Extrusion Conditions Research Articles

α-Amylase reactive extrusion enhances the protein digestibility of saponin-free quinoa flour while preserving its total phenolic content

The original cellular structure and the presence of starch are known to reduce quinoa protein digestibility. Here, we aimed at optimizing an integrated single-step process exploiting the synergisms of amylolysis (<0.42% thermostable α-amylase, starch basis) and extrusion (at different temperature profiles) to enhance protein digestibility in saponin-free quinoa flour while minimizing polyphenol losses. In vitro protein digestion rate (velocity of substrate depletion) and extension (percentage of digested substrate at the end of the reaction) were significantly enhanced with every extrusion treatment, reaching up to four-fold faster protein digestion rate and up to 47% reduction of residual non-digested protein at 100 °C (last barrel temperature) and 0.36 g/100 g α-amylase concentration compared to native flour. Generally, reactive extrusion lowered the content of extractable (free) polyphenols and non-extractable proanthocyanins, but this effect was minimized at lower extrusion temperatures and higher α-amylase concentration. Contrarily, the more thermoresistant hydrolysable bound polyphenols increased in all cases, especially at harsh extrusion conditions.

Effects of protein formula and extrusion cooking conditions on the techno‐functional properties of texturised pea proteins

SummaryPea protein concentrate and isolate were blended to obtain protein blend formulas (PBFs) with three levels of protein content and investigated for their potential for developing texturised vegetable proteins (TVPs). PBFs were extruded at three screw speeds and two feed moisture contents to obtain TVPs. Nitrogen solubility index (NSI) and techno‐functional properties, i.e. water holding capacity, oil absorbance capacity, emulsion capacity and emulsion stability, of the raw materials and the TVPs were examined. Raising the protein content through PBF decreased NSI for both the raw formulas and the TVPs. Regardless of the PBF, extrusion processing substantially decreased NSI, but increased oil absorption capacity. Extrusion's impact on water holding capacity, emulsion capacity and stability was complex and might have been impacted by the protein content and source. Overall, PBF's impact on the techno‐functionality of TVPs was more pronounced than that of extrusion conditions. At higher PBF, the NSI, emulsion capacity and stability values of TVPs were negatively impacted, implying that high protein content does not equate to better TVP quality. Future, TVP techno‐functionality research should focus on a wider range of extrusion screw speed and feed moisture content or the effects of protein content and source.

Controlling degree of foaming in extrusion 3D printing of porous polylactic acid

PurposeThis paper aims to understand the effect of extrusion conditions on the degree of foaming of polylactic acid (PLA) during three-dimensional (3D) printing. It was also targeted to optimize the slicing parameters for 3D printing and to study how the properties of printed parts are influenced by the extrusion conditions.Design/methodology/approachThis study used a commercially available PLA filament that undergoes chemical foaming. An extrusion 3D printer was used to produce individual extrudates and print samples that were characterized using an optical microscope, scanning electron microscope and custom in-house apparatuses.FindingsThe degree of foaming of the extrudates was found to strongly depend on the extrusion temperature and the material feed speed. Higher temperatures significantly increased the number of nucleation sites for the blowing agent as well as the growth rate of micropores. Also, as the material feed speed increased, the micropores were allowed to grow bigger which resulted in higher degrees of foaming. It was also found that, as the degree of foaming increased, the porous parts printed with optimized slicing parameters were lightweight and thermally less conductive.Originality/valueThis study fills the gap in literature where it examines the foaming behavior of individual extrudates as they are extruded. By doing so, this work distinguishes the effect of extrusion conditions from the effect of slicing parameters on the foaming behavior which enhances the understanding of extrusion of chemically foamed PLA.

