基于粒子飞行特性及铺展行为的WC-10Co4Cr涂层孔隙形成机理研究

doi:10.15541/jim20170518

摘要/Abstract

摘要：

采用超音速等离子喷涂设备制备WC-10Co4Cr涂层, 通过调整喷涂功率得到了具有不同孔隙结构特征的涂层, 以液氮为冷却介质收集不同熔化状态下的飞行粒子, 并通过镜面钢收集熔滴撞击铺展之后所形成的扁平粒子, 采用扫描电子显微镜观察涂层、收集的飞行粒子及扁平粒子形貌, 采用透射电镜观察涂层显微组织结构。结果表明: 随着喷涂功率的增大, 涂层的大孔隙含量逐渐降低, 而当喷涂功率上升到60 kW时, 涂层内部出现较多的热裂纹, 涂层的显微硬度则随着功率的增加而先增大后减小, WC扁平粒子主要有四种类型, 包括熔化不佳、破碎型、气泡型及花瓣型, 孔隙的形成主要是由于“遮蔽效应”、微区气体作用、熔滴不充分润湿及气孔迁移等。

关键词: 等离子喷涂, WC涂层, 飞行粒子, 熔滴, 孔隙, 扁平粒子

Abstract:

The supersonic plasma spray equipment was utilized to fabricate WC-10Co4Cr coatings. Four spraying parameters with different spraying powers were employed to obtain coatings with different porous structure. The liquid nitrogen was used to freezing in-flight particles with different molten status. The individual splat was deposited on mirror polished stainless steel at preheating temperature of about 200℃. The scanning electron microscopy (SEM) was used to observe the morphologies of coating, raw spraying powder, freezing particle, and individual splat. The field emission microscopy (FEM) was utilized to observe the microstructure of coating, while the energy dispersive spectrometer (EDS) was used to analyze the composition. The results show that with increment of spraying power, the large size pores kept decreasing. With 60 kW spraying power, a few thermal cracks appeared within the coating due to the heat accumulation. Micro hardness of the coatings increased firstly and then decreased with the increment of spraying power. Solidified morphologies of individual splat could be distinguishe as four types, namely, partially melted type, fragmented type, bubble-like type, as well as flower-like type. Pores within the WC-10Co4Cr were mainly formed by shadowing effect of solidified coatings and substrate, gas effect of the micro valley, insufficient wetting of droplet, as well as the pore migration within the liquid phase of the splat.

Key words: plasma spray, WC coatings, in-flight particles, molten droplets, pores, splat

中图分类号:

TQ174

陈书赢, 马国政, 何鹏飞, 刘喆, 刘明, 邢志国, 王海斗, 王海军. 基于粒子飞行特性及铺展行为的WC-10Co4Cr涂层孔隙形成机理研究[J]. 无机材料学报, 2018, 33(8): 895-902.

CHEN Shu-Ying, MA Guo-Zheng, HE Peng-Fei, LIU Zhe, LIU Ming, XING Zhi-Guo, WANG Hai-Dou, WANG Hai-Jun. Pore Formation Mechanism of WC-10Co4Cr Coatings Based on Collected In-flight Particles and Individual Splat[J]. Journal of Inorganic Materials, 2018, 33(8): 895-902.

图/表 11

图1 喷涂粉末的(a)整体形貌和(b)高倍形貌照片

Fig. 1 (a) Overall morphology and (b) magnification morphology of spraying particles

表1 WC-10Co4Cr涂层工艺参数

Table 1 Spraying parameters of plasma sprayed WC-10Co4Cr coatings

Parameters	1	2	3	4
Flow of Ar/(L•min^-1)	140	140	140	140
Spraying power/kW	45	50	55	60
Spraying distance/mm	100	100	100	100
Powder feeding rate/(g•min^-1)	50	50	50	50

图2 飞行粒子液氮淬冷收集工装

Fig. 2 Liquid nitrogen quenching device of in-flight particles

图3 单个扁平粒子收集过程示意图

Fig. 3 Schematic of individual splat collecting process

图4 不同喷涂功率制备的涂层平均显微硬度

Fig. 4 Average micro-hardness of coatings fabricated with different spraying powers

图5 不同喷涂功率制备的WC涂层截面形貌

Fig. 5 Cross-sectional morphologies of WC coatings fabricated with different spraying powers(a) 45 kW; (b) 50 kW; (c) 55 kW; (d) 60 kW

图6 涂层中(a) WC晶粒及非晶形貌和(b) WC扩渗形貌, (c) A区域和(d) B区域的EDS能谱图

Fig. 6 TEM morphologies of (a) WC grain and amorphous phase and (b) diffusion of WC in coating, with EDS analysis of point A (c) and point B (d) in (a)

图7 收集到粒子的典型表面形貌照片

Fig. 7 Surface morphologies of typical collected particles(a) Overall and (b) magnified morphologies of fully melted particle; (c) Overall and (d) magnified morphologies of particle with pore; (e) Overall and (f) magnified morphologies of partially melted particle

图8 WC粒子截面形貌照片

Fig. 8 Cross-sectional morphologies of WC particles(a) Overall and (b) magnified morphologies of original spray particle; Particles collected by liquid nitrogen with dense structure (c), small-size pores (d) and large-size pores (e, f)

图9 (a)熔化不佳(45 kW), (b)破碎型(60 kW), (c)气泡型(50 kW), (d)花瓣型(55 kW)的单个扁平粒子形貌

Fig. 9 Individual splat morphologies of (a) partially melted type, (b) fragmented type, (c) bubble-like type and (d) flower-like type obtained at 45 kW, 50 kW, 55 kW and 60 kW

图10 (a)熔化不佳和(b)花瓣型的扁平粒子截面形貌照片

Fig. 10 Cross-sectional morphologies of individual splat (a) partially melted type and (b) flower-like type

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