Structure and High-temperature Wear Behavior of Zr Modified Silicide Coatings Prepared on TC4 Alloy

doi:10.15541/jim20170006

Abstract

Abstract:

Zr modified silicide coatings were prepared on TC4 alloy by Si-Zr co-deposition, the wear behavior of the coatings were investigated at 600℃, and the wear mechanisms were discussed. The results show that the obtained coating has a multi-layer structure, consisting of a (Ti, X)Si₂ (X represents Zr, Al and V elements) outer layer, a TiSi middle layer and an inner layer composed of a mixture of Ti₅Si₄+Ti₅Si₃. Addition of Zr in the pack mixtures can reduce the residual stress in the coating by lowering the coating growth rate, leading to a more compact coating structure. The micro-hardness of the coating is obviously higher than that of TC4 alloy, which shows a decrease tendency from the coating surface to its substrate. The high temperature wear tests reveal that the Zr modified silicide coating can offer effective protection for TC4 alloy at high temperatures. When using GCr15 ball as the counterpart, very slight wear occurred on the worn surface of the coating, and the main wear manners should be the transfers of GCr15 to the coating surface besides a certain extent of oxidation wear. Sliding against Al₂O₃ ball, the main wear mechanisms of the coating are considered to be plough wear, fatigue wear, adhesive wear, and oxidation wear.

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Key words: TC4 alloy, silicide coating, Zr modification, coating structure, high-temperature wear, wear mechanisms

CLC Number:

TQ174

LI Xuan, TIAN Jin, TIAN Wei, XIE Wen-Ling, LI Xiu-Lan. Structure and High-temperature Wear Behavior of Zr Modified Silicide Coatings Prepared on TC4 Alloy[J]. Journal of Inorganic Materials, 2017, 32(10): 1102-1108.

Figures/Tables 6

Fig. 1 Cross-sectional BSE image (a), element concentration profiles (b) and XRD patterns (c) conducted on the outer and inner layers of the Zr modified silicide coating prepared on TC4 alloy at 1100 ℃ for 4 h

Table 1 Standard Gibbs formation energies and vapor pressures of the co-deposited species in the pack at 1000℃

Species	Δ_fG/(kJ•mol^-1)	Vapor pressure /(1.013×10⁵Pa)
ZrF₄	-757.2	3.55×10^-5
ZrF₃	-701.0	9.77×10^-7
ZrF₂	-569.7	3.68×10^-4
ZrF	-81.2	1.58×10^-9
SiF₄	-716.5	1.11×10^-6
SiF₃	-624.8	3.29×10^-11
SiF₂	-631.5	6.46×10^-8
SiF	-309.6	5.83×10^-13

Fig. 2 Micro-hardness distribution profile of the Zr modified silicide coating along direction from its near surface to the substrate

Fig. 3 Friction coefficients and mass losses of TC4 alloy and Zr modified silicide coating sliding against GCr15 balls at 600℃(a) Friction coefficient-time curves; (b) Mass losses of TC4 alloy, the coating and their GCr15 counterparts after sliding for 60 min

Fig. 4 Friction coefficients and mass losses of TC4 alloy and Zr modified silicide coating sliding against Al2O3 ball at 600℃(a) Friction coefficient-time curves; (b) Mass losses of TC4 alloy, the coating and their Al2O3 balls after sliding for 60 min

Fig. 5 Wear morphologies of the Zr modified silicide coating after sliding against GCr15 (a, a1 and a2) and Al2O3 (b, b1 and b2) balls at 600℃ for 60 min

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