Superior Slurry Erosion Behavior of a Casting NiCoCrFeNb_(0.45) Eutectic High Entropy Alloy

The flow passage components in hydraulic machinery will be eroded rapidly when running in sand water.The wear resistance of materials commonly used in hydraulic machinery needs to be improved to prevent the failure of hydraulic machinery.New wear-resistant materials are urgently needed to improve the service life of hydraulic machinery.Eutectic high entropy alloy(EHEA) is a new kind of alloys with in situ lamellar structure.NiCoCrFeNb_(0.45) EHEA has combined excellent strength and toughness.In this study,slurry erosion tests of NiCoCrFeNb_(0.45) EHEA were carried out with different impact angles and impact velocities using a rotary jet erosion test apparatus.The NiCoCrFeNb_(0.45)EHEA exhibited significant slurry erosion resistance compared with medium carbon steel 1045 and stainless steel 04 Cr13 Ni5 Mo.The erosion rate of EHEA is much slower.Compared with medium carbon steel and stainless steel,the erosion of EHEA is completed via the accumulation and removal of platelets after plowing and work hardening,accompanied by partial micro-cutting.     

冲蚀角对超音速火焰喷涂Cr3C2-NiCr涂层冲蚀磨损行为的影响

采用超音速火焰喷涂(high-velocity oxygen-fuel, HVOF)技术,在1Cr18Ni9Ti不锈钢表面制备Cr₃C₂-NiCr金属陶瓷复合涂层. 研究了涂层的显微组织、相组成以及涂层和不锈钢的冲蚀行为和机理,探讨了冲蚀角与耐冲蚀性能的关系规律. 结果表明,涂层组织结构致密均匀,主要由Cr₃C₂以及少量的Cr₇C₃, Cr₂₃C₆和(Ni, Cr)固溶体相组成. Cr₃C₂-NiCr涂层的耐冲蚀性能随着冲蚀角的增大而减小,在低冲蚀角下涂层的破坏形式主要为微切削,重量损失较低,表现出优异的耐冲蚀性能. 随着冲蚀角的增大,冲蚀沙粒对涂层产生垂直冲击作用,粘结相与硬质相之间产生裂纹导致粘结相脱落,硬质相失去粘结相的支撑作用而裸露出来,在冲蚀沙粒的持续攻击下剥落,形成许多小冲蚀坑. 随着剥落硬质相数量的增加,小冲蚀坑逐步发展为大冲蚀坑,重量损失较大,耐冲蚀性能较差.     

High-Temperature Erosion Resistance of FeBSiNb Amorphous Coatings Deposited by Arc Spraying for Boiler Applications

Erosive high-temperature wear in boilers is one of the main causes of downtime and one of the principal engineering problems in these installations. This article discusses the use of FeBSiNb amorphous coatings synthesized by arc spraying to improve elevated-temperature erosion resistance for boiler applications. The influence of test temperature, velocity, and impact angle on material wastage was revealed using air solid particle erosion rig. The experimental results showed that moderate degradation of the coating was predominant at lower impact velocity and impact angles, while severe damage arose for higher velocities and impact angles. The erosion behavior of the coating was sensitive to test temperature. The erosion rates of the coating decreased as a function of environment temperature. The relationship between microstructure and erosion resistance of the coating was also analyzed in details. The FeBSiNb coating had excellent elevated-temperature erosion resistance at temperatures at least up to 600 °C during service.     

Phase Selection and Microhardness of Directionally Solidified AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

In the present work, the solidification behaviors and microhardness of directionally solidified AlCoCrFeNi_2.1 eutectic high-entropy alloy (EHEA) obtained at different growth velocities are investigated. The microstructure of the as-cast AlCoCrFeNi_2.1 EHEA is composed of bulky dendrites (NiAl phase) and lamellar eutectic structures, indicating that the actual composition of the alloy slightly deviates from the eutectic point. However, it is interesting to observe that the full lamellar structure of this alloy is obtained through directional solidification. In order to explain this phenomenon, the maximum interface temperature criterion and the interface response function (IRF) theory are applied to calculate the velocity range of the transition from the primary phase to the eutectic, which is 1.2–2 × 10⁴ μm/s. Furthermore, microhardness is one of the important parameters to measure the mechanical properties of materials. Therefore, the microhardness test is performed, and the test result indicates that the microhardness (HV) increased with increasing growth velocity (V) or decreased with increasing lamellar spacing (λ). The dependences of λ and HV on V are determined by using a linear regression analysis. The relationships between the λ, V and HV are given as: $\lambda = 11.62V^{ - 0.48}$, HV = 305.5V 0.02and HV = 328.1λ^-0.04, respectively. The microhardness of the AlCoCrFeNi_2.1 EHEA increases from 312.38 HV to 329.54 HV with the increase in growth velocity (5–200 μm/s). Thus, directional solidification is an effective method to improve the mechanical properties of alloys.     

