Papers by Author: Tomasz Tokarski

Abstract: The results of the investigations on five different titanium alloys were presented in this paper. Two two-phase α+β alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo) as well as two β alloys (Ti-10V-2Fe-3Al and Ti-3Al-8V-6Cr-4Mo-4Zr) were studied. Moreover, Ti-48Al-2Cr-2Nb intermetallic alloy (γ alloy) was also investigated. All investigated alloys were tested in compression on Gleeble thermomechanical simulator under various strain rate and temperature conditions. Metallographic observations of the microstructure of tested samples allowed determining thermomechanical conditions under which dynamic recrystallization or recovery processes occurred in the investigated alloys. The obtained results also showed the importance of the influence of strong exothermic effect resulting from deformation process on recovery and recrystallization processes in these alloys. The methodology of distinguishing subgrains formed during recovery process from the grains resulting from recrystallization was also presented in this study.

Abstract: Method of scrap recovery by hot extrusion in a contrast to traditional aluminum recycling process distinguishes itself with a low energy consumption and high recovery efficiency. Additionally, this type of recycling allows to recover materials even from highly fragmented forms of metal like chips, foils or filings by omitting melting procedure. In the present study results of 413.0 aluminum chips plastic consolidation will be presented. Chips after machining process were used as a charge material for the entire recycling process. In order to determined the best emulsion elimination method, three separate processes such as centrifugation, annealing and pressing were carried out. In result dry, wet and cleaned chips in a form of cylindrical billets were hot extruded into longitudinal square cross-section profiles. Mechanical properties were examined by uniaxial tensile tests while microstructure observations were performed by means of scanning electron microscopy. It has been showed that emulsion elimination by annealing gives the best results while at the same time all extruded materials revealed no significant differences in mechanical properties.

Abstract: Ultra-fine grained metallic materials are characterized by higher mechanical properties comparing with their conventional equivalents. However increase in strength under static load is not always accompanied by improved fatigue behaviour. Previous investigations on submicrocrystalline RS442 aluminium alloy produced by plastic consolidation of rapidly solidified flakes in the extrusion process revealed increase in its high cycle fatigue bending strength caused by annealing at 450°C. The aim of present studies was to evaluate the influence of heat treatment – also precipitation hardening – on static mechanical properties (hardness, tensile and yield strength) and fatigue strength of the alloy determined in high cycle stress controlled bending tests. Correlation between microstructure, static mechanical properties and fatigue behaviour was analyzed too.

Abstract: In this work, hot extrusion of light metal scraps as a new way of plastic consolidation will be presented. This kind of material recovering is a promising alternative for conventional recycling processes. Nowadays discards from machining of semi-finished products are being recycled throughout re-melting processes. However, due to its significant susceptibility to oxidation most of the chips and scraps are burnt during the melting process. It has been already recognized that aluminum losses connected with this operation can reach from 40% to 50%. A technology that has been presented in this work combines cold compaction and hot extrusion of 413.0 aluminum alloy scraps. It was found that quality of as-extruded rods depends strongly on extrusion conditions. Higher extrusion speed leads to higher quality of rods surface. Additionally brittle Si and Al-Fe-Si particles increases overall mechanical properties in comparison to its industrial counterpart.

Abstract: The processes of spinning and flow forming of hard metal sheets made from nickel superalloy INCONEL can be realized cold or with heating - e.g. by a induction or laser. When metal sheet is heated it is necessary to measure the temperature field on heated area, because its determines the deformation susceptibility. To control the temperature field pyrometers and infrared cameras are used. Due to strong changes in the surface of a formed material, under temperature influence (oxidation) and the action of the forming rolls, it is necessary to determine the emissivity coefficient values as a function of temperature and surface conditions. The paper presents the concept of determining these values, as well as an alternative technique for measuring temperature field, based on the methods of image analysis.

Abstract: Compacts for the synthesis of composite zones in castings were obtained by cold pressing powders of the TiC reactants under a pressure of 250, 300, 500 and 600 MPa. The all compacts made under different pressures were placed in a mould cavity and poured with liquid unalloyed low-carbon steel. From the resulting casting, four composite zone A, B, C, D, produced in this casting by in situ method. In all composite zones, TiC and ferrite (αFe) were obtained. Additionally, in zones A, B and C the presence of graphite (C_gr) was also stated. The surface friction (S_f) of C_gr decreases in composite zones A ÷ D, while both the S_f of TiC and hardness VH30 increase in these zones with increasing compaction pressure of the reactants. Too low compaction pressure applied to the TiC reactants impedes the effective propagation of the reaction of synthesis.

Abstract: The present paper reports an experimental investigation of rapid solidification (RS) influence on the structure and mechanical properties of commercial AZ91 magnesium alloy. In order to obtain RS material melt spinning process was applied in protective atmosphere, resulting in formation of 50 to 100 μm thickness RS ribbons. Application of plastic consolidation (PC) by hot extrusion to the highly fragmented magnesium strips allowed to obtain high bulk strength material. It was found that yield strength (YS) and ultimate tensile strength (UTS) of RS+PC material with comparison to the cast and extruded samples were increased from 220 MPa to 303 MPa and from 287 MPa to 385 MPa, respectively, while plasticity of the RS material was slightly decreased. It was noticed that the grain size of both materials was at the same level of 2 μm, thus higher mechanical properties of RS material was ascribed to dispersion strengthening caused by the high amount of fine (below 50 nm in diameter) Mg₁₇Al₁₂ phases evenly distributed in the material structure.

Abstract: The present paper is aimed at investigations of mechanical properties and structure of technical purity aluminum powders prepared by plastic consolidation process. The research work is focused on effective improvement of mechanical properties of material while keeping the conductivity at high level. It is well known that application of rapid solidification method with hot extrusion technique leads to grain refinement, as so according to Hall-Petch rule, improvement in mechanical properties of material can be expected. Furthermore, additional material strength can be obtained by aluminum oxides from free surface of powders that became internal boundaries during consolidation process. Aluminum powders atomized by air, argon and water were cold compacted and extruded at temperatures of 325°C and 375°C. For comparison purposes the same extrusion conditions were applied to cast aluminum. In order to analyze effect of recrystalization process during hot extrusion operation, different extrusion temperatures were chosen. Tensile tests as well as micro-hardnes measurements showed significant increase in mechanical strength for RS samples in comparison to conventionally cast material. Structural observations by means of transmission electron microscopy revealed that grain size of materials extruded at the given temperature was at the same level, however amount and distribution of oxides particles differs significantly. It was considered that differences in strength between individual RS material were attributed to this effect.

Abstract: Magnesium and its alloys are attractive candidates for automotive and aerospace applications due to their relatively high strength and low density. However, their low ductility determined by hcp structure of material results in limitation of plastic deformation processing. In order to improve ductility as well as mechanical properties, structure refinement processes can be used. It is well known that effective refining of the material structure can be achieved by increasing the cooling rate during casting procedures, hence rapid solidification process (RSP) has been experimented for the fabrication of magnesium alloys. The present paper reports an experimental investigation on the influence of rapid solidification on the mechanical properties of AM60 magnesium alloy. In order to obtain RS material melt spinning process was applied in protective atmosphere, resulting in formation of RS ribbons. Following consolidation of the RS material is necessary to obtain bulk material with high mechanical properties, as so hot extrusion process was applied. It was noticed that application of plastic consolidation by hot extrusion is the most effective process to achieve full densification of material. For comparison purposes, the conventionally cast and hot extruded AM60 alloy was studied as well. The purpose of the present study was to investigate in detail the effect of rapid solidification and extrusion temperature on the structure and mechanical properties of the materials.