Heat Treatment Strategy Research Articles

Effect of heat treatment on the gas-atomized nickel‑aluminum bronze feedstock powders for cold spray

Due to the high strength of the nickel‑aluminum bronze (NAB), the cold spray deposition efficiency of the NAB powders was less than satisfactory. To improve the deformation behavior of powder, different heat treatment strategies were adopted for gas atomized NAB powders and then the heat-treated powders were deposited on NAB substrates using a high-pressure cold spray system. For various powders and their corresponding deposits, a series of related characterizations were performed. The results indicate that the microstructure of the gas-atomized powder was mainly composed of martensitic β′ and bainite α with high hardness, resulting in low deposition efficiency and poor bonding between particles and particles in the prepared deposits. An effective technique of heat treatment can eliminate the non-equilibrium structure in the gas atomized powder, reduce the hardness of the powder, and significantly improve the deposition efficiency and enhance particle interface bonding.

Ti-Fe Phase Evolution and Equilibria Toward β-Ti Superalloys

Recent design and development of precipitate reinforced refractory metal alloys demonstrate the possibility of A2 + B2 bcc superalloys as a new class of high temperature materials. Existing β-Ti alloys do not typically employ reinforcement with intermetallics, as in other high temperature alloys; to this effect sufficient additions of Fe, a low cost β-Ti stabiliser, can promote formation of an ordered-bcc intermetallic phase, β′-TiFe (B2), offering scope to develop a β + β′ dual-phase field. However, key uncertainties exist in the base Ti-Fe binary. The current research evaluates the formation of ordered-bcc TiFe precipitates within a disordered-bcc β-Ti matrix through variable heat treatment strategies. The microstructure optimisation has revealed new insight into the Ti-Fe phase equilibria at near eutectoid temperatures in the purported dual-phase field, where a complex interplay between β-Ti, β′-TiFe and α-Ti exists.

Effect of Aging Temperature on the Microstructure and Mechanical Properties of a Novel β Titanium Alloy

High-strength metastable β titanium alloys are promising structural materials to be used in aviation industries. In order to achieve a high strength level, solid solution treatment within β region and subsequent low-temperature aging are usually necessary to obtain fine α precipitates. The selection of the aging temperature is considered critical to the mechanical performance of metastable β titanium alloys. In this work, we investigated the effect of aging temperature on the microscopic structure and mechanical properties of a novel type of titanium alloy TB18 (Ti-4.5Al-5Mo-5V-6Cr-1Nb). A series of aging treatments were conducted on TB18 specimens at 510 °C, 520 °C, 530 °C, and 540 °C after the solid solution treatment at 870 °C. On the basis of the systematic results of scanning electron microscope and transmission electron microscope, the behavior of the α phases affected by the varied aging temperatures were studied. As the aging temperature rose, the grain width of the α phase increased from 60 nm (510 °C) to 140 nm (540 °C). For the TB18 samples aged at 510 °C and 540 °C, the tensile strength/yield strength/impact toughness values were 1365 ± 3 MPa/1260 ± 0.9 MPa/26.5 ± 1.2 J/cm2 and 1240 ± 0.9 MPa/1138 ± 0.8 MPa/36.2 ± 1.3 J/cm2, respectively. As a result, the tensile performance and the grain width of the α phase agreed well with the Hall–Petch relationship. This work offers valuable support for both theoretical analyses and the heat treatment strategies on the novel TB18 titanium alloy.

Effect of Co content on microstructure and mechanical properties of maraging steel

Effect of Co element on the microstructure and mechanical properties of maraging steel is studied and summarized. The microstructure and mechanical properties of five different compositions of maraging steels were characterized and tested in three heat treatment states, with the heat treatment schemes of homogenization treatment at 1300 °C × 10h, solution treatment at 800 °C × 2h, and aging treatment at 480 °C × 5h. The research has discovered that increasing the Co content in three different heat treatment states can lead to a reduction in the size of the original austenite grains and the width of martensite laths. In the aged state, higher Co content causes the precipitation phase to transform from an ellipsoidal Mo-rich phase to a needle-like Ni3(Mo, Ti) phase. These changes in the size, shape, and density of the precipitated phases result in a more pronounced effect of precipitation strengthening, leading to a significant increase in the material's strength.

