Brittle Temperature Research Articles

Integrated Control of Thermal Residual Stress and Mechanical Properties by Adjusting Pulse-Wave Direct Energy Deposition

Directed energy deposition with laser beam (DED-LB) components experience significant residual stress due to rapid heating and cooling cycles. Excessive residual tensile stress can lead to cracking in the deposited sample, resulting in service failure. This study utilized digital image correlation (DIC) and thermal imaging to observe the in situ temporal evolution of strain and temperature gradients across all layers of a deposited 316 L stainless steel thin wall during DED-LB. Both continuous-wave (CW) and pulsed-wave (PW) laser modes were employed. Additionally, the characteristics of thermal cracks and geometric dislocation density were examined. The results reveal that PW mode generates a lower temperature gradient, which in turn reduces thermal strain. In CW mode, the temperature–stress relationship curve of the additive manufacturing sample enters the “brittleness temperature zone”, leading to the formation of numerous hot cracks. In contrast, PW mode samples are almost free of cracks, as the metal avoids crack-sensitive regions during solidification, thereby minimizing hot crack formation. Overall, these factors collectively contribute to reduced residual stress and improved mechanical properties through the adjustment of pulsed-wave laser deposition.

Radiation and thermal embrittlement of RPV steels: the links of embrittlement mechanisms, fracture modes and microcrack nucleation and propagation properties. Part 3: Brittle fracture modelling and analysis of the link of microcrack nucleation and propagation properties and embrittlement mechanisms

Radiation and thermal embrittlement of RPV steels are studied from viewpoint of links of brittle fracture properties on micro- and macroscales. Brittle fracture properties on macroscale (such as fracture toughness and fracture stress) and the critical parameters controlling nucleation and propagation of microcracks are determined on the basis of the probabilistic brittle fracture model Prometey. The experimental and numerical investigations are performed for 2Cr–Ni–Mo-V steel and A533 steel used for RPVs of WWER and PWR types. RPV steels are studied in the following states: (1) the initial (as-produced) state; (2) the thermally-embrittled state modelling hardening mechanism of embrittlement; (3) the thermally-embrittled state modelling non-hardening mechanism of embrittlement; (4) the irradiated state. The test results of various specimens (smooth and notched round bars and cracked compact tension specimens) from the investigated steels in various states are represented over brittle fracture temperature range. Brittle fracture modelling is performed with the Prometey model for all the above specimens, and the experimental and numerical results are compared. On the basis of the obtained results the links between embrittlement mechanisms, fracture modes and microcrack nucleation and propagation properties are found.

Prevention of solidification cracking in alloy 718 additive manufacturing by laser metal deposition method based on control guidelines for weld solidification cracking

The chemical composition of alloy 718 powder was optimized to suppress a solidification cracking in the additive manufactured part by the laser metal deposition method. The relationship between the condition of additive manufacturing and defects was evaluated. A lack of fusion was observed on the low heat input (low energy density), and the solidification cracking occurred on the high heat input (high energy density). The powder composition of alloy 718 was attempted to be optimized from a theoretical approach of the solidification cracking susceptibility. It was found that Si and B had a significant influence on the solidification cracking, therefore a preventive powder with reduced Si and B was developed. The effects of Si and B on solidification cracking were compared by reproducing the solidification conditions during additive manufacturing and evaluating the solidification brittle temperature range (BTR) using the Varestraint test. It was found that the BTR of the preventive material was smaller, and the solidification cracking susceptibility was improved. In addition, the solidification cracking did not occur in additive manufacturing using the preventive powder. In other words, it is suggested that the countermeasure for weld solidification cracking leads to the prevention of solidification cracking in additive manufacturing directly, and the effectiveness of the optimization of powder composition was verified.

