Heat-treated Specimens Research Articles

Effect of Interdendritic Precipitations on the Mechanical Properties of GBF or EMS Processed Al-Zn-Mg-Cu Alloys

The effects of nanoprecipitations on the mechanical properties of Al-Zn-Mg-Cu alloys after GBF (gas bubbling filtration) and EMS (electromagnetic stirring) casting were investigated. Dendritic cell structures were formed after GBF processing, while globular dendritic structures were nucleated after EMS processing. Equiaxed cell sizes were smaller in the EMS-processed specimens compared to the GBF-processed specimens, confirmed by EBSD (electron backscatter diffraction) analysis. Nanoprecipitations of η′ phases inside of dendrites were observed by TEM (transmission electron microscope), and other Fe-bearing compounds were located in the dendritic boundaries. The yield strength of the T4 and T6 heat-treated specimens was close to 400 MPa and 500 MPa, respectively. Fractographic analysis was performed to investigate the effect of precipitations on tensile fracture.

Fatigue crack growth under mixed-mode I + II and I + III in heat treated 42CrMo4 steel

The paper contains the results of an experimental investigation of fatigue crack development under mixed-mode I + II and I + III in heat-treated 42CrMo4 steel. Tests were performed on heat-treated compact tension shear specimens and rectangular cross-section specimens for mixed-mode I + III. Mixed-mode I + II tests were conducted for 30 and 60° loading angle, while the test for I + III mixed-mode was conducted for 30 and 45°. Additionally, the paper presents fracture analysis results of fatigue crack path development.

Effects of processing parameters on the fracture behaviour of cold roll bonded and accumulative roll bonded Al–Cu lamellar composites

Al–Cu composites were fabricated by cold roll bonding (CRB) and accumulative roll bonding (ARB) processes. The effects of different parameters were investigated on the failure mechanism of the composites. A scanning electron microscope (SEM) and an optical microscope (OM) were used to characterise the microstructures of the resulting composites. The peeled surfaces of the CRBed material revealed that micro-cracks were formed almost perpendicular to the rolling direction and caused the premature failure of the bonding during the peeling test. Also, tensile, microhardness and shear punch tests were conducted on the Al–Cu composites produced under different conditions. Failure analysis of the non-heat-treated composites revealed that the layers separated from the middle of ARBed specimens. However, these centre-line separations were alleviated in composites subjected to heat treatment, even though the initiation of inter-lamellar micro-cracks were observed due to the formation of intermetallic compounds for heat-treated specimens.

Effects of solution treatment temperature and time on the porosities and mechanical properties of vacuum die-casted and T6 heat-treated Al–Si–Mg alloy

Al–Si–Mg cast alloys can be imparted with a wide range of mechanical properties through heat treatment, thus meeting the required performance of various vehicle components. However, because of the characteristics of the high-pressure die casting process, the gas porosities in the casting can lead to blisters during the solution treatment of die-casting parts. Therefore, systematic studies on the solution temperature and solution time are required to prevent such blisters. In this study, the gas porosity and mechanical properties of T6 heat-treated specimens were evaluated under various solution treatment conditions. As the solution treatment temperature and time increased, the numbers and volume of individual gas porosity increased. On the other hand, there were little changes in the shrinkages upon heat treatment. As solution temperature and time increased, the area fraction of the eutectic Si particles and Mg2Si decreased slightly, whereas the area and sphericity of the eutectic Si and Mg2Si increased. As the solution treatment temperature and time increased, the ultimate tensile strength and yield strength increased, whereas the elongation tended to decrease. However, the maximum UTS and YS were obtained on treatment at 520 °C for 1.5 h.

