Comparison of Two Metallic Additive Manufacturing Technologies: Selective Laser Melting and Electron Beam Melting

This general review paper compares two powder-bed fusion metallic additive manufacturing processes. The method is by reviewing past literature from sources such as scientific databases, journals, conferences and webpages. The scope of this review is on the selective laser melting and electron beam melting additive manufacturing method. The findings have shown large advances in the manufacturing quality of these two methods commercially. This review thus facilitates the choice of using either a laser based or electron based method for a given application.Published versio

The Singapore bond market : its development and future directions.

The purpose of this project is to investigate the underlying factors that are hindering the development of the Singapore Bond Market and to solicit recommendations from the professionals in the industry on ways to help this development

A Hot Cross Bun sign from diffusion tensor imaging and tractography perspective

A "Hot Cross Bun" sign on T2-weighted MRI was described as a result of selective loss of myelinated transverse pontocerebellar fibers and neurons in the pontine raphe with preservation of the pontine tegmentum and corticospinal tracts (CST). However, neuropathologic studies showed contradicting results with no sparing of the CST. This is a pictorial and quantitative demonstration of the sign on diffusion tensor imaging and tractography, which provides the imaging evidence that is consistent with neuropathologic findings

Geometrical-based characterisation of complex ti-6al-4v parts fabricated by selective electron beam melting

In an additive manufactured metallic part, distinct and different microstructure and mechanical properties may exist on different areas due to differences in shape and location. Two parts, one with straight-finned structure and one with curvefinned structure, were fabricated by selective electron beam melting method using prealloyed Ti-6Al-4V powder. Microstructural characterization of these two parts that have varying fin thickness and shape were carried out in order to investigate the synthetically influence of build geometry and in-fill hatching strategy on selective electron beam melting. It was found that the β-spacing is larger in the curve-finned structure, leading to a lower micro-hardness as compared to the straight-finned structure. It suggests a slower cooling rate in the curve-finned structure due to the differences in build geometry and infill hatching strategy.Published versio

Revealing competitive columnar grain growth behavior and periodic microstructural banding in additively manufactured Ti-6Al-4 V parts by selective electron beam melting

Powder-bed fusion additive manufacturing of Ti-6Al-4 V has been of tremendous interest in both academia and industry. As the two ubiquitous microstructural features, columnar grain and microstructural banding in selective electron beam melting of Ti-6Al-4 V are systematically studied by experimental and simulation methods. Three basic build geometries (i.e. V-, I- and A-shaped parts) are employed to study the columnar grain growth behavior. We find that columnar prior β-Ti grains grow epitaxially and competitively by following the classic competitive grain growth model in additive manufacturing of Ti-6Al-4 V. It results in increasingly stronger crystallographic texture with the rising build height. We also observe the consistently occurring microstructural banding (∼100 µm in period) normal to build direction due to the overlapped heat affected zones that are formed in the layerwise thermal cyclic process. In addition, a large quantity of sub-columnar grains exist within the microstructure for selective electron beam melted Ti-6Al-4 V. It is demonstrated that the periodic microstructural banding determines the appearance of sub-columnar grains which may affect the competition behavior for the growth of columnar grains.NRF (Natl Research Foundation, S’pore)Accepted versio

Anisotropy and heterogeneity of microstructure and mechanical properties in metal additive manufacturing: A critical review

Metal additive manufacturing (AM) has developed rapidly over the last decade to become a disruptive technology capable of revolutionizing the way that products from various industrial sectors such as biomedical, aerospace, automotive, marine and offshore are designed. Early adopters of the technology like the biomedical and aerospace industries have shown that the better-designed components offer substantial performance improvements over current designs. However, in-depth and comprehensive views on the microstructure and mechanical properties of additively manufactured metals and alloys are less reported. To realize the full design potential that metal AM can offer, especially for load-bearing structural components, it is imperative to provide a thorough understanding on the anisotropic and heterogeneous microstructure and mechanical properties that often occur within metal AM parts. This paper outlines a broad range of metal AM technologies and reviews literatures on the anisotropy and heterogeneity of microstructure and mechanical properties for metal AM parts. It can be highlighted that the contributing factors to the anisotropy and heterogeneity within metal AM parts were either their unique microstructural features or manufacturing deficiencies. Concluding remarks on the state-of-the-art research regarding this topic and the possible solutions to overcome the anisotropy and heterogeneity of metal AM parts are provided.ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio