两种镍基合金喷焊层的相分布与热疲劳性能

利用扫描电子显微镜、X射线衍射仪及透射电子显微镜观察分析了含Cu和Mo(Ni-A)、不含Cu和Mo(Ni-B)两种镍基合金喷焊层样品的组织、相分布和成分分布,分别测定了基体部位、热影响区、结合区及涂层内的显微硬度.利用高频加热炉对两种喷焊层进行了热疲劳实验,对经热疲劳实验后喷焊层微观组织进行了观察,分析了喷焊层内的相分布和成分分布状态,探讨了热疲劳裂纹产生和扩展的过程及规律.结果表明:两种喷焊层内均有针状富Cr第二相弥散分布,具有较好的热疲劳性能.Ni-A样品喷焊层可以分成两个区域:在靠近基体的区域均匀地分布着块状富Cr第二相;在离表层200μm左右的区域内分布有针状富Cr第二相,体积比块状富Cr第二相小几十倍.Ni-B样品喷焊层内只有针状富Cr第二相,在整个喷焊层内均匀分布.Ni-A样品喷焊层由于过渡区域的存在,具有比Ni-B样品喷焊层更好的热疲劳性能.热疲劳实验前后样品的EDS分析结果表明两种喷焊层内的各相有较好的热稳定性.

Phase distribution and thermal fatigue property of two kinds of Ni-based alloy spray-welding coatings

SEM, TEM and X-ray diffraction methods were used to observe and analyze the microstructure, phase distribution and composition distribution of Cu and Mo-containing (Ni-A) and Cu and Mo-free (Ni-B) Ni-based alloy spray-welding coatings. The micro-Vickers hardness of the matrix and the heat-effected, combined and coating areas was measured. The thermal fatigue process was actualized by an induction heater to investigate the phase morphology and composition distribution and the phenomenon of thermal cracks appearing and spreading. Experimental results show that there exists needle Cr-rich phase with excellent thermal fatigue property in both Ni-A and Ni-B coatings. Ni-A coating can be divided into two areas:one is round-shaped Cr-rich phase which distributes near the matrix uniformly and the other is needle-shaped Cr-rich phase which distributes near the surface with a distance of about 200μm away from the outer surface of the coating. The volume of the needle-shaped Cr-rich phase is smaller than that of the roundshaped Cr-rich phase by several ten times. Compared with Ni-A coating, Ni-B coating has only needle-shaped Cr rich phase distributing in the spray coating uniformly. The thermal fatigue property of Ni-A coating is better than that of Ni-B because of a transition area in Ni-A coating. The results obtained by EDS analysis show that there is almost no diffusion of elements in Ni-A and Ni-B coatings during the thermal experiment and the two types of coatings have excellent thermal stability.