Modelling drug degradation of amorphous solid dispersion during twin-screw extrusion

Twin-screw extrusion is one of the major technologies for solid dispersion in the pharmaceutical industry. However, the thermal exposure to the drug during extrusion can easily trigger and exacerbate drug degradation. A conventional method for investigating drug degradation in extrusion is trial-and-error, which can consume much time and material. We propose to model drug degradation kinetics and combine it with thermal history simulation to predict drug degradation. Ritonavir and copovidone were used as a model system of solid dispersion. Hydantoin aminoalchol was the major degradant of RTV in extrudate. In studying the RTV degradation kinetics, only in nitrogen atmosphere, RTV degradation pathway in TGA or DSC was like the degradation pathway in extrusion. The mixing and solubilization of RTV in copovidone also prevented RTV from degrading to oxazolidine derivative. The degradation samples were collected at various temperatures and at different times. The data was fitted into first-order kinetics model to get degradation rates constant at each temperature. The degradation rate constants were fitted into the Arrhenius equation with an activation energy of 159.3 kJ/mol, and a pre-exponential of 1.23 × 1017. An array of extrusion conditions was developed and analyzed via design of experiment (DOE). Relying on the measured melt temperature and residence time after kneading element and die, we simulated the thermal history in the section between kneading element and die. The RTV degradation kinetics in conjunction with simulated thermal history predicted degradation and achieved a 78% regression.

Study on thermal–mechanical coupling of vehicle battery module embedded with double-V cellular structure

To further enhance the thermal–mechanical performances of battery module, a novel lithium-ion battery module with double-V cellular structure (DVCS) is proposed. Firstly, the temperature field distributions of battery module are acquired by employing ANSYS/ Fluent simulation analysis software. Subsequently, mechanical properties of the DVCS are acquired and quasi-static compression test is also executed to verify the accuracy of theoretical predictions and emulation analysis. Then, the thermo-mechanical coupling models of DVCS are established, and the optimal geometric parameters of DVCS can be obtained through multi-objective thermal–mechanical coupling optimization method. Based on the above, density gradient of the DVCS can be defined based on the temperature field distribution of battery module. Eventually, in comparisons to battery module with single cooling tube and battery module with the optimal DVCS, the maximum temperature of battery module with density gradient DVCS is 304.97 K at 3C discharge rate, which decreases by 4.51 % and 3.16 %, respectively, the maximum temperature difference of battery module with density gradient DVCS is 4.97 K, which decreases by 74.36 % and 66.71 %, accordingly. As for extrusion conditions, the maximum intrusion displacements of battery module with density gradient DVCS are 0.2295 mm and 0.6518 mm along X and Y directions, separately, which decrease by 94.54 % and 86.87 % compared with those of battery module with single cooling tube. The results indicate that the dissipation efficiency, temperature uniformity and collision performances of battery module with density gradient DVCS can be improved greatly.

The Use of Hot Melt Extrusion to Prepare a Solid Dispersion of Ibuprofen in a Polymer Matrix.

In this work, we report the use of the hot melt extrusion method in harsh extrusion conditions, i.e., screw rotation speed of 250 rpm, temperature above 100 °C, and two mixing zones, in order to obtain an amorphous dispersion of an active pharmaceutical ingredient (API) that is sparingly soluble in water. As a polymer matrix Eudragit EPO (E-EPO) and as an API ibuprofen (IBU) were used in the research. In addition, the plasticizer Compritol 888 ATO (COM) was tested as a factor potentially improving processing parameters and modifying the IBU release profile. In studies, 25% by weight of IBU, 10% of COM and various extrusion temperatures, i.e., 90, 100, 120, 130, and 140 °C, were used. Hot melt extrusion (HME) temperatures were selected based on the glass transition temperature of the polymer matrix (Tg = 42 °C) and the melting points of IBU (Tm = 76 °C) and COM (Tm = 73 °C), which were tested by differential scanning calorimetry (DSC). The thermal stability of the tested compounds, determined on the basis of measurements carried out by thermogravimetric analysis (TGA), was also taken into account. HME resulted in amorphous E-EPO/IBU solid dispersions and solid dispersions containing a partially crystalline plasticizer in the case of E-EPO/IBU/COM extrudates. Interactions between the components of the extrudate were also studied using infrared spectroscopy (FTIR-ATR). The occurrence of such interactions in the studied system, which improve the stability of the obtained solid polymer dispersions, was confirmed. On the basis of DSC thermograms and XRPD diffractograms, it was found that amorphous solid dispersions were obtained. In addition, their stability was confirmed in accelerated conditions (40 °C, 75% RH) for 28 days and 3 months. The release profiles of prepared tablets showed the release of 40% to 63% of IBU from the tablets within 180 min in artificial gastric juice solution, with the best results obtained for tablets with E-EPO/IBU extrudate prepared at a processing temperature of 140 °C.

