Centro de Estudos Municipais e Metropolitanos: CEMME

1 fôlder (4 p.) : color. ; 14 x 21 cmFôlder de apresentação do "Centro de Estudos Municipais e Metropolitanos (CEMME)", departamento da Fundação João Pinheiro (FJP), mostrando seus objetivos e projetos para o segundo semestre de 1996 e primeiro semestre de 1997

Microstructure, texture and tensile behavior of pulsed electrodeposited Ni-Al composites produced using organic additive-free sulfamate bath loaded with Al nanoparticles

Nickel and Ni-Al composites with varying Al nanoparticle content were produced by pulsed electrodeposition using an organic additive-free sulfamate bath. The as-deposited Ni-Al composites exhibited increased compressive residual stresses with increasing Al nanoparticles. Detailed microstructural investigation revealed that Al codeposition led to significant refinement of the columnar morphology and grain structure of Ni matrix along with a texture change from strong to fiber texture parallel to the growth direction. The as-deposited Ni with bimodal grain structure displayed good tensile strength and ductility. The microhardness and tensile strength of the Ni deposits were increased initially with Al content and then decreased at higher particle content. Particle induced grain refinement and texture changes could be related to change in the growth of upcoming Ni nuclei on to the surface of well-dispersed Al nanoparticles. Significant grain refinement and lesser internal stresses along with good particle distribution and relatively harder fiber texture at lower particles concentration collectively contributed to the observed higher strengths in Ni-Al composites as compared to Ni deposits. There was substantial change in fracture morphology from spherical dimples to flat regions with increasing Al content due to agglomeration of nanoparticles at higher particle loading

Pulsed electrodeposition and hardness of microstructurally graded iron

Functionally graded materials (FGM) are designed to acquire a desired spectrum of properties within a material with a gradual variation in either microstructure, composition or porosity across the thickness. Microstructurally graded iron with grain sizes from nanocrystalline/sub-microcrystalline to microcrystalline range can facilitate novel applications which demand an optimum combination of strength and toughness with good corrosion resistance. The present study was aimed at providing methods to synthesize and engineer microstructurally graded iron with ultra-fine and coarse grained structure using pulsed electrodeposition. The effect of various parameters like CaCl2 and saccharin contents in the chloride electrolytic bath, pH of the bath and applied current density on developing the microstructurally graded iron deposits was studied. The CaCl2 concentration in the bath has a profound effect on development of microstructure and crystallographic texture. With increasing current density, pH of the bath and saccharin content, there was significant refinement of the grain structure. The microstructurally graded iron deposit produced under optimized electrodeposition conditions exhibited a gradual variation in hardness ranging from similar to 3 GPa to 10 GPa

Superplasticity in electrodeposited nanocrystalline nickel

Electrodeposited nanocrystalline Ni films were processed with different levels of S, to evaluate the role of S on superplasticity. All the materials exhibited high strain rate superplasticity at a relatively low temperature of 777 K. Microstructural characterization revealed that the S was converted to a Ni3S2 phase which melts at 908 K; no S could be detected at grain boundaries. There was no consistent variation in ductility with S content. Superplasticity was associated with a strain rate sensitivity of similar to 0.8 and an inverse grain size exponent of similar to 1 both of which are unusual observations in superplastic flow of metals. Based on the detailed experiments and analysis, it is concluded that superplasticity in nano-Ni is related to an interface controlled diffusion creep process, and it is not related to the presence of S at grain boundaries or a liquid phase at grain boundaries. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Deformation-induced thermally activated grain growth in nanocrystalline nickel

Grain growth during indentation at low temperatures has been taken to imply that grain growth is largely stress induced and athermal in nanometals. Indentation experiments on electrodeposited nano-Ni indicate clearly that the load required for grain growth decreases with an increase in temperature, suggesting strongly that concurrent grain growth is thermally activated. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

On the exothermic peak during annealing of electrodeposited nanocrystalline nickel

Nanocrystalline metals frequently exhibit poor thermal stability, and the exothermic peak in differential scanning calorimetry is usually attributed to grain growth. We show from experiments on electrodeposited nano-Ni with varying levels of S, and tests with microcrystalline Ni and S powders, that the exothermic peak is associated with the formation of a nickel sulfide phase and concurrent grain growth. Analysis suggests that segregation plays a more important role in limiting grain growth than second-phase particles in nano-Ni. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Effect of initial texture on deformation-induced grain growth in pulsed electrodeposited microcrystalline copper

