Selective laser melting (SLM) is an additive manufacturing technique. It allows elements with very complex geometry to be produced using metallic powders. A geometry of manufacturing elements is ...based only on 3D computer-aided design (CAD) data. The metal powder is melted selectively layer by layer using an ytterbium laser. This paper contains the results of porosity and microhardness analysis made on specimens manufactured during a specially prepared process. Final analysis helped to discover connections between changing hatching distance, exposure speed and porosity. There were no significant differences in microhardness and porosity measurement results in the planes perpendicular and parallel to the machine building platform surface.
15-5PH, a martensitic, precipitation hardening stainless steel, can easily form a martensite structure during rapid solidification, especially in the selective laser melting (SLM) process. In our ...study, the 15-5PH/Gr composites with different mass ratios (0 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%) of graphene nanoplates (GNPs) were successfully prepared using SLM technology. Through the observation of optical microscopy images and Raman spectra, it is discovered that the GNPs are uniformly dispersed in the 15-5PH/Gr composites. Based on this phenomenon, a flow model is established to explain the process of the secondary dispersion of the GNPs in the molten pool at high temperatures, and then we come up with a mechanism for it. Besides, it is found that GNPs have a strong inhabiting effect on phase transformation of 15-5PH/Gr composites during the rapid solidification of the SLM process, and the inhibition will be enhanced as the GNPs content increases. The mechanical properties of metal matrix composites (MMCs) are significantly influenced by the changes in phase and additive content. According to the mechanical property tests on the 15-5PH/Gr composites, it is found that their ductility and impact toughness have maximum values of 41.1 ± 1.3% and 194.9 ± 3.1 J/cm2 respectively, and the friction coefficient of the 15-5PH/Gr composites have a minimum value of 0.34. Compared with the SLM-ed 15-5PH, the improvement of mechanical properties of the 15-5PH/Gr composites on ductility, impact toughness and wear resistance are increased by 130.9%, 97.3% and 45.2% respectively.
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The paper presents the results of tests of surface waviness of samples made in the powder bed fusion technology. The models were built using 316L steel-based powder with high corrosion resistance. ...The samples were placed on the construction platform at three different angles (0°, 45°, 90°) in XZ plane. Then, using an optical profilometer, the parameters of the geometric structure of the surface of the primary profile and the separated waviness component were measured. Analyzing the results of the test, it can be stated that the orientation of model arrangement has an impact on the quality of the technological surface texture, what has significance impact on wear processes and mechanical properties.
The main objective of this article is to familiarize readers with the first outputs from PhD research by David Bricín, especially with the metallographic analysis, which was carried out on the first ...series of printed samples. The PhD thesis deals with the processing of powder mixtures based on WC-Co using selective laser melting (SLM) and other technologies. This article specifically deals with the use of SLM for the processing of a WC-Co powder mix. The grains of this powder mixture are not granular, but separate grains of carbides and binders. This powder blend was processed on a 3D SLM printer using various printing parameters. Variable parameters included laser power and scanning speed. Other print parameters were kept constant. The properties of the powder mixture and the printed samples were evaluated by metallographic analysis using light and scanning electron microscopy. These analyses were further supplemented by X-ray diffraction phase analysis, chemical analysis by EDX, and analysis of mechanical properties by compression strength testing. The evaluation of the analyses determined how the printing parameters and the type of powder used affect the development and distribution of the structure in the printed samples and how the mechanical properties of the print are then affected. For example, it has been found that increasing the scanning speed results in a more pronounced mixing between the carbide grains and the binder, which then has a positive influence on the mechanical properties of the print. In addition, the experiments found the energy at which the porosity in the printed samples was significantly reduced, and the direction in which further experiments are to take.
We study the influence of a one-time stop in the course of manufacturing of products by the SLM technology on the structure and mechanical properties of specimens of Inconel 718 alloy with an aim to ...establish their serviceability. The specimens are produced on the equipment of different manufacturers both with stops in the process of printing and without stops. The mechanical properties are determined in tensile tests according to the requirements of GOST 1497 (ІСО 6892-84). It is shown that they are improved both in the case of continuous technological processes and in the presence of a stop in the course of production of the specimens.
