Initial Hardness Research Articles

Thermal Stability and Thermal Fatigue Resistance Improvement of New High Toughness 5% Cr Hot Working Die Steel

This work developed a new high toughness 5% Cr martensitic hot working die steel (GYDCK-20), which exhibits better thermal stability and thermal fatigue resistance than AISI H13 steel. The concrete study involves: conducting on the evolution of microstructures and mechanical properties of two steels during the 60-hour holding process at 600°C, as well as the thermal fatigue behavior under the cyclic heating-water quenching conditions. The experimental results showed that in the case of ensuring the same initial hardness of two steels (43-43.5 HRC), GYDCK-20 emerged better thermal stability and superior toughness after 60-hour holding process at 600°C. After thermal cycling was increased from 1000 to 2000 times, the average crack length growth rate of GYDCK-20 was 31.8% lower than that of H13 and the maximum crack width growth rate was 35.1% lower than that of H13. It was found that thermal fatigue cracking was dominated by transgranular propagation at lower cycle numbers, while more inclined to propagate along the grain boundaries at higher cycle numbers. The higher toughness of GYDCK-20 steel promotes the dispersion of thermal stress, thereby enhancing the thermal fatigue resistance. It is mainly attributed to the lower V content of GYDCK-20 steel, which reduces the density of large-sized MC primary carbides. On the other hand, the lower Si content promotes the dissolution of cementite particles, and the secondary carbides precipitate in a smaller and uniformly distributed form, which hinders the propagation of thermal fatigue cracks, while also delays the coarsening of the fatigue-adverse phase M23C6 carbides.

Irradiation-Induced Microstrain and Dislocation Density in Additively Manufactured 316H Stainless Steel

This study investigated the response of additively manufactured (AM) 316H stainless steel (SS) compared to its conventionally manufactured counterpart under simulated irradiation conditions. We irradiated both types of steels with 0.5 MeV H+ ions at room temperature and analyzed their microstructural and mechanical properties. X-ray diffraction revealed higher initial dislocation densities in AM SS due to its fabrication process. Interestingly, at lower irradiation doses (0.6 dpa), the AM SS showed a decrease in microstrain, while the conventional SS showed an increase. This suggests differing defect annihilation mechanisms. At 6.0 dpa, AM SS exhibited a rise in mi- crostrain and dislocation density, potentially due to saturation effects. Conversely, conventional SS showed a decrease, possibly indicating disordering from the irradiation. Microhardness measure- ments supported these findings, with AM SS displaying a more gradual response compared to the pronounced hardening and softening observed in conventional SS. Tensile testing revealed lower hardening and strength in irradiated AM SS compared to its pristine state. Scanning electron mi- croscopy showed contrasting fracture behavior between the two steel types, with AM SS exhibiting less embrittlement despite its higher initial hardness. Overall, AM SS demonstrated superior mi- crohardness and microstructural integrity after irradiation, suggesting its potential for applications in harsh irradiated environments.

Data-driven predictions of retained austenite content and yield strength and elucidation of the sliding wear performance of carbide-free bainitic steels

Carbide-free bainitic (CFB) steels have drawn much attention due to their high strength and toughness. The present work aims to build machine learning (ML) based surrogate models to predict retained austenite (RA) content and yield strength (YS) of isothermal transformed CFB steels and study the sliding wear performance. The input data for ML prediction were related to compositions, heat treatment process, and phases. The Random Forest regression and Gaussian process regression were respectively selected to build the predictive models for RA content and YS. Result shows that the predicted RA content agrees well with the experimentally determined ones in steel with high stability of untransformed austenite. For YS prediction, the present surrogate model can predict YS of CFB steels even without additional microstructural information such as dislocation and effective substructure size. Steels with different YS and RA content were designed to study the sliding wear performance. Result shows that the dominant wear mechanism of the tested steels is abrasive wear and the weight loss is inversely proportional to hardness when the load and wear distance are constant. Increasing YS and RA content can increase the initial hardness and work hardening ability at the worn surface, thereby enhancing wear resistance.

