Ton C. Bor

Bio: Ton C. Bor is an academic researcher from University of Twente. The author has contributed to research in topics: Porosity & Curvature. The author has an hindex of 7, co-authored 15 publications receiving 182 citations.

Measuring the spreadability of pre-treated and moisturized powders for laser powder bed fusion

Abstract: For AM processes—specifically Laser Powder Bed Fusion (L-PBF) processes—powder flowability is essential for the product quality, as these processes are based on a thin layer spreading mechanism. However, the available techniques to measure this flowability do not accurately represent the spreading mechanism. Hence, this paper presents two novel applicator tools specifically designed to test the spreadability of l -PBF powders in thin layer application. The results were checked by running standard tests to analyze the powder morphology, moisture content, chemical composition and flowability using the Hall-flowmeter. For this study, four common l -PBF metal powders were selected: Inconel 718, Ti6Al4V, AlSi10Mg and Scalmalloy. From the as-received state, drying (vacuum and air) and moisturizing treatments were applied to compare four humidity states and investigate the feasibility of pre-treating the powders to remove moisture, which is known to cause problems with flowability, porosity formation and enhanced oxidation. The tests reveal that AlSi10Mg is the most susceptible alloy to moisture and oxygen pick-up, considerably decreasing the spreadability and relative density on the build platform. However, the results also reveal how challenging the direct measurement of moisture levels in metal powders is.

Lifetime Assessment of Load-Bearing Polymer Glasses : An Analytical Framework for Ductile Failure

Abstract: The most widespread application of polymers in structural applications is their use as pipe material for e.g., gas distribution systems. Pipes have a design lifetime of typically 50 years, which rules out real-time lifetime assessment methods. Here, an engineering approach is presented, which makes it possible to predict long-term ductile failure of loaded glassy polymers based on short-term tests. The approach is based upon the hypothesis that failure is governed by accumulation of plastic deformation up to a critical strain. A pressure-modified Eyring relation is employed to calculate the accumulation of plastic strain for any simple loading geometry. It is demonstrated that the approach can produce accurate quantitative time-to-failure predictions for loaded PC specimens and uPVC pipe segments.

Effects of powder reuse on the microstructure and mechanical behaviour of Al-Mg-Sc-Zr alloy processed by laser powder bed fusion (LPBF)

Abstract: Laser powder-bed fusion (LPBF) technology is one of the additive manufacturing (AM) processes that uses metal powder to produce parts for various industry sectors such as medical, aerospace, automotive and oil & gas. As an ‘additive’ based process, the material is selectively melted by a focused laser. By this working principle material is added in a layer-by-layer approach only where is needed. Therefore, this technology enables a high reduction of waste by avoiding chips typically generated in ‘subtractive’ based processes such as milling and drilling. However, to ensure lower waste consumption the metal powder surrounding the solidified part must be reused in subsequent build jobs. Current knowledge on the effect of powder reuse on LPBF builds is mostly limited to titanium- and nickel- based alloys. The aim of this paper is to study the effect of powder reuse on Al–Mg–Sc–Zr, a high strength aluminium-based alloy, manufactured by LPBF. Here, powder properties such as morphology, composition, particle size distribution are studied of virgin (pristine) and reused Al–Mg–Sc–Zr powder. The mechanical properties of specimens made of virgin powder and after four build cycles are analysed and compared to assess the influence of a mixture of virgin and reused powder material on the consolidated material properties. In general, the powder does not present large differences in composition and morphology, only the reused powder presents coarser particle size distribution (PSD) as previously observed in other alloy compositions. The microstructure of the studied specimens is very similar unlike the porosity. The specimens built with reused powder show a few small micro-sized pores which do not show significant differences in the mechanical properties. In fact, the ultimate tensile strength (UTS) and elongation to break of specimens, respectively built with virgin and reused powder are 565 MPa, 13% and 537 MPa, 11%. Based on the obtained results, it is concluded that it is feasible to reuse Al–Mg–Sc–Zr powder in four subsequent build jobs with proper powder sieving and a rejuvenation step mixing 40% of virgin powder.

