Influence of process gas during powder bed fusion with laser beam of Zr-based bulk metallic glasses

Zr-based bulk metallic glasses offer a unique combination of hardness, high strength, and high elastic limits. Yet, manufacturable size and complexity are limited due to the required cooling rates. Short laser-material interaction times together with layer-wise and selective energy input allows the laser powder bed fusion process to largely overcome those restrictions. Still, the complex process-material interactions inhere numerous uncertainties. In the present work, additively manufactured Zr-based bulk metallic glasses produced under three different process gases are investigated by calorimetry, x-ray diffraction, and bending tests. A strong dependence between the thermophysical properties, flexural strength, and the applied atmosphere is found

Reconstruction of Indian Ocean summer monsoon dynamicsat Nam Co using lipid biomarkers since 24 cal ka BP

Abstract HKT-ISTP 2013 B

Speeding up additive manufacturing by means of forming for sheet components with core structures

A new process combination route consisting of additive manufacturing (AM) with a subsequent forming operation is proposed. The process route has the opportunity to increase the efficiency of the AM process route up to 360%. Stainless steel 316L sheets with different core structures (similar to sandwich sheets) are produced by AM, characterized, and formed in a die bending operation. The bending characteristics of this novel semi-finished product can be accurately predicted in a numerical simulation. The new process route is discussed in detail and compared to conventional AM parts in terms of the production efficiency

Mitigating oxygen pick-up during laser powder bed fusion of Ti-6Al-4V by limiting heat accumulation

The dissolution of oxygen in Ti-6Al-4V during laser powder bed fusion (L-PBF) is a limitation for the final ductility of the produced components and a challenge for the end-users. In the present work, the effect of the residual oxygen in the process atmosphere of a laboratory scale L-PBF machine, as well as the role of heat accumulation, are studied. It was shown that oxygen content in the as-built Ti-6Al-4V is determined by the size of the scanned area and build time. The heat accumulation aspect was investigated by adjusting the inter-layer time (ILT), by increasing the recoating time or the number of produced parts. The results showed that oxygen pick-up could be limited by reducing residual oxygen level in the atmosphere or heat accumulation. A 400 ppm O2 reduction measured at the top of a 70 mm column was achieved by increasing the ILT manually by 4.5s, and a 1200 ppm O2 reduction by increasing the scanned area by 7 times. By doing so, the hardness at full height was reduced by approximately 30 HV10. It is shown that design features characterised by high aspect ratio can absorb significant amount of oxygen resulting in increased brittleness

Application and modelling of hybrid stereolithography injection mould tooling

The use of stereolithography (SL) to make injection moulding tools has been shown previously to be an efficient way of producing rapid tools for simple geometries, aiming at small lot sizes with an acceptable degree of accuracy. This paper highlights the unexplored potential of using SL inserts in hybrid tools using practical experiments and FEA mould filling models. The practical experiments reveal problems incurred by uneven flow as a result of differential thermal conductivity between dissimilar mould materials in a hybrid tool. The FEA flow models confirm that this uneven flow would be anticipated when using FEA software. A further FEA stress analysis predicts that catastrophic mould failure will be expected under some conditions and these reflect the results found in the practical experiments. The use of a homogeneous SL tool eliminates the issues caused by uneven mould filling but results in thermal distortion of the female mould. Ultimately a SL tool backfilled with low melt point alloy provides a solution that eliminates the problems of uneven filling and thermal distortion

Control of residual oxygen of the process atmosphere during laser-powder bed fusion processing of Ti-6Al-4V

The effect of the residual oxygen concentration in the process atmosphere during laser-powder bed fusion (L-PBF) of Ti-6Al-4V was investigated, using an external oxygen monitoring system equipped with two types of oxygen sensors typically used in L-PBF hardware: a lambda probe and an electrochemical oxygen sensor. The recordings of the oxygen variations during L-PBF highlighted that the electrochemical sensor is more reliable than the lambda probe, whose signal showed a maximum deviation of about 700 ppm O2\ua0after 7 h, attributed to its sensitivity to hydrogen present in the system. The study revealed that proper monitoring of the oxygen in the laboratory scale L-PBF system used is necessary to limit oxygen and nitrogen pick-ups by the built material. Concentrations as high as 2200 ppm O2\ua0and 500 ppm N2\ua0in the Ti-6Al-4V part built under standard conditions were measured, compared to maximum levels of 1800 ppm O2\ua0and 250 ppm N2\ua0with the external oxygen control. In addition, the findings underline the critical effect of the component design, such as the high aspect ratio columns or the lattice structures, on the heat accumulation in case of Ti-6Al-4V, leading to enhanced oxygen and nitrogen pick-up, as high as 600 ppm O2\ua0and 150 ppm N2\ua0difference between the bottom and top of the cylindrical samples of 70 mm height used in this study. The determination of tensile properties of samples built at different heights put in evidence the detrimental effect of the oxygen increase with build height on the ductility, which decreased from 12% to below 6% between the bottom and top positions. This work highlights that the possible presence of impurities in the L-PBF atmosphere can have harmful impact on the properties of Ti-6Al-4V components, which can be mitigated adjusting the oxygen control system