Investigation of the Effect of Ageing Temperature on a Set of Steel 15NiCuMoNb5 (WB36) Service Properties. Part III. Effect of Thermal Aging on Mechanical Properties and Critical Brittleness Temperature

Investigation of the Effect of Ageing Temperature on a Set of Steel 15NiCuMoNb5 (WB36) Service Properties. Part III. Effect of Thermal Aging on Mechanical Properties and Critical Brittleness Temperature

Effect of cobalt on Microstructure and toughness properties of 9Cr-1.8W-0.4Ni-xCo weld metal

In this research, microstructural characterization and mechanical properties of 9%Cr, 0.4%Ni (including W and Mo) steel weld metal with alloyed cobalt were investigated. Due to their strong creep resistance, oxidation resistance, and low thermal expansion, 9%Cr steels are used in nuclear power plants, petrochemical industries, and fossil fuel-powered power plants that operate in high temperature conditions. In this context, weld metals comprising 0.5 %, 1 % and 1.5 % cobalt and cobalt-free weld metal were produced by SMAW (shielded metal arc welding) technique. Microstructure of the weld metals were characterized with optical microscope (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Also, XRD analysis was performed on the bulk samples and precipitated carbide/nitride phases extracted from the weld metals. In addition, differential scanning calorimetry (DSC) was used to determine the phase transformations. Thermo-Calc modeling study was also performed. Hardness, tensile and Charpy-V impact tests were carried out to determine the mechanical properties. The hardness did not change significantly when cobalt up to 1.5 % in the weld metal. However, with the increase of cobalt, the yield and tensile strength increased without affecting the elongation value too much. In the Charpy impact tests performed at different temperatures (−40 °C, −20 °C, +20 °C, +40 °C, +60 °C), the amount of cobalt increased toughness, especially at +40 and + 60oC temperatures. Ductile brittle transformation temperature (DBTT) of the weld metal with 1.5 % Co decreased from 29 °C to 15 °C compared to cobalt free weld metal. It is thought that this may be caused by the further separation of C, Cr and W from the matrix through forming precipitate by the cobalt effect. Besides the mechanical properties, microstructure was also affected by adding Co with inhibition of delta ferrite formation which decrease the toughness. Curie temperature increased with increasing cobalt content detected by DSC.

Structural Optimization of PA12/MVQ@POE-g-MAH Ternary Composite for Superior Toughness and Low-Temperature Resistance.

To enhance the low-temperature toughness and resistance of the engineering plastic polyamide PA12, this study introduces novel PA12/MVQ@POE-g-MAH ternary composites using a two-step process and dynamic curing. Analytical results indicate that incorporating MVQ@POE-g-MAH into the PA12 matrix markedly enhances its toughness and heat resistance. As the MVQ@POE-g-MAH content increases, the elongation at break of PA12 composites significantly expands from 52.83% to 204.69%, and the notch impact strength escalates from 8.69 to 74.34kJ m-2. In addition, the brittleness temperature of PA12 decreases from -59.5 to -67.0°C. Experimental findings confirm that POE-g-MAH is dispersed at the interface between MVQ and PA12, creating an encapsulated structure of MVQ@POE-g-MAH. This enhancement significantly broadens the potential applications of PA12 by improving its toughness, and resistance to both low and high temperatures, as well as impact endurance.

ФИЗИКО-ХИМИЧЕСКИЕ СВОЙСТВА ПОЛИМЕРНО-БИТУМНЫХ ВЯЖУЩИХ, МОДИФИЦИРОВАННЫХ ШУНГИТОМ РАЗЛИЧНЫХ МЕСТОРОЖДЕНИЙ КАРЕЛИИ

The use of polymer-bitumen binders as part of an asphalt concrete mixture allows to improve the quality of road surfaces. The most commonly used polymer is styrene and butadiene copolymer, however, it does not provide sufficient durability of asphalt concrete and has a high cost. There is a positive experience in solving these problems through the use of polymer composites filled with fine powders. One of the promising polymer fillers is shungite. The purpose of this work was to study the effect of shungite from various deposits of Karelia on the structure and properties of polymer-bitumen binder. It was found that the introduction of shungite in the amount of 5 wt.% changes the physico-chemical characteristics of polymer-bitumen binders: the viscosity and softening temperature increase markedly, the temperature of brittleness, as well as extensibility and elasticity change to a lesser extent. Changes in these properties indicate the structuring of the binder by finely dispersed shungite. This phenomenon may be associated with the transfer of bitumen from a volumetric to a structured state due to its interaction with the surface of the shungite powder, as well as due to the diffusion of low-molecular components of the binder into the pores of the filler. Moreover, shungite samples from different deposits do not affect the studied characteristics in the same way. The explanation for this may lie in the different content of active adsorption centers on the surface of shungite, which is in a linear relationship with the main characteristics of the polymer-bitumen binder modified with shungite.

