Low weight and high strength are significant factors in the current decade’s spread of composite sandwich materials. Previous studies have proven that forming stiffening ribs in these materials through the Single Point Incremental Forming (SPIF) process is possible and gives encouraging results. On the other hand, knowledge of residual stress (RS) values that form during the manufacturing process is essential, as they may affect the structural integrity of manufactured elements, whether in compression or tension. The investigation of the RS in the composite materials formed by the SPIF process using the XRD method was very limited in the previous studies, so this research aims to apply the X-ray diffraction (XRD) method to determine RS on the part of the LITECOR® sandwich material formed using SPIF. LITECOR® consists of a plastic core between two layers of steel. In this study, three types of LITECOR® were used with differing plastic core thicknesses of 0.8, 1.25, and 1.6 mm, while the steel layers’ thickness remained the same at 0.3 mm. The axial and traverse RSs were measured in five positions on both sides of the formed part. It was found that the achieved RSs varied from tensile to compressive along the formed regions. It was found that the residual stress values in both directions were inversely proportional to the thickness of the plastic core. It was noted that the highest RS values were in the unformed base metal, after which the RS was reduced on both sides of the SPIF-formed region, followed by a rise in the RS at the concave of the SPIF-formed region. The maximum measured RS for X-axes was 1041 MPa, whereas, for Y-axes, it was 1260 MPa, both of which were recorded on the back side at a thickness of t = 0.8 mm.
Corrosion rates of aluminum in phosphoric (V) acid solutions were determined gravimetrically in a presence of sodium molybdate which acts as an inhibitor. Inhibition efficiencies were calculated. The most effective corrosion inhibition was observed for 0.5 M H3PO4 and 100 mM of Na2MoO4. Since insoluble corrosion products precipitated onto specimens and influenced the determined corrosion rates, an analysis of a morphology of the specimens was performed by using a scanning electron microscope. The corrosion products are composed of Mo, P, Al and O. An Mo/P atomic ratio varied between 0.8 and 1.6 depending on the concentrations of phosphoric (V) acid and sodium molybdate. For three concentrations of H3PO4, the concentration ranges of sodium molybdate, where the gravimetric method may be applied were determined.
Przedstawiono ocenę wpływu warunków procesu napawania laserowego na morfologię mikrostruktury i właściwości napoiny wytworzonej na podłożu z nadstopu niklu Inconel 738LC, z którego wytwarza się elementy części gorącej silnika lotniczego. Proces prowadzono za pomocą lasera dyskowego TruDisk 1000 firmy TRUMPF o mocy 1 kW z różnymi wartościa-mi prędkości napawania -od 400 do 700 mm/min. Materiałem dodatkowym był proszek stopu kobaltu -Stellite 694. Określo-no stopień oddziaływania warunków procesu napawania laserowego na skład chemiczny i morfologię składników fazowych mikrostruktury oraz wpływ objętości względnej materiału podłoża w napoinie na jej twardość. SŁOWA KLUCZOWE: napawanie laserowe, podłoże Inconel 738LC, napoina Stellite 694, morfologia mikrostruktury, twardość napoinyIn this paper the influence of laser cladding process parameters on microstructure and hardness of Stellite 694 coatings deposited onto Inconel 738LC alloy substrate is presented. Laser cladding process was carried out using Yb:YAG -TRUMPF TruDisk 1000 disc laser with maximum power of 1 kW in continuous wave mode. Laser cladding head velocity from 400 to 700 mm/min was applied. The effect of process parameters on chemical composition, microstructure morphology was examined by means of optical microscopy and scanning electron microscopy. The influence of volume fraction of substrate in the coating on its hardness was determined. KEYWORDS: laser cladding, Inconel 738LC substrate, Stellite 694 coating, microstructure, hardness Łopatki turbiny gazowej pracują w trudnych warunkach -są narażone na oddziaływanie wysokiej temperatury, środowiska gazów utleniających oraz dużych obciążeń mechanicznych. Te elementy produkuje się z żarowytrzy-małych materiałów, przede wszystkim z nadstopów niklu, a także żelaza i kobaltu. Nadstopy niklu charakteryzują się szczególnie dobrą żarowytrzymałością oraz odpornością na zmęczenie cieplne [1,2].Analiza danych literaturowych wskazuje, że zużycie pióra łopatki najczęściej następuje wskutek erozji. Dodatkowo półki łopatek tworzące zewnętrzny pierścień turbiny są narażone na zużycie ścierne. W miejscach