Laser powder bed fusion of Cu-Ti-Zr-Ni bulk metallic glasses in the Vit101 alloy system

Laser powder bed fusion (PBF-LB/M) of bulk metallic glasses (BMGs) has experienced growing scientific and industrial interest in the last years, with a special focus on application relevant systems based on zirconium. The high cooling rates and the layer-wise build-up process allow overcoming size and geometry limitations typical for conventional casting routes. Yet, the novel production approach requires different alloy characteristics than casting processes. The present work reports for the first time on the PBF-LB/M-processing of three CuTi-based bulk metallic glass formers in the Vit101 system, allowing to exceed the mechanical performance of most additively formed Zr-based BMGs. Furthermore, the influence of alloy properties like thermal stability and toughness on the PBF-LB/M applicability are systematically studied. Thermal stability plays a minor role to produce amorphous specimen, while notch toughness is found to be a more crucial aspect to achieve parts with low defect density and resulting high mechanical performance. The results suggest fundamentally different alloy development strategies adapted to the needs of the PBF-LB/M-process, leaving classical casting-based optimization of glass forming ability behind and evolving towards a rather toughness-oriented optimization

Cardiovascular Safety During Treatment With Baricitinib in Rheumatoid Arthritis

OBJECTIVE: To assess the frequency of cardiovascular and venous thromboembolic events in clinical studies of baricitinib, an oral, selective JAK1 and JAK2 inhibitor approved in more than 50 countries for the treatment of moderately-to-severely active rheumatoid arthritis (RA). METHODS: Data were pooled from 9 RA studies. Placebo comparison up to 24 weeks included data from 6 studies. Randomized dose comparison between baricitinib doses of 2 mg and 4 mg used data from 4 studies and from the associated long-term extension study. The data analysis set designated "All-bari-RA" included all baricitinib exposures at any dose. RESULTS: Overall, 3,492 RA patients received baricitinib (7,860 patient-years of exposure). No imbalance compared to the placebo group was seen in the incidence of major adverse cardiovascular events (MACE) (incidence rates [IRs] of 0.5 per 100 patient-years for placebo and 0.8 per 100 patient-years for 4 mg baricitinib), arterial thrombotic events (ATE) (IRs of 0.5 per 100 patient-years for placebo and 0.5 per 100 patient-years for 4 mg baricitinib), or congestive heart failure (CHF) broad term (IRs of 4.3 per 100 patient-years for placebo and 2.4 per 100 patient-years for 4 mg baricitinib). Deep vein thrombosis (DVT)/pulmonary embolism (PE) were reported in 0 of 1,070 patients treated with placebo and 6 of 997 patients treated with 4 mg baricitinib during the placebo-controlled period; these events were serious in 2 of 6 patients, while all 6 had risk factors and 1 patient developed DVT/PE after discontinuation of the study drug. In the 2 mg-4 mg-extended data analysis set, IRs of DVT/PE were comparable between the doses across event types (IRs of 0.5 per 100 patient-years in those receiving 2 mg baricitinib and 0.6 per 100 patient-years in those receiving 4 mg baricitinib). In the All-bari-RA data analysis set, the rates were stable over time, with an IR of DVT/PE of 0.5 per 100 patient-years. CONCLUSION: In RA clinical trials, no association was found between baricitinib treatment and the incidence of MACE, ATE, or CHF. With regard to incidence of DVT/PE, 6 events occurred in patients treated with 4 mg baricitinib, but no cases of DVT/PE were reported in the placebo group. During longer-term evaluation, the incidence of DVT/PE was similar between the baricitinib dose groups, with consistent IR values over time, and this was similar to the rates previously reported in patients with RA