This paper presents a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic nondestructive evaluation techniques. These SHG techniques exploit the material nonlinearity of metals in order to measure the acoustic nonlinearity parameter, $$\beta $$
 . In these measurements, a second harmonic wave is generated from a propagating monochromatic elastic wave, due to the anharmonicity of the crystal lattice, as well as the presence of microstructural features such as dislocations and precipitates. This article provides a summary of models that relate the different microstructural contributions to $$\beta $$
 , and provides details of the different SHG measurement and analysis techniques available, focusing on longitudinal and Rayleigh wave methods. The main focus of this paper is a critical review of the literature that utilizes these SHG methods for the nondestructive evaluation of plasticity, fatigue, thermal aging, creep, and radiation damage in metals.

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Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals

Boron modified titanium alloys

A Review on High-Strength Titanium Alloys: Microstructure, Strengthening, and Properties

As a crucial branch for titanium industry, high-strength titanium alloys (HS-TAs, with UTS ≥ 1100 MPa) are indispensable structural materials for advanced engineering applications such as aerospace and marine fields. Along with the expansion of HS-TAs’ market, achieving satisfying synergies of high strength, high ductility (elongation ≥ 6%) and high toughness (KIC ≥ 50 MPa⋅m1/2) has been identified as the uppermost technical bottleneck for their research and development. To overcome the challenge, two primary strategies have been initiated by the titanium community, developing novel alloys and innovating processing technologies. For the former, a dozen of newly-developed alloys were reported to exhibit excellent strength-ductility-toughness combinations, including Ti-5553, BT22, TC21 and Ti-1300, for which the ideal mechanical performances were based on specific microstructures realized by low impurity rate (e.g. oxygen content ≤ 0.15 wt%), complicated processing and complex heat treatment. For the latter, several innovatory forging and heat treatment technologies were originated for the mature alloys to optimize their balanced property by extraordinary microstructural characteristics. In this review, we provide a comprehensive overview over the research status, processing and heat treatment technologies, phase transformation, processing-microstructure-property correlation and strengthening-toughening mechanism of HS-TAs for aerospace engineering applications manufactured via melting-forging process. Finally, the prospects and recommendations for further investigation and development are proposed based on this review. 

High-strength titanium alloys for aerospace engineering applications: A review on melting-forging process

Liquid phase sintering, heat treatment and swaging studies on three tungsten heavy alloys, 93W–4.9Ni–2.1Fe (wt%), 93W–4.2Ni–1.2Fe–1.6Co (wt%) and 93W–4.9Ni–1.9Fe–0.2Re (wt%) were carried out in detail with respect to microstructure, tensile and impact properties. All the alloys were sintered and swaged to 40% deformation. The results indicate that Re addition reduces the grain size of the alloy compared to W–Ni–Fe and W-Ni-Fe-Co alloys. W–Ni–Fe–Re alloy shows superior tensile properties in heat treated condition as compared to W–Ni–Fe and W–Ni–Fe–Co alloys. SEM study of fractured specimens clearly indicates that the failure in case of W–Ni–Fe–Re was due to transgranular cleavage of tungsten grains and W–W de-cohesion. W–Ni–Fe and W–Ni–Fe–Co alloys also failed by mixed mode failure. However, in these cases, ductile dimples corresponding the failure of the matrix phase was rarely seen. Thermo-mechanical processing resulted in significant changes in mechanical properties. While W–Ni–Fe–Re alloy showed the highest tensile strength (1380 MPa), W–Ni–Fe–Co exhibited the highest elongation (12%) to failure. A detailed analysis involving microstructure, mechanical properties and failure behavior was undertaken in order to understand the property trends.

Effect of alloying addition and microstructural parameters on mechanical properties of 93% tungsten heavy alloys

Present work describes the development of microstructure, texture, tensile flow and work hardening behavior of tungsten heavy alloys in swaged and swaged + aged conditions. The microstructural attributes of both the alloys such as the average W-grain size, shape, volume fractions of matrix phase and contiguity are nearly same in swaged and swaged + aged conditions. The textures of W-grains and matrix are different in swaged and swaged + aged alloys. The overall ODF intensities of W-grains and matrix phase are moderate and weak, respectively. Both the alloys show higher strength and slightly lower elongation after aging of the swaged samples. The aging has significantly reduced the impact toughness values of both the alloys in swaged condition. The true stress–true strain plots of both the alloys in swaged and swaged + aged conditions exhibit continuous increase in stress from σYS to σUTS (except yield point phenomenon in swaged + aged samples). Both the alloys in swaged + aged condition reveal the presence of yield point phenomenon. Bulk hardness values of both the alloys increase from swage to swaged + aged conditions. The true stress–true plastic strain curves on log–log scale of both the alloys in swaged and swaged + aged conditions display single slope only and follow Swift constitutive equation due to presence of pre-strain in the materials. The overall nature of the instantaneous curves is same in swaged and swaged + aged conditions. These curves exhibit three distinctive regimes of strain hardening that are stage I, stage II and stage III. The linear part of stage III has been explained using KME model in both alloys.

Microstructure, Texture, Tensile Flow and Work Hardening Behavior of Tungsten Heavy Alloys in Swaged and Swaged + Aged Conditions

The present work illustrates the deformation behaviour of tungsten heavy alloys (WHAs) using first-principles calculation under tensile stress of three virtual alloy systems comprising the matrix p...

T.K. Nandy

Papers

Microstructure, Texture, Tensile Flow and Work Hardening Behavior of Tungsten Heavy Alloys in Swaged and Swaged + Aged Conditions

Effects of Co and Co + Mo additions on tensile properties of tungsten heavy alloys: first-principles study and experimental investigations

On the development of porous nickel through gelcasting technique