The integrated design and manufacturing of aerospace metal optical mirrors can be challenging for rapid manufacturing with traditional techniques while maintaining mechanical integrity and meeting ...mass limitations. Hybridized additive/ultra-precision machining process is a promising approach to fabricate optical surfaces on AlSi10Mg alloy to meet the optical demands and mechanical performances. However, the fundamental investigation of ultra-precision machining of optical surfaces on additively manufactured AlSi10Mg alloy is still lacking, delaying the application of this technology. In this study, the microstructure, mechanical properties, and machinability of AlSi10Mg alloys produced by laser powder bed fusion (LPBF) were investigated, including the effect of heat treatment. A superior surface finish was achievable on the as-built alloy due to the unique fine cellular microstructure that aided the cutting process. Surfaces with roughness of ∼4 nm Ra and excellent mechanical properties with tensile strength of up to ∼491 MPa were obtained. In contrast, the large silicon particles that formed during heat treatment led to the deterioration of machined surface quality with an achievable roughness of ∼9 nm Ra along with the reduction in tensile strength to ∼283.5 MPa. Subsurface TEM analysis on the machined as-built sample indicated that the nano-scale silicon particles in the cellular microstructure boundary of the alloy and the semi-coherent relationship between silicon particles and the aluminum matrix avoided the generation of machined surface damages. New insights into the relationships between the additive manufacturing process, microstructure, and machinability are detailed to highlight the potential of hybrid manufacturing technology for high-strength and high-surface-quality parts.
In selective laser melting (SLM), support structures play a critical role in successful printing. Despite its necessity, the removal of support structures after printing becomes a challenging task ...which is usually time-consuming and labour-intensive. Mechanical post-processing can be employed to facilitate the automatic removal of support structures with higher efficiency. However, the mechanical forces of a machining process such as milling can cause the cone supports to tilt, collapse and be pulled up. This paper presents a novel method to improve the machinability of cone support structures. In this method, the epoxy resin is filled into the gaps between the entire cone support structures to form a solid composite structure after the epoxy resin is fully cured. The relationship between the force components in various directions during support removal is theoretically analyzed. The method is studied in terms of cutting performance, cutting force and energy, tool wear, workpiece surface damage and corrosion behaviour. On top of rectifying the problems of resultant support tilting and collapsing, the cutting force, specific cutting energy, tool wear and damage to the workpiece surface are significantly reduced, and the corrosion behaviour of the samples is slightly improved due to better surface quality after support removal. A finite element model is constructed for analysis of the underlying mechanisms. This paper addresses the research gap on the corrosion behaviour of the workpiece after support removal, and the newly developed method can be further applied to the machining of other types of support structures in SLM.
Display omitted
•A novel method is developed to solve the support tilting and collapsing problems during removal.•The force components in various directions during support removal are theoretically analyzed.•The cutting force, tool wear and damage to the workpiece surface are significantly reduced.•The corrosion behaviour of the samples sees signs of improvement.•A finite element method model is developed to reveal the underlying mechanisms.
Although maraging steel materials have been widely used in the laser powder bed fusion (LPBF) process, there are few reports on the behaviour of thermal expansion, which is an important indicator for ...materials used in machinery, moulds, aerospace, new material development, etc. The unique process of LPBF causes the difference in performance between LPBFed parts and their traditional counterparts. In this regard, thermal expansion is an important factor for phase transition investigation. In this study, a highly sensitive computer-controlled dilatometer was used to systematically study the thermal expansion behaviour along different orientations during continuous heating and corresponding phase transition. The scanning electron microscope, electron backscatter diffraction and microhardness testing were used to study the fine cellular/columnar structures, martensite lath, textures and formation mechanism of precipitates in the as-built and heat-treated samples. The results show an abnormal thermal expansion behaviour and phase transition during continuous heating for both samples with different building directions. For the as-built and direct ageing-treated OX samples (parallel to the building direction), the first step reversion of martensite to austenite is much stronger than the second step. After solution treatment and solution+ageing treatment, both OX and OZ (perpendicular to the building direction) samples display similar thermal expansion curves and a typical two-step martensite-to-austenite reversion. The increase of the austenite phase during the heating process leads to a quick shrinkage with a negative coefficient of thermal expansion (CTE) in the solution-treated and solution+ageing-treated OX samples. However, a very small shrinkage with a positive CTE appears in the as-built and direct ageing-treated OZ samples. Overall, the as-built and ageing-treated samples show differences in phase transition due to precipitation behaviour.
