Optimizing the process parameters for additive manufacturing of glass components by selective laser melting: Soda-lime glass versus quartz glass

Additive manufacturing by selective laser melting (SLM) is generally applicable to glasses while insufficient resistance of the material to thermal shocks due to local laser heating may result in cracking and a high viscosity of glass melt is responsible for incomplete powder consolidation related to residual porosity. The present work shows that preheating up to 350 °C is sufficient to avoid cracking of soda-lime glass. Preheating of quartz glass up to 730 °C considerably decreases the residual porosity, which is explained by acceleration of powder consolidation by the viscous-flow mechanism of glass particles' coalescence. Variation of the preheating temperature is an effective tool to control consolidation of glass powder and to avoid cracking.

The Effect of Nitrogen Linear Flow on Lubricant Removal and Sintering Densification of Alumix 431D Grade Powder

ECKA Granules Alumix 431D commercial grade, press ready, pre-alloyed aluminium-based powder containing 1.5 mass% of Acrawax C was used to study the effect of nitrogen linear flow on de-lubrication and sintering densification. In situ dimensional changes were controlled by dilatometry. Microstructural observations of sintered compacts were also performed. The results clearly showed the strong influence of nitrogen linear flow on de-lubrication, and thus on the sintering behaviour of the examined powder. High nitrogen linear flow is required to produce the desired sintered microstructure—characterised by residual porosity. In contrast, at low nitrogen velocity, the lubricant removal is not complete, which in turn significantly impedes densification.

Porosity distribution in metal injection molded parts

Metal injection molding technology is commonly used in production of small and very complex parts. Residual porosity is unavoidable characteristic of P/M parts, affecting their final properties. During injection molding phase powder-binder separation can occur, causing green density variation through cross section of the part. This behaviour is particularly pronounced as complexity of the parts increases. As a consequence, zones with different density and residual porosity can be seen after sintering. In this regard, porosity and hardness distribution of the sintered ring-shaped part is analysed and presented in the paper.

Acoustic characterization of silica nanoparticle-impregnated Kevlar fabric

Silica nanoparticle-impregnated Kevlar (SNK) fabric has better specific ballistic performance in comparison to its neat counterparts. For multifunctional structural applications using lightweight composites, combining this improved ballistic functionality with an acoustic functionality is desirable. In this study, acoustic characterization of neat and SNK samples is conducted using the normal-incidence impedance tube method. Both the absorption coefficient and transmission loss (TL) are measured in the 60–6000 Hz frequency range. The influence of parameters such as number of layers of neat or treated fabric, percentage by weight of nanoparticle addition, spacing between fabric layers, and residual porosity is examined. It is found that while absorption decreases with an increase in nanoparticle addition for frequencies above about 2500 Hz, increasing the number of layers shifts peak absorption to lower frequencies. By introducing an air-gap behind the fabric layer, dominant low-frequency (1000–3000 Hz) absorption peaks are obtained that correlate well with natural modes of mass-equivalent thin plates. Examining the influence of residual porosity by laminating the SNK samples reveals that it contributes to about 30–50% of the total absorption. Above about 1500 Hz, 3–5 dB of TL increase is obtained for SNK samples vis-à-vis the neat samples. TL is found to increase beyond that of the neat sample above a threshold frequency when an air-gap is introduced between two SNK layers. With an increase in the weight of nanoparticle addition, measured TL tends to be closer to mass law predictions. This study demonstrates that SNK fabric could provide improved acoustic performance in addition to its ballistic capabilities, making it suitable for multifunctional applications and could form the basis for the development of simplified models to predict the structural acoustic response of such nanoparticle–fabric composites.

The Influence of the Process Parameters on the Densification and Microstructure Development of Laser Powder Bed Fused Inconel 939

This work aims to investigate the effect of the process parameters on the densification and microstructure of Inconel 939 (IN939) alloy processed by laser powder bed fusion (LPBF). IN939 is a Ni-based superalloy with high creep and corrosion resistance that can be used up to around 850 °C under load, resulting in higher operative temperatures than the ones commonly allowed for Inconel 718 and Inconel 625 alloys (around 650 °C). However, this alloy can suffer from poor weldability involving possible crack formation. In order to minimize the residual porosity and the cracking density, specific process parameters were investigated. The parameters to generate IN939 samples almost pores-free (porosity ≤0.22%) with a cracking density ≤1.36 mm/mm2 as well as samples almost crack-free (≤0.10 mm/mm2) with limited residual porosity (≤0.89%) were determined. The microstructure revealed fine dendritic/cellular structures with the formation of sub-micrometric phases. A high concentration of these phases was also found along the intergranular cracks, suggesting that their presence, coupled to the high thermal stresses, can be the primary reason for crack formation during the LPBF process.

АЛМАЗНЕ ВИГЛАДЖУВАННЯ ДЕТАЛЕЙ З НЕКОМПАКТНИХ СПЛАВІВ НА ОСНОВІ АЛЮМІНИДІВ ТИТАНУ

Parameter research results of the residual porosity of the surface layer of samples of the alloy Ti - 45Al-3Nb - Y2O3 (OX45 - 3ODS) based on titanium aluminides obtained by selective laser sintering from the effect on the parameters of the residual porosity of diamond smoothing with different modes and conditions are presented in current article. Based on the results of variance analysis, the effect of diamond smoothing modes and their pairwise interaction on the porosity parameters of the surface layer is estimated. The regularities of changing the parameters of the pore space of the surface layer of the samples (area, perimeter, eccentricity, and fractal dimension of the pore boundaries) from the feed, the force on the vigilator and its radius are established. It has been determined that for the effective application of the established modes, it is necessary to take into account the initial porosity, which has a random distribution over the surface area of the samples under study. A correlation analysis using the Pareto diagram is performed. The magnitude of the effect of diamond smoothing modes on the residual porosity is determined. The adequacy and homogeneity of the mathematical model are estimated based on the Fisher and Cochren criteria. The optimization of steeple climbing modes has been performed. The optimal processing conditions have been established from achieving a minimum residual porosity in the surface layer. Technological limitations have been determined using diamond tapping for hardening non-compact materials. Further studies are necessary for the practical application of the technology of smoothing materials based on titanium aluminides.