Enhanced Droplet Erosion Resistance of Laser Treated Nano Structured TWAS and Plasma Ion Nitro-Carburized Coatings for High Rating Steam Turbine Components

This article deals with surface modification of twin wire arc sprayed (TWAS) and plasma ion nitro-carburized X10CrNiMoV1222 steel using high power diode laser (HPDL) to overcome water droplet erosion occurring in low pressure steam turbine (LPST) bypass valves and LPST moving blades used in high rating conventional, critical, and super critical thermal power plants. The materials commonly used for high rating steam turbines blading are X10CrNiMoV1222 steel and Ti6Al4V titanium alloy. The HPDL surface treatment on TWAS coated X10CrNiMoV1222 steel as well as on plasma ion nitro-carburized steel has improved water droplet resistance manifolds. This may be due to combination of increased hardness and toughness as well as the formation of fine grained structure due to rapid heating and cooling rates associated with the laser surface treatment. The water droplet erosion test results along with their damage mechanism are reported in this article.     

Water Droplet Erosion Behavior of High-Power Diode Laser Treated 17Cr4Ni PH Stainless Steel

This article deals with water droplet erosion (WDE) behavior of high-power diode laser (HPDL) treated 17Cr4Ni PH stainless steel. After HPDL treatment, the water droplet erosion resistance (WDER) of 17Cr4Ni PH stainless steel has not improved. The main reason is the surface hardness, which has not improved after HPDL treatment though the microstructure has become much finer. On the other hand, precipitation hardening of the alloy at 490°C for 3 h has resulted in improved WDER more than twice. This is because of its increased microhardness and improved modified ultimate resilience (MUR), and formation of fine grained microstructure. The WDER has been correlated with MUR, a single mechanical property, based upon microhardness, ultimate tensile strength, and Young’s modulus. WDERs of HPDL treated, untreated, and precipitation hardened 17Cr4Ni PH stainless steel samples were determined using a WDE test facility as per ASTM G73-1978. The WDE damage mechanism, compared on the basis of MUR and scanning electron micrographs, is discussed and reported in this article.     

High Power Diode Laser Surface Treatment to Minimize Droplet Erosion of Low Pressure Steam Turbine Moving Blades

This article deals with the high power diode laser (HPDL) surface treatment to overcome water droplet erosion of Low Pressure Steam Turbine (LPST) moving blades used in high rating conventional, critical and super critical thermal power plants. The materials generally used in these steam turbines are titanium alloy (Ti6Al4V), precipitate hardened stainless steel (17Cr-4Ni PH), X20Cr13 and X10CrNiMoV1222 steels. During incubation period as well as under prolonged testing, the HPDL surface treatment of these materials except for 17Cr-4Ni PH steel has enhanced the droplet erosion resistance significantly. This is due to increased hardness and formation of fine-grained martensitic phase due to rapid heating and cooling rates associated with laser treatment. The droplet erosion results of HPDL laser surface treatment of all these materials and their analysis form the main part of the article.     

Laser Treatment of Textured X20Cr13 Stainless Steel to Improve Water Droplet Erosion Resistance of LPST Blades and LP Bypass Valves

X20Cr13, a martensitic stainless steel, is commonly used for the manufacture of low pressure steam turbine (LPST) moving blades and LP bypass valves of fossil fuel and nuclear power plants. The LPST blades, at present, are laser surface treated to improve their water droplet erosion (WDE) resistance. The laser-treated X20Cr13 stainless steel has improved the water droplet resistance (WDER) several times compared to untreated ones. Further improvements are being carried out by providing a carbide-based HVOF coating having appropriate surface roughness or by creating textured surfaces and treating with a high power diode laser. The surfaces, having appropriate roughness, absorb more laser energy, resulting in improved microstructure, microhardness, modified ultimate resilience, and thicker hardened layer. The WDER of laser-treated textured X20Cr13 stainless steel has improved significantly compared to the untextured ones. The WDE test results of laser-treated textured and untextured X20Cr13 stainless steel along with their microhardness, modified ultimate resilience, microstructure, SEM, and XRD analysis are discussed and reported in this paper. The laser-treated textured X20Cr13 stainless steel is highly suitable for LP bypass valves and LPST blades for achieving a thicker hardened layer with lesser heat input to the components.     

