ABSTRACT
The main objective of the present work is to determine the effects of laser processing on properties of WC-Co electro-spark deposited (ESD) coatings on steel substrates. Tungsten carbide coatings have been applied to steel substrates using a manual electrode feeder, model EIL-8A. The laser beam processing (LBP) of electro-spark coatings was performed using an Nd:YAG fiber laser. The microstructure and properties of laser treated/melted coatings were evaluated by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), surface geometric structure (SGS) and roughness measurements and adhesion, microhardness, residual stresses, corrosion resistance and application tests. The obtained experimental data were subjected to statistical analysis and multidimensional numerical and visual exploratory techniques. It has been shown conclusively that the laser-treated ESD WC-Co coatings are characterized by lower microhardness, higher resistance to corrosion, increased roughness and better adhesion to the substrate. LBP homogenizes the chemical composition, refines the microstructure and heals microcracks and pores of ESD coatings. The laser treated ESD WC-Co coatings can be used in frictional sliding nodes (e.g., on the front seal rings used in pumps) and as protective layers.
ABSTRACT
The work presents a possibility of fabrication of inexpensive iron-based powders intended to form the matrix in sintered diamond-impregnated tool components. In this study, a finely dispersed, pre-alloyed steel powder, containing over 95 wt.% Fe, has been designed and fabricated by means of a proprietary process developed at AGH-University of Science & Technology. It has been shown that the experimental powder can be consolidated to a closed porosity condition (>95% theoretical density) by pressure-less sintering at a temperature below 900 °C. The as-consolidated material is characterized by an excellent combination of hardness (~250 HV) and mechanical strength (>1200 MPa in 3-point bending) that meets the diamond tooling requirements. Its properties can be modified to some extent by varying the cold forming pressure and sintering temperature.
ABSTRACT
Five heart recipients were followed up with mycophenolate mofetil and low dose cyclosporine due to progressive severe chronic postcyclosporine renal failure. Cyclosporine was gradually withdrawn and finally eliminated from immunosuppressive regimen to slow the rate of renal function loss. Improvement of renal function was observed. In the follow up after cyclosporine elimination no risk increase of acute rejection and no deterioration of left ventricle function was observed. Non-calcineurin inhibitors model in heart recipients can be the treatment of choice (but only in very selective cases) in patients with severe chronic renal insufficiency.
Subject(s)
Calcineurin Inhibitors , Cyclosporine/adverse effects , Heart Transplantation/immunology , Immunosuppression Therapy/methods , Mycophenolic Acid/analogs & derivatives , Renal Insufficiency, Chronic/chemically induced , Adult , Aged , Calcineurin/metabolism , Cyclosporine/administration & dosage , Dose-Response Relationship, Drug , Follow-Up Studies , Glomerular Filtration Rate/drug effects , Graft Rejection/drug therapy , Graft Rejection/immunology , Humans , Immune Tolerance/drug effects , Immunosuppressive Agents/administration & dosage , Immunosuppressive Agents/adverse effects , Male , Middle Aged , Mycophenolic Acid/administration & dosage , Renal Insufficiency, Chronic/physiopathology , Renal Insufficiency, Chronic/prevention & control , Retrospective Studies , Treatment OutcomeABSTRACT
BACKGROUND: Pulmonary hypertension (PH) with pulmonary vascular resistance (PVR) 320-480 ARU resistant to therapy is a contraindication for orthotopic heart transplantation (HTX). AIM OF THE STUDY: evaluation of pulmonary hypertension in candidates for heart transplantation. STUDY POPULATION AND METHODS: 44 patients (pts) with dilated cardiomyopathy (Group I) and 34 patients with ischemic heart disease (Group II) were assessed. Evaluation of PH was done according to the following protocol: 1st measurement (cardiac catheterization): PVR (pulmonary vascular resistance) > or = 320 ARU--infusion of NTG (nitroglycerine) 1 microg/kg/min. (during 10 min.), 2nd measurement: PVR > or = 320 ARU--infusion of NTG 2 microg/kg/min. (during 10 min.), 3rd measurement: final PVR evaluation. If PVR was less than 320 ARU in 2nd or 3rd measurement, the reversibility of PH was diagnosed, and when PVR > or = 320 ARU was observed in 3rd measurement, fixed PH was diagnosed. RESULTS: No significant difference in baseline PVR between the groups was observed (Group I--332,7 ARU and Group II--327.6 ARU). In 23 patients with PVR > or = 320 ARU reduction of mean values of PVR, MPAP (mean pulmonary artery pressure) and TPG (transpulmonary gradient) was seen (p < 0.001), significantly more prominent in 11 pts from Group I. There was no correlation between duration of the disease and degree of PH. HTX was performed in 25 patients. PVR at 72 hours after HTX was similar in 7 pts with reversible PH and 18 pts with PVR < 320 ARU in 1st measurement. CONCLUSIONS: 1. Nitroglycerine used according to the protocol is sufficient in determining PH. 2. The reversibility of PH could depend on type of cardiomyopathy but not directly on symptom duration.
