Douglas A. Rebinsky

Ultrasonic Characterization of the Mechanical Properties of Nano‐Structured Diamond‐Like Carbon Thin Films

Two ultrasonic non‐destructive evaluation methods were applied to characterize the mechanical properties of nano‐structured diamond‐like carbon hard coatings in this work. Guided‐wave phase velocity spectra were measured using the photoacoustic guided‐wave technique and Line‐focus Acoustic Microscopy. The measured dispersion curves by the two methods were independently analyzed by a nonlinear optimization approach using an appropriate multi‐layer material model. The measured Young’s moduli using the ultrasonic techniques were compared with nano‐indentation tests and good quantitative agreement was found.

Brillouin Scattering and Laser‐Saw Technique for Elastic Property Characterization of Diamond‐like Carbon (DLC) Films

In this work we have combined two methods, surface Brillouin scattering and laser‐surface acoustic wave (SAW) technique, to determine both bulk and shear moduli of diamond‐like carbon (DLC) films. The velocities of the longitudinal and shear waves within the coating were accurately measured hence it. is expected that the estimates for the elastic moduli of thin diamond‐like carbon (DLC) films (0.5–3μm thick) are reasonable. Error in Young’s modulus was relatively small in comparison to that for Poisson’s ratio.

Acoustic Microscopy, Brillouin Scattering and Laser-Saw Technique for Defect Characterization in DLC Films

DLC films are beginning to find their way into industrial applications to prolong the life of machine components. Preliminary wear tests on nano-structured DLC coated samples demonstrated an appreciable improvement in pitting resistance and usable life. One of the key parameters that have great impact on the wear resistance of a material is its microstructure. The acoustic microscope was developed as a tool for studying internal microstructure of non-transparent solids and now it is widely used for detection of cracks and subsurface defects. Despite the expedient use of this NDE technique, quantitative characterization of the imaged defects is rarely completed because the theory describing image formation caused by subsurface defects is complicated (Lobkis et al., 1995) and it requires knowledge of the material’s elastic properties. In this article, we used scanning acoustic microscopy (Leitz ELSAM) to detect and analyze defects in thin chromium-alloyed DLC (Cr-DLC) films. Surface Brillouin scattering (SBS) and detection of the surface acoustic waves (SAWs) by laser (Laser-SAW technique) were applied to measure elastic properties of the films.

Photoacoustic characterization of the mechanical properties of thin film materials

Two high frequency photoacoustic techniques were applied to investigate the mechanical properties of two sets of thin film materials in this work. Broadband photoacoustic guided-wave method was used to measure the guided-wave phase velocity dispersion curves of nano-structured diamond-like carbon hard coatings. The experimental velocity spectra were analyzed by a nonlinear optimization approach in conjunction with a multi-layer wave-propagation model. The derived Young’s moduli using the broadband photoacoustic technique were compared with line-focus acoustic microscopy and nano-indentation tests and good quantitative agreement is found. In a second set of experiments, ultra-thin two-layer aluminum and silicon nitride thin film materials were tested using the femtosecond transient pump-probe method using high frequency bulk waves generated by the ultra-fast laser pulses. The measured moduli of silicon nitride thin layers are in the range of 270 - 340 GPa. Photoacoustic methods are shown to be suitable for in-situ and non-destructive evaluation of the mechanical properties of thin films.

Imaging Defects in Thin DLC Coatings Using High Frequency Scanning Acoustic Microscopy

In this work high frequency scanning acoustic microscopy was employed to nondestructively characterize subsurface defects in chromium containing DLC (Cr‐DLC) coatings. Subsurface defects as small as one micron were successfully detected in a flat Cr‐DLC coated steel coupon. Depth of the imaged subsurface defects was estimated using a simple geometrical acoustics model. The nature of the subsurface defects was investigated by using FIB/SEM technique. Curved Cr‐DLC coated components including a roller and gear tooth were also imaged, and the encountered challenges were addressed.

A Rapid Ultrasonic Method for Nondestructive Thickness Mapping of Bronze Liner in Steel-Backed Bearing Sleeves

In this paper a nondestructive, automatic, ultrasonic scanning method was developed to permit rapid thickness mapping of the bronze liner in a steel‐backed bearing sleeve. Because the sound velocity in bronze was unknown, an indirect two‐step approach was used: the first step utilized a simultaneous velocity and thickness mapping method to measure the total wall thickness while the second step measured the thickness of the steel backing. The difference of the two obtained thickness maps yielded the thickness map of the bronze liner. Comparison to destructive examination results showed a measurement accuracy of approximately 20 μm or 2%.