Tribological Behavior of 316L Stainless Steel Fabricated Using Metal Extrusion Additive Manufacturing Under Dry and Simulated Body Fluid‐Lubricated Conditions

Herein, the tribological behavior of 316L stainless steel (SS) fabricated using metal extrusion additive manufacturing (MEAM) is investigated both under dry and simulated body fluid (SBF)‐lubricated conditions. The results and mechanisms are compared with those of 316L SS fabricated via selective laser melting (SLM) and hot rolling (HR). Under dry‐friction conditions, the 316L SS fabricated via MEAM shows inferior tribological performance compared with those fabricated via SLM and HR, primarily because of its lower initial hardness and better plasticity, which increase both abrasive and adhesive wear. Under SBF‐lubricated conditions, the tribological performance of the 316L SS fabricated via MEAM is comparable to that fabricated via HR and superior to that fabricated via SLM. The wear rate of the MEAM‐fabricated 316L SS is 16.8% and 3.2% lower than SLM‐ and HR‐fabricated, respectively. The numerous pores on 316L SS serve as traps for wear particles, which contribute to the reduction of three‐body wear. In terms of wear under SBF‐lubricated conditions, MEAM technology appears to be a promising method for the fabrication of customized 316L orthopedic implants.

Improvement of gummy candy structure by gelling ingredients and cooling temperature

AbstractGummy candies achieve their widespread appeal through a unique textural profile. The combination of springiness, chewiness, and a potential initial hardness upon biting (depending on formulation) creates a multi‐sensory eating experience. The readily soluble sugars and other components contribute to the quick dissolution and ease of digestion. Therefore, we conducted research to develop gummy candies made from structural materials of gelatin combined with agar and maltose syrup and evaluated the effect of ingredient ratios on the candy's structural and sensory properties. Sweetener maltose syrup (DE = 42) and a suitable content of agar supplementary had a significant influence on the structure of the product (p < 0.05). The structure of gummy candies was analyzed by the structure measuring instrument TPA (structure profile analysis) combined with sensory evaluation. The process of manufacturing candy involves the melting and homogenization of all constituent ingredients, followed by a sequence of freezing and cool drying to complete the production. The most interesting candies were made with agar 0.5%, gelatin 10% (powdered gelatin with Bloom 250), saccharose 30%, maltose syrup 10%, citric acid 0.1%, and pure water before being chilled at 4 °C for 4 h. This property remained unchanged during the 6‐month storage period in anaerobically sealed packaging, at room temperature.

Evaluation of the cumulative effect of photodynamic therapy and local fluoride on the microhardness and topography of demineralized enamel and cementum surfaces

BackgroundThe present study aimed to determine the cumulative effect of two photodynamic therapy methods with methylene blue and indocyanine green and two topical fluoride therapy methods with fluoride varnish and silver diamine fluoride alone and in combination on the microhardness and topography of demineralized enamel and cementum surfaces. Materials and methodsSeventy-two sound human teeth were selected, and their buccal and lingual surfaces were assigned to two main groups of enamel and cementum using simple randomization. The initial surface hardness (SH) of the enamel and cementum in each sample was determined using a micro-Vickers hardness tester using a 200-g force in 10 s. Then artificial caries was induced by immersion in a demineralizing/remineralizing solution (i.e., each tooth provided two samples, one on the buccal aspect and the other on the lingual aspect). Each enamel/cementum main group was divided into two subgroups using simple randomization based on the local fluoride type (fluoride varnish and silver diamine fluoride) and the type of the photosensitizer agent (methylene blue and indocyanine green). Finally, 16 groups were achieved (n = 9). The final surface hardness of the enamel and cementum samples was determined as described above. Finally, the sample surfaces were prepared for the surface topography evaluation under a scanning electron microscope. The baseline microhardness was compared between the 16 study groups in the first step using one-way ANOVA. Then, three-way ANOVA was used to evaluate the effect of fluoride, laser, and surface (enamel and cementum) on microhardness. ResultsAll the groups exhibited decreased microhardness due to the induction of artificial caries. In both main groups of enamel and cementum, the lowest decrease in microhardness was recorded with combined photodynamic therapy and methylene blue photosensitizer material and fluoride varnish (15.1 % for cementum and 16.7 % for enamel), and the highest decrease in microhardness was recorded in the methylene blue group (35.7 % for cementum and 34.9 % for enamel). ConclusionThe combination of photodynamic therapy with the photosensitizer substance methylene blue or indocyanine green together with fluoride varnish or silver diamine fluoride is effective on the remineralization of demineralized enamel and cementum. Although there is no difference between the combination of photodynamic therapy with fluoride varnish compared to fluoride varnish alone, both of these treatments are more effective than using photodynamic therapy alone.

