Different studies have been reported on phase transformations and mechanical property variations with various phases in Ti-6Al-4V. Owing to the good corrosion resistance and biocompatibility, Ti-6Al-4V is also widely used in making load-bearing metal implants. Ti-6Al-4V combines the benefits of high strength, light weight, formability and corrosion resistance and finds applications in aircraft structural components, aerospace fasteners, high-performance automotive parts, marine applications, medical devices, and sports equipment. By varying the volume fractions of the two phases present in the alloy, various combinations of strength and toughness can be achieved. The type and amount of various phases formed during thermal/thermo-mechanical treatments influence both the mechanical as well as the elastic properties of α + β titanium alloys. However, these techniques were developed for soft materials with moduli smaller than 10 GPa. They have been found to be useful in probing material properties with enhanced sensitivity, less surface damage and also at larger distances. Besides contact-resonance based methods, multi-frequency AFM techniques have also been used for measurement of elastic and damping properties in living cells, proteins and polymers.
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In recent years, AFAM has been extensively used to determine elastic stiffness or damping properties in nano-crystalline nickel, PMMA films, NiMnGa films, Arabidopsis plant, polystyrene–propylene blends, nickel base alloys, ferritic steels, and metallic glasses. An improved UAFM technique was used for mapping the resonance frequency and the quality factor, Q, in carbon reinforced plastics composites. have studied elastic and damping properties in a dual-phase steel by using resonance ultrasound microscopy (RUM), which is a contact-resonance based technique but limited to micrometer resolution. have discussed in detail the development of contact-resonance force microscopy techniques for quantitative measurements of nanomechanical properties.
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In AFAM, the transducer is placed under the sample and periodic displacements of the sample are sensed by the cantilever when in contact. In UAFM the cantilever is excited by attaching a transducer to the cantilever base.
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UAFM and AFAM work with a similar principle and only vary in the excitation of the cantilever. Over the last two decades many contact-resonance-based atomic force microscopy (AFM) techniques, such as ultrasonic atomic force microscopy (UAFM), and atomic force acoustic microscopy have emerged for the characterization of elastic properties of materials with nanometer resolution.
JMATPRO RAFAEL CRACK
The knowledge of elastic properties of the individual phases is important for studying their deformation behavior, crack nucleation and propagation, dislocation activity and interaction with grain boundaries and also even helps in understanding the bulk elastic properties of multiphase materials. The physical and mechanical properties of the individual phases govern the respective properties of the multiphase structural materials. Keywords: atomic force acoustic microscopy contact resonances damping indentation modulus Ti-6Al-4V The effect of heat treatments on the ultrasonic attenuation in the bulk sample could also be understood based on the damping measurements on individual phases using AFAM.
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The average modulus of the specimens estimated by AFAM technique is found to be within 5% of that obtained by ultrasonic velocity measurements. The volume fractions of the phases and the modulus measured through AFAM are used to derive average modulus of the bulk sample which is correlated with the bulk elastic properties obtained by ultrasonic velocity measurements.
JMATPRO RAFAEL SOFTWARE
Volume fractions of the individual phases were determined by using a commercial material property evaluation software and were validated by using X-ray diffraction (XRD) and electron back-scatter diffraction (EBSD) studies on one of the heat-treated samples. The study indicated that in a Ti-6Al-4V alloy the metastable β phase has the minimum modulus and the maximum damping followed by α′- and α-phases. The cantilever dynamics model considering damping, which was proposed recently, has been used for mapping of indentation modulus and damping of different phases in a metallic structural material. The evaluation of the data is based on the mass distribution of the cantilever with damped flexural modes. The real and imaginary parts of the contact stiffness k * are obtained from the contact-resonance spectra and by using these two quantities, the maps of local elastic stiffness and the damping factor are derived. The distribution of elastic stiffness and damping of individual phases in an α + β titanium alloy (Ti-6Al-4V) measured by using atomic force acoustic microscopy (AFAM) is reported in the present study.