Effect of extrusion processing parameters on structure, texture and dietary fibre composition of directly expanded wholegrain oat-based matrices

Oat flour mixed with 30 g/100 g rice flour was extruded with a twin-screw extruder using a central composite orthogonal design. Temperatures (120 °C,140 °C, 160 °C) and moisture (14.5 g/100 g, 17.7 g/100 g, 20.6 g/100 g) were adjusted during extrusion, while screw speed was kept constant (400 rpm). Extrudates were analysed for structure (expansion, density, microstructure), texture (hardness), β-glucan (molecular weight and extractability), as well as fibre content. Expansion varied between 250 and 329%, density between 165 and 457 kg/m3 and hardness between 27 and 64 N. The response surface model showed that more expanded, less dense and less hard extrudates were achieved at low moisture, while high temperature resulted in lower density and hardness. Significant differences in β-glucan extractability were observed depending on extrusion conditions, with values ranging between 0.64 and 1.31 g/100 g. β-glucan extractability correlated with positively with porosity, and negatively with moisture content during extrusion, cell wall thickness and density. The results indicate that conditions that produce a more porous, crispier structure, also increases β-glucan extractability.

Investigation of die designs on welding quality and billet material utilisation for multi-container extrusion of wide stiffened aluminium panels

Wide stiffened aluminium panels are extensively used in aerospace, marine, and civil industries due to their light-weight structure and high stiffness. In this paper, a wide stiffened aluminium panel was manufactured using the principle of the multi-container extrusion, and a comparative study was conducted using two different die designs at the same extrusion condition, in which metal flow behaviour, extrusion force, welding quality, and billet material utilisation have been investigated numerically. Additionally, the effect of extrusion speed on the extrusion process was evaluated with the modified design. It was shown that, compared with the initial design, better metal flow behaviour can be obtained in the modified design. Multi-container extrusion greatly reduces the extrusion force, and the modified design results in a more uniform extrusion force for each extrusion container. The total extrusion force for the modified design is slightly higher compared with the initial die design, due to the increased friction in the upper die channels and the second-step welding chamber. Besides, the modified design of the multi-container extrusion can obtain better welding quality evaluated by different welding criteria, and the extrusion speed has a minor effect on the welding quality. The most notable feature is that the modified design greatly improves the material utilisation, which could save 39.5% material compared to the initial design.

High moisture extrusion of soybean-wheat co-precipitation protein: Mechanism of fibrosis based on different extrusion energy regulation

The soybean-wheat co-precipitation protein (SWCP) is a composite protein that possesses a shared internal structure and a high nutritional value derived from the combination of soybean and wheat. However, the process of fibrosis formation during high moisture extrusion utilizing SWCP as a raw material for plant-based meat analogs has not been thoroughly well investigated. This study aims to examine the relationship between the formation of protein fiber and its molecular structure under varying extrusion parameters by extruding SWCP, blend protein (BP), soy protein isolate (SPI), and wheat protein (WP) with high moisture extrusion. Under identical extrusion conditions, SWCP extrudates exhibited greater fibrous structures, a higher total color variation index, and a lower browning index than BP extrudates. The textural properties of SWCP extrudates were significantly enhanced with increasing screw speed and temperature, with a maximum value of 1.91 N/N. Extrudates with higher moisture content resulted in decreased hardness, tensile strength, and chewiness. The extrusion process led to the formation of porous structures within the protein fibers, with water molecules primarily existing as immobilized water within the network structure (immobilized water content was 77.15%–92.84%). Compared to SWCP extrudates, water in BP extrudates was more prone to migrate. The structural analysis of the protein showed that during the extrusion process, the α-helix and β-sheet changed to β-turn and random coil structure. Hydrogen bonds, hydrophobic interactions, and disulfide bonds played a marginally more important role in stabilizing the protein structure of SWCP and BP extrudates. In conclusion, our research results showed that co-precipitation protein can have a positive impact on the quality characteristics of extrudates, and extrusion parameters have a significant effect on the formation of the fibrous structure of extrudates.