气体携砂对弯头局部冲蚀规律实验探讨

通过电火花数控线性切割机将弯头沿轴向剖开的实验方法,研究了SiO₂颗粒对弯头冲蚀后的壁厚损失及微观形态,并分析了弯头磨损的分布与强度。结果表明,管流状态下颗粒对弯头的冲蚀主要集中于弯头外半圈,弯头外半圈质量损失与弯头内半圈质量损失比 (定义为α) 随着颗粒粒径增大而增大;小粒径颗粒对弯头冲蚀区域的影响较大而对壁厚损失影响相对较小,弯头 (R=1.5D) 最大冲蚀角为55°,此时颗粒对壁面的冲蚀作用最大,最容易造成磨损刺穿而导致弯头失效;冲蚀坑随着颗粒粒径增大而变大,但数量相对减少,颗粒对弯头的主要磨蚀机理是变形磨损,次要机理是低角度的微削磨损,它们的综合影响造成了弯头的穿孔刺漏。     

SiO2-BN复相陶瓷润湿性及其接头微观组织

采用座滴法开展Ag-21Cu-4.5Ti合金钎料对SiO₂-BN复相陶瓷润湿与铺展行为研究. 利用SEM、XRD分析润湿界面微观组织以及形成机理. 通过调控SiO₂-BN复相陶瓷中BN含量,研究Ag-21Cu-4.5Ti/SiO₂-BN复相陶瓷润湿体系的润湿模型. 结果表明,Ag-21Cu-4.5Ti/SiO₂-BN复相陶瓷润湿体系的典型界面反应产物为TiN和TiB₂,随着体系BN含量的增加,润湿性逐渐变好. 对SiO₂-BN复相陶瓷与Nb进行钎焊试验,典型界面组织为SiO₂-BN复相陶瓷/TiN + TiB₂/Ti₂Cu + (Ag,Cu)/(βTi,Nb)/Nb. 接头抗剪强度随着钎焊时间升高先增大后减小,当钎焊温度为880 ℃,保温时间10 min时,钎焊接头抗剪强度最高,到达39 MPa.     

冻融循环-紫外辐照复合侵蚀下钢化玻璃表面受风沙冲蚀损伤的力学机理

目的研究冻融循环-紫外辐照复合因素侵蚀作用对钢化玻璃抗冲蚀性能的影响,并探究钢化玻璃表面冲蚀损伤的力学机理。方法根据内蒙古中西部地区风沙环境特征,对冻融循环-紫外辐照复合因素侵蚀作用下的钢化玻璃进行风沙冲蚀试验,并结合接触力学、断裂力学、摩擦学理论,在单颗粒冲蚀普通环境钢化玻璃的情况下,分析钢化玻璃冲蚀损伤的一般力学机理,应用扫描电子显微镜(SEM)和激光共聚焦显微镜(LSCM)分析二维、三维损伤形貌,并与理论分析进行对比。结果钢化玻璃冲蚀率随着冻融循环次数及紫外辐照等效时间的增加而增加。冲蚀速度由14 m/s增加到30 m/s时,钢化玻璃冲蚀率从0.010 mg/g增加到0.768 mg/g。冲蚀角度由15°增加到90°时,钢化玻璃冲蚀率从0.004 mg/g增加到0.453 mg/g。结论冻融循环-紫外辐照复合侵蚀作用会使钢化玻璃的抗冲蚀性能减弱。冲蚀速度的增大会使冲蚀颗粒在钢化玻璃表面产生更大的冲击接触力,使压痕深度和径向裂纹增大,从而使钢化玻璃在颗粒反复冲击下的剥落材料体积增大,故冲蚀率随冲蚀速度的增大而增大,高冲蚀速度下钢化玻璃表面压痕深度及径向裂纹长度的增长率更快,故钢化玻璃冲蚀率在高冲蚀速度下增长更快。钢化玻璃冲蚀率随着冲蚀角度的增大而增大,钢化玻璃在中高角度下的冲蚀机理为微观切削原理,冲蚀范围较广,冲蚀深度较浅,极高角度下的冲蚀机理为压痕断裂,冲蚀范围较为集中,冲蚀深度较大。     

