Cosmin Codrean

Mechanical Behaviour of Nickel Based Amorphous Alloys during Tensile Test at Different Strain Rates

Nickel based amorphous alloys have been developed in ribbons form by planar flow casting method and were subjected to tensile tests. For this purpose, specimens with calibrated area were obtained by electroerosion cutting method and tested at tensile test with different strain rates. Following the results obtained during the tests, the mechanical properties have been determined and compared and the fracture behaviour has been analyzed by scanning electron microscopy.

Induction Brazing of Copper Parts Using Amorphous Brazing Alloys

Brazing alloys with amorphous structure have excellent technological properties (tensile, wetting), having a self-fluxing character. The brazed joints have good mechanical and corrosion resistance. In this work an amorphous alloy, ribbon form, for brazing of copper pipe components, was elaborated. The brazed joints were analyzed by optical and electronic microscopy. The brazing alloy is self-fluxing and has good tensile and wetting properties. The structure in the brazed joint is monophasic due to the optimization of the process parameters (voltage and brazing time).

Modelling of Resistance Brazing Process Using Factorial Design

The actual state of technological development needs to extend the brazing field of stainless steels and non-ferrous alloys based on Cu, Al, Ni, Co, Ti in leading industries, such as aerospace, energy, chemical, etc. The brazing process is influenced by a large number of parameters, which affects the quality of the joint. This paper presents a mathematical model of resistance brazing process of copper-stainless steel using a factorial experiment. The parameters considered important and which will be analyzed during this experiment are the brazing current, time and force. The output data is given by the quality of brazed joint, represented by shear strength. The objectives of this experiment are establishing the Pareto chart of the effects, the main effects of the parameters, how the response changes during the experiment when each of these factors is changed, and process optimization.

Numerical Model of Thermal Field Developed in Fe67Cr4Mo4Ga4P12B5C4 Bulk Amorphous Alloy Processing

Metallic amorphous materials were developed during 80’s as new materials, with very interesting industrial properties (heat conductivity, magnetic properties, fusion temperature, corrosion resistance, etc.). Technology to obtain these materials, based on very rapid cooling of a melted alloy with glass forming ability, has limitations for the dimensions of the products that can be obtained with amorphous structure (thickness has to be very thin), which can be overpassed by development of bulk amorphous alloys with high glass forming ability and good control of the cooling speed. Numerical modeling of thermal field during ultra-high cooling, developed in researches presented in this paper, allows researchers to estimate the results of applying in reality certain cooling conditions. This model will help developers of bulk amorphous alloys in checking if are ensured conditions to obtain an amorphous alloy with fewer experimental tests, less time and low expenses.

A Comparison between Hardness, Corrosion and Wear Performance of APS Sprayed WC-CoMo and WC-Co Coatings

In order to be competitive, it is demanded to have thin, tough and long lasting coatings. An important aspect is to use stable deposition technologies. As Cr assures wear, corrosion and high temperature resistance, the most employed coatings in industry generally contain Cr. Nevertheless, Cr is a hazardous element for the humans’ health, therefore, sustainable alternatives are needed to be implemented. The aim of this work is to investigate the microstructure, hardness, corrosion resistance and wear behavior of the novel WC-CoMo compared to conventional WC-Co coatings. So far, WC-CoMo coatings are not part of state of the art regarding the Atmospheric Plasma Sprayed (APS) coatings. WC-Co powder in plain form and mechanically mixed with Mo was deposited using the APS method on standardized Type A Almen Strips (C67 steel). The size of the powder grains varies between 5 µm and 30 µm. The obtained samples were investigated by means of Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy, X-Ray Diffraction, and hardness, wear and corrosion behavior were also evaluated. Results revealed formation of different intermetallic phases around the WC particles, which have a benefic influence on the coating characteristics and microstructure.