Nutritional Characteristics of New Generation Extruded Snack Pellets with Edible Cricket Flour Processed at Various Extrusion Conditions.

As new sources of proteins, edible insects may be excellent additives in a new generation of environmentally friendly food products that are nutritionally valuable, safe, sustainable, and are needed in today's world. The aim of this study was to determine the effect of the application of cricket flour on extruded wheat-corn-based snack pellets' basic composition, fatty acids profile, nutritional value, antioxidant activity and selected physicochemical properties. Results showed that the application of cricket flour had a significant impact on the composition and properties of snack pellets based on wheat-corn blends. In newly developed products, the enhanced level of protein and almost triple increase in crude fiber was found as an insect flour supplementation reached 30% level in the recipe. The level of cricket flour and the applied processing conditions (various moisture contents and screw speeds) significantly affect the water absorption and water solubility index and texture and color profile. Results revealed that cricket flour application significantly increased the total polyphenols content in the assessed samples in comparison to plain wheat-corn bases. Antioxidant activity was also noted to be elevated with increasing cricket flour content. These new types of snack pellets with cricket flour addition may be interesting products with high nutritional value and pro-health properties.

Texture evolution and serrated failure of AZ31B alloy subjecting to equal channel angular extrusion

Equal channel angular extrusion (ECAE) is considered the most promising method for improving strength and ductility. The microstructures after ECAE have been extensively studied for Mg alloys relating to mechanical properties. However, the changes in texture and their relationship with the prior conditions, extrusion conditions and extrusion directions are rarely studied. In the current work, the changes in texture of AZ31B Mg alloys were investigated along the normal direction (ND), transverse direction (TD), and rolling direction (RD) after ECAE processing one pass. The results revealed a rule that the AZ31B alloy follows for texture changes, where the basal texture (namely the focused c-axis) orients 45º or nearly orients 45º, regardless of the pre-extrusion texture, extrusion temperature, and extrusion rate. Interestingly, serrated failure sorely occurs along the ND for all extrusion conditions, due to the basal slip in an unfavorable orientation and the shear plane not parallel to either pyramidal slip directions.

Investigation of high rate mechanical flow followed by ignition for high-energy propellant under dynamic extrusion loading

Investigating the ignition response of nitrate ester plasticized polyether (NEPE) propellant under dynamic extrusion loading is of great significant at least for two cases. Firstly, it helps to understand the mechanism and conditions of unwanted ignition inside charged propellant under accident stimulus. Secondly, evaluates the risk of a shell crevice in a solid rocket motor (SRM) under a falling or overturning scene. In the present study, an innovative visual crevice extrusion experiment is designed using a drop-weight apparatus. The dynamic responses of NEPE propellant during extrusion loading, including compaction and compression, rapid shear flow into the crevice, stress concentration, and ignition reaction, have been firstly observed using a high-performance high-speed camera. The ignition reaction is observed in the triangular region of the NEPE propellant sample above the crevice when the drop weight velocity was 1.90 m/s. Based on the user material subroutine interface UMAT provided by finite element software LS-DYNA, a viscoelastic-plastic model and dual ignition criterion related to plastic shear dissipation are developed and applied to the local ignition response analysis under crevice extrusion conditions. The stress concentration occurs in the crevice location of the propellant sample, the shear stress is relatively large, the effective plastic work is relatively large, and the ignition reaction is easy to occur. When the sample thickness decreases from 5 mm to 2.5 mm, the shear stress increases from 22.3 MPa to 28.6 MPa, the critical value of effective plastic work required for ignition is shortened from 1280 μs to 730 μs, and the triangular area is easily triggering an ignition reaction. The propellant sample with a small thickness is more likely to stress concentration, resulting in large shear stress and effective work, triggering an ignition reaction.

