Subsequent Heat Research Articles

Structure and mechanical properties of PR-03N18K9M5TYu steel grade fabricated by selective laser melting and post-processing

We fabricate samples of PR-03N18K9M5TYu steel (equivalent to ChS4) using selective laser melting (SLM) in a nitrogen atmosphere. Our research focused on the influence of hot isostatic pressing (HIP) combined with heat treatment (HT), specifically hardening and aging, on the steel's structure and its physical and mechanical properties (σucs, σys, δ, ψ). Through tensile testing, we evaluated the impact of post-processing treatments (HIP followed by HT) on the material's strength. We also assessed how different post-processing protocols affected residual porosity. Our findings indicate that samples exhibiting the highest strength and plastic properties correspond to those with the least structural defects and minimal residual porosity. In-depth microstructural analysis revealed that the optimal structure–a fine-grained, homogeneous configuration–is achieved via the combined application of SLM, HIP, and subsequent HT. The improvement in mechanical properties can be primarily attributed to the dispersed hardening effect, which is a consequence of the precipitation of the superfluous Ni3Ti phase. Fractographic examination revealed that the post-processing leads to a ductile and dimple fracture, occurring through mechanisms of shearing and detachment, giving rise to mixed-type fractures. The samples that displayed superior mechanical properties were characterized by a homogenous ductile intergranular fracture surface with clear evidence of plastic deformation. We measured the hardness (Н), modulus of elasticity (Е), and elastic recovery via indentation methods. The post-processing treatments notably enhanced material hardness and elastic modulus, with an increase from H = 4.6 GPa and E = 194 GPa in the sample post-HIP to H = 8.5 GPa and E = 256 GPa following HIP coupled with hardening and aging.

Manufacturing of aluminium/copper/nickel(powder) metal intermetallic composite by accumulative roll bonding and subsequent heat treatment

This study investigates the annealing effect on the tensile properties of aluminium (Al)/copper (Cu)/nickel (Ni)(powder) composite fabricated utilising the accumulative roll bonding (ARB) technique up to 11 passes. The results showed that the composite transformed into a layer/powder-reinforced fabric by increasing the applied strain. After the 11th pass, the Al and Cu layers and Ni powder were uniformly distributed in the composite. The tensile strength decreased for the second pass and increased as the ARB process proceeded. Upon annealing temperature and time increase, the tensile strength of the 3rd pass increased and for the 11th pass decreased. Also, as the annealing temperature and duration extended, the elongation for the 3rd and 11th passes fluctuated and remained almost unchanged.

Microstructure evolution and mechanical properties of new Co-free maraging steel produced by wire arc additive manufacturing

In this work, P-MIG is used as additive process, a new low-cost Co-free maraging steel wire is used as raw material to additive manufacturing block component, and the microstructure and mechanical properties of the component is investigated. The microstructure of the component is composed of martensite and austenite, and the closer to the bottom, the more serious the elemental segregation and the more austenite content. From the top to the bottom the high-angle grain boundaries increase and the grain size decrease, the difference of the heat dissipation condition and the thermal cycle are the reasons for this phenomenon. The texture of austenite is mainly Cube texture, and the texture of martensite is Rotated Cube texture and Goss texture. The tensile strength of XD, YD, ZD three directions is 1172 ± 15 MPa, 1021 ± 7 MPa, 1139 ± 16 MPa, respectively, impact toughness is 64.7 ± 1.6 J/cm2, 51.1 ± 5.6 J/cm2, 51.4 ± 3.1 J/cm2, respectively, TRIP effect occurs in the process of tensile, the main mode of fracture in tensile and impact is toughness fracture. The microhardness decreases gradually from bottom to top, which is due to the short-lived aging strengthening by thermal cycle, the change of grain size and GND density. The results of the work reveal the successful application of the new low-cost Co-free maraging steel wire in WAAM and provide an important reference for the adjustment of additive process, subsequent heat treatment and the adjustment of wire composition.

