Post-production Heat Treatment Research Articles

Deformation-induced γ → αʹ-martensitic transformation in austenitic stainless steel obtained by electron beam additive manufacture

The relationship between strain hardening and kinetics of deformation γ → αʹ phase transformation in chromium-nickel steel Fe–19Cr–9Ni–0.7Ti–0.06C wt. % obtained by electron beam additive manufacture was studied under uniaxial static tension at room temperature and at liquid nitrogen temperature. Additively-produced steel had a two-phase (γ + δ) structure with an increased content of δ-ferrite (≈14 %). Post-production heat treatment at 1100 °С (for 1 h) allowed to reduce its volume content down to 6 %, that is, a predominantly austenitic structure in steel was close to those for analogues obtained by traditional metallurgical methods. Plastic deformation of additively-produced steel was accompanied by the formation of deformation αʹ-martensite, the volume fraction of which increased with an increase in the strain and with a decrease in the test temperature. Using the method of magnetophase analysis, it was shown that at room temperature, kinetics of the deformation γ → αʹ transformation was sluggish and it, as well as the stage and magnitude of the strain hardening, weakly depended on the content of δ-ferrite in the structure of steel obtained by the additive method. At the same time, increased content of the δ-phase under these deformation conditions contributed to an increase in the yield strength and reduced elongation to failure of the additively obtained samples. At low-temperature deformation, when the rapid kinetics of deformation γ → αʹ transformation was observed, the formation rate of αʹ-martensite under plastic deformation was slower and strain hardening was weaker in steel with a larger volume fraction of δ-ferrite than those in the samples with low content of δ-phase.

Study of the Influence of Heat Treatment on OSB Panels Produced with Eucalyptus Wood in Different Layer Compositions

In view of the lack of studies aimed at producing and assessing the effects of heat treatment of Oriented Strand Board (OSB) panels, this paper evaluated the thermal degradation kinetics of the raw materials, and the physical and mechanical properties of the panels made with eucalyptus wood and castor oil-based polyurethane adhesive. The OSB panels were subjected to post-production heat treatment (at 175 and 200 °C), replacing the use of wood chemical preservatives. Furthermore, the quantity of materials varied in the face:core:face layers in the proportions of 25:50:25 and 30:40:30, aiming to evaluate the possibility of structural applications for the panels. The results were statistically analyzed and compared with the specifications and classifications for OSB indicated by the European Standard EN 300 and the literature. The application of heat treatment improved the physical properties by decreasing the interaction with water and did not reduce the mechanical properties below the recommended levels. The variation in layer proportions indicated that all of them can be adopted without compromising the panel’s physical-mechanical performance. All treatments are compatible with the EN 300 classification for OSB/4 (heavy duty load-bearing boards for use in humid conditions), presenting technical feasibility and excellent structural profile for civil construction applications.

Neutron diffraction residual stress determinations in titanium aluminide component fabricated using the twin wire-arc additive manufacturing

In recent years, twin wire-arc additive manufacturing (T-WAAM) technique has been considered as a promising method of fabricating and shaping titanium aluminide components with high efficiency and low cost. However, excessive thermal input of the non-consumable tungsten electrode arc deposition induces significant residual stresses in the buildup component, thus accurate measurement of residual stresses is necessary for T-WAAM buildup part quality assessment. In the present research, non-destructive neutron diffraction residual stresses measurements on as-fabricated and heat-treated T-WAAM produced Ti48Al titanium aluminide components are performed. To exclude the influence of initial large T-WAAM residual stresses on d 0 hkl sample alignment, different d 0 hkl sample dimensions are designed: one is normal thin slice and the other is the meshed sample. According to the obtained results, the conducted post-production heat treatment has partially released initial residual stresses. Also, the meshed design of d 0 hkl sample shows better measurement accuracy than the simple sliced d 0 hkl sample. In addition, T-WAAM fabricated titanium aluminide wall component performs featured tensile-compressive alternating residual stress distribution induced by the layer-by-layer arc deposition.

