of fig9 the sample of in 100 alloy was found to have excellent resistance to time dependent crack propagation when treated according to the method of the present invention in this example the in 100 was heated and annealed at above the solvus temperature and the alloy was cooled at a controlled cooling rate of 117 u00b0 f 47 3 u00b0 c per minute the crack growth rate is measured and plotted in fig1 it is obvious from the figure that the results further demonstrate the validation of the invention inasmuch as there is excellent resistance to time dependent crack propagation displayed from the data of fig1 from the foregoing examples and discussion it is clear that the heat treatment that combines a supersolvus solution annealing and a controlled cooling afterward can impart to high strength superalloys good crack growth resistance especially under time dependent conditions the method of this invention provides improvements in fatigue crack propagation for alloys which have a relatively high volume concentration of u03b3 39 precipitate for significant results u03b3 39 volume concentration should be at least 45 in practicing the present invention care should be exercised in the cooling of a specimen which has been supersolvus annealed as has been taught clearly above the rate of cooling affects the properties of the specimen relating to fatigue crack propagation and lower rates of cooling have been discovered to reduce fatigue crack propagation at the same time it is recognized that very slow cooling rates may depending on the alloy involved result in lower levels of strength in.