There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test...

Metal Additive Manufacturing: A Review of Mechanical Properties

Transient liquid phase (TLP) bonding is a relatively new bonding process that joins materials using an interlayer. On heating, the interlayer melts and the interlayer element (or a constituent of an alloy interlayer) diffuses into the substrate materials, causing isothermal solidification. The result of this process is a bond that has a higher melting point than the bonding temperature. This bonding process has found many applications, most notably the joining and repair of Ni-based superalloy components. This article reviews important aspects of TLP bonding, such as kinetics of the process, experimental details (bonding time, interlayer thickness and format, and optimal bonding temperature), and advantages and disadvantages of the process. A wide range of materials that TLP bonding has been applied to is also presented. Partial transient liquid phase (PTLP) bonding is a variant of TLP bonding that is typically used to join ceramics. PTLP bonding requires an interlayer composed of multiple layers; the most common bond setup consists of a thick refractory core sandwiched by thin, lower-melting layers on each side. This article explains how the experimental details and bonding kinetics of PTLP bonding differ from TLP bonding. Also, a range of materials that have been joined by PTLP bonding is presented.

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Overview of transient liquid phase and partial transient liquid phase bonding

Wire feeding can be combined with different heat sources, for example, arc, laser, and electron beam, to enable additive manufacturing and repair of metallic materials. In the case of titanium alloys, the vacuum operational environment of electron beam systems prevents atmospheric contamination during high-temperature processing and ensures high performance and reliability of additively manufactured or repaired components. In the present work, the feasibility of developing a repair process that emulates refurbishing an “extensively eroded” fan blade leading edge using wire-feed electron beam additive manufacturing technology was examined. The integrity of the Ti6Al4V wall structure deposited on a 3 mm thick Ti6Al4V substrate was verified using X-ray microcomputed tomography with a three-dimensional reconstruction. To understand the geometrical distortion in the substrate, three-dimensional displacement mapping with digital image correlation was undertaken after refurbishment and postdeposition stress relief heat treatment. Other characteristics of the repair were examined by assessing the macro- and microstructure, residual stresses, microhardness, tensile and fatigue properties, and static and dynamic failure mechanisms.

Titanium Alloy Repair with Wire-Feed Electron Beam Additive Manufacturing Technology

Friction stir welding (FSW), being an enabling solid-state joining technology, can be suitably applied for the assembly of lightweight magnesium (Mg) alloys. In this investigation, friction stir lap welded (FSLWed) joints of AZ31B-H24 Mg alloy were characterized in terms of the welding defects, microstructure, hardness, and fatigue properties at various combinations of tool rotational rates and welding speeds. It was observed that the hardness decreased from the base metal (BM) to the stir zone (SZ) across the heat-affected zone (HAZ) and thermomechanically affected zone (TMAZ). The lowest value of hardness appeared in the SZ. With increasing tool rotational rate or decreasing welding speed, the average hardness in the SZ decreased owing to increasing grain size, and a Hall–Petch-type relationship was established. Fatigue fracture of the lap welds always occurred at the interface between the SZ and TMAZ on the advancing side where a larger hooking defect was present (in comparison with the retreating side). The welding parameters had a significant influence on the hook height and the subsequent fatigue life. A relatively “cold” weld, conducted at a rotational rate of 1000 rpm and welding speed of 20 mm/s, gave rise to almost complete elimination of the hooking defect, thus considerably (over two orders of magnitude) improving the fatigue life. Fatigue crack propagation was basically characterized by the formation of fatigue striations concomitantly with secondary cracks.

/pdf/microstructure-and-fatigue-properties-of-a-friction-stir-lap-1qvulpqqv7.pdf

Microstructure and Fatigue Properties of a Friction Stir Lap Welded Magnesium Alloy

The focus of this study was to evaluate the possibility of extending the service life of an Inconel® alloy 718 (IN 718) aero-engine turbine using the linear friction welding (LFW) process. In particular, the repair of a blade integrated disk (BLISK) through replacement of blades damaged in-service was emulated by LFW virgin IN 718 to in-service IN 718. The virgin–in-service (V–IS) welds were then characterized to evaluate the evolution in the microstructural features, such as the grain size, δ phase, MC-type carbides and MN-type nitrides, across the weld region. In the as-welded condition, the weld and thermomechanically affected zones exhibited highly integral characteristics (i.e., no oxides, voids, or contamination), as well as no constitutional liquation of secondary phases (e.g., carbides and Laves phases). In the weld zone, grain refinement of the austenite (γ) matrix was observed, using electron back scattered diffraction (EBSD), and related to the occurrence of dynamic recrystallization during LFW. The microhardness and tensile mechanical properties of the weldments were investigated in the as-welded condition and compared to weldments with a standard post-weld heat treatment (PWHT). The results suggest that the LFW process is a promising technology for refurbishing IN 718 aero-engine components.

Mechanical properties and microstructural evolution of in-service Inconel 718 superalloy repaired by linear friction welding

In this study, an analysis of elastic residual stress in Inconel ® 718 (IN 718) linear friction welds (LFWs) was carried out. In particular, the suitability of LFW for manufacturing and repair of aero engine components was emulated by joining virgin and in-service (extracted from a turbine disk) materials. The evolution in the residual strains and stresses in the heat-affected zone (HAZ), thermomechanically affected zone (TMAZ) and dynamically recrystallized zone (DRX) of the weld was characterized using the neutron diffraction and contour methods. The results provided insight into diverse challenges in quantitative analysis of residual stresses in welded IN 718 using diffraction techniques. Specifically, judicious selection of the beam width, height and stress-free lattice spacing were seen to be crucial to minimize measurement error and increase accuracy. Further, the contour method – a destructive technique relying on capturing the stress relaxation after electrical discharge machining – was used to characterize the residual stress distribution on two-dimensional plane sections of the welds. Both techniques suggested an increasing magnitude of residual stress originating from the base metal that reached a peak at the weld interface. Both methods indicated that the peak magnitude of residual stresses were below the yield stress of IN 718.

Residual stress analysis in linear friction welded in-service Inconel 718 superalloy via neutron diffraction and contour method approaches

A detailed microstructural analysis was performed on a difficult-to-weld nickel-base superalloy, IN 738, subjected to linear friction welding and Gleeble thermomechanical simulation, to understand the microstructural changes induced in the material. Correlations between the microstructures of the welded and simulated materials revealed that, in contrast to a general assumption of linear friction welding being an exclusively solid-state joining process, intergranular liquation, caused by nonequilibrium phase reaction(s), occurred during joining. However, despite a significant occurrence of liquation in the alloy, no heat-affected zone (HAZ) cracking was observed. The study showed that the manufacturing of crack-free welds by linear friction welding is not due to preclusion of grain boundary liquation, as has been commonly assumed and reported. Instead, resistance to cracking can be related to the counter-crack-formation effect of the imposed compressive stress during linear friction welding and strain-induced rapid solidification. Moreover, adequate understanding of the microstructure of the joint requires proper consideration of the concepts of nonequilibrium liquation reaction and strain-induced rapid solidification, which are carefully elucidated in this work.

Priti Wanjara

Papers

Titanium Alloy Repair with Wire-Feed Electron Beam Additive Manufacturing Technology

Microstructure and Fatigue Properties of a Friction Stir Lap Welded Magnesium Alloy

Mechanical properties and microstructural evolution of in-service Inconel 718 superalloy repaired by linear friction welding

Residual stress analysis in linear friction welded in-service Inconel 718 superalloy via neutron diffraction and contour method approaches

Analysis of Microstructural Changes Induced by Linear Friction Welding in a Nickel-Base Superalloy