Pore Formation Mechanism of WC-10Co4Cr Coatings Based on Collected In-flight Particles and Individual Splat

doi:10.15541/jim20170518

Abstract

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

CLC Number:

TQ174

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.

Figures/Tables 11

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

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

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

Fig. 3 Schematic of individual splat collecting process

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

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

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)

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

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)

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

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

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