Preparation and Quasi-Isentropic Loading Characteristics of Ti-Pt Periodically Modulated Gradient Material

The quasi-isentropic loading technique based on wave impedance gradient materials is a crucial method for understanding the dynamic response characteristics of materials, which is essential for enhancing material service performance. In this study, Ti-Pt periodically modulated gradient materials were successfully prepared using electron beam evaporation deposition technology. By adjusting the thickness of the two components (Ti and Pt single layers) within the periodic layers, a macroscopic gradient in wave impedance was achieved. The total thickness error between the measured gradient material and the theoretical design was only 1.67%, with an average hardness and elastic modulus of 2.8 and 99.8 GPa, respectively. The interfaces between the internal layers of the material were clear, and no metal alloy phases were detected in the phase analysis. The Ti-Pt periodically modulated gradient material was loaded onto a 5 μm-thickness Al target by a one-stage light gas gun, generating a shock-quasi-isentropic loading waveform within the Al target. Numerical simulation results showed good agreement in the rising trend with the experimental curve. For the 5 μm-thickness Al target, the particle velocity, stress, and strain rate curves exhibit significant fluctuations in the quasi-isentropic stage, with the strain rate curve oscillating continuously between positive and negative values with large amplitudes. Stress contour maps indicate that the loading process of the periodically modulated gradient material involved the chasing, superposition, and integration of multiple wave systems. Simulation shows that when the target thickness is 60 μm, the wave systems complete integration and change into continuous compression wave loading. Based on the simulation result, light gas gun loading experiment for the Al target with a thickness of 60 μm were conducted. The particle velocity and stress curves in the quasi-isentropic stage change into smooth loading waveforms, and the strain rate curve remains overall positive, achieving a good quasi-isentropic loading. This indicates that the periodically modulated gradient material and target thickness need to be designed to match each other. The results of this study provide a guidance for the application of novel periodically modulated gradient structures.