Wear performance of titanium and niobium added MOS₂ coatings under isobutane exposure

As conventional refrigerants phased out, Hydrocarbons such as Isobutane emerged as the main alternative in refrigeration industry. However, compatibility of these new ozone friendly refrigerants with compressor oils and bearing materials need to be evaluated. This study investigates wear performance of Titanium and Niobium added MoS₂ coatings running against 100Cr6 steel under isobutane exposure. Wear performance is established under starved lubrication condition by comparing the maximum achieved sliding distance before the sudden increase and fluctuation of the friction curve. Sinter steel samples were coated with MoS₂, MoS₂-Ti, MoS₂-Nb thin films by magnetron sputtering. The concept of durability distance has been defined as the distance until a sudden fluctuation of the friction curve is observed. It was found that addition of Titanium and Niobium adversely affects wear performance of the MoS₂ coatings under isobutane exposure. This can be attributed to the possible degradation of MoS2 lamellar structure that acts as solid lubricant under such exposure.