Numerical Modeling of Thermal Field Distribution during Friction Stir Welding (FSW) of Dissimilar Materials

Friction Stir Welding (FSW) is an innovative solid state welding process, relatively new in industry, which allow welding of two or more materials which have very different properties, particularly thermal properties as fusion temperature, thermal expansion coefficient, specific heat and thermal conduction and have a predisposition to form intermetallic brittle phases, neither one of the components to be weld reach to the melting point. Being a solid state welding process temperature field is very important for the quality of the welded joint, and a lot of researches focused on this topic. This paper presents some results in modeling and estimation of thermal field developed during FSW of dissimilar joints, using Finite Element Analysis. Numerical modeling of thermal field allows engineers to predict, in advance, the evolution of temperature and to estimate the behavior of the welded materials during the welding process. This will reduce significantly the time and number of experiments that have to be carried out, in the process of establishing a good FSW technology, as well as reducing significantly the cost of the tests.

Crystallization of Ni-Cr-Si-B and Ni-Cr-Fe-Si-B Amorphous Alloys

Ni based amorphous alloys with Si and B, which can also, contains Fe and Cr, prepared by rapid solidification, have low melting temperatures. This fact increases their susceptibility to be joined by welding and brazing. The glass forming ability (GFA) is conditioned also by the crystallization delay, due to certain chemical composition of the alloys. The thermal stability of these alloys was revealed by DTA analysis and structural characteristics were investigated by XRD. Applying an annealing at temperatures between 420°C and 540°C, with 30 minutes maintaining time, allowed the investigation of phase occurred during the crystallization and the estimation of the crystalline grains dimensions.

Mechanical Behavior of Fe60Co14Ga2P10B5Si3Al3C3 Bulk Metallic Glass

Development of Fe-based bulk metallic glasses (BMG) with good mechanical and soft magnetic properties has become a major objective in the materials science field. Bulk metallic glasses present an interesting combination of properties. They exhibit very high strength (both in tension and compression), large elastic elongation limit, high hardness, excellent corrosion resistance, and good soft magnetic properties. These properties makes them suitable for many applications like high resistant control cables, pressure vessels, micro-components, pressure sensors, microgears for motors, magnetic cores for power supplies and hard fibers in composite materials. Multi-component Fe60Co14Ga2P10B5Si3Al3C3 bulk metallic glass was synthesized in rod form with a diameter of 1 mm by copper mould casting technique using raw industrial materials. The obtained alloy was analyzed by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) techniques, in order to determine the phase constituent, the thermal stability and the fracture surfaces of as-cast samples. The mechanical behaviour was investigated by microhardness and compression tests. The values recorded for hardness and fracture strength includes this alloy in the category of high resistant materials.

Corrosion Resistance Testing of the Galvanized Sheet Metal Braze Welding Joints

The joining of the galvanized sheet is normally difficult to be done with classical methods, requiring special attention to the specific problems involved during the welding process. This paper presents the development of the joint technology by Cold Metal Transfer (CMT) of galvanized steel sheet using as filler material a CuSi wire electrode. The salt fog corrosion test was made to certify anticorrosive protection of the galvanized sheet metal joints. This test revealed a minimal deterioration of the galvanized zinc coating during welding and also confirms that using adequate technology galvanized steel can be weld without affected anticorrosive protection of the zinc layer.Experimental researches include optimization of the welding technology using CMT concept; technical skill development solutions of the joints; elaboration and implementation of laboratory advanced technology; experimentation and demonstration of technology functionality by obtaining of braze welded joints corrosion resistant.

Simulation of Thermal Field in Fe73Cr2Ga4P13Si5C3 Bulk Metallic Glasses

This paper presents some results for numerical simulation of the thermal field developed during rapid cooling of iron base alloy (Fe73Cr2Ga4P13Si5C3), to obtain bulk metallic glasses. Technology of rapid cooling gives the possibility to obtain bulk metallic alloys with an amorphous structure which can be used for industrial applications like magnetic shields. Validity of the numerical model of the cooling process was confirmed by the X-ray diffraction analysis. Once the model being validate, it can be used to optimize the rapid cooling process and casting mold geometry to be able to investigate the possibility to obtain larger amorphous bulk components.