Investigation on the cold deformation strengthening mechanism in MP159 alloy

Composite electron-diffraction patterns (EDPs)for any specified fee matrix orientation containing deformation twin and/or strain-induced hexagonal clo se-packed epsilon martensite (shortened as hcp phase or hcp platelet subseq uently) related to the matrix:by Specific orientation relationships have be en computed and plotted. These results helped us-to select the favorable fe e matrix orientation for distinguishing between deformation twin and hcp:ph ase and to index experimental EDPs obtained by using transmission electron microscopy (TEM). The identification of structure features in cold-drawn MP 159 alloy with 48 pet reduction in:cross-sectional area was performed by us ing TEM, combined with the results from the computer-simulated composite ED Ps. Investigation results demonstrated that the closely spaced, intersectin g network of fine platelets formed during cold drawing is deformation twins , and no reliable evidence has been found for the presence of hcp phase, wh ich was generally believed to explain the high strength attained in cold-dr awn MP159 alloy in some literature. It follows that the significant increas e in the strength due to cold working in MP159 alloy results predominately from the formation of the intersecting network of thin deformation twin pla telets, which act as "cells" or "subgrains" and provide strong barriers to the movement of dislocations over large distances. In addition, the relativ ely high dislocation density makes a certain contribution to strengthening.