The influence of grain structures on resonance behavior near phase transitions

Inhomogeneities such as grains or plastically deformed regions in materials locally change sound wave velocities and introduce scatter in the pattern of expected resonance frequencies. The accompanying variation in the components of the free energy may promote, or block, nucleation and growth of new phases near transition temperatures. Lanthanides and martensites are two groups of materials with complex phase structures where control of the phase transformation is important in technological applications. Complex oxide minerals with a wide variety of phase structures are important in understanding the behavior of the earth’s crust. The influence on mechanical resonances of both the micro (meso) structures and the appearance and growth of phases near transition temperatures will be discussed. Experimental data on resonance behavior in inhomogeneous materials (largely lanthanides, transition metals, and silicates), where attempts have been made to control the scale and type of microstructure as they approach phase transitions will be presented. [This work receives support from DOE Grant No. DE-FC52-06NA27616 through the University of Nevada Terawatt Facility.]