Junlan Wang

In this study, Cu/Ni and Cu/Al multilayers, with individual layer thickness varying from 25 nm to 200 nm, and co-sputtered Cu-Ni and Cu-Al single layer films were deposited at room temperature via magnetron sputtering and further annealed from 100 °C to 300 °C. The mechanical and microstructural properties of the as-deposited and annealed samples were characterized by nanoindentation, x-ray diffraction, and scanning electron microscopy. Both multilayer systems exhibit an increase in hardness with increasing annealing temperature. However, the Cu/Ni system shows a gradual and moderate hardness increase (up to 30%) from room temperature to 300 °C, while the Cu/Al system displays a sharp hardness surge (~150%) between 125 °C and 200 °C. The co-sputtered Cu-Ni and Cu-Al samples consistently demonstrate higher hardness than their multilayered counterparts, albeit with distinctly different temperature dependence—the hardness of Cu-Ni increases with annealing temperature while Cu-Al maintains a constant high hardness throughout the entire temperature range. The distinct thermal strengthening mechanisms observed in the two metallic multilayer systems can be ascribed to the formation of solid solutions in Cu/Ni and the precipitation of intermetallic phases in Cu/Al. This study highlights the unique advantage of intermetallic strengthening in metallic multilayer systems.

In this study, Cu/Ni and Cu/Al multilayer thin films with individual layer thickness varying from 25 nm to 200 nm were deposited at room temperature and further annealed up to 300 ℃. The mechanical and microstructural properties of the multilayers were characterized by nanoindentation, x-ray diffraction, and scanning electron microscopy. Both systems exhibited an increase in hardness with increasing annealing temperature. However, the Cu/Ni system showed a gradual and moderate (up to 30%) hardness increase from room temperature to 300 ℃, while the Cu/Al system showed a sharp increase (~150%) between 125℃ and 200℃. This distinct strengthening behavior is attributed to solid solution formation in Cu/Ni and diffusion-activated intermetallic formation in Cu/Al.

Additive manufacturing (AM) has emerged as a crucial technology in recent decades, particularly within the aerospace industry. However, the thermally cyclic nature of these processes introduces significant variations and defects in microstructure, which can adversely affect final part performance and hinder the widespread adoption of the technology. Traditionally, characterization of AM parts has relied on conventional bulk testing methods, which involve analyzing many samples to gather sufficient data for statistical analysis. Unfortunately, these methods are unable to account for local nanoscale variations in material properties caused by the microstructure, as they measure a single averaged property for each tested sample. In this work, we use AM Inconel 718 as a model system in developing a novel approach to correlate nanomechanical properties obtained through nanoindentation with microstructure obtained through electron backscatter diffraction (EBSD). By associating mechanical properties obtained from each indent with the corresponding crystallographic direction, we calculate the weighted average hardness and modulus for each orientation. This enables us to generate inverse pole figure maps depicting the relationship between mechanical properties and crystallographic direction. Our method yields results in good agreement with literature when calculating the part modulus and hardness, while effectively capturing nanoscale variations in properties across the microstructure. The key advantage of this methodology is its capability to rapidly test a single AM part and generate a large dataset for statistical analysis. Complementing existing macroscale characterization techniques, this method can help improve AM part performance prediction and contribute to the wider adoption of AM technologies in the future.

Strong thermal effect on microstructure and mechanical properties of Ti/Ni multilayer thin films was observed from in situ heating during deposition and subsequent annealing. Films deposited at low-temperature show preferred crystallographic texture for both Ti and Ni layers, with columnar structure extending through the layers. The columnar structure becomes more distinct and complete with the increase of temperature up to 300 °C, and meanwhile, more atomic diffusion and intermixing occur along the Ti/Ni interfaces, promoting the formation of Ti-Ni intermetallic precipitates. High-temperature deposition causes disintegration of the layered structure. Columnar Ti-Ni alloys and further recrystallized alloys were detected with the preferred crystallographic texture. For material strength, an increased hardness trend was observed with increasing deposition temperature even with much larger grain size compared to room temperature case. Furthermore, for multilayer systems deposited under low temperature, post-annealing resulted in higher hardness with minimal microstructure modification, with more strengthening observed in lower deposition temperature case.