Papers by Keyword: Heat Treatment

Abstract: A study of the mechanical properties of hybrid additive manufactured IN718 components is presented, optimising mechanical properties due to an in-situ high-speed milling and different heat treatment processes. At first, the impact of different heat treatment processes is investigated, as the changes in microstructure during the process lead to different mechanical properties. Static and dynamic mechanical load behaviour is tested, quantifying microstructural changes by means of the Ultimate Tensile Strength (UTS) and the endurance limit. Furthermore, sole PBF-LB/M- and hybrid built components are compared, investigating the effect of a surface finish on the static and dynamic load behaviour, as superficial cracks and melting errors diminish the UTS and the endurance limit of PBF-LB/M-built components. Within these experiments, a change of fatigue behaviour for the heat-treatedstates can be observed, compared to the as-built state of the PBF-LB/M, as the development of different phases during heat treatment leads to an improvement of the endurance limit for, e.g., solution and ageing treated components. Additionally, the improvement of the surface quality to Ra = 2 µm leads to a significant increase of the dynamic mechanical load behaviour of hybrid-built components, as superficial cracks and surface defects are reduced.

Abstract: Controlling nanomaterials' morphology and molecular structures offers many advantages, such as tunable material properties, lightweight, and high surface-to-volume ratio. Studies have focused on electrospinning as one of the most effective methods in fabricating nanofibrous materials and have closely considered various post-fabrication techniques to improve mechanical properties. This work investigates the effect of constrained heating at 100°C, 110°C and 120°C on the morphology, the static and dynamic mechanical properties, and crystallization properties of electrospun Poly(vinyl) alcohol (PVA) nanofibrous membranes. Constrained heating of PVA nanofibrous membranes at 120°C has the best overall improvement. As compared to unheated samples, the Young’s modulus is multiplied by more than 3, the tensile strength increases more than 75%. At the same time, the fiber diameter decreases from 282.4 nm to 222.2 nm, and the degree of crystallinity and crystallite size increases by more than 10% and about 75%, respectively. This change in molecular structure and the increase in mechanical properties suggest that constrained heating should be further explored to diversify load bearing applications.

Abstract: 17-4 Precipitation hardenable (PH) stainless steel (SS) is useful for applications that require a combination of high strength and corrosion resistance. However, when produced through selective laser melting (SLM), it has a distinct microstructure with significant composition and phase variations based on the process parameters and post processing heat treatment conditions. Therefore, the present study examines how process parameters, such as scanning speed and hatch distance, affect the microstructural, and corrosion characteristics of additively manufactured (AM) 17-4 PH stainless steel samples. Post-processing heat treatment resulted in a uniform and reproducible microstructure in SLM samples. Heat-treated AM samples were assessed in a 3.5 wt. % NaCl solution using electrochemical impedance spectroscopy (EIS). The specimen with an energy density of 39.06 J/mm³ exhibited the lowest open circuit potential value, indicating a favorable tendency to form a passive film. The sample with 66.96 J/mm³ exhibits enhanced corrosion resistance attributed to robust protective performance facilitated by a dense network of precipitates and finer grain size. This heightened resistance is further supported by the sample's highest corrosion layer resistance and charge transfer resistance.

Abstract: Advanced high-strength steels (AHSS) have their current applications directed mainly to the automotive industry, where they use modern metallurgical techniques to develop microstructures with retained austenite, which leads to an improvement in the combination of strength and ductility through transformation-induced-plasticity (TRIP). The main priority of the research work will be a detailed examination and optimization of the heat treatment parameters of medium-manganese steels, specifically by the Quenching and Partitioning (Q&P) method and the expansion of experimental data related to the increase of wear resistance of these materials. The issue of the application of medium-manganese high-strength AHSS steels in the field of tribology is currently very relevant. Mid-manganese AHSS steels, which show significant wear resistance, have the potential to replace traditional Hadfield Mn steels that contain 10-14 wt. % manganese. With the help of specifically designed heating and cooling cycles, it is possible to improve their wear resistance through metastable retained austenite, which has significant potential in demanding industrial environments. This scientific study examines the possibilities of increasing the economic efficiency of the production and use of AHSS steels in various industrial areas and at the same time reducing costs compared to expensive wear-resistant steels. A key aspect of the research is the experimental evaluation of heat treatment optimization to maximize resistance to mechanical damage and extend the life of materials in various applications.

Abstract: In this paper, the steels used in MN knife mills, which are used for plastic recycling, are investigated. 90MnCrV8 steel is commonly used in these mills, which will be replaced by X153CrMoV12 steel. The main goal of the presented contribution is to perform tribological tests and verify the wear rate of both steels experimentally with subsequent practical verification in the knife mill MN. Partial results relate to the analysis of hardness, roughness, and overall wear mechanism. A hardened steel ball of material G40 with a diameter of 4.76 mm was used as the contact material. The steel ball performed reciprocal linear motion on the surface of the experimental materials at room temperature and without the use of lubrication. The measurements were carried out in three-time intervals of 20, 30 and 40 min. The experimental material X153CrMoV12 can fully replace the material 90MnCrV8 in processes where its degradation occurs due to the friction mechanism. The material X153CrMoV12 showed significantly better results in all the values ​​we measured. It can be expected that the knife in the MN knife mill made of X153CrMoV12 steel will last several times longer in the working environment, which was also proven by practical verification in production.

