Ionelia Voiculescu

Chemical and Mechanical Characterization of AISI 304 and AISI 1010 Laser Welding

This paper addresses to the dissimilar laser welding of AISI 304 and AISI 1010 steel thin sheets. Cracks-free dissimilar edge fillet welds have been conducted using a Nd:YAG laser. Geometrical, microstructural, chemical, and mechanical proprieties of the welds were investigated using electron microscopy, EDS and tensile test assisted by digital image correlating. The proper results were achieved at an energy density of 88 J/mm2 using a 0.4 mm laser spot diameter. An austenite-ferrite structure characterizes the weld bead and the precipitation of the chromium carbide at the grain limits was observed in the heat affected zone. Good tensile behavior was obtained; dissimilar joint was fractured on the carbon steel side at 482 MPa and 0.35 stain.

Dual Coating Laser Cladding of NiCrBSi and Inconel 718

This paper presents an alternative approach to obtaining crack- and pore-free NiCrBSiFeCuMoC hard coatings on a low alloy steel substrate through coaxial laser cladding, by using Inconel 718 as a buffer layer between the hard coating and the base material. The presence of the buffer layer reduces the overall cracking susceptibility of the hardfacing material by reducing the compressive stresses developed during the cladding process and ensuring a more uniform heat distribution gradient at the surface of the material than the base metal alone, which provides an additional hardness and wear coefficient increase of 7% and improves the corrosion resistance of the obtained materials by 20%, in comparison with the reference sample obtained without an intermediate layer, by using the same operational parameters and minimizes elemental dilution with the substrate. Our method could prove useful in increasing the quality and life cycle of expensive high-performance hard-coated materials, especially those working under demanding operational and environmental conditions.

Stainless Steels with Biocompatible Properties for Medical Devices

Stainless steels, commercial as well as with special properties, are the principal metallic materials used for medical devices manufacturing. Stainless steels for medical devices should have superior mechanical properties, as: hardness, wear resistance, tensile strength, elongation, fracture toughness, creep resistance etc. This paper aims to present experimental researches regarding the obtaining in vacuum arc remelting device (VAR) of austenitic and martensitic stainless steels and their characterization from microstructure and microhardness point of view.

Inertial system used to analyze normal and pathological human gait

Human motion analysis is one of the research directions which shows an increased interest worldwide due to the complete information we can get on human walking, normal or pathological, in order to confirm or exclude a diagnosis or to monitor patients who are receiving motor recovery program. In accordance with these new requirements a number of facilities were developed that provide information about variables, parameters and determinants of human gait allowing a complete analysis of it, but most are dependent on laboratory use, so we designed a device that can be used both laboratory and ambulatory, with a high degree of portability due to its small size and autonomy of the battery for several hours.

Chemical elements diffusion in the stainless steel components brazed with Cu-Ag alloy

The paper presents the study of diffusion of chemical elements through a brazing joint, between two thin components (0.5mm) made of stainless steel 304. An experimental brazing filler material has been used for brazing stainless steel component and then the diffusion phenomenon has been studied, in terms of chemical element displacement from the brazed separation interface. The filler material is in the form of a metal rod coated with ceramic slurry mixture of minerals, containing precursors and metallic powders, which can contribute to the formation of deposit brazed. In determining the distance of diffusion of chemical elements, on both sides of the fusion line, were performed measurements of the chemical composition using electron microscopy SEM and EDX spectrometry. Metallographic analysis of cross sections was performed with the aim of highlight the microstructural characteristics of brazed joints, for estimate the wetting capacity, adherence of filler metal and highlight any imperfections. Analyzes performed showed the penetration of alloying elements from the solder (Ag, Cu, Zn and Sn) towards the base material (stainless steel), over distances up to 60 microns.

