为提高钛合金TC4的抗高温氧化性能,采用激光表面合金化技术在钛合金表面制备不同Nb掺杂量的Ti-Al合金化层.采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)、箱式电阻炉等对合金化层的组织结构和高温氧化行为进行分析测试.结果表明,合金化层主要组成物相为TiAl以及少量的Ti3Al相.Nb主要以置换溶质原子的形式固溶于合金化层中.合金化层组织均匀,与基体呈典型的冶金结合,在不含Nb的Ti-Al合金化层中发现大量的表层裂纹及少量的贯穿性裂纹,而在Nb掺杂的合金化层中未发现明显的宏观裂纹.合金化层在800℃保温1000h的氧化增重显著低于基体,表现出优异的抗高温氧化性能.相比而言,随着Al含量和Nb掺杂量的提高,合金化层的抗高温氧化能力也随之提高.Nb掺杂提高Ti-Al合金化层抗高温氧化性能的作用机理包括减少TiO2中的空位缺陷、细化氧化物颗粒及促进Al2O3的形成.
Ti-Al alloyed coatings with different Nb doping contents were fabricated on TC 4 titanium alloy by laser surface alloying to improve high temperature oxidation resistance of the alloy .Struc-tures and high temperature oxidation behaviors of the alloyed coatings were analyzed and tested by X-ray diffraction (XRD) ,scanning electron microscope (SEM ) ,energy dispersive spectrometer (EDS) and box-type resistance furnace .The results show that the alloyed coatings consist of TiAl and Ti3Al , and no niobium compound are formed in Ti-Al-Nb alloyed coatings .The alloyed coatings are uniform and exhibit excellent metallurgical bonding with the substrates .A large amount of surface cracks and a few penetrating cracks are formed in Ti-Al alloyed coating without Nb doping ,while no obvious cracks are formed in Ti-Al alloyed coating with Nb doping .The oxidation mass gains of all the alloyed coatings were significantly lower than those of the substrate .The alloyed coatings with Nb doping ex-hibit more excellent high temperature oxidation resistance due to the beneficial machanism of Nb do-ping .The mechanism of Nb doping on improving high temperature oxidation resistance of Ti-Al al-loyed coatings includes reducing the defect concentration of TiO2 ,refining oxide grains and promoting the formation of Al2O3 .
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