Solution Heat Treatment Conditions Research Articles

Surveying the Effects of Aging a High C-Containing Co-Based Superalloy From the As-Cast and Solution Heat-Treated Conditions

The microstructure of the high carbon-containing cobalt-based superalloy, Co-101, has been studied in the as-cast state and following a variety of heat treatments. In the as-cast state both M7C3 and Mo-rich M23C6 carbides were observed in the interdendritic regions. After thermal exposure at temperatures between 1000 °C and 1250 °C for 1, 10, and 100 hours, the M7C3 interdendritic carbide network was observed to transform into a Mo-lean M23C6 carbide. These changes were rationalized with thermodynamic calculations. The carbide transformation liberated carbide-forming elements that resulted in the precipitation of intragranular carbides in the dendritic regions at temperatures below 1150 °C. These carbides in the cast-aged material preferentially formed at the dendrite peripheries early during exposure, leading to wide particle size distributions. Peak hardness in the cast-aged material was attained within the first 10 hours of exposure and softening was observed thereafter. After solution heat treating at 1250 °C for 10 hours, the microstructure of Co-101 comprised an M23C6 interdendritic carbide network and solid solution dendrites supersaturated with carbide-forming elements. Subsequent aging of this microstructure for 100 hours at 900 °C led to a high number density and narrow particle size distribution of intragranular carbides. The characteristics of these carbides in the solution-aged material resulted in greater hardness, which was retained for longer durations of exposure, than the cast-aged specimens.

Effect of solution heat treatment on the microstructure and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam

The effect of various solution heat treatment temperatures (i.e., 1120, 1160, 1200 and 1240 °C) on the microstructure, grain morphology and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam (PBF-LB) was investigated. Microstructural analyses showed that the high-temperature gradient and rapid solidification of the PBF-LB processing caused different resulting microstructures compared to conventionally produced counterparts. The melt pool morphologies and laser scanning paths were examined in the as-fabricated samples in the XZ- and XY-planes, respectively. After the application of solution heat treatment at 1120 °C, the as-fabricated PBF-LB initial microstructure was still apparent. For solution heat treatments of 1200 °C and above, the melt pool and scanning path morphologies disappeared and converted into a mixture of columnar grains in the XZ-plane and equiaxed grains in the XY-plane. On the other hand, large equiaxed grains were observed when the samples were solutionized at 1240 °C. Additionally, γ′ phase precipitated within the matrix after all solution heat treatment conditions, which led to increase in the microhardness values. According to electron backscatter diffraction (EBSD) analyses, both as-fabricated and solution heat-treated samples had intense texture with {001} plane normal parallel to the building direction. The first recrystallized grains began to appear when the samples were subjected to the solution heat treatment at 1160 °C and the fraction of the recrystallized grains increased with increasing temperature, as supported by kernel average misorientation (KAM) and grain spread orientation (GOS) analyses.

The effect of increasing hafnium on the microstructure, phase transformation temperatures and hardness of TiPtHf potential shape memory alloys

Shape Memory Alloys (SMAs) are popular due to their ability to regain their original shape after plastic deformation. Binary TiPt alloys have low shape memory effects and as such, alloying elements are added to improve these properties. The effect of alloying and increasing the Hf in binary Ti50Pt50 to form ternary Ti50Pt50−xHfx (x=6.25,12.5 and 18,25 at.%) on the microstructure, transformation temperatures and hardness in the as cast and solution heat treatment conditions were investigated. In the as-cast condition SEM EDS analysis showed that alloying with Hf resulted in the formation of dark grey interdendritic regions comprised of Ti-rich phases and the increase in Hf content (at. %) led to an increase in the size of these interdendrites. Solution heat treatment (SHT) of the alloy led to a decrease in the size of the dark grey interdendritic regions and the formation and increase of dark black regions with increasing Hf content (at. %). Differential scanning calorimetry showed that partial substitution of Pt with 6.25 at. % Hf decreased the transformation temperature of the alloy below that of Ti50Pt50 in both conditions. Increase in to Hf 12.5 and 18.25 at. % increased the transformation temperatures above those of Ti50Pt50 binary alloy in both conditions. SHT of 12.5 at. % Hf significantly reduced the AS and MS temperatures. Alloying and increase in Hf content (at. %) increased the hardness of the alloys above that of Ti50Pt50. SHT increased the hardness of the alloys above that of Ti50Pt50 and the as-cast alloys.

