激光沉积CoCrFeNiSi-(Al,Ti)非等原子比高熵合金涂层腐蚀行为研究

Corrosion Behavior of Laser Deposited Non-equiatomic CoCrFeNiSi-(Al,Ti)HEA Coatings

目的研究Al、Ti元素对激光沉积CoCrFeNi系高熵合金涂层耐蚀性能影响,并对影响程度进行比较。方法采用激光沉积技术在316L不锈钢表面制备CoCrFeNiSi_(0.5)、CoCrFeNiSi_(0.5)Al_(0.5)、CoCrFeNiSi_(0.5)Ti_(0.5)、CoCrFeNiSi_(0.5)Al_(0.5)Ti_(0.5)等4种成分的高熵合金涂层,并通过X射线衍射仪(XRD)、金相显微镜(OM)、场发射扫描电镜(FESEM)以及电化学工作站等设备对高熵合金涂层凝固组织形貌、微观组织形貌、微区成分分布、耐腐蚀性能等方面进行分析研究。结果激光沉积CoCrFeNiSi_(0.5)高熵合金涂层物相由单一面心立方(FCC)相构成;CoCrFeNiSi_(0.5)Al_(0.5)高熵合金涂层的主要物相变成体心立方(BCC)相,并形成沿晶界网状分布的Cr3Si相;CoCrFeNiSi_(0.5)Ti_(0.5)高熵合金涂层的主要物相仍为FCC相,但枝晶间区域内形成G相(Ni16Ti6Si7),枝晶内区域形成长条状Cr_(15)Co_(9)Si_(6)相;CoCrFeNiSi_(0.5)Al_(0.5)Ti_(0.5)高熵合金涂层的主要物相为BCC相,枝晶间区域G相含量较CoCrFeNiSi_(0.5)Ti_(0.5)合金涂层有所降低,枝晶内区域形成弥散分布的方形纳米Fe3Al相。激光沉积CoCrFeNiSi-(Al,Ti)非等原子比高熵合金涂层在0.5 mol/L H2SO4溶液中的耐蚀性大小依次为CoCrFeNiSi_(0.5)Ti_(0.5)>CoCrFeNiSi_(0.5)Al_(0.5)Ti_(0.5)>CoCrFeNiSi_(0.5)>CoCrFeNiSi_(0.5)Al_(0.5)。浸蚀后,CoCrFeNiSi_(0.5)高熵合金涂层以均匀腐蚀为主,CoCrFeNiSi_(0.5)Al_(0.5)涂层产生严重的晶间腐蚀,CoCrFeNiSi_(0.5)Ti_(0.5)涂层主要为枝晶间区域的点蚀,CoCrFeNiSi_(0.5)Al_(0.5)Ti_(0.5)涂层枝晶间区域的点蚀程度明显高于CoCrFeNiSi_(0.5)Ti_(0.5)涂层,且枝晶内区域的纳米第二相颗粒发生脱落。结论在酸性溶液环境中,相较于Al元素,Ti元素可更有效地提升激光沉积CoCrFeNi系高熵合金涂层的耐蚀性能。

The laser deposited CoCrFeNi based high entropy alloy(HEA)coatings can possess better corrosion resistance than the austenitic and ferritic stainless steels,and are expected to be applied to the anticorrosive coating on the materials serving in the harsh environment,such as marine industry,petrochemical industry,aerospace,etc.As two commonly used elements for improving the corrosion resistance of CoCrFeNi based HEA coatings,the individual effect of Al or Ti element on the corrosion resistance of CoCrFeNi based HEA coatings has been well studied,but it is still lack of the research aiming at comparing which of these two elements has more significant effect on the coatings.This work aims to compare the effects of Al and Ti element on the corrosion behaviors of non-equiatomic CoCrFeNiSi-(Al,Ti)HEA coatings.The CoCrFeNi HEA,Al,Si,and Ti powder were used to prepare the mixture powder according to the composition of CoCrFeNiSi_(0.5),CoCrFeNiSi_(0.5)Al_(0.5),CoCrFeNiSi_(0.5)Ti_(0.5),and CoCrFeNiSi_(0.5)Al_(0.5)Ti0.5.The HEA coatings were prepared by a semiconductor laser(LDM-2500-60)with coaxial powder feeding method on the 316L substrates.The phase structure of the laser deposited coatings was analyzed by an X-ray diffractometer(XRD,D8 Advance,Bruker).The microstructure of the longitudinal section(plane perpendicular to the laser scanning direction)of the coatings was observed by an optical microscope(OM,Axio Vert.A1,Zeiss).The microstructure of the surface of the coatings before and after corrosion was studied by a field emission scanning electron microscope(FESEM,SU-8010,Hitachi),while the micro-area composition was analyzed by the supporting energy dispersive spectroscopy(EDS).The corrosion behaviors of the HEA coatings in 0.5 mol/L H2SO4 solution were studied by an electrochemical workstation(CS350,Wuhan Corrtest).The results indicated that the laser deposited CoCrFeNiSi_(0.5) HEA coatings were composed of face-centered cubic(FCC)phase.The major phase of CoCrFeNiSi_(0.5)Al_(0.5)HEA coatings changed to body-centered cubic(BCC)phase and the Cr3Si phase distributed along the grain boundaries was established.The major phase of CoCrFeNiSi_(0.5)Ti_(0.5)HEA coatings maintained FCC phase,but a large quantity of G phase(Ni16Ti6Si7)was formed in the interdendritic(ID)region and the long-strip Cr_(15)Co_(9)Si_(6)phase was formed in the dendritic(DR)region.The major phase of CoCrFeNiSi_(0.5)Al_(0.5)Ti0.5 HEA coatings was BCC phase and the content of G phase distributed in the ID region was much lower than that in CoCrFeNiSi_(0.5)Ti_(0.5)HEA coatings.Furthermore,a large number of dispersed square nanoparticles were formed in the DR region.The corrosion resistance of laser deposited nonequiatomic CoCrFeNiSi-(Al,Ti)HEA coatings in 0.5 mol/L H2SO4 solution could be ordered as CoCrFeNiSi_(0.5)Ti_(0.5)>CoCrFeNiSi_(0.5)Al_(0.5)Ti0.5>CoCrFeNiSi_(0.5)>CoCrFeNiSi_(0.5)Al_(0.5).After immersion in the 0.5 mol/L H2SO4 solution,the CoCrFeNiSi0.5 HEA coatings exhibited relatively uniform corrosion and the CoCrFeNiSi_(0.5)Al_(0.5)HEA coatings indicated severely intergranular corrosion.CoCrFeNiSi_(0.5)Ti_(0.5)and CoCrFeNiSi_(0.5)Al_(0.5)Ti0.5 HEA coatings mainly presented pitting corrosion in the ID region,while the latter had a higher extent of pitting corrosion and the nanoparticles in the DR region fell off.In general,compared with Al element,Ti element can improve the corrosion resistance of laser deposited CoCrFeNi based HEA coatings more effectively in acidic solution environment,due to the better protective effect produced by the passivation film.This work can provide theoretical references and data supports for the research and development of HEA anticorrosive coatings serving in the harsh environment.