预烧结对低压烧结WC-Co硬质合金组织和性能的影响

采用原位还原碳化反应制备超细WC-10%Co,在1250、1300、1350、1380℃进行预烧结处理,得到的预烧结块体在1450℃、5 MPa氩气条件下进行低压二次烧结;分析对比了预烧结块体和二次烧结块体的显微组织,并对二次烧结合金进行了性能测试.结果表明:不同温度预烧结块体经低压二次烧结后,可有效抑制晶粒异常长大现象,二次烧结后合金具有高的断裂韧性,最高值达16.1MPa·m^-1/2.在1 350、1 380℃下预烧结块体经低压二次烧结后均具有均匀的合金组织,其中经过1380℃预烧结块体横向断裂强度为3260 MPa.     

Tribological behavior of nanostructured high velocity oxy-fuel (HVOF) thermal sprayed WC-17NiCr coatings

In this research, the nanostructured WC-17NiCr cermet coatings were developed using the high velocity oxy-fuel (HVOF) thermal spraying processes on ACI CD4MCu cast duplex stainless steel substrates, widely used in pump industry for abrasive wear protection of surfaces. The coatings, sprayed by both robotic and manual methods, had two different fuel (methane) to oxygen ratios (FTOR), namely 0.68 and 0.62. Using different analytical and microstructural techniques, the microstructural characteristics of the powder particles and mechanical, microstructural, and tribological properties of the coatings were determined. Different morphologies were assigned to sprayable particles, namely spherical, apple, donut, irregular, and mixed. It was revealed that the rate of WC decarburization had increased with increasing the FTOR. In contrast, the scanning electron microscopy and image analyses showed that the lowest porosity percentage was obtained for the robotically-sprayed coating with 0.68 FTOR. The Vickers microhardness increased along with fracture toughness, which can be attributed to the effect of the ‘duplex structure’ associated with the particle outer coating of Co and is a novelty in the research. The pin-on-disk reciprocal sliding wear tests at various loadings had shown different wear rates in the coatings. It was inferred that the wear performance was improved with the microstructural homogeneity, hardness, and the fracture toughness in the coatings. In all coatings, lower coefficient of friction (COF) was observed at higher loads. Finally, the wear mechanisms involved in the wear processes were identified as deformation and removal of the binder, fracture and pullout of the carbide particles, and delamination and spallation of the splats.     

Microstructure and Wear Resistance Evolution of HVOFSprayed WC-（W,Cr）2C-Ni Coating with Post Heat Treatment In Air Atmosphere

WC-(W,Cr)2C-Ni coating was prepared on 1Cr18Ni9Ti stainless steel and C-276 Ni-base Hastelloy by high velocity oxy-fuel(HVOF)spraying.The effect of post heat treatment in air atmosphere on the microstructure,phase composition,microhardness,fracture toughness,and wear resistance of HVOF-sprayed WC-(W,Cr)2C-Ni coating was investigated.The microstructure and phase composition of the coatings were analyzed by means of field emission scanning electron microscopy(FESEM)and X-ray diffraction(XRD).The microhardness and fracture toughness of the coatings were measured using a microhardness tester and a Vickers hardness tester.Moreover,dry friction and wear behavior of the coatings sliding against Si3N4 ball was investigated using an oscillating friction and wear tester;and the worn surfaces of the coatings were analyzed by means of scanning electron microscopy(SEM).It was found that heat treatment within 500-800°C resulted in crystallization of amorphous phase in as-sprayed coating,generating nanoscale new phases such as NiWO4,CrWO4 and Cr2WO6.Besides,heat treatment led to increase of the microhardness of as-sprayed coating,and the highest microhardness was obtained after heat treatment at 800°C.The fracture toughness and wear resistance of the as-sprayed coating increased with increasing heat treatment temperature up to 700°C but tended to decrease with further elevating temperature.In other words,the mechanical properties and wear resistance of the as-sprayed coatings were worsened owing to excessive growth of oxidation grains and depletion of ductile Ni binder after heat treatment above 700°C.Thus it was suggested that as-sprayed ceramic composite coating should be post heat treated in air at a moderate temperature of 700°C so as to achieve the optimized mechanical properties and wear resistance.     

