Microstructure evolution during warm deformation of low carbon steel with dispersed cementite

The microstructure evolution and mechanical behavior during large strain of a 0.16%C-Mn steel has been investigated by warm torsion tests. These experiments were carried out at 685°C at equivalent strain rate of 0.1 s . The initial microstructure composed of a martensite matrix with uniformly dispersed fine cementite particles was attained by quenching and tempering. The microstructure evolution during tempering and straining was performed through interrupted tests. As the material was reheated to testing temperature, well-defined cell structure was created and subgrains within lath martensite were observed by TEM; strong recovery took place, decreasing the dislocation density. After 1 hour at the test temperature and without straining, EBSD technique showed the formation of new grains. The flow stress curves measured had a peculiar shape: rapid work hardening to a hump, followed by an extensive flow-softening region. 65% of the boundaries observed in the sample strained to ε = 1.0 were high angle grain boundaries. After straining to ε = 5.0, average ferrite grain size close to 1.5 μm was found, suggesting that dynamic recrystallization took place. Also, two sets of cementite particles were observed: large particles aligned with straining direction and smaller particles more uniformly dispersed. The fragmentation or grain subdivision that occurred during reheating and tempering time was essential for the formation of ultrafine grained microstructure.

Avaliação do comportamento mecânico sob deformação da liga Ti- 30Ta visando aplicações biomédicas

Titanium and its alloys have been used for biomedical applications due their excellent properties such as high corrosion resistance, biocompatibility and mechanical properites. In this study, microstructural and mechanical properties of Ti-30Ta alloy was evaluated during its processing. Ti-30Ta alloy ingots were produced from sheets of commercially pure titanium (99.9%) and tantalum (99.9%). Its melting was realized in arc melting furnace in an argon atmosphere. After homogenizing at 1200ºC, ingots were cold worked by swaging. Samples with 13 mm in diameter were obtained. They were forging at the reduction ratios of 15%. After deformation, microstructure was evaluated by optical microscopy in each condition. Also, Vickers microhardness of samples was measured and phase constitution was evaluated using XRD analysis

Changes of microstructure in alpha AgZn during post-deformation annealing after cold-rolling

The annealing processes of deformation-induced defects after cold-rolling to about 30 and 60% thickness reduction were investigated for Ag-21, 23, 28 at% Zn by means of residual electrical resistivity, microhardness, light microscopy and transmission electron microscopy (TEM) Three annealing stages have been detected and consistently interpreted as annealing-out of mainly point defects and their agglomerates (stage I), formation of dislocation cells and recrystallized strain-free grains (stage II) and grain growth (stage III). Further, it is tried to determine the evolution of defect production (point defects and dislocations) during rolling deformation from measured changes of electrical resistivity and microhardness. Copyright (C) 1996 Acta Metallurgica Inc.

Microstructural Characterization of Ti-6Al-7Nb Alloy After Severe Plastic Deformation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Different responses in bulk density and saturated hydraulic conductivity to soil deformation by logging machinery on a Ferralsol under native forest

Ferralsols have high structural stability, although structural degradation has been observed to result from forest to tillage or pasture conversion. An experimental series of forest skidder passes in an east Amazonian natural forest was performed for testing the effects of mechanical stress during selective logging operations on a clay-rich Ferralsol under both dry and wet soil conditions. Distinct ruts formed up to 25 cm depth only under wet conditions. After nine passes the initially very low surface bulk density of between 0.69 and 0.80 g cm(-3) increased to 1.05 g cm(-3) in the wet soil and 0.92 g cm(-3) in the dry soil. Saturated hydraulic conductivities, initially > 250 mm h(-1), declined to a minimum of around 10 mm h(-1) in the wet soil after the first pass, and in the dry soil more gradually after nine passes. The contrasting response of bulk density and saturated hydraulic conductivity is explained by exposure of subsoil material at the base of the ruts where macrostructure rapidly deteriorated under wet conditions. We attribute the resultant moderately high hydraulic conductivities to the formation of stable microaggregates with fine sand to coarse silt textures. We conclude that the topsoil macrostructure of Ferralsols is subject to similar deterioration to that of Luvisols in temperate zones. The stable microstructure prevents marked compaction and decrease in hydraulic conductivity under wetter and more plastic soil conditions. However, typical tropical storms may regularly exceed the infiltration capacity of the deformed soils. In the deeper ruts water may concentrate and cause surface run-off, even in gently sloping areas. To avoid soil erosion, logging operations in sloping areas should therefore be restricted to dry soil conditions when rut formation is minimal.

Effect of heat treatment on microstructure and mechanical properties of Ti-5wt-%Ni alloys for use as biomaterial

Titanium alloys are among the most important and frequently used class of biomaterials. In addition to biocompatibility, it is important that an implant material present satisfactory mechanical properties that allow long term use in the body. To improve such properties, different heat treatments are used, as well as doping with oxygen. The presence of interstitial oxygen in the crystal lattice causes deformation, increases the hardness, and causes modifications in anelasticity, thereby decreasing the elastic modulus. In this study, an alloy was prepared by arc melting precursor metals, heat and mechanically treated, and doped with oxygen, resulting in samples with different processing conditions. In each condition, the alloy was characterised in terms of amount of oxygen, X-ray diffraction, and optical microscopy. In addition, properties of the alloy, such as hardness and elastic modulus, were analysed.