Production of aluminum alloy-based metal matrix composites using scrap aluminum alloy and waste materials: Influence on microstructure and mechanical properties

Rare earth metals are used in semiconductors, solar cells and catalysts. This review focuses on the background of oxide metallurgy technologies, the chemical and physical properties of rare earth (RE) metals, the background of oxide metallurgy, the functions of RE metals in steelmaking, and the influences of RE metals on steel microstructures. Future prospects for RE metal applications in steelmaking are also presented.

Effects of Rare Earth Metals on Steel Microstructures

Effect of rare earth element yttrium addition on microstructures and properties of a 21Cr–11Ni austenitic heat-resistant stainless steel

The fatigue of impellers and blades

This article aims to present a comprehensive review of the recent efforts and advances in applying machine learning (ML) techniques in the area of diagnostics and prognostics of rolling element bearings. The significant goal of this study is to review, recognize and evaluate the performance of various ML techniques and compare them on criteria's such as reliability, accuracy, robustness to noise, data volume requirements and implementation aspects. The merits and demerits of the reviewed ML techniques have been comprehensively analyzed and discussed. A comparative benchmarking of the performance of the reviewed ML algorithms is provided both from the viewpoint of theoretical aspects and industrial applicability. Finally, the potential challenges that come along with the implementation of ML technology are discussed in detail that will likely play a major role in prognostics and health management of rolling element bearings. It is expected that this review would serve as a reference point for researchers to explore the opportunities for further improvement in the field of ML-based fault diagnosis and prognosis of rolling element bearings.

A systematic review of machine learning algorithms for prognostics and health management of rolling element bearings: fundamentals, concepts and applications

Udimet-500 alloy is a high-strength nickel-bases super alloy used for turbine blades applications. It is primarily strengthened by very fine precipitates called gamma prime (γ′) which coarsened with time when exposed to high temperature. In this study, Udimet-500 alloy in the standard aged condition was exposed at 850–1100 °C for 25–100 h in air. The change in the size of γ′ with respect to the high temperature exposure was characterized using scanning electron microscope. A systematic coarsening of the γ′ was observed with the change in the exposure temperature/time. The γ′ size in the virgin sample was 0.1 μm while after high temperature exposures it coarsened to 1 μm. The Larson-Miller parameter (LMP) of the high temperature exposure was also measured. It was found that the LMP had power relation with the γ′ size. In addition, degradation of the primary as well as secondary carbides was also observed which can be used as add-on microstructural information in high temperature exposure. Elevated temperature exposure (≥1000 °C) also lead to (a) near surface de-alloying, (b) precipitation of needle-like Ti-rich phase and (c) depletion of γ′. It may contribute in the accelerated corrosion and loss of strength of alloy.

Effect of high temperature exposure on the microstructure of Udimet-500 super alloy

An aero engine failed due to the misalignment of the ball bearing fitted on the main shaft of the engine.

Failure Analysis of an Aero Engine Ball Bearing

Fatigue failure of a centrifugal compressor

The mechanical behavior of an extruded aluminum alloy pipe has been investigated after repeated failures in an oil and gas industry. The pipe failures occurred by longitudinal cracking, and the mechanical properties of the pipe were blamed for the failure. The relevant critical properties of the pipe including basic tests of hardness, tensile, and impact behavior were measured, and extended fatigue testing of the material was conducted. Microstructural examination revealed a recrystallized grain structure and clusters of constituent particles aligned in the direction of extrusion. Tensile testing in both the longitudinal and circumferential directions showed virtually identical yield and tensile strengths. However, the material exhibited higher toughness in the longitudinal direction. Impact test showed that the energy absorbed during fracture was four times higher in the longitudinal direction. Fatigue testing displayed a shorter fatigue life in the transverse direction. The study showed that the microstructure after extrusion and the distribution of the constituent particles have a pronounced effect on the mechanical behavior of the extruded pipe and induced anisotropy in the material performance. Performance of the material can be improved by choosing the proper extrusion ratio to control the microstructure and by controlling the density and distribution of the constituent particles.

Effect of Microstructural Anisotropy on Mechanical Behavior of a High-Strength Al-Mg-Si Alloy

Eutectic Al-Si alloys find their applications in moderate to severe tribological conditions, for example: pistons, casings of high speed pumps and slide sleeves. The higher hardness, so the better tribological properties, are originated by the formation of a silicon rich secondary phase, however, the morphology of the secondary phase drastically influence the toughness of the alloy. Microstructural modifiers are used to control the toughness which modifies the Si rich secondary phase into dispersed spherical structure instead of needle-like network. In the present study, a mixture of chemical fluxes was used to modify the Si phase. The alloy was cast into a sand mold and characterized by scanning electron microscopy, energy dispersive spectroscopy, hardness testing and tensile testing. It was found that the morphology of the Si phase was altered to acicular structure due to the modification process. In comparison, the un-modified alloy contained Si phase in needle-like structure. The effect of modifier was also pronounced on the mechanical properties, where increase of 50% in yield strength, 56% in tensile strength and 200% in elongation occurred. A discernable raise in strain hardening component indicated the improved strain harden ability and formability of the modified alloy.

http://iopscience.iop.org/article/10.1088/1757-899X/146/1/012033/pdf

Effect of micro-structural modifier on the morphology of silicon rich secondary phase and strain hardening behavior of eutectic Al-Si alloy

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