In Situ Scanning Electron Microscopy Investigation of Failure Mechanisms in Multilayer Coatings.

Ti-Al-Si target and Cr-Si target are sputtered alternately to develop a multi-layered nitride coating on a steel mold to improve die-casting lifetime. Prior to the multi-layer deposition, a CrN layer is developed as a buffer layer on the mold to suppress the diffusion of reactive elements and enhance the cohesive strength of the multi-layer deposition. Approximately 50 nm CrSiN and TiAlSiN layers are deposited layer by layer, and form about three μm-thickness of multi-layered coating. From the observation of the uncoated and coated steel molds after the acceleration experiment of liquid metal injection casting, the uncoated mold is severely eroded by the adhesion of molten metallic glass. On the other hand, the multi-layer coating on the mold prevents element diffusion from the metallic glass and mold erosion during the experiment. The multi-layer structure of the coating transforms the nano-composite structured coating during the acceleration test. Since the nano-composite structure disrupts element diffusion to molten metallic glass, despite microstructure changes, the coating is not eroded by the 1,050 oC molten metallic glass.

Superlubricity of multilayer titanium doped DLC coatings by using low SAPS organic additives in base oil

Nanostructured AlTiSiN/CrVN/ZrN coatings synthesized by cathodic arc deposition- mechanical properties and cutting performance

Development of diamond-like carbon (DLC) coatings with alternate soft and hard multilayer architecture for enhancing wear performance at high contact stress

Rowhammer is a known security vulnerability in recent Dynamic Random Access Memory (DRAM) devices, where repeated access to an array of memory can flip the bits in the adjacent row owing to the charge leakage/ capacitive coupling. Several studies have documented the Rowhammer effect [1, 2]and Google's project zero demonstrates two working examples of a security exploit [3]. Furthermore, many published scenarios highlight that scaled DRAM below 32nm [1]is exposed to potential hacking attacks because of the Rowhammer problem [3], owing to reduced spacings in DRAM bits. Thus, it is only natural to test any new upcoming technology for a similar problem. Though the working mechanisms of DRAM and spin transfer torque magnetic random access memory (STT-RAM) are drastically different, whether the STT-RAM is also potentially vulnerable to an analogous Rowhammer effect or not is not documented or discussed in literature. While the mechanism of failure is high enough charge leakage in DRAM, the corresponding mechanism in STT-RAM may be the lowering of the thermal barrier because of the dipolar magnetic field exerted by adjacent selected bits. The lowering of the thermal barrier in turn can increase the probability of an erroneous bit flip. To ascertain whether the effect is substantial, nearest (A bit) and next nearest neighbour bits (B bit) adjacent to an unselected bit (O bit) are simulated as shown in Fig 1. The bit diameter is 55nm and the center to center bit spacing is 200 nm. The magnetic field at the O bit is simulated, when all the A and B bits have been assumed to have the magnetization pointing in the same direction. While this configuration does not necessarily conform to the conventional idea of selecting an adjacent row of bits or even both the adjacent rows (double sided hammering), it provides a scenario where the most favorable conditions for an erroneous bit flip can be evaluated in STT-RAM. Three magnetic layers are assumed in each bit separated by appropriate non-magnetic regions corresponding to the STT-RAM stack. The top most layer corresponds to the Free layer (FL) and can be flipped while the others are held fixed. While calculating the magnetic field at the O bit, the middle layer is assumed to have a magnetization opposite to the topmost and bottom layers. The other configuration in which the topmost layers is flipped and is parallel to the middle layer is known to give a smaller magnetic field. A magnetostatic calculation is done to determine the magnetic field at the site of the FL layer of the O bit. The average of the field over the entire volume of the O bit is evaluated as a function of bit spacing using magnetostatic calculations as shown in Fig 2. For the largest bit spacing of 200 nm the simulated field is only around 7 Oe while for a 100nm bit spacing it increases to 60 Oe. The analytical calculation assumes each magnetic layer in each bit to be a point. The vector sum of all of these at the location of the O bit is shown here. The discrepancy between the simulated and the analytical results increases as the bit spacing decreases. This is because of the assumption that each layer is assumed to be a point. To assess the impact of these fields, the string method is used to evaluate the energy barrier between two magnetic states corresponding to 0 or 1 stored on the O bit. Inset of Fig 2shows that for a field of 7 Oe the change in energy barrier is less than 1 kT which is not large enough to cause an appreciable change in the bit error rate. For example based on Eqn 18 of [4]the bit error rate will only double for a 1 kT change in energy barrier assuming a retention time of 10 years and a relaxation time of 1 ns. Even for a bit spacing of 150 nm the increase in the BER will be less than an order of magnitude. However for a smaller bit spacing of 100 nm the BER can go up by 3 orders of magnitude. Therefore, as it stands rowhammer effect in STT-RAM does not appear to be appreciable at the 200 nm bit spacing. However at lower bit spacings the effect might become prominent and would require additional design rules to circumvent. As in the case of DRAM different techniques might have to be adopted to mitigate the problem.

