S.K. Mishra

Bio: S.K. Mishra is an academic researcher from Raja Ramanna Centre for Advanced Technology. The author has contributed to research in topics: Laser rapid manufacturing & Laser power scaling. The author has an hindex of 11, co-authored 15 publications receiving 513 citations. Previous affiliations of S.K. Mishra include Homi Bhabha National Institute.

Investigating laser rapid manufacturing for Inconel-625 components

Abstract: This paper presents an investigation of laser rapid manufacturing (LRM) for Inconel-625 components. LRM is an upcoming rapid manufacturing technology, it is similar to laser cladding at process level with different end applications. In general, laser-cladding technique is used to deposit materials on the substrate either to improve the surface properties or to refurbish the worn out parts, while LRM is capable of near-net shaping the components by layer-by-layer deposition of the material directly from CAD model. In the present study, a high-power continuous wave (CW) CO 2 laser system, integrated with a co-axial powder-feeding system and a three-axis workstation were used. The effect of processing parameters during LRM of Inconel-625 was studied and the optimum set of parameters for the maximum deposition rate was established employing Orthogonal L9 array of Taguchi technique. Results indicated that the powder feed rate and the scan speed contributed about 56% and 26%, respectively to the deposition rate, while the influence of laser power was limited to 10% only. Fabricated components were subjected to non-destructive testing (like—ultrasonic testing, dye-penetrant testing), tensile testing, impact testing, metallographic examinations and micro-hardness measurement. The test results revealed defect-free material deposition with improved mechanical strength without sacrificing the ductility.

Investigations on the influence of composition in the development of Ni-Ti shape memory alloy using laser based additive manufacturing

Abstract: Among the various shaped memory alloys (SMA), nitinol (Ni–Ti alloy) finds applications in automotive, aerospace, biomedical and robotics The conventional route of fabrication of SMA has several limitations, like formation of stable secondary phases, fabrication of simple geometries, etc This paper reports a novel method of fabricating SMA using a laser based additive manufacturing technique Three different compositions of Ni and Ti powders (Ni-45% Ti-55%; Ni-50% Ti-50%; Ni-55% Ti45%) were pre-mixed using ball-milling and laser based additive manufacturing system was employed to fabricate circular rings The material properties of fabricated rings were evaluated using Scanning Electron Microscopy (SEM), Differential scanning calorimeter (DSC), X-ray diffraction (XRD) system and micro-hardness test All the characterized results showed that SMA could be manufactured using the laser based additive manufacturing process The properties of laser additive manufactured SMA (Ni-50% Ti-50%) were found to be close to that of conventionally processed SMA

Laser rapid manufacturing on vertical surfaces: Analytical and experimental studies

Abstract: Analytical and experimental studies on geometrical aspects of the deposited tracks were carried out at different processing parameters for laser rapid manufacturing (LRM) in vertical surface configuration using AISI type 304 stainless steel powder on the substrate of the same material. The vertical downward shift of the deposited track and its peak due to the gravity flow of the melt were found to follow quadratic dependence on the track height. The downward rounded bulging was found to be quite significant for the scan speeds lesser than 200 mm/min, while this was insignificant for the scan speeds more than 400 mm/min. A set of consolidated processing parameters for continuous material deposition was identified. The threshold value of laser energy and powder fed, both per unit traverse length for the continuous deposition were found to be ~ 96 J/mm and ~ 0.006 g/mm respectively. The maximum powder catchment efficiency was ~ 42% for stand-off distances in the range of 15–18 mm. The surface waviness factor was found to decrease from ~ 0.95 to ~ 0.05 when the overlap index was increased from 30% to 80%. The study provides a deeper insight into the ensuing geometrical aspects of the tracks using LRM in vertical configuration.

