铌合金表面渗镀复合涂层及其抗氧化研究

Oxidation Resistance Enhancement of Nb-Based Alloy with Composite Coatings Synthesized by Pack Cementation and Electroless Plating

利用包埋渗结合化学镀技术在铌合金表面制备了复合涂层,研究了涂层在退火过程中的元素扩散行为及涂层的高温抗氧化性能。结果表明:复合涂层以晶态Ni和Al_3Nb相为主;退火过程中渗层中的Al元素向外扩散,涂层转变为晶态,形成了Ni Al_3、Al_3Nb、Ni Al相。对退火前后的涂层进行1000℃恒温氧化实验,20 h后沉积态涂层的增重为7.7 mg/cm^2,表面主要含Ni O、Al_2O_3、Ni Al相;退火态涂层样品的增重为4.9 mg/cm^2,表面生成了Al_2O_3、NiNb_2O_6、NiAl_2O_4等相。氧化后涂层与基体结合良好。退火态涂层表面由于富Al元素,氧化后形成较多的Al_2O_3,比沉积态的涂层能更有效地减缓氧化进程,提高铌合金的抗氧化性。

The composite coatings were synthesized by pack cementation and electroless plating on substrate of Nb-based alloy C103. The influence of post-annealing on the microstructures,phase structures,high temperature oxidation- resistance and interfacial adhesion of the coatings was investigated with X- ray diffraction,energy dispersive spectroscopy,scanning electron microscopy,transmission electron microscopy and electronic balance. The results show that the annealed composite coatings significantly increased the oxidation resistance of C103 alloy. For example,Ni and Al3 Nb grains dominated the as- deposited coatings,and surface segregation of Al in annealing resulted in formation of Ni Al3,Al3 Nb and Ni Al compounds. Oxidized at 1000 ℃ for 20 h,the Al2O3,Ni Nb2O6 and Ni Al2O4 phases formed on the annealed coatings covered with Al- rich layers. Formation of Al2O3 layer in oxidation possibly explained the enhancement of the oxidation resistance of the C103 surfaces. Strong interfacial adhesion was observed in both the as- deposited and annealed coatings.