Inorganic Phosphate Effect in a Hydrogen Peroxide-based Bleaching Agent: Physicochemical, Mechanical, and Morphological Properties of Dental Enamel.

This in vitro study aimed to assess the impact of incorporating calcium glycerophosphate (CaGP) and sodium fluoride (NaF) in addition to 35% hydrogen peroxide concerning the enamel mechanical and morphological properties. Specimens of bovine enamel were chosen based on their initial surface hardness (SHi) and subsequently divided into five gel groups (n=12): 1) 35% Hydrogen Peroxide (HP) Gel; 2) HP + 0.1% NaF Gel (HP/NaF); 3) HP + 0.25% CaGP Gel (HP/CaGP); 4) HP + 0.1% NaF + 0.25% CaGP Gel (HP/NaF/CaGP) and 5) HP Blue 35% Gel (HP Blue). The bleaching gels were applied thrice, for 40 min, at intervals of 7 days each. After 21 days, the final surface hardness (SHf), integrated hardness (IH), Polydispersity Index (PdI) and Zeta Potential (Zp), surface roughness (Ra, after and before), and surface/structural analysis by Scanning Electron Microscopy (SEM) were determined. The data were submitted to ANOVA (one-way and two-way) followed by the Student-Newman-Keuls test (α=0.05). The addition of NaF to HP reduced demineralization by 11.5% in relation to HP (p<0.05). The NaF/CaGP association reduction is 22.8 and 20% higher in comparison to HP/NaF/CaGP and HP Blue, respectively. The IH when the PH/NaF/CaGP bleaching gel was applied, was 14% higher compared to HP and HP Blue groups. It can be concluded that the association of NaF and CaGP with the 35% hydrogen peroxide gel (HP/NaF/CaGP) significantly changed tooth enamel demineralization in terms of surface, depth, roughness, and enamel morphology.

