Functionally Graded Material (FGM) is necessary for successful performance of two dissimilar materials joint, specifically when there is a large difference in the thermophysical properties of the materials and the joints are subjected to cyclic loading and extreme duty conditions. Laser Additive Manufacturing using Direct Energy Deposition (LAM-DED) is one of the advanced additive manufacturing processes favored for fabrication of FGMs. In the present work, an indigenously developed LAM-DED system is deployed for fabricating FGM of Ni-Cr-B-Si and SS316L. Parametric study is performed by varying the laser power, scan speed and powder feed rate and process parameter combination is identified for depositing uniform and continuous Ni-Cr-B-Si tracks with aspect ratio greater than 5. The identified process parameter combination is deployed for fabricating FGM of Ni-Cr-B-Si and SS316L and the composition of fabricated FGM is confirmed using Energy Dispersive Spectroscopy analysis. The surface topography analysis using Scanning Electron Microscopy indicates that the amount of partially melted powders increases with the increase in concentration of SS316L. Microstructure of as-built deposit is primarily dendritic with fine dendrites of similar to 5 mu m. Micro-hardness and Single Cycle Automated ball indentation (SC-ABI) measurements indicates higher hardness and lower energy storage capacity for Ni-Cr-B-Si rich region as compared to SS316L rich region. The highest microhardness value of 645.23 HV1.96N is observed at the top layer of the graded deposit where Ni-Cr-B-Si fraction is 100%. SC-ABI testing indicates that the energy storage capacity of the material increases with increasing concentration of SS316L with similar trend for maximum displacement of the indenter. Further, LAM-DED deposits are heat-treated in muffle furnace at 900 Deg. C for two hours. The microstructural examination of thus heat-treated samples shows recrystallized grains in the Ni-Cr-B-Si rich region while dendritic microstructure is retained at the SS316L rich region. X-ray diffraction studies shows the difference in the diffraction patterns of as-built and heat-treated deposits with the absence of Ni3B phases in heat-treated samples. Microhardness studies indicate a large difference in hardness values in as-built and heat-treated deposits with a micro-hardness of 255.6 HV1.96N for 100% Ni-Cr-B-Si. SC-ABI studies show that heat treatment improves the energy absorbing capacity of the graded deposit. This study paves a way for the fabrication of Ni-Cr-B-Si and SS316L FGM with tailored mechanical and microstructural properties.

Laser additive manufacturing (LAM) is a laser based solid freeform fabrication method used for “feature based design and manufacturing”. One of the interesting applications of LAM is the fabrication of functionally graded materials (FGM) for joining materials with different thermophysical properties. In the present work, a 2 kW fiber based LAM system is deployed for the fabrication of functionally graded Ni-Cr-B-Si alloy on SS 316L. Functional grading is achieved by varying the composition of NiCr-B-Si alloy and SS 316L. Trial experiments are performed to optimize the process parameters for LAM of Ni-Cr-B-Si layers on preheated substrate of SS 316L with qualification criteria of uniform regular crack free deposit. The microstructure and the mechanical properties are investigated using optical microscopy, microhardness and ball indentation testing. The optical microscopic examination revealed that a uniform regular crack free deposition could be made at optimum process parameters. The microstructural examination revealed the presence of dendritic microstructure at the top most layers. Subsequently, a gradual transition from dendritic to cellular microstructure is observed in lower layers. Vickers microhardness testing showed a gradual decline in the hardness of the sample from Ni-Cr-B-Si to SS 316L. The average hardness of 430.63 HV0.2 of 100% Ni-Cr-BSi is reduced to 185.5 HV0.2 at the substrate. Variation of hardness and energy stored by the material can be clearly observed from Ni-Cr-B-Si to other graded composition through ball indentation studies.

Description: This book covers several key areas in relation to materials processing under the influence of external fields, such as physical phenomena, analytical and numerical models, experimental studies, physical modeling, and the development of new processes. The external fields impacting materials processing include electrical, magnetic and acoustic. Specific processing areas focused on in the book are molten materials processing, solidification processing, and solid state materials processing. A collection of papers from the 2007 TMS Annual Meeting & Exhibition held in Orlando, Florida, February 25 March 1, 2007.

