Effect of microstructure refinement of pure copper on improving the performance of electrodes in electro discharge machining (EDM).

The paper presents an analysis of the impact of plastic deformation using hydrostatic extrusion (HE) on the structural, mechanical and functional properties of pure copper for use as electrodes in the process of electro discharge machining (EDM). As part of the research, copper was subjected to the HE process with the maximum cumulative true strain equal to ɛcum = 3.89 obtained in 5 stages. The result was, a refinement of the microstructure with the grains elongated in the direction of extrusion, with a cross-sectional size of d2 = 228 nm. As the obtained material can be potentially used in the process of electro discharge machining, the copper specimens after the HE process were subjected to a comprehensive analysis to determine the mechanical, physical and functional properties of the material. A significant increase in strength (UTS) and yield strength (YS) of the HE-processed copper was obtained, reaching respectively UTS = 464 MPa and YS = 456 MPa at the maximum strain of ɛ = 3.89. Despite the clear strain-induced strengthening of the material, a very high electrical conductivity of not less than 97% was obtained. The electrodes made of copper after HE process have reduced erosion wear while maintaining a comparable or better quality of the machined surface. The best results were obtained for finish machining, where the electrical discharge wear was lower by 60% compared to the electrode made of non-processed copper. In addition, an improvement in the surface quality after the EDM process by 25% was observed when using the HE-processed electrodes.

Thermo-Mechanical Treatment for Reducing the Wear Rate of CuCrZr Tool Electrodes during Electro-Discharge Machining.

The research presented in this paper focused on optimising the process of unconventional plastic forming by hydrostatic extrusion (HE) with post-processing heat treatment of a copper alloy (CuCrZr) for electro-discharge machining (EDM) applications. The treatment was carried out in such a way as to obtain a material with an improved microstructure, characterised by a significant increase in hardness and strength while maintaining a high electrical conductivity, thus achieving the main goal of reducing electrode wear in the EDM process. As part of the research, a material with an ultrafine-grained structure was obtained with an average grain size of d2 = 320 nm and a much higher strength of UTS = 645 MPa compared to the material in the initial state (UTS = 413 MPa). The post-processing treatment (ageing) allowed us to obtain a material with a high electrical conductivity after the HE process, at 78% IACS. The electrodes made of CuCrZr subjected to HE had a reduced electrical discharge wear in relation to electrodes made of the initial material. The best results were obtained for electrodes made of the material subjected to a five-stage HE process combined with ageing at 480 °C for 1 h. The electrical discharge wear in these electrodes was reduced by more than 50% compared to electrodes made of non-deformed copper.

In-situ experimental study on hydro-borehole technology application to improve the hard coal excavating techniques in coal mine.

The hydro-mining technology is considered as a promising method of bituminous coal excavation. The paper presents the results of the in-situ experimental campaign and modelling of hydro-cutting technology application. The proposed innovative technology was tested in terms of the effects of the distance between the outlet of water from the nozzle and a sidewall, pressure of the water jet, as well as the type of a nozzle on hydro-mining effectiveness. The hydro-cutting tests of coal seam performed in the Experimental Mine "Barbara" in Poland proved that the increase in water pressure in the range 20-40 MPa only slightly affects the coal face structure, while high pressure, of 80-100 MPa, has a significant impact on a coal face structure. The experimental results also showed the major effects of operating time as well as the distance of the water jet on the effectiveness of coal face mining.

The impact of severe plastic deformations obtained by hydrostatic extrusion on the machinability of ultrafine-grained Ti grade 2 intended for fasteners.

The study aimed to examine the effect of the hydrostatic extrusion (HE) process on the machinability of Ti grade 2 (Ti) in the turning process. After the deformation with true strain ɛ = 2.28, the microstructure was significantly refined to a grain size of 100 nm, resulting in an increase in the mechanical properties, UTS strength by 190%, YS yield strength by 230%Cutting forces for Ti in the initial state and after HE were analyzed at cutting depths ap = 0.3 mm and 0.5 mm, the variables were cutting speed Vc (20, 30 and 50 m/min) and feed rate f (0.08 and 0.13 m/s).The impact of the microstructure refinement in Ti after HE on the high cutting depth machinability deterioration (ap = 0.7 mm) was identified. This phenomenon is particularly noticeable at lower cutting speeds Vc = 20 and 30 m/min at which cutting forces are higher. Application tests of Ti after HE showed a significantly lower susceptibility to buckling during threading. As a result of the tests carried out for the Ti in the initial state, it was not possible to achieve the tolerance of pitch diameter of the thread required by standards, d2 at two of the three cutting depths tested. In turn, for the Ti after HE, the thread tolerances required by the standards were achieved for all tested cutting depths.