Importance of the Heat Treatment Scheme on Self-Reducing Reactive Silver Inks

Importance of the Heat Treatment Scheme on Self-Reducing Reactive Silver Inks

Enhanced strength of additively manufactured Inconel 718 by means of a simplified heat treatment strategy

This study simplified the heat treatment route and reduced the post-processing burden for laser powder bed fusion IN718 (a nickel-based superalloy). The tailored route retained advantageous microstructures and improved tensile strength when compared to the conventional post-processing strategy. The implementation of a single pre-aging step (combining the stress relief, HIP, and solution steps into one) and a single-step aging treatment (as opposed to two-step aging) resulted in a total heat treatment time of 15 h, which is far shorter than the conventional five-step strategy (42 h). The grain structure, pore structure, and room-temperature tensile properties were measured for three material conditions: the as-built condition, the baseline condition (a conventional five-step heat treatment route), and the HIP1020RQSA condition (novel high pressure rapid quenching HIP treatment followed by a single-step age). In the HIP1020RQSA condition, the high pressure (200 MPa), short hold time at a carefully selected temperature (0.5 h at 1020 °C), and rapid quenching (2150 °C/min) were implemented. Unique findings in the microstructure include generation of localized micro-scale recrystallization throughout the retained columnar grain and sub-grain structures, internal pore closure with a shortened HIP soak time, incomplete dissolution of Laves phase, and the absence of δ phase. The single step aging treatment also generated γ′ and γ′′ precipitates. The HIP1020RQSA treatment improved the yield strength of the baseline condition from 1112 MPa to 1209 MPa, decreased total elongation from 24.9% to 23.2%, and still exceeds the minimum Z direction (build direction) tensile properties outlined in ASTM F3055–14a.

Unleashing multi-scale mechanical enhancement in NiTi shape memory alloy via annular intra-laser deposition with homogenized Ti2Ni nanoprecipitates

Additive manufacturing (AM) of composition-sensitive NiTi shape memory alloys (SMAs) is hindered by uncontrollable non-equilibrium microstructures, leading to functional performance degradation and limitations in high-throughput net-shaping applications. To address these challenges, we propose a novel approach combining annular intra-laser directed energy deposition (AIL-DED) with a tailored gradient post-treatment process. This enables the fabrication of nanocomposite microstructures in NiTi SMAs with precise control over the homogenization of Ti2Ni nanoprecipitates. In-situ monitoring and characterization of thermal history, microstrain, and constitutional phases, were utilized to uncover the relationship between multi-scale structural features and mechanical responses. The interplay between laser reflectivity, energy input, and lattice thermal vibrations affects forming quality in AIL-DED. Dynamic temperature variations were studied before reaching thermal equilibrium, revealing insights into thermal and mechanical interactions during the process. These findings contribute to understanding challenges in fabricating high-quality NiTi SMAs. Examining phase transformation behavior and its correlation with processing parameters deepens understanding of microstructural evolution and provides insights for tailoring material properties. The stress relaxation and dislocation evacuation at elevated temperatures caused the expansion of lattice and interplanar spacing in the age-treated SMA's B2 matrix phase, exhibiting a stable two-step phase transformation behavior (B19′↔R↔B2). AIL-DED combined with two-stage heat treatment strategy demonstrated enhanced homogeneity of non-equilibrium microstructures, resulting in the formation of high-density, well-dispersed Ti2Ni nanoprecipitates, with a semi-coherent interface to B2 matrix. The combination of load-bearing strengthening through well-dispersed Ti2Ni nanoprecipitates and Orowan strengthening at the semi-coherent interface yielded simultaneous enhancements in nanohardness, ultimate compressive strength, compressive fracture strain, and deformation recovery, following the AIL-DED combined with two-stage heat treatment process. The fracture mechanism transitioned from a mixture of brittle-ductile behavior to predominantly ductile characteristics. This study provides valuable insights that advance additive manufacturing and enhance the functional performance of SMAs in critical applications.