Study of the efficiency of sodium silicate water softening processes

The current state of natural water resourses requires preliminary softening for almost all drinking waters and waters for energy purposes. Therefore, the search for effective softening technologies and reagents is especially relevant today. Researches in this field are constantly increasing every year due the intensive quality deterioration of the natural waters. The processes of calcium and magnesium ions removing from water are on central place in such researches. It is traditionally considered that magnesium ions are more difficult to remove from water than calcium ions because magnesium ions form less quantity of insoluble compounds. The total efficiency of water softening processes depends on the residual content of both cations. Therefore, researchers also pay a lot of attention to magnesium ions removing. Sodium hydroxide and sodium phosphate are considered as a perspective reagents in such processes. However, the use of first reagent is associated with a significant increase of pH index, and the use of second reagent requires a big quantity of the reagent and needs the alkaline medium for sufficient efficiency. Therefore, in this work, we investigated the effectiveness of sodium silicate in the processes of magnesium and calcium ions removing from the aqueous medium. A characteristic feature of the solid phase formation in reaction between magnesium cations and silicate anions is the significant reaction dependence on the pH index. In neutral environment, the formation of a solid phase in model solutions was not visually fixed. However, some decrease of water hardness after filtering through "blue tape" filter paper is still observed. And it is decrease with increasing of pH index. The most effective softening process can be obtained at pH levels &gt; 10. It was not possible to obtain any positive results during study of settling and filtering processes of the formed solid phase. At the same time, the ratio between the components and the initial water hardness does not affect the clarification process practically. However, sodium silicate can be quite effective in stoichiometric or higher ratios. But a significant disadvantage of such method is a pH index increasing when the components are mixed. It requires futher adjusting the pH level in the treated water. And this is aditional stage of water treatment. It was not possible to obtain positive results when aluminum hydroxide was used as a settling and filtering intensifier. With the ratio K = [SiO32-, mg-eq]/[Mg2+, mg-eq] = 1 and different doses of aluminum ions, there is no significant intensification of sedimentation processes in the range of aluminum ions doses from 10 to 70 mg/dm3. And with aluminum doses less than 30 mg/dm3, there is even inhibition of the settling process. Like in the case of sodium silicate silicate treatment of magnesium containing solutions, the precipitation of calcium silicate strongly depends on the pH level. High efficiency of process is observed only in a highly alkaline environment. Under other conditions, the softening efficiency is significantly reduced. With an excess or lack of a precipitant, more compact particles are formed. The settling process for such particles occur more faster. At the same time, for a stoichiometric or near ratio between the components, particles of the branched structure are formed. Such particles settle twice slowly and occupy a larger imaginary volume. With a stoichiometric ratio of components, the speed is significantly slowed down, and when K = [SiO32-, mg-eq]/[Ca2+, mg-eq] ≥ 1,0 all filter pores are blocked during the first 10 min and liquid phase transportation stops. Reducing the initial water hardness to 20 mg-eq/dm3 does not significantly change the situation. Clarification of the suspension occurs partially. A significant amount of suspended particles remains in the mother solution. The flocculating ability of silicon compounds does not appeared under these conditions. When the content of calcium ions is reduced to 10,2 mg-eq/dm3, treatment with an equivalent amount of sodium silicate does not lead to a solid phase formation. Although after filtering through the "blue tape" filter the water hardness decreases. At the same time, the filtration properties of the solid phase formed during the softening process are the same as the filtration properties of carbonates, phosphates and hydroxides, so the reagent cannot be recommended for use in low- and medium-productivity systems, where the filtration is a main phase separation process.

A methodological study of the hardness of cooked Chinese noodles based on the texture analyzer

Abstract A generic instrumental analysis method, matched with sensory evaluation, for the hardness test of Chinese dried noodles after cooking, was established in this study. The cut and compression mode was compared at first, followed by an analysis of the hardness response curve obtained from cut code with three-stage. Then the reliability of this method was verified with 20 commercially available noodles. Results showed that the hardness difference between the two samples obtained using compression mode was only 0.087 %. In contrast, a 6.34 % difference was obtained using cut mode with the hardness value of 296.12 ± 6.10 g and 278.47 ± 12.22 g, respectively. Three parameters, including initial hardness (F 1), material hardness (K), and final hardness (F 2), were extracted from the shear curve to characterize the hardness of cooked noodles. A ranking difference of F 1, F 2, and K between 20 commercially available noodles was found, which illustrated various characteristics of cooked noodles. In summary, the cut mode was more suitable for determining the hardness of cooked noodles; F 1, F 2, and K, obtained from a three-stage analytical method for the inner and outer hardness of cooked noodles characterization, had excellent performance to match with sensory evaluation.

A detailed study on the cooking kinetics of fresh and hard to cook common beans (Phaseolus vulgaris L.): A case study on bean accessions of different market classes