自支撑金刚石膜冲蚀磨损研究

在研制的高压气动冲蚀磨损实验系统中对自支撑金刚石膜(抛光和未抛光)的冲蚀磨损进行了研究.比较了冲蚀磨料(SiO2,Al2O3,SiC和玻璃珠)、冲蚀角度、冲蚀速度,以及冲蚀时间对冲蚀磨损率的影响.利用扫描电子显微镜(SEM)观察了冲蚀磨损后金刚石膜表面形貌,对其进行了Raman光谱分析,并测定了抛光金刚石薄膜红外透过率的变化.结果表明,随冲蚀磨料硬度、冲蚀角度以及冲蚀速度的增加,自支撑金刚石膜的冲蚀磨损率增加.由于抛光和未抛光的金刚石薄膜表面形貌的差异,使得它们的冲蚀磨损率随冲蚀时间的变化过程不同.Raman光谱检测结果显示,由于冲蚀作用,金刚石膜表面部分碳的键合类型发生改变.冲蚀磨损使得抛光金刚石薄膜红外透过率降低,采用180目SiC磨料,在134 m/s的速度下冲蚀4 h,红外透过率降低约20%.     

Hydraulic erosion of concrete by a submerged jet

The hydraulic erosion of concrete is often found in civil and marine engineering construction. The present study explores the effects of several erosion parameters on the material loss of a concrete specimen subject to the hydraulic flow produced by a submerged jet. Such an investigation has rarely been reported in the literature. The concrete specimen has a typical compressive strength of 35 MPa, and the experimental parameters include the exposure time, incidence angle, standoff distance, and the hydraulic jet pressure. The impinging velocity is estimated based on the distance considered in the round jet model. The regression analysis shows the relationship between each parameter and the material loss. One finds that the material loss is proportional to the exposure time and the hydraulic pressure. The maximum erosion lies at an incidence angle of around 30° to 45° and is affected by the fourth-order polynomial of impinging velocity. The result of the present study provides a reference to engineering practice where concrete erosion is a concern.     

WC-Co-Cr涂层和0Cr13Ni5Mo基材的气体喷砂冲蚀行为

研究不同结构HVOF热喷WC-Co-Cr涂层和0Cr13Ni5Mo基材的冲蚀行为,重点分析高速粒子冲击下涂层孔洞和层状结构等缺陷在不同攻角下的作用,提出高攻角气体喷砂冲蚀模型,解释了WC-Co-Cr涂层和0Cr13Ni5Mo基材的冲蚀行为规律。结果表明:低攻角时,涂层与基材的损伤机制均以微切削去除为主,涂层还伴有少量剥落,WC-Co-Cr涂层的耐冲蚀性能一般优于基材,但高孔隙率涂层更易切削导致冲蚀率比基材高。随攻角增大,涂层冲蚀率呈上升趋势而基材冲蚀率下降。高攻角时,层状结构明显的涂层其裂纹更易在层间萌生和扩展导致片状剥落,高孔隙率反而有利于吸收冲击能量和抑制裂纹扩展;基材则出现严重塑性变形。在气体喷砂条件下,涂层的层状结构对法向冲击极为敏感,攻角高于45°后,WC-Co-Cr涂层的冲蚀率为基材的1.3～4.1倍。     