Printing of complex free-standing microstructures via laser-induced forward transfer (LIFT) of pure metal thin films

Abstract: A combined approach of laser-induced forward transfer (LIFT) and chemical etching of pure metal films is studied to fabricate complex, free-standing, 3-dimensional gold structures on the few micron scale. A picosecond pulsed laser source with 515 nm central wavelength is used to deposit metal droplets of copper and gold in a sequential fashion. After transfer, chemical etching in ferric chloride completely removes the mechanical Cu support leaving a final free-standing gold structure. Unprecedented feature sizes of smaller than 10 μm are achieved with surface roughness of 0.3 to 0.7 μm. Formation of interfacial mixing volumes between the two metals is not found confirming the viability of the approach.

Three-dimensional porous hollow fibre copper electrodes for efficient and high-rate electrochemical carbon dioxide reduction

Abstract: Aqueous-phase electrochemical reduction of carbon dioxide requires an active, earth-abundant electrocatalyst, as well as highly efficient mass transport. Here we report the design of a porous hollow fibre copper electrode with a compact three-dimensional geometry, which provides a large area, three-phase boundary for gas–liquid reactions. The performance of the copper electrode is significantly enhanced; at overpotentials between 200 and 400 mV, faradaic efficiencies for carbon dioxide reduction up to 85% are obtained. Moreover, the carbon monoxide formation rate is at least one order of magnitude larger when compared with state-of-the-art nanocrystalline copper electrodes. Copper hollow fibre electrodes can be prepared via a facile method that is compatible with existing large-scale production processes. The results of this study may inspire the development of new types of microtubular electrodes for electrochemical processes in which at least one gas-phase reactant is involved, such as in fuel cell technology.

A low-cost alumina-mullite composite hollow fiber ceramic membrane fabricated via phase-inversion and sintering method

Abstract: With abundant bauxite mineral as starting material, a low-cost alumina-mullite composite hollow fiber ceramic membrane (HFCM) was fabricated via phase-inversion method followed by high temperature sintering. Process parameters, including bore fluid flow rate and air-gap distance, which affect structure and properties of the HFCM were systematically explored. A low bore fluid flow rate would lead to the deformation of inner walls of the HFCM as a result of insufficient solidification, while a large air-gap distance would induce the distortion of finger-like voids. Effects of sintering on the microstructure, pore size distribution, nitrogen gas flux and mechanical properties were investigated in details. Acid-base titration was first proposed to quantitatively determine concentration of surface active sites of membrane surface after sintering. An increase in sintering temperature leads to significantly enhancing strength but almost linearly reduces concentration of active surface hydroxyl sites. Compared with its alumina counterpart, this low-cost composite membrane can be sintered at lower sintering temperature, and exhibits higher mechanical strength and active surface hydroxyl site concentration.

β-Sialon ceramic hollow fiber membranes with high strength and low thermal conductivity for membrane distillation

Abstract: Novel microporous β-Sialon (Si 6– z Al z O z N 8– z , z = 1–4) ceramic hollow fiber membranes have been successfully prepared by a combined phase-inversion and sintering method. The influence of dispersant concentrations on the viscosity curve was first studied to obtain a stable precursor suspension. Different z value and sintering temperature were studied to get asymmetric hollow fibers with a good combination of high bending strength (369 MPa), suitable pore size (0.8 μm), large gas and water flux, which are suitable for membrane distillation (MD). The membranes also exhibited a much lower thermal conductivity. After modified to hydrophobic by grafting fluoroalkylsilane (FAS), the membranes were applied to vacuum membrane distillation (VMD) and direct contact membrane distillation (DCMD). They exhibited satisfactory water flux and a salt rejection rate of 99–100% for both methods. Most importantly, the permeate flux in DCMD reaches 63% of that in VMD due to the lower thermal conductivity, indicating their potential industrial applications.