Effect of Heat Treatment of 316L Stainless Steel Produced by Selective Laser Melting (SLM)

Selective Laser Melting (SLM) shows a big potential within additive manufacturing of metals. The competitive mechanical properties compared to conventional processes as well as the geometry freedom are the main advantages of SLM. 316L stainless steel has been investigated in previous works regarding microstructure and mechanical properties. However, the influence of heat treatments has not been fully reported yet. This work studies the influence of different heat treatments applied to 316L stainless steel produced by SLM. The microstructure evolution was investigated for different conditions. Tensile, Charpy and hardness tests were performed on the as built and heat treated samples.Mechanical Engineerin

Phase stability during martensitic transformation in ZrCu intermetallics: crystal and electronic structure aspects

This article is dedicated to the estimation of the relative stability for B2, B19` and Cm phase in ZrCu intermetallic compound through the ab-initio electronic structure calculations and subsequent crystal structure Rietveld refinement. The information about electronic and crystal structure of phases in ZrCu will allow selecting for this high temperature shape memory alloy such alloying elements that will significantly improve shape memory behavior through definite structural changes

Producing Crack-Free, High Density M2 HSS Parts by Selective Laser Melting: Pre-Heating the Baseplate

Cracks and delamination, resulting from residual stresses are a barrier in the world of Additive Manufacturing and Selective Laser Melting (SLM) that prohibits the use of many metals in this field. By preheating the baseplate, thermal gradients are lowered and stresses can be reduced. In this work, some initial tests were performed with M2 Tool Steel. Results show that pre-heating enables the production of dense M2 parts. The influence of pre-heating on density and mechanical and physical properties is investigated. The paper shows many promising results for the production of SLM parts in materials that are very sensitive to crack formation and delamination. When using a pre-heating of 200°C, crack-free parts were produced with a relative density of 99.8%.Mechanical Engineerin

Design Enhancement of Biomedical Scaffolds Made By Selective Laser Melting

Selective laser melting (SLM) is increasingly used to fabricate biomedical scaffolds. However, the intrinsic specifications of the process such as laser spot size, layer thickness, and particle size limit the production accuracy, altering the geometrical characteristics and mechanical properties of the scaffolds. This work attempts to assess and improve the mechanical properties of TiAl6V4 biomedical scaffolds by eliminating/modifying the sharp and thin nodes (as the main source of stress concentrations and lowering the mechanical properties). This is carried out through a gradual increase of the beam (strut) thickness around the nodes where corresponding struts meet. The compression performance of these scaffolds was assessed and compared to common examples (unaltered struts) and to scaffolds designed with thicker struts in the centre of the beams (demonstrating the largest contrast). The findings prove that the thickening of the nodal points improves the strain distribution while maintains the mechanical properties at an identical solid volume fraction. This can be used to improve the scaffold design by a gradual strut thickness (in a comparable volume fraction) for an improved bio-mechanical performance.Mechanical Engineerin

Shape Memory Effect Driven by Diffusionless and Diffusional Transformations at Elevated Temperatures

Several alloy systems can be selected for high-temperature shape-memory alloys, defined as alloys with stable reverse martensitic-transformation temperatures above 100°C. However, due to the lack of minimum quality standards for stability, ductility, functional behaviour, and reliability, no successful applications have been realised so far. Nevertheless, research on high-temperature shape-memory alloys (HTSMA) is an important topic not only for scientific reasons but also due to the market pull. This paper reviews some novel HTSMA systems showing shape-memory effect at elevated temperatures driven by martensitic (diffusionless) and diffusional transformationsМожно привести достаточное количество систем сплавов, которые подпадают под определение высокотемпературных сплавов с эффектом памяти формы — сплавов, в которых стабильное обратное мартенситное превращение протекает при температурах выше 100°C. К сожалению, до сих пор не известно ни одного случая успешного применения высокотемпературных сплавов с эффектом памяти формы в силу отсутствия требований к их стабильности, пластичности, функциональному поведению и надежности. Тем не менее, исследования высокотемпературных сплавов с эффектом памяти формы являются важными не только с точки зрения фундаментальной науки, но и благодаря требованиям рынка. Настоящая работа посвящена рассмотрению некоторых новейших систем высокотемпературных сплавов с эффектом памяти формы, который определяется как мартенситным (бездиффузионным), так и диффузионными превращениямиМожна навести певну кількість систем сплавів, що можуть бути визначені, як високотемпературні сплави з ефектом пам’яті форми, що в свою чергу визначаються як сплави зі стабільними температурами зворотного мартенситного перетворення, вищими за 100°C. На жаль, невідомо жодного випадку успішного застосування високотемпературних сплавів з ефектом пам’яті форми, завдяки відсутності вимог щодо їх стабільності, пластичності, функціональної поведінки та надійності. Не зважаючи на це, дослідження високотемпературних сплавів з ефектом пам’яті форми є важливим не тільки з точки зору фундаментальної науки, але й завдяки вимогам ринку. Дана робота присвячена розглядові деяких новітніх систем високотемпературних сплавів з ефектом пам’яті форми, що зумовлений мартенситним (бездифузійним) та дифузійним перетворенням

Rheological behavior of β-Ti and NiTi powders produced by atomization for SLM production of open porous orthopedic implants

The growing interest for Selective Laser Melting (SLM) in orthopedic implant manufacturing is accompanied by the introduction of novel Ti alloys, in particular β-Ti for their excellent corrosion resistance as well as favorable combination of high mechanical strength, fatigue resistance and relatively low elastic modulus. As part of the SLM process for producing quality β-Ti parts powder flowability is essential to achieve uniform thickness of powder layers. In this work the flowability of different gas atomized β-Ti, including NiTi, powders has been studied. Their rheological properties were compared to those of commercially available plasma-atomized Ti–6Al–4V powder using a newly developed semi-automatic experimental set-up. Not only the particle size, shape and size distribution of the powders display a large influence on the powder flowability but also particle surface properties such as roughness, chemical composition and the presence of liquid on the surface of the particles. It was found that plasma or gas atomization production techniques for SLM powder have a considerable effect on the particle topography. Among the powders studied regarding SLM applicability only rheological properties of the fine size fraction (25–45 μm) of Ti–45Nb didn't conform to SLM processing requirements. To improve flowability of the Ti–45Nb powder itwas annealed both in air and argon atmosphere at 600 °C during 1 h, resulting in an improved rheological behavior suitable for SLM processing

AMBRA1 is able to induce mitophagy via LC3 binding, regardless of PARKIN and p62/SQSTM1

Damaged mitochondria are eliminated by mitophagy, a selective form of autophagy whose dysfunction associates with neurodegenerative diseases. PINK1, PARKIN and p62/SQTMS1 have been shown to regulate mitophagy, leaving hitherto ill-defined the contribution by key players in 'general' autophagy. In basal conditions, a pool of AMBRA1 - an upstream autophagy regulator and a PARKIN interactor - is present at the mitochondria, where its pro-autophagic activity is inhibited by Bcl-2. Here we show that, upon mitophagy induction, AMBRA1 binds the autophagosome adapter LC3 through a LIR (LC3 interacting region) motif, this interaction being crucial for regulating both canonical PARKIN-dependent and -independent mitochondrial clearance. Moreover, forcing AMBRA1 localization to the outer mitochondrial membrane unleashes a massive PARKIN- and p62-independent but LC3-dependent mitophagy. These results highlight a novel role for AMBRA1 as a powerful mitophagy regulator, through both canonical or noncanonical pathways