difference in thermal expansion coefficients is large the gradient must be small to minimize stress if the difference in thermal expansion coefficients is small then the gradient can be steeper with no detrimental affect to the performance of the layer a linear compositional gradient is most preferred although gradients that vary exponentially or by any other equation are possible it is also possible to prepare layers with fluctuating gradients that is with the cyclic increasing and decreasing of the first and second powders the compositionally graded layers are typically 20 50 u03bcm thick at thicknesses much greater than 50 u03bcm the mechanical properties of the coating such as mechanical shock resistance degrade the deposition of a sublayer 19 can be easily incorporated into the method shown in fig2 accordingly first powder 11 is introduced alone into the deposition chamber 12 from feeder 13 which is equipped with means of controlling the powder feed rate powder 11 is directed into stream 16 of the plasma torch flame where it melts or at least softens it is then accelerated onto the substrate 17 after a sufficient thickness ca 20 u03bcm has been deposited the second feeder 15 is turned on and the process continues as described.