Effects of post-production heat treatment on the mechanical and corrosion behaviour of CoCrMoW alloy manufactured through selective laser melting

In this work, the matrix of CoCrMoW alloy fabricated by selective laser melting is mainly γ-Co phase. After the aging treatment at 750 °C, lamellar ε-Co phase formed according to a Shoji-Nishiyama orientation relationship with γ-Co phase and nanometer-scaled Co3(Mo,W)2Si precipitation uniformly distributed on the matrix, the strength and corrosion resistance increased, but the ductility decreased. After the solution treatment at 1200 °C, recrystallization happened, the fine columnar sub-grains of γ-Co phase in the as SLMed alloy were replaced by larger grains mainly with large-angle grain boundaries, the ductility increased, but the tensile strength and corrosion resistance decreased. Results of this work can provide a perspective towards microstructure regulation of SLMed CoCrMoW alloy.

Effect of Joule-Heating Treatment on the Microstructure and Physical Properties of 16-Stranded Compressed Copper Wires

Compressed wires are produced by cross-sectionally compressing stranded conductors, which results in a smaller conductor diameter. This also leads to a lower weight wire, because a thinner external insulated coating can be used, compared to the low-voltage wires typically used in automobiles. However, a post production heat treatment of the compressed wires is required because plastic deformation occurs during compression after drawing the wires. In this study, the work hardening of stranded compressed copper wires was controlled by Joule-heating, and the resulting changes in microstructure, mechanical, and electrical properties after various annealing voltages (0, 25, 27, 31, 35, and 39 V) were observed. The results confirmed that as the annealing voltage increased from 0 to 31 V, the anisotropic deformation texture with a <111> orientation as the main component was reduced, and micrograins were generated throughout the stranded wires via recrystallization. At an annealing voltage above 31 V, the grains grew to be more than twice as large as those before heat treatment. At an annealing voltage of 31 V these structural changes contribute to the elongation increase of the compressed wires to 28.34%, and an improvement in electrical resistance to 145.85 mΩ.

Enhancement of inverted organic solar cell parameters by post-production annealing process

The post-production thermal annealing process of the polymer photoactive layer of organic solar cells at ideal temperatures is one of the crucial factors for solar cell performance since the photovoltaic performance of polymer-based organic solar cells is strongly affected by thermal annealing of the photoactive layer. In this study, inverted organic solar cells with enhanced efficiency using a blended poly (3-hexyl-thiophene) (P3HT) and phenyl C61butyric acid methyl (PCBM) subjected to post-production thermal annealing have been reported. The confocal Raman and atomic force microscopy measurements were performed to obtain the information about the material properties and surface morphology of electron selective layer of ZnO and polymer photoactive layer of P3HT:PCBM. To find out the ideal temperature for annealing, the post-production heat treatment procedure was applied to the polymer photoactive layer in between 90 °C and 210 °C by 20 °C steps. The current density versus voltage (J-V) measurements of Glass/ITO/ZnO/Polymer/MoO3/Ag devices showed that the application of post-production heat treatment to the polymer photoactive layer with a temperature of around 150 °C significantly enhanced the solar cell parameters of devices. The power conversion efficiency (PCE) values were calculated as 1.90% and 3.91% for the reference device without annealing and the annealed device at 150 °C, respectively. Additionally, it was observed that the performance of the solar cell increased due to the decrease in R S value and the increase in the roughness of the polymer surface with annealing process.

Effect of Heat Treatment in Different Atmospheres on Thermally Evaporated ZnS films

In this study, the properties of ZnS films which can be used as a buffer layer in photovoltaic thin film solar cell technologies were tried to be improved by applying post-production heat treatments. ZnS films were subjected to annealing processes in Nitrogen, Argon and Air atmospheres with an atmosphere-controlled heat treatment system and the effects of these atmospheres on the films were investigated. As a result of XRD analysis, it was determined that all films show a preferential orientation towards the (111) ZnS plane. The crystallite size of the ZnS film increased with the applied heat treatment. It was also confirmed by transmittance measurements that the ZnS film annealed in air is partially oxidized and contains the secondary ZnO phase in its structure. Optical band gap values for ZnS films were found to be 3.53–3.56 eV. The refractive index values of the films were determined by spectroscopic ellipsometry. Two-probe technique was used to determine the electrical resistivity and heat treatment caused a decrease in the resistivity values of the films. Surface analyzes of the films were performed with the help of AFM and SEM measurements. As an outcome of this study, it has been revealed that the surfaces of ZnS films can be modified by heat treatment in Argon atmosphere. The production of ZnS films and their optimization with subsequent heat treatments were carried out, and ZnS films with high transmittance and improved morphology were obtained. These materials can be used as buffer layer or window layer in CZTS, CIGS and CdTe based solar cells.

