The copper coating has been proposed to stiffen the niobium superconducting cavity in order to reduce its deformations under Lorentz forces. The environment of thermal spray process is very important to get the wanted copper properties, as a consequence, the Inert Plasma Spray (IPS) process was used to realize the copper coating onto niobium. With the use of X-ray diffraction method, the radiocrystallographic elastic constants (REC) of the IPS copper coating have been measured firstly, and then, in using the measured REC, the residual stress distribution has been determined secondly as a function of the depth in the copper coating and in the substrate.