Effect of polysaccharides on the rheological behaviour of soy-wheat protein aggregation and conformational changes during high-moisture extrusion.

Due to the extrusion black box effect, polysaccharides determine the formation of meat-like fibrous structures by modulating the flow behaviour and structural changes of plant proteins under high-moisture extrusion conditions. However, the is limited knowledge on the mechanism of resolution. This study simulated the rheological properties of soy protein-wheat protein under 57% moisture conditions with addition of 4% sodium alginate (SA), 2% xanthan gum (XG), and 2% maltodextrin (MD). Effect of these polysaccharides on the aggregation behaviour and conformation of raw protein during high-moisture extrusion was investigated. It was revealed that the three polysaccharides were effective in increasing the interaction between proteins and between proteins and water. Among them, 4% SA elicited a significantly stronger storage modulus (gelation behavior) compared to the control. Analysis of different zones of extrudates by protein electrophoresis, particle size, and turbidity showed that SA-4% was able to form more high molecular protein aggregates (> 245 kDa) and promoted cross-linking of low molecular subunits (< 48 kDa), resulting in moderately sized protein aggregated particles. Fluorescence and UV spectra showed the transformation of protein tertiary structures in different extrusion zones, confirming that the key extrusion zone for protein conformational transformation by polysaccharides is the die-cooling zone. Furthermore, stretching of polypeptide chains and accelerated protein rearrangement facilitated the formation of more fibrillar structures. Theoretical support for polysaccharide modulation of plant protein quality in high moisture extruded products is provided by this study. This article is protected by copyright. All rights reserved.

Die Design and Finite Element Analysis of Welding Seams during Aluminum Alloy Tube Extrusion

Hollow tubes are generally manufactured using porthole die extrusion. A finite element software QForm is used to analyze the material flow of aluminum alloy A6061 tubes inside a specially designed porthole die during tube extrusion. High welding pressure and shorter transverse seam length are required for a sound product. Various extrusion conditions and die geometries and dimensions affect the bonding strength of the products. In this paper, the effects of die geometries on the welding pressure are discussed using the Taguchi method. The simulation results show that a higher welding pressure is obtained with a larger porthole radius, a larger welding chamber height, and a larger bearing length, while a larger bridge width increases the welding pressure slightly. For transverse seam lengths, a shorter transverse seam length can be obtained with a smaller porthole radius and a smaller welding chamber height, and a shorter bridge width and bearing length decrease the transverse seam length slightly. The transverse seam region and flow patterns are observed. Tube expanding tests were also conducted. From the expanding test results, it is known that the fracture position did not occur at the welding line and the bonding strength could reach up to 160 MPa.

Optimisation of extrusion conditions for production of antioxidant-rich extruded breakfast cereals from purple sweet potato (Ipomoea batatas L.) and red rice using response surface methodology

Purple sweet potato powder (PSPP) is rich in anthocyanins and other polyphenols that provide excellent antioxidant and other biological activities with potential health benefits. In the present work, the response surface methodology (RSM) was used to optimise the extrusion processing conditions to develop healthy breakfast cereals. The independent variables studied included barrel temperature, screw speed, and feed moisture. The linear terms of barrel temperature and feed moisture content were found to be the significant (p &lt; 0.05) factors affecting the product's functional and physicochemical properties. The expansion property of extrudate significantly (p &lt; 0.001) increased at low temperature, high screw speed, and low feed moisture. The recommended optimum extrusion conditions of barrel temperature, screw speed, and feed moisture content were at 157.0°C, 126.0 rpm, and 13.0%, respectively; and under these optimum conditions, significantly high retention (75.0%) of anthocyanin content was detected. Furthermore, scanning electron micrographs depicted that the optimised breakfast cereals had a better cell structure with smoother and thinner cell walls than the non-optimised samples.

