Preheated Samples Research Articles

Comprehensive analysis of chemical composition, electronic, luminescent, and electrical properties of amorphous graphite-silicon carbide thin films: A comparative study of as-deposited and post-annealed states

Graphite/SiC (GSC) thin films were synthesized on silicon substrates via a spray method, depositing a Si-graphite solution on preheated silicon samples at 350 °C, followed by annealing at 800 °C for 4 h. A systematic approach was employed to ensure the effective incorporation of graphite into the SiC material during solution preparation. Various analytical techniques, including XPS, UPS, Reflection Energy Electron Loss Spectroscopy (REELS), PL, AFM, and Hall effect measurements, were employed for comparative analysis of the chemical composition, morphological, electrical, and optoelectronic properties of as-deposited and annealed GSC films. XPS analysis revealed the presence of Si—C and graphitic bonds in the as-deposited GSC, with a significant compositional shift to oxygen-rich graphite oxide/oxycarbides after annealing. REELS demonstrated increased bandgap and bulk plasmon energy due to surface oxidation, while UPS highlighted a high electronic density in the as-deposited film, diminishing after annealing. AFM revealed a tendency of as-deposited GSC grains to form smaller, sharper structures after annealing, resulting in smoother and more homogeneous surface morphology. Phase AFM confirmed graphite incorporation at grain boundaries and within the bulk, forming a composite structure. PL spectra of the as-deposited film exhibited a broad visible emission with distinct sub-peaks linked to SiC bandgap transitions and carbon-rich defects. Chromaticity diagrams indicated suitability for white LED applications. Hall effect measurements showed excellent electrical properties of the as-deposited GSC film, with high carrier density and mobility, which reduced significantly after annealing, transitioning the material to a more insulating state. These findings collectively provide a comprehensive understanding of GSC thin films’ properties and their potential applications.

Precooked state based on protein denaturation kinetics impacts moisture status, protein oxidation and texture of prepared chicken breast

The quality of meat in prepared dishes deteriorates due to excessive protein denaturation resulting from precooking, freezing, and recooking. This study aimed to link the precooked state with chicken breast's recooked quality. Cooked Value (CV), based on protein denaturation kinetics, was established to indicate the doneness of meat during pre-heating. The effects of CVs after pre-heating on recooked qualities were investigated compared to fully pre-heated samples (control). Mild pre-heating reduced water migration and loss. While full pre-heating inhibited protein oxidation during freezing, intense oxidation during pre-heating led to higher oxidation levels. Surface hydrophobicity analysis revealed that mild pre-heating suppressed aggregation during recooking. These factors contributed to a better texture and microstructure of prepared meat with mild pre-heating. Finally, a potential mechanism of how pre-heating affects final qualities was depicted. This study underlines the need for finely controlling the industrial precooking process to regulate the quality of prepared meat.

The influence of temperatures on the mechanical properties and fracture behavior of rocks under mixed mode I/II loading

A comprehensive understanding of the fracture behavior of pre-heated rocks under to mixed mode I/II loading is crucial for deep underground engineering. The effect of high temperature on the fracture process zone (FPZ) and fracture toughness of rocks was experimentally investigated using semi-circular bend (SCB) samples. Surface displacement and associated strain field under loading were captured using digital image correlation. The results showed that the mechanical properties of SCB samples gradually decreased with increasing temperature. Rocks exposed at temperature exceeding 600 °C demonstrated a significant reduction in peak load, generalized stiffness, fracture toughness, and absorbed energy. Moreover, the load–displacement curves and macroscopic fracture characteristics of pre-heated SCB samples revealed a transition from brittleness to ductility with increasing temperature under mixed mode I/II loading. Both the length and width, as well as the crack tip opening displacement of the FPZ, increased with rising temperature. At lower temperatures (25 ∼ 400 °C), the ratio of FPZ length to width typically ranged between 2 and 3. While, at elevated temperature (600 ∼ 1000 °C), this ratio expanded to between 3 and 4. The initiation of thermally induced cracks in rocks will accelerate damage evolution under mixed mode I/II loading, as indicated by the development of the maximum principal strain with displacement. Scanning electron microscopy and polarization microscopy images of the microscopic fracture morphology in pre-heated rocks illustrated isolated and dispersed microcracks appeared at lower temperatures, whereas at elevated temperatures, intricate microcrack networks and broken grains were observed.

In Situ Microstructure Modification Using a Layerwise Surface-Preheating Laser Scan of Ti-6Al-4V during Laser Powder Bed Fusion.