Determine hardness and torsional resistance of AISI/SAE 4340 steel, treated by quenching at 860°C and tempering at 300°C, 350°C and 400°C

The present work consists in performing a quenching and tempering heat treatment to AISI 4340 steel at different temperatures in order to determine the torsional resistance and hardness, and thus, to make a comparison between the supply material and the heat-treated material to verify if its chemical and mechanical properties are improved. From the above, the results show that there is an in-crease in hardness between the different heat-treated specimens. In addition, an increase in its mechanical properties such as torsional resistance is provided, and it is concluded that performing a heat treatment has great benefits depending on how the AISI 4340 steel is going to be used.

Low Cycle Fatigue Characteristics of Oxygen-Free Copper for Electric Power Equipment

The effect of heat treatment on tensile and low cycle fatigue properties of the oxygen-free copper for electric power equipment was investigated. The heat treatment at 850 °C for 20 min, which corresponds to the vacuum brazing process, caused the grain growth and relaxation of strain by recrystallization, and thus, the residual stress in the oxygen-free copper was reduced. The tensile strength and 0.2% proof stress were decreased, and elongation was increased by the heat treatment accompanying recrystallization. The plastic strain in the heat-treated specimen was increased compared with that in the untreated specimen under the same stress amplitude condition, and thus, the low cycle fatigue life of the oxygen-free copper was degraded by the heat treatment. Striation was observed in the crack initiation area of the fractured surface in the case of the stress amplitude less than 100 MPa regardless of the presence of the heat treatment. With an increase in the stress amplitude, the river pattern and the quasicleavage fracture were mainly observed in the fracture surfaces of the untreated specimens, and they were observed with striations in the fracture surfaces of the heat-treated ones. The result of the electron backscattered diffraction (EBSD) analysis showed that the grain reference orientation deviation (GROD) map was confirmed to be effective to investigate the fatigue damage degree in the grain by low cycle fatigue. In addition, the EBSD analysis revealed that the grains were deformed, and the GROD value reached approximately 28° in the fractured areas of heat-treated specimens after the low cycle fatigue test.

Effect of heat treatment on grain boundary carbides and primary water stress corrosion cracking resistance of Alloy 182 weld

Alloy 182 welds were heat-treated at 600, 620, and 650 °C for 10 h. The primary water stress corrosion cracking initiation test showed significant improvement in the cracking resistance of the heat-treated specimens over the as-welded specimens. Microstructure analysis demonstrated that Cr23C6 grain boundary carbides dominated in the as-welded specimen, while Cr7C3 carbides were dominant after heat treatment. The depth of grain boundary oxidation ahead of the crack tip was large for the as-welded specimen, but less for the heat-treated specimens. Therefore, the presence of Cr7C3 carbides, in part, contributed to the improved cracking resistance of the Alloy 182 weld.

Multiphysics simulation and validation of microwave melting characteristics of AA6061 by finite element analysis

Microwave processing of metallic material is an emerging process compared to conventional ones. In the present work microwave heating of bulk specimen of AA6061 is studied experimentally and numerically to understand heating behaviour of metal sample and tooling materials in an electromagnetic field. A three-dimensional model of the process has been generated using the COMSOL Multiphysics tool. The electric field distribution has been observed with a maximum value of 4.29 × 104 (V/m) in the centre of the cavity. The average volumetric heating rate has been reached to above 700°C within 600 s. The resistive losses have been observed with the value of 2.37 × 106 (W/m3) due to electromagnetic field distribution and tooling material properties. Temperature profiles obtained through experimental trials and simulation studies have been analysed and found in almost similar propensity within 5% of error.

Contribution of hot isostatic pressing on densification, microstructure evolution, and mechanical anisotropy of additively manufactured IN718 Ni-based superalloy