Enhanced strength-ductility synergy of laser powder bed fused Inconel 718 via tailoring grain structure and precipitates

Inconel 718 fabricated by laser-powder bed fusion (L-PBF) exhibits a hierarchical microstructure, rendering traditional standard heat treatment processes not entirely suitable. To enhance the tensile properties, a novel heat treatment strategy to simultaneously tailor the grain structure and precipitates of L-PBFed Inconel 718 is proposed. This study aims to investigate the effects of homogenization time, coupled with water cooling, on grain structure, precipitation, and room-temperature tensile properties. The results demonstrate that increasing the homogenization time from 1 h to 4 h results in a significant improvement of tensile ductility by 33.7%, while maintaining higher tensile strength compared to the wrought counterparts. The utilization of water cooling following homogenization effectively suppresses the formation of undesirable δ phases and promotes the precipitation of γ′′ phases during subsequent aging treatment, leading to exceptional tensile strength. Furthermore, the prolonged homogenization time facilitates recrystallization and promotes uniform deformation between adjacent grains, thereby enhancing the material's ductility. This study provides theoretical guidance for the development of customized heat treatment processes to achieve superior mechanical properties in additive-manufactured metallic materials.

Crystallographic analysis of a new heat treatment strategy for improving the mechanical properties of powder metallurgical steel

ABSTRACT In this study, the effects of complex phase(CP) microstructures obtained by applying various heat treatment routes on the impact toughness properties of unalloyed high carbon powder metallurgy (PM) steels containing 1.2% carbon by weight were investigated. For this purpose, after applying quenching and tempering heat treatment to the sintered samples, they were partially austenitised at 800°C for 5 min, cooled in water (γ + Fe3C), and tempered for 1 h. The mechanical performances of CP microstructures were compared with sintered, quenched, and conventional quenched tempered specimens, respectively. The crystallographic analyses and dislocation densities of the samples, which were microstructurally characterised by SEM and TEM analyses, were determined by the XRD device. The hardness and impact toughness values of the samples with CP microstructures were improved by 64% and 23%, respectively, compared to the initial sample.

Heat Transfer Analysis of MgB2 Coil in Heat Treatment Process for Future Fusion Reactor

State of the art MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is reviewed as a potential material for the poloidal field (PF) coils of the future fusion reactor due to its high critical temperature and low material cost. The heat treatment process is a crucial step in the development of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> magnets. The temperature lag in heat treatment of large magnets can lead to insufficient thermal reaction time. It may be infeasible to control the temperature of a magnet according to the heat treatment scheme recommended for the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire. Hence, the heat treatment process of a large magnet needs to be evaluated. Therefore, the dynamic temperature distribution of a MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> PF coil is obtained by simulating the heat transfer in heat treatment process. A suitable heat treatment schedule for a large magnet is proposed and the experimental results of a sub-size Cable-In-Conduit Conductor manufactured with MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> strand confirmed the feasibility of the newly proposed heat treatment process. The results provide a reference for the heat treatment method of a future larger MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> coil.