An innovative in situ thermal approach in the domain of LPBF for Ti-6Al-4V fabrication has been carried out with results directing towards an improved fatigue life without the need for post-processing. The thermal process involves an additional laser scan with different process parameters to preheat the selected regions of each layer of the powder bed prior to their full melting. This preheating step influences the cooling rate, which in turn affects surface characteristics and subsurface microstructure, both of which are directly correlated with fatigue properties. A thorough analysis has been conducted by comparing the preheated samples with reference samples with no preheating. Without any additional thermal processing, the preheated samples showed a significant improvement over their reference counterparts. The optimized preheated sample showed an improved prior β-grain distribution with a circular morphology and thicker α laths within the even finer prior β-grain boundaries. Also, an overall increment of the c/a ratio of the HCP α has been observed, which yielded lattice strain relaxation in the localized grain structure. Furthermore, a less-profound surface roughness was observed in the preheated sample. The obtained microstructure with all these factors delivered a 10% improvement in its fatigue life with better mechanical strength overall.

Temperature effect of rockburst in granite caverns: insights from reduced-scale model true-triaxial test

To investigate the influence of thermal treatment on the rockburst in granite caverns, true-triaxial compression tests were conducted on pre-heated granite cubic samples containing a circular through-hole using a true-triaxial test system, and the micro camera was used to monitor and record the rockburst process in realtime. Test results show that the uniaxial compressive strength and elastic modulus first increase and then decrease as the temperature increases, which reach the maximums at 200 °C and sharply decrease at temperatures from 400 to 600 °C. The density and P-wave velocity decrease and the peak strain increases with increasing temperature. The main failure mode is X-shaped shear-tension failure at 25 and 200 °C, and single-slope shear failure at 400 and 600 °C. Thermal treatment exhibits slight effect on the rockburst incubation process in granite caverns. The stress required for rockburst decreases when the temperature increases or decreases from 200 °C. The higher the temperature, the lower the required stress. At 25 and 200 °C, rockburst is violent, and fine particles and large slabs are mainly produced; at 400 and 600 °C, the intensity of rockburst is relatively weak, and fine particles are mainly generated. Thermal treatment exhibits double effects on rockburst. The mechanism of thermal treatment on granite rockburst is the strengthening effect caused by water loss and the weakening effect caused by thermal expansion cracking. This study can provide theoretical guidance for the stability analysis and rockburst prevention of temperature-affected granite caverns.

Влияние термизации натуральных сыров на их функциональные свойства

The research featured the effect of thermal treatment on various types of natural cheeses and their functional properties, i.e., grating and shredding, melting, fat-release, browning, blistering, and elasticity. Natural and preheated samples underwent a point-scale assessment developed specifically for pizza cheeses by the All-Russian Scientific Research Institute of Butter- and Cheese-Making (Uglich, Russia). Thermal treatment improved the functional properties of natural cheese. In addition, preheated cheese proved to be a more effective and economical pizza ingredient.

Effects of Base Metal Preheating on the Microstructure, Mechanical Properties, and Corrosion Resistance of UNS S32750 SDSS Pulsed Nd:YAG Laser Welding

Super duplex stainless steel has a microstructure consisting of equal proportions of austenite and ferrite. However, welding with Nd:YAG pulsed laser results in an imbalanced microstructure that compromises the steel’s properties. This paper studied the effects of preheating the base metal on pulsed Nd:YAG laser welding. Four conditions were evaluated (no preheating and heating at 100 °C, 200 °C, and 300 °C). The analysis included studying the microstructure, microhardness, and corrosion resistance. Preheating the base metals was found to be an effective method for increasing the volume fractions of austenite. The preheated samples showed an improvement in corrosion resistance compared to the untreated sample. The microhardness varied, with the ferrite amount being higher in the untreated sample.

Preheating Influence on the Precipitation Microstructure, Mechanical and Corrosive Properties of Additively Built Al-Cu-Li Alloy Contrasted with Conventional (T83) Alloy.