Modification and characterization of the Al concentration induced precipitate in the Fe3Al-based iron aluminide fabricated using the wire-arc additive manufacturing process

Fe 3 Al based alloys have been continuously attractive to the fossil energy industry due to the excellent high temperature oxidation resistance and strength, light weight and low materials cost. In recent years, to overcome the fabrication difficulty of Fe 3 Al based alloys and reduce the room temperature induced high manufacturing cost, the twin wire-arc additive manufacturing (WAAM) technique is invented. During the post-production heat treatment aiming to modify the as-fabricated microstructures, the Al concentration induced precipitates are reported in the previous research, which can effectively refine the initial large grains and weaken the WAAM induced microstructural anisotropy. Therefore, the further characterization on the precipitate is meaningful for the development of the innovative WAAM in the Fe 3 Al fabrication. In the present research, to further characterize such Al concentration induced precipitates and find the functioning mechanism on the material properties, the precipitates are modified using various heat treatments and subsequently characterized in detail using microscopies and room temperature tensile test. According to the results, the Al concentration induced precipitates are characterized as the long-range ordered D0 3 structured Fe 3 Al superlattice. And the generation of such superlattice precipitates in the Fe 3 Al matrix performs dislocation pinning effect thus improves the alloy strength. However, the strengthening by D0 3 superlattice precipitates cannot compensate the tensile property anisotropy, thus the grain refinement is still the key to break down the large columnar grains and further improve the mechanical properties. • Fe 3 Al D0 3 superlattice precipitates are confirmed in WAAM produced Fe 30Al alloy. • D0 3 superlattice precipitates strengthen the alloy by dislocation pinning. • Heat treatments show little effect on the property anisotropy of WAAM made Fe 30Al. • Fracture morphology variation of Fe 30Al alloy is found by the heat treatment.

Microstructure and Mechanical Properties of Ti-6Al-4V Manufactured by Selective Laser Melting after Stress Relieving, Hot Isostatic Pressing Treatment, and Post-Heat Treatment

Additive manufacturing (AM) is defined as a technology performed for tooling applications. It is used for manufacturing tools that have complex shapes and figures. In this study, an extensively applied Ti-6Al-4V alloy was made using the selective laser melting method. Post-production heat treatments were applied to decrease thermal stresses and to enhance the mechanical properties and the microstructure. The study investigates the fatigue mechanical properties, microstructure, hardness, and porosity of the AM Ti-6Al-4V after stress relieving (SR) and after SR followed by hot isostatic pressing (HIP). The samples’ upper and lower parts were independently examined to determine the effects of thermal conditions and the heat treatment of the microstructure. The microstructures were examined through optical microscopy, scanning electron microscopy and x-ray diffraction methods. The mechanical properties were investigated through microhardness testing, alongside assessment by fatigue testing at room temperature. The findings demonstrated that the microstructure after SR at 704 °C for 2 h is 100% fine martensitic α'-Ti, with a microhardness value of 408 HV. Air and furnace cooled samples have a more homogenous structure and are characterised by mixture (α + β) with microhardness values of 382 and 356 HV, respectively. After HIP at 920 °C and 100 MPa for 2 h was applied, the martensite was converted into a lamellar (α + β) microstructure, whereby the α phase is presented as fine needles situated among the β ridges in the microstructure, with the existence of the prior β grain boundary.