Obtaining high-strength carbon fiber based on polyphenylene sulfide by ATL method with laser heating

The method of manufacturing high-strength structural carbon fiber from toupreg based on PPS-214 grade polyphenylene sulfide (Fortron, Germany) and AS4 high-strength carbon fiber (Hexcel, USA) using a promising ATL-technology (Automated Tape Laying) with laser heating is considered. The technology was adapted for the material under study, laboratory models in the form of plates were made, physical and mechanical tests of laboratory samples were carried out. The quality of the binder distribution and the presence of defects were assessed by raster electron microscopy. The influence of the reinforcement, pressing and vacuum heat treatment schemes on improving the mechanical properties of the studied carbon fiber was investigated. It has been found that the samples subjected to vacuum heat treatment have higher mechanical properties due to an increase in the adhesion of the toupreg tapes to each other and the removal of discontinuities formed during the calculation. The value of the ultimate strength at interlayer shear of samples made using a parallel-diagonal scheme increases by 108%, at bending by 370% and by 65% at compression.By processing the toupregs by the ATL with laser heating and subsequent thermal treatment of the products, it is possible to obtain high-strength structural materials with improved physical and mechanical properties, as well as high repeatability and equality of properties throughout the area of the products, even using complex reinforcement schemes.

Role of δ-phase on Mechanical Behaviors of Additive Manufactured Inconel 718: Detailed Microstructure Analysis and Crystal Plasticity Modelling

In this work, a multi-scale approach was applied to reveal the evolution mechanisms of the δ (Ni3Nb) phase and the resultant mechanical responses in wire-arc additive manufactured (WAAM) Inconel (IN) 718. Several heat treatment strategies, consist of homogenization, intermediate heat treatment and aging process, were firstly conducted to produce δ phases with different characteristics. The early evolution of the δ phase was then analyzed in detail via transmission electron microscopy. The nanoindentation and tensile tests were also used to verify the strengthen response of δ phase. Moreover, a crystal plasticity finite element (CPFE) model, taking into account the different configurations of δ phase, was developed to study and predict the micro deformation behavior. Results revealed that when the intermediate heat treatment time exceeded 1 h, the formation of the main strengthening phase γ" was constrained by the δ phase, accompanied by the coarsening of γ". The decrease of γ" phase and the destruction of coherent γ"/γ interface are the main causes of strength loss in the WAAMed IN718. The intergranular dislocation transmission was hindered by the δ phase, thereby increasing the grain boundary strength. However, the needle-like δ phase within the grain may cause premature fracture due to strain localization, thereby reducing the material properties. The evolution mechanisms of the δ phase obtained in this study provides theoretical guidance for the optimization of the microstructures and mechanical properties of WAAM Inconel 718.

Impact of Post-Process Heat Treatments Performed on Ti6Al4V Titanium Alloy Specimens Obtained Using LPBF Technology

Additive manufacturing technology has emerged over the past decade as one of the best solutions for building prototypes and components with complex geometries and reduced thicknesses. Its application has rapidly spread to various industries, such as motorsport, automotive, aerospace, and biomedical. In particular, titanium alloy Ti-6Al-4V, due to its exceptional mechanical properties, low density, and excellent corrosion resistance, turns out to be one of the most popular for the production of parts with additive manufacturing technology across all the market segments listed above. However, when producing components using Laser Powder Bed Fusion (LPBF) technology, it is always necessary to perform appropriate heat treatments whose main purpose is to reduce the residual stresses typically generated during the manufacturing process. Post-process heat treatments on Ti6Al4V components obtained by way of additive technology have been extensively studied in the literature, with the aim of identifying optimal thermal cycles, which may allow for the effective reduction of residual stresses combined with proper microstructural conditions. However, despite the usual target of maximizing relevant mechanical properties, it is mandatory for industrial production to achieve a robust process, i.e., minimizing the sensitivity to noise-induced variation. Therefore, the aim of the present work is to compare several post-process heat treatment strategies by performing different thermal cycles in the temperature range of 750–955 °C and investigating how these affect the average mechanical properties and their variance. The treated samples are then analyzed running a complete mechanical and microstructural characterization, and the latter particularly focused on the determination of the typical microstructure present in the treated samples by using the XRD technique.