In this paper, the high strength and lightweight Al-Cu-Li alloy (AA2099) is considered in as-built and preheated conditions (440 °C, 460 °C, 480 °C, 500 °C, and 520 °C). The purpose of this study is to investigate the influence of laser powder bed fusion (LPBF) in situ preheating on precipitation microstructure, mechanical and corrosive properties of LPBF-printed AA2099 alloy compared to the conventionally processed and heat-treated (T83) alloy. It is shown that precipitations evolve with increasing preheating temperatures from predominantly globular Cu-rich phases at lower temperatures (as-built, 440 °C) to more plate and rod-like precipitates (460 °C, 480 °C, 500 °C and 520 °C). Attendant increase with increasing preheating temperatures are the amount of low melting Cu-rich phases and precipitation-free zones (PFZ). Hardness of preheated LPBF samples peaks at 480 °C (93.6 HV0.1), and declines afterwards, although inferior to the T83 alloy (168.6 HV0.1). Preheated sample (500 °C) shows superior elongation (14.1%) compared to the T83 (11.3%) but falls short in tensile and yield strength properties. Potentiodynamic polarization results also show that increasing preheating temperature increases the corrosion current density (Icorr) and corrosion rate. Indicated by the lower oxide resistance (Rox), the Cu-rich phases compromise the integrity of the oxide layer.

Densification and Immobilization of AgI-Containing Iodine Waste Forms Using Spark Plasma Sintering

In this study, porous Ag-xerogel (Ag-Xero), Ag-faujasite (Ag-FAU) zeolite, and Ag-mordenite (Ag-MOR) zeolite sorbents were loaded with iodine gas [I2(g)] under saturated conditions at 150 °C for 24 h, followed by densification and consolidation into monolithic waste forms using spark plasma sintering (SPS). For Ag-Xero materials, SPS pellets were made with as-loaded samples, while others were made with preheated (PH; 500 °C for 2 h) samples to help with densification. SPS processing was conducted at 50 MPa under different temperatures (T = 200–800 °C) for different times (t = 0.5–30 min), where eleven AgI-Xero samples, five AgI-FAU, and two AgI-MOR separate samples were produced. The primary goal was to look for the optimum processing parameters for each material to yield pellets with high iodine retentions, high densities, and low porosities while preventing AgI decomposition. The Ag-Xero showed the highest iodine loadings (qe = 470 mg g–1) compared to Ag-FAU (qe = 368 mg g–1) and Ag-MOR (qe = 108 mg g–1). Measured iodine concentrations were the highest in AgI-Xero pellets without PH, followed by AgI-Xero with PH, AgI-FAU, and then AgI-MOR. Silver utilization (I/Ag on a mol % basis) values were in the order of AgI-MOR ≈ AgI-Xero (no PH) > AgI-Xero (PH) > AgI-FAU. Chemical durabilities of SPS-densified AgI-Xero (PH) pellets were very favorable, with lower releases than SPS pellets made from AgI-Xero samples without PH. These results show promise for iodine waste form production.

Investigation of the synergetic regulation of O2/Ar preheating treatment and sodium salt addition on semichar combustion characteristics

Using Raman spectroscopy, temperature-programmed desorption (TPD) and laser-induced breakdown spectroscopy (LIBS), the relationship between microstructural characteristics and molecular emissions was determined. It can be concluded that the enhancement of C2 and CN emissions was related to the generation of small aromatic rings and C(O) groups. Compared with the Ar preheating treatment, the presence of additional amount of O2 and sodium salt accelerated the dissociation of the large aromatic ring skeleton, leading to the significant enhancement of small aromatic rings, C(O) and CONa groups. Subsequently, the combustion performance of preheated semichar was investigated by the TG-DTG method. The experimental results demonstrated that pretreatment under oxidizing atmospheres (without and with sodium salt addition) enhanced the comprehensive combustion index (S) and the combustion stability (Rw) of semichars. The corresponding combustion activation energy (E) was weakened. Furthermore, the DFT method was used to analyse the combustion behaviours of semichars. This result demonstrated that preheating treatment (with or without sodium participation) altered the distribution of the Hirshfeld atomic charge (ADCH) of preheated samples, and the combustion essence of semichar was the fracture and recombination of aromatic clusters. For the semichar preheated in the O2/Ar atmosphere, the energy gap of the most optimized pathway was 436.26 kJ/mol. When sodium participated in the oxidizing pretreatment, the energy gap of the most optimized pathway was 413.80 kJ/mol. The positive effect of sodium on the combustion performance of semichar was identified, which was in good agreement with the experimental results.

