17 with turbine blades 16 coupled thereto allows the abrasive components 21 to abrade the abradable component 23 when there is no clearance between the respective components a particular aspect of the abrasive component 21 is the ability to withstand repeated and severe encounters with the abradable component 23 with only minimal loss of material from the abrasive component 21 and preferential wear of the abradable component 23 thus instead of a rubbing interface between the components 21 and 23 when the radial clearance therebetween has disappeared the abrasive component 21 cuts the abradable component 23 to maintain a minimum clearance therebetween the abrasion of the abradable component 23 by the rotating abrasive component 21 forms a fluid passageway between the rotating components the turbine blade 16 can be of a wrought or cast structure in the preferred embodiment the gas turbine blade 16 is a unitary cast single crystal alloy structure produced by a precision casting operation utilizing various super alloy compositions various types of nickel super alloy compositions and manufacturers of such compositions are known to those skilled in the art most super alloy compositions of interest are complicated mixtures of either titanium tin vanadium aluminum molybdenum silicon neodymium and other select materials or nickel cobalt chromium aluminum titanium iron tungsten tantalum rhenium and other select elements a preferred group of materials are generally known by the following tradenames cmsx 3 cmsx 4 and marm 247 and are readily available and known to people of ordinary skill in the art however the application of the.