Microstructural defects and mechanical anisotropy are regarded as the main obstacles in additively manufactured, laser powder bed fusion (LPBF) IN718 superalloy, decelerating industrial development of the related components. Hot isostatic pressing (HIP) is an effective solution to overcome these challenges. In this study, standard heat treatment (HT) with and without prior HIPing was applied to the LPBF IN718 and the impacts of the HIP operation on microstructures and room- and high-temperature mechanical anisotropy were studied. Observations showed that intrinsic pores and large contour defects were significantly closed by HIPing and consequently the relative density enhanced from 99.50% to 99.96%. The highly distorted columnar structure of the HT specimen was broken down due to recrystallization, and an equiaxed morphology with about 5-time coarser grain size appeared in the HIP + HT specimens. Although too many transgranular precipitates were observed in the HT microstructure, they were just formed at grain boundaries when HIP was carried out before HT. Furthermore, the formation of nano-scale γʺ/γʹ/γʺ co-precipitates was favored by HIPing which had a positive effect on strengthening. It was also found that prior HIPing effectively mitigated mechanical anisotropy both at room- and high-temperatures by influencing several factors. The degree of room-temperature mechanical anisotropy was reduced from 11.6% (HT) to 3.5% (HIP + HT) by HIPing and mitigated from 4% to 2% at 650 °C. While the fracture mechanism was orientation-dependent in the HT samples, it was completely ductile for the HIP + HT samples in all circumstances.

Effect of heat treatment on the microstructure and mechanical properties of cryogenic rolling 2195 Al–Cu–Li alloy

Cryogenic deformation had been proved to promote the strength and toughness in several kinds of alloys. The microstructure responses and mechanical properties of cryogenic rolling 2195 Al–Cu–Li alloy after heat treatment were investigated systematically in this study. The annealed 2195 Al–Cu–Li alloy plates were subjected to cryogenic rolling to a reduction of 80% at −190 °C, followed by the solid solution at 540 °C for 2 h and aging treatment at 175 °C for different durations. Both the tensile strength and ductility of heat-treated specimen increased compared with the as-rolled sample, while the yield strength of the cryogenic rolling sample was higher anomaly. In addition, the tensile strength, yield strength, and elongation of the heat-treated samples increased firstly and then decreased with the increase of aging time. The number of T1 phases was initially increased with the aging time extended to 12 h and decreased after the aging duration was increased to 16 h. While the number of θ' gradually decreases with aging time increased. Based on the precipitation kinetics, aging kinetics, and dislocation theory, a physically based model considering the variation of dislocation density and volume fraction of the T1 phase and aging duration was established in this paper, which is in good agreement with the experimental data. Meanwhile, a strong connection between the dislocation density and fraction of the T1 phase and aging duration is established.

The influence of process parameters on the impact resistance of 3D printed PLA specimens under water-absorption and heat-treated conditions

Purpose The purpose of this paper is to analyse the effect of water absorption and heat treatment on the impact strength of three-dimensional (3D) printed Izod specimens. A low-cost post-processing technique is proposed to improve the impact strength of 3D printed parts substantially. Design/methodology/approach In the present work, the effect of water absorption and the heat-treatment on the impact resistance of 3D printed poly-lactic acid parts possessing different layer-height, build-orientation and raster-orientation was studied. Water absorption tests were conducted in distilled water and it was observed that the water- absorption in specimens follows the Fickian diffusion mechanism. A set of specimens was heat-treated at 120°C for 1 h using an induction furnace. Post water absorption and heat-treatment a significant increase in the impact resistance is noticed and especially a steep increase in impact resistance is observed in heat-treated specimens. Findings Experimental findings show that raster orientation played a major role in the impact resistance of a 3D printed structure in comparison to other process parameters. The order of influence of process parameters on the impact strength of specimens was disclosed by the mean effect plots. In terms of processing time and cost, the post-processing heat-treatment approach was found to be convenient compared to the water absorption technique. Originality/value This paper presents a new set of low-cost post-processing techniques (water-absorption and heat-treatment) for improving the impact strength of 3D printed specimens.

