Materials Science Forum Vols. 775-776

Abstract: The influence of particle size of the load in the structure and morphology of the composite is an important factor in their final properties. This study will evaluate the behavior of the load of nickel ferrite calcined at different temperatures (700, 900 and 1200 ° C) with the polyamide matrix 6. In the preparation the polymer matrix was previously been dried in a vacuum oven at 80 ° C/48hs for eliminating humidity, and then the load was incorporated in the form of powders calcined at three temperatures in the mass concentration of 50%. Thereafter, the mixture was compressed to obtain composites, which were characterized by XRD and SEM. The results show XRD characteristic peaks of nickel ferrite and polyamide 6, showing that the calcination caused an increase in crystallinity of the load. SEM results show that the calcination caused an increase in the size of the agglomerates of the load, favoring significant changes in the morphology of the composite.

Abstract: Shape memory alloys (SMAs) represent a unique class of materials that undergo a reversible phase transformation (martensitic transformation) allowing these materials to display dramatic pseudoelastic stress-induced deformations and shape memory temperature-induced deformations that are recoverable. Among the known shape memory alloys, NiTi is the most commonly used because of its excellent mechanical properties, corrosion resistance and biocompatibility. This work studied the influence of two parameters of heat treatment (temperature and time) on martensite phase transformation temperature (M_S) in a Ni-Ti (48,8 wt % Ti) shape memory alloy, using a factorial design (2²). The aim of our research was to establish a mathematic model of the technological process, useful for controlling of martensite phase transformation temperature. The two factors, temperature and time, have an important influence on M_S.

Abstract: This work evaluates, by means of its morphological characterization, a new Al-2.0wt%Si-2.5wt%Cu alloy produced by direct casting under electromagnetic stirring for thixoforming process. The alloy was submitted to re-heating treatment in two conditions of solid fractions, 45% and 60%, for 0, 30, 90 and 210 s. Re-heating treatment times promote solid phase particles globularization, presenting average grain sizes of approximately 90 μm for both solid fraction. These results show that the alloy is viable for thixoforming process, especially in the condition of 90 s of treatment time at 45% and 60% of solid fraction, that presents grain size about 90 μm and shape factor higher than 0.60. Another important fact about the small grain/primary particle size is related to the use of electromagnetic stirring in its production, that promotes the breakdown of the material structure and consequently stimulates globularization.

Abstract: This work investigates the microstructural changes developed during the solution annealing treatment under different conditions for the steel UNS S31803. The studied material was submitted to solution anneal at 1100°C for 30, 120 and 240 min, followed by cooling in water, air and furnace. The results evaluation was based on micrographic analysis and the results showed the influence of treatment period and cooling rates in distribution and morphology of austenitic phase. It was observed the same morphology of austenitic phase in all treatment conditions, however, the volume fraction of this phase increased with the treatment period increase, and further refinement with lower cooling rates. It was found that the solution treatment by longer period with the lower cooling rate significantly enhanced the intermetallic phases transformation. The intermetallic phases precipitation could be detected when the samples were solution-treated for 120 and 240 min and cooled at furnace.

Abstract: The martensitic stainless steels are applied in specific conditions due to theirs corrosion and mechanical resistance. The study of these steels after heat treatment is relevant because it may involve the production and development of new steels with better properties for several applications. This study investigates the effect of heat treatment of quenching and tempering in two martensitic steels - 13Cr2Ni0.1C and 13Cr1Ni0.15C (% weight). Dilatometric tests were performed in the samples after melting process in order to obtain the initial and final temperatures of formation of austenite and martensite. The results showed that the quenched samples have the highest hardness and a martensitic microstructure with delta ferrite presence. On the other hand, the samples after tempering showed different matrix suggesting that the martensite decomposition with no change of the delta ferrite.

Abstract: The 4340 are classified as ultra-high strength steels used by the aviation industry and aerospace applications such as aircraft landing gear and several structural applications, usually in quenched and tempered condition. In this situation occurs reduction of toughness, which encourages the study of multiphasic and bainític structures, in order to maintain strength without loss of toughness. In this study, ferritic-pearlitic structure was compared to bainitic and martensitic structure, identified by the reagents Nital, LePera and Sodium Metabisulfite. Sliding wear tests of the type pin-on-disk were realized and the results related to the microstructure of these materials and also to their hardnesses. It is noted that these different microstructures had very similar behavior, concluding that all three tested pairs can be used according to the request level.

Abstract: This study aims to characterize the microstructure of the complex phase steel (CP). Using the conventional and colored metallographic analysis with 3% Nital etchant, sodium metabisulfite 10% and LePera. Techniques were applied in this work of optical microscopy, using, besides the lighting in bright field, dark field illumination of the reverse contrast in bright field illumination, the method of polarized light, which generates colorful contrast, providing a complementary identification phases present in the microstructure, and the system by differential interference contrast (DIC). The results obtained by metallography CP indicates that the steel has a microstructure composed of ferrite, retained austenite, bainite and martensite and precipitates arranged in a refined and complex morphology. Besides bright field illumination others optical microscopys techniques such as dark field illumination were applied.

Abstract: TRIP (Transformation Induced Plasticity) and DP (Dual-Phase) steels are written in a new series of steels which present excellent mechanical properties. As for microstructure aspect, TRIP steels consist on a ferrite matrix with a second phase dispersion of other constituents, such as bainite, martensite and retained austenite, while dual-phase steels consist on martensite dispersion in a ferrite matrix. In order to identify the different microconstituents present in these materials, microstructure characterization techniques by optical microscopy (using different etchants: LePera, Heat-Tinting and Nital) and scanning electron microscopy were carried out. This being so, microstructures were correlated with mechanical properties of materials, determined by means of tensile tests. It is concluded that steels assisted by TRIP effect have a strength and elongation relation higher than the dual-phase one. With microstructure characterization, it was observed phases present in these materials microstructure.

Abstract: This paper proposes the reduction of warping after the machining of alloys of brass with lead. For this purpose the brass alloys were submitted to heat treatment and analyzed before and after the machining process. Elongation and dimensional variation, microstructure and chemical microanalysis of the samples were assessed. It was found that warping may be related to the chemical composition of the alloy, added to the rolling process used to obtain the material to be machined. The results showed that heat treatment before the machining process eliminates the warping seen in the workpieces.

Abstract: The present work analyses the microstructure of quenched and cyclic compressed Ti-Mo alloys that possess non-elastic effects and reversible martensitic transformations. Quenched samples were subjected to cyclic compression tests up to 10% strain per cycle. The structure of these alloys, composed of β (BCC) phase with minor participations of α (HC); α (orthorhombic); w (HCC) and α (HC) phases, apparently had suffered a gradual α α α β transformation with increasing Mo content. It was found that the cyclic compression did not promote relevant alterations in the phase composition. Both the alloys electrical resistivity and microhardness were found to be sensitive not only to the Mo content but also to the accumulated deformation. Alloys with 8 and 10% Mo content exhibited low elastic modulus combined with low residual strain, which indicates a possible superelastic behavior.