800 to 1600 °C. The coarse-grained WC powder with an average particle size of 6 μm, submicrocrystalline WC powder with an average particle size of 150 nm and two nanocrystalline WC powders with average sizes of particles 60 and 20 nm produced by a plasma-chemical synthesis and high-energy ball milling, respectively, have been used for synthesis of hardmetals. It is established that ternary Co₆W₆C carbide phase is the first to form as a result of sintering of the starting powder mixture. At sintering temperature of 1100-1300 °C, this phase reacts with carbon to form Co₃W₃C phase. A cubic solid solution of tungsten carbide in cobalt, β-Co(WC), is formed along with ternary carbide phases at sintering temperature above 1000 °C. Dependences of density and microhardness of sintering hardmetals on sintering temperature are found. The use of nanocrystalline WC powders is shown to reduce the optimal sintering temperature of the WC-Co hardmetals by about 100 °C.     

热处理对等离子喷涂WC-12Co涂层-基体结合性能的影响

通过等离子喷涂制备WC-12Co涂层,经过对涂层进行不同温度热处理并对其进行微观结构的表征和力学性能的测试;研究不同热处理后涂层性能和结构的变化,并通过扫描电镜、能谱分析仪等分析手段对等离子喷涂制备的WC-12Co涂层进行显微结构分析。结果表明:经过热处理后涂层基体的界面硬度得到提高,结合强度也得到提高。     

Al-Mg2Si复合涂层在3.5％NaCl水溶液中的腐蚀磨损性能研究

目的研究Al-Mg_2Si复合涂层在3.5%NaCl溶液中的腐蚀-磨损性能。方法用电化学工作站(CHI660E)、腐蚀-磨损试验机测试试样的电化学行为及实时监测在3.5%NaCl溶液中的开路电位、摩擦系数和干摩擦性能,并采用扫描电镜(SEM)、超景深三维显微镜对磨痕特征进行表征。结果镁合金自腐蚀电位为-1.4888V,腐蚀电流密度为2.817×10~(-3) A/cm~2。与镁合金基体相比,Al-Mg_2Si复合涂层的自腐蚀电位正移了0.5288V,腐蚀电流密度降低了3个数量级。腐蚀磨损过程中,Al-Mg_2Si复合涂层的开路电位(OCP)为-0.9202 V,比镁合金基体高0.5713 V。干摩擦过程中,复合涂层的稳定摩擦系数为0.28,比镁合金低0.07。复合涂层干、湿磨损率相差44.72×10~(-4) mm~3/(N?mm),其值是镁合金基体干、湿磨损率相差值的0.52倍,且均远远大于各自纯机械磨损率。结论在腐蚀磨损过程中,腐蚀是造成磨蚀损失的主要原因,且Al-Mg_2Si复合涂层的耐磨蚀性能优于镁合金基体。     

Effects of particle density on depositing properties of WC-17Co by HVOF process

The in-flight and deposition properties of three types of WC-17 Co powder with different particle densities during a high-velocity oxygen fuel （HVOF） thermal spray process were investigated. Three types of powder exhibited similar velocity upon impact on the substrate surface. The powder with the lower particle density exhibited a higher temperature upon impingement process, resulting in the generation of a higher flattening ratio. Thus, the coating derived from the powder with the lower particle density possessed superior micro-hardness, porosity and surface roughness. However, the coating with the lowest particle density showed the poorest fracture toughness because of the generation of the largest amount of amorphous phase.     

超音速等离子喷涂制备WC-12Co涂层的性能特点

超音速等离子喷涂由于喷射粒子的飞行速度(400～500m/s)相对于普通等离子喷涂(＜200m/s)有了大幅提高,所制备的WC-12Co涂层具有更高的显微硬度和结合强度.用SEM和XRD分析了两种不同等离子喷涂工艺获得的涂层的相结构和显微组织,结果表明超音速等离子喷涂WC-12Co涂层综合性能要优于普通等离子喷涂.     

热处理对X80管线钢CO2腐蚀行为的影响

分析了热处理对X80管线钢显微组织的影响,采用失重法研究了试样在模拟地层水中的CO2腐蚀情况,观察试样的宏观腐蚀形貌,综合分析组织对X80管线钢CO2腐蚀行为的影响.结果表明:X80钢经调质处理后得到索氏体,正火得到珠光体.调质处理后,试样较原始硬度都有所提高,850℃淬火+ 550℃回火试样的耐CO2腐蚀性能最好,腐蚀速率为0.5285 mm/a.X80管线钢的原始组织的腐蚀情况主要为点蚀,调质处理试样出现均匀腐蚀,而正火试样只是局部存在明显点蚀.     

热处理工艺对无铅黄铜腐蚀行为的影响

通过向Cu-Zn二元合金中添加高锌当量的铝、镁、硅元素,采用普通铸造法制备了以β相为基体的无铅黄铜,并对其进行670℃×3h固溶,油淬后进行270℃×2h时效,考察了所制备合金在热处理前后的腐蚀行为。结果表明,热处理态的无铅黄铜腐蚀电流密度与脱锌腐蚀速率减小,24h后的脱锌腐蚀层厚度仅为118μm,耐腐蚀性能良好。     

A Comparison of Mechanical and Tribological Behavior of Nanostructured and Conventional WC-12Co Detonation-Sprayed Coatings

In the present study, WC-12Co coatings were deposited by detonation-spraying technique using conventional and nanostructured WC-12Co feedstock at four different oxy/fuel ratios (OF ratio). The coatings exhibited the presence of phases like W₂C and W due to the decarburization of the WC phase, and the proportions of these phases were higher in the nano WC-12Co coatings compared with conventional WC-12Co coatings. Coating hardness and fracture toughness were measured. The tribological performance of coatings was examined under dry sand rubber wheel abrasion wear, and solid particle erosion wear conditions. The mechanical and wear properties of coatings were influenced by degree of decarburization and more so in the case of nanostructured WC-Co coatings. The results indicate that the extent of decarburization has a substantial influence on the elastic modulus of the coating which in turn is related to the extent of intersplat cracking of the coating.     

The Effect of Heat Treatment on the Corrosion Behavior of X-Ray-Amorphous Chromium Electroplates on Copper

The morphology and anodic behavior of heat-treated X-ray-amorphous chromium electroplates on copper are investigated with the use of digital microscopy and slow voltammetry in 1 N sulfuric acid solutions, respectively. The temperature of heat treatment substantially affects the behavior of a coating predetermined by the existence of pores and cracks, which may originate from blisters and somatoids formed during the electrodeposition. The treatment at 100°C improves the protective properties of a coating. In a temperature range from 100 to 400°C, the coating undergoes cracking, which results in the formation of pores and a noticeable increase in the dissolution currents. However, at 500°C, the protective properties of the coating increase again, seemingly due to the thermal oxidation of copper, which results in sealing through pores and cracks in the coating. At a temperature of 600°C, the protective properties finally disappear because of the phase transition of copper oxide in pores and the crystallization of the coating itself.