Influence of Strain Rates during Severe Plastic Strain Processes on Microstructural and Mechanical Evolution in Pure Zinc.

The study presents an analysis of the influence of the plastic strain rate on the mechanical and structural properties of pure zinc. Thanks to the use of unconventional methods of plastic processing, the process of the equal channel angular pressing (ECAP) and the process of hydrostatic extrusion (HE), the tests were performed in a wide range of plastic strain rates, between 0.04 s-1 and 170 s-1. Plastic strain rate changes were carried out in the course of the significant plastic strain processes, and not on previously deformed samples. All tests were carried out at a constant value of plastic strain rate, ε ~ 2. A strong influence of the plastic strain rate on changes in the microstructure in zinc was observed during the tests. For the rates in the range of 0.04 s-1 to 0.53 s-1 its bimodal nature was observed, and in the range of 7 s-1 to 170 s-1 high homogeneity and evenness of grains related to the processes of continuous dynamic recrystallization was noticed. The effect of the strong homogenization of the microstructure was the increase in mechanical properties, yield point and tensile strength to the maximum values of UTS = 194 MPa, YS = 145 MPa at a strain rate of 170 s-1. Compared to the material with a bimodal microstructure, an over seven-fold increase in the elongation value was observed.

Mechanical Reinforcement of Polyamide 6 by Cold Hydrostatic Extrusion.

This paper presents the effect of severe plastic deformation obtained using the cold hydrostatic extrusion (HE) method on the mechanical and structural properties of polyamide 6 (PA6). As a result of the plastic strain, a significant increase in ultimate tensile strength and tensile modulus were observed. Tensile strength rose by almost 500%, up to the level of 508 MPa, whereas the tensile modulus rose by about 65%. Flexural modulus increase was also observed to 3230 MPa, i.e., by approx. 160%. As a result of high plastic deformation, the structure of the polyamide 6 changed significantly, as evidenced by its fibrous nature as presented in the results of the scanning electron microscopy inspection (SEM). The surface quality of products investigated was tested using profilometry.

Microstructural Investigation of a Friction-Welded 316L Stainless Steel with Ultrafine-Grained Structure Obtained by Hydrostatic Extrusion.

The paper presents the microstructural investigation of a friction-welded joint made of 316L stainless steel with an ultrafine-grained structure obtained by hydrostatic extrusion (HE). Such a plastically deformed material is characterized by a metastable state of energy equilibrium, increasing, among others, its sensitivity to high temperatures. This feature makes it difficult to weld ultra-fine-grained metals without losing their high mechanical properties. The use of high-speed friction welding and a friction time of <1 s reduced the scale of the weakening of the friction joint in relation to result obtained in conventional rotary friction welding. The study of changes in the microstructure of individual zones of the friction joint was carried out on an optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and electron backscattered diffraction (EBSD) analysis system. The correlation between the microstructure and hardness of the friction joint is also presented. The heat released during the high-speed friction welding initiated the process of dynamic recrystallization (DRX) of single grains in the heat-affected zone (HAZ). The additional occurrence of strong plastic deformations (in HAZ) during flash formation and internal friction (in the friction weld and high-temperature HAZ) contributed to the formation of a highly deformed microstructure with numerous sub-grains. The zones with a microstructure other than the base material were characterized by lower hardness. Due to the complexity of the microstructure and its multifactorial impact on the properties of the friction-welded joint, strength should be the criterion for assessing the properties of the joint.

On-Pump vs Off-Pump coronary artery bypass surgery in atrial fibrillation. Analysis from the polish national registry of cardiac surgery procedures (KROK).

