G.P. Dinda

Pulsed laser deposition of hydroxyapatite thin films on Ti–6Al–4V: Effect of heat treatment on structure and properties

Hydroxyapatite (HA) is an attractive biomaterial that has been widely used as a coating for dental and orthopedic metal implants. In this work, HA coatings were deposited on Ti-6Al-4V substrates by laser ablation of HA targets with a KrF excimer laser. Deposition was performed at ambient temperature under different working pressures that varied from 10(-4) to 10(-1) torr of oxygen. The as-deposited films were amorphous. They were annealed at 290-310 degrees C in ambient air in order to restore the crystalline structure of HA. The coatings morphology, composition and structure were investigated by scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction techniques. Mechanical and adhesive properties were examined using nanoindentation and scratch tests, respectively. The stability of the HA coatings was tested under simulated physiological conditions. This study reveals that the combination of pulsed laser deposition and post-deposition annealing at 300 degrees C have the potential to produce pure, adherent, crystalline HA coatings, which show no dissolution in a simulated body fluid.

Microstructural Characterization of Laser-Deposited Al 4047 Alloy

Direct metal deposition (DMD) technology is a laser-aided rapid prototyping method that can be used to fabricate near net shape components from their CAD files. In the present study, a series of Al-Si samples have been deposited by DMD in order to optimize the laser deposition parameters to produce high quality deposit with minimum porosity and maximum deposition rate. This paper presents the microstructural evolution of the as-deposited Al 4047 sample produced with optimized process parameters. Optical, scanning, and transmission electron microscopes have been employed to characterize the microstructure of the deposit. The electron backscattered diffraction method was used to investigate the grain size distribution, grain boundary misorientation, and texture of the deposits. Metallographic investigation revealed that the microstructural morphology strongly varies with the location of the deposit. The layer boundaries consist of equiaxed Si particles distributed in the Al matrix. However, a systematic transition from columnar Al dendrites to equiaxed dendrites has been observed in each layer. The observed variation of the microstructure was correlated with the thermal history and local cooling rate of the melt pool.

Chemically sensitive free-volume study of amorphization of Cu60Zr40 induced by cold rolling and folding

With the aim to contribute to a microscopical understanding of the processes of solid-state amorphization, the chemically sensitive technique of background—reduced Doppler broadening of positron-electron annihilation radiation in combination with positron lifetime spectroscopy and microstructural characterization is applied to a free volume study of the amorphization of Cu60Zr40 induced by consecutive folding and rolling. Starting from the constituent pure metal foils, a nanosale multilayer structure of elemental layers and amorphous interlayers develops in an intermediate state of folding and rolling, where free volumes with a Zr-rich environment occur presumably located in the hetero-interfaces between the various layers or in grain boundaries of the Cu layers. After complete intermixing and amorphization, the local chemical environment of the free volumes reflects the average chemical alloy composition. In contrast to other processes of amorphization, free volumes of the size of few missing atoms occur...

New Routes for Synthesizing Massive Nanocrystalline Materials

New opportunities for fabricating massive nanocrystalline materials in bulk quantities are required for facilitating the transition of nanocrystalline solids from laboratory samples to technologically relevant materials. Advanced options might be based on combining different nonequilibrium processing routes sequentially, such that an initially metastable state is continuously energized and successively driven farer away from thermodynamic equilibrium. The current paper presents recent results on the evolution of nanoscaled microstructures resulting from combinations of different plastic deformation treatments or of vitrification and severe plastic deformation.

A descriptive framework for additive remanufacturing systems

Additive manufacturing, which is envisioned to transform manufacturing by offering extraordinary levels of customisation and agility, has also been shown to be transformative to remanufacturing. High value end–of–life cores are able to be restored to original equipment manufacturer specifications for a fraction of the price of new production using advanced condition assessment and material deposition technologies. However, this capability is only realised if advanced technologies work in harmony to assess, reprocess, and inspect end–of–life cores. In this paper, we describe a framework for remanufacturing systems that aims to take advantage of additive manufacturing processes to remanufacture end–of–life cores. The presented framework is divided into three critical stages; condition assessment and digitisation, material deposition, and reprocessing and final inspection. Technology advancements and current challenges are discussed for each stage and a case study is presented to further illustrate the three stages of the additive remanufacturing system framework.

Direct Laser Metal Deposition of Eutectic Al-Si Alloy for Automotive Applications

Various additive manufacturing techniques have been able to manufacture Al-Si hypo- and hyper-eutectic alloys but practical implementation of additive manufacturing of Al-Si alloys in automotive industry still remains a big challenge. This paper deals with the challenges of building tall wall and cuboid shapes eutectic Al-Si components by direct laser metal deposition technique for automotive applications. Microstructural investigation using optical and scanning electron microscopy revealed a 99.9% dense component with very fine hypoeutectic microstructure. Tensile test showed an impressive elongation of 9% with an ultimate tensile strength of 225 MPa. This investigation revealed that direct laser metal deposition could be successfully implemented on automotive shock tower hood without any distortion or bending. This paper also presents the effect of various laser deposition parameters like laser power, powder flow rate, and scanning speed on the microstructure and mechanical properties distribution from substrate to deposit.

