Although metallic glasses have the ability to be processed in a manner similar to plastics, their sensitivity to oxygen at elevated temperatures introduces additional difficulties during processing operations. Measuring temperature consistently and accurately inside of a vacuum system involving reactive molten metals, radio frequency fields—and oftentimes rapidly moving parts—is known to be a difficult problem. Often times processing is done with a “best guess” for temperatures. This talk will discuss our progress in radiometry to perform noncontact temperature measurements. We employ a number of methods to develop a calibration standard for metallic glasses, and perform the first noncontact temperature measurements of a series of ingots during semi-solid forging. The first rough estimates for viscosity during the processing of metallic glass matrix composites will also be presented.

Exploring Domain Switching in Ferroelectrics for Structural Applications by C. Stan Wojnar

Ferroelectric materials such as lead zirconate titanate are used in a wide variety of sensors and actuators. In most cases, such applications only utilize the piezoelectric (i.e. linear) response of zirconate titanate while its ferroelectric properties remain untapped. In this talk, the various applications of zirconate titanate will be discussed along with their associated limitations, which motivates exploring the mechanical behavior of zirconate titanate (in particular its viscoelastic properties) throughout the full, non-linear ferroelectric response arising due to domain switching. To characterize the influence of domain switching on the viscoelastic response of zirconate titanate, a method and apparatus called broadband electromechanical spectroscopy is presented. Using this technique, the viscoelastic properties (specifically dynamic stiffness and loss tangent) are measured throughout the entire electric displacement hysteresis. Results show substantial increases in mechanical damping during domain switching, which points towards potential applications for vibration damping—of great need in aerospace structures. Insight into the material behavior obtained from broadband electromechanical spectroscopy is applied to demonstrate potential applications of domain switching in structures, viz. set-and-hold actuation and structural damping.

This event is one in the Caltech Kavli Nanoscience Institute / JPL Microdevices Lab Monthly Seminar Series.