Experimental investigation on cold-formed steel hollow sections with moderate heat treatment under combined compression and cyclic lateral loads

This paper presents an experimental investigation on cold-formed steel rectangular and square hollow sections (RHSs and SHSs) with subsequent heat-treatment under combined compression and cyclic lateral loads. A total of 25 specimens designed with different parameters, including slenderness ratios (b/t and d/t) and axial load ratio (n) ranging from 0 to 0.5 were tested. Material tests were carried out to confirm the material ductility requirements stated in Eurocode being reached. Failure modes, moment-rotation curves, secant stiffness, energy dissipation and plastic hinge length presented were analysed. In addition, deformation capacity was evaluated in terms of maximum and ultimate rotations. The comparison results between plastic rotation limits proposed by design codes and the test results indicate that AISC 341-16 is more suitable for the design of cold formed hollow sections with moderate heat treatment under this investigation, though the recommended reduction factor of axial load might be conservative.

Pool boiling heat transfer: Thermal performance for alternating and extended operational conditions

Oxide formation on metallic heat transfer surfaces poses a risk parameter in high-power thermal systems maintained by multi-phase cooling. In spite of the significance for practical applications, the potential change in chemistry and morphology on the surfaces exposed to continuous or alternating boiling process plays a vital role in heat transfer efficiency. In this comprehensive study, the effect of heat flux rate, boiling crisis, operation time, surface roughness, and pre-oxidation by the system calibration on oxide layer formation and its inevitable effect on boiling heat transfer (BHT) have been evaluated separately. A sort of experimental scenarios rather representing real operating conditions encountered in phase-change cooling apparatuses were carried out on smooth and rough copper substrates in saturated de-ionized water at atmospheric pressure. In order to practice the scenarios, a series of subsequent critical heat flux (CHF) runs and continuous boiling operations at certain heat flux levels ranging between 15 and 60 W/cm2 were performed within different numbers and sequences as a part of the Design of Experiments (DOE). Each operating scenario was analyzed and compared individually, while questions regarding the effect of the number of CHF runs, heat flux level during long-term operation, surface roughness, pre-oxidation, and rigorous long-term stability operation on boiling heat transfer were examined exhaustively. As a result, CHF and maximum heat transfer coefficient (HTC) of all surfaces exposed to boiling processes considerably enhanced at different rates corresponding to applied scenarios. The rate of heat flux level applied on heating surfaces was not determined to be a significant factor, whereas the HTC and CHF enhanced as the number of subsequent boiling crises (CHF runs) ultimately raised. On the other hand, HTC of the surface non-exposed to CHF runs demonstrated a drastic enhancement by 45% after 24 h of continuous boiling exposure at 45 W/cm2 compared to initial performance with 1.0 W/cm2K. The heat transfer from the surfaces exposed to extended long-term operations showed a final stable thermal behavior, while CHF values doubled from an initial value of approximately ∼73 W/cm² to 144.7 W/cm2 as exposure time increased. X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and scanning electron microscope (SEM) analyses were executed to evaluate the influence of micro-nano-scale oxide particles/layers developed on the heater surfaces and to interpret the changes in heat transfer performance.

Improved L-Asparaginase Properties and Reusability by Immobilization onto Functionalized Carbon Xerogels.

Enzyme immobilization can offer a range of significant advantages, including reusability, and increased selectivity, stability, and activity. In this work, a central composite design (CCD) of experiments and response surface methodology (RSM) were used to study, for the first time, the L-asparaginase (ASNase) immobilization onto functionalized carbon xerogels (CXs). The best results were achieved using CXs obtained by hydrothermal oxidation with nitric acid and subsequent heat treatment in a nitrogen flow at 600 °C (CX-OX-600). Under the optimal conditions (81 min of contact time, pH 6.2 and 0.36 g/L of ASNase), an immobilization yield (IY) of 100 % and relative recovered activity (RRA) of 103 % were achieved. The kinetic parameters obtained also indicate a 1.25-fold increase in the affinity of ASNase towards the substrate after immobilization. Moreover, the immobilized enzyme retained 97 % of its initial activity after 6 consecutive reaction cycles. All these outcomes confirm the promising properties of functionalized CXs as support for ASNase, bringing new insights into the development of an efficient and stable immobilization platform for use in the pharmaceutical industry, food industry, and biosensors.

Drought priming-induced stress memory improves subsequent drought or heat tolerance via activation of γ-aminobutyric acid-regulated pathways in creeping bentgrass.