The Influence of Processing Conditions on the Mechanical Properties of Poly(Acrylonitrile-Butadiene-Styrene)/ Poly(Methyl Methacrylate) (ABS/PMMA) Blends

Poly(methyl methacrylate) (PMMA) can improve the mechanical and optical properties of poly(acrylonitrile-butadiene-styrene) (ABS). The blends of ABS and PMMA are applied to produce electrical enclosures with high requirements for gloss and hardness. Knowledge about the processing conditions that influence the blends of polymers is important to achieve the best material properties. In our research described here, ABS/PMMA blends and their testing samples were separately prepared under various processing conditions based on polymer blending theory. The influence of extrusion (times) and injection (temperatures and pressures) conditions on the mechanical properties and morphologies of the ABS/PMMA blends were investigated. Appropriate processing conditions and optimal mechanical properties of the ABS/PMMA blends were obtained. The blends following extrusion processing twice had better impact strength, tensile properties, and bending properties than those prepared with only one extrusion processing. The blends prepared under injection processing conditions (220 °C, 70 MPa) had better mechanical properties than those prepared under other conditions. Therefore, it was possible to correlate the processing conditions with the evaluated mechanical properties.

Dissolution and reprecipitation of 14H-LPSO structure accompanied by dynamic recrystallization in hot-extruded Mg89Y4Zn2Li5 alloy

We investigate the variation induced in long-period stacking ordered (LPSO) structures, dynamic recrystallization (DRX), and mechanical performance of hot-extruded Mg89Y4Zn2Li5 alloys fabricated at different extrusion speeds (Ve = 0.4, 0.8, 1.0, 1.2 mm/s) and die angles (α = 30°, 60°, 90°) under 400 °C, the dissolution and reprecipitation of 14H LPSO structure accompanied by DRX process are then clarified in detail. Upon all extrusion conditions, the block 18R LPSO structures elongate in the extrusion direction, while the lamellar 14H LPSO structures dissolve under the deformation strain. In addition, due to discontinuous and continuous DRX mechanisms, all hot-extruded alloys have a full DRX microstructure consisting of equiaxed recrystallized grains, but the DRX grain size reduces when both extrusion speed and die angle decrease. Note that, in the interior of DRX grains, thin LPSO lamellae mixing 14H, 18R and 24R structures nucleate and dynamically precipitate due to the dissolution of the original lamellar 14H LPSO structures. Furthermore, the hot-extruded Mg89Y4Zn2Li5 alloy becomes stronger as decreasing of the extrusion speed and die angle, whereas the ductility remains nearly constant. Finally, the hot-extruded Mg89Y4Zn2Li5 alloy achieves an excellent strength-ductility balance at a relatively low extrusion speed (0.4 mm/s) and small die angle (30°) mainly due to the elongated 18R LPSO structure, fine and full DRX microstructure, thin mixed LPSO precipitates in the DRX grains, twins and dislocations.

