Thermocyclic Treatment Research Articles

Analysis of patterns in the formation of phase composition during thermal and thermocyclic treatment of maraging steel

The paper studies changes in the phase composition of typical maraging steel. The analysis performed made it possible to determine the amount of retained austenite depending on the modes of thermal and thermocyclic treatment with heating in the temperature range of α-γ transformation. The processes occurring during heating in the region of α-γ transformation are divided into two temperature regions. As a result, it is noted that the identified patterns in the formation of the phase composition during thermal and thermocyclic treatment with the temperature range of α-γ transformation make it possible to both control changes in the phase composition and properties of steel and predict these changes.

Friction behavior of 30CrNi2MoVA gun barrel steel after thermo-cyclic treatment: Air and simulated seawater

The influence of gun barrel erosion has been proposed, but the research on the wear behavior of gun steel during the initial extrusion phase remains limited. This study employed an experimental approach to investigate the wear of 30CrNi2MoVA gun steel after untreated (25 °C) and thermal cycling treatments (400 °C and 800 °C) under both air and simulated seawater environments. In the air environment, abrasive wear and adhesive wear mechanisms were prominently observed. In the simulated seawater, abrasive wear mechanism was predominant. In both environments, the surface morphology and wear profiles of the untreated samples were similar, exhibiting a negative interaction phenomenon. After thermal cycling treatment, the corrosion wear resistance of 30CrNi2MoVA steel were significantly reduced. Among them, the material performance is the lowest at 800 °C. Therefore, this study provides theoretical and experimental evidence for improving the friction and wear performance of gun barrel rifling during the bullet extrusion process.

Mechanical Properties of High Entropy Alloys Based on Rare Earth Elements with Yttrium and Scandium

Abstract—The high-entropy alloys GdTbDyHoSc and GdTbDyHoY having equiatomic composition are considered as promising materials for magnetic cold generators. The results of the alloys structure and chemical composition investigation are presented in this paper. The solidus and liquidus temperatures of the alloys under investigation were determined by the method of differential scanning calorimetry. Based on these data, an experimental mode of thermocyclic treatment was selected. There were no signs of alloys destruction after five cycles testing for heat resistance in the following regime: 15 min exposition at 1073 K (~0.6 of the melting temperature) and subsequent quenching in room temperature water. It was found that the applied heat treatment led to an increase in the hardness of the alloys by 2–3 times and a decrease in wear resistance by 4–40 times, depending on the composition of the alloys and the number of heat treatment cycles. A significant change in the properties of alloys is associated with the formation of oxides of the REM2O3 type not only on the surface of the alloys, but also in their volume, which is due to the high chemical activity of rare earth metals (REM). The presented data will be useful for the development of modes of thermal and thermomechanical processing of various alloys.

Effect of Thermocycling Treatment on Physicomechanical Properties of Low-Carbon Martensitic Steel 15Kh2G2NMFB for Parts of Precision Devices

Effect of Thermocycling Treatment on Physicomechanical Properties of Low-Carbon Martensitic Steel 15Kh2G2NMFB for Parts of Precision Devices

Study of regularities of structural-phase transformations during thermocyclic treatment of tool steels

Movement of carbon atoms to dislocations reduces the specific volume of the martensite phase, which, in turn, affects the general level of volumetric changes that occur as a result of phase transformations during quenching. The measurements carried out on samples of steel ShX15 showed that the minimum increase in geometric dimensions is observed. Intermediate tempering and re-quenching do not change this pattern. At the same temperature, for this steel grade, the minimum degree of martensite tetragonality was recorded. This study has shown that to obtain a high level of final properties of tool steel, the most optimal is to obtain a substructure with a high level of defectiveness of the crystal structure of steel. It was found that the use of thermal cycling treatment contributes to an increase in the level of defectiveness of the crystal structure. It was also found that the use of aqueous solutions of polymers as a quenching medium makes it possible to obtain a cooling rate less than in oil quenching, which helps to reduce the level of quenching stresses.