Recurrent drought can induce stress memory in plants to induce tolerance to subsequent stress, such as high temperature or drought. Drought priming (DP) is an effective approach to improve tolerance to various stresses; however, the potential mechanism of DP-induced stress memory has not been fully resoved. We examined DP-regulated subsequent drought tolerance or thermotolerance associated with changes in physiological responses, GABA and NO metabolism, heat shock factor(HSF) and dehydrin (DHN) pathways in perennial creeping bentgrass. Plants can recover after two cycle of DP, and DP-treated plants had significantly higher tolerance to subsequent drought or heat stress, with higher leaf RWC, Chl content, photochemical efficiency, and cell membrane stability. DP significantly alleviated oxidative damage through enhancing total antioxidant capacity in response to subsequent drought or heat stress. Endogenous GABA was significantly increased by DP through activating glutamic acid decarboxylase activity and inhibiting GABA transaminase activity. DP also enhanced accumulation of NO, depending on NOS activity, under subsequent drought or heat stress. Transcript levels of multiple transcription factors, heat shock proteins, and DHNs in the HSF and DHN pathways were up-regulated by DP under drought or heat stress, but there were differences between DP-regulated heat tolerance and drought tolerance in these pathways. The findings indicate that under recurrent moderate drought, DP improves subsequent tolerance to drought or heat stress in relation to GABA-regulated pathways, providing new insight into understanding of the role of stress memory in plant adaptation to complex environmental stresses.

Enhanced dynamic-mechanical property and microstructural mechanism of a FeCoNiCrMo0.2 high-entropy alloy fabricated using powder bed fusion

Powder bed fusion (PBF), along with subsequent heat treatment, plays a crucial role in enhancing the impact toughness of FeCoNiCrMo0.2 high-entropy alloys (HEAs) and expanding their potential applications in field for high-speed deformation. In this study, the dynamic-mechanical properties and microstructure of the as-built PBF–FeCoNiCrMo0.2 HEAs and quenched PBF–FeCoNiCrMo0.2 HEAs heated at 600–750 °C for 8 h were investigated. As the heating temperature increases, the columnar grains and cellular structures undergo coarsening and the dislocation density gradually decreases. Moreover, higher heating temperatures facilitate the precipitation of Mo-rich second phases. This occurrence can be primarily attributed to the segregation of Mo at the boundaries of the as-built specimens. Consequently, in the quenched specimens, the μ phases are predominantly distributed along the boundaries of the cellular structures. In the quenched Q700 specimen (heated at 700 °C for 8h), the size and volume fraction of the μ phases are measured to be 63.4 nm and 3.59%, respectively. Additionally, under the same condition, the Q700 specimens also exhibited a relatively slight increase in the size of the cellular structures. The impact energy absorption, dynamic yield strength, and dynamic compressive strength of the Q700 quenched specimens were found to be 210.1 MJ/m3, 1066 MPa, and 1649 MPa at a strain rate of 1840 s−1. These values represent a dramatic improvement of 38.1%, 52.7%, and 14.7% higher in comparison to those of the as-built specimens. Under impact deformation, the presence of the μ phases plays a significant role in impeding the movement of dislocations by acting as a pinning agent for the boundaries of the cellular structures, thereby enhancing the strength. Simultaneously, the cellular structures were significantly elongated to form the deformation bands and to coordinate the impact deformation, leading to good impact energy absorption. In combination, the synergistic strengthening and toughening effect of the μ phases and the elongated cellular structures contribute to a remarkable improvement in the impact toughness of the PBF-HEAs.