Additive manufacturing technologies are beginning to shift toward hybridization with subtractive processes and it is vital to identify techniques that can enhance the machinability of the ...difficult-to-cut additively manufactured metals and offer easy integration. The mechanochemical effect, which can be induced by surfactant, is a feasible solution for hybrid integration due to the beneficial enhancements to the cutting performance, online integrability, and negligible impact on the AM process as compared to cutting fluids, cryogenic cutting, etc. To realize the successful integration of the mechanochemical effect and hybrid additive/subtractive manufacturing, micro-cutting of AMed high-strength maraging steel was performed to study the relationship between microstructural features, mechanical properties, cutting performance and effectiveness of the mechanochemical effect. The results show that the mechanochemical effect was successfully induced in the as-built and solution-treated steels by inhibiting dislocation movement to induce the embrittlement of chip surface and strain localization within the chip, thereby leading to substantial reductions in cutting forces of up to 35.24 % and 53.09 %, respectively, with significant improvement in the machined surface quality. However, the presence of 7.7 nm nanoparticles in the age-treated steels renders the mechanochemical effect ineffective in improving machinability. The nanoparticles sharply increased the strength, hardness, and brittleness of the AMed maraging steel where the brittleness replaced the role of surfactant that suppressed plasticity in the chip free surface. The notion was affirmed by the similarities between the cutting chips of the brittle aged steel without surfactant and the as-built steel with surfactant. This study systematically revealed the underlying mechanism of inducing the mechanochemical effect during the micro-cutting of AMed high-strength materials with different microstructures and mechanical properties. More importantly, it is evident that the mechanochemical effect is a highly feasible solution for enhanced hybrid manufacturing, especially for robot-based fabrication works that involve high degrees of freedom and large working ranges but are limited by low mechanical stiffness.
Display omitted
•The mechanochemical effect affects the machinability of as-built AMed metals.•Chip morphology, cutting force and surface quality are influenced by mechanochemical effect.•Material flow characteristics in the chips of AMed metals are investigated by image analysis.•Mechanochemical effect manifestations depend on the presence of nanoparticles.•Nanoparticles in the work material show the strongest influence on the mechanochemical effect.
Objective
The aim of this study was to investigate the association between periodontitis and total serum cholesterol level in patients with type 2 diabetic nephropathy (T2DN).
Background
...Periodontitis is now recognized as the sixth complication of diabetes and can also affect other complications of diabetes, including nephropathy and coronary artery diseases. Studies have considered dyslipidemia as a risk factor for exacerbation of periodontitis.
Methods
A total of 119 T2DN patients with chronic periodontitis were included in this observational study. Participants were stratified into the Normal (serum total cholesterol <5.17 mmol/L, n = 89) and the Dyslipidemia groups (serum total cholesterol ≥5.17 mmol/L, n = 30). Participants completed a validated questionnaire that collected information on oral hygiene behaviors and knowledge of oral health and underwent a clinical oral examination. The number of remaining teeth, probing depth (PD), clinical attachment level (CAL), and bleeding index (BI) was recorded. Physical examination and laboratory tests (fasting plasma glucose, serum glycosylated hemoglobin (HbA1c), total cholesterol, high‐density lipoprotein‐cholesterol (HDL‐C), low‐density lipoprotein‐cholesterol (LDL‐C), triglyceride, and high‐sensitivity C‐reactive protein levels) were performed.
Results
Means of CAL and BI were significantly higher in the Dyslipidemia group compared with the Normal group. In the Dyslipidemia group, PD and percent of sites with PD ≥4 mm were positively correlated with urinary albumin/creatinine ratios; PD and percent of sites with PD ≥4 and PD ≥5 mm were positively correlated with HbA1c level; a number of remaining teeth were negatively correlated with serum LDL‐C level. After adjusting for age, gender, body mass index, smoking, FPG, and serum HbA1c and triglyceride levels, BI was found to be positively associated with dyslipidemia in T2DN patients with periodontitis.