Effect of the post-production heat treatment on phase evolution in the Fe3Ni–FeNi functionally graded material: An in-situ neutron diffraction study

Functionally graded material has been increasingly attractive due to the locally designed and optimized material properties. In the present paper, to achieve high thermal lattice structural stability and high corrosion resistance in each side of one bulk material, an Fe3Ni–FeNi compositionally graded material (FGM) bulk sample has been fabricated using an innovative wire-arc additive manufacturing process. A subsequent homogenization post-production heat treatment is applied to stabilize the phase composition and eliminate the possible segregation in the as-fabricated sample. Meanwhile, the high intensity neutron diffraction instrument WOMBAT is conducted to measure the phase evolution processes in the bulk sample in-situ, thus the thermal induced lattice evolutions of Fe3Ni and FeNi can be accurately obtained dynamically in the function of time. According to the results, the WAAM has successfully fabricated the target FGM with uniform Ni content gradient. However, hot cracking defects are found in the bulk sample because of the inadequate interpass temperature setting. As analyzed from neutron diffraction results, the homogenization heat treatment has improved the phase thermal stability of the FGM and the application temperature of the Fe3Ni–FeNi FGM should be limited under 630 °C.

Influences of postproduction heat treatments on the material anisotropy of nickel-aluminum bronze fabricated using wire-arc additive manufacturing process

The anisotropy of wire-arc additively deposited nickel-aluminum bronze alloy is studied by microstructure observation and room temperature mechanical property testing. The applied heat treatments have effectively modified the as-fabricated {0 1 1} , {1 1 1} texture into {1 1 1}. According to the microstructures, the single tempering has resulted in lowest anisotropy while heat treatment with prior homogenization and quenching process induces even intensified annealing textures. However, as shown by the tensile tests, the quenching process is necessary for favorable mechanical properties in the wire-arc additive manufacturing fabricated nickel-aluminum bronze component; therefore, a balance between homogenization annealing and κ-phase precipitation is indicated. Meanwhile, the function of κ-phase precipitates on grain rotation and growth during post-production heat treatment is explained in detail.

On microstructural homogenization and mechanical properties optimization of biomedical Co-Cr-Mo alloy additively manufactured by using electron beam melting

The electron beam melting (EBM), a layer-by-layer additive manufacturing (AM) technique, has been recently utilized for fabricating metallic components with complex shape and geometry. However, the inhomogeneity in microstructures and mechanical properties are the main drawbacks constraining the serviceability of the EBM-built parts. In the present study, we found remarkable microstructural inhomogeneity along build direction in the EBM-built Co-based alloy, owing to the competitive grain growth and subsequent isothermal γ-fcc → ε-hcp phase transformation, which affects the corresponding tensile properties significantly. Then, we succeeded in eliminating the inhomogeneities, modifying the phase structures and refining grain sizes via comprehensive post-production heat treatment regimes, which provides a valuable implication for improving the reliabilities of AM-built metals and alloys. The Co-based alloy can be selectively transformed into predominant ε or predominant γ phase by the regime, and the grains were refined to 1/10 of the initial sizes by repeated heat treatment. Finally, we investigated the tensile properties and fracture behaviors of the alloy before and after each heat treatment. The γ → ε strain-induced martensitic transformation is the major deformation mode of the γ phase, meanwhile the formation of stripped ε phase at {111}γ habit planes contributed to a good combination of strength and ductility. Nevertheless, the ε phase was deformed mainly by (0001)ε <11 2¯0 >ε basal and {1 1¯00}ε <11 2¯0 >ε prismatic slip systems, exhibiting very limited ductility and strength. In addition, the ε grains act as secondary hardening factor in the samples consisting of dual γ/ε phase, leading to a non-uniform deformation behavior.