BACKGROUND: No single randomized study has ever before addressed the safety of On-Pump coronary artery bypass grafting (CABG) vs Off-Pump CABG in the setting of atrial fibrillation (AF) and data from small observational samples remain inconclusive. METHODS AND FINDINGS: Procedural data from KROK (Polish National Registry of Cardiac Surgery Procedures) were retrospectively collected. Of initial 188,972 patients undergoing CABG, 7,913 presented with baseline AF (76.0% men, mean age 69.1±8.2) and underwent CABG without concomitant valve surgery between 2006-2019 in 37 reference centers across Poland. Mean follow-up was 4.7±3.5 years (median 4.3 IQR 1.7-7.4). Cox proportional hazards models were used for computations. Of included patients, 3,681 underwent On-Pump- (46.52%) as compared to 4,232 (53.48%) who underwent Off-Pump CABG. Patients in the latter group less frequently were candidates for complete revascularization (P<0.001). In an unadjusted comparison, On-Pump surgery was associated with significantly worse survival at 30 days: HR: 1.28; 95%CIs: (1.07-1.53); P = 0.007. Along the 13-year study period, the trend shifted in favor of On-Pump CABG: HR: 0.92; 95%CIs: (0.83-0.99); P = 0.005. After rigorous propensity matching, 636 pairs were identified. The direction and magnitude of treatment effects was sustained with HRs of 3.58; (95%CIs: 1.34-9.61); p = 0.001 and 0.74; [95%CIs: 0.56-0.98]; p = 0.036) for 30-day and late mortality respectively. CONCLUSIONS: Off-Pump CABG offered 30-day survival benefit to patients undergoing CABG surgery and presenting with underlying AF. On-Pump CABG was associated with significantly improved survival at long term.

Expression of sex steroid receptors and aromatase in adipose tissue in different body regions in men with coronary artery disease with and without ischemic systolic heart failure.

Background: The hormonal metabolism of adipose tissue differs across regions of fat. This issue has never been verified in male patients with coronary artery disease (CAD) with and without systolic heart failure (SHF).Methods: We examined 90 male patients with CAD with and without SHF and 42 healthy controls.Results: In patients with CAD with and without SHF, androgen receptor (AR) expression in adipose tissue of the lower leg was higher than AR expression of the thoracic wall and epicardial adipose tissue (EAT) (both p < .0001 for SHF patients and both p < .001 for patients without SHF). Expression of aromatase in adipose tissue of the lower leg among patients with CAD and SHF was higher than aromatase expression of the thoracic wall and EAT (p < .001 and p < .05, respectively), and in patients without SHF, it was higher only than aromatase expression of the thoracic wall (p < .05). There were no differences in expression of estrogen receptor (ER) between three regions of adipose tissue both in men with CAD with and without SHF.Conclusions: In male patients with CAD, site-related differences of adipose tissue in expression of AR and aromatase are present regardless of coexisting SHF with the highest hormonal activity within peripheral subcutaneous adipose tissue.

Surgical ablation for atrial fibrillation during isolated coronary artery bypass surgery.

OBJECTIVES: Our goal was to evaluate early sequelae and long-term survival in patients undergoing isolated coronary artery bypass grafting (CABG) with concomitant surgical ablation for atrial fibrillation (AF). METHODS: Procedural data from KROK (Polish National Registry of Cardiac Surgery Procedures) were collected. A total of 7879 patients with underlying AF underwent isolated CABG between 2006 and 2018 in 37 reference centres across Poland. The mean follow-up was 4.7 ± 3.5 years [median (interquartile range) 4.3 (1.7-7.4)]. Propensity score matching and Cox proportional hazards models were used to compare isolated CABG + ablation with isolated CABG. RESULTS: Of the included patients, 346 (4.39%) underwent surgical ablation. Patients in this group were significantly younger (66.4 ± 7.5 vs 69.2 ± 8.2; P < 0.001) but had a non-significant, different baseline surgical risk (EuroSCORE: 2.11 vs 2.50; P = 0.088). After a rigorous 1:3 propensity matching (LOGIT model: 306 cases of isolated CABG + ablation vs 918 of isolated CABG alone), surgical ablation was associated with a lower 30-day risk of death [risk ratio 0.37, 95% confidence interval (CI) 0.15-0.91; P = 0.032] and multiorgan failure (risk ratio 0.29, 95% CI 0.10-0.94; P = 0.029). In the long term, surgical ablation was associated with a significant 33% improved overall survival rate: hazard ratio 0.67, 95% CI 0.49-0.90; P = 0.008. The benefit of ablation was sustained in the subgroups but was most pronounced in lower risk older patients (age >70 years, P = 0.020; elective status, P = 0.011) with 3-vessel disease (P = 0.036), history of a cerebrovascular accident (P = 0.018) and preserved left ventricular function [left ventricular ejection fraction >50%; P = 0.017; no signs of heart failure (per New York Heart Association functional class); P = 0.001] and those undergoing on-pump CABG (P < 0.001). CONCLUSION: Surgical ablation for AF in patients undergoing isolated CABG is safe and associated with significantly improved long-term survival.