ich styku stosuje się zatem warstwy ochronne materiału o większej odporności na ścieranie w porównaniu z materiałem podłoża, którym zazwyczaj jest nadstop niklu. Wspomniane warstwy wytwarza się ze stopów kobaltu z dużą zawartością chromu i wolframu (Stellity), a także ze stopów kobaltu z molibdenem, chromem, wolframem i krzemem (stopy Tribaloy). Gatunki tych stopów charakteryzują się dużą twardością (55÷60 HRC) w porównaniu z nadstopami niklu (35 HRC) oraz dobrą odpornością na pełzanie i zużycie ścierne [3÷5].Warstwy ochronne o dobrej odporności na ścieranie otrzymuje się w procesach napawania gazowego, napawania elektrycznego, natryskiwania plazmowego lub napawania laserowego. Napawanie laserowe jest nowoczesną metodą pozwalającą na uzyskanie warstw o prognozowanych właściwościach użytkowych. Ten proces najczęściej prowadzi się z użyciem laserów diodowych, dyskowych i CO 2 [6÷8], a charakteryzują go: długość fali ...
The influence of cooling conditions and surface topography after finish turning of Ti6Al4V titanium alloy on corrosion resistance and surface bioactivity was analyzed. The samples were machined under dry and minimum quantity lubrication (MQL) conditions to obtain different surface roughness. The surface topographies of the processed samples were assessed and measured using an optical profilometer. The produced samples were subjected to electrochemical impedance spectroscopy (EIS) and corrosion potential tests (Ecorr) in the presence of simulated body fluid (SBF). The surface bioactivity of the samples was assessed on the basis of images from scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analysis. The inspection of the surfaces of samples after turning under dry and MQL conditions revealed unevenly distributed precipitation of hydroxyapatite compounds (Ca/P) with a molar ratio in the range of 1.73–1.97. Regardless of the cutting conditions and surface roughness, the highest values of Ecorr ~0 mV were recorded on day 7 of immersion in the SBF solution. The impedance characteristics showed that, compared to the MQL conditions, surfaces machined under dry conditions were characterized by greater resistance and the presence of a passive layer on the processed surface. The main novelty of the paper is the study of the effect of ecological machining conditions, namely, dry and MQL cutting on the corrosion resistance and surface bioactivity of Ti6Al4V titanium alloy after finish turning. The obtained research results have practical significance. They can be used by engineers during the development of technological processes for medical devices made of Ti6Al4V alloy to obtain favorable functional properties of these devices.
Advanced aircraft gearboxes operate under high mechanical loads. Currently, aircraft gears are manufactured from chromium–nickel–molybdenum steel grades such as AISI 9310 or Pyrowear 53. The major causes of gear failure are wear and fatigue cracking. As the crack initiation occurs predominantly on the component surface, the gears are routinely subjected to surface hardening processes such as low-pressure carburizing and case hardening. The gears are manufactured in a multiple operation process, in which teeth grinding is a crucial step. Selection of improper grinding conditions can lead to local heat concentration and creation of grinding burns, which are small areas where microstructure and properties changes are induced by high temperature generated during grinding. Their presence can lead to significant reduction of gear durability. Therefore destructive and non-destructive (NDT) quality-control methods such as chemical etching or magnetic Barkhausen noise (MBN) measurements are applied to detect the grinding burns. In the area of a grinding burn, effects related to the over-tempering or re-hardening of the carburized case may occur. In this paper, the results of the studies on the characterization of microstructure changes caused by local heating performed to simulate grinding burns are presented. The areas with the over-tempering and re-hardening effects typical for grinding burns were formed by laser surface heating of carburized AISI 9310 steel. Analyses of the microstructure, residual stresses, retained austenite content, and non-destructive testing by the MBN method were performed. The correlation between the MBN value and the properties of the modified surface layer was identified. It was also found that the re-hardened areas had similar characteristics of changes in the Barkhausen noise intensity, despite the significant differences in the width of the overheated zone, which depended on the laser-heating process conditions.
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