Sameehan S. Joshi

Laser assisted high entropy alloy coating on aluminum: Microstructural evolution

High entropy alloy (Al-Fe-Co-Cr-Ni) coatings were synthesized using laser surface engineering on aluminum substrate. Electron diffraction analysis confirmed the formation of solid solution of body centered cubic high entropy alloy phase along with phases with long range periodic structures within the coating. Evolution of such type of microstructure was a result of kinetics associated with laser process, which generates higher temperatures and rapid cooling resulting in retention of high entropy alloy phase followed by reheating and/or annealing in subsequent passes of the laser track giving rise to partial decomposition. The partial decomposition resulted in formation of precipitates having layered morphology with a mixture of high entropy alloy rich phases, compounds, and long range ordered phases.

Amorphous Coatings and Surfaces on Structural Materials

Metallic glasses show a unique combination of high strength, excellent corrosion, and wear resistances because of their amorphous structure having a short-range order. In spite of excellent properties, the application of metallic glasses is restricted because of their inherent limitations in the bulk form, including limited tensile ductility. Using metallic glasses as the coatings for structural applications is an attractive way of taking advantage of their superior properties. Additionally, metallic glass-based composites having crystalline phases embedded in a amorphous matrix have also shown improved properties. Thus, metallic glasses can be synthesized as the coatings or subjected to surface modification to provide functionally superior surfaces. This article is a review of metallic glass-based coatings and surface modification of metallic glasses to achieve functionally superior surfaces for structural applications. Essential theoretical concepts were discussed which influence the processing. Common ways of processing along with the influence of various processing parameters were explored. Some non-conventional techniques which emerged as a result of continued efforts were also taken into account. Corrosion and wear properties of these materials along with the underlying mechanisms were discussed in detail. Focus was given to the recent product level applications explored in the open literature. Current challenges in the field were reviewed and guidelines for the future developments were provided.

Dynamic crystallization during non-isothermal laser treatment of Fe–Si–B metallic glass

Fe–Si–B metallic glass foils were subjected to non-isothermal laser treatment to induce crystallization, and the effect of laser fluence on crystallite size was investigated. Temperature, and corresponding heating and cooling rates generated during laser processing of metallic glass were estimated using multiphysics computational models. Estimation of the onset and arrest temperatures of crystallization was based on the results obtained using the thermal model. Crystallite size was measured with the aid of x-ray diffraction and transmission electron microscopy. The fraction of crystallization was estimated with a differential scanning calorimetry. Crystallite size increased with laser fluence in the initial stages and saturated later within the laser fluence range (0.6–0.9 J mm−2) explored in the current efforts. The fraction of crystallization steadily increased with the increase in laser fluence. Unlike conventional processes, in the present situation the dynamic effects during laser processing dominated the crystallization and growth process. Rapid heating rates during laser processing led to a shift in the onset of crystallization temperature to a higher level. Faster cooling rates prematurely arrested the crystallite growth yielding much finer crystallite sizes.

Tensile behavior of laser treated Fe-Si-B metallic glass

Fe-Si-B metallic glass foils were treated with a linear laser track using a continuous wave Nd-YAG laser and its effect on the overall tensile behavior was investigated. Microstructure and phase evolutions were evaluated using X-ray diffraction, resistivity measurements, and transmission electron microscopy. Crystallization fraction was estimated via the differential scanning calorimetry technique. Metallic glass foils treated with the lower laser fluences (<0.49 J/mm2) experienced structural relaxation, whereas higher laser fluences led to crystallization within the laser treated region. The overall tensile behavior was least impacted by structural relaxation, whereas crystallization severely reduced the ultimate tensile strength of the laser treated metallic glass foils.

Machining of Bone and Hard Tissues

This book provides an in-depth review of state-of-the-art orthopaedic techniques and basic mechanical operations (drilling, boring, cutting, grinding/milling) involved in present day orthopaedic surgery. Casting a light on exploratory hybrid operations, as well as non-conventional techniques such as laser assisted operations, this book further extends the discussion to include physical aspects of the surgery in view of material (bone) and process parameters. Featuring detailed discussion of the computational modeling of forces (mechanical and thermal) involved in surgical procedures for the planning and optimization of the process/procedure and system development, this book lays the foundations for efforts towards the future development of improved orthopaedic surgery. With topics including the role of bone machining during surgical operations; the physical properties of the bone which influence the response to any machining operation, and robotic automation, this book will be a valuable and comprehensive literature source for years to come

Crystallisation behaviour during tensile loading of laser treated Fe–Si–B metallic glass

Effect of tensile loading on crystallisation behaviour of as-cast and laser thermal treated Fe–Si–B metallic glass foils was investigated. Tensile loading lacked any marked influence on the crystallisation behaviour of as-cast and structurally relaxed laser-treated metallic glass foils. Furthermore, the average crystallite/grain size in partially crystallised laser-treated metallic glass foil was nearly equal to the average crystallite/grain size in the region away from the fracture of the same partially crystallised laser-treated metallic glass foil after tensile loading. However, a significant crystallite/grain growth/coarsening of the order of two and half times was observed in the fractured region compared to the region around it for the laser-treated partially crystallised metallic glass foils. The simultaneous effects of stress generation and temperature rise during tensile loading were considered to play a key role in crystallite/grain growth/coarsening.

Potential Automation of Bone Machining

The ultimate aim of research related to surgery is to reduce human dependency during operational procedures. The current chapter focuses on such automation efforts undertaken in the field of bone machining. State of the art in the field has been presented. The need for such efforts arises from the fact that involvement of human being in the surgery as an operator requires a lot of experience to develop the precise skills and it always involves a risk of human error. Another important aspect is the constraint on geometry which can be machined in manual operation. With this background, the efforts related to automation and robotics in the field of bone machining are described.

Temperature Evolution During Bone Machining

The heat evolved during any machining operation as a secondary effect (in mechanical machining) and/or primary or inherent effect/source (in beam based machining) results in temperature increase of the bone.

Computational Modeling in Bone Machining

In general machining of materials is a complex process involving several process and material parameters. During machining, multiple physical phenomena are associated with combination of these process and material parameters. These physical phenomenon may occur simultaneously or in sequence rendering the process of machining very complex.

Non-conventional and Hybrid Methods of Bone Machining

Having explored the basics of important fundamental contact (mechanical) and non-contact (thermal) operations involved in machining of the bones, the discussion will proceed towards some of the non-conventional techniques.