Crystal orientation changes of Ag thin films on the Si(111) substrate due to tribo-assisted recrystallization

Crystal orientation changes of Ag thin films due to the tribo-assisted recrystallization have been studied using grazing incidence X-ray diffraction with synchrotron radiation. After preparation of an Si(111) √3 × √3-Ag surface, a 5-nm-thick Ag film was deposited on the surface at the substrate temperature of 303 K in an ultra-high vacuum chamber. The friction experiments were carried out using a diamond pin-on-plate type tribometer just after the Ag deposition in the same UHV chamber. We found that the coefficient of friction of the Ag films on the Si(111) √3 × √3-Ag surface decreases from 0.07 to 0.03, with increasing reciprocal sliding cycles. In synchronization with the coefficient change, Ag{100} grains are gradually disappearing. As a result, the Ag{111} grains cover the entire surface after 50 sliding cycles. Moreover, we found that the domain size of the Ag{111} grains increases with increasing reciprocal sliding cycles by measuring the rocking curve width. These results directly show that the Ag(111) plane is the sliding plane of friction and the coefficient of friction of Ag films is determined by the fraction of the Ag(111) grains in the Ag films. Moreover, to clarify the reaction between the Ag film and the Si substrate due to the tribo-assisted recrystallization, the substrate strain has been studied by an extremely asymmetric X-ray diffraction technique using synchrotron radiation.     

Effect of 50 MeV Li ion irradiation on electrical, optical and mechanical properties of 4,4′-dimethylbenzophenone

4,4′-Dimethylbenzophenone (DMBP) single crystals were irradiated at room temperature and at liquid nitrogen temperature with 50 MeV Li³⁺ ions at fluences 1 × 10¹² and 1 × 10¹³ ions/cm². The dielectric constant and dielectric loss as a function of frequency of the applied ac field in the range from 20 Hz to 1 MHz and at temperatures ranging from 313 to 353 K were analyzed. The dielectric constant decreases with increase in frequency for all the temperatures. The dielectric constant and dielectric loss increase with fluence. Optical absorption was measured at different conditions. UV-Vis studies reveal the decrease in bandgap. The unirradiated as well as irradiated crystals were characterized by photoluminescence. Ion-induced changes were also studied with respect to their mechanical response using the Vicker’s microhardness technique and parameters including fracture toughness, brittleness index and yield strength are calculated.     

Microstructure and mechanical properties of polycrystalline-Ag/amorphous-CoZrNb multilayers

Ag/CoZrNb multilayers were prepared by direct current magnetron sputtering. Their microstructure, hardness, elastic modulus and plastic deformation were investigated by X-ray diffraction, high-resolution transmission electron microscopy, X-ray absorption near-edge structure, field emission scanning electron microscopy and nanoindentation technique. The results show that the multilayers have well modulated structure. For all the multilayers, Ag layer is polycrystalline structure, while CoZrNb layer is amorphous structure. With the decrease of modulation periodicity the elastic modulus decreases due to the compliant interface. The polycrystalline Ag layer not only makes the hardness enhanced with the decrease of modulation periodicity, but also restricts the propagation of shear bands and promotes the nucleation of new shear bands, which may be of help for the plasticity enhancement of amorphous CoZrNb layer.     

Role of oxidation on LME of T91 steel studied by small punch test

A new technique for LME studies has been designed that makes use of the SPT coupled with a XPS/Auger spectroscopy analysis. The interface between the material (T91 steel) and the liquid metal (PbBi) can be varied to investigate the interplay between the oxide nature or the thickness and crack initiation induced by a liquid metal. It is shown in this work that LME can occur in some conditions on pre-oxidized surfaces indicating that there are other interfacial conditions than the oxide free intimate contact that could be detrimental to materials in contact with a liquid metal.     

Finite elements modeling of multilayers of Cr/CrN

One of the most used methods for modeling different materials and their properties has been finite elements. In this work, mechanical properties of Cr/CrN multilayer coatings have been modeled by using finite elements, varying the period of layers (1, 5, 10 and 20 bilayers) and the thickness of the films between 0.5 and , in order to determine the behavior of the system. For this model, the software ANSYS was used to carry out simulation of the indentation process. For the analysis, a conical Berkovich indenter was built. The simulation consists in generating the stress-strain curves in the charge mode for obtaining Young's modulus of the total system, including the substrate, which is made by stainless steel 304. The curves showed a tendency of increasing of Young's modulus as a function of number of layers and thickness, which means an increasing in hardness.     

