Preplaced Technique Research Articles

Gas tungsten arc cladding on AZ31B magnesium alloy substrate with Al, Co and TiN mixed precursor powders

This present research paper discusses about the fabrication of metal matrix composite coating on AZ31B magnesium alloy substrate with Al, Co and TiN mixed precursor powders by gas tungsten arc (GTA) cladding process. Firstly, Co and TiN powders were mixed properly in the ratio of 1:1. Thereafter, three samples with different compositions of 20 wt% (Co + TiN)), 25 wt% (Co + TiN)), 30 wt% (Co + TiN)) and balance aluminium powder were developed by preplaced technique. The samples were heated by TIG torch at the optimized parameter as current of 110 Amp, voltage of 25 V, welding speed of 4.23 mm/s and thermal energy of 3.12 kJ/cm. After melting and solidification metallurgical bonding between coating and substrate occurs. The microstructure and chemical composition of the coated samples were analysed by field emission scanning electron microscope (FESEM) and energy dispersive spectroscopy (EDS) respectively. The micro hardness of coated samples were analysed by Vickers micro hardness testing. It was found that with increase in percentage content of Co + TiN the amount of microhardness increases. Furthermore, it was found that the value of maximum microhardness was 422 HV0.1, which was nearly seven times higher than that of the magnesium alloy substrate (64 HV0.1).

Microstructure and Mechanical Properties of Metal Powder Treated AISI-430 FSS Welds

An innovative yet simple technique for the inoculation of the weld pool of commercial AISI 430 Ferritic Stainless Steel (FSS) with metal powders for grain refinement is discussed. Aluminum or titanium powder in varying amounts introduced into the weld pool via a powder preplacement technique was melted under a tungsten inert gas (TIG) torch. This strategy of inoculating the welds offers dual benefits of grain refinement and constriction in the weld geometry. The addition of the metal powders constricts the HAZ by as much as 50% of the conventional weld providing a grain refinement index (GRI) of about 0.8 in titanium powder treated welds. It equally emerged that weld property is not influenced by the grain size alone but equally by the amount of delta ferrite in the microstructure.

Influence of niobium on the microstructure and wear resistance of iron-based hardfacings produced by pre-placement technique—a novel approach

This study introduces a novel approach to produce hardfaced alloys via pre-placement technique using the shielded metal arc welding process. The comparison between the microstructural, mechanical, and tribological properties of the Nb-free and Nb-additive hardfacings was characterized by optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray mapping, dry sliding wear, and hardness measurements. From the optical microscopy results, it was observed that the hardfacing alloys obtained by pre-placement technique with premixed powders are free of pores or cracks and show good metallurgical bonding with the substrate. SEM images revealed that the Nb-additive alloys are comprised of net-like carbides in interdendritic region and NbC particles in the matrix with a grain size ranges from 0.5–2 μm, which were found to be beneficial for enhanced hardness and wear resistance. Nb-additive alloy showed 2.63% increase in wear resistance in comparison with the Nb-free hardfacing. It has shown possible to obtain the high hardness and wear-resistant hardfacings with pre-placement technique.

Dry sliding adhesive wear characteristics of Fe-based hardfacing alloys with different CeO2 additives – A statistical analysis

In the present investigation, four different rare earth (RE) additive iron-based hardfacing alloys were prepared by the shielded metal arc welding process with pre-placement technique. The objective was to examine the effect of dry sliding wear parameters and to develop a statistical regression model using full factorial approach. A regression equation was developed and validated with a number of test cases. The morphology of worn surfaces and corresponding wear debris was studied in order to examine the wear mechanism using SEM. The RE additive alloys exhibited a significant improvement in macrohardness and wear resistance. The microstructure was refined at first and then coarsened with the increase of RE additions. The optimal amount of RE was found to be 4wt%.