A large-scale study was conducted to obtain a more holistic understanding of the cooking behavior for different bean accessions in terms of cooking kinetics and time to cook. Fresh and aged soaked beans from twenty-four accessions were assessed for texture evolution during cooking at 95 °C using the most informative objective compression texture analysis method. Texture evolution was modelled by the conventional fractional conversion model as well as modified three-parameter models to capture the lag phase. The initial texture varied across bean accessions and is significantly positively related to bean size. Significant but limited differences in initial texture on ageing were observed, the difference being accession dependent. The texture evolution during cooking, cooking kinetics and time to cook varied across bean accessions and storage conditions and all bean accessions developed the hard to cook defect. The softening rate constants for fresh beans were significantly higher (0.026–0.053) and more variable than for aged beans (0.008–0.014, almost similar values). Fresh and aged beans of a given accession softened to similar levels of final relative hardness. The lag phase was more prominent in aged beans (up to ≈25 min) than non-aged beans (0–7 min). Therefore, the difference in time to cook for fresh beans across accessions is mainly determined by the difference in initial hardness and cooking rate constant, while for aged beans these differences depend on initial hardness and lag time and to a lesser extent on the cooking rate constant.

A Comparative Study on the Wear Behavior of Quenched-and-Partitioned Steel (Q&amp;P) and Martensite Steel (Q&amp;T)

The wear resistance of quenched-and-partitioned steel (Q&amp;P) compared to martensite steel (Q&amp;T) remains unclear. In this research, the wear resistance of Q&amp;P steel and Q&amp;T steel was researched by the means of the abrasive wear (AW) and impact abrasive wear (IAW) tests. The results show that abrasive ploughing was the main reason causing the material loss of Q&amp;P and Q&amp;T steel, while Q&amp;T steel was subjected to severe fatigue spalling in the impact abrasive wear tests. Under the abrasive wear test, Q&amp;T steel has better wear resistance due to its higher initial hardness. Under the impact abrasive wear test, Q&amp;P steel has better wear resistance. This is because the formation of the deformed layer, which consists of finer grains and newly formed martensite in the worn subsurface, increased the hardness of the Q&amp;P steel, causing the hardness of the worn subsurface in Q&amp;P steel to be higher than that of Q&amp;T steel. Furthermore, Q&amp;P steel has better resistance to cracks nucleation and propagation compared to Q&amp;T steel. As a result, less material loss was caused by fatigue spalling in Q&amp;P steel under the impact abrasive wear tests.

Nanostructuring of an additively manufactured CoCrFeNi multi-principal element alloy using severe plastic deformation: Comparison of two materials processed by different laser scan speeds

Experiments were conducted to reveal the refinement of the microstructure and the evolution of the hardness of an additively manufactured (AM) CoCrFeNi multi-principal element alloy (MPEA) processed by severe plastic deformation (SPD) using high pressure torsion (HPT) technique. AM was carried out by laser powder bed fusion (L-PBF) technique at two different laser scan speeds. The as-built alloys for both laser scan speeds have a single-phase face-centered cubic (fcc) structure with <110> fiber texture parallel to the building direction. X-ray line profile analysis (XLPA) revealed that the dislocation density was considerably high even in the AM-processed state before HPT (3 × 1014 m−2) which increased by two orders of magnitude during HPT. The saturation of the lattice defects (dislocation density and twin fault probability) as well as the crystallite size occurred at a shear strain of about 10 during HPT. In both AM-processed alloys, <111> fiber texture developed parallel to the normal of the HPT-processed disks. For both laser scan speeds, the initial grain size in the AM-processed samples was refined from 70 to 90 μm to the nanocrystalline regime after 10 turns of HPT. Additionally, nanotwins formed with a probability of about 3 %. The initial hardness of the AM-processed MPEA samples for both laser scan speeds was 2700–2800 MPa, which is superior to that of CoCrFeNi produced by casting (about 1380 MPa). This can be explained by the high dislocation density in the AM-processed specimens. The formation of nanostructure with high lattice defect density during HPT resulted in a very high hardness value of about 5500 MPa in the AM-processed CoCrFeNi MPEA samples for both laser scan speeds.