Tribological and anti-corrosion properties of Ni-W-CeO2 coatings against molten glass

Composite plating was used to prepare Ni-W infused rare earth oxide CeO₂ composite coatings. The high temperature friction behavior and corrosion resistance of the coatings against molten glass were investigated by using a high temperature tribometer. A microhardness tester and an environmental scanning electron microscope equipped energy dispersive spectroscopy were employed to investigate the microhardness and the surface morphology of the composite coatings respectively. The results show that the brittle fracture, high temperature tribological properties and the corrosion resistance of Ni-W infused CeO₂ coatings are superior to those of a standard Ni-W coating. CeO₂ particles decrease the friction coefficient from nearly 0.5 to about 0.25 during the composite coatings sliding against the molten glass at about 973 K, and proper quantities of CeO₂ decrease the variation of the friction coefficient value. Furthermore, CeO₂ can improve the corrosion resistance of the Ni-W coatings at high temperature effectively.     

Microstructural investigation of alumina implanted with 30 keV nitrogen ions

Among ceramics, alumina is being widely used as biomaterials now these days. It is being used as hip joints, tooth roots etc. Ion implantation has been employed to modify its surface without changing it bulk properties. 30 keV nitrogen with varying ion dose ranging from 5 × 10¹⁵ ions/cm² to 5 × 10¹⁷ ions/cm² is implanted in alumina. Surface morphology has been studied with optical microscope and atomic force microscope (AFM). Improvement in brittleness has been observed with the increase in ion dose. Compound formation and changes in grain size have been studied using X-Ray diffraction (XRD). AlN compound formation is also observed by Fourier transform infrared spectroscopy (FTIR). The change in the grain size is related with the nanohardness and Hall-Petch relationship is verified.     

The effect of applied substrate negative bias voltage on the structure and properties of Al-containing a-C:H thin films

Al-containing hydrogenated amorphous carbon (Al-C:H) films were prepared using a magnetron sputtering Al target in the CH₄ and Ar mixture atmosphere with various applied substrate pulse negative bias voltages. The hydrogen content and internal stress of the film decrease dramatically with the substrate pulse bias voltage increase. However, the hardness values of the films keep at high level (∼ 20 GPa) without any obvious changes with the increase of the applied substrate pulse bias voltages. The Al-C:H film prepared at applied substrate high bias voltage shows a long wear life and low friction coefficient.     

Cr1−xAlxN coatings deposited by lateral rotating cathode arc for high speed machining applications

In this work, a series of Cr_1−xAl_xN (0 ≤ x ≤ 0.7) coatings were deposited on high speed steel substrates by a vacuum arc reactive deposition process from two lateral rotating elemental chromium and aluminum cathodes in a flowing pure nitrogen atmosphere. The composition, structural, mechanical, and tribological properties of the as-deposited coatings were systematically characterized by energy dispersive analysis of X-rays, X-ray diffraction, nanoindentation, and ball-on-disc tribometer experiments. All of the as-deposited CrAlN coatings exhibited a higher hardness than CrN, showing a maximum hardness of about 40 GPa (at around X = 0.63) which is twice higher than that of the CrN. The wear performance under ambient conditions of the CrAlN coatings was found much better, with both lower friction coefficient and wear rate, than TiAlN coatings deposited by the same technique. The wear rate of the CrAlN coatings against alumina counterpart was about 2-3 orders in magnitude lower than that of the TiAlN coatings. Selected CrAlN coatings with the highest hardness were also deposited on some WC-based end-mills. An evident better performance of the CrAlN-coated end-mills was observed than the TiAlN-coated ones for cutting a hardened tool steel material under high speed machining conditions.     

Towards an atomistic understanding of solid friction by computer simulations

Friction between two solid bodies in sliding motion takes place on a large spectrum of length and time scales: From the nanometer/second scale in an atomic force microscope up to the extremely macroscopic scales of tectonic motion. Despite our familiarity with friction, fundamental questions about its atomistic origins remain unanswered. Phenomenological laws that describe the friction in many systems were published more than 300 years ago by Amontons: The frictional force is proportional to the applied load and independent of the apparent area of contact. The atomistic origins of this simple law is still controversial. Many explanations, which seemed to be well-established until recently, have been called into question by new experimental results. Computer simulations have also revealed flaws in previous theoretical approaches and led to new insights into the atomistic processes responsible for friction. In this paper, selected computer simulation studies of friction will be discussed. Special attention will be given to how it is possible to gain insight into tribological processes that take place on macroscopic time scales with the help of atomistic computer simulations which are typically constrained to the nanometer and nanosecond regime.