Oxide Dispersion Strengthened Nickel Based Alloys via Spark Plasma Sintering

Oxide dispersion strengthened (ODS) nickel based alloys were developed via mechanical milling and spark plasma sintering (SPS) of Ni–20Cr powder with additional dispersion of 1.2 wt% Y2O3 powder. Furthermore, 5 wt% Al2O3 was added to Ni–20Cr–1.2Y2O3 to provide composite strengthening in the ODS alloy. The effects of milling times, sintering temperature, and sintering dwell time were investigated on both mechanical properties and microstructural evolution. A high number of annealing twins was observed in the sintered microstructure for all the milling times. However, longer milling time contributed to improved hardness and narrower twin width in the consolidated alloys. Higher sintering temperature led to higher fraction of recrystallized grains, improved density and hardness. Adding 1.2 wt% Y2O3 to Ni–20Cr matrix significantly reduced the grain size due to dispersion strengthening effect of Y2O3 particles in controlling the grain boundary mobility and recrystallization phenomena. The strengthening mechanisms at room temperature were quantified based on both experimental and analytical calculations with a good agreement. A high compression yield stress obtained at 800 °C for Ni–20Cr–1.2Y2O3–5Al2O3 alloy was attributed to a combined effect of dispersion and composite strengthening

Pulmonary arterial pressure detects functional mitral stenosis after annuloplasty for primary mitral regurgitation: An exercise stress echocardiographic study

Introduction: The restrictive mitral valve annuloplasty (RMA) is the treatment of choice for degenerative mitral regurgitation (MR), but postoperative functional mitral stenosis remains a matter of debate. In this study, we sought to determine the impact of mitral stenosis on the functional capacity of patients. Methods: In a cross-sectional study, 32 patients with degenerative MR who underwent RMA using a complete ring were evaluated. All participants performed treadmill exercise test and underwent echocardiographic examinations before and after exercise. Results: The patients� mean age was 50.1 ± 12.5 years. After a mean follow-up of 14.1 ± 5.9 months (6�32 months), the number of patients with a mitral valve peak gradient >7.5 mm Hg, a mitral valve mean gradient >3 mm Hg, and a pulmonary arterial pressure (PAP) �25 mm Hg at rest were 50, 40.6, and 62.5, respectively. 13 patients (40.6) had incomplete treadmill exercise test. All hemodynamic parameters were higher at peak exercise compared with at rest levels (all P <.05). The PAP at rest and at peak exercise as well as peak transmitral gradient at peak exercise were higher in patients with incomplete exercise compared with complete exercise test (all P <.05). The PAP at rest (a sensitivity and a specificity of 84.6 and 52.6, respectively; area under the curve AUC =.755) and at peak exercise (a sensitivity and a specificity of 100% and 47.4%, respectively; AUC =.755) discriminated incomplete exercise test. Conclusion: The RMA for degenerative MR was associated with a functional stenosis and the PAP at rest and at peak exercise discriminated low exercise capacity. © 2017, Wiley Periodicals, Inc

Pulmonary arterial pressure detects functional mitral stenosis after annuloplasty for primary mitral regurgitation: An exercise stress echocardiographic study

Introduction: The restrictive mitral valve annuloplasty (RMA) is the treatment of choice for degenerative mitral regurgitation (MR), but postoperative functional mitral stenosis remains a matter of debate. In this study, we sought to determine the impact of mitral stenosis on the functional capacity of patients. Methods: In a cross-sectional study, 32 patients with degenerative MR who underwent RMA using a complete ring were evaluated. All participants performed treadmill exercise test and underwent echocardiographic examinations before and after exercise. Results: The patients� mean age was 50.1 ± 12.5 years. After a mean follow-up of 14.1 ± 5.9 months (6�32 months), the number of patients with a mitral valve peak gradient >7.5 mm Hg, a mitral valve mean gradient >3 mm Hg, and a pulmonary arterial pressure (PAP) �25 mm Hg at rest were 50, 40.6, and 62.5, respectively. 13 patients (40.6) had incomplete treadmill exercise test. All hemodynamic parameters were higher at peak exercise compared with at rest levels (all P <.05). The PAP at rest and at peak exercise as well as peak transmitral gradient at peak exercise were higher in patients with incomplete exercise compared with complete exercise test (all P <.05). The PAP at rest (a sensitivity and a specificity of 84.6 and 52.6, respectively; area under the curve AUC =.755) and at peak exercise (a sensitivity and a specificity of 100% and 47.4%, respectively; AUC =.755) discriminated incomplete exercise test. Conclusion: The RMA for degenerative MR was associated with a functional stenosis and the PAP at rest and at peak exercise discriminated low exercise capacity. © 2017, Wiley Periodicals, Inc

Mechanical Alloying of Lanthana-Bearing Nanostructured Ferritic Steels

A novel nanostructured ferritic steel powder with the nominal composition Fe–14Cr–1Ti–0.3Mo–0.5La2O3 (wt.%) was developed via high energy ball milling. La2O3 was added to this alloy instead of the traditionally used Y2O3. The effects of varying the ball milling parameters, such as milling time, steel ball size and ball to powder ratio, on the mechanical properties and microstructural characteristics of the as-milled powder were investigated. Nanocrystallites of a body-centered cubic ferritic solid solution matrix with a mean size of approximately 20 nm were observed by transmission electron microscopy. Nanoscale characterization of the as-milled powder by local electrode atom probe tomography revealed the formation of Cr–Ti–La–O-enriched nanoclusters during mechanical alloying. The Cr:Ti:La:O ratio is considered “non-stoichiometric”. The average size (radius) of the nanoclusters was about 1 nm, with number density of 3.7 × 1024 m−3. The mechanism for formation of nanoclusters in the as-milled powder is discussed. La2O3 appears to be a promising alternative rare earth oxide for future nanostructured ferritic steels