Adrian Barylski

The Influence of Plastic Deformation Performed before and after Electron Beam Irradiation on the Morphology and Structural Properties of UHMWPE

The paper presents changes in UHMWPE morphology and structure caused by irradiation with an electron beam and plastic deformation. The input material consisted of two grades of polyethylene, i.e. GUR 1050 and GUR 1020 (Poly Hi Solidur Medi TECH), used for producing the bearing components of endoprostheses applied in total joint alloplasty. Tests involved three groups of samples: the ones subjected to modification through radiation (N) only, those modified by plastic deformation before (ON) and after (NO) irradiation with an electron beam (N). The obtained variants were subjected to comprehensive morphological and structural tests, which made it possible to document changes in the lamellar structure (SEM) and orientation of the crystalline structure (SAXS) as well as to determine the content of the crystalline phase (DSC) and to define crosslinking density.

Changes in UHMWPE Morphology and Structure after Irradiation with an Electron Beam and Thermal Treatment

The paper presents changes in UHMWPE morphology and structure induced by exposure to a beam of electrons and thermal processing applied after the modification through irradiation. Two groups of samples were tested: those that underwent modification through irradiation only and those that underwent a sequential process which consisted of radiation modification and thermal processing. The obtained variants were subjected to comprehensive morphological and structural tests, which made it possible to: document changes in the lamellar structure (SEM); determine the content of crystalline phase (DSC); determine the degree and density of crosslinking; state the degree of polymer oxidation (FTIR); examine the influence of the irradiation dose on the intensity of free radicals occurrence (EPR) and to determine the effectiveness of their elimination using recrystallisation in an oxygen-free environment.

Characteristics of the tribological properties of oxide layers obtained via thermal oxidation on titanium Grade 2

Thermal oxidation is an effective technique for modifying the surface of titanium and its alloys in order to improve their poor tribological properties. This paper presents the results of tests concerning titanium Grade 2 subjected to thermal oxidation at 600 ℃ and 700 ℃ for 72 h. The morphology of the surface of the formed oxide scale was determined. The surface of a specimen oxidised at 600 ℃ was unevenly covered by very fine oxide particles. Raising the temperature to 700 ℃ made it possible to cover the entire examined surface with an oxide layer. The obtained scale was characterised by the presence of large irregularly shaped agglomerated oxide particles. Tribological tests showed that the presence of an oxide layer on the surface of titanium significantly improved the resistance of the interacting tribological couple to sliding wear. The obtained 3D isometric images of the trace of wear showed that the formed traces differed in terms of width, depth and shape. It was shown that the area of the cross section of the trace of wear decreased as the temperature of thermal oxidation increased. Scanning electron microscopic observations of traces of wear formed following tribological interaction with an Al2O3 ball showed, in a non-oxidised specimen and a specimen oxidised at 600 ℃, the presence of alternating morphologically varied areas formed as a result of corrugation wear. The oxide layer obtained at 700 ℃ has the highest resistance to sliding wear and completely eliminates the adverse corrugation wear phenomenon.

THE INFLUENCE OF THE TIME OF TECHNOLOGICAL SOAKING OF NITRIDED EN-X37CrMoV5-1 TOOL STEEL AT A HIGHER TEMPERATURE ON THE STRUCTURE, MICROHARDNESS, AND TRIBOLOGICAL WEAR OF THE SURFACE LAYER

