STUDY OF THE EFFECT OF THIN HARD COATINGS ON THE RESISTANCE OF HIGH STRENGTH-TO-MASS RATIO COMPONENTS

The rising need of lightening mechanical components by means of broader and broader use of light alloys is becoming crucial for the coming future. In the automotive and aerospace industries, for example, the request for more power with lower gas emissions is expected to acquire more and more importance. The fatigue behaviour of light alloys, however, is often worse than the one of traditional construction steels. The wear resistance, surface hardness and load bearing capacity can represent weak points for the former materials too. As a result, suitable surface treatments – such as thin hard coating deposition – may be decisive for improving their properties and make such properties be at least similar to the ones shown by the steels. Thin hard coatings deposited by means of physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques are, for the time being, wide spread in an increasing number of technological applications. The broad use of thin hard coatings is mainly due to the improvements achieved in the tribological and corrosion behaviour of the coated components and has concurred to consolidate the deposition techniques and justify the growing interest of researchers. Recent research studies, both experimental and numerical, have also demonstrated that thin hard coatings can prove effective in increasing the fatigue resistance of mechanical components and machine elements. The application of such coatings gives rise to surface modifications in the substrate which have been widely investigated with respect to the corrosion and wear resistance. As far as the fatigue resistance is concerned, in case of compressive residual stresses induced by the deposition process in correspondence of the surface layers of the base material, an increase of the fatigue limit, therefore of the number of load cycles until failure, is possible. The developed doctoral research activity has tried to go in depth through the fatigue and contact/rolling contact fatigue behaviour of thin hard-coated mechanical components. Experimental, numerical and statistical methods were used to study different bulk materials and coatings. Particular attention has been paid to those applications where increasing the fatigue limit of mechanical components can represent a decisive factor for performance elevation. Also, theoretical-numerical models enabling a designer to foresee the performance of coated components under fatigue and contact/rolling contact fatigue conditions were applied and proposed with good results. These procedures enable reliable fatigue life prediction of thin hard-coated components and were applied, in particular, to gears. The number of cycles necessary to achieve specified crack depths, until final failure, in coated and uncoated steel and titanium transmission spur gears was evaluated with one of the aforementioned previsional procedures. CrN and TiN coatings PVD-deposited on, respectively, steel and titanium base material were analyzed in this case and measurements of surface micro-hardness and residual stress fields were used in the calculations. As far as the fatigue tests on coated and uncoated specimens are concerned, several rotating bending experiments were carried out on both steel and light alloys. Different PVD and CVD coatings were deposited and the fatigue behaviour of the coated base materials was compared with the one shown without coating. The influence of the presence of both coating and a notch on the fatigue behaviour of coated titanium alloy specimens was also studied both numerically and experimentally. The contact and rolling contact fatigue behaviour of coated components was investigated with experimental, numerical and statistical methods. CrN PVD-coated and uncoated case hardened automotive transmission spur gears were investigated by means of numerical models and experimental contact fatigue tests. A suitable theoretical-numerical procedure able to predict the number of cycles necessary to promote initial fatigue damage at the contact area was developed and the results were compared with the experimental ones. Furthermore, this procedure was used to collect the data necessary to apply an advanced statistical method – namely Design and Analysis of Computer Experiments – to achieve the optimization of parameters influencing the fatigue and the rolling contact fatigue behaviour of coated components. Such parameters were related to both coating and base material. The presence of the self-equilibrated residual stresses induced by the coating deposition process was accurately simulated in the numerical models

A Numerical Method to Predict the RCF Behaviour of PVD-coated Transmission Gears and Experimental Results

This work studies the rolling contact fatigue (RCF) behaviour of case-hardened transmission gears for racing motorcycles both numerically and experimentally. Both as-produced and PVD-WC/C coated conditions are analyzed. Finite element models of the gears were developed and a calculation procedure was applied to predict their RCF life. The Ti-6Al-4 V alloy was also considered to investigate the mass decrease of the components. RCF tests were carried out in both dry and lubricated conditions. The experimental results were compared with the numerical ones to check the reliability of the predictive method proposed