On the modeling of dry sliding adhesive wear parameters of vanadium additive iron-based alloys at elevated temperatures

Abstract In this paper, three different vanadium additive iron based hardfacing alloys were developed using shielded metal arc welding process with pre-placement technique — a newly developed approach to produce hardfaced coatings. The influence of the increased vanadium content on the hardness and dry sliding adhesive wear characteristics of alloys was investigated. A reciprocating wear test rig was used to study the effect of load and temperature on the alloys having variation in their vanadium content using a full factorial design of experiment approach. The increased vanadium content was found to be beneficial to enhance the macrohardness and adhesive wear resistance of the vanadium additive alloys in comparison to the non-vanadium additive alloy with no evidence of cracks or porosity. A significant reduction in weight loss of alloys containing higher vanadium content was observed from the main effect plots. Based on the significance of interactions, the regression equation was developed and validated with a number of test cases. The optimization of the control factors was also performed using a multi-response optimization technique. The confirmatory tests carried between the predicted and the experimental results exhibited the accuracy of the optimized input variables within ± 4.63% against an output of 0.007 g.

Grain Refinement in Medium Chromium Ferritic Stainless Steel Welds via Aluminum Powder Addition

Grain refinement in medium chromium ferritic stainless steel weld was attempted via elemental (aluminum) powder pre-placement technique prior to melting under a TIG torch. A Box-Behnken experimental design was adopted with current, travel speed and the amount of aluminum powder added as the process factors for producing weld pool. The resolidified weld tracks were characterized using microscopy, microhardness and mechanical testing. The degree of grain refinement achieved was evaluated using a scaling index known as Grain Refinement Index (GRI). The findings showed that the GRI is influenced by the concentration of the aluminum powder introduced into the melt pool. Furthermore, high GRI does not necessarily translate to better mechanical properties relative to the conventional weld. This suggests that the grain size effect might not be the only factor influencing the property of weld metal. However, weld track treated with 0.08mg/mm2 of aluminum powder exhibited about 20% improvement in properties relative to the conventional weld made under the same energy conditions.

Grain Refinement in Medium Chromium Ferritic Stainless Steel Welds via Aluminum Powder Addition

Grain refinement in medium chromium ferritic stainless steel weld was attempted via elemental (aluminum) powder pre-placement technique prior to melting under a TIG torch. A Box-Behnken experimental design was adopted with current, travel speed and the amount of aluminum powder added as the process factors for producing weld pool. The resolidified weld tracks were characterized using microscopy, microhardness and mechanical testing. The degree of grain refinement achieved was evaluated using a scaling index known as Grain Refinement Index (GRI). The findings showed that the GRI is influenced by the concentration of the aluminum powder introduced into the melt pool. Furthermore, high GRI does not necessarily translate to better mechanical properties relative to the conventional weld. This suggests that the grain size effect might not be the only factor influencing the property of weld metal. However, weld track treated with 0.08mg/mm2 of aluminum powder exhibited about 20% improvement in properties relative to the conventional weld made under the same energy conditions.

XRD and XPS studies on surface MMC layer of SiC reinforced Ti–6Al–4V alloy

Overlapping tracks were produced by laser processing using a powder SiC (∼6 μm) preplacement technique which has been developed to modify the surface structure of a Ti–6Al–4V alloy. A continuous-wave CO 2 laser was used for the processing which produced six overlapping tracks covering 14 mm across the surface of a 10 mm thick plate. Under spinning beam conditions, a surface alloyed/metal matrix composite (MMC) layer over 300 μm in depth was produced on the alloy. The surface contained a complex microstructure, but with no cracks and only two pores at the melt/HAZ interface. Using XRD and XPS analysis, it was shown that the solidified melt consisted of α′-Ti, Ti 0.55C 0.45 and Ti 5Si 3 phases, which vary with melt depth and with the particular group of overlapping tracks examined. Therefore, no new phases to those previously identified in single track laser processing experiments were found in this work.

