As very well summarised by a previous post, sulphidation occurs to high temperature alloys when operated at such temperatures in contact with the sulphur content in aviation fuels. Not just turbine blades but also combustion components.
On turbine blades, the attack tends to occur to the pressure surface at about 2/3 height where the combustor peak outlet temperature occurs.
If sulphidation is a problem the manufacturer would normally coat the aerofoil with diffused materials which resist the effects of high temperature sulphides. For example aluminium or more recently platinum.