Owing to the presence of large fraction of grain boundaries, deformation-induced grain growth is commonly observed in fine-grained electrodeposited metals. Here we demonstrate that microcrystalline copper (d similar to 1-10 mu m) with different textures produced by electrodeposition exhibit significant deformation-induced grain growth in tension by coalescence along with twin boundary migration and detwinning. Oriented growth with the formation of a cube texture was noted in the deformed samples. There was an increased fraction of twin boundaries with large angular deviation from Brandon's criterion during deformation

Microstructural stability and superplasticity in an electrodeposited nanocrystalline Ni-P alloy

Stabilization of nanocrystalline grain sizes by second phase particles can facilitate superplasticity at high strain rates and/or low temperatures. A metastable single phase nano-Ni-P alloy prepared by electrodeposition, with a grain size of similar to 6 nm, transforms to a nanoduplex structure at T> 673 K, with similar to 4 vol.% Ni3P particles at triple junctions and within Ni grains. The nanoduplex microstructure is reasonably stable up to 777 K, and the growth of Ni grains occurs in a coupled manner with the growth of Ni3P particles such that the ratio of the two mean sizes (Z) is essentially constant. High temperature tests for a grain size of 290 nm reveal superplastic behavior with an optimum elongation to failure of 810% at a strain rate of 7 x 10(-4) s(-1) and a relatively low temperature of 777 K. Superplastic deformation enhances both grain growth and the ratio Z, implying that grain boundary sliding (GBS) significantly influences the microstructural dynamics. Analysis of the deformation processes suggests that superplasticity is associated with GBS controlled by the overcoming of intragranular particles by dislocations, so that deformation is independent of the grain size. The nano-Ni-P alloy exhibits lower ductility than nano-Ni due to concurrent cavitation caused by higher stresses. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Mechanical characteristics and electrochemical behaviour of electrodeposited nanocrystalline iron and iron-nickel alloy

Interstitial free (IF) steel exhibits high formability but relatively lower strength and poor wear resistance, whereas nanocrystalline materials provide excellent mechanical properties due to their high grain boundary area. The present study is aimed at amalgamation of nanocrystalline materials to IF steels in the form of hard coatings to assess the wear and corrosion resistance. Nanocrystalline Fe and Fe-Ni alloy, with grain size of similar to 25 nm, produced by pulsed electrodeposition were used to investigate micro-wear and electrochemical behaviour. As compared to IF steel, nanocrystalline Fe and Fe-Ni showed nearly five-fold increase in hardness and 50% reduction in wear volume loss. Higher corrosion rates of nano crystalline Fe are kinetically favoured due to high grain boundary region and lack of passive film formation. Alloy deposition of nanocrystalline Fe with Ni (similar to 2.6 wt.%) has proved to be beneficial for improving corrosion resistance without substantial compromise in its wear resistance. (C) 2017 Elsevier B.V. All rights reserved

Microstructure and mechanical behavior of annealed MP35N alloy wire

In a previous paper, the microstructure, monotonic, and cyclic response of as-drawn similar to 100 pm diameter MP35N low-Ti alloy wire were presented and discussed. In this sequel paper, the effects of annealing the same cold-drawn wire on microstructure and mechanical properties are examined. Specifically, segments of the wire were annealed for 1 h at 973 K, 1023 K, 1073 K, 1123 K and 1173 K in a vacuum furnace. The resulting microstructure was characterized by SEM, EBSD and TEM and compared to the asdrawn microstructure. In-situ heating in the TEM of MP35N ribbon in a similarly cold worked condition enabled corroboration of microstructure evolution during annealing. Annealed wires were tested monotonically and cyclically in uniaxial tension at room temperature, the latter using a stress ratio (R) of 0.3. In addition, the annealed wires were tested cyclically at R= -1 using the rotating beam bending fatigue test. Post-deformation structures and fracture surfaces were characterized using TEM and SEM respectively. Annealing the cold drawn wire results in recrystallization and grain growth; the extent is dependent on the annealing temperature. Deformation twin boundaries in the as-drawn structure illustrate faceted bulging and eventually complete elimination, the microstructure evolving into fine equiaxed grains containing coarser annealing twins with no significant change in texture. Yield strength decreases rapidly with recrystallization to almost half the value of the as-drawn condition, but is accompanied by an increase in modulus (by similar to 25%) and tensile elongation reaching 30%. Cyclic response by the way of S-N curves is not enhanced by annealing on an absolute stress scale (due to the loss in yield strength) although the annealed wires are cyclically superior when the stress data are normalized by yield stress. (C) 2015 Elsevier B.V. All rights reserved