Cavitation Erosion Behavior of HPDL-Treated TWAS-Coated Ti6Al4V Alloy and Its Similarity with Water Droplet Erosion

Twin wire arc-sprayed (TWAS) coating of commercially available SHS 7170-cored wire was obtained on Ti6AL4V alloy, and to improve its properties, it was further surface treated with high-power diode laser (HPDL). The cavitation erosion (CE) resistance of TWAS-coated samples was evaluated as per ASTM G-32-2003 and it was compared with laser-treated and untreated Ti6Al4V alloys. The CE resistance of TWAS-coated SHS 7170 samples after HPDL treatment has improved significantly. The main reasons for its improvement are elimination of pores, increased fracture toughness, reduced hardness, and brittleness. The CE resistance of HPDL-treated TWAS coating is compared with water droplet erosion resistance. It is observed that there is a similarity in the both the phenomenon.     

High-Power Diode Laser-Treated 13Cr4Ni Stainless Steel for Hydro Turbines

The cast martensitic chromium nickel stainless steels such as 13Cr4Ni, 16Cr5Ni, and 17Cr4Ni PH have found wide application in hydro turbines. These steels have adequate corrosion resistance with good mechanical properties because of chromium content of more than 12%. The 13Cr4Ni stainless steel is most widely used among these steels; however, lacks silt, cavitation, and water impingement erosion resistances (SER, CER, and WIER). This article deals with characterizing 13Cr4Ni stainless steel for silt, cavitation, and water impingement erosion; and studying its improved SER, CER, and WIER behavior after high-power diode laser (HPDL) surface treatment. The WIER and CER have improved significantly after laser treatment, whereas there is a marginal improvement in SER. The main reason for improved WIER and CER is due to its increased surface hardness and formation of fine-grained microstructure after HPDL surface treatment. CER and WIER of HPDL-treated 13Cr4Ni stainless steel samples have been evaluated as per ASTM G32-2003 and ASTM G73-1978, respectively; and these were correlated with microstructure and mechanical properties such as ultimate tensile strength, modified ultimate resilience, and microhardness. The erosion damage mechanism, compared on the basis of scanning electron micrographs and mechanical properties, is discussed and reported in this article.     

Cavitation Erosion Characteristics of Nitrocarburized and HPDL-Treated Martensitic Stainless Steels

This article deals with plasma ion-nitrocarburising and high power diode laser (HPDL) surface treatment of 13Cr4Ni and X10CrNiMoV1222 martensitic stainless steels to enhance their cavitation erosion resistance. These steels are commonly used in hydro turbines and boiler feed pumps. These treated steels have been evaluated for cavitation erosion resistance and it has been observed that the plasma ion-nitrocarburising process has significantly enhanced the cavitation erosion resistance as compared to untreated steel whereas HPDL-treated steels have shown marginal improvement. This is due to formation of high hardness nitrides during nitrocarburising and formation of moderate hardness martensitic phase due to rapid heating and cooling rates involved in HPDL treatment. The cavitation erosion and micro-hardness data of plasma ion-nitrocarburized as well as HPDL-treated steel samples and their comparison with hard deposits such as stellite and HVOF coating form the main part of the article.     

High Power Diode Laser-Treated HP-HVOF and Twin Wire Arc-Sprayed Coatings for Fossil Fuel Power Plants

