Yu. S. Petronyuk

High-resolution ultrasonic ultrasound methods: Microstructure visualization and diagnostics of elastic properties of modern materials (Review)

High-resolution ultrasonic methods are briefly reviewed. Special attention is paid to the principles underlying acoustic microscopy, since exactly they provide the high resolution necessary for modern technologies. Examples of acoustic images of fullerite ceramics, metals, and carbon materials are given.

Microstructure, elastic and electromagnetic properties of epoxy-graphite composites

A set of epoxy resin-based composites filled with 0.25 – 2.0 wt.% of commercially available exfoliated graphite (EG) and thick graphene (TG), prepared by suspending EG particles in cyclohexane, and submitting the suspension to a series of grinding and ultrasonic dispersion steps, was produced. The microstructure of such epoxy-graphite composites has been studied by the impulse acoustic microscopy technique. According to acoustic microscopy data, exfoliated graphite microparticles have been well dispersed in the epoxy matrix. TG nanoflakes demonstrated persistent tendency to clustering and formation of agglomerates. The addition of graphite particles in small amount (0.25 – 2.0 wt.%) did not influence the bulk elastic properties of epoxy-graphite composite materials. Being extremely lightweight, 0.003 g cm−3, EG had a lower percolation threshold than TG, at the level of 1-1.5 wt.% against 2.1-3.2 wt.%, respectively. As a result, epoxy composites filled with 1.0-2.0 wt.% EG provided high electromagnetic (EM) interference shielding both at microwave and THz frequencies. In contrast, no significant influence of TG loading was observed at low weight fraction (up to 2 wt.%) on the EM performance of epoxy composites.

Novel hybrid ultrahard material

A novel hybrid ultrahard polycrystalline composite material has been produced by the reinforcement of the polycrystalline diamond composite thermostable material with a CVD grown polycrystalline diamond. It has been found that a thermal treatment of a polycrystalline diamond grown at high pressure ensures an increase of the CVD diamond hardness from 77 to 140 GPa. Tests of drilling tools have shown that in turning granite of the XI drillability index the wear intensity of rock destruction elements of the hybrid ultrahard material is lower than that of rock destruction elements of polycrystalline diamond composite thermostable material by a factor of 14.

Effect of heat treatment on the elastic characteristics of a bulk amorphous Zr-Cu-Ni-Al-Ti alloy

The changes in the elastic properties of a bulk Zr52.5Cu17.9Ni14.6Al10Ti5 metallic glass exposed to heat treatments at temperatures of up to 700°C were studied by acoustic methods. An anomalous decrease in the alloy shear modulus (to values lower than that in the amorphous state) was found after the first stages of nanocrystallization.

Bulk microstructure and local elastic properties of carbon nanocomposites studied by impulse acoustic microscopy technique

Bulk microstructure and elastic properties of epoxy-nanocarbon nanocomposites for diverse types and different content of carbon nanofiller has been studied by using impulse acoustic microscopy technique. It has been shown occurrence of various types of mesoscopic structure formed by nanoparticles inside the bulk of nanocomposite materials, including nanoparticle conglomerates and nanoparticle aerogel systems. In spite of the bulk microstructure, nanocarbon composites demonstrate elastic uniformity and negligible influence of nanofiller on elastic properties of carbon nanocomposite materials.

Interaction of Short Pulses of Focused Ultrasound with Interfaces and Plane-Parallel Objects

Short pulses of focused ultrasound are effective instrument for measuring local velocity values of bulk acoustic modes and for studying local elastic properties of solids (microacoustical technique). The probe beam is originally formed in a coupling fluid and penetrates in the solid body as convergent beams of longitudinal and transverse elastic waves. Primary and repeated reflections at the front and back object surfaces give rise a series of time-resolved echo signals. Measuring time intervals between echo pulses gives propagation times through the object for diverse modes of elastic waves and makes it possible to find values of sonic velocities and elastic moduli.

Microacoustic study of anisotropy in optically isotropic pyrolytic nanocarbon

Elastic anisotropy was observed experimentally in pyrolytic nanocarbon, which is characterized by optical methods as an isotropic material. It is shown by methods of acoustical microscopy that, when an ultrashort pulse of focused ultrasound passes through a plate of such a material, splitting of the probe pulse occurs, which is caused by the excitation of longitudinal and both modes of transversal elastic waves in the volume of the material. Measurements of the sound velocity showed that pyrolytic nanocarbon has orthotropy and layered distribution of bulk elastic characteristics. The results obtained show a high efficiency of microacoustic methods for detection of anisotropy in weakly anisotropic textured materials, whose anisotropy is difficult to characterize by other methods.

Thermal oxidation and photo- and biodestruction of the statistical copolymer of ethylene with carbon monoxide

Thermal and photooxidation of the statistical copolymer of ethylene containing 1.5% carbonyl units -C(O)- by molecular O2 was studied at 160–200°C in the presence and absence of phenyl-β-naphthylamine (PNA) antioxidant. The incorporation of a small number of -C(O)- groups into the polyethylene chain insignificantly decreased the rate of thermal (dark) oxidation but substantially accelerated oxidation under the action of light. At the same time, the oxidation of the copolymer occurred at a lower rate than the oxidation of pure polyethylene (PE), which was evidence of an important role played by intramolecular oxidation chain propagation in PE, which is disturbed already at a comparatively low fraction of foreign units. Phenyl-β-naphthylamine noticeably decelerated oxidation. The rate of polymer biodestruction was much higher than the rate of PE biodestruction. The influence of biodestruction on the physicomechanical properties of samples was studied by ultrasonic microscopy. The velocity of sound propagation in PE was somewhat lower compared with the ethylene-carbon monoxide copolymer (ECO). Clearly, the introduction of a small amount of CO molecules into the polyethylene chain changed the microstructure of PE. The structure of ECO was more ordered and denser because of plasticization by metabolites.

High-Resolution Ultrasound Technologies for Studying Biological Objects

Russian experience in the development of high-resolution ultrasound technologies for bioimaging is considered. Two types of ultrasound biomicroscopy (UBM) systems for the in vivo imaging of skin are described: a UBM system based on a resonant transducer with the electrical excitation of probing pulses and a UBM system based on a wideband polyvinylidene difluoride detector (PVDF) with laser thermoelastic excitation of the probing pulses.

Studying the Degradation of Reinforced Composites by High-Resolution Ultrasonic Means

Nondestructive means of pulsed acoustic microscopy are used to visualize and assess the bulk microstructure of carbon fiber reinforced composites. Irreversible changes in the composite structure under the influence of external mechanical and climatic factors are studied, and the dynamics of the accumulation and growth of microscopic defects leading to destruction is studied. Ultrasonic explorations are conducted at frequencies of 50–100 MHz. It is shown that scattered (diffracted) radiation participates in image formation; this makes it possible to detect small cavities (detachment of reinforcing fibers), clusters of microscopic defects, and inclined extended cracks oriented along the fibers’ packing. These cracks are precursors to the brittle fracture of a composite, and their visualization is difficult with standard ultrasonic methods.