CHEMICAL MODIFICATION OF ROAD PETROLEUM BITUMEN WITH MALEIC ANHYDRIDE AND POLYETHYLENE GLYCOLS

A number of problems arise in the production and application of road bitumen. One of them is unsatisfactory operational characteristics, mainly heat resistance, elasticity and adhesion between the binder and aggregate. With an increase in the intensity of traffic, an increase in the volume of heavy goods transportation, the mass of cars, together with the influence of weather and climate factors on the structure, this leads to the destruction of the road surface. The work describes the results of the study of the process of chemical modification of road petroleum bitumen with maleic anhydride and polyethylene glycols (PEG) to obtain bitumen-polymer mixtures, which, in addition to good heat resistance, also have high elasticity. When modifying road bitumen with maleic anhydride, the latter acts as a certain narrowing link, which contains on the one hand a double bond that interacts with bitumen, and on the other hand an anhydride group that can interact with various polymers containing functional groups (hydroxyl, epoxy and other). Further, by adding a polymer to maleinized bitumen (bitumen modified with maleic anhydride), the resulting bitumen-polymer mixtures can be given various properties (heat resistance, elasticity, adhesion, and others). Polyethylene glycol is a cheap polymer capable of interacting with the anhydride group of maleic anhydride in bitumen on the hydroxyl group. It was established that the effect of maleic anhydride and maleic anhydride together with PEG on the heat-resistant characteristics of bitumen is the same regardless of the modification conditions. Compared to the original bitumen, the obtained BPS is characterized by a higher softening temperature, lower penetration and ductility. The temperature of brittleness is not rapid, but it is increasing. The influence of the used modifiers on bitumen elasticity is significant and depends on the modification conditions. It was established that PEG 2000 is the optimal PEG for modifying maleinized bitumen, from the point of view of ensuring good bitumen elasticity.

Study of brittle fracture and temperature resistance in the range of 20-11000С of autoclaved cellular reinforced materials

In this paper, the study of cellular autoclaved reinforced material resistant to brittle fracture and temperatures in the range of 20-1100С. The analysis of the results shows that the studied cellular autoclaved reinforced materials by the value of F (brittle fracture criterion) will not brittle fracture under conditions of a sharp change in temperature from 20 to 300 °C because the value of F ≤ 4. It was determined that on the wall system made of blocks of the material in question with a density of 400 kg/m3, 10 days after the completion of masonry under standardized fire exposure for 180 minutes in the temperature range of 20-1100 °C, there was no loss of thermal insulation, bearing capacity and integrity of the samples. During the tests, the maximum temperature values in the middle of the cross-section of the samples did not exceed 97°C. The values of As, Af, Amin for the test time of 182 minutes were 175074, 175212, 168560 Сmin, respectively, which meets the criterion requirements of DSTU B V.1.1-19:2007 and ensures the fire resistance class REI 180.

A Physically-Based Criterion for Determining the Critical Brittleness Temperature from Charpy Impact PRV Tests for Reactor Steels and Their Welds

A Physically-Based Criterion for Determining the Critical Brittleness Temperature from Charpy Impact PRV Tests for Reactor Steels and Their Welds

Effect of Single Crystal Growth and Solidification Grain Boundaries on Weld Solidification Cracking Behavior of CMSX-4 Superalloy

