Cavitation erosion resistance characteristics of HVOF and HVAF procesd86WC-10Co4Cr hydro turbine coatings HVOF和HVAF工艺喷涂水力发电机86WC-10Co4Cr涂层的抗气蚀性能比较
R.K.Kumar1,M.Kamaraj2,S.Seetharamu1
北京东方润鹏科技有限公司译文及供稿きみはぐ
1Materials Technology Division,Central Power Rearch Institute,Bengaluru560080,India
2Department of Metallurgical and Materials Engineering,Indian Institute of Technology-Madras),Chennai600036,India Abstract摘要
The hydro plants utilizing silt-laden water for power generation suffers from vere metal wastage due to both particle induced erosion and cavitation.High Velocity Oxy-Fuel process(HVOF)bad coatings is widely adopted to improve the erosion life. The High velocity Air Fuel(HVAF)technology,provides higher particle velocities and lower spray temperatures and gives den and substantially non-oxidized coating.The cavitation resistance of86WC-10Co4Cr type HVOF coating procesd at 740m/s spray particle velocity has been compared with two HVAF coatings made at895m/s and1010m/s.The mechanical properties such as porosity,hardness,indentation toughness and cavitation resistance were
investigated.The progress in the surface damage morphology during cavitation was analyd in SEM.The weight loss of cavitated surface was measured at different intervals.The homogeneity of the cohesion between different layers has been examined qualitatively through the measurement of scratch depth across the cross ction.The HVAF coatings have shown lower porosity level,higher hardness and improved cavitation resistance.Both delamination and complete detachment of the WC grains was obrved in HVOF coating while the volume of the affected area is considerably low in HVAF coating.
现今，水力发电厂利用淤泥水发电多会遭遇严重的金属损耗，这多是由于粒子引起的侵蚀和气蚀造成的。利用HVOF（氧气助燃）超音速火焰喷涂工艺生产的涂层已被广泛应用，用以提高设备的侵蚀寿命。HVAF（空气助燃）超音速火焰喷涂技术，提供更高的粒子速度和较低的喷涂温度，因此可获得更加致密的非氧化涂层。在HVOF粒子速度达到740m/s、HVAF粒子速度在895m/s和1010m/s时喷涂86WC-10Co4Cr，并对2个工艺喷涂涂层做机械性能对比，包括孔隙率、硬度、压痕韧性、耐气蚀等在内的机械性能都进行了检测。在扫描电子显微镜(SEM)下分析气蚀过程中涂层的表面破坏情况。在不同时间段测试受侵蚀涂层表面的重量损耗。通过横
截面划痕深度的测量来定性检测各个涂层的粘结强度的均匀性。HVAF涂层显示出了较低的孔隙率、较高的硬度和优秀的耐气蚀性能。在HVOF喷涂涂层中可以观测到碳化钨颗粒的起皮和脱落现象，此
现象在HVAF涂层的受害区域出现相对较少。
沈阳英语翻译
1.Introduction介绍
The components of hydro plants utilizing silt-laden water for power generation suffers from vere metal wastage due to high velocity particle induced erosion and cavitation. Most of the rvice failures are attributed to the combined effect of cavitation and silt assisted erosion[1-2].The phenomenon of cavitation erosion gets aggravated under high turbulent conditions of fluid flow containing the suspended particles[3-5].The application of WC bad hard coatings procesd through HVOF is widely adopted to achieve improved rvice life.The cavitation resistance performance is readily affected by their hardness and toughness properties.The spray particles get heated up to a relatively higher temperatures and thus occurrence of W2C phas due to decarburization is well known in HVOF coatings.The HVAF technology utilizes air–fuel mix combustion rather than oxygen-fuel mix,provides higher particle velocities coupled with lower The potential of HVAF technology in terms of superior abrasion and slurry wear resistance has been well reported [6,7].However,the cavitation resistance of WC-CoCr coatings is not widely reported.
现今，水力发电厂利用淤泥水发电多会遭遇严重的
金属损耗，这多是由于粒子引起的侵蚀和气蚀造成的。多数服役设备故障都归咎于气蚀和淤泥侵蚀的综合影响[1-2]。在含有悬浮粒子的水流湍急的情况下气蚀现象会更加恶化[3-5]。利用HVOF工艺喷涂碳化钨类的硬质涂层已被广泛应用，来提升设备服役质量。涂层的耐气蚀性能基本受其硬度和强度的影响。众所周知，使用HVOF喷涂经常会出现喷涂
粒子在较热温度下脱碳造成的W
2
C相。HVAF工艺使用空气混合燃料而不是HVOF的氧气混合燃料，这样可以在更低的喷涂温度下提供更快的粒子速度。HVAF技术喷涂的涂层应对泥浆工况具有更好的耐磨和耐侵蚀性已被广泛报道[6,7]。但WC-CoCr涂层的
耐气蚀性还不为业界广泛熟知。
2.0Experimental program实验项目
2.1Materials and coating preparation材料和涂层准备
Two HVAF coatings of86WC-10Cr-4Co procesd at particle velocities of1010m/s and895m/s and o
面试英语口语
ne HVOF coating at particle velocity of740m/s were made onto stainless steel substrate.The sintered and agglomerated type spray powder of1.2µm carbide grain was ud.The coating morphology,porosity,hardness and the indentation toughness of coatings was evaluated at a test load of10kg on the coating cross ction.The cavitation erosion resistance was evaluated using a vibratory type cavitation test rig for duration of10hours.The diamond polished specimen of size15x15x7mm3was ud.
