Ultrasonic microhardness

Ultrasonic Microhardness. A new microhardness test using ultrasonic vibrations has been developed and offers some advantages over conventional microhardness tests that rely on physical measurement of the remaining indentation size (6). The ultrasonic method uses the DPH diamond indenter under a constant load of 7.8 N (800 gf) or less. The hardness number is derived from a comparison of the natural frequency of the diamond indenter when free or loaded. Knowledge of the modulus of elasticity of the material under test and a smooth surface finish is required. The technique is fast and direct-reading, making it useful for production testing of similarly shaped parts. 

Other hardness-testing techniques are frequently employed but will not be discussed here these include ultrasonic microhardness, dynamic (Scleroscope), durometer (for plastic and elastomeric materials), and scratch hardness tests. These are described in references provided at the end of the chapter. 

Phase Structure Lattice parameter (room temperature) (A) Density (gcm ) Nano- hardness (GPa) Microhardness (100 g load) (GPa) Young s modulus (from nanohardness) (GPa) Yoimg s modulus (Ultrasonic) (GPa)... 

The composite, metal substrate, and braze foils (two layers, -100 pm total thickness) were sliced into 2.54 cm x 1.25 cm x 0.25 cm pieces and ultrasonically cleaned in acetone for 15 min. The braze foil was sandwiched between metal and composite, and a normal pressure of 1.2-4.7 kPa (0.38-1.5 N) was applied to the assembly. The assembly was heated in a furnace to -15-20 °C above the braze liquidus under vacuum (10 torr), soaked for 5 min., and slowly cooled to room temperature. The brazed joints were prepared for metallography and examined with a Scanning Electron Microscope (SEM) coupled with energy dispersive x-ray spectroscope (EDS) on a JEOL-840 A unit. Microhardness scans were made with a Knoop micro-indenter on a Struers Duramin A-300 machine under a load of 200 g and loading time of 10 s. 

Yoon, H.S. and Katz, J.L. 1976b. Ultrasonic wave propagation in human cortical bone II. Measurements of elastic properties and microhardness. /. Biomech. 9 459. 

In one such test, the alloys studied were subjected to cavitation produced ultrasonically in distilled water by the piezoelectric device shown in Fig. 6. The damage produced then is evaluated metallographicaUy and by microhardness measirrements. 

Many techniques have been developed to measure the Young s modulus and the stress of the mesoscopic systems [12, 13]. Besides the traditional Vickers microhardness test, techniques mostly used for nanostructures are tensile test using an atomic force microscope (AFM) cantilever, a nanotensile tester, a transmission electron microscopy (TEM)-based tensile tester, an AFM nanoindenter, an AFM three-point bending tester, an AFM wire free-end displacement tester, an AFM elastic-plastic indentation tester, and a nanoindentation tester. Surface acoustic waves (SAWs), ultrasonic waves, atomic force acoustic microscopy (AFAM), and electric field-induced oscillations in AFM and in TEM are also used. Comparatively, the methods of SAWs, ultrasonic waves, field-induced oscillations, and an AFAM could minimize the artifacts because of their nondestructive nature though these techniques collect statistic information from responses of all the chemical bonds involved [14]. 

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