Perimeter procedure to produce average equivalent area grain size

A new method of perimeter procedure to produce average equivalent area grain size on orientation imaging microscopy (OIM) micrograph was developed. When the OIM micrograph was exported with the practical size of pixel equal to the electron backscattering diffraction (EBSD) step size, the expression for perimeter procedure in producing the average equivalent area radius is r¯_p=(2A_mP_m+w_b2E_s)±w_b2E_s (P_m and A_m are the perimeter and area of grains, respectively, which can be measured using commercial image pro plus software; w_b is the pixel width of the grain boundary which is suggested to set as 1 and E_s is the EBSD step size). Experiments were conducted and the four methods intercept procedure, planimetric procedure, perimeter procfedure and statistical method were adopted to measure the average grain sizes for different conditions (polygonal grains and compressed polygonal grains, different EBSD step sizes, different grain boundary widths). The results showed that the average grain size by perimeter procedure remained relatively unchanged and close to the true average grain size for all conditions. It was demonstrated that perimeter procedure has an advantage in that it can produce reliable average grain size even when the pixel step size relative to the grain size is relatively large.