| dc.description.abstract | Metals and alloys are extensively used to prepare a wide variety of biomedical implants. The commonly employed materials are stainless steel (SS), cp-Ti, Ti-6Al-4V, etc., because of their biocompatibility and corrosion resistance. The implants that are currently used are manufactured using conventional metal processing techniques such as deep drawing, casting, rolling, forging, grinding, moulding or hydro forming. As a consequence, all the implants produced have defined geometries with little scope for variation. However, patient anatomy varies significantly based on age, gender, physique, etc., and requires patient-specific customizable implants. With the advancements in the field of manufacturing, various additive manufacturing techniques have become viable to 3D print parts with complex and tailored geometries. Selective laser melting (SLM) is a popular additive manufacturing technique where the laser serves as the heat source. The parts printed by SLM exhibit limitations like porosity, micro-cracks, tensile residual stresses, unfavorable microstructure and surface roughness, etc. This thesis described two novel strategies that were employed to overcome these limitations of SLM: 1) heat treatment to induce globularized bimodal microstructure for maximum toughness, and 2) surface mechanical attrition treatment (SMAT) to enhance the surface properties. The thesis is organized in various chapters as follows.
In Chapter 1, a literature review of additive manufacturing and its advantages, applications and limitations have been discussed. The literature reports to overcome these limitations have been mentioned. Also presented is the background of the two strategies employed in this work, i.e., heat treatment and surface mechanical attrition treatment leading up to the genesis of thesis.
In Chapter 2, details of experimental procedures and characterization techniques have been mentioned that are commonly employed in the entire work.
In Chapter 3, the globularization induced in the SLM Ti-6Al-4V alloy after heat treatment to enhance the strength and ductility has been described. This part discusses an innovative strategy to obtain the bimodal microstructure consisting of globular α in additively manufactured Ti-6Al-4V alloy by heat treatment alone. The heat treatment schedule involves repeated thermal cycling close to but below the β transus temperature to form globular α eliminating the need for plastic deformation prior to heat treatment. A mechanism is proposed to explain the formation of globular α. The bimodal
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microstructure thus produced led to a significant improvement in the ductility by 80% and the toughness by 66 %, which are desirable for structural applications
In Chapter 4 the effect of SMAT on SLM Ti-6Al-4V alloy has been investigated. The as-printed samples were shown to have low hardness, weak texture, tensile residual stresses at the surface, poor fatigue performance, low wear resistance, highly rough surface and low cell attachment. Hence, to enhance the performance, the changes in the surface properties in response to SMAT were carried out. The SMAT treatment was found to enhance the hardness by 37 %. Increase in hardness at the surface led to increase in wear resistance. The SMAT treatment has imparted favorable compressive residual stresses at the surface. These improved the fatigue performance. The SMAT has enhanced the cell response considerably. The corrosion resistance has lowered slightly after SMAT because of increase in number of defects and charge carrier density.
In Chapter 5, all the outcomes of this work have been compiled the scope of the future work has also been discussed briefly | en_US |