Effect of Ce content on precipitation behavior in S31254 super austenitic stainless steel

The precipitation of Cr- and Mo-rich σ phases will seriously deteriorate the corrosion resistance and mechanical property of super austenitic stainless steel S31254. The precipitation of σ phase in S31254 containing B and Ce can be effectively inhibited by heat treatment to regulate trace elements. In this study, slow cooling combined low-temperature diffusion treatment (SCLDT) was adopted in S31254 containing B and Ce. Furthermore, the role of Ce was explored by comparing the precipitation behavior of samples with different Ce content. The results show that this new heat treatment strategy can better exert the inhibition effect of B and Ce on the precipitation of σ phase, and the inhibition effect is more obvious when the content of Ce is higher. It was found that the distribution of elements in the adjacent area of Ce at the GBs was almost the same as that in the matrix, which indicated that Ce could inhibit the formation of the precipitates along the GBs, and thus resulting in the precipitates distributed discontinuously. Besides, the B element was soluble in Mo-rich precipitates, and the B-containing precipitates was distributed in serrated pattern at GBs. In the 50Ce samples, serrated precipitates are more likely to form at the GBs, and the amount of precipitates was significantly reduced and discontinuities increased. Due to the homogeneous distribution of Cr in the serrated precipitates and their adjacent matrix zones, the phase interface has better resistance to intergranular corrosion.

Thermal deformation behavior and constitutive model of 42CrMo4 steel

42CrMo4 steel is a widely used high-strength alloy steel in various large-bearing manufacturing fields. The rheological stress curve of 42CrMo4 steel with the best heat treatment scheme was obtained through the thermal compression experiment. A mathematical model was established using the hyperbolic sine function to relate deformation temperature, strain rate, and flow stress during thermoplastic deformation. The flow stress curves of 42CrMo4 alloy steel show typical dynamic recovery and recrystallization characteristics.

SAG usage wear-resistant steel with rare retained austenite achieve trade-off between impact toughness and strength

The impact toughness is the key to determine the service life of high strength wear-resistant steel for the lining boards of large-scale semi-autogenous grinding mill (SAG). It is difficult to predict the impact fracture failure of lining boards when SAG is running, which can cause damage to equipment once it occurs. Therefore, novel high strength wear-resistant steel was designed to improve impact toughness in this study. It is interestingly found that the microstructure contained finer bainite/martensite, and rare retained austenite (around 2 vol.%), which achieved trade-off between impact toughness and strength after the optimal heat treatment scheme (900 °C normalizing → 900 °C quenching → 300 °C tempering). The element segregation of Al and Si was improved and the start temperature of martensitic transformation during quenching was reduced, resulting in the refinement of martensite laths. Thus, the higher density of high-angle grain boundary (HAGB) and dislocation were obtained, which contributed to excellent impact toughness. Based on the instrumented impact curve, the total impact energy can be divided into four parts: elastic deformation energy (Ee), plastic deformation energy (Ed), crack stable propagation energy (Ep1) and crack unstable propagation energy (Ep2). Traditional toughening mechanisms focus on Ep1, which was based on the tortuous crack propagation path. Our experimental results show that Ed was another effective control unit to ensure the toughness. The difference between Ed and Ep1 in improving absorption energy was discussed in detail by combining HAGB density and dislocation density.

Effects of natural aging on the artificial aging kinetics and responses of Al–5Mg–3Zn–1Cu (wt.%) alloy

