Process-Structure-Property Relationships of AISI H13 Tool Steel Processed with Selective Laser Melting

Due to a good combination of high hardness, wear resistance, toughness, resistance to high operating temperatures, and fairly low material cost, AISI H13 tool steel is commonly used in the manufacture of injection molds. Additive manufacturing (AM) such as selective laser melting (SLM), due to the layer-wise nature of the process, offers substantial geometric design freedom in comparison with conventional subtractive manufacturing methods, thereby enabling a construction of complex near-net shape parts with internal cavities like conformal cooling channels. The quality of SLM-manufactured parts mainly depends on the part geometry, build orientation and scanning strategy, and processing parameters. In this study, samples of H13 tool steel with a size of 10 × 10 × 15 mm3 were SLM-manufactured using a laser power of 100, 200, and 300 W; scanning speed of 200, 400, 600, 800, 1000, and 1200 mm/s; and hatch spacing of 80 and 120 µm. A constant layer thickness of 40 µm, 67° scanning rotation between subsequent layers, and a stripe scanning strategy were maintained during the process. The samples were built considering a preheating of 200 °C. The relative density, surface roughness, crack formation, microstructure, and hardness were evaluated. The relative density is shown to increase with increasing the volumetric energy density up to a value of about 60 J/mm3 and then no significant increase can be pointed out; the maximum relative density of 99.7% was obtained. A preheating of 200 °C generally aids to increase the relative density and eliminate the crack formation. The microstructure of built samples shows fine equiaxed cellular-dendritic structure with martensite and some retained austenite. The microhardness of the as-built samples was found to vary from 650 to 689 HV 0.2, which is comparable to a conventionally produced H13 tool steel

How Good Is Trans Abdominal Ultrasound for Evaluating NAFLD in the General Population? A Cross-Sectional Study

Nonalcoholic fatty liver disease (NAFLD) is one of the most common cause of liver test abnormality and chronic liver disease in the world and can increase liver related mortality. Association of NAFLD with metabolic syndrome increase mortality due to cardiovascular disease too. NAFLD is categorized histologically into the nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). Liver biopsy has been known as gold standard of evaluating NAFLD, but this procedure is invasive. It is time to replace available and easier way to diagnose, and predict the prognosis for better management of NAFLD. This study was comparing the result of transabdominal ultrasonography with Fibroscan as a new and accurate method for evaluating severity of fatty liver disease. This was a cross-sectional study that was conducted using 101 patients with NAFLD. All patients who had TUS by one experienced radiologist and fibro scan at the same time were included. Visual liver echogenicity was basis of grading in TUS. Fibro scans results are based on controlled attenuation parameters (CAP) which is not operator dependent. Other information, such as age, waist, and BMI, were also gathered. TUS has a low value for the diagnosis of liver fibrosis in NAFLD patients and predicting prognosis. TUS has a good correlation with fibroscan in grade 0 and 1of fatty liver, but in grade 2 and 3 of fatty liver, we can not rely on TUS for accurate grading