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Cast alloy soldering is a serious issue of a modern high pressure die casting (HPDC) industry. It endangers the die integrity, affects the casting quality and causes considerable ...production downtime, which altogether raise production costs. Development of new soldering resistant materials and coatings for HPDC dies is a promising approach in a struggle for the reduction of soldering effects. Performance of new materials for such application is most appropriately evaluated by laboratory tests. One of the tests is the ejection test in which a force required to eject a pin sample from a casting presents a measure of the cast alloy soldering tendency. In this paper, comparison between two currently used and one newly proposed method for the production of pin-casting assemblies is presented. For this purpose, pins made of X27CrMoV51 steel, and Al–Si–Cu cast alloy were used. The ejections of the pin samples were carried out on tensile testing machines, and force displacement diagrams were recorded. After the ejections, casting and pin surfaces were visually examined. The employed casting methods were numerically simulated. For the methods used so far, it was found that uniformity of a pin-casting contact is disrupted by the presence of shrinkage cavities, oxide films, and sinking-in of the casting surfaces. These imperfections formed due to inadequate casting filling and solidification conditions. On the other side, the newly designed method resulted in a uniform and a high-quality pin-casting contact, obtained through a casting process characterized with more severe soldering conditions. Consequently, for new method the recorded force and work of the ejection force are significantly higher and the cast alloy is evenly distributed on pin surfaces. New method more realistically replicates the conditions that exist between paired materials in real HPDC process. It is also simple for use and results are repeatable with a reasonable scatter.
Industrial evaluation of duplex PVD hard coatings for HPDC Kovačević, Lazar; Terek, Pal; Miletić, Aleksandar ...
Journal of the Brazilian Society of Mechanical Sciences and Engineering,
05/2018, Letnik:
40, Številka:
5
Journal Article
During high pressure die casting (HPDC), molten metal is injected into the tool cavity where it reaches high velocities that cause substantial wear of the tool components. In order to mitigate this ...problem, different surface treatments are sometimes employed for high production tools. The most common treatments are nitriding and physical vapor deposition (PVD) of hard coatings. Within this study, effectiveness of two duplex PVD hard coatings, CrN and TiAlN, was tested on core pins, which are the most endangered elements of high pressure die casting tools. Core pins were tested in four industrial production runs of an automotive component. In every run, the tool was mounted with one pin that was PVD-coated, and one that was gas-nitrided. Nitrided core pins were used as a base standard since the nitriding is the most commonly used surface treatment. TiAlN-coated pins were able to complete a full production run of 22,000 shots without significant damage. CrN coating showed somewhat higher soldering tendency and erosion rates. Considering that the untreated core pins were able to withstand only 5500 shots, it can be concluded that duplex PVD coatings can significantly improve tool lifetime. Additionally, results indicate that often disregarded variances in casting temperature or in cleanliness of ingots used in production can significantly influence wear performance of HPDC tools. Analysis of the production costs has shown that the application of duplex TiAlN coating on the core pins can lead to significant savings for tested automotive components.
In this study, high-temperature tribological behavior of nanolayered TiAlN/TiSiN coating was evaluated against the Al2O3 counter-body using a pin-on-disk tribometer. The coating was deposited on the ...WC-Co substrate, in an industrial unbalanced magnetron sputtering system. Tribological tests were conducted at room temperature, 500, 600, 700, and 760 °C, in air and nitrogen atmospheres. After the tests, the coating was examined using confocal microscopy, tactile profilometry, scanning electron microscopy, focused ion beam, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and secondary ion mass spectrometry. The coating retained its microstructure and mechanical properties after exposure to high temperatures. At lower temperatures coating exhibited abrasive and adhesive wear mechanisms, while at higher temperatures abrasive and oxidative wear mechanisms were observed. In high-temperature tests, AlO, TiO and SiO were detected inside of wear tracks, in both atmospheres. However, the oxide thickness was significantly lower in tests with nitrogen atmosphere. Additionally, the top of the oxide layer was enriched in AlO with respect to TiO and SiO. The enrichment of AlO was more pronounced in nitrogen atmosphere. The coating tested in air exhibited slightly higher and more unstable coefficient of friction (COF) values, than in nitrogen atmosphere. This is attributed to the increased oxidation in air atmosphere. At room temperature tests in nitrogen, the wear rate was approximately 3 times lower than in air. At higher temperatures the wear rate was lower than at room temperature, in both atmospheres, due to formation of protective oxides. However, with the increase in testing temperature the wear rate increased. The reason for such behavior is the loss of substrate's and coating's hardness at high temperatures, and thickening of the oxide layer which accelerated its removal. The latter effect is not so pronounced in nitrogen atmosphere due to thinner oxide layer, which agrees with the lower wear rate in nitrogen atmosphere at high temperatures than in air.
•At high temperatures, nanolayered TiAlN/TiSiN coating shows lower wear rate.•AlO, TiO and SiO were detected inside the wear tracks at high temperatures.•Coefficient of friction values are lower and more stable in nitrogen tribo-tests.•Wear rate in nitrogen is lower than in air at the same temperature.•The enrichement of Al2O3 is observed in the oxide layer above 600 °C.
