Mejoramiento de las propiedades mecánicas y tribológicas del acero AISI 4340 tratado térmicamente, utilizando un recubrimiento de multicapas de TiN/TiAlN

RESUMEN: Multicapas de TiN/TiAlN (nitruro de titanio/nitruro de titanio aluminio) se depositaron por la técnica de la pulverización catódica d.c. reactiva utilizando blancos de titanio y de aluminio de 10 cm de diámetro, con una pureza de 99,9%, en una atmósfera de argón y nitrógeno (Ar/N), aplicando una temperatura de 300°C y una presión de 7x10-3 mbar al sustrato. Como sustratos se utilizaron silicio (100) y acero AISI 4340 tratado térmicamente con una dureza de 54 Rockwell C (HRC, aproximadamente 5,4 GPa). Recubrimientos de TiN/TiAlN con un contenido de Al de 70% y un espesor total de 4 µm se investigaron en función del número de multicapas y sus propiedades mecá- nicas y tribológicas se compararon con las de las muestras de acero sin recubrir. La estructura cristalina de las muestras recubiertas se analizó mediante difracción de rayos X, la morfología y topografía con microscopia electrónica de barrido (SEM) y microscopia de fuerza atómica (AFM). La dureza se determinó mediante nanoindentación, mientras que la resistencia al desgaste se caracterizó a través de mediciones de pin on disc. Para las 150 multicapas de TiN/TiAlN se obtuvo un incremento en la dureza y en el módulo de Young de 62% y 70% respectivamente, en relación a las 30 bicapas iniciales, y de 740% y 202% respectivamente, comparado con el acero AISI 4340 sin recubrir. Finalmente, el coeficiente de fricción se redujo de 0,55 a 0,20 y la rugosidad de 60 nm a 3,2 nm para las probetas de acero recubiertas con 150 bicapas de TiN/TiAlN, lo cual condujo a una mayor resistencia al desgaste del sistema de recubrimiento.ABSTRACT: TiN/TiAlN (titanium nitride/titanium aluminum nitride) multilayer were deposited by d.c. reactive magnetron sputtering using titanium and aluminum targets with 10 cm in diameter and 99.9% purity in an argon/nitrogen (Ar/N) atmosphere, applying a substrate temperature of 300°C and a pressure of 7x10-3 mbar. Silicon (100) and heat treated AISI 4340 steel samples with a hardness of 54 Rockwell C (HRC, approximately 5.4 GPa) were utilized as substrate. TiN/TiAlN coatings with 70% aluminum and 4 µm total thickness were investigated as function of multilayer number and their mechanical and tribological properties compared to the uncoated steel samples. The crystalline structure of the coated samples was analyzed through X-ray diffractometry and its morphology and topography using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Hardness was determined by means of nanoindentation, while wear resistance was characterized through pin on disc measurements. A hardness and Young Modulus increment from 62% and 70% respectively, were obtained for 150 multilayer of TiN/TiAlN related to 30 bilayers and from 740% and 202% respectively, compared with the uncoated AISI 4340 steel samples. Finally the friction coefficient was reduced from 0.55 down to 0.20 and the roughness from 63 nm to 3.2 nm for the steel samples coated with 150 bilayers of TiN/TiAlN, what conduced to a greater wear resistance of the coating system

Albiglutide and cardiovascular outcomes in patients with type 2 diabetes and cardiovascular disease (Harmony Outcomes): a double-blind, randomised placebo-controlled trial

Background: Glucagon-like peptide 1 receptor agonists differ in chemical structure, duration of action, and in their effects on clinical outcomes. The cardiovascular effects of once-weekly albiglutide in type 2 diabetes are unknown. We aimed to determine the safety and efficacy of albiglutide in preventing cardiovascular death, myocardial infarction, or stroke. Methods: We did a double-blind, randomised, placebo-controlled trial in 610 sites across 28 countries. We randomly assigned patients aged 40 years and older with type 2 diabetes and cardiovascular disease (at a 1:1 ratio) to groups that either received a subcutaneous injection of albiglutide (30–50 mg, based on glycaemic response and tolerability) or of a matched volume of placebo once a week, in addition to their standard care. Investigators used an interactive voice or web response system to obtain treatment assignment, and patients and all study investigators were masked to their treatment allocation. We hypothesised that albiglutide would be non-inferior to placebo for the primary outcome of the first occurrence of cardiovascular death, myocardial infarction, or stroke, which was assessed in the intention-to-treat population. If non-inferiority was confirmed by an upper limit of the 95% CI for a hazard ratio of less than 1·30, closed testing for superiority was prespecified. This study is registered with ClinicalTrials.gov, number NCT02465515. Findings: Patients were screened between July 1, 2015, and Nov 24, 2016. 10 793 patients were screened and 9463 participants were enrolled and randomly assigned to groups: 4731 patients were assigned to receive albiglutide and 4732 patients to receive placebo. On Nov 8, 2017, it was determined that 611 primary endpoints and a median follow-up of at least 1·5 years had accrued, and participants returned for a final visit and discontinuation from study treatment; the last patient visit was on March 12, 2018. These 9463 patients, the intention-to-treat population, were evaluated for a median duration of 1·6 years and were assessed for the primary outcome. The primary composite outcome occurred in 338 (7%) of 4731 patients at an incidence rate of 4·6 events per 100 person-years in the albiglutide group and in 428 (9%) of 4732 patients at an incidence rate of 5·9 events per 100 person-years in the placebo group (hazard ratio 0·78, 95% CI 0·68–0·90), which indicated that albiglutide was superior to placebo (p<0·0001 for non-inferiority; p=0·0006 for superiority). The incidence of acute pancreatitis (ten patients in the albiglutide group and seven patients in the placebo group), pancreatic cancer (six patients in the albiglutide group and five patients in the placebo group), medullary thyroid carcinoma (zero patients in both groups), and other serious adverse events did not differ between the two groups. There were three (<1%) deaths in the placebo group that were assessed by investigators, who were masked to study drug assignment, to be treatment-related and two (<1%) deaths in the albiglutide group. Interpretation: In patients with type 2 diabetes and cardiovascular disease, albiglutide was superior to placebo with respect to major adverse cardiovascular events. Evidence-based glucagon-like peptide 1 receptor agonists should therefore be considered as part of a comprehensive strategy to reduce the risk of cardiovascular events in patients with type 2 diabetes. Funding: GlaxoSmithKline