Recent studies have indicated only limited agreement between theoretically calculated X-ray absorption, fluorescence, and electron penetration correction factors and calibration curves obtained from alloy standards in binary systems. For some practical metallurgical problems, including diffusion gradient studies, intermediate phase identifications, etc., where analytical precision is required, alloy standards must be employed.

Most metallurgical investigations, however, are concerned with alloys containing a variety of elements. The use of theoretical calculations in these analyses is severely limited. At present, the precision of analyzed chemistries in such systems is somewhat poorer than the precision of the measured X-ray intensity values. Methods for applying combinations of theoretically calculated corrections, extrapolations from nominal alloy chemistries, etc. have been employed which yield reasonable analytical precisions but at best are first-order approximations. Approximate calculations for use in determining the chemistries of fine precipitates or inclusions where matrix excitation is unavoidable are also discussed.