Improvement of thermocyclic treatment technology to increase wear resistance of gears

The technology of thermocyclic treatment of fine‑module gears has been improved, which makes it possible to increase their wear resistance by 30–40 %. Gears were subjected to preliminary cyclic heating and subsequent impulse hardening. In all cases of hardening, a martensitic structure is formed, which provides high rigidity of the material. The sizes of martensitic plates depend on the heating temperature during quenching. During cyclic heat treatment up to a temperature of 450 °C, the sizes of austenite grains and martensite plates did not depend on temperature.

Decreasing Gear Wear by Improved Thermocyclic Treatment

Decreasing Gear Wear by Improved Thermocyclic Treatment

Investigation of the Effect of Thermocyclic Treatment on the Mechanical Properties of Steel

The evolution of the steel structure under thermocyclic action is considered. The possibility of increasing the complex of mechanical properties of steels after thermocyclic treatment is shown.

Replacement working body material as a way to increase reliability of road construction machines

Introduction. On the example of a motor grader knife, ways of increasing the reliability of road construction machines (RCM) operation are evaluated. For this purpose, the analysis of force effects nature on the working body of the RCM is carried out and its design features are highlighted (the presence of a welded joint). Based on the analysis, the range of characteristics necessary for making a decision on the possibility of replacement the material of the RCM working body is determined. Additionally, its thermocyclic treatment (TCT) is carried out. Experimental studies of the effect of this thermal impact type on the structure and properties of steels are described.Materials and methods. With the help of metallographic analysis, the author investigates the influence of the number of thermal effects cycles on the grain size and the complex of various materials physical and mechanical characteristics of road construction machines working body at various stages of the thermocyclic treatment.Results. It is determined that an increase in the level of the investigated steels physical and mechanical characteristics is possible through the use of TCT due to the obtaining of a fine-grained metal structure. The dependences of the main physical and mechanical characteristics of the investigated steels (ultimate strength and yield strength) on the number of thermal effects cycles are considered. Correlation relationships are selected to describe these dependencies. The relationship between the yield strength and ultimate strength of 09G2S and 30MnB5 steels and the grain size is considered. In addition, studies of the steels fatigue characteristics are carried out; data on determining the microhardness are presented for the welded joint. For various operating temperatures, fractographic studies are carried out on samples after cyclic loading.Discussion and conclusion. Based on a comparative analysis of the complex of physical and mechanical characteristics, the author made a conclusion about the possibility of replacing steel 09G2S with steel 30MnB5.

Bonding between implant attachment pickup materials and CAD-CAM denture base material

Statement of problemAdequate bonding between pickup material and the newer generation of prepolymerized polymethyl methacrylate (PMMA) for computer-aided-design and computer-aided manufacturing (CAD-CAM) dentures is essential to the success of treatment. However, studies on the bond between these 2 materials are lacking. PurposeThe purpose of this in vitro study was to evaluate the bond strength of 3 different chairside implant LOCATOR attachment pickup material groups and prepolymerized PMMA by investigating their pushout force. Material and methodsPrepolymerized PMMA, (Lucitone 199) was used as the denture base material. The material was cut into 25×25×5-mm disks, and a Ø6.5-mm hole was drilled into the center of the disks. Six pickup materials from 3 groups were tested: composite resin with bonding agent (N=3, EZ PickUp, Quick Up, and Triad gel), composite resin without bonding agent (N=1, Chairside), and acrylic resin (N=2, Jet denture repair acrylic, and Duralay). All materials were prepared as per the manufacturers’ recommendations and were used to fill the center hole. The specimens were left for 48 hours to completely polymerize before testing. Half of the specimens from each material then received thermocycling treatment. All specimens were subjected to axial pushout testing with a universal testing machine. ResultsIn the nonthermocycled specimens, Duralay and Jet denture repair acrylic resin showed significantly higher pushout force than that of the other groups (P<.001). Triad gel showed higher pushout force than EZ PickUp and Quick Up (P<.001). Chairside showed the lowest push-out force. The same trend was also observed in the thermocycled specimens. The peak pushout force of nonthermocycled Chairside composite resin was significantly lower than that of thermocycled Chairside composite resin (P=.03). Conversely, the peak pushout force of nonthermocycled EZ PickUp specimens was significantly higher than that of thermocycled EZ PickUp specimens (P=.01). Variation in fracture patterns among groups was observed, and the correlation between pushout force and fracture patterns was recorded. ConclusionsTwo materials from the acrylic resin group, Jet denture repair acrylic and Duralay, showed higher pushout forces, indicating a better bond with Lucitone 199 CAD-CAM denture base material compared with other tested materials, including composite resin with bonding agent (EZ PickUp, Quick Up, and Triad gel) and composite resin without bonding agent (Chairside).

