Advanced Materials Research Vol. 939

Abstract: The present study deals with a new design of aluminium alloy based composites reinforced with SiC particles and Si/Al₂O₃ powders through combined methods of powder metallurgy and thixoforming. Moreover, recycled machining chips are used as raw material, specifically AA7075 chips generated in the aeronautical industry. The proposed method is based on forming at high temperatures a compacted mixture of metal chips and reinforcing particles, with the metal in thixotropic semi-solid condition. Composites containing different SiC weight fractions (10, 20 and 30%) were produced and had their microstructure analyzed. Mechanical properties were evaluated by means of micro-indentation tests. General results show the feasibility of producing composites by the proposed route. Products with good mechanical properties could be obtained. The process, even still not completely optimized as some improvement still must be achieved, can bring a new possibility for the production of a noble material from recycled wastes, particularly important in the high energy spending Al industries.

Abstract: Generally, all insulating materials were regarded as the non machinable workpiece for the electrical discharge machining (EDM) method. About twenty years ago, many insulating ceramics turned to the machinable materials for EDM using the assisting electrode method which was proposed by our research group. The machining mechanism was already explained with the surface adhesion phenomena [1]. In this process, many unstable discharge phenomena occurred such as concentrate, short circle and long pulse. It was clarified that they generated frequently on the high electrical resistance surface. The EDMed surface became rough and uneven on the unstable discharged area. In this paper, to obtain the good and even EDMed surface on the large removal area same as small area machining for Sinking-EDM, the effects of electrode size and shape were investigated. Considering the path of discharge supply energy on the high resistivity surface, new machining method was proposed which was named as the scanning machining method, and the ability of this method for practical use was confirmed with Si₃N₄ insulating ceramics. Using the new proposal method, better surface roughness and the sharp corner edge shape could be machined on the large area EDMed surface.

Abstract: The aim of this work is to determine the effect of a reinforcing phase and manufacturing conditions on the structure and properties of newly developed nanostructural powders of composite materials with the aluminium alloy matrix reinforced with natural halloysite nanotubes. Composite materials were manufactured employing as a matrix the air atomized powders of AA 6061 aluminium alloy and as a reinforcement the halloysite nanotubes. Composite powders of aluminium alloy matrix reinforced with 5, 10 and 15 wt.% of halloysite nanotubes were fabricated by high-energy mechanical alloying using a planetary mill. Elaborated composite powders were characterized for their apparent density, microhardness, particle size distribution and microstructure. A structure of newly developed nanostructured composite materials reinforced with halloysite nanotubes prove that a mechanical alloying process allow to improve the arrangement of reinforcing particles in the matrix material. A homogenous structure with uniformly arranged reinforcing particles can be achieved by employing reinforcement with halloysite nanotubes if short time of mechanical alloying is maintained thus eliminating an issue of their agglomeration.

Abstract: In the present work, fusion-joining of vacuum high pressure die cast (HPDC) aluminum alloy A356 and wrought alloy 6061 by applying Gas Metal Arc Welding (GMAW-MIG) process was investigated to understand the effect of the MIG process on the microstructure and tensile behaviors of the base joined alloys (T6 Heat treatment A356 and 6061). The microstructures of the base metal (T6 heat treatment A356 and 6061), Heat Affected Zone (HAZ) and Fusion Zone (filler metal ER4043) were analyzed by Scanning Electron Microscopy (SEM) and optical microscopy. The results of tensile testing indicated that, the ultimate tensile strength (UTS) and yield strength (YS) of V-HPDC alluminium A356 subjected to T6 thermal treatment were relatively low, compared to both wrought alloy 6061 and the filler metal (ER 4043). The microstructure analysis showed that the low strengths of T6 A356 alloy should be at least attributed to the absence of the magnesium-based intermetallic phase, coarse grain structure and the presence of porosity, which resulted from the HPDC process, MIG welding and thermal treatment.

Abstract: A mixture of structural functions can be accomplished using different reinforcements in epoxy-nickel matrix composites. In the frame of the common research project, mechanical and physical properties of the epoxy resin-nickel matrix composites containing extremely fin aluminum and fine waste elastomer powders were studied. A comprehensive study is given with different static and dynamic aspects as a function of composition, frequency and temperature. Two types of waste elastomeric powders were used for the reinforcement: Styrene-Butadyene Rubber SBR and Ethylene Vinyl Acetate (EVA). All of the composites were fabricated by mixing during 4h and then put in an ultrasonic dispersion for 1h. After that, a detail analyses has been carried out by means of Dynamic Mechanical Thermal Analysis (DMTA), microindentation and wear - scratch test. Dielectric properties (Permittivity (ε′)) and dielectric loss angle tangent (tan delta) were investigated using a Dielectric Thermal Analyzer (Rheometric Scientific) at three different frequencies (1 kHz, 10 kHz, 100 kHz) from room temperature up to 280°C. Wear of surface resistance measurement has been carried out by scratch test with a normal of 2.06N load with the frequency of 10Hz in two different number of cycles; 50000 and 100000. After the test, damaged zone were measured by 3D optical roughness meter to characterize damage occurred after the scratch test.

