Influence of Microstructure on Ultrasonic Velocity in Nimonic Alloy PE16

Superalloys are widely used for many advanced applications. The alloys with optimum properties are obtained by introducing suitable microstructure through thermomechanical treatments. Characterization of microstructure and determination of mechanical properties of these alloys using ultrasonic parameters should help in quality control during heat treatment and identifying changes in microstructure during service. This study is aimed at demonstrating such a possibility in a selected precipitation hardenable nickel base superalloy, Nimonic alloy PE16. As part of this study, the influence of various secondary phases, γ′, MC and M23C6 on ultrasonic velocity is reported. Ultrasonic velocity has been selected as this parameter had been widely used for microstructural characterization and mechanical property determination in various materials [1–6]. γ′ is a coherent and ordered FCC phase having composition Ni3 (Al, Ti). The strengthening is achieved by the presence of γ′ in the microstructure. MC and M23C6 are respectively the Ti rich (Ti, Mo) C and Cr rich (Cr, Fe)23C6 carbides. The carbide phases are introduced to obtain better high temperature creep properties

Energy Distribution for SH-Waves in Slightly Anisotropic Materials

Many polycrystalline metal aggregates display a slight amount of anisotropy due to texture that develops during fabrication procedures such as rolling. This macroscopic anisotropy produces a birefringence of SH-waves propagating normal to the plate, i.e., the velocity of SH-waves polarized parallel to the rolling direction is usually faster than that of SH-waves polarized perpendicular to the rolling direction. For polarization angles not in or perpendicular to the rolling direction the wave is assumed to split into two waves, one polarized parallel and one polarized perpendicular to the rolling (similar to what is observed for particular propagation directions in single crystals). However slightly anisotropic materials have only a small percentage of preferential grain alignment, the bulk of the grains being of random orientation. In consideration of these materials being nearly isotropic, having slight anisotropy superimposed, and the possibility of multiple textures, we address the energy distribution of SH-waves as a function of polarization angle with respect to the material symmetry axes and the transducer orientation. The importance of considering attenuation in this work is also addressed

Design and Fabrication of an Industrial-Grade Instrument to Measure Texture and Predict Drawability in Sheet Metal

Texture in sheet metal must be controlled in the rolling process to assure the fabrication properties desired in later manufacturing. Drawability is one of the required engineering properties in a family of applications including beverage cans, propane tanks, and automotive parts

Determination of Grain-Size Distributions from Ultrasonic Attenuation

The overall research goal of this project is the nondestructive measurement of grain-size distribution parameters using ultrasonic attenuation. Ultrasonic attenuation α is dependent upon the sound wavelength (λ), the size of the grains (D), and in many cases elastic constants and sound velocities of the material. Assuming that multiple scattering can be ignored, the expression for the wavelength dependence of the attenuation is 1 α(λ)=∫0∞N(D)α(λ,D)dD where N(D) is the grain-size distribution. In previous work [1] the sizes were assumed to be distributed following a power-law with exponent γ: 2 N(D)=KD−γ,

Spin-valley phase diagram of the two-dimensional metal-insulator transition

Using symmetry breaking strain to tune the valley occupation of a two-dimensional (2D) electron system in an AlAs quantum well, together with an applied in-plane magnetic field to tune the spin polarization, we independently control the system's valley and spin degrees of freedom and map out a spin-valley phase diagram for the 2D metal-insulator transition. The insulating phase occurs in the quadrant where the system is both spin- and valley-polarized. This observation establishes the equivalent roles of spin and valley degrees of freedom in the 2D metal-insulator transition.Comment: 4 pages, 2 figure

Digital Measurement of Ultrasonic Velocity

The ultrasonic material evaluation has been applied to composite materials and nonhomogeneous materials. In quantitative evaluation of these materials the ultrasonic velocity and attenuation are widely used. In addition acoustoelastic stress measurement requires high precision measurement of the ultrasonic velocity

Microstructure Characterization with a Pulsed Laser Ultrasonic Source

Localized heating produced by absorption from a pulsed laser provides an efficient noncontacting source of ultrasonic waves in materials. This paper describes the results of experiments conducted to illustrate the feasibility of this type of source fot microstructure characterization in metal and ceramic materials. Piezoelectric and capacitive wide bandwidth detection transducers have been used to record attenuation and scattering in these materials for comparison with the conventional pulse echo technique. The laser source was found to be art efficient, versatile, and wide bandwidth noncontacting source

Ultrasonic Monitoring of Reaction Bonding Silicon Nitride

A method is discussed to use ultrasonic techniques to monitor the reaction bonding of silicon nitride. Reaction bonding takes place in a nitrogen atmosphere heated up to 1390°C. As with many sensors used in hostile environments, it is difficult to design the ultrasonic sensor in a way that provides optimal clarity of the signal. The sensing system has to be designed within physical limitations on access to the furnace and it has to satisfy considerations on the design of a cooling system for the ultrasonic transducer. These limiting factors have been overcome so that ultrasonic signals have been obtained during processing, albeit with a significant noise level. Signal processing techniques have been developed which make it possible to obtain information on changes in phase velocity and attenuation during reaction bonding. The signal processing techniques have the potential to be implemented in real time for the monitoring of the progress of the reaction. This information can then be used for process control feedback.</p