Solid-Particle Erosion Behaviour of WC/Ni Composite Clad layers with Different Contents of WC Particles

Abstract: We investigated the solid particle erosion behaviour of WC-reinforced Ni-matrix based laser clad layers to improve the performance of engineering components for potential power plant applications. WC-reinforced Ni-matrix based laser clad layers having various compositions of WC (5, 10 and 15 wt%) were deposited on austenitic stainless steel substrates. The laser clad layers were characterised using optical and scanning electron microscopy, microhardness testing and air-jet erosion testing. In solid particle erosion studies using the air-jet erosion tester, the set of testing parameters, including air-erodent compositions, erodent particle velocities and impact angles, was selected by using the Taguchi technique. The morphologies of the worn surfaces were used to predict the wear mechanisms. The results of a microstructural examination of the cross-sections of laser clad revealed a good metallurgical bond between the WC-reinforced Ni matrix and the austenitic stainless steel substrate. Dissociation/partial melting/full melting of WC particles was not observed in the laser clad layers. The microhardness value in the laser cladding zone was between 900–2400 VHN, while it was 230–270 VHN on the substrate. The results of erosion wear studies of the WC-Ni laser clad surface revealed that the erosion behaviour of the WC-Ni laser clad is primarily governed by erodent jet velocity followed by impact angle. The erosion does not much depend on the Ni-concentration in the MMC or the erodent feed rate. The wear signature at the erosion wear surface indicated that the erosion was primarily governed by a ductile erosion mechanism followed by the removal of WC particles from the matrix. The erosion resistance of the Ni-clad layer with WC was found to be at least four times higher than that without WC particles. The quantified contribution of various erosion parameters is useful for function-based design of components with extended service life.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Laser additive manufacturing of metallic components: materials, processes and mechanisms

Abstract: Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM proc...

An overview of Direct Laser Deposition for additive manufacturing; Part II: Mechanical behavior, process parameter optimization and control

Abstract: The mechanical behavior, and thus ‘trustworthiness’/durability, of engineering components fabricated via laser-based additive manufacturing (LBAM) is still not well understood. This is adversely affecting the continual adoption of LBAM for part fabrication/repair within the global industry at large. Hence, it is important to determine the mechanical properties of parts fabricated via LBAM as to predict their performance while in service. This article is part of two-part series that provides an overview of Direct Laser Deposition (DLD) for additive manufacturing (AM) of functional parts. The first part (Part I) provides a general overview of the thermo-fluid physics inherent to the DLD process. The objective of this current article (Part II) is to provide an overview of the mechanical characteristics and behavior of metallic parts fabricated via DLD, while also discussing methods to optimize and control the DLD process. Topics to be discussed include part microstructure, tensile properties, fatigue behavior and residual stress – specifically with their relation to DLD and post-DLD process parameters (e.g. heat treatment, machining). Methods for controlling/optimizing the DLD process for targeted part design will be discussed – with an emphasis on monitored part temperature and/or melt pool morphology. Some future challenges for advancing the knowledge in AM-part adoption are discussed. Despite various research efforts into DLD characteristics and process optimization, it is clear that there are still many areas that require further investigation.

Laser aided direct metal deposition of Inconel 625 superalloy: Microstructural evolution and thermal stability

Abstract: Direct metal deposition technology is an emerging laser aided manufacturing technology based on a new additive manufacturing principle, which combines laser cladding with rapid prototyping into a solid freeform fabrication process that can be used to manufacture near net shape components from their CAD files. In the present study, direct metal deposition technology was successfully used to fabricate a series of samples of the Ni-based superalloy Inconel 625. A high power CO2 laser was used to create a molten pool on the Inconel 625 substrate into which an Inconel 625 powder stream was delivered to create a 3D object. The structure and properties of the deposits were investigated using optical and scanning electron microscopy, X-ray diffraction and microhardness test. The microstructure has been found to be columnar dendritic in nature, which grew epitaxially from the substrate. The thermal stability of the dendritic morphology was investigated in the temperature range 800–1200 °C. These studies demonstrate that Inconel 625 is an attractive material for laser deposition as all samples produced in this study are free from relevant defects such as cracks, bonding error and porosity.