Influtnce analysis of 09Г2С and 30MnB5 steels thermo cyclic treatment on strength characteristics of road construction machines working bodies

Introduction. The ways of increasing the reliability of road construction machinery operation are considered. As a result, an option is proposed to replace the used 09Г2С steel with 30MnB5 boron steel. Using the example of a motor grader blade, the force effects on this working body of the road construction machinery are analyzed. In order to increase the level of physical and mechanical characteristics of 09Г2С and 30MnB5 steels, they are additionally exposed to thermo cyclic treatment. The experimental studies about the influence of this type thermal action on the structure and properties of steels are described. The comparative analysis of the obtained characteristics allows making a conclusion about the possibility of the considered replacement.Materials and methods. Through the metallographic analysis the influence of the number of thermal effects cycles on the grain size of steel is investigated. Alongside a set of physical and mechanical characteristics of these steels was determined at various stages of the thermo cyclic treatment.Results. It was determined that an increasing the level of physical and mechanical characteristics of the studied steels is possible through the use of thermo cyclic treatment. This is achieved by producing a fine-grained metal structure with a higher strength. The dependence of the tensile strength and yield strength of the steels under investigation on the number of cycles of thermal action is considered. Some correlation relationships were selected to describe these dependencies. The relationship between the yield stress and ultimate strength of 09Г2С and 30MnB5 steels and the grain size is considered. All investigated dependencies are presented in graphical form.Discussion and conclusion. Based on a comparative analysis of the complex of physical and mechanical characteristics, the conclusion about the possibility of replacing 09Г2С steel with 30MnB5 steel was made.

The Influence of Thermocyclic Treatment on the Structure and Mechanical Properties of Pseudo-Alpha Titanium Alloys for Steam Turbine Blades

The influence of thermal cycling treatment of pseudo-α-titanium alloys OT4 and VT20 on their structural and substructural characteristics, as well as their mechanical properties is considered. A significant change in structural characteristics is established. This contributes to an increase in the strength properties of alloys with satisfactory ductility and high-temperature strength.

Influence of thermal cycling modes on VK8 hard alloy mechanical and tribological properties

