等离子活化烧结制备AlCoCrFeNi高熵合金涂层及其磨损与腐蚀性能

Wear and Corrosion Properties of AlCoCrFeNi High Entropy Alloy Coatings Prepared by Plasma Activated Sintering Process

目的 利用高熵合金涂层耐磨性能和耐腐蚀性能俱佳的特点,在进一步提升304不锈钢耐腐蚀性能的基础上,改善304不锈钢基体的耐磨性。方法 在304奥氏体不锈钢基体表面利用等离子活化烧结技术快速制备出AlCoCrFeNi高熵合金涂层;利用扫描电子显微镜、能谱仪、X射线衍射仪等设备分析涂层的组织形貌、元素分布及物相结构;采用显微硬度计、摩擦磨损仪、电化学工作站等设备测试涂层与基体的硬度分布、磨损特性及电化学腐蚀特性。结果 在保温温度1 000℃、压力70 MPa、保温时间10 min的制备条件下,涂层与基体间界面冶金结合良好,结合处并未发现孔洞和裂纹等缺陷;随着烧结温度的升高,涂层内部气孔逐渐减少,涂层主要由网状的FCC相和分布于其间的BCC相+B2相组成;与304不锈钢基体相比,涂层的硬度显著增大,在相同载荷(20 N)下涂层的平均摩擦系数降低(0.138),与基体磨损表面严重的黏着和剥落不同,涂层磨面无明显的黏着和剥落现象,仅有少量犁沟出现;点蚀是涂层和基体在质量分数为3.5%的Na Cl溶液和模拟海水中的主要腐蚀形式,相较于基体,涂层在质量分数为3.5%的NaCl溶液和模拟海水中的自腐蚀电位E_(corr)分别提高了约0.3、0.1 V,自腐蚀电流密度J_(corr)分别下降了约2个和1个数量级。结论 等离子活化烧结技术能够同步、快速地实现涂层致密化和界面高质量结合,AlCoCrFeNi高熵合金涂层对304不锈钢基体耐磨与耐腐蚀性能的提升效果明显,上述结果证实了利用高熵合金来改善不锈钢基体的综合使用性能是可行途径。

The high entropy alloys(HEAs)have excellent mechanical and chemical properties,such as high hardness and strength,wear resistance and good resistance to oxidation and corrosion.However,the higher cost of HEAs limits their large-scale industrial application.As an alternative to fabricate bulk HEAs,preparing HEAs coatings on inexpensive substrate has drawn extensive attention.The austenitic stainless steel is widely used for mechanical parts though it has poor wear resistance.Therefore,it is of interests to improve the wear and corrosion resistance of 304 stainless steel simultaneously by high entropy alloy coatings.The work aims to improve the wear resistance of 304 stainless steel substrate on the basis of further improving the corrosion resistance of 304 stainless steel according to the excellent wear resistance and corrosion resistance of high entropy alloy coating.The AlCoCrFeNi high entropy alloy coatings were rapidly prepared by the plasma activated sintering(PAS)technology with the initial powders fabricated via vacuum atomization.The microstructure of the coatings and the interfaces was observed by scanning electron microscope(SEM),and the phases were analyzed by X-ray diffractometer(XRD).The elemental distribution was identified by energy dispersive spectroscopy(EDS).The hardness wear resistance and electrochemical corrosion resistance of the coatings were tested.The bonding between the coating and substrate was perfectly metallurgical at holding temperature of 1 000℃,pressure of 70 MPa and holding time of 10 min,and no residual defects such as holes and cracks were found at the interface.The Al and Co elements diffused significantly across the interface,benefiting from the effect of the electric current and pressure used in the PAS process.In the range of 900~1 000℃,the pores of the coating gradually decreased with the increase of the sintering temperature.The coating mainly consisted of the reticulated FCC phase where the BCC phase and B2 phase formed alternately.The average friction coefficient of the coating sintered at 1 000℃(0.138)was significantly lower than that of the substrate(0.456)under the same testing loading(20 N).No obvious sticking and peeling phenomenon but slight furrows could be observed on the polished surface of the coating,which was remarkably different from the substrate.Abrasion wear was the main wear mechanism of the coating.Compared to the 304 stainless steel,the microhardness of the coating sintered at 1 000℃increased obviously(562HV under 200 g with the holding time of 15 s),which was responsible to the excellent wear resistance of the coating.Both the coating and substrate underwent pitting corrosion in 3.5wt.% NaCl solution and simulated seawater,respectively.Compared with the substrate,the self-corrosion potential E_(corr)of the coating sintered at 1 000℃increased by approximately 0.3 V and the self-corrosion current density I_(corr)was reduced by two orders of magnitude in 3.5wt.%Na Cl solution.Furthermore,the charge transfer resistance R_(ct)of the coating sintered at1 000℃(564.9 kΩ·cm^(-2))was considerably higher than that of the 304 stainless steel(17.1 kΩ·cm^(-2)),revealing lower kinetic of the corrosion reaction.The PAS technology enables densification and high-quality interface bonding simultaneously.As a result,the AlCoCrFeNi high-entropy alloy coating effectively improves the wear resistance and corrosion resistance of the 304 stainless steel substrate.It indicates that using high-entropy alloy to enhance the comprehensive performances of the stainless steel is a feasible way.