An investigation of properties of FGM and wafer structures produced with laser direct metal deposition

Existing range of metallic alloys and structures possess a series of physical and mechanical properties that deem them useful or unusable in certain applications or environments. A solution to the cases where metallic alloys lack specific properties and therefore cannot function satisfactorily is to develop new innovative materials which possess the desired characteristics. These characteristics may include tailored mechanical, thermal and functional properties. Laser Direct Metal Deposition technique was used to create such innovative metallic structures to overcome some limitations of existing alloys. Laser assisted direct metal deposition offers endless opportunities to create innovative structures to further improve material performance and characteristics. The results offer a series of solution as well as pathways for development of further structures

Investigation of metallic structure with negative thermal expansion: a review

Materials with negative thermal expansion (NTE) properties have numerous applications that interest design engineers and scientists in aerospace, electronics, dentistry and other industries and fields that at some stage experience unwanted thermal expansion in parts. This paper reviews research done on developing metal alloys or solid structures from combination of metal alloys that demonstrate negative thermal expansion properties. The review shows that a variety of alloys, composites and structures have been used to develop NTE metallic structures some of which have achieved significant successes in doing so. In order to fabricate parts from a mix of alloys or a structure comprising a series of layers from various alloys, a technology with high flexibility was needed. Traditional welding or casting methods could not offer such capabilities. Direct Metal Deposition (DMD) is a technology that uses laser energy to melt metal powder injected coaxially with the laser beam on substrates and create shapes and structures directly from CAD models with none or minimal metallurgical defects. The technology will be used to explore the manufacture of complex structures with NTE properties using a range of alloying powders

Thermal expansion of functionally graded and wafer-layered structures produced by laser direct metal deposition

A range of engineering alloys was selected to create two distinct sets of structures. One was functionally graded materials (FGM)-using pairs of these alloys-and the second type was a series of wafer-layered structures using pairs of these alloys in different combinations. The aim of this investigation was to identify unique sets of structures of alloys which provide very different coefficients of thermal expansion (CTE) compared to those of individual elements. The process used to create these structures was laser direct metal deposition (DMD) additive manufacturing technology. The linear thermal expansion coefficients of these samples were measured and the results show that specific sets of FGM and wafer type structures of specific constituent metal alloys can be fabricated by DMD, in which the overall coefficient of thermal expansion of these new structures is significantly different from that of each alloy when measured individually. FGM and wafer type structures of specific constituent metal alloys have lower CTE than those of original alloys

Tensile strength of functionally graded and wafer layered structures produced by direct metal deposition

Purpose - This paper aims to investigate the changes in tensile properties of novel functionally graded materials (FGMs) and wafer structures created by direct metal deposition (DMD) additive manufacturing (AM) technology. Design/methodology/approach - Laser-assisted DMD was used to create two innovative sets of metallic structures - the functionally graded and wafer-layered structures - using pairs of six different engineering alloys in different combinations. These alloys were selected due to their high popularity within a diverse range of industries and engineering applications. The laser-assisted DMD was selected as a suitable technique to create these complex structures because of its capability to deposit more than one alloy powder at a time. After creation of these structures, their tensile strength was tested in a series of tensile tests and the results were compared with those of single alloy samples. Findings - It was observed that the mechanical properties of FGMs and wafer structure samples were clearly different from those of the single alloy samples, a fact which creates a whole pool of opportunities for development of new materials or structures with desired mechanical properties that cannot be achieved in single alloy parts. Originality/value - The study demonstrates the application of the DMD process to produce unique structures and materials, which would be high in demand in engineering applications, where metallic parts are exposed to high loads and where excessive tensile stresses may adversely affect the performance of such parts

Study of lead-induced neurotoxicity in cholinergic cells differentiated from bone marrow-derived mesenchymal stem cells

The developing brain is susceptible to the neurotoxic effects of lead. Exposure to lead has main effects on the cholinergic system and causes reduction of cholinergic neuron function during brain development. Disruption of the cholinergic system by chemicals, which play important roles during brain development, causes of neurodevelopmental toxicity. Differentiation of stem cells to neural cells is recently considered a promising tool for neurodevelopmental toxicity studies. This study evaluated the toxicity of lead acetate exposure during the differentiation of bone marrow-derived mesenchyme stem cells (bone marrow stem cells, BMSCs) to cholinergic neurons. Following institutional animal care review board approval, BMSCs were obtained from adult rats. The differentiating protocol included two stages that were pre-induction with beta-mercaptoethanol (BME) for 24 h and differentiation to cholinergic neurons with nerve growth factor (NGF) over 5 days. The cells were exposed to different lead acetate concentrations (0.1-100 mu m) during three stages, including undifferentiated, pre-induction, and neuronal differentiation stages; cell viability was measured by MTT assay. Lead exposure (0.01-100 mu g/ml) had no cytotoxic effect on BMSCs but could significantly reduce cell viability at 50 and 100 mu m concentrations during pre-induction and neuronal differentiation stages. MAP2 and choline acetyltransferase (ChAT) protein expression were investigated by immunocytochemistry. Although cells treated with 100 mu m lead concentration expressed MAP2 protein in the differentiation stages, they had no neuronal cell morphology. The ChAT expression was negative in cells treated with lead. The present study showed that differentiated neuronal BMSCs are sensitive to lead toxicity during differentiation, and it is suggested that these cells be used to study neurodevelopmental toxicity