Application of the subsecond calorimetry technique with both contact and radiance temperature measurements: case study on solid phase tungsten at very high temperatures

This work presents an application of the subsecond calorimetry technique at very high temperatures, which uses both contact and radiance temperature measurements. This technique is normally applied for thermophysical characterization of high temperature solid phase materials in the temperature range from ambient up to about 2600 K, which is the limit of the standard tungsten-rhenium thermocouple use. Simultaneously with contact temperature measurements, noncontact or radiance temperature detection may be performed in the approximate range from 1000 to 2600 K in order to acquire information on spectral normal emissivity of specimen under test. In this study, however, the specimen is heated above 2600 K and, then, the temperature is measured only by the noncontact mean. In the extended temperature range, the obtained values of the spectral normal emissivity are extrapolated for each experimental run, which makes possible a conversion from radiance to absolute specimen temperature. In order to test this application, a pure polycrystalline specimen of tungsten in the form of rod, 3 mm in diameter and 200 mm in length, has been used. The specimen has been heated in vacuum environment of about 10–4 mbar by short pulses of high DC current with a gradual increase of the total heating time from about 0.5–2.5 s. During the specimen heating and the beginning of the cooling period, four sets of experimental data have been recorded and reduced by using the corresponding data reduction procedure. Obtained results of specific heat and specific electrical resistivity from ambient to 3700 K, total hemispherical emissivity from 1000 to 3700 K and spectral normal emissivity from 1000 to 2600 K (extrapolated to 3700 K) are presented, discussed and compared with related literature data.

Hydrogen Diffusion and Trapping in Laser Additively Manufactured Ultra-High Strength AerMet100 Steel

Hydrogen trapping and the permeation behavior of laser additively manufactured (LAM) AerMet100 (UNS K92580) steel with an as-deposited specimen (AD) and after three types of heat-treated specimens (bainite microstructure [BM], tempered bainite and martensite microstructure [TBMM], and tempered martensite [TM]) was investigated. At least three types of different hydrogen traps were identified in each microstructure of the LAM steel, including both reversible and irreversible H traps. For as-deposited microstructure, the main reversible H trap states are related to the precipitation of M3C carbides associated with a detrapping activation energy (Ed) of 17.3±0.2 kJ/mol. After heat treatment, the dominant reversible hydrogen trap states in the tempered martensite microstructure have a different Ed value of 19.3±0.5 kJ/mol, which is attributed to the precipitation of highly coherent M2C carbides. In comparison with the reported Ed value of approximately 21.4 kJ/mol for main reversible hydrogen traps in wrought UNS K92580 steel, the lower Ed value in the LAM steel is closely related to the composition change of M2C carbides. In all of the H precharged samples, the diffusible and total H concentration of the TM specimen and the TBMM specimen are about three to four times higher than that of the AD specimen and the BM specimen. The TM specimen with tempered martensite microstructure has the highest diffusible and total H concentration due to its high density of dominantly reversible H traps. The effective hydrogen diffusion coefficient (Deff) of the LAM steel is on the order of 10−9 cm2/s, and decreases with increasing density of the dominant reversible H traps brought about by heat treatment. The LAM steel has a comparable Deff of about 2.8 × 10−9 cm2/s compared to the wrought steel of a similar yield strength (∼1,750 MPa),

Effects of heat treatment on microstructures and mechanical properties of GH4169/K418 functionally graded material fabricated by laser melting deposition

Blade-Integrated Disk is a perspective one-piece design strategy of turbine engine components with high efficiency of air compression. In this work, a functionally graded material composed of GH4169 and K418 is processed by laser melting deposition technique, followed by suitable heat treatment to optimize the microstructures and mechanical properties. Microstructure characterization, tensile and small punch creep tests of the functionally graded GH4169/K418 specimens were conducted. It is found that the as-built functionally graded material exhibits the continuous microstructure and the gradual composition transition region without sharp interfaces and hot cracks. The tensile yield strength, ultimate strength and elongation of the graded specimens at fracture achieved 726 MPa, 1044 MPa and 13.2%, respectively after the specimens were heat-treated through homogenization at 1100 °C for 1.5 h, solution treatment at 980 °C for 1 h and standard double aging. The creep life of the GH4169/K418 graded specimens at 650 °C and 850 N was mainly affected by the microstructure formed at different build heights of the as-built and heat-treated specimens. The relationship between the microstructures and tensile as well as creep properties of the graded specimens is elucidated.