Hard alloys are popular materials widely used in the toolmaking industry. Refractory carbides included in their composition make carbide tools very hard (80 to 92 HRA) and heat-resistant (800 to 1000 °С) so as they can be used at cutting speeds several times higher than those used for high-speed steels. However, hard alloys differ from the latter by lower strength (1000 to 1500 MPa) and the absence of impact strength, and this constitutes an urgent problem. We studied the influence of thermal cycling modes on the mechanical and tribological properties of VK8 (WC–8Co) hard alloy used in the manufacture of cutters and cutting inserts for metal working on metal-cutting machines. As the object of study, we selected 5×5×35 mm billets made of VK8 (WC–8Co) alloy manufactured by powder metallurgy methods at Dimitrovgrad Tool Plant. The following criteria were selected for heat treatment mode evaluation: Vickers hardness, flexural strength, and mass wear resistance (as compared to the wear of asreceived samples that were not heat treated). Plates in the initial state and after heat treatment were subjected to abrasion tests. Wear results were evaluated by the change in the mass of plates. Regularities of the influence of various time and temperature conditions of heat treatment on the tribological properties of products made of VK group tungsten hard alloys were determined. An increase in the number of thermal cycling cycles improved such mechanical properties of the VK8 hard alloy as strength and hardness. When repeating the cycles five times, an increase in abrasive wear resistance was obtained compared to the initial nonheat-treated sample. The elemental composition of the VK8 hard alloy changed insignificantly after thermal cycling, only a slight increase in oxygen was observed on the surface of plates. The grain size after thermal cycling increased in comparison with the initial VK8 hard alloy. It was found that VK8 hard alloy thermocyclic treatment leads to a change in the phase composition. X-ray phase analysis showed the presence of a large amount of α-Co with an hcp-type lattice on the surface of a hard alloy and a solid solution of WC in α-Co. A change in the cobalt modification ratio causes a decrease in microstresses. An analysis of the carbide phase structure state showed that the size of crystallites and microstresses changed after thermal cycling. The lattice constant of the cobalt cubic solid solution decreased, which may indicate a decrease in the amount of tungsten carbide and carbon dissolved in it. Statistical processing of experimental results included the calculation of the average value of the mechanical property, its dispersion and standard deviation in the selected confidence interval.

THE EFFECT OF THERMOCYCLING ON MARGINAL SEALING ABILITY OF MTA PLUS AND BIODENTINE WHEN USED AS ROOT-END FILLING MATERIALS

Background:Marginal microleakage occurs when restorations are poorly adapted to the cavity walls which leads to penetration of bacteria, fluid and nutrient into the marginal gap. Aim: The study aimed to evaluate the effect of thermocycling on marginal sealing ability of two root-end filling materials i.e. MTA Plus and Biodentine. Materials and Methods: An in vitro study was conducted at Department of Conservative Dentistry and Endodontics in Institute of Dental Sciences (IDS), Jammu, Jammu and Kashmir, India. Forty extracted teeth with single root were decoronated maintaining a standardized length of 16mm. Biomechanical preparation and obturation was done for all the teeth. Samples were stored at 37oC and 100% humidity for seven days. Apical 3mm was resected and cavities were prepared which were randomly divided into two experimental groups with twenty samples each. The cavities were filled with MTA Plus in group I and Biodentine in group II. These groups were further divided into two subgroups of ten each (n=10). The second subgroup of both the groups did not receive any treatment and the first subgroup samples were subjected to 500 thermocycles in water bath at temperature ranges between 5oC and 55oC with a dwell time of 30 second. The samples were immersed in methylene blue dye and after through washing they were sectioned longitudinally. Examination was done under stereomicroscope to measure the depth of penetration. Statistical Analysis: The data collected were put to statistical analysis by one-way ANOVA (analysis of variance) and post hoc tests. Results: The average depth of dye penetration was least for Biodentine when thermocycling treatment was not given (0.13mm) and maximum value was depicted by MTA Plus when undergone thermal cycles (0.57mm). It is also noted that no significant difference is seen in Biodentine with or without artificial aging procedure. Conclusion:Biodentine showed least amount of microleakage, thus a better sealing ability.Alsothere was little effect of thermocycling onmicroleakage of both the materials.

NON-STATIONARY SURFACE TEMPERATURE FIELD LAYER OF METAL WITH PERIODIC ENERGY ACTION ON SURFACE

Under the influence of temperature fluctuations, the properties of metals can change. Thermocyclic treatment of metals, in particular steels, requires accurate detection of patterns of non-stationary temperature field in the treated metal layer. An expression was obtained for the deviation of the temperature from the value of its instantaneous equilibrium distribution for a one-dimensional homogeneous model of finite length under conditions of periodic energy action on its active surface. This solution was applied to the low carbon steel sample.

