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Owing to the diffusion of Si elements towards the metal substrate and the "pesting" behavior caused by volatilization of MoO 3 , magnetron-sputtered MoSi 2 coating is highly susceptible to failure and unable to protect the metal substrate from oxidation. In this work, therefore, an MoSi 2 (N) interlayer was sputtered on Mo substrates as the diffusion barrier, followed by deposition of Si-doped MoSi 2 (i.e., MoSi 2 (Si)) layer to suppress the "pesting" behavior. The as-deposited coatings were annealed subsequently at 1000 °C in an Ar atmosphere to obtain a stable structure. To evaluate the oxidation resistance, the annealed coating was heated in a muffle furnace in air at 700 °C, 1000 °C and 1200 °C for different durations. The coating structure, surface morphology, cross section and chemical composition were examined by X-ray diffraction, field emission scanning electron microscopy, and energy dispersive spectroscopy. The results showed the MoSi 2 (N) interlayer was amorphous and kept the most stable thermal stability at Ar/N 2 flow rate of 20/20 sccm. It effectively blocked the downward diffusion of Si. Free state Si elements only diffused towards the coating surface. "Pesting" pores in the MoSi 2 (Si) layer were repaired by the growth of SiO 2 layer via the preferential oxidation of Si. The mechanism for the enhanced oxidation resistance was explained through a model. • Amorphous MoSi 2 (N) interlayer is an effective diffusion barrier. • MoSi 2 (N) interlayer blocks diffusion of Si elements in MoSi 2 (Si) coating to enhance oxidation resistance of Mo substrate. • "Pesting" pores are repaired by growth of SiO 2 layer via oxidation of Si. [ABSTRACT FROM AUTHOR]

A novel Cr barrier layer was designed for suppressing the interdiffusion of an AlSi alloy coating on stainless steel. Without a Cr barrier layer, the same coating experienced a severe element interdiffusion upon exposure to high-temperature air. The rapid upward movement of the Fe atoms induced the formation of the (FeAl + Fe 2 Al 5) alloy compounds and eventually led to severe volume shrinkage and the ultimate fracture of coating. The significant downward diffusion of the (Al + Si) atoms not only triggered numerous pores but also induced the accumulation of the FeAl alloy compound in the substrate resulting in extreme interfacial cracking. In contrast, a diffusion barrier layer comprising (Cr 2 O 3 + SiO 2) and Al 2 O 3 was formed in the coating with a Cr layer during high-temperature exposure, effectively preventing the rapid elemental interdiffusion. Moreover, it inhibited the formation of the (FeAl + Fe 2 Al 5) alloy compounds in the coating as well as prevented the accumulation of the FeAl in the substrate. The obvious upward diffusion of Cr atoms further healed these pores induced by the downward diffusion of (Al + Si) atoms. The strong barrier capability of this composite oxide layer and the healing effect of Cr diffusion eventually led to an improved oxidation resistance of the Cr-coated layer. • Effect of Cr layer on the oxidation resistance of AlSi alloy coating was investigated. • The Cr diffusion triggered the growth of the (Al 2 O 3 + SiO 2) and Al 2 O 3 barrier layer. • This oxide barrier layer effectively suppressed severe inerdiffusion of Fe and Al. • The sufficient upward diffusion of Cr induced a significant self-healing effect. • The AlSi alloy coating with a Cr layer showed an improved oxidation resistance. [ABSTRACT FROM AUTHOR]

A novel Cr barrier layer was designed for suppressing the interdiffusion of an AlSi alloy coating on stainless steel. Without a Cr barrier layer, the same coating experienced a severe element interdiffusion upon exposure to high-temperature air. The rapid upward movement of the Fe atoms induced the formation of the (FeAl + Fe 2 Al 5) alloy compounds and eventually led to severe volume shrinkage and the ultimate fracture of coating. The significant downward diffusion of the (Al + Si) atoms not only triggered numerous pores but also induced the accumulation of the FeAl alloy compound in the substrate resulting in extreme interfacial cracking. In contrast, a diffusion barrier layer comprising (Cr 2 O 3 + SiO 2) and Al 2 O 3 was formed in the coating with a Cr layer during high-temperature exposure, effectively preventing the rapid elemental interdiffusion. Moreover, it inhibited the formation of the (FeAl + Fe 2 Al 5) alloy compounds in the coating as well as prevented the accumulation of the FeAl in the substrate. The obvious upward diffusion of Cr atoms further healed these pores induced by the downward diffusion of (Al + Si) atoms. The strong barrier capability of this composite oxide layer and the healing effect of Cr diffusion eventually led to an improved oxidation resistance of the Cr-coated layer. • Effect of Cr layer on the oxidation resistance of AlSi alloy coating was investigated. • The Cr diffusion triggered the growth of the (Al 2 O 3 + SiO 2) and Al 2 O 3 barrier layer. • This oxide barrier layer effectively suppressed severe inerdiffusion of Fe and Al. • The sufficient upward diffusion of Cr induced a significant self-healing effect. • The AlSi alloy coating with a Cr layer showed an improved oxidation resistance. [ABSTRACT FROM AUTHOR]