Effect of precipitation state on plastic anisotropy in sheets of the age-hardenable aluminium alloys AA 6016 and AA 7021

We analyse flow stress, work hardening and plastic anisotropy of two heat-treatable Al alloys of the AA 6xxx and AA 7xxx series in dependence on state and morphology of the age-hardening precipitates. Sheets in the solution heat-treated condition were subjected to various ageing treatments in order to vary the precipitation state while maintaining crystallographic texture and grain shape. Accordingly, differences in the anisotropy obtained for various temper conditions could directly be attributed to the precipitates. Plastic anisotropy was assessed from the in-plane variations in yield strength and plastic strain ratios (r values). The texture-induced anisotropy was further modelled with polycrystal-plasticity simulations; therewith, the anisotropy obtained in the solution heat-treated, i.e. particle-free, sheets could be explained. In alloy AA 6016 with shearable needle-shaped β′′-particles, the effect of precipitates on plastic anisotropy was negligible compared to the pervasive effect of texture. Alloy AA 7021 containing plate-like η′-particles with low aspect ratio displayed a noticeable weakening of the texture-induced anisotropy with progressing heat treatment and the resulting changes in precipitation state. This weakening of anisotropy was attributed to the development of non-directional back-stresses due to the storage of Orowan loops around the non-shearable η′-precipitates during the early stages of straining.

Laser powder bed fused Inconel 718 in stress-relieved and solution heat-treated conditions

Inconel 718 superalloy cylindrical rods were fabricated using the laser powder bed fusion (L-PBF) technology in the vertical orientation. The rods were stress-relieved at 980 °C for 15 min before cutting them from the build plate. The microstructure in this condition exhibited a significant amount of undesirable needle-like δ-phase precipitates and a small amount of interdendritic Laves phase that is finer in size. Differential Scanning Calorimetry (DSC) was used to determine the temperatures for solid-state phase transformations and appropriate temperature for solution-treatment. Solution-treatment was performed at 1065 °C for 1 h, followed by air cooling. The microstructures were characterized with specific reference to δ-phase and Nb segregation. Solution-treatment at 1065 °C was found to result in a significant elimination of micro-segregation (mainly Nb), complete dissolution of δ phase, considerable Laves dissolution, and partly undissolved carbide particles (few nm in size). Solution-treatment did not produce a significant change in the grain morphology (columnar dendritic) on a plane parallel to the build direction but more recrystallized and equiaxed grains were formed on a plane perpendicular to the build direction. The hardness of the solution-treated sample is comparable with wrought 718 alloys but lesser (115 HV) than in the stress-relieved condition attributing to the annihilation of dislocation tangles.

Evaluation of Vickers Hardness Number of Al-Si Alloy Under Heat Treated Conditions

The paper deal with the hardness property assessment of various Al-Si alloys under heat treated conditions. The tested specimens have the compositions of Si with percentages such as 12 18 and 24. The fabrication of the selected composition is carried out by melting the material to the melting temperature of around 800°C. The material is subjected to solutionised heat treatment for 3 hours at 500°C, 520°C and 535°C and quenched in water. Further aging is carried out at 155°C for 2 hours, 5 hours and 8 hours respectively for 500°C, 520°C and 535°C of solution heat treatment condition. The hardness property is evaluated using Vickers Hardness tester as per the standards of ASTM- E92. Thorough comparison of Vickers hardness number is performed among the as- cast and various heat treated environment. Desirable properties of alloy are observed at 520°C solutionised heat treatment & 5 hours of precipitation hardening at 155°C for 18% of Silicon composition. The hardness value decreases due to the increase in percentage of silicon and the values are observed.