Survival after surgical ablation for atrial fibrillation in mitral valve surgery: Analysis from the Polish National Registry of Cardiac Surgery Procedures (KROK).

OBJECTIVES: Surgical ablation for atrial fibrillation (AF) performed at the time of other valvular- or nonvalvular cardiac procedure is a mainstay of therapy; yet the data regarding its influence on remote survival are sparse. We aimed to evaluate late survival in patients undergoing mitral valve (MV) surgery with concomitant surgical ablation for AF. METHODS: Procedure-related data from the Polish National Registry of Cardiac Surgery Procedures (Krajowy Rejestr Operacji Kardiochirurgicznych) were retrospectively collected. A total of 11,381 patients with baseline AF (46.6% men; mean age 65.6 ± 9.0 years) undergoing MV surgery between 2006 and 2017 in 37 reference centers across Poland and included in the registry were analyzed. Median follow-up was 5 years (mean, 4.6 years; interquartile range, 1.9-7.9 years). Cox proportional hazards models were used for computations. Propensity score matching for the comparison of MV + ablation versus MV alone was performed. RESULTS: Of included patients, 2449 (21.5%) underwent surgical ablation for AF. Patients in this group were significantly younger (63.8 ± 8.7 years vs 66.1 ± 9.0 years; P < .001) and were at lower baseline surgical risk (EuroSCORE, 2.86 vs 3.69; P < .001). During the 12-year study period, there was a significant survival benefit (hazard ratio, 0.71; 95% confidence interval, 0.63-0.79; P < .001) for MV + ablation compared with MV alone. After rigorous propensity matching (logit model, 1784 pairs) surgical ablation was associated with nearly 20% improved survival (hazard ratio, 0.82; 95% confidence interval, 0.70-0.96; P = .011). Benefit of surgical ablation was maintained in subgroup analyses, yet most benefit was appraised in low-risk patients such as those with EuroSCORE of 2 to 5 or age < 50 years. CONCLUSIONS: Concomitant surgical ablation for AF in patients undergoing mitral valve procedures is safe, feasible, and significantly improves late survival.

Giant saccular superior vena cava aneurysm-a rare and difficult clinical case.

A superior vena cava (SVC) aneurysm is an extremely rare case of vascular malformation in the chest cavity. This is a report of a case of a 57-year-old woman with a saccular SVC aneurysm which was 8 cm wide. The chest computed tomography (CT) scan confirmed a giant 75 mm × 79 mm × 81 mm mass containing the contrast medium from SVC, constricting the right lung parenchyma, narrowing the right innominate vein, in contact with the anterolateral chest cavity wall, and adjoining the superior mediastinum. Under general anesthesia and employing the median sternotomy approach, using a cardiopulmonary bypass (CPB), the venous aneurysm was successfully resected. The postoperative period was uneventful. Radical surgical resection using a sternotomy and a CPB is recommended.

Can cardiopulmonary bypass system with blood priming become a new standard in coronary surgery?