Abstract: The effects of heat treatment in different ambient pressures or oxygen concentration on the wettability of the titanium (Ti) surface were examined. Polished titanium plates were heat-treated at various temperatures and periods in the pressure-controlled or oxygen concentration-controlled atmospheres. The wettability was evaluated by water contact angle measurement. The X-ray photoelectron spectroscopy was performed on the heat-treated and stored Ti surface to analyze adsorbates and surface products. The heat-treated Ti in the atmospheric air became hydrophilic due to the desorption of hydrocarbons on the surface. Then, the adsorption of hydrocarbons during storage in the atmospheric air returned its wettability to that before heating. On the other hand, the heat-treated Ti in a vacuum (low ambient pressures) or low oxygen concentration became hydrophobic due to an increase in the CH/OH (hydrocarbon/hydroxyl group) ratio on the surface. The wettability of hydrophobized Ti retained its wettability during storage in the atmospheric air.

Abstract: Additive manufacturing (AM) has gained significant attention as a promising technique for producing complex-shaped components, particularly in the aerospace and biomedical industries. However, post-processing steps, such as heat treatment, can significantly influence the mechanical properties of additively manufactured parts. This research investigates the effect of supertransus heat treatment on the compressive behavior of Ti-6Al-4V (ELI) alloy produced through additive manufacturing. The specimens were subjected to a series of heat treatment cycles, including solution treatment and aging above the β-transus temperature range. Compressive tests were conducted on as-received and heat-treated samples to evaluate their mechanical properties and deformation behavior. Microstructure characterization was performed using optical microscopy (OM) and scanning electron microscopy (SEM). The results revealed that the microstructure of the as-built material primarily consisted of columnar grains and acicular α' martensite. Significant variations in microstructure were observed in heat-treated samples, particularly with changes in the cooling rate. The microstructure changes closely correlated with the compressive properties of the heat-treated samples. The heat-treated samples showed a reduction in compressive strength compared to the as-received samples but exhibited improved elongation behavior. These findings contribute to the broader understanding of post-processing effects on the mechanical properties of additively manufactured materials, enabling the development of high-performance components for various applications.

Abstract: Cement-based piezoelectric composites (PECs) consist of calcium aluminate cement (CAC) and lead zirconate titanate (PZT), each accounting for 50 vol.% that can be used for structural health monitoring (SHM) due to their excellent compatibility with cementitious structures. The presence of free water inside the specimen significantly affects the polarization difficulty and piezoelectricity of PEC. Four treatment methods include vacuum drying, ethanol dehydration, non-heat treatment (untreated), and heat treatment to reduce free water in specimens. Experimental results show that reducing the free water content of PEC specimens through vacuum drying, ethanol dehydration, and heat treatment during the manufacturing process can enhance PEC performance. The free water reduction effect of PEC specimens was most with the heat treatment, followed by ethanol dehydration, and least by vacuum drying. The specimen’s dielectric loss and relative permittivity before polarization decreased if heat treatment and ethanol dehydration were applied. Heat-treated specimens provide optimal relative permittivity and piezoelectric strain constant after polarization. For the piezoelectric voltage constant, ethanol dehydration of the specimen is better than other treatments. The treatment method affects the resonance frequency value and the electromechanical coupling coefficient of the specimen. Water removal of specimens is not a suitable treatment method to increase the electromechanical coupling coefficient.

Abstract: A dilute Al-0.083Sc-0.21Zr-0.07Y-0.025Co-0.063Ni-0.10Si (in wt.%) alloy is investigated by hardness and conductivity tests and phase obervation via TEM, HREM and STEM-EDS analysis. The results showed that the alloy achieved a peak hardness of 54.5 HV after annealing at 400°C for 36h while electrical conductivity also reached a plateau. Al₃(Sc,Zr,Y) phase, AlFeNi phase and AlScNiSi phase co-exist in the alloy. Al₃(Sc,Zr,Y) phase possessed spherical shape with a dense distribution and a size range of 6-13nm, the average size, volume fraction and number density were 9.0nm, 0.38% and 6.07×10²¹, respectively. The quantity of AlFeNi phase and AlScNiSi phase are quite small and they had a sparse distribution. Thereinto, the former one possessed rod shape and was coherent with the matrix. Co did not participiate phase formation. This provided a new thought for heat-resistant alloy design.

Abstract: The 7xxx series Al-Zn-Mg-Cu alloys are stronger than other age-hardenable aluminum alloys at their maximum aging state (T6). Despite having a wide range of applications currently, 7075 aluminum (AA7075) still has certain restrictions because of flaws such stress corrosion cracking (SCC) susceptibility. Here, AA 7075-T6 aluminum alloys underwent a salt spray corrosion test to study pitting corrosion. A shot-blasting procedure in a solution containing 3.5% sodium chloride was also used after heat treatment and aging for five days. Refined microstructure, residual stress, and other surface features were identified. Localized corrosion and the propagation of stress cracks were evaluated in relation to the surface properties, including the treated microstructure and residual stress. The aged sample's microstructure was better after heat treatment compared to the control sample after shot peening. The elongation was caused by the maximum strength's value dropping from 476 MPa to 375 MPa. Due to the dispersion of precipitates during curing, the heat treatment caused the depth of stress corrosion cracking for the double shot to decrease.