With the goal to produce a hard and tough coating intended for tribological applications, CrAlN/TiSiN nanolayer coating was prepared by alternative deposition of CrAlN and TiSiN layers. In the first ...part of the article, a detailed study of phase composition, microstructure, and layer structure of CrAlN/TiSiN coating is presented. In the second part, its mechanical properties, fracture and tribological behavior are compared to the nanocomposite TiSiN coating. An industrial magnetron sputtering unit was used for coating deposition. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for compositional and microstructural analysis. Mechanical properties and fracture behavior were studied by instrumented indentation and focused ion beam techniques. Tribological properties were evaluated by ball-on-disk test in a linear reciprocal mode. A complex layer structure was found in the nanolayer coating. The TiSiN layers were epitaxially stabilized inside the coating which led to formation of dislocations at interfaces, to introduction of disturbances in the coating growth, and as a result, to development of fine-grained columnar microstructure. Indentation load required for the onset of fracture was twice lower for the nanolayer CrAlN/TiSiN, compared to the nanocomposite TiSiN coating. This agrees very well with their mechanical properties, with H3/E2 being twice higher for the TiSiN coating. However, the nanolayer coating experienced less severe damage, which had a strong impact on tribological behavior. A magnitude of order lower wear rate and four times lower steady state friction coefficient were found for the nanolayer coating.
In the process of high pressure die casting of aluminium alloys tool surfaces are severely damaged by cast alloy sticking and soldering which promote galling during casting ejection. As a ...consequence, casting quality is lowered and production efficiency is reduced. Although die casting tools are greatly improved by application of diffusion layers and surface coatings, effects of surface topography on performance of such treated tools are scarcely recognized. This investigation gives an insight in the effects of surface topography on the sticking tendency and galling of Al–Si alloy toward the H11 steel, plasma nitrided steel, and duplex treated steel with CrN and TiAlN PVD top coatings. The sticking tendency was evaluated by ejection test during which the force required to eject the sample from the casting was measured. It was found that the ejection force does not depend on chemical composition of the investigated materials. However, the ejection force of coated samples strongly depends on their surface topography. The coated samples which were polished after the deposition exhibited the highest ejection force. Wear conditions inherent in this specific tribo-system are recognised and interpreted for surfaces with different topography.
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•Sticking tendency of cast Al–Si alloy was investigated by employing ejection test.•Hot-working tool steel, nitrided and duplex treated surface layers were examined.•Ejection force is found to be independent of the surface chemical composition.•Ejection force of CrN and TiAlN coated samples increased with decrease in roughness.•Coatings post deposition polishing enhances adhesive wear and raises ejection force.
The machining characteristics of electrical discharge machining (EDM) directly depend on the discharge energy which is transformed into thermal energy in the discharge zone. The generated heat leads ...to high temperature, resulting in local melting and evaporation of workpiece material. However, the high temperature also impacts various physical and chemical properties of the tool and workpiece. This is why extensive knowledge of development and transformation of electrical energy into heat is of key importance in EDM. Based on the previous investigations, analytical dependence was established between the discharge energy parameters and the heat source characteristics in this paper. In addition, the thermal properties of the discharged energy were experimentally investigated and their influence on material removal rate, gap distance, surface roughness and recast layer was established. The experiments were conducted using copper electrode while varying discharge current and pulse duration. Analysis and experimental research conducted in this paper allow efficient selection of relevant parameters of discharge energy for the selection of most favorable EDM machining conditions.
Titanium nitride (TiN) films have been deposited by physical vapour deposition (PVD), with BALZER equipment, and ion beam assisted deposition (IBAD) process, in DANFYSIK chamber. TiN thin films were ...grown, during IBAD process, by evaporation of Ti in presence of N
2 and simultaneous bombarded with Ar
+ ions. The evolution of the microstructure from porous and columnar grains to densel packed grains is accompanied by changes in mechanical and physical properties.
Coatings deposited by physical vapor deposition (PVD) significantly reduce the wear of high pressure die casting tools; however, cast alloy soldering still has a strong negative effect on production ...efficiency. Although a lot of research has been already done in this field, the fundamental understanding of aluminum alloy soldering toward PVD coatings is still scarce. Therefore, in this work the performance of CrN duplex coatings with different roughness is evaluated by a modified ejection test performed with delayed (DS) and conventional casting solidification (CS). After the ejection tests, sample surfaces and layers were subjected to comprehensive characterizations of their morphological and chemical characteristics. Considerably lower values of the ejection force were recorded in DS experiments than in CS experiments. Surface roughness played an important role in the CS experiments, while samples with different surface topographies in the DS experiments performed in a similar fashion. The decrease in the ejection force, observed in DS tests, is attributed to the formation of a thick Cr–O layer on CrN coating which reduced soldering and sliding friction against thick Al–O casting scale. The Cr–O layer formed in DS experiments suffered from diffusion wear by cast alloy. The observed oxidation phenomena of nitride coatings may be utilized in a design of non-sticking coatings.
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