Single-crystal superalloys have been popularly employed in high-temperature parts of gas turbines, such as blades. However, the welds of such alloys are highly susceptible to solidification cracking, which limits their applicability to high-temperature turbine blades. In this study, the effects of characteristics of weld solidification on solidification cracking susceptibilities (solidification brittle temperature range, BTR) were fundamentally investigated for the CMSX-4 single-crystal superalloy. We applied a transverse-Varestraint test procedure for both the linear and oscillated arc welds by changing the weld solidification characteristics, such as the degree of single crystal growth and formation of solidification grain boundaries. The BTR for the CMSX-4 alloy is 336 K for linear welding condition, whereas the values are 434 K and 342 K for 0.6 and 1.5 Hz oscillated welds. Interestingly, the BTR continuously increases with the weld oscillation frequency. By contrast, almost no changes in the weld mushy-zone temperature range are theoretically calculated for each welding condition via the diffusion-controlled Scheil model. The mechanism underlying the increase in BTR under oscillation welding is clarified based on the relationship between the achievement ratio of the weld single crystal growth and fraction of high-angle (>15<sup>o</sup>) solidification boundaries, which affect severe dendrite coalescence undercooling. The lower fraction of the high-angle weld solidification grain boundaries attributed to the superior achievement ratio of weld single crystal growth, which reduces the dendrite coalescence undercooling and BTR. Consequently, it enhances the solidification crack propagation resistance.

Analysis of calculation methods for determining the brittleness temperature of bituminous binders

Problem. One of the common causes of premature destruction of road surfaces is the unsatisfactory low-temperature properties of bituminous binders and asphalt concrete. Currently existing methods of determining the low-temperature properties of road bituminous binders are based on the use of complex and expensive laboratory equipment and involve the highly professional specialists in the testing and interpretation of the obtained data. Meanwhile, calculation methods for determining the brittleness temperature of bitumen and bituminous binders can be useful quite often for the preliminary assessment of low-temperature characteristics of binders. Goal. The purpose of the completed work is to establish the principle used in calculation methods for determining the brittleness temperature of bituminous binders and to estimate the possibility and feasibility of using various methods for evaluating the low-temperature characteristics of binders used in the road industry of Ukraine. Methodology. To achieve the goal, an analysis of literary sources devoted to calculation methods for evaluating low-temperature characteristics of bituminous binders was carried out, and a comparison of brittleness temperature values determined by experimental and calculation methods was performed. Results. During the analysis of literary sources, it was established that the vast majority of currently known calculation methods for determining the brittleness temperature of bitumen are based on the establishment of a relationship between standard indicators of their quality – penetration at 25 ºС, brittleness temperature (as the temperature at which penetration is equal to 1.25 × 0 .1 mm) and the temperature of softening (as the temperature at which the penetration is equal to 800 × 0.1 mm). Calculation methods for determining the brittleness temperature are based on the principle proposed by W. Heuckel, namely the temperature-penetration dependence, which is linear in a wide temperature range. Practical value. The accuracy of determining the brittleness temperature according to domestic calculation methods was checked and the most acceptable one was established, which allows to calculate the brittleness temperatures that are the least different from those experimentally determined by the Fraas method.

Testing the impact energy and determination of the brittleness temperature of the welded joint of steel A516 Gr.70

Most problems with steel structures occur in the welded joint or its immediate vicinity. For this reason, special attention is paid to testing the properties of the welded joint. Fractures of welded steel structures in operating conditions have led to the need to study the influence of temperature on the behavior of steel and welded joints. For the purpose of these tests, the critical test conditions (temperature) that cause brittle fracture are defined. The paper will present the results of experimental tests of the impact energy of the welded joint of steel A516 Gr.70. Impact energy testing at different temperatures was done with the aim of determining the brittleness transition temperature of the base metal and components of the welded joint. Also, these tests should give an assessment of the influence of temperature on the ratio of the crack formation energy Wiu, and the crack propagation energy Wa in the total fracture energy Wt. This test procedure determines the tendency to brittle fracture, that is, the tendency to increase brittleness during exploitation. The obtained results are most often used for ongoing quality control and evaluation of material homogeneity.