超音速火焰喷涂WC-10Co4Cr涂层的耐滑动磨损行为

采用超音速火焰喷涂(HVOF)工艺制备微米结构WC-10Co4Cr涂层,分别采用金相显微镜、扫描电镜(SEM)、X射线衍射(XRD)和滑动磨损设备分析涂层的微观结构和滑动磨损行为。结果表明:采用液体煤油燃料HVOF喷涂的微米结构WC-10Co4Cr涂层的脱碳程度较低,涂层中仅出现WC和W2C相,而无η相(Co3W3C、Co6W6C)以及软相W。涂层微观结构致密,孔隙率约为1%,平均显微硬度为1 322HV0.3;在相同试验条件下,WC-10Co4Cr涂层的摩擦因数(约0.8)高于不锈钢(1Cr18Ni9Ti)的摩擦因数(约0.5),其滑动体积损失量仅为不锈钢涂层的1/146,具有优异的抗滑动磨损性能。涂层在滑动磨损过程中首先是粘结相的脱落,然后是WC颗粒的磨损。     

残余应力对涂覆WC-17Co涂层的Ni718合金弯曲疲劳寿命的影响

利用超音速火焰喷涂技术在Ni718合金表面制备WC-17Co涂层,对喷涂后的试样进行150℃? h 和300℃? h 保温热处理,利用Almen试片曲率法计算不同热处理条件下涂层中的残余应力,利用反复弯曲试验测试试样的疲劳寿命,分析残余应力对试样疲劳寿命的影响。结果表明在疲劳循环过程中,裂纹在涂层中萌生并向涂层/基体界面处扩展,最后扩展至基体内部形成最终断裂。涂层中的残余压应力能够抑制疲劳裂纹的产生和扩展。当经过保温处理后涂层中的残余压应力降低,导致试样的疲劳寿命随热处理的温度上升而下降。     

超音速等离子喷涂超细WC-12Co涂层的性能

采用超音速等离子喷涂系统,分别制备了超细WC-12Co涂层和普通WC-12Co涂层.研究了喷涂粒子在射流中的特性,分析了涂层形貌、成分和相组成,并对两涂层的常规性能(结合强度、显微硬度、孔隙率和耐冲蚀性能)进行了表征.结果表明,超细WC-12Co喷涂粒子在束流中速度更快(500 m/s),两涂层中WC相的氧化、失碳和分解程度比普通等离子喷涂时低.相比之下,超细WC-12Co涂层显微硬度(1350 HV0.3)和结合强度(65 MPa)更高,孔隙率(0.6%)更低,耐冲蚀磨损性能相当.     

Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed(HVOF) technique WC-17 Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope(SEM), energy dispersive X-ray spectroscopy(EDX), and X-ray diffractrometry(XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy(OM), and surface topography. The experimental results reveal that the WC-17 Co coating adjusted the boundary between the partial slip regime(PSR) and the slip regime(SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate's coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating's higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17 Co coating in prevention of rotational fretting wear.     

Morphology and carbon content of WC-6%Co nanosized composite powders prepared using glucose as carbon source

Pure WC-6%Co nanosized composite powders were synthesized via a low-temperature method. The effects of carbon source on microstructure characteristic of composite powders were investigated, and the effects of heat-treatment parameter on carbon content of composite powders were also discussed. The results of SEM and XRD revealed that the carbon decomposing from glucose was more active than carbon black. Therefore, WC-Co nanosized composite powders could be synthesized at 900 °C for 1 h under a hydrogen atmosphere. The individual WC grains were bonded together into a long strip under the action of cobalt. The results of carbon analysis revealed that the total carbon content decreased with the increase of the temperature in the range of 800–1000 °C. Moreover, the total carbon content and the compounded carbon increased with the increase of the flow rate of H₂ in the range of 1.1–1.9 m³/h.     

Electromagnetic coupling field strengthening of WC-TiC-Co cermet tools

This work proposes the application of pulsed electromagnetic coupling field processing (EMCFP) to enhance the lifetime and cutting performance of WC-15TiC-6Co cermet tool for the first time. Firstly, the developed electromagnetic field coupling equipment is introduced, the treatment process is analyzed, and the magnetization characteristics of WC-15TiC-6Co cermet tool are evaluated. Secondly, the strengthening effect of the EMCFP treatment is demonstrated by mechanical properties testing and cutting experiments, which reveal that the optimally treated tools exhibit a fracture toughness increased by 18%, an average cutting temperature decreased by 10%, and a friction coefficient for the rank face decreased by 7.9%. Collectively, these enhancements result in a tool lifetime increased by a factor of 1.92 relative to the lifetime of untreated tools. In addition, the results of simulation demonstrate that the simultaneously pulsed magnetic and electric fields contribute toward greater magnetic flux density and current density on the surface of the WC-15TiC-6Co cermet tool than would be obtained from the magnetic and electric fields alone.     

Research on Ultrafine WC-lOCo Cemented Carbide with High Properties

WC- 10Co nanocomposite powder produced by spray pyrolysis-continuoas reduction and carbonization technology was used, and the vacuum sinteriag plus sinterhip process was cdopted to prepare ultrafine WCCo cemented carbide. The microstructure, grain size, porosity, density, Rockwell A hardness （ HRA ）, transverse rupture strength （ TRS ） , saturated magnetization and coercivity force were studied. The experimental results show that average grain size of the sample prepared by vacuum sintering plas sinterhip technology was about 420 nm, transverse rupture strength was more than 3460 MPa, and Rockwell A hardness of sintered specimen was more than 92.5. Ultrafine WC- 10Co cemented carbide with high strength and high hardness is obtained.