What is the material that is used for turbine blades that has the highest melting point?
Gases temperature on the turbine blades can reach 1700-1800K. There is no material which can withstand such a temperature in conjunction with enormous centrifugal forces. 

That's why blades are not only made of nickel superalloys, coated with ceramics, but also are "film-cooled". 

They have radial micro-passages where compressed air from high pressure compressor is fed. Most advanced designs also have micro-holes along that passages on the leading and trailing edge of the blade, which are the hottest points on the blade. This enables cooling blades down with air (air from HP compressor heats up to 400-500K, while blades work at 600-700K) and also creates a film of protective air over blade's surface, which prevents direct contact of blade and exhaust gases. That's because most of the heat transfer occurs by thermal conductivity at direct contact, and much less - by heat radiation.