Texturized vegetable protein from a faba bean protein concentrate and an oat fraction: Impact on physicochemical, nutritional, textural and sensory properties

Texturized vegetable protein (TVP) from a blend of faba bean protein concentrate and an oat beta-glucan rich fraction was produced by low-moisture extrusion to combine nutritional benefits of both ingredients. The effect of extrusion conditions (temperature in zone 6 (HZ6), feed rate (FR) and moisture content (MC)) on physicochemical, nutritional, textural, and sensory attributes was studied. Overall, effect of the FR and MC of the blend showed greater impact on TVP properties rather than the temperature. TVPs produced at 28.5%, 5 Kg/h and 150⁰C and at 30.8%, 4 Kg/h and 160⁰C for MC, FR and HZ6, respectively, presented improved properties to be further formulated into a meat analogue product. The beta-glucan content of TVP (5.6g/100g dm) was high enough to reach >1 g beta-glucan per serving in a final food product (e.g., vegan burger), which qualifies for the health claim “reduces low-density lipoprotein (LDL)-cholesterol” approved by the European Food Safety Authority. The combination of these ingredients resulted simultaneously in an improved composition of essential amino acids and increased the protein quality of the blend as the calculated digestible indispensable amino acid score (DIAAS) improved from 72.2 (beta-glucan rich fraction alone) or 76.1 (faba bean protein concentrate alone) to 90.2 (blend).

Analysis of solid-state welding in extruding wide aluminium hollow profiles using a new three-container extrusion system

A novel multi-container extrusion has recently been proposed to extrude multiple billets simultaneously for manufacturing thin-walled wide engineering components with greatly reduced force. The metal flow behaviour and solid-state welding in the process are crucial factors that influence the final product quality and industrial application. In this study, thin-walled wide AA6063 hollow profiles were extruded by three-container extrusion technology under different combinations of extrusion temperature and speed. The bonding quality of the welds that formed between the adjacent billets during the extrusion process was experimentally evaluated via tensile tests of specimens at different positions of the extrudates. A three-dimensional numerical model was established and validated to characterise the metal flow behaviour and the solid-state welding. Ten points in the first 140 mm of the weld of the extrudate were traced to investigate the flow paths and the related physical information such as pressure, effective stress, velocity and strain rate to reveal the weld formation mechanism. The simulated results showed that the whole three-container extrusion process includes five stages, i.e. separation stage, smooth flow stage, welding chamber filling stage, die bearing breakthrough stage and steady extrusion stage. By evaluating the simulated results and the tensile testing results, the pressure-time (Q) criterion was found able to evaluate the welding quality individually for each extrusion condition, while the pressure-time-flow (K) criterion appeared suitable to predict the welding quality for various extrusion conditions within a small range of critical limits.

Nitriding Effect on the Tribological Performance of CrN-, AlTiN-, and CrN/AlTiN-Coated DIN 1.2367 Hot Work Tool Steel

In this study, heat-treated and multisurface engineered DIN 1.2367 tool steel was subjected to room and elevated temperature wear tests, and the effect of nitriding on its tribological behavior was investigated. CrN, AlTiN, and CrN/AlTiN coatings with a total thickness of 2 µm were obtained by arc cathodic physical vapor deposition on conventional heat-treated and gas-nitrided steels. The white layer formed during nitriding was removed, and a diffusion layer (100 µm) was achieved in the cross section of the steel having a tempered martensitic matrix. The highest surface hardness was attained with an integral coating (CrN/AlTiN), and surface hardness increased even more after nitriding due to the formation of a multicomponent ceramic layer on top of the diffusion layer. The room temperature wear tests performed against an alumina counterpart revealed that (i) CrN/AlTiN-coated steel had the highest friction coefficient of 0.26, which further increased to 0.33 by nitriding due to the increase in shear strength, and that (ii) with increasing surface hardness, the specific wear rates (W) of the heat-treated and coated steels could be ranked as follows: WCrN/AlTiN < WAlTiN < WCrN. The wear rates decreased when nitriding was carried out prior to coating. In order to simulate the aluminum extrusion conditions, hot wear behavior of the surfaces against AA6080 alloy at 450 °C was investigated. The hot wear tests revealed that (i) high friction coefficients were reached due to the adhesive characteristic of aluminum to the surfaces, (ii) the nitrided and CrN/AlTiN-coated sample exhibited the lowest wear rate among all studied surfaces, and (iii) the film damage on the worn surfaces mostly occurred in the form of droplet delamination.