摘要
钼及其合金具有优异的高温力学性能和耐蚀性能,以及相比于钨、铌、钽更为便宜的价格,因而在电子器件、发热元件、玻璃纤维加工、测温用保护管以及航空航天等尖端领域拥有较为广泛的运用。但是,钼的抗氧化能力较差,这在很大程度上限制了钼在高温领域的应用。因此,研究和提高钼及其合金的抗氧化性能有着重要意义。硅化物涂层具有高温自愈合能力,能对基材起到良好的保护作用,因此成为钼及其合金基体材料高温防护涂层的研究热点。研究人员对钼及其合金表面硅化物涂层的改性已开展了广泛的探索,如:(1)采用渗氮、渗硼、渗铝等方式引入有益元素,实现单一元素改性;(2)利用多种元素进行复合改性或形成梯度化涂层;(3)引入增强相对涂层进行改性。渗氮改性改变了硅化钼涂层的微观结构,使涂层与基体间的热膨胀系数更为接近。渗硼改性能改善涂层的自愈合能力,形成的T2(Mo5SiB2)合金层能降低硅的内扩散速率。渗铝改性使硅化物涂层在低温氧化时形成Al 2O 3-SiO2薄膜,有助于防止MoSi 2涂层的低温“pesting”失效。在复合改性与形成梯度化涂层方面,渗碳改性可利用涂层中各元素与基体的反应形成梯度化涂层,改善涂层与基体的热膨胀系数差异并阻碍有益硅向基体扩散。渗铬改性则利用铬元素富集在涂层表层,抑制涂层氧化时硅元素的内扩散和MoO 3的挥发。渗钛改性涂层中,钛元素的合金化作用可形成C11b/C40双相结构,其可以改善涂层的高温延展性,且在氧化时形成的致密Si-Ti-O玻璃层能增强涂层的抗氧化能力。此外,利用含锆增强相(如Zr 2和ZrSi2)改性的硅化物涂层在高温氧化下生成高熔点ZrO2颗粒,从而在涂层表面形成“骨骼”结构,提升涂层的抗氧化性能。而引入晶须增强相后,晶须的拔出桥连与裂纹转向机制能有效提高涂层的强度和韧性,抑制涂层中裂纹的扩展。基于国内外对单一硅化物和改性硅化物涂层的研究结果,可以总结得出,硅化物涂层抗氧化影响因素主要包括低温“pesting”氧化、涂层与基体间的互扩散、涂层与基体间的热膨胀系数差异。本文结合国内外研究近况,综述了钼及钼合金表面单一硅化物涂层与改性硅化物涂层的研究现状,以及影响硅化物涂层抗氧化性能的关键因素,并简要分析了该领域尚待研究和解决的问题。
Molybdenum has been widely used in electronic devices,heater elements,glass fiber processing,thermometry protective tubes and aerospace crafts,by virtue of its excellent high-temperature mechanical properties,corrosion resistance,and a cheaper price compared to tungsten,niobium and tantalum.However,poor antioxidant ability has limited the further application of molybdenum under high temperature circumstances.This exaggerates the importance of research and improvement for antioxidant ability of molybdenum and its alloys. The silicide coating,with high-temperature self-healing ability,has been regarded as a promising protection for Mo and Mo alloys substrates against oxidation.Thus extensive research has been done to improve silicide coatings,which includes:(i) single element modification by nitriding,boronizing,aluminizing,etc.,(ii) multi-element modification and the formation of composition-graded coating,and (iii) introducing reinforcement phases.Nitriding can change the microstructure of silicide coating,and consequently reduce the difference in thermal expansion coefficient (CTE) between coating and substrate.Boronizing can improve the coating's self-healing ability and result in the formation of T2 (Mo 5SiB 2) alloy layer which suppresses the internal diffusion of Si.Aluminizing makes the coating to generate Al 2O 3-SiO2 thin film under low-temperature oxidative condition,and thus is conducive to the prevention of "pesting" failure of MoSi 2 coating.In respect of multi-element modification,carburizing can lead to the reaction between coating elements and substrate to form graded coating.The enrichment of Cr on coating surface by chromizing reduces the internal diffusion of Si and the volatilization of MoO 3.The high-temperature ductility and anti-oxidation properties of the silicide coating can be improved by titanizing.The former is the consequence of C11b/C40 dual-phase structure caused by the alloying effect of titanium,while the latter comes from the formation of dense Si-Ti-O compound glass.In addition,Zr-containing reinforcements (e.g.ZrB 2 and ZrSi 2) can also be used to modify silicide coatings.And high-melting-point phase ZrO2 generated at high temperatures in modified coatings play a "skeleton" role in the oxide scale improving anti-oxidation properties of coating.On the other hand,by adding whiskers as reinforcing particles,coating is promoted in strength and toughness and crack propagation is restrained,owing to pull out,bridging and crack deflection effects of the whiskers.It can be concluded,based on the domestic and foreign studies upon element modification of silicide coating,that the key factors influencing oxidation resis- tance of silicide coating are "pesting" oxidation,inter-diffusion between coating and substrate,and difference of CTE between coating and substrate. This review provides a comprehensive description over the global research works on silicide coating modification,by adding single element in isolation or using multiple elements in combination or introducing reinforcement.It also gives an analysis for the key factors related to oxidation resistance of silicide coating,and an outlook on the future research.
作者
何浩然
许俊强
苗欣
刘奇
薄新维
HE Haoran;XU Junqiang;MIAO Xin;LIU Qi;BO Xinwei(School of Chemistry and Chemical Engineering,Chongqing University of Technology,Chongqing 400054;Chongqing Materials Research Institute Co.,Ltd.,Chongqing 400707;The 49th Research Institute of China Electronics Technology Group Corporation,Harbin 100048)
出处
《材料导报》
EI
CAS
CSCD
北大核心
2019年第19期3227-3235,共9页
Materials Reports
基金
重庆市重点产业共性关键技术创新专项项目(cstc2015zdcy-ztzx5005)~~
关键词
钼
钼合金
硅化物
抗氧化
涂层
灾难性氧化
梯度涂层
增强相
渗氮
渗硼
渗铝
渗钛
渗碳
渗铬
molybdenum
molybdenum alloys
silicide
anti-oxidation
coating
"pesting" oxidation
graded coating
reinforcement
nitriding
boronizing
aluminizing
titanizing
carburizing
chromizing