Comprehensive microstructural investigation during dissimilar transient liquid phase bonding cobalt-based superalloys by BNi-9 amorphous interlayer foil

Cobalt-based X-45 and FSX-414 superalloys with interlayer BNi-9 have been bonded by a transient liquid phase bonding process at a constant temperature of 1150 °C with the holding times of 1, 10, 60, 120, 180 and 240 min. Microstructural changes of base metals showed that the conditions of 1150 °C/240 min can be used to joint base metals, in such a way that the primary carbides of M 6 C and M 23 C 6 are significantly dissolved in the matrix, forming a supersaturated solid solution. Examination of the bonded specimens showed that during heating up to the bonding stage, Nickel-rich carbo-boride deposits are formed at the interface between the filler metal and the base alloys due to the solid-state diffusion of boron element. The next generation of carbo-borides is formed in the diffusion affected zone of the base metals, which are also Cobalt–Chromium–Tungsten–Molybdenum-rich carbo-borides. Bonding at 1150 °C/1 min resulted in lack of complete diffusion of boron element into the base metals; quasi-eutectic compounds γ, Ni 3 B and CrB were formed in the centerline of the bond and, increasing the holding time causes the interdiffusion of alloying elements of base metals and the interlayer and leads to the uniformity of the chemical composition along the joint. Bonding under standard solution heat treatment condition (1150 °C/240 min) completely removes the diffusion affected zone on the 45-X side.

Effects of Alloying Elements Additions on Ambient Temperature Performance of Al–Si–Cu–Mg Base Alloys

The present study was carried out to investigate the effects of Ni, Mn, Zr, and Sc additions, individually or in combination with other additives, on the microstructure and tensile properties of 354 casting alloy (Al—9wt%Si—1.8wt%Cu—0.5wt%Mg) at room temperature. Tensile tests were carried out in the as-cast, solution heat-treated, and aged conditions using different aging temperatures and times. Six alloys were prepared using the 354 alloy, comprising a) the base 354 alloy (G1) and five other alloys (G6 to G10) containing Ni, Mn, Sc, Zr, added individually or in combination, and comprising one experimental alloy (G7) containing no copper. Among the alloys containing transition element additions (G6 through G10), the highest tensile and yield strength values are obtained with alloy G7 (2wt% Ni and 0.25wt% Zr but no Cu) in the as-cast and solution heat-treated conditions; alloys G8 and G10 also display a significant increase in tensile strength and ductility in the as-cast and solution heat-treated conditions. Solution heat treatment significantly improves strength and quality of these alloys even if they contain higher Fe and Mg levels compared to the base alloy. Holding the tensile samples of T6-treated G1 alloy resulted in a marked increase in the density of precipitated phase in the form of fine spherical particles. Increasing the holding time prior to deformation to 100 h resulted in the change in the morphology of the Al2Cu precipitates into thin platelets distributed in two perpendicular directions.

Effect of Transition Metals Addition on Tensile Properties of Al–Si–Cu-Based Alloys at 25 °C and 250 °C: Role of Heat Treatment

The tensile data showed that strength and percent elongation of the Zr-containing 354 (Al–9%Si–1.8%Cu–0.5%Mg) alloys increased in the one-step solution heat-treated condition compared to the as-cast case. The multi-step solution heat treatment displayed higher tensile properties than those achieved with single-step solution heat treatment. The use of the T6 treatment, incorporating the multiple solution heat treatment, allows for maximum dissolution of the copper phases in the multiple stages of solution treatment, resulting in the greatest improvement in the alloy strength. The best tensile properties of alloys tested at room temperature after stabilization at 250 °C for 200 h are obtained with the T6 heat treatment. The addition of Zr, Ni, and Mn to Al–Si alloys improves the high-temperature tensile properties of the 354 alloy. Alloys containing 2%Ni or 0.75%Mn perform better in case of high-temperature conditions, with 1-h stabilization at 250 °C. After 200-h stabilization at 250 °C, the strength of the T6-treated alloys—regardless of the type of solution heat treatment process, is reduced considerably, while the ductility is increased, with base alloy showing the highest percent elongation, ~ 19%. The reduction in strength may be attributed to the alloy softening which occurs after such long stabilization time at the high testing temperature (250 °C).