Peering into Batteries: Electrochemical Insight Through In Situ and Operando Methods over Multiple Length Scales

Oxidation behavior, microstructure evolution and thermal stability in nanostructured CrN/AlN multilayer hard coatings

Wear and failure mechanisms of multilayered PVD TiN/TaN coated tools when milling austenitic stainless steel

This study investigates the mechanical and tribological properties of monolayer TiN coatings and multilayer TiN/TiCN coatings deposited via direct current magnetron sputtering onto titanium substrates (VT1-0). The coatings were characterized by microstructure, nanohardness, elastic modulus, and tribological performance under lubricated friction conditions. Scanning electron microscopy (SEM) revealed that the coatings exhibit a uniform microstructure without visible defects and a typical columnar growth morphology. Nanoindentation tests demonstrated that the multilayer TiN/TiCN coatings possess enhanced hardness (up to 23.5 GPa) and elastic modulus (191 GPa) compared to the monolayer TiN, attributed to interlayer strengthening effects and redistribution of residual stresses. Tribological tests using a ball-on-disk configuration under lubricated conditions showed that the multilayer coatings exhibit a significantly lower coefficient of friction (0.10–0.13) and improved wear resistance compared to the TiN coating. This behavior is associated with TiCN layers, which reduce interfacial adhesion, promote uniform load distribution, and facilitates the formation of a protective tribofilm. The results confirm that the TiN/TiCN multilayer coatings offer superior mechanical and tribological properties, making them promising candidates for engineering components operating under friction and wear conditions.

Microstructure and properties of TiB2/Cr multilayered coatings with double periodical structures

The difference in mechanical properties between the TiB2 coating and the Ti6Al4V substrate can deteriorate the wear resistance of the TiB2 coating. To enhance the TiB2-based coating’s ability to deform in coordination with the ductile Ti6Al4V substrate and improve its tribological performance, the TiB2/Cr multilayer coatings were designed and deposited on Ti6Al4V substrates by magnetron sputtering. Results reveal that the FEM stress distribution of the TiB2/Cr multilayer coatings was optimized by varying the ceramic–metal thickness ratio (Q). As Q decreased from 1.0 to 0.5, the fracture toughness and adhesion strength of the coatings improved. The multilayer coating with Q = 0.5 exhibited the best toughness, crack propagation resistance (CPRs), and the smallest equivalent stress area, leading to a threefold enhancement in wear resistance compared to the TiB2 monolayer coating. However, further reduction of Q to 0.3 diminished wear resistance due to low hardness and significant stress concentration. Thus, there is an optimal balance between hardness, toughness, and stress distribution for achieving improved wear resistance in the multilayer design. Moreover, a notable correlation was observed between CPRs and the wear resistance of TiB2/Cr multilayer coatings.

Microstructure, mechanical and tribological characterization of CrN/DLC/Cr-DLC multilayer coating with improved adhesive wear resistance

Understanding failure in nanomaterials is critical for the design of reliable structural materials and small-scale devices with nanoscale components. No consensus exists on the effect of flaws on fracture at the nanoscale, but proposed theories include nanoscale flaw tolerance and maintaining macroscopic fracture relationships at the nanoscale with scarce experimental support. We explore fracture in nanomaterials using nanocrystalline Pt nanocylinders with prefabricated surface notches created using a "paused" electroplating method. In situ scanning electron microscopy (SEM) tension tests demonstrate that the majority of these samples failed at the notches, but that tensile failure strength is independent of whether failure occurred at or away from the flaw. Molecular dynamics simulations verify these findings and show that local plasticity is able to reduce stress concentration ahead of the notch to levels comparable with the strengths of microstructural features (e.g., grain boundaries). Thus, failure occurs at the stress concentration with the highest local stress whether this is at the notch or a microstructural feature.

The study of the tribological properties of TiB2/Cr multilayered coatings over a wide temperature range

Microstructures and properties of Zr/CrN multilayer coatings fabricated by multi-arc ion plating