Machinability of INCONEL718 Alloy with a Porous Microstructure Produced by Laser Melting Powder Bed Fusion at Higher Energy Densities

Products produced by additive manufacturing (AM) seek to exploit net shape manufacturing by eliminating or minimizing post-process stages such as machining. However, many applications which include turbo machinery components with tight dimensional tolerances and a smooth surface finish will require at least a light machine finishing stage. This paper investigates the machinability of the additively fabricated INCONEL718 (IN718) alloy produced by laser melting powder bed fusion (LM-PBF) with different levels of spherical porosity in the microstructure. The literature suggests that the band width for laser energy density, which combines the various scan process parameters to obtain a low spherical type porosity in the LM-PBF IN718 alloy (~1%), has wide breadth. With the increasing laser energy density and above a threshold, there is a rapid increase in the spherical pore size. In this paper, three tube samples each with different levels of spherical porosity were fabricated by varying the laser energy density for LM-PBF of the IN718 alloy within the stable and higher energy density range and the porosity measured. A low laser energy density was avoided due to balling up, which promotes highly irregular lack of fusion defects and poor consolidation within the alloy microstructure. An orthogonal turning test instrumented, with a three-component dynamometer to measure the cutting forces, was performed on AM produced IN718 tube samples under light cut conditions to simulate a finish machining process. The orthogonal turning tests were also performed on a tube sample obtained from the wrought extruded stock. The machining process parameters, which were studied include varying the cutting speed at three levels, at a fixed feed and under dry cut conditions for a short duration to avoid the tool wear. The results obtained were discussed and a notable finding was the higher rate of built-up-edge formation on the tool tip from the AM samples with a higher porosity and especially at a higher cutting speed. The paper also discusses the mechanisms that underpin the findings.     

The impact of hepatitis C virus infection on survival in dialysis patients: meta-analysis of observational studies

The impact of hepatitis C virus (HCV) infection on mortality of patients receiving regular dialysis remains unclear. The assessment of the natural history of HCV in dialysis population is difficult because of the low progression of HCV-related liver disease over time and the reduced life expectancy in patients with end-stage renal disease. The aim of the study was to conduct a systematic review of the published medical literature concerning the impact of HCV infection on the survival of patients undergoing maintenance dialysis. The relative risk of mortality was regarded as the most reliable outcome end-point. Study-specific relative risks were weighted by the inverse of their variance to obtain fixed- and random-effects pooled estimates for mortality with HCV across the published studies. We identified seven studies involving 11 589 unique patients on maintenance dialysis; two (29%) were case-control studies. Pooling of study results demonstrated that presence of anti-HCV antibody was an independent and significant risk factor for death in patients on maintenance dialysis. The summary estimate for adjusted relative risk (aRR) (all-cause mortality) was 1.34 with a 95% confidence interval (CI) of 1.13-1.59. Heterogeneity statistics, R(i) = 0.48 (P-value by Q-test = 0.13). In a sensitivity analysis including only (n = 5) cohort studies, the pooled aRR was 1.38 (95% CI, 1.20-1.59); heterogeneity statistics R(i) = 0.46. As a cause of death, hepatocellular carcinoma and liver cirrhosis were significantly more frequent among anti-HCV-positive than -negative dialysis patients. Our meta-analysis indicates that anti-HCV-positive patients on dialysis have an increased risk of mortality compared with HCV-negative patients. The excess risk of death in HCV-positive patients may be at least partially attributed to chronic liver disease with its attendant complications.     

Epileptic phenotypes in children with respiratory chain disorders

Purpose: Epilepsy is a commonly reported but rarely described clinical hallmark of mitochondrial respiratory chain defects (RCDs) with encephalopathy. Methods: From 1990–2006 we collected data about 56 children with RCD (single, n = 24 or multiple, n = 20 mitochondrial complex deficiencies; mtDNA mutation, n = 11; mtDNA depletion n = 10 of 21; and nuclear gene mutation n = 11). Epileptic features were reviewed retrospectively. Results: First seizures were frequently (47 patients, 82.5%) preceded by failure to thrive, psychomotor delay, ataxia, or multisystemic dysfunction. Sixty percent of the patients had several seizure types. Six age‐related epilepsy phenotypes could be identified: status epilepticus complicating neonatal multivisceral deficiency (2 patients), neonatal myoclonic encephalopathy (3 patients), infantile spasms (8 patients), refractory or recurrent status epilepticus (21 patients), epilepsia partialis continua (4 patients), and myoclonic epilepsy (18 patients). Except for infantile spasms, epilepsy was difficult to control in most patients (95%). Valproate was administered to 25 patients, one of whom developed acute liver failure 6 days later. Twenty‐two patients (45%) died, half of them within 9 months from the onset of epilepsy. Discussion: In RCD, epilepsy is not only difficult to control but its occurrence often indicates a severe turn in the course of the disease. For one‐third of the patients, classical biochemical measures failed to reveal any abnormality and RCD could be detected in the liver only.