Exploring microstructural evolution, nitrogen depth profile, and dry wear performance in 31CrMoV9 steel through combined severe shot peening and plasma nitriding

The present study investigates the influence of severe shot peening (SSP) on the plasma nitriding behavior and sliding wear performance of 31CrMoV9 steel. Initially, the steel was austenitized at 880 °C, followed by oil quenching, and tempering at 520 °C for one hour. These samples were shot peened using high-carbon steel shots, resulting in an enhancement in surface hardness up to 447 HV, gradually converging to the initial martensitic hardness after 140 µm depth. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) scrutinized the initial and surface treated martensitic samples. Afterward, the plasma nitriding treatments were carried out at temperatures of 400 °C, 450 °C, and 500 °C for 8 hours in a 30% N2 + 70% H2 atmosphere and 300 Pa pressure. Microhardness testing, SEM, XRD, and glow-discharge optical emission spectroscopy (GDOES) evaluated both plasma nitrided (PN) and severe shot peened/plasma nitrided (SSP-PN) samples. Cross-sectional SEM observations revealed compound layer thicknesses of approximately 2.8 µm, 5.0 µm, and 6.3 µm for PN samples at 400 °C, 450 °C, and 500 °C, respectively. SSP-PN samples exhibited a substantial increase — roughly 71%, 44%, and 33% increase, respectively, compared to PN samples. GDOES analysis supported this trend and indicated enhanced nitrogen diffusion depth, particularly evident in SSP-PN samples at consistent temperatures. The XRD results showed the stability of Fe4N, Fe2–3N, and CrN phases at all three nitriding temperatures. Furthermore, the intensity of these phases increases with temperature and is augmented by the application of the SSP. Microhardness measurements indicated hardness escalation: from 775 HV to 980 HV at 400 °C, 932 HV to 1096 HV at 450 °C, and 1011 HV to 1205 HV at 500 °C due to SSP. Finally, the wear performance was investigated between the non-nitrided, SSP, PN, SSP-PN, samples. Initially, SSP led to decreased wear performance up to 500 m, followed by improved behavior up to 1500 m. At 400 °C, the SSP-PN sample exhibited a 12% lower wear rate than PN. At 450 °C and 1500 m, the SSP-PN sample displayed a 24% reduction, while at 500 °C, it showed a 27% reduction compared to PN. SEM observations indicated abrasion as the primary wear mechanism across all samples. The overall results indicated a significant similarity in the nitrogen depth profile, hardness depth, and wear performance between the SSP-PN sample at 450 °C and the PN sample at 500 °C. The fact suggested a potential reduction of approximately 50 °C in the typical plasma nitriding temperature for 31CrMoV9 steel as a result of the SSP process.

Effects of Stocking Density and Pre-Slaughter Handling on the Fillet Quality of Largemouth Bass (Micropterus salmoides): Implications for Fish Welfare.

There is currently insufficient acknowledgment of the relationship between fish welfare and ultimate fillet quality. The purpose of this study was to assess the impacts of pre-slaughter handling and stocking density as fish welfare markers on fillet quality of largemouth bass (Micropterus salmoides). Fish from three stocking densities of 35, 50, and 65 kg·m-3 were reared in a recirculating aquaculture system (RAS) for 12 weeks and received commercial feed. Ultimately, the fish were either stunned with percussion on the head (control group) or subjected to air exposure for 3 min (anoxia group) before stunning and subsequent collection of blood and fillet samples. Western blot analysis revealed the degradation of actin in both groups. Additionally, higher oxidation progress and lower hardness and pH were observed in anoxia compared to the control group. We observed higher hardness at 35 kg·m-3 in anoxia compared to 50 and 65 km-3. The initial hardness values at 35, 50, and 65 km-3 were 1073, 841, and 813 (g) respectively in the anoxia group. Furthermore, the anoxia and control groups had rigor mortis after 6 and 10 h, respectively. Cortisol and glucose levels, and oxidative enzymes activity were higher in anoxia than in the control group. In conclusion, oxidation induced by anoxia likely plays a crucial role as a promoter of the quality deterioration of largemouth bass fillets.

Explaining the improving effect of dough crumb-sheet composite rolling on fresh noodle quality: From microstructure and moisture distribution perspective.