Study of the electronic, optical, elastic and infrared properties of trigonal Mg3As2

Trigonal Mg3As2 is a narrow band gap semiconductor, which makes it possible for many technical applications. However, its fundamental properties, such as electronic, optical, elastic and infrared properties, are still not well studied. Here we systematically studied its these properties with the help of first principles calculations. Band structure is obtained and the origins of the bands are revealed by the calculated partial density of states. Its bonding property is analyzed based on the computed electron density difference and Bader charges. Optical dielectric function and the related quantities are derived and discussed. Its mechanical stability and anisotropy is confirmed by the calculated elastic constants. The phonon vibrational modes in its Brillouin zone center are assigned and infrared emission spectrum is simulated. The reason for the disappearance of one infrared peak in the simulated infrared spectrum is revealed. The brittleness, hardness and melting temperature of this crystal are also predicted. The present study can enrich our understanding of trigonal Mg3As2 and facilitate its future applications.

Bionic Micro-Texture Duplication and RE3+ Space-Selective Doping of Unclonable Silica Nanocomposites for Multilevel Encryption and Intelligent Authentication.

High-capacity optical data storage and information encryption by using glass substrates are fascinating due to merits of expanding the functionality and applicability of the optoelectronic field. However, the development of glass substrate-based multi-dimensional information encryption methods has remained a challenge because of the high hardness, brittleness and melting temperature of glasses. Herein, inspired by the unique natural structure of plant leaves, multicolor micro-texture-based physical unclonable functions (PUFs) fluorescence glass labels (MTPLs) are exploited by using ultraviolet photocurable silica nanocomposites and soft replication method. It is the first time that simultaneous rare-earth ion (RE3+ ) space-selective doping and bionic micro-texture replication onto transparent glass have been realized, in which the doping position and fluorescence color of RE3+ and height information of unclonable micro-texture can be selectively equipped for multilevel information encryption. The prepared micro-scale MTPLs are endowed with tunable multilevel authentication models, including macro-scale multicolor fluorescent 2D patterns, micro-scale pattern, color 3D information and intelligence authentication. A high-performance anti-counterfeiting platform with interactive authentication is also established based on the high robustness and security of MTPLs. Such unclonable bionic MTPLs based on RE3+ space-selective doping and micro-texture duplication provide an effective and potentially universal approach for multilevel encryption and intelligent authentication.

Thermal resistance of steels with increased strength properties for pressure vessels of advanced VVER reactors of various designs

The paper considers the results of structural studies and mechanical tests after a long-term thermal exposure of laboratory heats of the metallurgically improved 15Kh2NMFA steel and steel with an increased content of nickel considered as materials for the pressure vessels of advanced VVER-type reactors of various designs. It has been shown that, both for the improved 15Kh2NMFA steel and the high-nickel steel, there are no signs of grain boundary embrittlement after an segregation provoking embrittlement heat treatment. This is explained by the extremely low grain boundary segregation of phosphorus in the initial state caused by a high degree of the structure dispersity as well as by rather a low content of impurities. Besides, no changes have been found in the yield strength value for the improved 15Kh2NMFA steel, which agrees with the structure investigation results. For the high-nickel steel, a tendency towards a minor yield strength decrease by 5 to 10% and a regular reduction of the critical brittleness temperature has been revealed. A decrease in the mechanical properties has been caused by a relatively low temperature of tempering for the high-nickel steel and, accordingly, by the potential occurrence of the structure recovery during long-term thermal exposure, as evidenced by the results of an X-ray diffraction analysis. Despite the structure recovery in the high-nickel steel under the long-term thermal exposure, the main strengthening carbide phases remain stable. Due to this, the yield strength value remains at a relatively high level that exceeds the values for the modern VVER-type vessel steels, even in the case of a thermal exposure much in excess of the expected operating conditions for advanced VVER reactors. The observed decrease of critical brittleness temperature during the long-term thermal exposure contributes to an increase in the steel resistance to brittle fracture.