Conclusion
T2DN patients with chronic periodontitis had a 2.355‐fold higher risk of developing dyslipidemia, implying an important relationship between periodontitis and blood lipid control among T2DN patients.
Aims/hypothesis
The use of oral glucose-lowering drugs, particularly those designed to target the gut ecosystem, is often observed in association with altered gut microbial composition or functional ...capacity in individuals with type 2 diabetes. The gut microbiota, in turn, plays crucial roles in the modulation of drug efficacy. We aimed to assess the impacts of acarbose and vildagliptin on human gut microbiota and the relationships between pre-treatment gut microbiota and therapeutic responses.
Methods
This was a randomised, open-labelled, two-arm trial in treatment-naive type 2 diabetes patients conducted in Beijing between December 2016 and December 2017. One hundred participants with overweight/obesity and newly diagnosed type 2 diabetes were recruited from the Pinggu Hospital and randomly assigned to the acarbose (
n
=50) or vildagliptin (
n
=50) group using sealed envelopes. The treatment period was 6 months. Blood, faecal samples and visceral fat data from computed tomography images were collected before and after treatments to measure therapeutic outcomes and gut microbiota. Metagenomic datasets from a previous type 2 diabetes cohort receiving acarbose or glipizide for 3 months were downloaded and processed. Statistical analyses were applied to identify the treatment-related changes in clinical variables, gut microbiota and associations.
Results
Ninety-two participants were analysed. After 6 months of acarbose (
n
=44) or vildagliptin (
n
=48) monotherapy, both groups achieved significant reductions in HbA
1c
(from 60 to 46 mmol/mol from 7.65% to 6.40% in the acarbose group and from 59 to 44 mmol/mol from 7.55% to 6.20% in the vildagliptin group) and visceral fat areas (all adjusted
p
values for pre–post comparisons <0.05). Both arms showed drug-specific and shared changes in relative abundances of multiple gut microbial species and pathways, especially the common reductions in
Bacteroidetes
species. Three months and 6 months of acarbose-induced changes in microbial composition were highly similar in type 2 diabetes patients from the two independent studies. Vildagliptin treatment significantly enhanced fasting active glucagon-like peptide-1 (GLP-1) levels. Baseline gut microbiota, rather than baseline GLP-1 levels, were strongly associated with GLP-1 response to vildagliptin, and to a lesser extent with GLP-1 response to acarbose.
Conclusions/interpretation
This study reveals common microbial responses in type 2 diabetes patients treated with two glucose-lowering drugs targeting the gut differently and acceptable performance of baseline gut microbiota in classifying individuals with different GLP-1 responses to vildagliptin. Our findings highlight bidirectional interactions between gut microbiota and glucose-lowering drugs.
Trial registration
ClinicalTrials.gov
NCT02999841
Funding
National Key Research and Development Project: 2016YFC1304901.
Graphical abstract
This paper focuses on the influence mechanism of process parameters on the geometry morphology and microstructure characteristic of single-track and multi-track 316L/CuSn10 multiple materials ...manufactured by laser powder bed fusion (LPBF). The width of single-track increases with the increase of laser power and layer thickness, and decreases with the increase of scanning speed. Both variations in the copper content and wetting angle of the molten pool were investigated. In addition, the comparison of defect characteristics shows that the scanning speed and layer thickness have a greater influence on the formation of single cracks. The traces of Marangoni convection are observed directly in the centre of the molten pool due to the difference in microstructure between 316L and CuSn10 alloys. It is found that the copper penetration cracks appear on the steel side at the molten pool bottom. Moreover, fine grains appear in the copper-rich region, and the large-angle grain boundary distribution seems to be the reason for the concentration of dislocations. Four types of crack formation mechanisms are found in the cross section of the multi-track: crack formation inside the molten pool, passing through the track boundary, extending to the steel substrate, and copper penetration cracks.
•316L/CuSn10 single and multiple track manufactured by LPBF was investigated.•Thermal stress and liquid copper penetration are the main cause of microcracks.•Copper diffusion causes fine grains, distributed LAG boundaries and dislocations.•Four types of cracks were found in the cross section of the multiple track.
PDF