A new technique known as dough crumb-sheet composite rolling (DC-SCR) was used to improve the quality of fresh noodles. However, there is a dearth of theoretical investigations into the optimal selection of specific parameters for this technology, and the underlying mechanisms are not fully understood. Therefore, the effects of dough crumb addition times in DC-SCR on the texture, cooking, and eating quality of fresh noodles were first studied. Then, the underlying regulation mechanism of DC-SCR technology on fresh noodles was analyzed in terms of moisture distribution and microstructure. The study demonstrated that the most significant enhancement in the quality of fresh noodles was achieved by adding dough crumbs six times. Compared with fresh noodles made without the addition of dough crumbs, the initial hardness and chewiness of fresh noodles made by adding six times of dough crumbs increased by 25.32% and 46.82%, respectively. In contrast, the cooking time and cooking loss were reduced by 28.45% and 29.69%, respectively. This quality improvement in fresh noodles made by DC-SCR came from the microstructural differences of the gluten network between the inner and outer layers of the dough sheet. A dense structure on the outside and a loose structure on the inside could endow the fresh noodles made by DC-SCR with higher hardness, a shortened cooking time, and less cooking loss. This study would provide a theoretical and experimental basis for creating high-quality fresh noodles.

Comparison of Softening Behavior and Abrasive Wear Resistance between Conventionally and Additively Manufactured Tool Steels

Directed energy deposition (DED) is a powerful method for hard‐facing the existing tool components. Herein, three tool steel grades including a newly developed maraging steel (NMS), a cold work tool steel (V4E), and a high boron steel (HBS) are cladded on a hot work tool steel substrate. After tempering, the cladded tool steels are exposed to high temperatures at 600, 700, and 800 °C for 3 h to evaluate their softening resistance. The results show that all three tool steel grades have a significant hardness drop when the softening temperature reaches 700 °C. The investigated NMS has the lowest initial hardness in the tempered state but the best softening resistance. In contrast, HBS has the highest initial hardness but the worst softening resistance among the three steel grades. V4E tool steel has a moderate softening resistance compared to the other two steel grades. The factors contributing to the softening resistance have been discussed. Corresponding conventional tool steels are also adapted as references for comparison. Except for the NMS, the additive manufacturing tool steel samples have a better softening resistance than the conventional counterparts owing to more alloying elements trapped in the matrix. The abrasive wear resistance of the tempered and softened tool steels manufactured by DED and conventional methods is also evaluated and the wear mechanism is discussed. Besides the hardness, the free spacing λ between coarse hard particles is one of the major factors influencing the abrasive wear resistance.

The use of mouthwash containing trimetaphosphate as an adjunct therapy to fluoridated toothpaste reduces enamel demineralization

IntroductionThe decline in dental caries has been attributed to the widespread use of fluoride (F). Two forms of presentation are fluoridated toothpaste (FT) and mouthwash (MW), widely used by the population. Materials and methodsThis study aimed to evaluate in vitro the effects of combining FT and MW, whether supplemented with sodium trimetaphosphate (TMP) or not, on dental enamel demineralization. Bovine enamel blocks (n = 60) were selected based on initial surface hardness (SHi) and divided into 5 experimental groups (n = 12 each): I) Placebo Toothpaste (without F/TMP); II) 1100 ppm F Toothpaste (FT); III) 1100F associated with a MW at 100 ppm F (FT + MW 100F); IV) 1100F associated with a MW at 225 ppm F (FT + MW 250F); and V) 1100F associated with a MW at 100 ppm F supplemented with 0.4 % TMP (FT + MW 100F-TMP). The blocks were treated twice a day, undergoing 5 pH cycles over 7 days. Thus, the percentage change in surface hardness (%SH), integrated subsurface hardness loss (ΔKHN), and the concentration of F, phosphorus (P), and calcium (Ca) in the enamel were determined. The data were submitted to ANOVA and Student-Newman-Keuls test (p < 0.001). ResultsThe 1100F group was statistically inferior to the groups associated with MW for %SH, ΔKHN, and the concentration of P and Ca in the enamel (p < 0.001). Blocks treated with FT + MW 225F and FT + MW 100F-TMP showed significantly lower %SH compared to the other groups (p < 0.001). The FT + MW 100F - TMP group exhibited the lowest depth mineral loss (ΔKHN), and higher concentration de P in enamel (p < 0.001). ConclusionThe adjunct use of MW with FT produces a greater protective effect in inhibiting enamel demineralization, and the supplementation of TMP to the MW with 100F provides a superior effect compared to MW with 225F. Clinical significanceThis combination of treatments could be regarded as one of several alternative fluoride supplements for subjects at elevated risk of caries.

