Microplasma-sprayed multilayer coatings for electric heating elements

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

Fig. 8

Parameters of MPS of electrically insulating and resistive coatings

Parameters	Coating
	Al2O3	TiO2
Electric current, I (A)	45	40
Voltage, U (V)	30	28
Spraying distance, H (mm)	150	150
Plasma-forming gas (Ar) flow rate, Gpl (slpm)	1.3	1.3
Shielding gas (Ar) flow rate, Gsh (slpm)	4.0	4.0
Powder feed rate, Ppow (g·min−1)	1.2	2.0

Chemical composition of carbon steel St3 according to Ukrainian State Standard DSTU 2651:2005, 2015

Elements	Wt.% of elements
C	0.14–0.22
Si	0.15–0.30
Mn	0.40–0.65
Ni	<0.3
Cu	<0.3
Cr	<0.3
As	<0.08
N	<0.008
S	<0.05
P	<0.04
Fe	Balance amount

The CTE values depending on the parameters of the MPS of TiO2 powder

Run	I (A)	Gpl (slpm)	H (mm)	Ppow (g·min−1)	CTE, %
					Experimental	Calculated
1	45	2.0	160	1.8	75	74
2	45	2.0	80	0.6	89	96
3	45	1.0	160	0.6	44	44
4	45	1.0	80	1.8	78	84
5	35	2.0	160	0.6	47	50
6	35	2.0	80	1.8	88	91
7	35	1.0	160	1.8	28	38
8	35	1.0	80	0.6	65	61
9	40	1.5	120	0.8	68	64

Parameters of the metallization figure depending on the parameters of the MPS of TiO2 powder

Run	I (A)	Gpl (slpm)	H (mm)	Ppow (g·min−1)	Metallization figure height, h (mm)	Large axis, L (mm)	Small axis, l (mm)
1	45	2.0	200	1.8	2.21	9.2	7.5
2	45	2.0	100	0.6	1.04	6.3	4.7
3	45	1.0	200	0.6	0.53	8.2	7.4
4	45	1.0	100	1.8	2.31	7.2	5.6
5	35	2.0	200	0.6	0.35	8.8	6.2
6	35	2.0	100	1.8	2.27	8.6	6.6
7	35	1.0	200	1.8	0.81	7.2	7.0
8	35	1.0	100	0.6	1.34	7.6	5.4

Intervals of variation of the parameters of MPS of electric heating tracks (TiO2)

Levels of variation	Factors
	Electric current, I (A)	Plasma-forming gas flow rate, Gpl (slpm)	Spraying distance, H (mm)	Powder feed rate, Ppow (g·min−1)
Upper level +	45	2.0	160	1.8
Lower level −	35	1.0	80	0.6
Base level 0	40	1.5	120	1.2
Variation intervals	5	0.5	40.0	0.6