Autor: JORGE LEOBARDO ACEVEDO DAVILA
This research examined the influence of process parameters influencing the deposit of a coating structure Diamalloy 1008 (FeCrMo alloy mixture) applied by oxyfuel highspeed (HVOF) on steel samples grade D2 tool. This type of coating is commonly used as protection against wear and corrosion. But it has the ability to rebuild areas damaged by weathering and erosion. The formulation of the mathematical model of the temperature with respect to the deposition of repair material on the substrate prior to impact, to assess the behavior of the particle trajectory, in order to predict the behavior under the conditions of liquid, slurry and solid.
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The austenitic stainless steels of type 304L are alloys which have carbon content below 0.03%.
Applications of this stainless steel includes tubing for cooling systems in the automotive industry. The
present study was conducted to evaluate the effect of variables involved in welding operations by the
GTAW process of an austenitic stainless steel pipe grade 304L on characteristics as penetration and
mechanical properties. Some variables to consider are travel speed and shielding gas mixture. An
analysis of variance was used to determine which variable promotes the greatest impact in this process.
According obtained results, hydrogen content has an important effect on penetration; mechanical
properties were not affected by changing considered variables.
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Transient liquid phase (TLP) bonding of 304 stainless steel with nickel based filler metal, BNi-9, was performed to
study the influence of silicon nanoparticles (NPs) on the mechanical and structural properties of the bonding area.
It was found that silicon NPs act as a melting point depressant in the brazing process; the formation of silicon TLP
induces the dissolution of elements of the metal filler and promotes a uniform distribution in the bonding area.
Silicon NPs induce the development of smaller eutectic structures in the melting zone; it has been related to
microhardness measurements, which are lower when the silicon NPs are used in the brazing process.
The truck assembly used in the mining industry involves a considerable amount of welding
applications, where the materials that have to be joined differ in metallurgical and mechanical
properties. The complexity in the analysis of these joints increases when the welding is developed on
large thickness plates, in which are necessary to apply a controlled sequence of welding beads (multi
pass welding). This paper presents an analysis by finite element method of the evolution in the thermal
history, microstructure and strain produced by a multipass Gas Metal arc welding process, applied to
the welded joint of Hardox 400 and ASTM 514 plates. Besides this a comparison between the
analytical results and experimental data was made, and it was found that this method can be efficiently
used to accurately determine appropriate welding parameters of such components.
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Aluminum/Graphite composites (Al/C composites) have the advantages of Al (light weight, easy
machinability and good heat conduction) in combination with the advantages of C whiskers (High
Youngs Modulus, small to negative CTE, high tensile strength and high thermal conductivity).
However, Metallographic analysis, EDX and microhardness profile revealed that fibers react with
molten aluminum to form the detrimental Al4C3 phase in the HAZ and fusion zone. In order to gain
information about temperature transformation and formation conditions, scanning electron microscopy,
and termochemistry analysis were used. For experiments, were used power density (I), pulse width (t),
frequency (F), travel speed (S) and filler material (M) as independent variables. Thereby, was found
that the main process variables that influence the formation of Al4C3 are pulse duration and welding
speed, and that the effect of these variables cannot be explained only by using a thermodynamic model,
requiring a subsequent kinetic analysis.
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Tungsten nanoparticles (NP's) were impregnated in fractured samples of a Co-based alloy in order to evaluate their effect over the microstructure of the joint during a brazing process. The structure and morphology of the tungsten NP's were characterized by high resolution transmission electron microscopy (TEM). The brazing filler metal selected for this work was Nicrobraz 210 and it was characterized by scanning electron microscopy (SEM) and Spectrometry X-Ray Fluorescence. Cracks were generated in Co-based alloy rectangular samples of 10 mm x 10mm x 60 mm by bending them with a mechanical testing machine; these fractures were inspected by SEM. For the impregnation of the cracks with NP's, a mixture of 0.5 g of tungsten NP's in 100 ml of ethanol was sonicated for 15 min. This sonicating time promotes the diffusion of tungsten inside the microcracks. The 210-S filler metal was used in the cracked samples with and without tungsten NP's impregnation. The brazing process was conducted in a sealed tube furnace under an Ar gas flow at 1200 °C for 60 min.Brazed samples were analyzed by optical microscope and SEM. The interaction of tungsten nanoparticles with the metallic filler in the melting zone modified the size and the morphology of the formed phases into a finer and uniformly distributed microstructure.
tTungsten nanoparticles of 80 nm average particle size were utilized in the brazing of 304 stainless-steels.The nanoparticles were characterized by DTA and TEM, and the brazed samples were evaluated by SEMand Vickers microhardness tests. The interaction of the tungsten nanoparticles with the metallic fillerin the melting zone modified the size and morphology of the formed phases into a finer and uniformlydistributed microstructure. In samples treated at 1200◦C for 60 min, the microhardness decreased from310 to 170 HV, being the latter value, close to that of the base metal. The nanoparticles and the microcracksdevelop a synergistic effect when they are in contact with the liquid phase in such a way that a rise inthe threshold capillary-pressure leads to the filling of the interstices. The capillary-like system resultingfrom the wettability of the nanoparticles and microcrack surfaces by the liquid phase, leads to a solidifiedmicrostructure with fine and uniform phase distribution.