The paper concerns the assessment of the influence of the duration of high-temperature soaking of steel intended for dies for extruding aluminium profiles on the structure, microhardness, and tribological wear of the top layer. Gas nitrided hot work tool steel X37CrMoV5-1 (WCL) was used in the tests. For technological reasons, before the extruding process, such dies are pre-heated for several hours to a temperature ranging from 400°C to 600°C. Due to the possibility of various unplanned situations (failures), the soaking time may be extended even up to more than ten hours. Therefore, soaking was used after the nitriding process due to the application nature of the research whose purpose was to identify changes occurring in the nitrided layer after soaking of dies at a higher temperature (520°C) and before starting the extruding process, and thus to determine for how long the dies may be held in a furnace without undesirable changes in the top layer. The examined samples were soaked in an industrial furnace at 520°C for 2 h, 4 h, 6 h, 8 h, 10 h, and 12 h. Samples heated to 520°C and then immediately cooled down and the reference material which was not heated after the nitriding process were also examined for comparison purposes. The obtained results of the tests of the microhardness of the nitrided layer indicate that it decreased as the soaking time increased to 6 hours. After this time, that parameter is stabilised and further heating up to 10 hours does not cause a significant decrease in the microhardness of the top layer. A further decrease in the microhardness of the layer was observed for samples soaked for 12 hours. The results of tribological tests showed an analogous course of changes in the tribological wear of the examined material as the soaking time increased. The performed tests indicate the possibility of holding dies at a higher temperature (520°C) for 10 hours. Further soaking at this temperature causes adverse changes in the top layer. Słowa kluczowe: stal narzędziowa; X37CrMoV5-1; azotowanie; warstwa wierzchnia; mikrotwardość; zużycie tribologiczne. Streszczenie Praca dotyczy oceny wpływu czasu wygrzewania w podwyższonej temperaturze stali przeznaczonej na matryce do wyciskania profili aluminiowych na strukturę, mikrotwardość oraz zużycie tribologiczne warstwy wierzchniej. W badaniach stosowano stal narzędziową do pracy na gorąco X37CrMoV5-1 (WCL) poddaną procesowi azotowania gazowego. Matryce takie są przed procesem wyciskania poddawane wstępnemu nagrzewaniu do temperatury z przedziału 400°C do 600°C przez okres kilku godzin, co jest spowodowane względami technologicznymi. Z uwagi na możliwość wystąpienia różnych nieplanowanych sytuacji (awarii) czas wygrzewania może ulec wydłużeniu nawet do kilkunastu godzin. Zastosowany zabieg wygrzewania po procesie azotowania wynikał zatem z aplikacyjnego charakteru badań, które miały na celu określenie zmian zachodzących w warstwie azotowanej po wygrzewaniu matryc w podwyższonej temperaturze (520°C) przed rozpoczęciem procesu wyciskania, a tym samym określenie, przez jaki czas można przetrzymywać matryce w piecu bez pojawienia się niepożądanych zmian w warstwie wierzchniej. Badane próbki wygrzewano w piecu przemysłowym w temperaturze 520°C przez czas 2 h, 4 h, 6 h, 8 h, 10 h i 12 h. W celach porównawczych zbadano także próbki nagrzane do temperatury 520°C i od razu chłodzone oraz materiał wzorcowy, który nie był wygrzewany po procesie azotowania. Uzyskane wyniki badań mikrotwardości warstwy azotowanej wskazują na jej spadek wraz z rosnącym czasem wygrzewania do 6 godzin. Po tym czasie parametr ten ulega stabilizacji i dalsze wygrzewanie do 10 godzin nie powoduje istotnego spadku mikrotwardości warstwy wierzchniej. Dla próbek wygrzewanych przez okres 12 godzin odnotowano dalszy spadek mikrotwardości warstwy. Wyniki testów tribologicznych wykazały analogiczny przebieg zmian zużycia tribologicznego badanego materiału wraz z rosnącym czasem wygrzewania. Przeprowadzone testy wskazują na możliwość przetrzymywania matryc w podwyższonej temperaturze (520°C) przez okres 10 godzin. Dalsze wygrzewanie w tej temperaturze powoduje pojawienie się niekorzystnych zmian w warstwie wierzchniej. * Institute of Materials Science, Faculty of Computer Science and Materials Science, University of Silesia, ul. 75 Pułku Piechoty 1A, 41-500 Chorzów, Poland, e-mail: michal.dworak@us.edu.pl, tel. 323497641. 28 ISSN 0208-7774 T R I B O L O G I A 4/2017

The Influence of Plastic Deformation Performed before and after Electron Beam Irradiation on Mechanical Properties and Wear of UHMWPE

The paper compares the modification methods of polymers GUR 1050 and GUR 1020 by means of plastic deformation before (ON) and after (NO) irradiation with an electron beam (N). Evaluation of the effectiveness of the modification methods applied was carried out by means of micromechanical examinations and tribological tests on T-01 and T-05 testers (polymer/Vitalium alloy). The results of micromechanical, sclerometric and tribological tests indicate unequivocally the effectiveness of the modifications applied, as compared to the polymer modification through irradiation with an electron beam only. A decrease in hardness and elasticity modulus was found for materials subjected to the ON and NO technology as compared to N, while maintaining the growing trend of these values along with the applied radiation dose. There was also noted a large increase of the wear resistance coefficient, Wβ, and an increase of the microploughing component’s share in the wear mechanism β, which had a direct influence on the reduction of the linear wear by 2.5–3 times and a nearly twofold decrease of the mass wear. The surface subjected to friction processes became smoother and free of lamella fragments which were visible for the base material not subjected to any modifications. This was documented with the observations performed on a scanning microscope and in the stereometric examination of the surface.