BACKGROUND: Commonly used cardiopulmonary bypass systems with cardiotomy reservoir, oxygenator, and roller pump require preoperative crystalloid filling. Radical reduction of the filling fluid volume and replacing it with the patient's own blood has a fundamental impact on the outcome. AIM: A comparison of cardiopulmonary bypass filled with the patient's blood, applied in Poland for the first time, and the classical system filled with crystalloids. METHODS: Non-randomised trial in which patients undergoing coronary artery bypass grafting were divided into two groups: first operated on with use of cardiopulmonary bypass system with the patient's own blood priming, and a control group operated on with standard technique. Levels of haemoglobin (HGB), haematocrit (HCT), platelets, leukocytes, creatinine, protein, C-reactive protein, procalcitonin, volume of transfused blood products, postoperative drain output, time to extubation, and consumption of catecholamines were compared. RESULTS: The results of a study comparing the classical system with the blood-filled system (n = 60) showed a significantly smaller decrease in HGB and HCT levels (p = 0.001), resulting in reduction of blood product transfusions by 75% (p = 0.03). The new type of extracorporeal circulation reduced the total postoperative drain output by approximately 28% (p = 0.003). The systemic inflammatory response syndrome (SIRS) was less pronounced and the tissue perfusion was better due to smaller degree of haemodilution leading to better organ and heart protection. The patients required shorter mechanical ventilation times in the perioperative period. CONCLUSIONS: The use of a new system of cardiopulmonary bypass filled with the patient's blood reduces the postoperative decrease in HGB and HCT, the amount of transfused blood products, and total postoperative drain output. It also shortens the time spent on mechanical ventilatory support.

Late Cardiac Tamponade as a Result of Parietal Pericardium Erosion.

Late onset cardiac tamponade is a rare and particularly challenging (both from diagnostic and management perspectives) complication of intracardiac lead implantation. We present a case of a late tamponade leading to cardiogenic shock, which occurred 1,164 days after implantable cardioverter-defibrillator (ICD) implantation. Open repair revealed unusual and, to our knowledge, not yet reported mechanism of the disease. A pressure sore caused by an ICD lead was found in the parietal layer of pericardium with no visible damage to the visceral layer. Conservative management in the described clinical scenario could be fatal, thus awareness of this pathomechanism of tamponade is critical.

Bone marrow iron depletion is common in patients with coronary artery disease.

BACKGROUND/OBJECTIVES: Iron deficiency (ID) may be an important, treatable co-morbidity complicating cardiovascular diseases, but considerable uncertainty exists about the diagnostic accuracy of blood tests. Accordingly, we investigated the relationship between blood tests for ID and iron stores in bone marrow aspirates, the diagnostic gold-standard for ID, in patients with stable coronary artery disease (CAD). METHODS: Bone marrow aspirates were obtained from 65 patients with stable CAD undergoing cardiac surgery and 10 healthy controls. ID was defined as depleted extracellular iron stores (0-1 grade according to Gale scale) accompanied by ≤10% of erythroblasts containing iron. RESULTS: Bone marrow ID was found in 31 (48%) patients with CAD but in none of the controls (p<0.01). Amongst patients with CAD, ID was present in 10 of 16 (63%) with and 21 of 49 (43%) without anaemia (p=0.17). The clinical profiles of patients with and without ID were similar. Of circulating biomarkers of ID, serum soluble transferrin receptor had the strongest association with bone marrow ID (area under curve: 0.876±0.048, 95% confidence interval: 0.762-0.948, for cut-off of ≥1.32mg/L-sensitivity: 67%, specificity: 97%). CONCLUSIONS: Almost half of patients with stable CAD have profound bone marrow iron depletion that can be accurately assessed non-invasively using serum soluble transferrin receptor.

[Early bioprosthetic mitral valve thrombosis]. / Wczesna zakrzepica zastawki biologicznej w pozycji mitralnej.

We present a case of a 70 year-old woman operated due to severe mitral regurgitation. Early after surgery transthoracic echocardiography revealed the decreased effective orifice area of the implanted bioprosthetic valve and the stenotic features of transvalvular flow. Transesophageal echocardiography (TEE) disclosed a thrombotic cause of heterograft dysfunction. Due to the clinical deterioration and the unclear cause of prosthesis stenosis, the patient was reoperated. Intra-operatively bioprosthetic mitral valve thrombosis was confirmed. Precipitating factors of this rare complication including cardiac device related infective endocarditis (CDRIE) and the diagnostic applicability of TEE in this clinical scenario are discussed.

[Vascular anomaly - left anterior descending artery originating from right coronary sinus]. / Anomalia naczyniowa - odejscie przedniej tetnicy zstepujacej od prawej zatoki wiencowej.

A case of a patient with congenital anomaly of coronary blood vessels with left anterior descending artery starting from right coronary sinus is presented. The patient was operated on due to symptoms of myocardial ischaemia by carrying out an off-pump coronary artery bypass graft to left anterior descending artery and obtuse marginal artery, with a very good outcome.