A study of various heating effects on the microstructure and mechanical properties of AA6082 using EBSD and CPFE

The solution heat treatment (SHT) process resolving hardening precipitates in high strength aluminium alloys is a critical step for high-efficient forming processes, such as Hot Form Quench (HFQ®). SHT largely determines the overall cycle time of a forming process. However, effects of heating process parameters, such as the heating rate and soaking time, on the microstructure and the associated mechanical properties of aluminium alloy 6082, one of the most commonly used aluminium alloys, for HFQ applications, have not been systematically investigated. The aim of this study is to explore and understand the relationships among heat treatment conditions, grain microstructure and associated mechanical properties for AA6082. A series of uniaxial tensile tests conducted under various SHT conditions revealed significant variations on mechanical behaviour characterised by stress-strain curves. To correlate these stress-strain relationship with underlying microstructure, the grain and orientation distribution of each heat-treated sample were characterised by the electron backscatter diffraction (EBSD) technique. Due to the presence of a large number of microscopic variables, such as grain size, morphology, texture, grain boundary and etc., the crystal plasticity finite element (CPFE) modelling was employed to identify the key microscopic factors which determine the differences in the observed strength and ductility for all samples. A new CPFE model integrated with local strain criterion was proposed and validated to correlate the ductility and the strength with the material microstructure. This rigorous investigation provides more insights on how microstructure (grain size and texture) affects the mechanical behaviour for AA6082, which enables to enlarge the capability of HFQ for industrial applications.

An Investigation on Microstructure Evolution, Mechanical Properties, and Strain Aging of Mg-1.8Zn-0.7Si-0.4Ca Biomedical Alloy Processed by Equal Channel Angular Pressing

The influence of equal channel angular pressing (ECAP) on microstructure and mechanical behavior, as well as, strain aging during ECAP and post-ECAP of Mg-1.8Zn-0.7Si-0.4Ca biomedical alloy was examined. The alloy in solid solution heat-treated condition was processed by ECAP with route BC at 350 and 400 °C. The specimens ECAPed at 350 °C were aged at 125 and 150 °C for different times. The hardness and shear punch test results indicated that performing ECAP at 350 °C for 4 passes increases the hardness and shear strength of the alloy from 48 HV and 110 MPa to 71 HV and 188 MPa, respectively. It was revealed that the average grain size of the alloy decreases from 78 µm to about 3 µm after 4 passes of ECAP. Three precipitates of CaMgSi, Ca2Mg6Zn3, and Mg2Si were detected in the solid solution specimen. After 4 passes of ECAP at 350 °C, Ca2Mg6Zn3 was completely dissolved and the morphology of Mg2Si changed from Chinese script to fiber-shaped particles. Dynamic strain aging occurred at high-temperature ECAP, and the specimens were overaged during post-ECAP aging. Small MgZn particles were detected in the overaged sample.

Heat treatment influences densification and porosity of AlSi10Mg alloy thin-walled parts manufactured by selective laser melting technique

The fully dense thin-walled structures are very important for manufacturers and customers. Selective laser melting (SLM) is mainly employed for the fabrication of thin-walled and lightweight structures of aluminum alloys, titanium alloys, etc. The goal of the paper is to study the effect of heat treatments, i.e., solution heat treatment (SHT) and artificial aging (AA) on the densification and porosity of the thin-walled specimens. Thin-walled specimens with various wall thicknesses (i.e., from 0.50 to 5.0 mm) were fabricated using AlSi10Mg alloy powder with optimal process parameters on the SLM system. The relative densities of the heat-treated specimens were compared with the as-built test specimens. The porosity development during the process and their relationship with the relative density are also studied critically by applying Archimedes’ method and optical microscopic analysis. Results showed that the densification and porosity distribution behavior is changing with the variations in the wall thickness of specimens. The lowest relative density of 93.42% was obtained for 1.50-mm-wall-thickness specimen in SHT condition. The maximum relative density of 98.61% was achieved for 5.0-mm-wall-thickness specimen in the AA condition. Finally, it is concluded that the AA has a significant influence on the low-wall-thickness (i.e., from 0.50 to 2.0 mm) specimens, and the densification is improved, and porosities are reduced due to fine grain structure and strong bonding between particles.