Crystal-to-amorphous phase transformation in ternary shape memory alloys

This systematic study evaluates the role of important factors in crystal-to-amorphous phase transformation during severe plastic deformation in ternary shape memory alloys. Experiments coupled with thermodynamic calculations to obtain comprehensive interpretation on the amorphization in ternary shape memory alloys. Equiatomic binary NiTi together with ternary Ni–45Ti–5Hf and Ti–45Ni–5Cu (at%) alloys as alloy models were processed by high-pressure torsion (HPT) at room and cryogenic temperatures. The binary and Hf-added alloys revealed an amorphous structure with a few remaining nanocrystals, however, Cu-added ternary alloy showed resistance to the amorphization after HPT processing. The results revealed two key factors of preventing martensite-to-austenite transformation during deformation and the intrinsic potential of the material for amorphization drive crystal-to-amorphous phase transformation. Higher transformation temperatures, enthalpy and thermal hysteresis prevented martensite-to-austenite transformation, which therefore encouraged amorphization. In addition, a large negative heat of mixing, Gibbs energy for amorphization and a large atomic size mismatch are important factors in implementing crystal-to-amorphous phase transformation. This investigation is a step forward to a fundamental understanding of ternary or even compositionally complex shape memory alloys for microstructural engineering by providing a homogeneous ultrafine-grained structure due to amorphization and subsequent heat treatment to achieve superior shape memory effect and superelasticity.

Electrophoretic Deposition of Calcium Phosphates on Carbon-Carbon Composite Implants: Morphology, Phase/Chemical Composition and Biological Reactions.

Despite a long period of application of metal implants, carbon-carbon medical composites are also widely used for bone defect prosthesis in surgery, dentistry, and oncology. Such implants might demonstrate excellent mechanical properties, but their biocompatibility and integration efficiency into the host should be improved. As a method of enhancing, the electrophoretic deposition of fine-dispersed hydroxyapatite (HAp) on porous carbon substrates might be recommended. With electron microscopy, energy dispersion X-ray and Raman spectroscopy, and X-ray diffraction, we found that the deposition and subsequent heat post-treatment (up to the temperature of 400 °C for 1 h) did not lead to any significant phase and chemical transformations of raw non-stoichometric HAp. The Ca/P ratio was ≈1.51 in the coatings. Their non-toxicity, cyto- and biocompatibility were confirmed by in vitro and in vivo studies and no adverse reactions and side effects had been detected in the test. The proposed coating and subsequent heat treatment procedures provided improved biological responses in terms of resorption and biocompatibility had been confirmed by histological, magnetic resonance and X-ray tomographic ex vivo studies on the resected implant-containing biopsy samples from the BDF1 mouse model. The obtained results are expected to be useful for modern medical material science and clinical applications.

RGO/In2O3 heterostructures based gas sensor for efficient ppb-level n-butanol detection

The real-time and effective detection of n-butanol gas is particularly important in production and daily life due to its flammability, toxicity, and potential hazards to the environment. This article reports the preparation of hollow indium oxide spheres and rGO/In2O3 composites through a simple hydrothermal and subsequent heat treatment method. Test results indicate that the gas sensitivity of n-butanol can be significantly improved through rGO composites. The prepared hollow indium oxide spheres are composed of nanosheets with a diameter of probably 500 nm. After combination by rGO, the specific surface area and the proportion of adsorbed oxygen of the material are increased, both of which are advantageous for enhancing gas sensitivity abilities. At the optimum operating temperature of 160 °C, the response value of rGO/In2O3 complex sensor is 51–50 ppm of n-butanol, which is 3.6 times the response of pure In2O3. Gas sensors composed of rGO/In2O3 exhibit ultra-fast response time and low detection limit. Even for ppb grade (100 ppb) n-butanol gas, the response value is still 2.3. These characteristics make rGO/In2O3 a promising material for the preparation of high-performance n-butanol gas sensors. Besides, the gas-sensitive mechanism of the enhanced n-butanol sensing performances is also analyzed.

Deep purification of pesticide waste salt containing high-concentration organic pollutants by ethanol solvents washing and heating treatment

The increasing production of industrial waste salt has become a growing concern. These waste salts are usually filled or deposited without treatment, causing serious environmental pollution and a waste of salt resources. The ideal solution to this problem is to recycle the waste salts after the removal of organic pollutants. In this study, organic solvent washing and heating are chosen to deeply remove the organic pollutants from actual pesticide waste salts. The experimental results showed that the optimum removal efficiency of organic pollutants in waste salts achieves as high as 99.82% under the conditions of 3:5 mass-to-volume ratio of waste salts-to-ethanol (EA), heating temperature of 400 °C (60 min). In addition, the removal mechanism and migration pathways of organic pollutants in the washing and heating were proposed. Salts washing with EA could remove most of the organic pollutants and subsequent heating treatment could completely purify the waste salts without the emission of the harmful gaseous compounds. As the best eluent, EA can not only effectively remove organic pollutants, but also be readily recycled. At the same time, the EA washing and heating process could avoid the pollution of organic waste liquid and noxious tail gas. Therefore, the EA washing process has the advantages of green, high efficiency, safety and energy saving. The EA washing and heating effectively avoids the problem of environmental pollution caused by harmful gases generated by heating and promotes the purification process and reuse of industrial waste salts.