Fretting-fatigue is an important factor influencing service life of turbine blades. The present paper describes laser shock peening of potential crack nucleation site in the root region of steam turbine blade for its enhanced service life. The experimental study, performed with an in-house developed 2.5 J/7 ns Nd:YAG laser demonstrated that laser peening introduced a residual surface compressive stress of −260 to −390 MPa. Case depth of laser peened surface layer was found to be more than 900 μm.

The influence of low energy laser peening on fatigue lives of Ti-6Al-4V was investigated. Laser peening was carried out on Ti-6Al-4V samples. Laser peened samples were characterized by residual stress analysis, surface roughness measurements, X-ray diffraction, optical microscopy, nanoindentation hardness tests, scanning and transmission electron microscopy and fatigue testing. Laser peening resulted in the formation of nanocrystallites on the surface and near surface regions with associated increase in hardness and introduction of compressive residual stress. Owing to positive influence of nanostructured surface and compressive residual stress, fatigue lives of the laser peened samples were significantly increased compared to the unpeened samples.

Fatigue crack propagation, fracture toughness, and impact toughness of AISI 316L stainless steel fabricated by laser rapid manufacturing with a continuous wave CO2 laser have been systematically studied. Charpy impact toughness of laser rapid manufactured structures was found to be on par with its wrought counterpart. Steady state fatigue crack growth rate in laser rapid manufactured compact tension specimens of AISI 316L stainless steel, in the investigated stress intensity range (ΔK) of 11.4–24 MPa √m, was comparable to that of 20% cold worked wrought AISI 316 stainless steel. Fatigue crack propagation was found to be transgranular in nature. The initiation fracture toughness (J 0.2) was found to be in the range of 147–259 kJ/m2 while critical crack tip opening displacement (CTODc) fracture toughness values were found to be in the range of 0.5–0.64 mm. Fracture toughness values of laser rapid manufactured structures, although inferior to wrought 316 stainless steel, were comparable to that of its weld metal.

SAE 9260 spring steel specimens after enduring 50% of their mean fatigue life were subjected to laser shock peening using an in-house developed 2.5 J/7 ns pulsed Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser for studying their fatigue life enhancement. In the investigated range of process parameters, laser shock peening resulted in the extension of fatigue life of these partly fatigue damaged specimens by more than 15 times. Contributing factors for the enhanced fatigue life of laser peened specimens are: about 400 mu m thick compressed surface layer with magnitude of surface stress in the range of -600 to -700 MPa, about 20% increase in surface hardness and unaltered surface finish. For laser peening of ground steel surface, an adhesive-backed black polyvinyl chloride (PVC) tape has been found to be a superior sacrificial coating than conventionally used black paint. The effect of repeated laser peening treatment was studied to repair locally surface melted regions and the treatment has been found to be effective in re-establishing desired compressive stress pattern on the erstwhile tensile-stressed surface. (C) 2013 Elsevier Ltd. All rights reserved.

An experimental study was performed for non-destructive microstructural characterisation of laser surface treated AISI 1040 steel specimens with a portable X-ray diffraction based residual stress analysis system. Laser treated specimens were characterised by residual stress and (211) ferrite peak width measurements, and results were compared with those obtained by optical microscopy. The techniques were sensitive enough to distinguish four different cases arising during laser surface treatment, namely, no transformation hardening, insufficient hardening, adequate transformation hardening and surface melting. On the laser treated surface, the extents of laser melted zone and various microstructural zones of solid state transformation hardened region could be clearly identified. Although both the techniques provided fair estimate of total width of laser treated region, ferrite peak width is a more sensitive parameter to record microstructural transitions involving change in tetragonality of martensite. The technique has a potential for in situ microstructural analysis of ferritic steel weldments.