Enhancement in Activity and Reusability of Dry Amberlyst-15 Catalyst by Thermal Treatment for Production of Biodiesel from Karanja Oil

The effect of preheating Amberlyst-15 catalyst used for the biodiesel production reaction of Karanja oil was studied. The preheated Amberlyst-15 samples were characterized for their surface area and pore volume and by SEM, TGA and FTIR spectroscopy. A preheat temperature of 473 K was found to optimum. At this temperature, the surface area had increased and the sulfonic acid groups of Amberlyst-15 were retained. At 473 K preheated Amberlyst-15 gradually deactivated with reuse from a biodiesel yield of 85% to 27% in four runs at a reaction temperature of 393 K and methanol to oil ratio of 60:1. For the power-law model, the reaction order was 0.65, the rate constant at 373 K was 0.027 h-1 and activation energy was 86.98 kJ/mol.

Inactivation of Salmonella Enteritidis PT30 on black peppercorns in thermal treatments with controlled relative humidities

Traditional method utilizes steam to pasteurize low-moisture ingredients like black peppercorns and almonds. Exposure to steam results in direct condensation on the product, unfavorable for a broader range of food ingredients such as dried herbs, fruits, and ground materials. Recent studies on the thermal inactivation of Salmonella in low-moisture foods suggest that the relative humidity in treatment chambers is an important factor, besides temperature, that determines the death rate of bacteria. Thus, thermal treatments with controlled high relative humidity can be an effective method to replace steam pasteurization. No condensation will occur when the products are preheated to above the dew-point temperature of the hot air in the treatment chamber, thus eliminating the need for post-treatment drying. To prove this concept, a special device was developed that preheated samples in a dry environment before exposing them to a controlled relative humidity (RH) at a high temperature. Using this device, the death rate of Salmonella Enteritidis PT30 (S. Enteritidis) in black peppercorns was determined at 80 °C and three different RH levels (60, 70, or 80 %) after the innoculated samples were heated to 78oC. The results indicate that the treatments at 80 °C and 80 % RH for 3 min, 70 % RH for 9 min, and 60 % RH for 25 min caused 5.4 ± 0.2, 6.2 ± 0.6, and 6.1 ± 1.0 log reductions, respectively. No condensation was observed on all of the treated samples. The moisture content (wet basis) of fully pasteurized (5-log reduction) black peppercorns at 60, 70, and 80 %RH reduced from 9.7 ± 0.4 % (untreated) to 8.7 ± 0.5 %, 9.2 ± 0.4 %, and 9.2 ± 0.2 %, respectively, indicating that post-drying is not required after the treatments. This study demonstrated the potential of using short-time high-RH treatments to control pathogens in low-moisture foods without the need for post-treatment drying.

Effect of Fuel Preheating on Engine Characteristics of Waste Animal Fat-Oil Biodiesel in Compression Ignition Engine.

The present study aims at understanding the effects of fuel preheating on engine characteristics of waste animal fat-oil (WAF-O) biodiesel in a single-cylinder CI engine, with the preheating technique proposed as an effective means for enhancing the fuel properties. To understand the effects of the preheated fuel, the WAF-O biodiesel was preheated at 60, 80, 100 and 120 °C and tested along with neat diesel and unheated WAF-O biodiesel. For this purpose, biodiesel was produced from different animal wastes by means of KOH-assisted ethanol-based transesterification, reporting its maximum yield as 96.37 ± 1.8%, with significant distribution of unsaturated oleic acid, saturated palmitic acid and stearic acid. Upon evaluating its fuel characteristics as per ASTM D6751 standards, a rise in preheating temperature by 1 °C reduced the density and kinematic viscosity of WAF-O biodiesel by 0.383 kg/m3 and 0.025 mm2/s, respectively, and was explained by the weakening of intermolecular forces between its fatty acid ester molecules. Preheated samples reported superior combustion characteristics by exhibiting increased in-cylinder pressure (2.24%, on average) and heat release rates in addition to their shortened ignition delay (1–4 °CA). Furthermore, preheating of WAF-O biodiesel reduced its specific fuel consumption and increased its brake thermal efficiency by 7.86% (on average) and 9.23% (on average), respectively. However, higher preheating temperatures (>120 °C) resulted in increased fuel consumption owing to its varied flow characteristics. In addition to the changes in combustion characteristics, preheating WAF-O bio-diesel also resulted in reduced carbon monoxide, nitrous oxide and hydrocarbon emission by 13.88%, 7.21% and 26.94%, respectively, and increased carbon dioxide emission by 7.58%. Summing up, the enhancements in overall engine characteristics of preheated samples were accounted for by their improvised fuel injection characteristics due to their reduced density and viscosity, which ensured for their effective combustion.