Innovative local shear forming method for enhanced formability of tubular parts with high stiffened ribs

Large-sized thin-walled tubular parts with high stiffened ribs are key lightweight structural components used in transportation. To address the challenges of integral forming, a novel local shear forming (LSF) technique that combines the advantages of spinning and shear forging (SFG) is proposed. Finite element (FE) simulations and experimental work have revealed the distinct deformation mechanisms of local shear forming in contrast to those of conventional shear forging or spinning. During local shear forming, the surface material of the billet undergoes sequentially axial upsetting deformation, primary shear deformation, reverse shear deformation, circumferential tensile deformation and radial displacement to form the rib. Gradient plastic deformation is observed through the thickness of the formed wall rather than near the wall surface. The effects of local loading include reduction of the secondary shear deformation zone, reduction of circumferential constraint in the loading zone, material circumferential transfer, and expansion-shrinkage deformation of the billet. The former two decrease the rib thickness and promote radial transfer of the material. The latter two result in a significant strengthening of the formed rib and wall. Moreover, tearing and buckling are suppressed, which enhances the relative wedge thickness up to 50 % of the wall thickness of the billet. The aspect ratio of the formed rib can be as high as 3 for the high strength 2A12 alloy and 6 for the highly ductile 1A30 alloy. Shear deformation in the rib promotes recrystallization in the subsequent T6 heat treatment and refines the microstructure. Corrosion resistance is not degraded though microstructural change. Local shear forming shows good potential for forming tubular parts with an external rib structure.

Additive Metallization of Alumina with Copper-Titanium Powder Blends for Power Electronic Applications

Additive manufacturing shows great potential to further increase the performance of power electronic modules through novel packaging concepts. Such an approach is the integrated manufacturing of metal-ceramic substrates by means of laser powder bed fusion of metals (PBF-LB/M). With this layered additive manufacturing process, planar ceramic substrates can be metallized and electrically functionalized for power electronic applications. In this paper Al2O3 ceramic substrates are metallized via PBF-LB/M by selectively melting applied powder layers with software defined geometries. The investigated powders are mixtures of copper and titanium powders with 1 wt.%, 5 wt.% and 10 wt.% titanium in order to enable bonding by creating a titanium-oxide reaction layer at the interface to the ceramic. Shear tests and microstructural investigations show that a subsequent heat treatment increases the adhesion and density of the metallization. By energy dispersive X-ray microscopy (EDX) the partial formation of reaction layers is detected.

Formation of intraneuronal iron deposits following local release from nanostructured silica injected into rat brain parenchyma

Nanostructured materials with controllable properties have been used to cage and release various types of compounds. In the present study, iron-loaded nanostructured sol-gel SiO2–Fe materials were prepared and injected into the rat brain to develop a method for gradual iron delivery into the neurons with the aims to avoid acute iron toxicity and develop an animal model of gradual, metal-induced neurodegeneration. Nanoparticles were prepared by the traditional method of hydrolysis and condensation reactions of tetraethyl orthosilicate at room temperature and subsequent heat treatment at 200 °C. FeSO4 was added in situ during the silica preparation. The resulting materials were characterized by UV-VIS and infrared spectroscopies, X-ray diffraction, and N2 adsorption-desorption. An in vitro ferrous sulfate release test was carried out in artificial cerebrospinal fluid as the release medium showing successful ferrous sulfate loading on nanostructured silica and sustained iron release during the test time of 10 h. Male Wistar rats administered with SiO2–Fe nanoparticles in the substantia nigra pars compacta (SNpc) showed significant intraneuronal increase of iron, in contrast to the animals administered with FeSO4 that showed severe neuronal loss, 72 h post-treatment. Both treatments induced lipid fluorescent product formation in the ventral midbrain, in contrast to iron-free SiO2 and PBS-only injection controls. Circling behavior was evaluated six days after the intranigral microinjection, considered as a behavioral end-point of brain damage. The apomorphine-induced ipsilateral turns in the treated animals presented significant differences in relation to the control groups, with FeSO4 administration leading to a dramatic phenotype, compared to a milder impact in SiO2–Fe administrated animals. Thus, the use of SiO2–Fe nanoparticles represents a slow iron release system useful to model the gradual iron-accumulation process observed in the SNpc of patients with idiopathic Parkinson's disease.