Influence of NaCl environment on stress corrosion cracking of additive manufactured Ti-6Al-4V alloy

A slow strain rate test (SSRT) was performed to evaluate the stress corrosion cracking (SCC) of the Ti-6Al-4V alloy specimens developed by the Laser Powder Bed Fusion (LPBF) process. The test environment was open-air and 3.5% aqueous NaCl solutions. To study the crack growth mechanism and induced microstructure, a test was performed on the as-prepared specimen, the results were then compared with the heat-treated specimen. The strain rate was set to analyze the susceptibility of LPBF processed Ti-6Al-4V alloy specimens for stress corrosion cracking and its effect on the microstructure. The fractography analysis revealed that the shallow dimple was formed with the breaking planes of the α-lath separation and the geometry of the border profile of β-grains on the heat-treated specimen. Whereas, for the as-prepared specimen, the crack profile of the α′ - martensite structure was distinctly viewed. From the stress vs. strain and time curves of the SSRT results, this study provides an overview of the variation in the internal geometry of the Ti-6Al-6V alloy produced by the additive manufacturing process, which is hardly identified through rapid tensile testing. When comparing the SSRT results of the open air and aqueous NaCl solution, the dissolution of the passive layer from the surface of the additively produced Ti-6Al-4V alloy specimen in NaCl solution has significantly varied the tensile performance during the SSRT test. The dissolution was also confirmed by the XPS and the weight loss analysis.

Investigation of the Tribological and Mechanical Properties of Boron Steels in Terms of Potential Usage in Agricultural Applications

Boron steels are increasingly used material especially in industrial applications requiring high wear resistance. The main area of usage of this type of steel is tillage tools which are working in harsh conditions. In addition to the abrasive wear resistance, impact toughness is also required properties. In this study, the effect of cryogenic treatment on 30MnB5 boron steel used in agricultural mechanization is investigated in terms of the tribological and mechanical properties. Charpy impact test, the hardness and the abrasive wear tests are performed on untreated, heat treated and cryogenically treated of 30MnB5 steel. It is observed that the hardness of the specimen is slightly decreased but impact toughness is increased for the quenched and cryo treated specimen in comparison to conventionally heat-treated specimen.

Determination of the mixed mode I/II fracture characteristics of heat-treated granite specimens based on the extended finite element method

Previous researches mainly concentrate on investigating the mixed mode I/II fracture characteristics of heat-treated rocks through laboratory tests. This paper makes an effort to obtain the mixed mode fracture characteristics of heat-treated granite by means of the extended finite element method (XFEM), which is based on the cohesive zone model (CZM). The experimentally obtained unstable fracture toughness, tensile strength and tensile elastic modulus of the granite after being subjected to different high temperatures are integrated into the numerical simulation models to estimate the fracture behaviours of the cracked straight-through notch Brazilian disc (CSTBD) specimens under mixed mode loading. Findings and observations from this study indicate that by applying the unstable fracture toughness as the mode independent cohesive zone fracture parameter into the numerical models, although some limitations still exist, the numerical models can successfully predict the fracture loads and the crack propagation paths of the CSTBD specimens under mixed mode loading within the temperature range of 25–600 °C. This paper provides a numerical approach to investigate the mixed mode I/II fracture characteristics of thermally treated rocks.

