Stefan Szczepanik

FeAl materials from intermetallic powders

FeAl materials with the aluminium concentration of 40 at.% were prepared from intermetallic powders, obtained by milling and screening of the products of self-propagating high-temperature synthesis (SHS), carried out in a loosely packed mixture of elemental powders. Pressureless sintering of the compacted intermetallic powders yielded porous materials that were densified by hot forming. The properties of dense bodies were strongly related to the grain size of the starting intermetallic powders. Two fractions with grain sizes of less than 25 mm and in the range from 25 to 40 mm were investigated. The amount of an oxide phase distributed along the grain boundaries of the intermetallic matrix was remarkably higher in the former case. The oxide dispersions adversely affected the room temperature strength and ductility of the material. # 2003 Elsevier Science Ltd. All rights reserved.

Influence of Cold Working on Mechanical Properties of Al-SiC Composites

The main objective of this research was a study the simultaneous influence of cold working and particle reinforcement on mechanical properties of Al. The model composites were fabricated by cold pressing RAl1 aluminium and 5% and 10% SiC powders and hot extrusion with ratio 3.8 in isothermal conditions at 480°C with 90° die angle to 18 mm diameter. Some specimens were then cold drawn with linear velocity 1 m/min to 16% area reduction, and one specimen in 3 passes to 51% reduction in area. Mechanical properties of the near fully dense composites were determined by axial compression, bend tests and hardness measurement and their microstructures examined, showing near homogenous distribution of SiC particles in the aluminium matrix. The increase in Young’s modulus was from 67 to 74 GPa and to 82 GPa for 5% and 10% reinforcement, respectively. Drawing increased average yield strength from 70 to 100 MPa for Al, and from 74 to 110 MPa and from 80 to 115 MPa, for 5 and 10% reinforcement, respectively. The results indicate that there is a significant increase in E, in accord with the law of mixtures, through incorporation of SiC and a synergistic effect of SiC and plastic deformation during drawing on strength. An attempt is made to identify the various contributions to overall strengthening of Al by considering also Al-8.8Cu-6.3%Si-0.7Mg alloy. It appears that alloying and age-hardening have the greatest effect, but that contributions from hot, warm and cold working are not insignificant. As powder metallurgy processing is an important fabrication method, their incorporation into the processing schedule merits consideration.

Properties of Al-Si-Fe-Cu-Mg Alloy PM Composites Obtained by Closed -die Forging and Heat Treatment

Aluminium RAl-1 and its alloy Al17Si5Fe3Cu1.1Mg0.6Zr composite materials were manufactured from powder mixtures by cold pressing, hot closed-die forging at 480oC and heat treatment. Powders ranging in composition in 20 wt.% steps of the alloy were mixed in a Turbula mixer for 1 h. The preforms with alloy concentrations of 80 and 100 % were hot consolidated at 480oC and closed-die forged at the same temperature. The effect of chemical composition on microstructure and mechanical properties in bending and compression was examined. Bend strength ranged from 400 to 540 MPa, compression strength from 415 to 744 MPa and hardness from 32 to 203 HB. Simulated distribution of component materials for a cross-section of the forging and shapes of the materials were analysed using LARSTRAN/Shape finite element program and are qualitatively comparable with the results obtained by forging.

The Results Of The Investigation Of Thermomechanical Processing Of PM Steel

Hot die forging of PM steel is used to obtain products with high densities. The combination of this process with heat treatment of forgings directly after their forming is researched in order to reduce energy consumption in the manufacture of PM steel products. This work determined the influence of the cooling ratio directly after hot forging of PM steel samples on their structure and mechanical properties. The properties of the PM preforms were examined after sintering and after sintering, quenching into water and tempering for 1 h at 250, 350 and 550°C, respectively, as well as after forging at given temperatures and cooling in water and air, respectively. Forged steel after quenching was tempered at the same temperature as the sintered samples. Good mechanical properties were obtained by hot forging at 1100 °C. Sintered steel with 0.6 % Cgraphite is characterized by good hardenability and is susceptible to plastic forming at 1100 – 940 °C. During its cooling in air a bainitic‐martensitic structure is o...