Surface defects reduce Carbon Nanotube toxicity in vitro

The cytotoxicity of two different types of Multi-walled Carbon Nanotubes (MWCNTs) in A549 lung epithelial cells and HepG2 hepatocytes was investigated. One MWCNT still contained iron that was used as a catalyst during production, while the other one had all iron removed in a post-production heat treatment resulting in significantly fewer surface defects. The WST-8 assay was applied to test cell viability. To check the integrity of the cell membrane, we performed the lactate dehydrogenases assay (LDH) and measured the cellular production of reactive oxygen species (ROS). Finally, to examine cell proliferation, we conducted a cell cycle analysis. The results showed a dose- and time-dependent decrease in cell viability for both MWCNTs in both cell types. Moreover, a dose- and time-dependent increase in LDH leakage was detected, thereby indicating a decreased membrane integrity. The production of ROS was significantly increased in the case of the heat-treated MWCNTs. The heat-treated MWCNTs showed significantly stronger adverse effects when compared to the non-treated MWCNTs. Additionally, the heat-treated MWCNTs induced a dose-dependent cell cycle arrest in A549 cells. Both MWCNTs induced a significant cytotoxicity, whereby the heat treatment, leading to a decrease in surface defects, further increased the indicated adverse effects.

Laser Powder Bed Fusion: tailoring the microstructure of alloys for biomedical applications

Abstract Additive manufacturing (AM) is particularly attractive for biomedical applications, where complex geometries and a high degree of individualization are required. Laser powder bed fusion (LPBF) is an AM technology exploiting the action of a solid-state laser to locally melt a metal powder according to a computer aided design (CAD) model. In the present study, the EOS Cobalt Chrome SP2 (Co-Cr-Mo-W) and Ti64 (Ti6Al4V) powders were sintered by the system equipped with a Yb fiber laser. During LPBF, the Co-Cr-Mo-W metal powder undergoes total melting followed by rapid cooling, giving rise to athermal martensitic phase transformation from the high-temperature γ (fcc) phase to the low-temperature e (hcp) phase. This produces an intricate network of thin e-lamellae inside the γ phase matrix. After the firing cycle this structure is maintained, and a massive presence of coarse precipitates is also observed. Owing to the rapid cooling taking place during LPBF, in Ti6Al4V sintered samples only the acicular martensitic α’ phase is present. The firing cycle induces the β phase formation at the α plate boundaries and this microstructure leads to reduced values of strength, with respect to those of the as-sintered samples. The highlighted behaviors show that by tuning the post-production heat treatments it is possible to tailor the microstructure and the mechanical properties.

The influence of post-production heat treatment on the multi-directional properties of nickel-aluminum bronze alloy fabricated using wire-arc additive manufacturing process

In this paper, a nickel-aluminum bronze alloy component is built using wire-arc additive manufacturing process. In order to investigate the influence of anisotropy introduced by the wire-arc additive manufacturing process, the layer-by-layer manufactured components with different post-production heat treatments are characterized by optical and scanning electron microscopy morphologies, X-ray diffraction and mechanical tests in longitudinal, transverse and normal directions. The experimental results show that the deposit exhibits higher strengths in the longitudinal and transverse direction than in the normal direction. Also, the ductility of the alloy is significantly improved with the designed quenching and tempering method, and competitive mechanical properties are achieved when tempering temperature reaches 650 °C. In addition, the anisotropy in the additively manufactured alloy can be effectively modified by the quenching and tempering heat treatments.

Influences of postproduction heat treatment on Fe3Al-based iron aluminide fabricated using the wire-arc additive manufacturing process

In this paper, Fe3Al-based alloy with a designed 30 at% Al content is fabricated using an innovative wire-arc additive manufacturing process. In order to investigate the influences of postproduction heat treatments on the additively manufactured alloy, three postproduction heat treatment methods were applied to the as-fabricated material. The morphologies, phase constituents, and mechanical properties of samples produced by the different heat treatments were characterized and analyzed in detail. According to the results, the applied heat treatments can considerably change the microstructure and mechanical properties of the as-fabricated Fe3Al-based alloy. Also, the hardness and tensile properties of Fe3Al-based alloy are found relevant to the Al-rich precipitates observed in the morphologies, which are generated by the additional thermal processes on the homogenized Fe3Al-based alloy.