This study evaluates how heat treatment affects the structure and properties of the engineered composite material SD251-PH1. This material was formed by mixing two powder blends in a weight ratio of ...90 wt. % WC-Co powder SD251 with 10 wt. % of a PH1 precipitation hardening powder of the stainless steel. Samples were prepared from this mixture on an SLM additive device. The printed samples were then divided into groups. Some of them were left in the initial state and the rest were used for heat treatment based on the standard AMS 5659. Light and electron microscopy metallographic analysis together with X-ray diffraction analysis were then used to evaluate structural and phase changes in the prototype samples. The main attention was paid to changes in the phase composition of the samples. In addition, changes in the size and shape of the pores and tungsten carbide (WC) grains were studied. The metallographic analysis was supplemented by an evaluation of the changes in their mechanical properties and wear resistance. Vickers hardness measurements and the ball on disc test were used for this purpose. The experiments showed that the selected heat treatment processes precipitated new structural phases which differed from the original sample structure in terms of shape, size, chemical composition, and mechanical properties.
The rapid growth of modern industry has resulted in a growing demand for construction materials with excellent operational properties. However, the improved features of these materials can ...significantly hinder their manufacture and, therefore, they can be defined as hard-to-cut. The main difficulties during the manufacturing/processing of hard-to-cut materials are attributed especially to their high hardness and abrasion resistance, high strength at room or elevated temperatures, increased thermal conductivity, as well as resistance to oxidation and corrosion. Nowadays, the group of hard-to-cut materials is extensive and still expanding, which is attributed to the development of a novel manufacturing techniques (e.g., additive technologies). Currently, the group of hard-to-cut materials mainly includes hardened and stainless steels, titanium, cobalt and nickel alloys, composites, ceramics, as well as the hard clads fabricated by additive techniques. This Special Issue, “Advances in Hard-to-Cut Materials: Manufacturing, Properties, Process Mechanics and Evaluation of Surface Integrity”, provides the collection of research papers regarding the various problems correlated with hard-to-cut materials. The analysis of these studies reveals the primary directions regarding the developments in manufacturing methods, characterization, and optimization of hard-to-cut materials.
Purpose
The purpose of this paper is to assess the fatigue life of different sizes of HyFlex CM™ endodontic files when submitted to planar or to non-planar curvatures, and to two different rotational ...speeds, namely 500 rpm or 250 rpm. The influence of superimposing back and forth motion to rotational bending of endodontic files was also assessed.
Design/methodology/approach
In all, 64 HyFlex CM™ files of different sizes, namely ref. 0.04/20, 0.06/20, 0.04/35 and 0.06/35, were submitted to rotational bending tests at two different rotational speeds. The planar radius of curvature imposed to the endodontic files was about 4.5 mm, along an angle of 45°, in order to simulate an apical canal that would induce severe loading to the files during clinical treatment. Additionally, 11 Hyflex CM™ files ref. 0.04/20 were submitted to rotational bending tests at 500 rpm inside a mandible first molar manufactured through selective laser melting (SLM), aiming to simulate non-planar curvatures of a real tooth canal.
Findings
When considering planar curvature, the endodontic file ref. 0.06/20, tested at 250 rpm, has shown the highest fatigue resistance (4,185 revolutions, 1,004 seconds), while the lowest fatigue resistance was registered for instrument ref. 0.04/35 submitted to 500 rpm (747 revolutions, 89 seconds). Hence, depending on the rotational speed, surface finish and the size of the endodontic files tested (taper and tip’s diameter), significant differences in fatigue resistance were noticed. If non-planar curvatures were considered, the minimum fatigue resistance was equal to 107 seconds, and back and forth motion allowed extending the minimum fatigue lifetime to 140 seconds.
Originality/value
The fatigue resistance of endodontic files is frequently determined through in vitro fatigue tests carried out under single planar curvature or eventually under double planar curvatures. However, non-planar loadings are frequently induced on endodontic instruments when treating root canals with severe multiplanar curvatures. In the research herein presented, a mandible first molar was 3D printed by using the SLM technique in an AISI 316 L stainless steel and more realistic experimental fatigue tests were carried out.
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