Microhardness and microstructure characteristics of AZ91 magnesium alloy under different cooling rate conditions

The objective of the present work is to investigate the influence of aging time and cooling rate conditions on the microstructure and mechanical properties of AZ91 magnesium alloy. After solution heat treatment condition, samples were isothermally aged at 200 °C for various times ranging from 4 to 192 h followed by cooling in two different media: water and furnace which resulted in cooling rates of 20 °C s−1 (fast cooling rate) and 0.1 °C s−1 (slow cooling rate) respectively. The results revealed that the hardness values for the faster cooling rate are higher than that of the smaller cooling rate. Maximum hardness has been achieved after aging for 24 h for both two cooling conditions. The influence of both continuous and discontinuous precipitates of β-phase, as a function of aging time and cooling rate, on the age-hardening response has been elaborated. An artificial neural network (ANN) model was applied to simulate and predict the hardness profile of the investigated alloy. The experimental data were confirmed by the calculated results.

Effect of cryogenic treatment on the fracture toughness of aircraft aluminum alloy 7075

Influence of three types of the treatment on fracture toughness of the Al-7075 alloy was investigated in this study. Commercial Al-7075 alloy in the solid solution heat-treated condition was processed by hardening with post-cryogenic deformation treatment and PVD deposition titanium and copper coatings. The fracture toughness was estimated with using macroscopic and microscopic approaches. The conditions for the coincidence of the fracture toughness estimates between brittle fracture mechanics and the photometric analysis of structural images (PHASI) methods were achieved. The highest fracture toughness was obtained by applying hardening, cryogenic compression, ageing and deposition of the Ti-coating, leading to dispersion particles precipitation.

Elastic Properties of Novel Co- and CoNi-Based Superalloys Determined through Bayesian Inference and Resonant Ultrasound Spectroscopy

Bayesian inference is employed to precisely evaluate single crystal elastic properties of novel $$\gamma -\gamma '$$ Co- and CoNi-based superalloys from simple and non-destructive resonant ultrasound spectroscopy (RUS) measurements. Nine alloys from three Co-, CoNi-, and Ni-based alloy classes were evaluated in the fully aged condition, with one alloy per class also evaluated in the solution heat-treated condition. Comparisons are made between the elastic properties of the three alloy classes and among the alloys of a single class, with the following trends observed. A monotonic rise in the $$c_{44}$$ (shear) elastic constant by a total of 12 pct is observed between the three alloy classes as Co is substituted for Ni. Elastic anisotropy (A) is also increased, with a large majority of the nearly 13 pct increase occurring after Co becomes the dominant constituent. Together the five CoNi alloys, with Co:Ni ratios from 1:1 to 1.5:1, exhibited remarkably similar properties with an average A 1.8 pct greater than the Ni-based alloy CMSX-4. Custom code demonstrating a substantial advance over previously reported methods for RUS inversion is also reported here for the first time. CmdStan-RUS is built upon the open-source probabilistic programing language of Stan and formulates the inverse problem using Bayesian methods. Bayesian posterior distributions are efficiently computed with Hamiltonian Monte Carlo (HMC), while initial parameterization is randomly generated from weakly informative prior distributions. Remarkably robust convergence behavior is demonstrated across multiple independent HMC chains in spite of initial parameterization often very far from actual parameter values. Experimental procedures are substantially simplified by allowing any arbitrary misorientation between the specimen and crystal axes, as elastic properties and misorientation are estimated simultaneously.

The effects of heat treatment on microstructure and mechanical properties of rheocasting ADC12 aluminum alloy

The effects of heat treatment on microstructure and mechanical properties of rheocasting ADC12 aluminium alloy produced by gas induced semi-solid (GISS) technique were studied. The solution heat treatment performed at the temperature of 520°C under various solution treatment times for 2, 4, 6, 8, 10, and 12 h and followed by water quenching at room temperature. The results show that the optimum solution heat treatment condition for the non-dendritic structure of ADC12 aluminium alloy was 520°C for 8 h. The age hardening was also carried out at 170°C for different aging times of 6, 8, and 10 h, respectively. It was found that the artificial aging at 170°C for 6 h was sufficient to achieve the highest hardness of 73.2 HRB. This was due to the appropriate refinement of acicular eutectic structure.

