Effect of Post-Deposition Solution Treatment and Ageing on Improving Interfacial Adhesion Strength of Cold Sprayed Ti6Al4V Coatings

This study aims at investigating the effect of post-deposition solution treatment and ageing (STA) on improving the interfacial adhesion strength in cold spray (CS) Ti6Al4V coatings deposited on Ti6Al4V substrates, measured by the adhesive-free collar-pin pull-off (CPP) test. Solution treatment was performed at 940 °C for 1 h and ageing was carried out at 480 °C for 8 h. Investigations were carried out for specimens with three different pre-treatments of the substrate surface, namely grit-blasted, as-machined (faced on lathe machine), and ground. Additionally, the effect of post-deposition STA was studied in terms of phase analysis, microstructure, and porosity level. It was observed that STA led to complete interfacial mixing resulting in significantly improved adhesion strength (by more than 520%) with the maximum measured value of greater than 766 MPa for ground substrates, reaching 81% of the ultimate tensile strength of mill annealed Ti6Al4V.

Effect of interfacial properties on the damping performance of steel–polymer sandwich cantilever beam composites

The damping performance of lightweight steel/polymer/steel sandwich composites has been typically studied without considering the interface between the heterogeneous materials. Herein, the interface between the steel and polymer layers was investigated experimentally for various steels and polymers. Impact hammer tests revealed that the interfacial adhesion strength between steel and polymer did not significantly affect the loss factor of the sandwich cantilever beam composites. However, although very thin, the adhesive layer itself greatly influenced the vibration-damping performance of the composite. As such, previous three-layered (skin-core-skin) sandwich model without considering the properties of adhesive layer predicted different results from experiments. To accurately predict the loss factor of the sandwich, a five-layered sandwich model consisting of two skins, two adhesives, and a core layer was proposed and validated with experiments.

Corrosion Behavior of the Nickel/nickel Interface During the Copper Sacrificial Layer Releasing Process in Micro-Electroforming

The corrosion behavior of the Ni/Ni interface during the Cu sacrificial layer releasing process in micro-electroforming has been investigated. The XPS and SEM results reveal that the pre-existing passive layer and interfacial defects exist on the Ni/Ni interface. Compared with Ni base, the interface is prone to be attacked. Pitting corrosion occurs along interface boundary, which contains three main processes, pit initiation, pit growth and pits fusion, leading to a commensurate reduction in interfacial adhesion strength and ultimately structural integrity. The combination of the substrate modification and heat post treatment is an effective solution to avoid the localized corrosion. We believe that both the surface activation and thermally induced diffusion have worked.

Combinatorial Materials Design Approach to Investigate Adhesion Layer Chemistry for Optimal Interfacial Adhesion Strength

A combinatorial material adhesion study was used to optimize the composition of an adhesion promoting layer for a nanocrystalline diamond (NCD) coating on silicon. Three different adhesion promoting metals, namely W, Cr, and Ta, were selected to fabricate arrays of co-sputtered binary alloy films, with patches of seven different, distinct alloy compositions for each combination, and single element reference films on a single Si wafer (three wafers in total; W–Cr, Cr–Ta, Ta–W). Scratch testing was used to determine the critical failure load and practical work of adhesion for the NCD coatings as a function of adhesion layer chemistry. All tested samples eventually exhibit delamination of the NCD coating, with buckles radiating perpendicularly away from the scratch track. Application of any of the presented adhesion layers yields an increase of the critical failure load for delamination as compared to NCD on Si. While the influence of adhesion layers on the maximum buckle length is less pronounced, shorter buckles are obtained with pure W and Cr–Ta alloy layers. As a general rule, the addition of an adhesion layer showed a 75% improvement in the measured adhesion energies of the NCD films compared to the NCD coating without an adhesion layer, with specific alloys and compositions showing up to 125% increase in calculated practical work of adhesion.

A Study on Reduced/Absent Adhesion/Cap Layers for Optimized BEOL RC Performance

Lower RC delay is vital to achieve optimal and competitive circuit performance and hence drives the endlessly pursued BEOL integration scheme advancement. To date low-k dielectric materials, i.e., fluorine-doped oxides, carbon-doped oxide (SiCOH), to porous carbon-doped oxides (p-SiCOH) have been implemented. However, due to the process integration challenges with inherently weak low-k materials, the trend to pursue lower k dielectrics has come to a plateau as technology nodes scale down past 20/14nm. On the other hand, the trend of geometry layer thickness shrinking down, such as trench CD and height, via CD and height, etc., still continues for each advanced technology node. In the BEOL stack adhesion layers (oxide + gradient layers) (ALs) with higher k value were introduced to enhance interface adhesion strength between SiCOH/p-SiCOH and dielectric cap film (SiCN), which offset the intrinsic RC benefit from low-k dielectric material. At more advanced nodes and beyond, the combined ALs and cap film could be up to via or trench height, which poses a huge challenge to meet desired RC performance and technology node scaling. Therefore, the thickness reduction of ALs and cap film becomes necessary for further technology node scaling. In this study, samples with interfacial full ALs, reduced ALs and bulk only (no ALs) for p-SiCOH (k=2.75) on various cap films were prepared, such as SiCN, SiCN/ODC, SiCN/AlONx, etc. TOF-SIMS analyses was used to confirm the composition of the dielectric stacks and later check the debonded surface morphology. Four-point bend adhesion tests were conducted to evaluate interfacial adhesion strength. Results show the interfacial adhesion strength on samples with reduced Als and bulk only (no ALs) is dropped by ~20% and ~30%, respectively. Additional ODC layer on top of SiCN would increase the interfacial adhesion strength by ~10%. It is suggested that reduced ALs may be adequate to satisfy overall CPI requirement for the BEOL integration scheme of p-SiCOH on advanced dielectric cap films (AlN + ODC). The coupling capacitance reduction for a combined reduced ALs and advanced dielectric cap can be up to 16% at M0 level and 10% at Mx level for a 40nm metal pitch.