A comparative study of microstructure and mechanical behavior of CO 2 and diode laser deposited Cu-38Ni alloy

Cu–38Ni alloy was deposited on C71500 (Cu–30Ni) substrates by a laser-aided direct metal deposition technique using CO2 and diode lasers. Structure–property relationships of deposited specimens were investigated by optical microscopy, electron microscopy, X-ray diffraction techniques, and microhardness and tensile measurements. Laser-deposited specimens’ microstructures were primarily dendritic, forming columnar grains growing epitaxially from the substrate and subsequent layers along the preferred crystallographic growth. The grain growth pattern and grain size distribution was significantly different in both specimens. The lattice parameter of the solid solution phase was relatively larger in diode laser-formed specimen; CO2 laser-formed specimens showed relatively higher but non-uniform hardness distribution whereas a very uniform hardness distribution was observed in diode laser formed specimens. Diode laser formed specimens showed higher tensile properties compared to CO2 laser formed specimens which were comparable to C71500 substrates. Microstructure and mechanical behavior were explained based on laser processing parameters.

Deformation processing of massive nanostructured materials

Abstract Deformation processing of initially polycrystalline material can lead to ultrafine-grained or even to nanocrystalline material, depending on the applied deformation route. In addition to different grain sizes, materials processed by different deformation methods also display different thermal stabilities. In order to analyze the impact of defects – particularly dislocations – near the grain boundaries, pure Pd and pure Ni have been processed sequentially by different methods. Transmission electron microscopy investigations at high resolution were conducted to characterize the microstructures of the materials. In addition, geometrical phase analysis was used to locate defects and visualize their strain fields. The results indicate that the presence of a high dislocation density at the grain boundaries increases the stability of the nanocrystalline structure against coarsening.

Microstructure and Mechanical Properties of Laser Deposited Ni/WC Metal Matrix Composite Coatings

In the present study, the feasibility of laser metal deposition of WC reinforced Nickel composite coatings was investigated for the application of hardfacing coating on copper. Ni/60WC MMC were fabricated on the surface of copper with a buffer layer of hastelloy C-276. Additional sets of samples were deposited on a 1020 mild steel substrate. Three principal experiments were conducted in a systematic order to understand the microstructural evolution of Ni/60WC MMC. A multi-track, single-track deposit, and remelting of the as-deposited surface were systematically investigated by optical and scanning electron microscopy. The results revealed microstructural element such as dendrites, equiaxed structure, eutectic structure, and several other complex carbide structures. It was observed that the presence of three principle phases in the deposit consisted of the primary WC, dendritic Ni, and a eutectic structure. Microhardness of the laser deposited samples indicated the gradual variation in hardness as the deposition transits from a highly conductive soft material to a hard facing coating. Homogenization of WC in Ni matrix was well realized in this study.

Microstructural characterization of pulsed laser-deposited hydroxyapatite thin films on TI-6AL-4V

Hydroxyapatite (HA), Ca10(PO4)6(OH)2, the main mineral component of natural bone (∼ 70%), shows the most desirable bone response among the bioactive materials. In the present study, HA coatings of approximately 2–3 µm thickness were deposited on Ti–6Al–4V substrate by KrF excimer laser (λ=248 nm, pulse repetition rate = 10Hz, pulse duration = 20 ns, Laser fluence = 3 J cm−2) ablation of HA targets. The deposition process was carried at room temperature under different chamber pressures (10−1–10−4 Torr of oxygen). The morphology and structure of the deposited layers were studied by scanning electron microscopy and X–ray diffraction analysis. Mechanical and adhesive properties of the coatings were evaluated through the Nanoindentation and scratch test, respectively. The XRD analysis revealed that as-deposited HA film is amorphous. However, for biomedical applications HA coatings should be crystalline, because amorphous HA films easily dissolve in body fluids. The initially amorphous pulsed laser deposited thin films were annealed at 300 °C for 4 h in ambient air in order to restore the crystalline structure. This study reveals that the pulsed-laser deposition followed by post deposition annealing is a promising technique to produce ideal crystalline adherent HA thin films.Hydroxyapatite (HA), Ca10(PO4)6(OH)2, the main mineral component of natural bone (∼ 70%), shows the most desirable bone response among the bioactive materials. In the present study, HA coatings of approximately 2–3 µm thickness were deposited on Ti–6Al–4V substrate by KrF excimer laser (λ=248 nm, pulse repetition rate = 10Hz, pulse duration = 20 ns, Laser fluence = 3 J cm−2) ablation of HA targets. The deposition process was carried at room temperature under different chamber pressures (10−1–10−4 Torr of oxygen). The morphology and structure of the deposited layers were studied by scanning electron microscopy and X–ray diffraction analysis. Mechanical and adhesive properties of the coatings were evaluated through the Nanoindentation and scratch test, respectively. The XRD analysis revealed that as-deposited HA film is amorphous. However, for biomedical applications HA coatings should be crystalline, because amorphous HA films easily dissolve in body fluids. The initially amorphous pulsed laser deposited t...