Influence of post fabrication heat treatments on the fatigue behavior of Ti-6Al-4V produced by selective laser melting

Selective Laser Melting (SLM) is characterized by a layer-wise building process that enables the near net shape production of parts with a high geometrical complexity. The SLM process leads to the build-up of thermal stresses, while the rapid solidification leads to segregation phenomena and the development of non-equilibrium phases. To reduce thermal stresses and to optimize the microstructure and the mechanical properties for the specific application, suitable post-production heat treatments should be defined. Four different heat treatments in vacuum of SLM Ti6Al4V were investigated in relation to the fatigue behavior. Tensile and fatigue specimens were produced with a SLM system using the optimized process parameters. Microstructures before and after heat treatment were characterized by metallographic methods. Two post fabrication heat treatments are promising in terms of fatigue strength of as-built SLM Ti6Al4V. The role of surface machining was also investigated for one heat treatment condition.

The effect of postproduction heat treatment on γ-TiAl alloys produced by the GTAW-based additive manufacturing process

Postproduction heat treatments were carried out on additively manufactured γ-TiAl alloys that were produced by using the gas tungsten arc welding (GTAW) process. The microstructural evolution and mechanical properties of both as-fabricated and heat-treated specimens were investigated to assess the effect of different heat treatment conditions, by using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Neutron Diffraction and tensile tests.The results indicated that heat treatment promotes the formation of the γ phase in the majority region after heat treatment at 1200°C for 24h, while a fully lamellar structure was formed in the near-substrate zone. The response to heat treatment at 1060°C/24h was markedly different, producing a fine lamellar structure with differing sizes in the majority region and near-substrate zone. These various microstructural characteristics determined the mechanical properties of the heat-treated samples. The heat-treated samples at 1200°C/24h exhibited lower UTS and microhardness values but higher ductility than the as-fabricated samples without heat treatment, while the 1060°C/24h heat treatment resulted in higher UTS and microhardness values but lower ductility. Due to the homogenous microstructure in the majority region after each postproduction heat treatment, the tensile properties were similar for both the build direction (Z) and travel direction (Y), thereby minimising the anisotropy that is exhibited by the as-fabricated alloy prior to heat treatment.

Effect of Post-production Heat Treatment on Particleboard from Sugarcane Bagasse

This study aimed to evaluate the effect of heat treatment on the physical and mechanical properties of particleboard from sugarcane bagasse. The experiment consisted of seven treatments arranged in a 2 × 3 factorial arrangement (two heat treatment times – 8 and 12 min, and three heat treatment temperatures – 200 °C, 230 °C, and 260 °C) and treatment control (without heat treatment). We evaluated the properties such as apparent density, water absorption after 2 and 24 h (WA2h andWA24h), thickness swell after 2 and 24 h (TS2h and TS24h), irreversible thickness swelling rate (ITS), internal bond, Modulus of Elasticity (MOE), and Modulus of Rupture (MOR) in static bending. In general, the use of heat treatment appeared very promising for improving the dimensional stability of sugarcane bagasse particleboard, without being made unviable by the mechanical properties reduction.

The Effect of Various Postproduction Heat Treatment on Lipid Composition and Oxidation in Chinese Nanjing Salted Duck

Traditional Nanjing salted ducks are cooked at low temperatures. However, factories in China that attempt to mass produce this meat require a heat-treatment stage to maintain the safety of this food product over longer storage periods. Conjugated diene, carbonyl, thiobarbituric acid-reactive substances, peroxide, and the compositions of fatty acids (FA) and triacylglycerols (TGs) were measured in Chinese Nanjing salted ducks following different heat treatments including a control, 99C, 108C, microwave and 121C heat treatments after packaging. Heat treatments increased (P < 0.05) carbonyl and peroxide values and the percentages of C18:2n6, C18:3n3, C20:4n6, polyunsaturated FAs, unsaturated FA and some TGs; however, heat treatments decreased (P < 0.05) C16:0, C16:1, C18:1, monounsaturated and saturated fatty acids, and other TG fractions in the duck meat especially after microwaving or being treated at 121C. Further research should explore modifying current preservation methods to improve meat quality. Practical Applications Heat treatment of packaged products is considered an effective method of increasing their shelf life. However, such treatment can also distort the flavor of products, largely because of lipid oxidation. This study investigated changes in lipid composition and oxidation in heat-treated ducks to indirectly explore the mechanism behind off-flavor formation.