Effects of natural aging (NA) on artificial aging (AA) behavior of Al–5Mg–3Zn–1Cu alloy were studied from the perspectives of kinetics and microstructure evolution. The results show that short-term NA (24 h) has marginal effects on AA at any temperature, as well as long-term NA (>240 h) on low-temperature AA (120 °C), but long-term NA can accelerate aging kinetics and alleviate severe hardening ability attenuation at high temperatures (>150 °C). Analysis of the precipitates evolution demonstrates that such attenuation is primarily attributable to coarsening and reduction of intragranular precipitates and is also slightly related to the formation of precipitate-free zone (PFZ). Three main factors cause the unfavorable microstructure in NA-free alloy at high temperatures AA: (1) Insufficient nucleation of intragranular precipitates induced by weakened nucleation driving force, larger critical nucleation radius, and rapid vacancy annihilation; (2) The nucleated precipitates are prone to coarsening; (3) The precipitation near grain boundary is obstructed due to the depletion of vacancies and solutes. Clusters formed during NA can inhibit the unfavorable microstructure by delaying the annealing out of excess vacancies, promoting the nucleation of precipitates, and elevating the activation energy for precipitation coarsening, thereby enhancing the hardening potential. This work is instructive for the formulation of heat treatment strategies for Al–Mg–Zn–Cu alloys with high Mg/Zn ratios.

Bonding mechanism and microstructural evolution in mechanically-alloyed nanodiamond-reinforced Al6061 composite particle deposits in cold spray

This study aimed at synthesizing a novel Al6061-ND metal matrix composite (MMC) particle feedstock via high-energy mechanical alloying (HE-MA) method for potential lightweighting applications. A material/milling design-of-experiment (DOE) was carried out to optimize the design parameters, including composite batch design, milling time, and ball diameter. It was found that the 5-mm diameter ball with 10:1 ball-to-powder ratio (BPR) could achieve the desired 5–100 μm particle size distribution (PSD) target with up to an 80 % yield within 2–4 h milling. Specifically, the addition of 1 wt% nanodiamond (ND), as opposed to 5 wt% or 10 wt%, in the MMC composite merited in its ability to produce superior PSD of the desired range. Despite milling being conducted in a controlled environment, oxide content was traced in the milled product indicating the need for a material-specific heat-treatment strategy incorporation. X-ray diffraction (XRD) analysis of both particles and deposits containing Al6061-1wt.%ND MMC revealed that (1) the synthesized Al6061 matrix contained nano crystallites in the order of 10–20 nm range; and (2) are linked to the pinning effect of the embedded ND in the matrix, respectively. High-resolution transmission electron microscopy (HRTEM) confirmed the formation of atomic-scale metallurgical bonding at the deposit-substrate interface, with conclusive evidence of the presence of ND in the Al matrix. Overall, the Al6061-1wt.%ND MMC, with optimized HE-MA synthesis method, was found to be a suitable candidate as feedstock for cold spray additive manufacturing of lightweight components.

A Predictive Model for the Non-Destructive Assessment of Stone Age Silcrete Heat Treatment Strategies

A Predictive Model for the Non-Destructive Assessment of Stone Age Silcrete Heat Treatment Strategies

Potential of Integrated Component-Driven Material Design to Improve Crash Box Performance

The crushing of crash boxes is a complex phenomenon characterized by a strong interaction of structural and material properties. Many attempts to improve their energy absorption by adopting one aspect resulted in unacceptable unprogressive bucking. Thus, special considerations are required for crash box optimization including both material and structural effects. In this study, the structural behavior of the crash box is analyzed and a new design approach is introduced to fulfill these requirements. Currently, components, processes, and materials are mainly developed independently. However, to exploit the full potential of modern materials in component design, integrative development work is necessary. Component performance-based requirements and corresponding local material properties must be taken into account concurrently. In this work, a component-driven material design approach is presented, in which local-material-property requirements are derived from component simulations. This new approach is demonstrated by the use case of a quasistatically deformed crash box produced out of steel DP600 for the optimization target “energy absorption”. The finite element simulations were carried out on the crash box, and required material properties for improving the crash box performance were derived based on the simulations. Heat treatment strategies were developed afterwards and experimentally validated to fulfill these requirements. The finite element (FE) simulations based on the experimentally extracted material properties reveal the potential of the component-driven material design approach to improve the crash box performance. The introduced approach enables exploiting the full energy-absorption capacity of the material while ensuring the desired service behavior of the component.