Morphogenesis of Silicovanadate Glasses: Investigation of Physical Properties

In this article, we demonstrate the synthesis and various characterizations of silicovanadate glasses of xSiO2 (100-x)V2O5 for x = (10-50) mol%, glasses which are prepared by the melt quenching method. FTIR spectra analysis confirms dominant chemical bonds among silicon, vanadium, and oxygen elements as expected. The assigned chemical bonds are Si-O-Si, O-Si-O, V-O-V, V=O, Si-O-V, O-H from FTIR spectra. The IR spectra of all glass specimens were baseline corrected and deconvoluted to distinct peaks of chemical bonds in overlapped Gaussians with employing computer program. The chemical bond's position shifted and affected due to the addition of vanadium pentaoxide by the heat treatment process. The X-ray diffractions (XRD) patterns of glass samples exhibit partial crystalline nature for 10S90V and 50S50V that is influenced by high-temperature application. The differential thermal analysis (DTA) of base and heat-treated specimen determines the glass transition (Tg), crystallization, and liquidus temperature with prominent exothermic and endothermic reactions. It is seen that the pH of the glass specimens abruptly changes due to the surface effect of V2O5 while bulk effects become robust after about 30 minutes. The measured hardness of three glass samples shows high HV-values and a slight linear increment is observed for higher V2O5 contents. The current-voltage (I-V) characteristic connected to the electrical conductivity of the glass specimen (20S80V) shows a relatively higher and non-linear trend of conductivity which reveals the behavior of a semiconductor. Moreover, temperature-dependent electrical resistivity measurement of the same sample (20S80V) manifests the semiconducting nature up to 427 °C as well.

Influence of heat treatment on the microstructure and corrosion properties of the Inconel-625 clad deposited by microwave heating

The present work explores the viability of using the microwave heating technique to apply Inconel-625 cladding to a stainless steel (SS-316) substrate. As-deposited clad specimens were subjected to various post-heat-treatments. These treatments included (1) a direct-aged (DA) treatment (2) solution at 981 °C followed by a DA treatment (981SHT) (3) solution at 1081 °C followed by DA treatment (1081SHT). Clad specimens displayed a gradual change in microstructure from planar to cellular to the dendritic depending upon the cooling rate experienced by the molten clad powder during the microwave cladding process. Due to precipitation of hardening particles (γ′), the heat-treated clad specimens displayed superior hardness than as-deposited clad specimen. In the interdendritic spaces/grain boundaries, heat-treatment at 981 °C induces a major reduction in the size of Laves process with a needle precipitation of δ (Ni3Nb) phase. Meanwhile, the heat-treatment at 1081 °C nearly dissolved the entire Laves phase in the microstructure. The corrosion test revealed that the coated samples at all conditions exhibit around 2 to 2.5 times more noble corrosion potential (corrosion resistance) than the uncoated samples. Moreover, the corrosion resistance of the post-treated sample decreases dramatically than that of the as-deposited clad sample, as heat-treatment improved the precipitate phase formation.

Usability of Ultrasonic Frequency Testing for Rapid Generation of High and Very High Cycle Fatigue Data.

Ultrasonic fatigue testing is an increasingly used method to study the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of materials. Specimens are cycled at an ultrasonic frequency, which leads to a drastic reduction of testing times. This work focused on summarising the current understanding, based on literature data and original work, whether and how fatigue properties measured with ultrasonic and conventional equipment are comparable. Aluminium alloys are not strain-rate sensitive. A weaker influence of air humidity at ultrasonic frequencies may lead to prolonged lifetimes in some alloys, and tests in high humidity or distilled water can better approximate environmental conditions at low frequencies. High-strength steels are insensitive to the cycling frequency. Strain rate sensitivity of ferrite causes prolonged lifetimes in those steels that show crack initiation in the ferritic phase. Austenitic stainless steels are less prone to frequency effects. Fatigue properties of titanium alloys and nickel alloys are insensitive to testing frequency. Limited data for magnesium alloys and graphite suggest no frequency influence. Ultrasonic fatigue tests of a glass fibre-reinforced polymer delivered comparable lifetimes to servo-hydraulic tests, suggesting that high-frequency testing is, in principle, applicable to fibre-reinforced polymer composites. The use of equipment with closed-loop control of vibration amplitude and resonance frequency is strongly advised since this guarantees high accuracy and reproducibility of ultrasonic tests. Pulsed loading and appropriate cooling serve to avoid specimen heating.