Effect of fine structure on the strength of nickel alloys
Particles of the second phase are the essential factor in strengthening resulting from the aging of nickel alloys containing aluminum and titanium. Precipitates of 200–500 A in size are responsible for the maximum strength. Hardness decreases as the result of overaging, which is accompanied by an increase in the dimensions of the particles to 1000 A and larger.
Fragmentation of blocks of the matrix also contributes somewhat to strengthening; the higher the degree of dispersity of the mosaic structure, the greater the effect. To determine the effect of the dimensions of blocks it is apparently necessary to take into account not only the relative change of their dimensions but also the absolute value. If the dimensions of the blocks in nickel alloys containing titanium and aluminum decrease from 1 to 0.2 μ as the result of aging, they increase the yield point only 10%.
One can increase the resistance of nickel alloys to rupture considerably if one obtains a mosaic structure in which the size of the blocks is one to two orders lower than is possible to achieve by ordinary aging. If this could be done the size of the blocks would be of the order of magnitude of the optimum size.
KeywordsAluminum Titanium Nickel Yield Point Fine Structure
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