Hafnium influence on the microstructure of FeCrAl alloys

Due to their special properties at high temperatures, FeCrAl alloys micro-alloyed with Zr can be regarded as potential materials for use at nuclear power plants, generation 4R. These materials are resistant to oxidation at high temperatures, to corrosion, erosion and to the penetrating radiations in liquid metal environments. Also, these are able to form continuously, by the self-generation process of an oxide coating with high adhesive strength. The protective oxide layers must be textured and regenerable, with a good mechanical strength, so that crack and peeling can not appear. To improve the mechanical and chemical characteristics of the oxide layer, we introduced limited quantities of Zr, Ti, Y, Hf, Ce in the range of 1-3%wt in the FeCrAl alloy. These elements, with very high affinity to the oxygen, are capable to stabilize the alumina structure and to improve the oxide adherence to the metallic substrate. FeCrAl alloys microalloyed with Hf were prepared using VAR (Vacuum Arc Remelting) unit, under high argon purity atmosphere. Three different experimental alloys have been prepared using the same metallic matrix of Fe-14Cr-5Al, by adding of 0.5%wt Hf, 1.0%wt Hf and respectively 1.5%wt Hf. The microhardness values for the experimental alloys have been in the range 154 ... 157 HV0.2. EDAX analyses have been performed to determine chemical composition on the oxide layer and in the bulk of sample and SEM analyze has been done to determine the microstructural features. The results have shown the capacity of FeCrAl alloy to form oxide layers, with different texture and rich in elements such as Al and Hf.

Finite Element Method for Simulating the Vickers Hardness Test

The purpose of the present paper is to present a different approach to the finite element modeling of the Vickers hardness test measurement, and to establish a numerical correlation between the Young modulus of a material and its hardness. In order to realize this, calculations were based upon the tensions acquired as a result of the hollow caused in the investigated materials by the indenter the maps of stresses. The present work demonstrates that from the results of the simulation based on the finite element method it is possible to compute a material’s hardness.

Obtaining and Characterization of Biocompatible Co-Cr as Cast Alloys

Biocompatible metallic materials used for surgical implants in human body should have superior mechanical properties, as: microhardness, wear resistance, tensile strength, elongation, fracture toughness, creep resistance etc. These results can be also obtained by strict setting and controlling of chemical composition, by adding chemical elements that lead at the improvement of the mentioned properties. In this paper has been presented experimental researches regarding the obtaining process of some biocompatible Co-Cr cast alloys, having different chemical compositions, using the method of vacuum induction melting (VIM). After the obtainment process, samples were characterised from microstructure and microhardness point of view.

The Influence of Chromium Content on the Structural and Mechanical Properties of AlCrxFeCoNi High Entropy Alloys

Many high entropy alloy systems have been exploited in the past decade and among them AlCrFeCoNi alloy is widely studied. The structural and mechanical properties of AlCrxFeCoNi alloy was studied in this paper for different content of chromium (atomic ratio, x= 0.2 to 2.0 at. %). In this study, ten samples having different chemical composition were prepared from raw materials using RAV equipment, type MRF ABJ 900. The microstructure features, crystallite sizes and microhardness depends on chemical composition of the alloy. The microhardness values for AlCrxFeCoNi (x = 0.2 to 2 at. %) increases from 389.6 to 562.6 HV0.1. The maximum value of microhardness for the high entropy alloy AlCrxFeCoNi (x = 1), has been obtained for 20.55 wt% Cr and has the value 562.6 HV0.1.

New FeMnSi+Al Alloy Proposed for High Damping Capacity Elements

High damping capacity materials present an increased interest in many applications were vibration and noise reduction is absolutely necessary. Metallic materials with a high internal friction (IF) are becoming valuable because of them usual mechanical properties that fulfill the damping capacity in applications. Some of the shape memory alloys present a huge damping capacity during the solid state transformation (M↔A) based on the re-orientation and accommodation of the material structure. Iron based shape memory alloy present the best advantages for industrial application as dumpers in different areas. Beside civil construction domain these materials can cover also applications in automotive industry as shock impact absorbers for low velocities as protection for engine parts and also for noise reduction. By these means in this article we analyze FeMnSi+Al alloy with a new chemical composition obtained through classical melting method in Ar controlled atmosphere.