涂层风沙冲蚀损伤表面分形维数预测模型

目的 建立涂层风沙冲蚀损伤表面分形维数预测模型,重构冲蚀损伤表面形貌,为涂层风沙冲蚀损伤表面形貌研究提供基础。方法 进行了聚氨酯防腐面漆涂层风沙冲蚀损伤试验,建立了多粒径粒子冲击模型,利用赫兹接触理论求解冲击损伤面积及其分布概率,分析表面损伤的演化规律得到损伤面积增长迭代关系式,结合分形分布理论求解损伤表面分形维数,分析不同参数对理论模型的影响。利用理论模型重构损伤表面形貌、预测表面分形维数并与试验结果进行对比分析。结果 冲蚀试验中,随冲蚀时间、角度的增加,随机均匀分布的损伤区域逐渐叠加联通,分形维数也随之增大;表面分形维数存在最大值,斜角度下单粒子冲击损伤区域为彗星形。理论模型中,主导粒子粒径越大,分形维数初期增长速度越慢;冲击损伤面积越大,分形维数初期增长速度越快;损伤尺度系数越大,分形维数最大值越大;冲蚀前损伤面积越大,初始分形维数越大。对比理论模型与试验结果,重构损伤表面形貌损伤演化规律与试验结果相似,表面形貌余弦相似性及分形维数相关性系数均大于0.9。结论 通过分析固体粒子冲蚀现象特点和试验结果,发现风沙冲蚀是非线性的反馈的动力学系统,涂层冲蚀表面形貌具有迭代的损伤演化过程。...     

高强钢金属芯焊丝E120C-K4熔敷金属粗晶区显微组织对冲击韧性的影响

采用焊接热模拟通过改变冷却时间(t_8/5),研究了金属芯焊丝E120C-K4多道焊熔敷金属模拟粗晶区(CGHAZ)显微组织对冲击韧性的影响规律. 结果表明,当t_8/5为6 ~ 12 s时,CGHAZ显微组织由蜕化上贝氏体、粒状贝氏体和针状铁素体组成,奥氏体晶粒内部形成复相分割结构,冲击韧性最好. 而当t_8/5为30 ~ 120 s时CGHAZ显微组织主要由粒状贝氏体和针状铁素体组成,冲击韧性下降. t_8/5为120 s时,冲击韧性最差,–40 ℃冲击吸收能量仅为24 J. t_8/5为6 ~ 12 s时韧性改善的关键是形成复相分割微观结构;晶粒细小;单位距离上大角度晶界数量多.     

Investigation of size effects on material behavior of thin sheet metals using hydraulic bulge testing at micro/meso-scales

Reliable material models are necessary for accurate analysis of micro-forming and micro-manufacturing processes. The grain-to-feature size ratio (d/D_c) in micro-forming processes is predicted to have a critical impact on the material behavior in addition to the well-known effect of the grain size (d) itself as manifested by the Hall–Petch relation. In this study, we investigated the “size effects” on the material flow curve of thin sheet metals under hydraulic bulge testing conditions. The ratio of the sheet thickness to the material grain size (N=t₀/d) was used as a parameter to characterize the interactive effects between the specimen and the grain sizes at the micro-scales, while the ratio of the bulge die diameter to the sheet thickness (M=D_c/t₀) was used to represent the effect of the feature size in the bulge test. Thin sheets of stainless steel 304 (SS304) with an initial thickness (t₀) of 51 μm and three different grain sizes (d) of 9.3, 10.6, and 17 μm were tested using five bulge diameters (D_c) of 2.5, 5, 10, 20, and 100 mm. A systematic approach for determining the flow curve of thin sheet metals in bulge testing was discussed and presented. The results of the bulge tests at different scales showed a decrease in the material flow curve with decreasing N value from 5.5 to 3.0, and with decreasing M value from 1961 to 191. However, as M value was decreased further from 191 to 49, an inversed relation between the flow curve and M value was observed; that is, the flow curve was found to increase with decreasing M value from 191 to 49, a new observed phenomenon that has never been reported in any open literature. New material models, both qualitatively and quantitatively, were developed to explain the size effects on the material flow curve by using the N and M as the characteristic parameters of relative size between the grain, the specimen (i.e., sheet thickness), and the part feature (i.e., bulge diameter). The explanation and prediction of the flow curve behavior based on these models were shown to be in good agreement with the bulge test results in this study and in the literature.     

