Analysis of X-ray diffraction patterns from mechanically alloyed Al-Ti powders

Abstract

X-ray diffraction (XRD) method is one of the most versatile tools to characterize various forms of materials. Simplicity and wealth of information from the spectrum makes it attractive for the evaluation of mechanical alloyed powders. However, careful interpretation of the solubility of minor phase is necessary due to the effect of particle size on the detection limit in XRD method. In this study, we demonstrate the inaccuracy of solubility from XRD analysis of nanosized particle system using Al-Ti as a model. Using transmission elec-tron microscopy (TEM), it is confirmed that large amount of nanosized Ti in Al matrix is not detected by XRD. The peak disappearance of minor phase can not be used to determine the solubility of mechanically alloyed powders. Lattice parameter change of the major phase should be used to assess the solubility limit of the minor phase in nanosized particle system. In addition, the possible sources of error are addressed when mechanically alloyed powders of Al-Ti system are characterized by the XRD method. Proper XRD analysis methods are suggested to determine the lattice parameter, solubility of minor elements, crystallite size and strain variance in the MA Al-Ti samples. Pure Al is used as an internal standard to correct instrumental broadening, the Al {111} peak is used to determine lattice parameter of Al, and the lattice parameter of Al is recommended to estimate the solubility of Ti in Al. The calculation of crystallite size and strain variance in the MA powders using Williamson-Hall equation is also discussed in detail.