Fatigue is a major life limiting factor affecting service life of low pressure steam turbine blades which, depending on turbine rating, are generally made of martensitic stainless steel or Ti6Al4V alloy. The results of the present study has demonstrated that with respect to conventional shot peening, laser peening brought more than two times longer mean fatigue life of Ti6Al4V alloy. Enhanced fatigue performance of laser peened specimens was attributed to the deeper peened layer and smoother finish. In the case of DIN X20Cr13 stainless steel, laser peening did not register significant improvement in fatigue resistance over shot peening. At maximum test stress of 550MPa, DIN X20Cr13 stainless steel specimens, shot peened and laser peened specimens exhibited comparable fatigue lives. However, at lower magnitude of maximum test stress of 400MPa, laser peened specimens displayed about 30% longer fatigue lives than their shot peened counterparts. Similar fatigue lives of shot peened and laser peened specimens of DIN X20Cr13 stainless steel specimens is attributed to comparable magnitude of surface residual stress and case depth produced by the two peening treatments.

Present experimental laser shock peening study on SAE 9260 spring steel, performed with an in-house developed 2.5J/7ns pulsed Nd:YAG laser, aimed to evaluate laser shock peening process as a possible alternative to existing shot peening practice for enhancing fatigue life of leaf springs. In the investigated range of process parameters, laser shock peening yielded largely comparable magnitude of surface compressive stress and shallower compressed surface layer than those achieved with existing shot peening practice. In contrast to considerably rougher shot peened surface with numerous defects, laser shock peening produced largely unaltered surface finish without peening-induced defects. With respect to shot peening, laser shock peening brought about significant increase in fatigue life. Improved fatigue performance of laser shock peened specimens is attributed to their better surface finish without peening-induced surface defects, which were potential fatigue crack nucleation sites in shot peened specimens.

This work deals with the influence of laser peening on the fretting wear behavior of Ti-6Al-4V. Laser peening was carried out on Ti-6Al-4V. The laser-peened surface was characterized by transmission electron microscopy. Surface roughness, nanoindentation hardness, residual stress, and tensile properties of the material in both laser-peened and unpeened conditions were determined. Fretting wear tests were conducted at different normal loads using a ball-on-flat contact geometry. Laser peening resulted in the formation of nanocrystallites on the surface and near-surface regions, increased hardness, and compressive residual stress. Laser peening did not affect the tensile properties and surface roughness significantly. There was no considerable difference between the values of the tangential force coefficient of laser-peened and unpeened samples. The fretting scar size, wear volume, and wear rate of laser-peened specimens were lower than those of unpeened samples. This may be attributed to an increase in surface hardness due to strain hardening and grain refinement at the surface and near-surface regions, higher compressive residual stress, and higher resistance to plastic deformation of laser-peened samples.

Laser shock peening usually requires the presence of a sacrificial coating to protect the substrate from undesirable thermal effects generated by laser irradiation. This paper describes an experimental study to identify an adherent sacrificial coating for laser peening of smooth metallic surfaces where black paint does not adhere well. Normal black polyvinyl chloride electrical insulation tape has been found to be a good choice as a sacrificial coating. Laser peening with black insulation tape generated effective laser peening in three different substrates, namely, Ti6Al4V alloy, SAE 9260 spring steel and DIN X20Cr13 martensitic stainless steel. The depth of peening was comparable or better than that generated with black paint. With respect to widely used black paint, black insulation tape not only provides clean, simple and uniform coating but also literally eliminates the time involved in its application (black paint requires multilayer coating with long intermediate curing periods) and removal.

TiC reinforced with Al13Fe4 matrix composite layer is produced on Al–Si alloy using 5kW CO2 laser. This attempt was made to identify the suitable coating compositions and laser processing parameters needed to form a TiC–Al13Fe4 composite layer. The study intended to form a composite layer which is having uniform TiC distribution, high hardness, high wear resistance and good adherence with substrate of Al–Si alloy. The results confirmed that the expected good quality composite layer has formed for the coating compositions of 75TiC–25Fe (wt%) and laser processing parameters of 2.5kW laser power and 1.5mmin−1 scanning speed. TiC particles size varies from 10 to 20μm are reinforced with in-situ formed Al13Fe4 matrix in the composite layer. The good quality composite layer is exhibited an average hardness of about 750HV and hardness distributions show very minimum fluctuations. The effect of TiC reinforcement with Al13Fe4 matrix in the composite layer displayed very less wear rate (3.98×10−7mgm−1) than the substrate (3.85×10−6mgm−1).