Study on Al2O3/Fe-Al gradient coating assisted prepared by ionic liquid for Lead-Bismuth eutectic corrosion resistance

Alumina coating which has excellent corrosion resistance to lead–bismuth eutectic (LBE) is very promising to be used in future LBE cooling system. In this paper, the Al2O3/Fe-Al gradient coating is prepared on the surface of SIMP steel assisted by ionic liquid aluminum electroplating and subsequent heat treatments and selective oxidation. The protective Al2O3 layer is composed of much γ-phase and a small amount α-phase. The Fe-Al transition layer is mainly composed of FeAl alloy phase. After being exposed for 600 h to LBE at 600 °C, the coating still maintains intact and dense structure and good compatibility to the substrate, effectively preventing the substrate steel from the corrosion attack of LBE. While obvious LBE attack can be observed in the compared bare steel. Finally, to verify the possibility of this approach preparing Al2O3/Fe-Al coating on complex geometries, we have also successfully prepared this sort of coating on the inner surface of a steel tube, indicating that this coating has a great application potential in the future.

Ultrastrong Nanocrystalline Inconel 718 Fabricated by Powder High‐Pressure Torsion and Annealing

In this study, bulk nanocrystalline material is fabricated from Inconel 718 powder through a process of powder high‐pressure torsion (HPT) and subsequent annealing heat treatment. Numerous dislocations generated during the powder HPT process successfully produced bulk Inconel 718 with nanocrystalline grains during the post‐annealing treatment. In addition, the Inconel 718 exhibited additional strengthening contributions such as dislocation strengthening by high pre‐existing dislocation density and precipitation strengthening from randomly distributed precipitates. As a result of these strengthening effects, the Inconel 718 showed ultrastrong yield strength of 1.40 GPa and ultimate tensile strength of 1.53 GPa. Although the elongation of 12.0% did not indicate good ductility, the proposed Inconel 718 boasted improved mechanical properties compared to previous studies of Inconel 718 fabricated by various processing methods. The prepared Inconel 718 and its fabrication technique suggest the potential for manufacturing ultrahigh‐strength bulk nanocrystalline materials not only for Inconel 718 but also for various metallic materials using powder metallurgy.

Efficient operation of earth–air heat exchanger system for air cooling in a hot climate based on a new control strategy

The present research contributes to filling a gap not covered in the previous studies on shallow geothermal applications using earth-to-air heat exchanger (EAHE) systems. The authors think that operating the EAHE continuously for long periods, as presented in many of the previous studies, is not efficient, and this is due to the following reasons:- At specific periods, especially during the night and early morning, the difference between the ambient air temperature (Tamb) and the undisturbed ground temperature (UGT) is small and even negative, meaning the ambient air is colder than the ground.- The continuous operation of the EAHE for a long time leads to the ground saturation with heat, which means that the ground cannot absorb more heat from the EAHE inlet air.So, the present study investigates performance improvement by applying a control strategy to the EAHE system according to two different modes: mode 1 and mode 2. These two operational modes depend on the difference between the ambient air temperature and the UGT value. In mode 1, the ambient air flows inside the EAHE and supplies fresh air to the building. This mode is applied when the temperature difference (Tamb-UGT) exceeds 1.5 οC. When the condition of mode 1 is not satisfied, mode 2 is used, where the ambient air bypasses the EAHE and is supplied directly to the ventilated space. To carry out the present investigation, a numerical model of the EAHE system is developed, and its results are validated against published data from the literature.The simulation of EAHE in Madinah City, KSA, presenting a hot climate region, has been carried out. The study's results confirmed that the control strategy is an efficient solution for the continuous operation of the EAHE. The applied control strategy guarantees that the air supplied to the building is the coldest among the ambient air and the EAHE outlet air. Also, it has been shown that when the control is applied (mode 2), the temperature of the air supplied to the building is 1.5 °C lower than that of the case related to mode 1. Finally, the results showed that the ground can be recovered thermally when the air bypasses the EAHE (mode 2). The ground temperature recovers almost to its undisturbed value during specific periods, which enhances the potential for subsequent heat absorption.