在不锈钢基体上分别用HVAF和HVOF喷涂86WC-10Cr-4Co涂层，前者以1010m/s和895m/s两种粒子速度、后者以740m/s的粒子速度喷涂。粉末使用碳化颗粒在1.2µm的烧结凝聚型粉末。并在涂层的横截面上以10kg的负荷试验评估涂层的形态学、孔隙率、硬度和压痕韧性。涂层的耐气蚀性试验则是使用振动型气蚀试验仪器历时10小时测量获得。测试对象是经金刚石抛光过尺寸15x15x7mm3的工件。
2.2.Mechanical properties机械特性:
The Vickers hardness of the coating was measured on the cross ction at a test load of300gm and the porosity was measured on the polished surface of the coatings by metallography.The average of eight hardness readings was reported.The toughness of coatings were measured bad on the crack length appeared under the test load of10kg on the cross ction and the fracture toughness was calculated according to Evans and Wilshaw equation.
在涂层横截面使用300gm负荷测量维氏硬度，用金相技术测量抛光涂层截面的孔隙率。平均读取了8组数据。涂层硬度值是基于横截面负荷10kg试验下出现的裂痕长度而测量的，断裂韧度则是通过EW公式（Evans and Wilshaw）计算的。
Table-1:Mechanical properties of coatings
表1：涂层机械性能
Coating 涂层Spray gun/
Nozzle
喷枪/喷嘴
Hardness
(HV0.3)
硬度
ace是什么意思Porositytrust me
孔隙率
Fracture
toughness
断裂韧度
(MPa m)
HVOF JP-50001180+700.98 3.34+0.7 HVAF-1AK-06/5L1320+400.46 6.1+0.6 HVAF-2AK06/5O1473+400.427.1+0.5The hardness of the HVAF coatings was comparatively higher than that of the HVOF coatings.The porosity of the coatings is also comparatively lower than that of HVOF. HVAF喷涂的涂层硬度相对要高于HVOF涂层的，孔隙率也相对低于HVOF涂层。
2.2.1Cavitation Erosion Resistance耐气蚀性:
The cavitation erosion test was conducted using a commercial ultrasonic processor as per ASTM G32-03[8]. Tap water was ud as the solution.The test specimen of size15x15mm2was cured below the oscillating horn tip with a gap of1mm.The frequency of the oscillator was20 kHz and the p
eak to peak amplitude was100µm.The weight loss of coatings was recorded after every1hr using an analytical balance with0.01mg resolution.Multiple specimens were ud for varied exposure tests.The tests were continued upto10hours until a steady rate of erosion loss was achieved.Fig.1shows cumulative weight loss of all three coatings.All the coatings have shown progressive metal loss with cavitation time.The reduction in mass loss of HVAF coatings after10hr.cavitation is obrved to be in the range of4to8.The steady rate of metal loss due to
Fig.1.Weight loss of coating with cavitation time 图1：随气蚀时间增加，涂层重量损耗cavitation of HVAF is obrved to be much lower(0.23to 0.78mg/h)compared to2.96mg/h in HVOF coatings.
通过使用ASTM G32-03超声波装置进行气蚀侵蚀试验[8]。测试液体为自来水，大小为15x15mm2的测量工件被固定在距离振荡超声波焊头焊嘴1mm 处。振子频率20kHz，最高峰值为100µm。使用0.01mg的电子分析天平每小时来测量涂层的重量损耗。在暴露试验中使用多个工件测试。试验持续多达10小时，直到出现稳定的侵蚀损耗。图1显示了3个涂层的累积重量损失。随着气蚀时间增加所有涂层的都继续出现金属损耗。在4—8的范围内显示HVAF涂层在10小时气蚀试验后重量损耗开始减少。通过观察发现，HVAF涂层(0.23至0.78mg/h)由气蚀造成的持续金属损耗率要大大低于HVOF涂层(2.96mg/h)。
2.2.2Scratch resistance measurements抗划痕测量: The measurement of interfacial cohesive strength of both HVOF and HVAF coatings was attempted qualitatively through scratch testing of the coatings on the cross ction, under max.load of200mN and the scratch velocity of
catti成绩查询10µm/s in a G200Nano Indenter.The Berkovich indentor was traverd from the interface to the surface as well as from surface to the interface and the scratch depth was monitored.Fig.2shows the results of the scratch depth measurements.
