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

This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Recent developments in stainless steels

In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

Research status of laser cladding on titanium and its alloys: A review

Additive manufacturing (AM) is a new paradigm for the design and production of high-performance components for aerospace, medical, energy, and automotive applications. This review will exclusively cover directed energy deposition (DED)-AM, with a focus on the deposition of powder-feed based metal and alloy systems. This paper provides a comprehensive review on the classification of DED systems, process variables, process physics, modelling efforts, common defects, mechanical properties of DED parts, and quality control methods. To provide a practical framework to print different materials using DED, a process map using the linear heat input and powder feed rate as variables is constructed. Based on the process map, three different areas that are not optimized for DED are identified. These areas correspond to the formation of a lack of fusion, keyholing, and mixed mode porosity in the printed parts. In the final part of the paper, emerging applications of DED from repairing damaged parts to bulk combinatorial alloys design are discussed. This paper concludes with recommendations for future research in order to transform the technology from “form” to “function,” which can provide significant potential benefits to different industries.

https://www.mdpi.com/2079-6412/9/7/418/pdf

State of the Art in Directed Energy Deposition: From Additive Manufacturing to Materials Design

In this work, several mixtures of self-fluxing NiCrBSi alloy powder and a nickel-clad WC powder (10 wt.% Ni and balance WC) were laser cladded on stainless steel substrates of austenitic type (AISI 304). The aim of the study was to determine the influence of the volume fraction of the reinforced WC particles on the formation and performance of the composite layer. The effect of other parameters of the treatment, such as the laser energy, beam profile, traverse speed and the mass rate of the feed powder was also investigated. Clad layers of 0.5–1.5 mm height were obtained, its microhardness measured and the microscopic morphology and distribution of tungsten carbide particles within the layer characterized by scanning electron microscopy (SEM). It was found that most clad layer properties such as its porosity, microhardness and homogeneity are determined by the percentage of WC particles in the mixture. Pores were observed for volume fractions roughly above 50%. Below this limit, homogeneous, dense and crack free clad layers were obtained, with measured hardness ranging between 600 and 1000 HV depending on the WC content.

Morphology and characterization of laser clad composite NiCrBSi–WC coatings on stainless steel

Laser cladding of tungsten carbides (Spherotene®) hardfacing alloys for the mining and mineral industry

The stresses generated in the laser cladding technique result from the high thermal gradients involved. They could lead to undesirable distortions or even crack formation, therefore the prediction of the temperatures, strains and stresses during the process results in its better understanding, besides, it could allow some optimization. A transient nonlinear thermomechanical FEM model was developed for this task. In order to validate its predictions, measurements by the energy dispersive X-ray diffraction (EDXRD) technique were performed at the European Synchrotron Radiation Facility (ESRF), for several samples with the Stellite 6B alloy on the AISI 304 stainless steel, and compared with the predictions.

Study of residual stresses generated inside laser cladded plates using FEM and diffraction of synchrotron radiation

CoMoCrSi alloys, mostly known as Tribaloy® family, combine well-known outstanding properties in terms of wear and corrosion resistance as well as in terms of mechanical strength. Compared to other wear resistant alloys, their performance is due to the presence of hard Laves phases rather than intermetallic carbides. Among the Tribaloy family, the T-800 alloy offers the best performance as a result of a higher amount of primary Laves phases. However, as a consequence of the brittle nature of these hard phases, the deposited alloy may present a relatively low resistance to crack initiation and propagation, particularly in laser cladding processing where thermal stresses are significant. A reduction in the volume fraction of these hard phase may be achieved by replacing some of the Laves phase components in the alloy (Co, Mo, Si) by Ni (T-900 alloy). Alternatively, it has been suggested that the addition of Fe could also lead to a significant reduction. The Fe addition can easily be accomplished in laser cladding process by dilution of the T-800 coating with the steel substrate. In this work a comparative study of microstructure, hardness and cracking susceptibility of low and high diluted T-800 and T900 coatings deposited by laser cladding is presented. A lower cracking ratio is obtained for the T-900 coatings at the cost of a lower hardness and wear resistance. No noticeable effect on the cracking susceptibility of the T-800 is found due to dilution with the substrate. However a change in its microstructure is observed giving superior hardness and wear resistance.

J.M. Amado

Papers

Morphology and characterization of laser clad composite NiCrBSi–WC coatings on stainless steel

Laser cladding of tungsten carbides (Spherotene®) hardfacing alloys for the mining and mineral industry

Study of residual stresses generated inside laser cladded plates using FEM and diffraction of synchrotron radiation

Characteristics of Tribaloy T-800 and T-900 coatings on steel substrates by laser cladding

Crack Free Tungsten Carbide Reinforced Ni(Cr) Layers obtained by Laser Cladding