Improvement of micro/nano-structure and corrosion resistance of TiCu alloy by addition of tin and their Sr-hydroxyapatite coating

This study explores the influence of tin (Sn) content on the properties of Ti7CuXSn (X = 2, 7, and 15 wt%) alloys, in both as-cast and heat-treated conditions. The investigation reveals that an elevated Sn content within the Ti7Cu alloy results in the formation of finer grain structures. Rapid quenching processes lead to the development of an ultrafine martensitic structure and the formation of (Ti,Sn)2Cu intermetallic compounds within the Ti7CuXSn alloys. Subsequent heat treatment processes induce the transformation of the ultrafine martensitic structure into a coarser one, accompanied by an increase in the volume fraction of (Ti,Sn)2Cu. X-ray diffraction (XRD) analysis validates the presence of α/α'-Ti(Sn,Cu) phases and (Ti,Sn)2Cu intermetallics across all alloy compositions. The Ti7Cu15Sn alloy demonstrates higher microhardness, primarily attributed to its smaller grain size, reduced lamellar spacing, and increased volume fraction of (Ti,Sn)2Cu. Furthermore, all specimens exhibit heightened microhardness following heat treatment due to the martensitic structure with heterogeneous and homogeneous nucleation of (Ti,Sn)2Cu intermediate growth. Electrochemical analysis reveals an enhanced corrosion resistance in the Ti7Cu15Sn alloy, attributed to its elevated Sn content. Nonetheless, the as-cast Ti7Cu15Sn alloy displays superior corrosion resistance, albeit with a marginal reduction in electrochemical performance following heat treatment. Surface characterization signifies the formation of a uniform oxide film, underscoring commendable corrosion resistance in both as-cast and heat-treated Ti7CuXSn alloys. Additionally, the study investigates the deposition of strontium (Sr)-doped ceramic coatings on as-cast Ti7Cu15Sn alloys. It is demonstrated that higher current density parameters yield denser and more crystalline Sr-HA coatings. Energy dispersive spectroscopy (EDS) mapping confirms the successful incorporation of Sr into the coating, showcasing its potential for applications in the field of biomedicine. Thus, this investigation highlights the significant impact of Sn content on microstructural refinement, enhancements in mechanical properties, and improved electrochemical performance within Ti7CuXSn alloys. These findings offer valuable insights for the design and optimization of alloy performance in diverse applications.

Investigations of Flow Boiling in Mini-Channels: Heat Transfer Calculations with Temperature Uncertainty Analyses

The article aims to explore boiling heat transfer in mini-channels with a rectangular cross-section using various fluids (HFE-649, HFE-7000, HFE-7100, and HFE-7200). Temperature measurements were conducted using infrared thermography for the heated wall and K-type thermocouples for the working fluid. The 2D mathematical model for heat transfer in the test section was proposed. Local heat transfer coefficients between the heated wall and the working fluid were determined from the Robin condition. The problem was solved by means of the finite element method (FEM) with Trefftz functions. The values of the heat transfer coefficient that were obtained were compared with the results calculated from Newton’s law of cooling. The average relative differences between the obtained results did not exceed 4%. The study included uncertainty analyses for temperature measurements with K- and T-type thermocouples. Expanded uncertainties were calculated using the uncertainty propagation and Monte Carlo methods. Precisely determining the uncertainties in contact temperature measurements is crucial to ensure accurate temperature data for subsequent heat transfer calculations. The results of the heat transfer investigations were compared in terms of fluid temperature, heat transfer coefficients, and boiling curves. HFE-7200 consistently exhibited the highest fluid temperature and temperature differences at boiling incipience, while HFE-7000 demonstrated the highest heat transfer coefficients. HFE-649 showed the lowest heat transfer coefficients. The boiling curves exhibited a typical shape, with a notable occurrence of ‘nucleation hysteresis phenomena’. Upon the analysis of two-phase flow patterns, bubbly and bubbly-slug structures were observed.