Abstract: Wear resistance is an important rubber compound property related to useful product life. The rubber compound properties that affect wear behavior are very complicated. Wear is related to a rubber compound’s cut resistance, tear resistance, fatigue resistance hardness, etc. The most commonly used test method to determine the wear resistance of rubber materials is abrasion test. Tested compounds are usually compared on a “volume loss” basis which is calculated from the weight loss and density of the compound. This method is known to be variable and doesn’t give additional information for the wear behavior. For this reason we propose alternative approaches for examination of the wear behavior of rubber composites, giving information not only for the wear resistance but also for elastic the modulus, stiffness of the material, damage mechanism, etc. Continuous multi-cycle indentation is used to determine the indentation hardness, elastic modulus and the stiffness with two indenter types –Vickers and sphero-conical. Comparison of both results is made in order to investigate the effect of the indenter type.

Abstract: The aim of this study is to examine the influence of the scrap material and the additional elements on the structure and mechanical properties of multi-phase system. All of the composites were fabricated by mixing during 4h and then put in an ultrasonic dispersion for 1h. After that, a detail analyses are carried out by the means of Dynamic Mechanical Thermal Analysis (DMTA), Microindentation and scratch test. The structure was investigated by Scanning Electron Microscopy (SEM). The present study will help to optimize the parameters of this newly designed composite material allowing to find different possibilities for the industrial applications and to contribute in the war with the waste rubber materials.

Abstract: MgZnCa amorphous matrix-based composites whereby reinforcing the matrix with suitable reinforcements to achieve enhanced mechanical, biomedical and anti-corrosion properties have been studied here. Here, MgZnCa-based composites have been developed with different amounts (0-25%wt) of yttria-stabilized zirconia (YSZ) reinforcement phase. The aim is to understand the corrosion behaviors of YSZ-reinforced MgZnCa-based composites in physiological saline solution. It is found that the incorporation of YSZ into amorphous MgZnCa matrix can cause crystallization of the amorphous matrix. The higher the YSZ introduced, the higher the degree of crystallization, and a fully crystalline matrix is obtained at a YSZ concentration of 25%. Electrochemical testing and ion release measurements, revealed that the composite with 8%YSZ possesses the smallest corrosion current density and the least ion release rate. Surface morphology analysis indicates a much stronger anti-corrosion ability of 8%YSZ-reinforced MgZnCa composite.

Abstract: This report aims to illustrate some multifaceted approaches for estimating fracture toughness of high-strength Ni-Cr-Mo low alloy steels in order to search for a suitable methodology for their rapid quality control in industrial production. The chemistry, microstructure, hardness, tensile and impact toughness properties of the selected AISI 4335 grade steels from different batches of commercial productions were assessed by standard methods. Measurement of plane strain fracture toughness (K_Ic), dynamic fracture toughness (K_Id) and fracture toughness using chevron notched bend bar specimens (K_Icv) have been done on the selected steels. The magnitudes of K_Ic depend on the amount of inclusions and tramp elements in different batches of production. The values of K_Id estimated by LEFM approach and K_Icv are in reasonably close agreement with K_Ic values but the latter methodology indicates the potential to be an alternate approach. Comparative assessments of K_Id and K_Icv values with respect to K_Ic values of the steels have been made using concepts based on fracture mechanics and inherent characteristics of test parameters.

Abstract: Shaping materials containing porous constituents is a critical issue. This work analyses the process of abrasive water-jet (AWJ) cutting applied to low density metal matrix composites (LD.MMCs) consisting of AA7075 alloy as matrix and porous, foamed particles of SiO₂/Al₂O₃/Fe₂O₃ or vermicular SiO₂/Al₂O₃/MgO, as reinforcements. Results show that although presenting lower density (from 1.09 g/cm³ to 1.59 g/cm³, depending on the particle type) and lower strength than the non-reinforced AA7075 alloy, the composites present some difficulties in AWJ cutting. Deflection of the jet was noticed, being more evident on vermiculite-reinforced samples. Anyhow machinability numbers for the composites analyzed are in the order of 20% higher than the AA7075 matrix alone. Jet deflection, surface quality and machinability number showed to be dependent on the internal structure of the porous ceramic particles: vermiculite can pull out under the jet while cinasite is more susceptible to suffer fracture. This mechanisms result in lower jet deflection, better surface and better overall machinability in the case of AA7075 / cinasite LD.MMC.