通过使用纳米测量仪G200Nano Indenter，在涂层横截面进行最大负载200mN和划痕速度10µm/s的定性划痕测试，以获得HVAF和HVOF涂层的交界面结合强度。Berkovich压头在涂层交界面和涂层表面间进行往复双向移动来监测划痕深度。图2显示了测量的划痕深度。
Fig.2.Scratch depth measurements of coatings
图2测量的涂层划痕深度
It has been obrved that the HVAF coatings show nearly a uniform increa in depth during both directional movements of the indenter.However,HVOF coatings show varied scratch depth with load indicating that the varied cohesive properties particularly at incread loads.
通过观察，测试探头在涂层交界面和涂层表面进行双向移动时，HVAF涂层密度趋近一致，而HVOF涂层的划痕深度变化不一，这说明随试验负荷增加HVOF涂层的结合强度也发生改变。
2.2.3Surface damage profiles表面划痕分布:
The evolution of surface damage during cavitation is obrved through SEM and results are shown in Fig.3.The damage is obrved to be initiated in the regions of porosity and progress during continued exposure resulting in large craters in the affected areas.The HVOF coatings have shown formation of deep pits with evidence of delamination of coating layer.The HVAF coatings have exhibited comparatively flat macro-eroded surface with abnce of deep pits and the volume of the affected area is considerably low.
通过金相技术观测随气蚀时间增加涂层表面破坏的演变过程，如图3所示。通过观察，涂层破坏最初出现在多孔区域，随着暴露时间增加受损害区域出现大的环状坑。HVOF涂层出现较深的麻点凹陷结构是喷涂层要起
皮的迹象。HVAF涂层显示出了较为扁平的宏观侵蚀表
Fig.3.Surface damage profiles of HVAF-1(A)and HVOF Coatings(B)after1h and10h exposure
图3.HVAF-1涂层(A)和HVOF Coatings涂层(B)在1小时和10小时暴露试验后的涂层破坏分布情况Under the conditions of low cohesive strength of built-up layers in the coating coupled with localized bubble implosion pressures,delamination of the layers becomes the mode of metal removal giving ri to incread rate of metal loss.The higher particle impaction velocities achieved during the HVAF process provides improved cohesion properties and hence the cavitation resistance.
结合强度低的喷涂涂层在局部气蚀泡沫破裂压力影响的情况下，涂层起皮必然会造成金属损耗，并加速金属损耗率。HVAF超音速火焰喷涂工艺提供了更高速的粒子冲击速度，从而改进涂层的粘合性能，增强了涂层的耐气蚀性能。
3.0Conclusions结论:
The systematic study on the comparative cavitation resistance of both HVOF and HVAF procesd tungsten carbide coatings indicate the following.
对超音速火焰喷涂HVOF和HVAF喷涂的碳化钨涂层的的耐气蚀性能进行系统的比较研究，表明如下：
1h10h
HVAF-
HVO 1h10h
A
B
∙HVAF coatings exhibit lower porosity,higher hardness and improved cavitation resistance compared to HVOF coatings.The higher toughness values and consistency in scratch depth results in HVAF coatings support this finding.
∙比起HVOF涂层来，HVAF涂层具有较低的孔隙率，较高的硬度和更强的耐气蚀性能。HVAF涂层的高韧度值和涂层划痕深度的一致性结果支持了这一发现。
∙Both delamination and complete detachment of the WC grains is obrved in HVOF and the improvement factor in cavitation resistance of HVAF is up to4.0.
∙观测到HVOF涂层的WC粒子相继出现起皮和完全脱落的现象，HVAF涂层的耐气蚀值提高到了4.0.∙The particle velocity appears to play an important role achieving den coating with lower porosity,improved cohesive strength and cavitation resistance in thermal spraying of86WC-10Co4Cr powders
∙在喷涂86WC-10Co4Cr粉末时，喷涂中的粒子速度对于形成具有较低孔隙率、较强结合强度和较高耐气蚀性的致密热障涂层具有重要意义。
∙Coating with combination of higher toughness and lower porosity are considered important for achieving improved cavitation resistance.
create table∙涂层若具有较高的韧性和较低的孔隙率，也增强涂层的耐气蚀性能。
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暮光之城4破晓下上映时间8.ASTM Std.G32,Annual Book of AST Stds V3,(2003)
