This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

Ti-based alloys are finding ever-increasing applications in biomaterials due to their excellent mechanical, physical and biological performance. Nowdays, low modulus β-type Ti-based alloys are still being developed. Meanwhile, porous Ti-based alloys are being developed as an alternative orthopedic implant material, as they can provide good biological fixation through bone tissue ingrowth into the porous network. This paper focuses on recent developments of biomedical Ti-based alloys. It can be divided into four main sections. The first section focuses on the fundamental requirements titanium biomaterial should fulfill and its market and application prospects. This section is followed by discussing basic phases, alloying elements and mechanical properties of low modulus β-type Ti-based alloys. Thermal treatment, grain size, texture and properties in Ti-based alloys and their limitations are dicussed in the third section. Finally, the fourth section reviews the influence of microstructural configurations on mechanical properties of porous Ti-based alloys and all known methods for fabricating porous Ti-based alloys. This section also reviews prospects and challenges of porous Ti-based alloys, emphasizing their current status, future opportunities and obstacles for expanded applications. Overall, efforts have been made to reveal the latest scenario of bulk and porous Ti-based materials for biomedical applications.

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New Developments of Ti-Based Alloys for Biomedical Applications

Our experts at TÜV Rheinland have many years of experience and practice in NDT techniques and strive to provide clients with the most fitted and tailored nondestructive method for their pressure equipment while offering reliable, timeand cost-efficient solutions. Acoustic emission testing is one of the most comprehensive and adapted proceduresto detect defects and flaws in your pressure equipment because it can be conducted during operation and does not require any interruption of activity. It also allows for global monitoring of the complete pressure equipment asset and is the best solution for vessels with complex geometries.

Acoustic Emission 방법의 공학적 응용

Restorative dental materials

For the last ten years, the application of high-technology processes to dental ceramics allowed for the development of new materials such as heat-pressed, injection-molded, and slip-cast ceramics and glass-ceramics. The purpose of the present paper is to review advances in new materials and processes available for making all-ceramic dental restorations. Concepts on the structure and strengthening mechanisms of dental ceramics are provided. Major developments in materials for all-ceramic restorations are addressed. These advances include improved processing techniques and greater mechanical properties. An overview of the processing techniques available for all-ceramic materials is given, including sintering, casting, machining, slip-casting, and heat-pressing. The most recent ceramic materials are reviewed with respect to their principal crystalline phases, including leucite, alumina, forsterite, zirconia, mica, hydroxyapatite, lithium disilicate, sanidine, and spinel. Finally, a summary of flexural strength data available for all-ceramic materials is included.

Recent Advances in Ceramics for Dentistry

Propagation phenomena of wideband guided waves in a bended pipe.

An experimental investigation of sensitivity in defect detection in welded elbow pipes using the T(0, 1) mode guided wave was carried out. A piezoelectric ring-shaped sensor system was cramped on one of the two straight parts in the straight-elbow-straight setting. An artificial defect was introduced into the other straight part. To evaluate the sensitivities, the depth of the artificial defect was gradually increased to 2.0 mm by 0.05 mm increments. The following are the obtained experimental results. (1) Spurious signals due to the two welds, which could be markedly changed by varying the welding conditions were found. (2) These spurious signals interfered with and masked the defect signal, but changes in signal amplitude owing to the incremental defect could be sufficiently detected. (3) Sensitivities of defect detection in welded elbow pipes were approximately 1/4–1/5 that in a straight pipe. At the end of the paper, the characteristics of the observed waveform in the welded elbow pipes are discussed for use in the guided wave inspection.

https://iopscience.iop.org/article/10.1143/JJAP.49.116602/pdf

Long-Range Testing of Welded Elbow Pipe Using the T(0,1) Mode Ultrasonic Guided Wave

Simultaneous measurement of the phase and group velocities of Lamb waves in a laser-generation based imaging method.

Hydrogen distribution in high-purity-based polycrystalline Al-5%Mg alloys prepared by changing the melting atmosphere was visualized by means of hydrogen microprint technique with electron backscattering pattern analysis after a tensile deformation at room temperature. The number of hydrogen atoms observed as silver particles on the slip lines was increased when the applied strain was increased. Hydrogen atom observed on the slip lines was totally increased when the melting atmosphere of the alloys was changed from argon to air. Hydrogen atom was observed at both slip lines and special grain boundaries when an air-melted specimen was deformed. It was shown that hydrogen atom accumulation at grain boundaries varied with the misorientation of grains and the angle to the tensile direction.

/pdf/visualization-of-hydrogen-distribution-in-tensile-deformed-3pmeakhzo7.pdf

Visualization of Hydrogen Distribution in Tensile-Deformed Al-5%Mg Alloy Investigated by means of Hydrogen Microprint Technique with EBSP Analysis

Wide range generation of the circumferential guided waves (C-GWs) propagating along the perimeter of a pipe has been carried out using a single shear wave sensor along with several tone-burst sources. The C-GWs are classified mainly into two propagation modes, circumferential shear horizontal (C-SH) and circumferential Lamb (C-Lamb) waves. The authors previously reported that a simple and selective generation of the two modes using a single shear wave sensor could be realized by changing the polarization direction of the sensor. When the polarization direction of the sensor is parallel or vertical to the axial direction of a pipe, either the C-SH or the C-Lamb wave is selectively generated. In this paper, a newly exploited signal processing method to obtain a wide-range time–frequency analysis for the C-GW is proposed using wavelet transformation along with various tone-burst signals swept in the required frequency range. Time–frequency analyses of the results for the C-SH and C-Lamb waves propagating along 30-mm outer diameter and 1-mm-thick aluminum pipe are shown in comparison with the theoretical dispersion relation of the propagation modes. Quantitative evaluations of this method are discussed based on the Reciprocity theorem and Fourier transformation.

https://iopscience.iop.org/article/10.1143/JJAP.47.3885/pdf

Kenichi Yoshida

Papers

Propagation phenomena of wideband guided waves in a bended pipe.

Long-Range Testing of Welded Elbow Pipe Using the T(0,1) Mode Ultrasonic Guided Wave

Simultaneous measurement of the phase and group velocities of Lamb waves in a laser-generation based imaging method.

Visualization of Hydrogen Distribution in Tensile-Deformed Al-5%Mg Alloy Investigated by means of Hydrogen Microprint Technique with EBSP Analysis

Tone-Burst Generation of Circumferential Guided Waves by a Bulk Shear Wave Sensor and Their Wide-Range Time–Frequency Analyses