Highly Transparent N-Type TiO<sub>2</sub> Coatings for Self-Cleaning Glass Application

Titanium dioxide (TiO2) has been exploited extensively as it shows remarkable performance in photocatalytic applications. TiO2 thin films can be deposited onto window glass which is workable for self-cleaning applications. In this article, we have studied the role of substrate temperature for spray pyrolysis (SP) of TiO2 thin films for studying self-cleaning applications. For thin film deposition, TiO2 sol is prepared by the sol-gel synthesis technique. The samples are deposited at room temperature and 250 °C, respectively. The samples are characterized via Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and UV-Vis spectroscopy to determine the morphology, surface roughness, and optical properties of the thin films. SEM and AFM results show that samples deposited at 250 °C (pre-heated samples) have uniform size distribution, and defined grain boundaries, respectively. The results also show that the pre-heated sample is highly transparent in the visible region of the solar spectrum when analyzed by the steady-state UV-Vis spectrophotometer. The wettability of the prepared thin films is measured, and the results show that the pre-heated sample shows a hydrophilic character. The self-cleaning property of prepared thin films is evaluated by the photodegradation of Rhodamine B dye. It is observed that the pre-heated substrates show better photoactivity in presence of UV light irradiation. Hence, due to their hydrophilic nature and better photoactivity, these pre-heated thin films deposited by spray pyrolysis can be employed as efficient coatings for self-cleaning glass applications.

Preparation, characterization and biocompatibility of nominal wollastonite/calcium hexaboride composites

Calcium silicate/calcium hexaboride (CaB6) composites were prepared via the wet precipitation chemical method. High quartz, calcium silicate (CaSi2O5), calcium hexaboride with weak cristobalite are the phases detected by XRD after heat-treatment at 550 °C/2 h. The thermal behavior shows clear exotherms at 821-889 °C and 950 °C which reflect the decomposition of CaB6 and the formation of the calciborite (CaB2O4). The microstructures of the samples were in the submicron or nano-scale range. Irregular particles in the form of clusters of the pre-mentioned phases were identified. On the other hand, soaking of the pre-heated samples for two weeks in SBF, shows spherical particles on the sample surfaces in nano-scale and submicron size of calcium phosphate, as surely detected by the energy dispersive x-ray microanalysis (EDX). The microanalysis of the SBF solution after soaking of samples for two weeks using induced coupled plasma (ICP) indicates the presence of residue of calcium and phosphate in the SBF. Also, the X-ray diffraction analysis and the FT-IR spectrum show the crystallization of hydroxyapatite and coesite and the presence of the phosphate bands. The obtained results designated that the prepared composites induced biocompatibility.

Method for recovering cubic boron nitride abrasive grains from vitrified cBN stones – A preliminary study

In this work, a process is established for recovering cubic boron nitride (cBN) grains from fired vitrified cBN products. The abrasive grains are recovered by an acid washing technique. Two methods were used to recover the abrasive grains, namely with and without pre-heating. Shape and surface characteristics of the recovered grains were analysed through optical microscopy and Scanning Electron Microscopy (SEM). The recovery yield of abrasive grain and bond percentage present in the abrasive tool was measured experimentally. From the experimental results, the maximum recovery yield of 81 percentage was obtained in the pre-heated sample. Bond free abrasive grains are also obtained from the pre-heated samples and confirmed through elemental analysis.

Recovery of calcium sulfide from Tunisian phosphogypsum and olive mill wastewaters: a thermogravimetric and kinetic study