This article deals with high power diode laser (HPDL) surface modification of twin wire arc-sprayed (TWAS) and high pressure high velocity oxy-fuel (HP-HVOF) coatings to combat solid particle erosion occurring in fossil fuel power plants. To overcome solid particle impact wear above 673 K, Cr₃C₂-NiCr-, Cr₃C₂-CoNiCrAlY-, and WC-CrC-Ni-based HVOF coatings are used. WC-CoCr-based HVOF coatings are generally used below 673 K. Twin wire arc (TWA) spraying of Tafa 140 MXC and SHS 7170 cored wires is used for a wide range of applications for a temperature up to 1073 K. Laser surface modification of high chromium stainless steels for steam valve components and LPST blades is carried out regularly. TWA spraying using SHS 7170 cored wire, HP-HVOF coating using WC-CoCr powder, Ti6Al4V alloy, and high chromium stainless steels (X20Cr13, AISI 410, X10CrNiMoV1222, 13Cr4Ni, 17Cr4Ni) were selected in the present study. Using robotically controlled parameters, HPDL surface treatments of TWAS-coated high strength X10CrNiMoV1222 stainless steel and HP-HVOF-coated AISI 410 stainless steel samples were carried out and these were compared with HPDL-treated high chromium stainless steels and titanium alloy for high energy particle impact wear (HEPIW) resistance. The HPDL surface treatment of the coatings has improved the HEPIW resistance manifold. The improvement in HPDL-treated stainless steels and titanium alloys is marginal and it is not comparable with that of HPDL-treated coatings. These coatings were also compared with “as-sprayed” coatings for fracture toughness, microhardness, microstructure, and phase analyses. The HEPIW resistance has a strong relationship with the product of fracture toughness and microhardness of the HPDL-treated HP-HVOF and TWAS SHS 7170 coatings. This development opens up a possibility of using HPDL surface treatments in specialized areas where the problem of HEPIW is very severe. The HEPIW resistance of HPDL-treated high chromium stainless steels and titanium alloys, HPDL-treated TWAS SHS 7170 and HP-HVOF coatings, and their micrographs and X-ray diffraction analysis is reported in this article.     

Advanced high-velocity oxygen-fuel coating and candidate materials for protecting LP steam turbine blades against droplet erosion

This paper describes the water droplet erosion characteristics of advanced high-velocity oxygen-fuel (HVOF) coating and the materials used for steam turbine blading. For droplet erosion study, round samples as per ASTM G73-98 (“Standard Practice for Liquid Impingement Erosion Testing,” Vol 03.02, Annual Book of ASTM Standards, ASTM, 2004) were selected. The materials commonly used for steam turbine blading are X20Cr13, X10CrNiMoV122, and Ti6Al4V. During incubation as well as in the long run, advanced HVOF coating has performed much better than all these materials. This is due to enhanced particle kinetic energy caused by optimum flow of oxygen and fuel injection by modifying the fuel injector. Droplet erosion test results of these materials and advanced HVOF coating along with their properties and damage mechanism are reported and discussed in this paper.     

激光表面纹理加工对Ti6Al4V空蚀性能的影响

采用激光表面改性的方法对Ti6Al4V合金进行纹理加工。采用表面粗糙度测试仪、接触角测量仪和X射线衍射仪对激光纹理加工试样的表面特性进行表征,采用磁致伸缩超声振动仪对试样的抗空蚀特性进行测试,采用光学显微镜和扫描电子显微镜对试样空蚀前、后的表面形貌进行观测。结果表明:经激光表面纹理加工,试样的硬度由337HV提高到550HV,水接触角增大10°;激光纹理加工试样的抗空蚀特性有所改善,特别是对于具有较小间距网格形状的表面纹理试样,其表面空蚀面积的比例小于抛光试样的1/10;激光纹理加工试样的抗空蚀特性的改善与硬度梯度效应、缓冲空泡运动和限域作用等效应相关。     

Enhanced Erosion Protection of TWAS Coated Ti6Al4V Alloy Using Boride Bond Coat and Subsequent Laser Treatment

The material commonly used in low-pressure high-rating super critical/ultra super critical steam turbines as well as guide and moving blades of high speed aero compressors is Ti6Al4V alloy. These blades are severely affected owing to erosion which leads to drop in efficiency and increase in maintenance cost. This article deals with SHS 7170 coating on Ti6Al4V alloy using twin wire arc spraying (TWAS), enhancing its bonding by providing a thin bond coat and then treating with high-power diode laser (HPDL). Significant improvement in erosion resistance of this multilayer coating has been achieved because of the formation of fine-grained micro structure due to rapid heating and cooling rates associated with the laser surface treatment. After laser surface treatment, the fracture toughness of this multilayer has improved manifold. The water droplet and particulate erosion test results along with the damage mechanism are reported and discussed in this article.     