Fatigue behavior of notched Ti-6Al-4V in air and corrosive environment

Abstract The broad use of titanium alloys in naval, automotive and aerospace applications expects the current research to shed light on the fatigue behavior of these materials in corrosive media and notched condition. In this respect, the fatigue behavior in air and NaCl solution of notched Ti-6Al-4 V flat dogbone samples was investigated. A step-loading method was used to generate data points on fatigue limit stress vs. Kt diagrams for a constant life of 200,000 load cycles at R = 0.1. Fracture surfaces were observed using stereoscopic microscope

Fatigue behavior of foreign object damaged 7075 heat treated aluminum alloy coated with PVD WC/C

AbstractThe effect of a physically vapor deposited (PVD) WC/C coating on the fatigue behavior of as produced and foreign object damaged (FOD) solution heat treated and aged 7075 aluminum alloy was studied. Coated and uncoated samples were tested under rotating bending to determine the fatigue strengths between 104 and 106 cycles in both damaged and smooth condition. FOD was produced with single shots of small hard steel spheres impacting at 100 m/s in the minimum cross section. SEM was used to characterize the features of the fracture surfaces

Five-year retrospective italian multicenter study of visceral leishmaniasis treatment

The treatment of visceral leishmaniasis (VL) is poorly standardized in Italy in spite of the existing evidence. All consecutive patients with VL admitted at 15 Italian centers as inpatients or outpatients between January 2004 and December 2008 were retrospectively considered; outcome data at 1 year after treatment were obtained for all but 1 patient. Demographic characteristics, underlying diseases, diagnostic procedures, treatment regimens and outcomes, as well as side effects were recorded. A confirmed diagnosis of VL was reported for 166 patients: 120 (72.3%) immunocompetent, 21 (12.6%) patients with immune deficiencies other than HIV infection, and 25 (15.1%) coinfected with HIV. Liposomal amphotericin B (L-AmB) was the drug almost universally used for treatment, administered to 153 (92.2%) patients. Thirty-seven different regimens, including L-AmB were used. The mean doses were 29.4 \ub1 7.9 mg/kg in immunocompetent patients, 32.9 \ub1 8.6 mg/kg in patients with non-HIV-related immunodeficiencies, and 40.8 \ub1 6.7 mg/kg in HIV-infected patients (P < 0.001). The mean numbers of infusion days were 7.8 \ub1 3.1 in immunocompetent patients, 9.6 \ub1 3.9 in non-HIV-immunodeficient patients, and 12.0 \ub1 3.4 in HIV-infected patients (P < 0.001). Mild and reversible adverse events were observed in 12.2% of cases. Responsive patients were 154 (93.3%). Successes were 98.4% among immunocompetent patients, 90.5% among non-HIV-immunodeficient patients, and 72.0% among HIV-infected patients. Among predictors of primary response to treatment, HIV infection and age held independent associations in the final multivariate models, whereas the doses and duration of L-AmB treatment were not significantly associated. Longer treatments and higher doses of L-AmB were not able to significantly modify treatment outcomes either in the immunocompetent or in the immunocompromised population

Chromosome conformation signatures define predictive markers of inadequate response to methotrexate in early rheumatoid arthritis

The authors would like to thank members of OBD Reference Facility Benjamin Foulkes, Chloe Bird, Emily Corfeld and Matthew Salter for expedient processing of clinical samples on the EpiSwitch™ platform and Magdalena Jeznach and Willem Westra for help with preparation of the manuscript. The study employed samples from the SERA Biobank used with permission and approval of the SERA Approval Group. We gratefully acknowledge the invaluable contribution of the clinicians and operating team in SERA. We would also like to thank Prof. Raju Kucherlapati (Harvard Medical School), and Prof. Jane Mellor (Oxford Univ.), Prof. John O’Shea (National Institute of Health) and Prof. John Isaacs (New Castle Univ.) for their independent and critical review of our study. A list of Scottish Early Rheumatoid Arthritis (SERA) inception cohort investigators is provided in Additional fle 1: Additional Note. Funding This work was funded by Oxford BioDynamics.Peer reviewedPublisher PD