Effects of Er:YAG laser pre-treatment on dentin structure and bonding strength of primary teeth: an in vitro study

BackgroundTo investigate the effects of Er:YAG laser pre-treatment on the dentin structure and shear bond strength of primary teeth.MethodsDentin specimens were prepared using freshly extracted intact primary molars and divided randomly into four groups based on the surface treatment applied. The control and etchant groups received no treatment and conventional acid etching treatment, respectively, while the energy and frequency groups received laser surface treatment with variable energy (50–300 mJ) and frequency (5–30 Hz) parameters. The morphology was observed using scanning electron microscopy. The surface-treated dentin slices were bonded to resin tablets, followed by thermocycle treatment. The shear strength was determined using a universal testing machine and de-bonded surfaces were observed using a stereomicroscope.ResultsSEM observation showed that the surface morphology of the dentin slices changed after etching as well as after Er:YAG laser pre-treatment with different energy and frequency values. The dentin tubules opened within a specific energy (50–200 mJ) and frequency (5–20 Hz) range. Beyond this range, the intertubular dentin showed cracks and structural disintegration. Shear strength tests showed no significant changes after acid etching. The shear strength increased significantly (P < 0.05) after Er:YAG laser pre-treatment compared with that of the control group. The shear strength increased within the same energy (50–200 mJ) and frequency (5–20 Hz) range as the tubule opening, but not significantly (P > 0.05). The most common mode of interface failure was adhesive (interface) failure, followed by mixed and resin cohesive failure.ConclusionsPre-treatment using Er:YAG laser opens the dentinal tubules without the formation of a smear layer and improves the bonding strength between the primary teeth dentin and the resin composites.

УЛУЧШЕНИЕ ПРОЧНОСТИ И ИЗНОСОСТОЙКОСТИ СТАЛЕЙ МАРКИ 65Г МЕТОДАМИ ТЕРМОЦИКЛИЧЕСКОЙ ОБРАБОТКИ

The article presents the results of experimental studies that establish the features of increasing the strength and wear resistance of steels after thermocycling. Thermocyclic treatment as a method of heat treatment is based on continuous accumulation from cycle to cycle of positive changes in the structure of metals. An important feature of the cycle is its intensity, the absence or the presence of short exposures, and the optimal range of temperature changes. The paper establishes the laws of the influence of the temperature-time parameters of thermocyclic processing on the physicomechanical properties of tool steel and the technology of hardening machine parts due to the intensification of diffusion processes, phase and structural transformations, which reduce the duration of heat treatment and improve the whole complex of mechanical properties, that is the reliability of machine parts. Based on theoretical and experimental studies, it has been established that the production of ultrafine grains contributes to an increase in the wear resistance of steels. When using thermal cycling, higher characteristics of mechanical properties were obtained, fracture toughness increased by 1.5 times, and wear resistance increased by 1.9 times. This is due to the nature of the resulting structure and the degree of grain refinement.

Decrease of degree of carbide nonuniformity in hypereutectoid steel by a thermocyclic treatment

Decrease of degree of carbide nonuniformity in hypereutectoid steel by a thermocyclic treatment

Quantitative Relationship Between the Nucleation Undercooling of Liquid Iron and Its Liquid Structure: Investigated by In Situ Synchrotron Radiation

The nucleation behavior of liquid iron with various iron oxides was investigated through an in situ synchrotron radiation analysis and undercooling measurements. When Al and Si were added into the liquid in an oxygen atmosphere, three typical nucleation behaviors with three different undercooling values were observed during a thermocycling treatment. Further investigation showed that the nucleation undercooling (ΔT) increased linearly with variations in the nearest neighbor distance (r1) values of the liquid.

Структурные особенности наноструктурного эквиатомного сплава TiNi при многократных мартенситных превращениях

The paper describes in detail a study dealing with the influence of multiple martensite transformations on the equiatomic alloy of the TiNi system microstructure. Thermocyclic treatment of the equiatomic alloy in the nanocrystalline state obtained by the intensive torsional plastic deformation method was carried out.