表面纹理和表面膜对Ti6Al4V合金空蚀特性的影响

为研究表面纹理和表面膜对材料抗空蚀特性的影响,采用激光表面改性的方法对Ti6Al4V合金进行纹理加工,在纹理加工试样上采用自组装技术制备自组装分子膜。采用接触角测量表征试样的表面特性,通过对试样的抗空蚀特性进行测试和对试样空蚀前后的表面形貌进行观测,分析试样的空蚀发生机制。结果表明,Ti6Al4V试样上激光加工表面纹理可显著提高其抗空蚀能力,纹理加工试样上制备自组装分子膜,由于具有疏水特性可以进一步改善试样的抗空蚀能力;网格纹理试样的抗空蚀能力由于表面硬度高、硬度梯度大及突起高硬度点分布均匀而强于直线纹理试样;沉积薄膜纹理试样的抗空蚀能力随着间距的增大而增大,未沉积薄膜试样的抗空蚀能力随着间距的增大而减小。     

低碳钢与304不锈钢的超声空蚀机理对比研究

目的研究低碳钢及304不锈钢在蒸馏水中的超声空蚀行为及损伤机理,并评价低碳钢及304不锈钢的抗空蚀能力,为抗空蚀材料的选择提供依据。方法采用符合ASTM国际标准的超声空蚀实验装置,开展低碳钢及304不锈钢在蒸馏水中不同时间的超声空蚀实验,从累积质量损失(失重)、累积质量损失率(失重率)、试样表面形貌和残余应力等方面对两种材料的超声空蚀行为进行描述和对比分析。结果低碳钢试样空蚀开始15 min后进入空蚀加速期,在90 min左右存在较短的空蚀稳定期,而后迅速进入空蚀衰减期;304不锈钢试样在空蚀30min内累积失重率变化缓慢,之后随着空蚀时间的延长而急剧增加,在120min后进入空蚀衰减期。低碳钢与304不锈钢的空蚀变形机制以滑移为主。随着空蚀的发展,低碳钢晶粒经历了晶粒取向→晶粒细化→晶界开裂→晶粒碎化→剥落的变化过程。而在同等实验条件下,304不锈钢试样的变化相对滞后,且残余应力值较大。结论由于空蚀裂纹在304不锈钢中的深层扩展受到奥氏体相的阻碍,从而对空蚀的发展产生关键的抑制作用,使得304不锈钢的抗空蚀能力较强。     

Influence of Laser Power on the Hardening of Ti6Al4V Low-Pressure Steam Turbine Blade Material for Enhancing Water Droplet Erosion Resistance

To overcome water droplet erosion of Ti6Al4V alloy blade material used in low-pressure steam turbine (LPST) of high-rating nuclear and super critical thermal power plants, high-power diode laser (HPDL) surface treatment at two temperatures corresponding to two different power levels was carried out. During incubation as well as under prolonged erosion testing, the HPDL surface treatment of this alloy has enhanced its resistance significantly. This is due to the formation of fine-grained martensitic (ά) phase due to rapid heating and cooling associated with laser treatment. The droplet erosion test results after HPDL surface treatment on this alloy, SEM, XRD analysis, and residual stresses developed due to HPDL surface treatment are given in this paper.     

17-4PH不锈钢表面激光熔覆钴基合金涂层的空蚀行为研究

采用激光熔覆方法在汽轮机叶片材料0Cr17Ni4Cu4Nb(17-4PH)沉淀硬化不锈钢表面制备Co基合金涂层,并研究其在蒸馏水和3%NaCl溶液中的空蚀行为.用扫描电子显微镜(SEM)及能谱(EDS)分析熔覆层的显微组织及元素分布并跟踪观察空蚀后试样表面的形貌;用X射线衍射仪(XRD)和显微硬度计分别检查空蚀前后熔覆...     

Ti-6Al-4V合金表面渗层制备及空蚀性能研究

目的利用化学热处理对钛合金表面进行扩渗处理,制备硬质表面渗层,以提高钛合金抗空蚀能力。方法采用氮气气氛下渗铝工艺对Ti-6Al-4V合金退火试样进行表面处理,获得硬质表面渗层。利用X射线衍射仪、扫描电子显微镜、能谱分析仪和显微硬度计表征分析表面渗层的物相组成、微观结构、元素分布及力学性能。利用超声波振动空蚀试验机,按照ASTM G32标准,测试表面渗层在去离子水中的空蚀性能,并结合空蚀后表面形貌和元素分布,研究分析其空蚀机理。结果扩渗处理在Ti-6Al-4V合金表面生成了具有较高显微硬度的表面渗层,其由最外面的化合物层和内部的扩散层构成。在1023 K温度下处理1 h的试样,其表面渗层均匀、致密、无微裂纹,在去离子水中空蚀12 h的累积质量损失最小,为未处理试样的18%,抗空蚀性能最好。随着处理时间的延长和处理温度的升高,渗层表面变得不平整,且表面凸出的硬质陶瓷颗粒物增多。硬质陶瓷颗粒物虽显著增加试样的显微硬度,但易诱发空泡生成,使抗空蚀性能变差。结论氮气下渗铝处理在Ti-6Al-4V合金表面获得的表面渗层可以改善合金的抗空蚀性能,而表面凸出的大小不均的硬质陶瓷颗粒物使表面渗层的抗空蚀性能减弱。     

