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

Additive manufacturing of metallic components – Process, structure and properties

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

Plasticity in small-sized metallic systems: Intrinsic versus extrinsic size effect

Shear-banding is a ubiquitous plastic-deformation mode in materials. In metallic glasses, shear bands are particularly important as they play the decisive role in controlling plasticity and failure at room temperature. While there have been several reviews on the general mechanical properties of metallic glasses, a pressing need remains for an overview focused exclusively on shear bands, which have received tremendous attention in the past several years. This article attempts to provide a comprehensive and up-to-date review on the rapid progress achieved very recently on this subject. We describe the shear bands from the inside out, and treat key materials-science issues of general interest, including the initiation of shear localization starting from shear transformations, the temperature and velocity reached in the propagating or sliding band, the structural evolution inside the shear-band material, and the parameters that strongly influence shear-banding. Several new discoveries and concepts, such as stick-slip cold shear-banding and strength/plasticity enhancement at sub-micrometer sample sizes, will also be highlighted. The understanding built-up from these accounts will be used to explain the successful control of shear bands achieved so far in the laboratory. The review also identifies a number of key remaining questions to be answered, and presents an outlook for the field.

Shear bands in metallic glasses

The formation of thick Ni-based coating on a steel substrate by coaxial laser cladding using the Nd:YAG 2 kW continuous laser was studied both from a theoretical and experimental point of view. The theoretical analysis concentrated on the transfer of laser irradiation and powder particles using a simple model of heat transfer to the substrate. This approach provides predictions of the laser power required for melting powder particles and substrate, respectively. For an appropriate experimental analysis of the main process parameters involved, a method based on a gradual change of a single processing parameter was examined. Correlations between the main processing parameters and geometrical characteristics of an individual laser track have been found and are discussed.

Analysis of coaxial laser cladding processing conditions

Secondary phases in AlxCoCrFeNi high-entropy alloys: An in-situ TEM heating study and thermodynamic appraisal

Ti–6Al–4V strengthened by laser melt injection of WCp particles

The objective of this work was to create Co-based coatings (compositionally close to Stellite 6) on compacted graphite and gray cast iron substrates with a high power laser (2 kW continuous Nd:YAG) cladding process. The relationships between the relevant laser cladding parameters (i.e. laser beam scanning speed, laser power and powder feeding rate) and the main geometrical characteristics of a single laser track (height, width, dilution, etc.) were examined. A gradual variation of a single processing parameter was used for an appropriate experimental analysis and statistical correlations study between main processing parameters and geometrical characteristics of an individual laser track. These relations lead to the design of a laser cladding processing map that can be used as a guideline for the selection and further tuning of proper processing parameters for laser cladding of extensive layer. The coatings with thickness from 1.0 to 3.3 mm were created on flat substrates without cracks and other major defects. The microstructural features of these coatings were studied using optical microscopy, scanning electron microscopy (Philips XL30 FEG), EDS (EDAX) and XRD. Mechanical properties were determined using microhardness measurement, scratch test (CSM Revetest) analysis at room temperature and using the tribotesting (CSM HT Tribometer) at room and elevated (up to 525 °C) temperatures.

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Vaclav Ocelik

Papers

Analysis of coaxial laser cladding processing conditions

Secondary phases in AlxCoCrFeNi high-entropy alloys: An in-situ TEM heating study and thermodynamic appraisal

Ti–6Al–4V strengthened by laser melt injection of WCp particles

Thick Co-based coating on cast iron by side laser cladding: Analysis of processing conditions and coating properties

SiCp/Ti6Al4V functionally graded materials produced by laser melt injection