The present study was conducted with the objectives of investigating antidiarrhoel activity of Vernonia cinerea whole plant (Family Compositae), collected from tarai region of Uttarakhand. The plant extracts were o btained via cold extraction method. For the purpose of evaluating antidiarrhoel efficacy of methanolic extract of the plant, rats were used as test animal. The time of onset of fir st wet faeces increased significantly and dose dependently by the extract. I t was excellent at higher doses (100 & 200 mg/kg body wt., orally). It indicated reduction in peristaltic movement of gastro intestinal tract of animals. The antidiarrhoel activity was further confirmed by its significant and dose dependent decrease in nu mber of wet faeces and number of total faeces in comparison to rats used as control.

The present paper describes an experimental hybrid welding study, involving CO2 laser and gas tungsten arc welding, on 6 mm thick austenitic stainless steel sheet. The study focused on real-time plasma monitoring during welding and metallographic examination of the resultant weldments. Coupling of laser-generated plasma and gas tungsten arc was achieved by introducing argon cross jet. The results of the study demonstrated that for obtaining deep hybrid welds, incident laser power density should be above a threshold to generate metal plasma on its own. An increase in arc current with laser power density below the threshold value resulted in broader conduction-limited welds without causing much change in the weld depth. Coupling of arc with laser also served to stabilize and enhance metal plasma formation, which, in turn, facilitated stabilization of the resultant welding process. Best hybrid welds were achieved when arc followed laser beam along the direction of welding.

Present paper describes microstructural and mechanical characterization of laser-clad composite joint made of Stellite 21 and type 316L stainless steel (SS). The study has been broadly performed on two kinds of laser-clad specimens viz. (i) involving direct deposition of Stellite 21 on SS and (ii) involving gradient in chemical composition across substrate/clad interface. Both kinds of specimens exhibited nearly similar tensile strength, which was higher than that of SS in the interface region. Inter-dendritic carbides provided low energy fracture path in laser-clad deposits of Stellite 21. Both direct and graded interfaces of laser-clad specimens exhibited superior fatigue strength than the SS substrate. Instrumented impact testing brought out distinct difference in the mode of crack propagation across direct and the graded clad specimens. In contrast to initiation-controlled brittle crack propagation across the interface region in “direct clad” specimens, crack propagation across “graded interface” was marked with significant plastic deformation.

An attempt was made to produce WC-iron silicide cladded layer on AISI 316L stainless steel by laser processing to obtain high hardness and lesser variations in hardness distribution in the layer. Different compositions of coating materials (WC, Si and Ni) and laser processing parameters were used. A good and defect free cladded layer of WC-iron silicide was obtained for an energy density of 22.5 J/mm(2) and coating composition of 40WC-40Si-20Ni (wt.%). The layer exhibited average hardness of about 883 HV with lesser variations in the hardness distribution and also higher wear resistance compared to the substrate. (C) 2008 Elsevier B.V. All rights reserved.

This paper deals with the study of Al-Si alloy laser melted with variable constituents of TiC and Fe coatings to generate TiC reinforced with Fe-Al matrix composite layer on it. This experimentation deals with the investigation of the quality of the composite layer generated by varying the process parameters and the coating composition. A superior composite layer is established when the variable processing parameters were of 2.5kW laser power and 1.5 m/min. scan speed for the coating composition of 25Fe-75TiC wt.%. This layer which consists of TiC reinforcement with Al-Fe matrix shows an average microhardness of about 750 HV and also exhibits pore and crack free surface. Bonding strength of the composite layer is also examined by the hardness test.