Metal matrix composite layer formation with 3 μm SiC p powder on IMI318 titanium alloy surfaces through laser treatment

Metal surface modification is frequently carried out to increase the life and performance of engineering components that undergo severe service conditions such as wear, erosion and corrosion, without the cost of treating the entire component. The development of a suitable high performance surface layer on substrate materials can combat many surface degradation mechanisms. The formation of an in-situ surface layer MMC by injecting ceramic particulates on laser melted surfaces can, in particular, be used in applications requiring a localised treatment without changing the properties of the bulk material. Using a high volume fraction (25–60vol%) of large (50–150μm) ceramic particles (TiC, SiC) on titanium surfaces, the surface hardness was found to increase between 1.1 to 4 times the base hardness (150 Hv). In the present work, a 5kW continuous wave carbon dioxide laser was used under both helium and nitrogen environments to introduce a smaller volume fraction of 3 μm SiC p particles using the powder preplacement technique on a laser melted IMI318 titanium alloy (Ti-6Al-4V) surface. By changing the laser processing parameters, graded microstructures with hardness gradients were obtained over a melt depth of about 1 mm. The tracks produced surface cracks, but of low intensities (0.1 to 0.3 No./mm). However, in some glazing conditions cracks were absent. Under a helium environment, most of the ceramic particles dissolved in the melt pool, and the microstructure consisted mainly of thread-like particles; some dendrites were also present near the surface and at the edges of the melt pool. Under a nitrogen environment, the tracks produced mostly dendritic structure with no SiC p particles in the melt zone. The hardness developed from a base hardness of 350 Hv to the range 600 to 1200 Hv and 600 to 1450 Hv for tracks processed in helium and nitrogen atmospheres respectively.

Laser processing of an aluminium AA6061 alloy involving injection of SiC particulate

In the present laser processing work, the powder injection technique was investigated as a method for producing a surface metal matrix composite (MMC) containing large SiC particulates (SiCp) (105–150 μm). This size is known to enhance the wear resistance of bulk aluminium-based composites. The effects of the laser-processing conditions, the powder feeding rate and the surface situations necessary to produce a well incorporated MMC on the surface were studied, and the microstructure examined. In previous work, laser processing involving the preplacement of SiCp was developed to create an AI-SiCp (≤45 μm) MMC layer on aluminium alloy surfaces. Some of these ideas were used in conjunction with the injection process in the present work to enhance the surface-wear resistance. The wear resistance of an MMC obtained by a single laser track with the injection technique was determined and compared with the base alloy and the MMC layer produced by the preplacement technique.

Nickel base wide gap brazing with preplacement technique Part 2 - Forl11ation mechanisms of macrovoids

AbstractMicrostructural inhomogeneities and variations in the extent of erosion of base metal in nickel base wide gap brazed joints produced by the preplacement technique with braze mixes of different gap filler contents were investigated, from which the flow behaviour of the braze mix constituents and the formation mechanisms of the various types of macrovoid were deduced. The results show that the formation of various types of macrovoid is closely related to the flow behaviour of the constituents of braze mixes during brazing, the latter in turn being strongly influenced by the braze mix ingredients, the brazing temperature, and the gap depth. For a wide gap brazed joint to be free from macrovoids, the braze mix must be sufficiently viscous to bridge the gap faying surfaces and must flow as a whole into the gap. Braze mixes with gap filler contents of 30–40% are ideal for such requirements. With too Iowa gapfiller content, the molten filler would flow preferentially ahead of the mass-of braze mix, leadi...

Nickel base wide gap brazing with preplacement technique Part 1 - Effect of l11aterial and process parameters on forl11ation of l11acrovoids

AbstractMacrovoids are voids resembling notches or cracks that can act as stress raisers in brazed joints. These are undesirable and should be eliminated if physical soundness of the joint is to be achieved. In the present work, nickel base wide gap brazed joints were produced by the preplacement technique, using Nicrobraz LC and Nicrogap 116 as afiller metal and gap filler, respectively. After brazing, the joints were sectioned depthwise, prepared metallographically, and examined by optical microscopy to detect the presence of macro voids, the latter being defined as voids of characteristic length greater than the mean diameter of gap filler particles in joints made with braze mixes, or larger than one tenth of the width of the gap in joints made with filler metals only. The results showed that three major types of macro void could be identified: irregularly shaped macrovoids throughout the longitudinal section of the joint (type 1); irregularly shaped macrovoids at the tail end of the joint (type 2); an...