熱間圧延中の低炭素鋼板の酸化皮膜の変形に及ぼすマンガンの影響

In hot rolling process of low carbon steel sheets, oxide scale formed on the sheets may result in surface defects on the rolled products. The major phase of the scale is wustite FeO, which shows sufficient plasticity to follow the sheet deformation only at elevated temperature. However, thick scale is cracked, fragmented and indented to the sheets by the rolling even at elevated temperature because scale surface is instantly cooled by cold rolls to brittle temperature. Therefore, thick scale should be removed by descalers just before the rolling. It is reported that manganese decreases the eutectoid temperature between ductile wustite and brittle magnetite. Therefore, manganese may have a positive effect to widen wustite window to lower temperature and to suppress surface defects. In this study, 0mass% and 2mass% manganese bearing steel sheets with controlled scale on surface were hot rolled in a laboratory. The sheets were reduced 30% in thickness by unlubricated rolling at temperature between 1173 K and 1373 K. Scanning electron microscopy on longitudinal section showed that manganese decreases crack depth and increases spacing between scales indented to the steel. It is concluded manganese makes the scale on steel more ductile and suppresses surface defects.

Evaluation of the influence of homogenization annealing on the critical brittle temperature of forged blanks from steel 15Kh2MFA-A

The effect of the homogenization annealing duration on the critical brittle temperature of 15Kh2MFA-A vessel reactor steel has been studied. The criterion for calculating the duration of the annealing is determined – this is the total duration of heating of the ingot and forging before the first and second removals. It is shown that in order to achieve Тк0 not less than minus 50°С, a total specific exposure at a temperature of 1220±20°С of not less than 2.5 min/mm of section is required.

Hot Ductility Evolution Mechanism of Titanium‐Bearing Microalloyed Steels

Titanium‐bearing (Ti‐bearing) microalloyed steels have high strength and toughness by grain refinement effect of carbonitride precipitates. However, they can induce surface cracks of continuous casting slab when the Ti alloyed content is high. A microalloyed steel with Ti content (0.10–0.15 wt%) is carried out by thermalmechanical simulator over 600–1350 °C to analyze hot ductility evolution mechanism. Fracture surface morphology, phase transition, and behavior of precipitates of the tensile samples are investigated by experimental detection and thermodynamic calculation. The ductility–temperature curves show that the third brittle temperature range is 600–890 °C, which is mainly attributed to the thin proeutectoid ferrite film and precipitated titanium carbonitride particles, widening the embrittlement temperature ranges through of steel. In addition, the tensile samples at 890–1350 °C have good hot ductility, indicating the dynamic recrystallization of deformed austenite can trigger grain boundaries migration away from cracks and avoid the side effect of the Ti (C,N) particles on hot ductility. The first brittle temperature range of 1350 °C‐melting point is mainly ascribed to the partial melting of the grain boundaries with element segregation of sulfur and phosphorus, and microporosity loose among dendrites.

Effects of ferrite content and concentrations of carbon and silicon on weld solidification cracking susceptibility of stainless steels

In the welding of austenitic stainless steels, the formation of approximately 5% δ-ferrite phase is often used to decrease the susceptibility to solidification cracking. The partition coefficients of impurity elements such as phosphorous and sulfur of the ferrite phase are high, which expand the temperature range of solidification. At the same time, it is well known that the solidification cracking susceptibility increases with increasing δ-ferrite content above 20%. Thus, high δ-ferrite content increases the solidification cracking susceptibility, even though the δ-ferrite phase has high solubility of the impurity elements. The aim of this work was to investigate the effects of the δ-ferrite content and the concentration of carbon and silicon on the solidification crack susceptibility of Fe–18%Cr stainless steel with various nickel concentrations. The ferrite content was controlled by adding various amounts of nickel. The brittle temperature range (BTR) hardly changed with increasing δ-ferrite content, regardless of the type and concentrations of carbon and silicon. Therefore, the effect of the ferrite content on solidification cracking susceptibility must be small. In addition, the BTR increased with the concentrations of carbon and silicon. The specimens containing higher concentrations of carbon exhibited higher BTRs than those containing silicon. It is considered that the solidification segregation corresponding to the partition coefficient of carbon to the δ-ferrite phase induces an increase in cracking susceptibility. In addition, the formation of austenite during solidification reduces cracking susceptibility owing to the higher solubility of carbon.