Atomic structure of clusters and GP-zones in an Al-Mg-Si alloy

The structures of atomic clusters and GP-zones preceding precipitation in an Al-0.70Mg-0.85Si-0.15Fe-0.25Mn (wt. %) alloy have been investigated by annular dark field scanning transmission electron microscopy imaging and density functional theory calculations. One analysed condition consisted of one-month natural aging, and another was in a pre-baked state after 24 h aging at 90 °C. To quantify the effect of clusters and GP-zones on microstructure development during a subsequent isothermal artificial aging at 185 °C, hardness evolution was measured, and precipitate statistics was performed at the peak hardness corresponding to 5 h aging. Several types of clusters and GP-zones have been observed and based on structure and visual appearance named 'Disordered Frank-Kasper', 'Square', 'Binocular', and 1β", 2β", 3β", 4β". The first four are most common in the natural aged condition and are associated with a well-known influence on the initial hardness evolution. The last three are fractions of the hardening β" phase and refer to the number of structural units they contain. These GP-zones have an increased density in the pre-baked condition, leading to a rapid increase in hardness during artificial aging and to a finer microstructure of high-density small needle precipitates at peak hardness.

A comparative study on the wear behavior of dual phase (DP) steel and quenching and partitioning (QP) steel

Present study aims to elucidate the wear resistance/morphology/mechanism at wear distances from 3 to 1000 m based on the microstructure and tensile properties in DP steel and QP steel with similar initial hardness by means of sliding wear test and electron microscopes. QP steel shows better wear resistance at higher wear distance over 150 m opposite to lower wear distance, compared to DP steel, due to continuous increase in hardened layer during wear test in QP steel. This is because of higher fraction of adhesive wearing (e.g., galling) without significant wear loss originated from higher capacity of strain−hardening caused by effective impacts of grain refinement of ferrite, transformation-induced plasticity, and multiphase hardening in QP steel.

Silver Alloy Surface Modification for Mechanical Property Enhancement in Aviation and Transportation

Silver alloys are often used for electrical switches in railway transportation. However, a well-known issue with these switches is their relatively short application period due to certain disadvantages of silver alloys, mainly their low hardness and low resistance to abrasive wear, in contrast to their excellent electrical conductivity. Therefore, the main goal of this study was to increase or maintain the hardness of the surface layer in order to extend the life of worn parts without compromising their electrical properties. Instead of ceramic particles, as in other studies, metallic powders were used, which could increase the electrical and/or thermal properties of silver alloys. The following work presents the use of laser processing as a relatively new technique for metal and metal alloy surface processing technology. In particular, a process based on the melting of silver (Ag) with metallic powders, such as chromium (Cr) and nickel (Ni) particles, is presented. The aim was for these powders to create intermetallic phases with a silver matrix in the obtained surface layer, significantly improving the mechanical properties based on the formation of the phases coherent or semi-coherent with the silver matrix. Regarding the original practical implications of this work, it was important to investigate the possibility of applying fibre laser for surface property enhancement. The scientific aim was to describe the changes in microstructure and compounds that occurred in the laser-remelted surface silver layer after Ni and Cr particles were fed into the basic silver material. It was concluded that the surface layer obtained after chromium application was without cracks and defects and had a higher hardness than the untreated material. A three-zone structure was also found in the obtained surface layer: (1) the remelted zone, (2) the heat-affected zone, and (3) the matrix material. The remelting zone revealed a higher hardness compared to the untreated material, reaching 92 HV0.3, which is more than twice the initial hardness value.