100,341 research outputs found
The compressibility behaviour of a new generation of coated metal/ceramic composite powders
No full textThe present work deals with the compressibility behaviour of a new generation of coated metal/ceramic composite powders. A commercial 316L stainless steel powder was coated with the alumina layer by an aqueous sol-gel colloidal process and then metal/ceramic composite materials were produced with core/shell structure. The powders were uniaxially cold pressed in a cylindrical die in the range from 200 to 1000 MPa. In order to reach the best green density, composite powders have been added with 1% in weight of lubricant. The compressibility behaviour was analysed using the equation P = P0.exp (-K.pn). P0 is the relative apparent density and p is applied pressure; K and n are the parameters with defined physic-metallurgical substance. The values of the parameters K and n were determined by regression analyses. The correlation coefficients r of experimental compaction curves were up to 0.98. The results showed that difference between metal/alumina weight ratios affected the compressibility parameters as well as compressibility curves
Influence of processing conditions on EN AW 2014 material properties and fracture behaviour
No full textThe paper deals with the influence of processing conditions on material properties and fracture behaviour of the aluminium alloy EN AW 2014, depending on various processing conditions (as-rolling, quenching, severe plastic deformation - SPD by equal channel angular pressing - ECAP and ageing). (Tensile tests were carried out at strain rate of 2.5 × 10−4 s−1.) The evaluated mechanical properties show that ECAP has the highest effect on formability and mechanical properties of the aluminium alloy EN AW 2014. Severe plastic deformation by means of ECAP causes rapid increase of strength and only partial decrease of ductility was achieved. Strengthening of material is caused by grains refinement, strain hardening of solid solution. Fractographical examinations revealed that there were two categories of dimples of transcrystalline ductile fracture, large dimples, formed by the intermetallic particles and small dimples, formed by submicroscopic and dispersive particle
Role of microstructural discontinuities in the soft magnetic composites with aluminium alloy addition
No full textThe paper focuses on the effect of both the aluminium alloy addition and microstructural inhomogeneties on the magnetic behaviour of soft magnetic materials tested at low frequencies. The IIPC material (base on the commercial Somaloy 1P powder) has been blended with different amounts of commercially aluminium alloy Alumix 321 (0, 5 and 10 wt %). Specimens with a different green density were obtained by pressing at a pressure in the range from 400 to 800 MPa. Different thermal treatments (in air or nitrogen at the maximum temperature of 500C for 30 min) were carried out on the evaluated systems. The microstructure investigation revealed that for materials with high aluminium alloy contents, pores are located nearby or around the aluminium alloy particles. The heat treatment regime resulted in a coarse-grained structure with a small number of inclusions within the grains and at the grain boundaries. The comparison of the results indicated that the magnetic properties were considerably dependent on the microstructural inhomogeneitie
Different formation routes of pore structure in aluminum powder metallurgy alloy
No full textIn powder metallurgy (PM), severe plastic deformation (SPD) is a well-known technological solution to achieve interesting properties. However, the occurrence of pores in the final product may limit these properties. Also, for a given type of microstructure, the stereometric parameters of the pore structures, such as shape (represented by Aspect and Dcircle) and distribution (fshape, and fcircle), decisively affect the final properties. The influence of different processing routes (pressing, sintering and equal channel angular pressing (ECAP)) on pore structures in an aluminum PMalloy is discussed. The nature of porosity, porosity evolution and its behavior is explored. The correlation between pore size and morphology is also considered. The final pore structure parameters (Aspect, Dcircle, fshape, and fcircle) of studied aluminum alloys produced by different processing routes depends on the different formation routes
The Porosity Evaluation during ECAP in Aluminium PM Alloy
No full textThe main aim of this paper is to show porosity evolution during application of various processing conditions including pressing, sintering and equal channel angular pressure. An aluminium based powder (AlMgSiCuFe) was used as investigated material. After applying dierent pressing pressures (400 and 600 MPa), specimens were dewaxed in a ventilated furnace at 400◦C for 60 min. Sintering was carried out in a vacuum furnace at 610◦C for
30 min. The specimens were processed by single equal channel angular pressure pass. A signicant disadvantage of powder metallurgy processing methods is the presence of porosity. Pores act as crack initiators and, due to
their presence, the distribution of stress is inhomogeneous across the cross-section and leads to reduction of the effective load bearing area. The equal channel angular pressure process, causing stress distribution in deformed
specimens, made the powder particles to squeeze together to such an extent that the initially interconnected pores transform to small isolated pores. The proposed safety diagram includes the combined effect of stress and strain behaviour during equal channel angular pressure. The safety line eliminates and quanties the effect of large pores as a potential fracture initiation sites with respect to the mechanical viewpoint
Wear Resistance of chromium pre-alloyed sintered steels
No full textThis paper deals with the influence of the processing conditions on the material properties and wear characteristics of chromium pre-alloyed sintered steels. Three different processing conditions were used, involving different cooling rates from the sintering temperatures of 1180°C and 1240°C. A conventional (slow) cooling condition and a new progressive condition, siinter hardening, were examined. The results showed that the typical microstructure characteristics of sintered steels represent an important parameter affecting their wear behaviour
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