人工模拟体液中pH值对离子注N人体医用合金腐蚀行为的影响

采用电化学测试技术研究了在人工模拟体液中pH值变化对离子注N人体用SUS316L不锈钢,Co-Cr合金,工业纯Ti和Ti-6Al-4V合金腐蚀行为的影响。结果表明,随着pH值的降低,试样的腐蚀电位负移,SUS316L不锈钢和Co-Cr合金的点蚀电位与缝隙腐蚀电位降低,使材料发生局部腐蚀的敏感性提高,工业纯Ti和Ti-6Al-4V合金的腐蚀电流密度增大,提高离子释放速度,加大对人体的潜在生理危害。     

Cr-Mn-N奥氏体-铁素体不锈钢的空蚀行为

利用超声振荡空蚀实验机对Cr-Mn-N奥氏体－铁素体不锈钢进行了空蚀研究。结果表明，低硬度Cr-Mn-N不锈钢的抗空蚀性能高于高硬度的0Cr13Ni5Mo不锈钢。空蚀过程中，Cr-Mo-N奥氏体－铁素体不锈钢中的铁素体优先脱落，空蚀表面的铁素体含量由19％迅速降低到6．9％后保持稳定。奥氏体易于在铁素体脱离后形成的蚀坑处开始脱落，加工硬化是该不锈钢吸收空蚀冲击能量的一个重要途径，是其硬度较低却表面出良好抗空蚀性能的重要原因。     

Ti3Al基合金的弹性变形能与空蚀

利用旋转圆盘装置研究了Ti3Al基合金Ti-24A1-15Nb-1Mo的空蚀行为，并用洛氏硬度仪模拟空蚀过程中微射流所产生的局部载荷对Ti-24A1-15Nb-1Mo合金的作用，测量了压头加载过程中该合金吸收的总能量和弹性变形能(选择我国水利机械常用0Cr13Ni5Mo马氏体不锈钢作对比材料)。结果表明：Ti-24Al-15Nb-1Mo合金的抗空蚀性能优于0Cr13Ni5Mo不锈钢，空蚀40h后前者的累积体积损失量仅为0．551mm^3，而后者的累积体积损失量达到2．615mm^3；在局部载荷作用下，Ti-24Al-15Nb-1Mo合金不仅有较高的加工硬化能力，而且有较好的弹性性能；在压痕试验中其弹性变形能在总变形能量中所占比例达到1／3。这些性能特点使Ti-24Al-15Nb-1Mo合金在空蚀过程中能吸收和释放较多的冲击能量，延缓裂纹形成，减少体积损失，呈现良好的抗空蚀性能。     

NiCrWFeSiBCCo合金涂层的组织与耐空蚀性

采用超音速火焰喷涂技术,在1Cr18Ni9Ti不锈钢基体表面制备NiCrWFeSiBCCo合金涂层. 采用金相显微镜(OM)、超景深体视显微镜(SM)、扫描电镜(SEM)观察涂层的显微组织和空蚀前后表面的微观形貌;采用表面粗糙度测试仪和显微硬度测试仪对涂层表面粗糙度和显微硬度进行表征;采用X-Ray衍射仪(XRD)分析涂层的相组成;采用磁致伸缩空蚀试验仪测定涂层的空蚀性能,并与1Cr18Ni9Ti不锈钢的空蚀性能进行比较. 结果表明,采用超音速火焰喷涂(HVOF)制备的NiCrWFeSiBCCo涂层组织均匀,结构致密(平均孔隙率为0.63%),硬度为1 004 HV,NiCrWFeSiBCCo涂层的抗空蚀性能明显优于1Cr18Ni9Ti不锈钢.