Microstructure, properties and thermal stability of W/B ₄ C multilayer coating synthesized by ion beam sputtering

Microstructure, hardness and toughness as well as the thermal stability of W/B ₄ C multilayer coating synthesized by ion beam sputtering were investigated. The results show well-defined layered structure and uniform monolayers can be found in the as-deposited multilayer coatings with various period thickness at fixed period ratio (W:B ₄ C = 1:1.5). The crystallinity of W layer and the roughness of W/B ₄ C interfaces are changed as the period thickness increasing. It can be concluded that the nano multilayer coatings have superior strengthening and toughening effects. The hardness of as-deposited (W _5.2nm /B ₄ C _7.6nm ) ₂₀ , (W _10.5nm /B ₄ C _15.8nm ) ₁₀ and (W _14.5nm /B ₄ C _21.5nm ) ₇ coatings is greatly enhanced and higher than that of pure B ₄ C coating, and the toughness of W/B ₄ C multilayer coating is significantly higher than that of pure B ₄ C coating. Subsequently, the investigations about thermal stability of (W _10.5nm /B ₄ C _15.8nm ) ₁₀ multilayer coatings indicate that the layered structural is stable when the heat treatment temperature is lower than 500 °C. With increasing of heat treatment temperature, the oxidation of W layer and the formation of WO ₃ compounds were found. The nano layered structure was dramatically destroyed accompanying severe oxidation and slight carbonization when the temperature increase up to 600 °C. The hardness of (W _10.5nm /B ₄ C _15.8nm ) ₁₀ multilayer coating increases up to 37 GPa when the coating is heat treated below 500 °C, while it declined sharply when the coating is heat treated at 600 °C due to the a degradation of layered structure. In addition, the toughness of the multilayer coatings monotonously decreases with the increase of heat treatment temperature.