Mechanical properties and fracture behavior of an ultrafine-grained Al-20 wt pct Si alloy

The effect of powder particle size on the microstructure, mechanical properties, and fracture behavior of Al-20 wt pct Si alloy powders was studied in both the gas-atomized and extruded conditions. The microstructure of the as-atomized powders consisted of fine Si particles and that of the extruded bars showed a homogeneous distribution of fine eutectic Si and primary Si particles embedded in the Al matrix. The grain size of fcc-Al varied from 150 to 600 nm and the size of the eutectic Si and primary Si was about 100 to 200 nm in the extruded bars. The room-temperature tensile strength of the alloy with a powder size \u3c26 μm was 322 MPa, while for the coarser powder (45 to 106 μm), it was 230 MPa. The tensile strength of the extruded bar from the fine powder (\u3c26 μm) was also higher than that of the Al-20 wt pct Si-3 wt pet Fe (powder size: 60 to 120 μm) alloys. With decreasing powder size from 45 to 106 μm to \u3c26 μm, the specific wear of all the alloys decreased significantly at all sliding speeds due to the higher strength achieved by ultrafine-grained constituent phases. The thickness of the deformed layer of the alloy from the coarse powder (10 μm at 3.5 m/s) was larger on the worm surface in comparison to the bars from the fine powders (5 μm at 3.5 m/s), attributed to the lower strength of the bars with coarse powders. © ASM International & TMS-The Minerals Metals and Materials Society 2005

Response of Mg Addition on the Dendritic Structures and Mechanical Properties of Hypoeutectic Al-10Si (Wt Pct) Alloys

Rapidly solidified hypoeutectic Al-10Si-xMg (x = 0, 5, 10 wt pct) alloys were produced by the melt-spinning method. The phase composition was identified by X-ray diffractometry, and the microstructures of the alloys were characterized by scanning electron microscopy. The melting characteristics were studied by differential scanning calorimetry and differential thermal analysis under an Ar atmosphere. The mechanical properties of the melt-spun and conventionally solidified alloys were tested by tensile-strength and Vickers microhardness tests. The results illustrate that the cooling rate and solidification time of 89 mu m thick melt-spun ribbon were estimated to be 2.97 x 10(7) K s(-1) and 9.31 x 10(-6) s, respectively. Nanoscale Si spot particles were observed growing on the surface of the dendritic alpha-Al matrix and the average sizes of these spots ranged from 10 to 50 nm. The improvement in the tensile properties and microhardness was related to structural refinement and the supersaturated alpha-Al solid solution; the nanoscale-dispersed Si spot particles made a significant improvement to the mechanical properties of the melt-spun ribbon. Detailed electrical resistivity tests of the ribbons were carried out at temperatures of 300 K to 800 K (27 A degrees C to 527 A degrees C)

Cardiovascular events associated with rofecoxib : final analysis of the APPROVe trial

Background: Selective inhibition of cyclo-oxygenase-2 has been associated with an increased risk of cardiovascular events in several clinical trials. The Adenomatous Polyp Prevention on Vioxx (APPROVe) study assessed the effect of 3-year treatment with a cyclo-oxygenase-2 inhibitor, rofecoxib (25 mg), on recurrence of neoplastic polyps of the large bowel. We report the cardiovascular outcomes of a long-term follow-up of participants in the trial. Methods: The APPROVe study is a multicentre, randomised, placebo-controlled, double-blind trial. 2587 patients with a history of colorectal adenomas were recruited at 108 centres worldwide during 2000 and 2001. Participants were followed for adverse events while on treatment and during the following 14 days. However, after early termination of treatment because of cardiovascular toxicity, we attempted to follow up all randomised patients for at least 1 year after stopping study treatment. External committees blindly assessed potential serious cardiovascular events. The focus of the analysis was the combined incidence of non-fatal myocardial infarction, non-fatal stroke, and death from cardiovascular, haemorrhagic, and unknown causes (Antiplatelet Trialists' Collaboration [APTC] combined endpoint). We used Cox proportional hazards regression to calculate endpoint hazard ratios. The study is registered with ClinicalTrials.gov, number NCT0282386. Findings: We obtained extended post-treatment cardiovascular follow-up data from 84% of participants, and extended mortality follow-up from 95%. In total, 59 individuals had an APTC endpoint in the rofecoxib group and 34 in the placebo group (hazard ratio 1.79, 95% CI 1.17-2.73; p=0.006). In the first year after cessation of treatment, there was a non-significant increase in the risks of APTC endpoints. The APTC hazard ratio did not substantially change over time. Interpretation: Use of rofecoxib is associated with increased rates of APTC events. Study data are compatible with an early increase in risk that persists for one year after stopping treatment