Changes of Free Radical Content in Exposed to Electrons GUR1020 and GUR1050 Polyethylene Types Intended for Endoprosthesis Acetabular Cups

The paper presents the results of the EPR examination of free radical content in GUR1020 and GUR1050 polyethylenes which were irradiated with an electron beam. Changes in the amount of radicals in the period of 12 months in the UHMWPE cross-linked with a dose of 26-156 kGy were analysed. Spectra registered 90 days after irradiation show a hyperfine structure. An image consisting of 7 characteristic lines is the most similar pattern that can be used to analyse this spectrum. Subsequent measurements (255 and 372 days after irradiation) produce images consisting of one resonance line. Alkyl and allyl radicals generated during the irradiation are the source of the EPR signal. The influence of atmospheric oxygen causes further changes of the radicals mentioned above, which leads to the formation of peroxyl radicals. The content of radicals in the polymer and its changes over time were calculated. The amount of radicals increases as the absorbed dose grows, but decreases over time. Comparative measurements of the material subjected to thermal processing at the temperature of 423 K have shown that in this case, no resonance lines are present, which testifies to the effective elimination of free radicals by means of UHMWPE recrystallisation.

Changes in the Molecular Structure of UHMW Polyethylene under the Influence of Thermal and Radiation Modification, as Well as Time

The paper presents the results of an examination of UHMW polyethylene type GUR1050 using the EPR, FTIR and SEM methods. The relationship between the number of radicals in the polymer and the absorbed dose of ionizing radiation has been shown. The radicals, being highly active macroparticles, disappear in time, so that after about a year their amount is reduced by approximately one order of magnitude. The disappearance of the radicals over time results in a change in EPR spectra, an increase in the degree of oxidation, and cross-linking. The most probable mechanisms are the formation of alkyl and allyl radicals and their gradual transitions, which lead to the absorption of atmospheric oxygen, and the recombination of radicals, which leads to the formation of cross linkages. Thermal treatment of the samples is an effective method of eliminating the radicals. Tribological tests and their analysis by means of SEM observation showed that the irradiated samples proved to have higher resistance to abrasion than the material that was not exposed to radiation.

The Influence of e-Beam Irradiation on the Morphology and Functional Properties of UHMWPE

The paper presents an analysis of the effectiveness of radiation modification of GUR 1050 and GUR 1020 polymers intended for endoprosthesis bearing components. It has been demonstrated through extraction and expansion that the crosslinking density increases as the applied dose of electron irradiation and the molecular weight of polyethylene grow. The recorded changes were accompanied by an increase in the degree of crystallinity, which was more significant in the case of the more heavy GUR 1050 (compared to GUR 1020). The morphological changes are supported by the results of micromechanical, sclerometric and tribological examinations. Tribological examinations were documented with SEM images of the surface of specimens subjected to oscillatory friction (roll-block tester). Series of crosswise valleys and projections, arranged along the friction direction, were found on the friction surface. The smoothening of the surface and a lack of lamella fragments on the base specimens which were not subjected to e-beam irradiation are observed along with a reduction of wear due to the increasing dose of irradiation.

The Influence of Plastic Deformation on Structure of Highly Crosslinked UHMWPE Intended for Endoprosthesis Cups

In this paper, an attempt has been made to determine the changes in the structure of UHMWPE under the influence of deformation, which can be the cause of the decrease of functional properties. It has been found that the degree of cross-linking slightly changes due to operational loads (deformation ef=0.15-0.6). The deformation leads, however, to the systematic lowering of the degree of crystallinity and an insignificant decrease of lamella width. Tests of wide- and small-angle X-ray scattering (WAXS, SAXS) prove that this is the result of operational deformation causing a rather weak texture of crystals and the fragmentation of some lamellae. Anisotropy of the lamellar structure also takes place, which changes 2D SAXS images into ellipses with a rapidly growing axial ratio with ef value.