基于有限元的20#钢冲蚀磨损行为模拟

目的研究固体颗粒对油气井管柱或地面油气输送管道材料的冲蚀磨损规律。方法通过对石英砂颗粒形状特征抽提了颗粒模型,采用有限元方法模拟了其对20~#钢的冲击磨损动力学行为。在不同冲击角度、不同颗粒粒径和不同冲击速度的条件下,分析材料表面冲击破坏应力特征和材料堆积形态。结果在给定的参数条件下,随着冲击角度的增大,最大等效应力先上升后下降,在40°时达到最大值1370 MPa。高角度冲蚀时,表现为凿坑和塑性挤出;低角度冲蚀时,以微切削和犁沟形唇为主,在冲蚀坑两侧及前端有材料堆积,冲蚀坑前端的变形唇高度逐渐增加,在40°时达到最大值0.019 85 mm。随着冲击速度的增大,最大等效应力单调增大,冲击坑深度变化不大,但冲击粒子前端的堆积材料明显增多,变形唇片高度增大。当粒径小于0.15 mm时,最大等效应力随粒径的增加而增大,粒径为0.15 mm时达到最大值1410 MPa。当粒径超过0.15 mm时,最大等效应力随粒径的增加而减小。随粒径的增加,冲蚀坑深度缓慢增加,粒子前端的变形唇片高度明显增加。结论采用有限元方法对石英砂冲击20~#钢的动力学行为进行了成功的模拟,获得了冲击角度、冲击速度以及颗粒粒径的变化对20~#钢冲击过程中应力分布、冲蚀形貌变化的影响规律。     

激光熔覆层冲刷腐蚀研究现状

冲刷腐蚀广泛发生在石油、化工等领域,并致使设备材料发生损伤或失效。材料经激光熔覆后得到具有特殊化学、力学性能,并能与基体材料形成冶金结合的涂层。从激光熔覆层冲刷腐蚀行为研究方法出发,简要概括了现场测试法、数值模拟法以及通过模拟真实工况进行实验室研究的三大类实验装置的优缺点,并对目前用于激光熔覆层冲刷腐蚀行为的表征方法进行了总结。然后介绍了激光熔覆层冲刷腐蚀机理的研究现状:冲刷腐蚀机制由电化学腐蚀、机械力磨损及二者交互作用构成,其中冲刷主要通过正应力和切应力两种侵蚀机制对腐蚀产生促进作用,而腐蚀则通过弱化涂层表面促进冲刷。随后,总结了激光熔覆层冲刷腐蚀行为的影响因素,并对熔覆材料自身因素、流体因素(流速、冲蚀角、固体颗粒及pH值、温度等)对激光熔覆层冲刷腐蚀行为的影响规律进行了分析和归纳。最后,基于冲刷腐蚀机理研究现状,从研究方法及影响因素等方面总结了目前激光熔覆层冲刷腐蚀研究中存在的问题,同时对未来的研究趋势进行了展望。     

钢结构镀锌涂层冲蚀磨损表面形貌及粗糙度

我国西北地区风沙特殊环境对该地区钢结构的耐久性和安全性影响严重。利用风沙环境侵蚀实验系统、扫描电子显微镜(SEM)和激光共聚焦显微镜(LSCM)研究钢结构镀锌涂层受风沙冲蚀磨损损伤行为和损伤形貌,并分析其表面粗糙度。结果表明:涂层材料的冲蚀损伤行为更加依赖于冲蚀角度,在不同冲蚀角度下风沙流对涂层材料的冲蚀磨损过程同时存在类似表面划伤和挤压变形剥落;涂层材料的冲蚀坑深度随着冲蚀速度的增大而增加,在90°时冲蚀坑深度大于45°时的冲蚀坑深度;在相同的冲蚀速度下,45°时表面平均粗糙度Sa和均方差Sq较90°时大,在相同的冲蚀角度下,Sa和Sq均随速度的增大而增大。在冲蚀中后期,粒子对凹凸不平的表面冲蚀磨损破坏严重,试件表面峰谷的形成和破坏导致冲蚀率增加。     

不同组元活性剂对不锈钢脉冲TIG焊熔池表面张力的影响

准确获取焊接条件下熔池金属表面张力的基础数据对深入理解焊接过程中熔池金属流动及传热机制、焊缝缺陷形成等具有重要意义，但实时测量十分困难. 采用激光视觉法测量了单一组元(TiO₂，CaF₂)及二组元(30%TiO₂ + 70%CaF₂，70%TiO₂ + 30%CaF₂)活性剂下304不锈钢脉冲钨极氩弧焊熔池振荡频率，并根据特定模式下熔池特征频率与表面张力的解析模型计算了熔池金属表面张力，分析了不同组元活性剂对熔池金属平均表面张力的影响规律，在此基础上研究了不同组元活性剂对焊缝熔深的影响和增加熔深的机理. 结果表明，TiO₂能够改变熔池金属表面张力温度梯度，使熔池金属流动方向发生变化，CaF₂能够降低熔池金属表面张力绝对值，使熔池金属流速增加；二组元活性剂增加熔深是熔池金属流速增加和表面张力温度梯度改变共同作用的结果.     