Large amounts of phosphogypsum (PG) and olive mill wastewaters (OMW) are rejected regularly in the environment. This paper deals with the valorization of both PG and OMW from Tunisia in order to recover calcium sulfide. It consists in studying the reduction of the former using the latter as a source of carbon, in nitrogen atmosphere with or without H2O vapor. Experiments were carried out by thermogravimetry in non-isothermal mode, and the solids were identified by X-ray diffraction. Raw (OMWR) and preheated samples (OMWP) of OMW were used, and the PG over OMW mass ratio was varied to find the stoichiometric proportion of the reaction between CaSO4 and carbon. It was found that in pure N2 atmosphere the use of OMW as a carbon source allows to significantly reduce both the onset reduction temperature and the reduction temperature interval: the PG reduction takes place in the temperature range of 600–750 °C (instead of 750–1080 °C with pure carbon) leading to CaS formation. Utilizing Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, Kissinger, Satava-Sestak and master plots methods, activation energies, pre-exponential factors and the mechanism models of the reduction reaction were determined. The best models for PG + OMWP at 1.42 mass ratio and PG + OMWR at 0.23 mass ratio mixtures are Avrami-Erofeev A3 and A2 mechanisms, respectively. The kinetic models corresponding to the latter mixtures are: $$\frac{{{\text{d}}\alpha }}{{{\text{d}}t}} = 2.68~ \times 10^{{13}} {\text{~exp}}\left( { - \frac{{242.70~ \times 10^{3} }}{{RT}}} \right) \times 3\left( {1 - \alpha } \right)\left( { - \ln \left( {1 - \alpha } \right)} \right)^{{{\raise0.7ex\hbox{$2$} \!\mathord{\left/ {\vphantom {2 3}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$3$}}}}$$ and $$\frac{{{\text{d}}\alpha }}{{{\text{d}}t}} = 1.32~ \times 10^{{12}} ~\exp \left( { - \frac{{214.92~ \times 10^{3} }}{{RT}}} \right) \times 2\left( {1 - \alpha } \right)\left( { - \ln \left( {1 - \alpha } \right)} \right)^{{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}}}$$ , respectively. In wet atmosphere, the conversion rate of this reaction decreases by about 16% and the determined activation energies in that atmosphere were higher than in pure N2 one, supposing that the reduction reaction was influenced negatively by the wet atmosphere.

Obtaining transparent silica glass from nano-silica hydrosol

Transparent silica glass is widely used in various fields. However, a simple and economical method of synthesis remains to be developed for high-precision device manufacturing. In this study, transparent silica glass is fabricated from low-cost commercial nano-silica hydrosol. To obtain transparent glass, the crystallization temperature of bulk materials must be higher than their densification temperature. Based on XRD analysis, impurity ions such as Na+ have a strong influence on the crystallization characteristics of sintered samples. Purification can be performed by soaking preheated samples in boiling water for a given duration. Transparent silica glass was obtained for purified samples from acidic silica hydrosol sintered at 900–950 °C. The optical characteristics of the samples were investigated for the presence of silica glass, and the transparency was enhanced for samples sintered in vacuum. The mechanical and dielectric properties of the sintered samples were also characterized.

Effect of mechanical alloying and preheating treatment on the phase transformation of the Al–Cu–Fe compacts annealed by microwave radiation

The present study investigated the effect of mechanical alloying (MA) time, preheating and annealing process on phase and microstructural transformations in Al65Cu23Fe12 (at%) alloys. To release stresses, a part of milled powder was heated at 150 °C for 20 min and then raw compacts of the as-synthesized powders and preheated ones were prepared and heated at selected temperatures from 200 to 800 °C using microwave radiation. The results showed that with increasing the time of mechanical alloying process, the morphology of the particles changed and nanometer spherical particles were formed. Also, β-Al(Cu,Fe) solid solution phase was formed after 16 h of mechanical alloying. After 30 h of mechanical alloying, the quasi-crystalline phase did not form directly under the conditions employed in this work. Comparison of preheated samples with samples without preheating process showed that the quasi-crystal phase was formed at 300 °C for preheated samples, while the β phase was formed for samples without preheating process. The results of phase analysis also showed that β-Al(Cu,Fe) and θ-Al2Cu phases along with the quasi-crystalline phase are the main phases in the samples. The annealing process of the samples using microwave radiation leads to the formation of a quasi-crystal phase at temperatures and times much lower than other annealing methods.

Fiber laser welding of hot stamping steel: effect of in situ annealing on the microstructure and mechanical properties

Advanced high-strength steel (AHSS) is a class of promising materials for safe and lightweight structural applications in the transportation industry due to its high energy absorption capacity during severe plastic deformation. However, some types of AHSS tend to become brittle after welding and fail during forming operations. This paper proposes a novel method of laser welding AHSS class of 22MnB5 steel by induction-heating the samples in the bainitic range, which was identified via a theoretical analysis using finite element and physical metallurgy modeling. The calculated annealing temperature was 485 °C, and the subsequent laser parameters were set at a power of 800 W and a welding speed of 2 m/min. The welds performed on such pre-heated samples showed a bainitic microstructure consisting of bainitic ferrite along with uniformly distributed ultrafine carbide precipitates, in contrast to an almost fully martensitic microstructure conducted at room temperature. The average value of microhardness in the heat-affected zone thus decreased from ~ 670 HV without pre-heating to ~ 280 HV with pre-heating. The laser welds with pre-heating exhibited not only a slightly higher yield strength and elongation, despite a slightly lower ultimate tensile strength, but also a superior drawability with an Erichsen index increase by 28% compared with the welds without pre-heating.