热喷涂FeCrAl/WC涂层的组织和高温冲蚀行为

采用粉芯丝材和高速电弧喷涂技术制备高温氧化环境下抗冲蚀磨损FeCrAl/WC涂层。用扫描电子显微镜、能谱仪和X射线衍射仪对FeCrAl/WC涂层的组织、成分和涂层表面冲蚀磨损形貌进行了分析。用自制的高温冲蚀磨损试验机对FeCrAl/WC涂层在不同温度、攻角下的冲蚀磨损性能进行了测试。结果表明 ,高速电弧喷涂FeCrAl/WC涂层具有颗粒增强复合材料的层状组织特征。 4 5 0℃以下 ,FeCrAl/WC涂层均呈现韧性冲蚀行为 ;90°攻角时不同温度以及 6 5 0℃时不同攻角对FeCrAl/WC涂层的冲蚀行为影响不大。温度高于 35 0℃ ,FeCrAl/WC涂层具有良好的全攻角冲蚀磨损抗力 ,6 5 0℃棱角状石英磨粒冲蚀条件下 ,FeCrAl/WC涂层的冲蚀磨损抗力为 2 0g钢的 1 .94～ 2 .0 3倍。探讨了FeCrAl/WC涂层高温冲蚀磨损机理     

Novel (CoFe_2NiV_(0.5)Mo_(0.2))_(100-x)Nb_x Eutectic High-Entropy Alloys with Excellent Combination of Mechanical and Corrosion Properties

The emergence of eutectic high-entropy alloys(EHEAs) offers new insights into the design of next generation structural alloys,which is due to their stable dual-phase microstructure and outstanding mechanical properties from room to elevated temperatures.In this work,a series of(CoFe_2 NiV_(0.5)Mo_(0.2))_(100-x)Nb_x(0≤x ≤12) EHEAs were designed and prepared via vacuum arc-melting.Typical eutectic microstructure composing lamellar face-centered cubic solid solution phase and C14 Laves phase appears in the as-cast EHEA when x=9.The microstructure turns to hypoeutectic or hypereutectic when x is below or beyond that critical value accordingly.The volume fraction of the hard Laves phase is proportional to the Nb addition,leading to the strength increment yet at the expense of ductility at room temperature.In particular,the EHEA having4 at% Nb shows a compressive strength of 2.1 GPa with an elongation to fracture of 45%,while EHEAs containing 9 and10 at% Nb exhibit ultrahigh yield strengths of over 1.4 GPa.The effect of Nb addition on the corrosion resistance of this Crfree EHEA system was also studied.The EHEA containing 9 at% Nb has the best anti-corrosion performance in the 3.5 wt%NaCl solution at 298±1 K,indicating a good combination of mechanical and corrosion properties.     

微粒子喷丸对靶材残余应力场的影响

为了研究微粒子喷丸多颗粒冲击靶材时的残余应力场,建立了1个中心粒子周边均布6个粒子的7粒子冲击模型。应用有限元软件,对微粒子搭接率、冲击速度、冲击角度、直径等喷丸工艺参数对中心粒子冲击坑中心点处残余应力场的影响进行了仿真研究。结果表明:当搭接率ζ≤0.5时,ζ的变化对残余压应力场深度没有影响,而ζ=0.75是表面残余压应力S_S变化的分界线,只有在ζ＞0.75时,残余压应力场的4个特征值才均随着ζ的增大而增大;增大微粒子直径、减小冲击角度,有利于增大残余压应力场的深度,但同时也会减小残余压应力场的大小。增大微粒子的冲击速度,残余压应力场的深度增大,而残余压应力场的大小呈现一定的波动性,但是两者均在冲击速度为200 m/s时取得最大。