Development of a Novel Degradation-Controlled Magnesium-Based Regeneration Membrane for Future Guided Bone Regeneration (GBR) Therapy

This study aimed to develop and evaluate the ECO-friendly Mg-5Zn-0.5Zr (ECO505) alloy for application in dental-guided bone regeneration (GBR). The microstructure and surface properties of biomedical Mg materials greatly influence anti-corrosion performance and biocompatibility. Accordingly, for the purpose of microstructure and surface modification, heat treatments and surface coatings were chosen to provide varied functional characteristics. We developed and integrated both an optimized solution heat-treatment condition and surface fluoride coating technique to fabricate a Mg-based regeneration membrane. The heat-treated Mg regeneration membrane (ARRm-H380) and duplex-treated regeneration membrane group (ARRm-H380-F24 h) were thoroughly investigated to characterize the mechanical properties, as well as the in vitro corrosion and in vivo degradation behaviors. Significant enhancement in ductility and corrosion resistance for the ARRm-H380 was obtained through the optimized solid-solution heat treatment; meanwhile, the corrosion resistance of ARRm-H380-F24 h showed further improvement, resulting in superior substrate integrity. In addition, the ARRm-H380 provided the proper amount of Mg-ion concentration to accelerate bone growth in the early stage (more than 80% new bone formation). From a specific biomedical application point of view, these research results point out a successful manufacturing route and suggest that the heat treatment and duplex treatment could be employed to offer custom functional regeneration membranes for different clinical patients.

Response of Varying Levels of Silicon and Transition Elements on Room- and Elevated-Temperature Tensile Properties in an Al–Cu Alloy

The research involved here was accomplished through a study of the tensile properties in both the as-cast and heat-treated conditions, where the effects of different heat treatments, i.e., T5, T6, T62 and T7, commonly applied to aluminum casting alloys were evaluated at ambient temperature and at high temperature (250 °C) using different holding or stabilization times at testing temperature. The tensile data showed that the ultimate tensile strength (UTS) and percentage elongation values of the six alloys increased in the one-step solution heat-treated condition compared to the as-cast case. The multi-step solution heat treatment displayed higher tensile properties than those achieved with the one-step solution treatment. The use of the T62 treatment (multi-step solution treatment followed by artificial aging) allows for maximum dissolution of the copper phases in the multiple stages of solution treatment, resulting in the greatest improvement in both UTS and yield strength (YS). At ambient temperature, T6 and T62 treatments provide the best improvements in both UTS and YS values of all alloys. The T62-tempered alloy showed maximum improvement with a UTS value of ~ 401.55 MPa. Likewise, in the Al–2%Cu–8%Si series the T62-tempered alloy displayed the highest UTS with a value of ~ 293.5 MPa. The YS values improved overall after solution treatment. The YS values followed the same trend as the UTS at both ambient and high-temperature testing. At high-temperature testing at 250 °C after one hour of stabilization, the UTS of the alloys increased with the T6 and T62 heat treatment conditions, but remained the same after T5 heat treatment; the highest UTS value was exhibited by the T62-tempered alloy with ~ 195 MPa.

Quantitative study of dissolution of Mg2Si during solution treatment in AA6014 alloy

The solution heat treatment of AA6014 sheet is important to meet the required dent resistance in assembled automotive structures. In this study, the effect of solution heat treatment conditions on the Mg2Si particle size distribution and volume fraction were quantitatively investigated using SEM observations, electrical conductivity, and hardness measurements. Precipitation during artificial aging was studied by DSC analysis. After soaking at 570 °C for 1min, the volume fraction of soluble Mg2Si was reduced dramatically from 1.58% to nearly zero. Hardness measurements, EC, and SEM characterization of T4 samples were compared as measures of Mg2Si dissolution.

Influence of thermally activated processes on the deformation behavior during low temperature ECAP

High strength aluminum alloys are generally hard to deform. Therefore, the application of conventional severe plastic deformation methods to generate ultrafine-grained microstructures and to further increase strength is considerably limited. In this study, we consider low temperature deformation in a custom-built, cooled equal channel angular pressing (ECAP) tool (internal angle 90°) as an alternative approach to severely plastically deform a 7075 aluminum alloy. To document the maximum improvement of mechanical properties, these alloys are initially deformed from a solid solution heat-treated condition. We characterize the mechanical behavior and the microstructure of the coarse grained initial material at different low temperatures, and we analyze how a tendency for the PLC effect and the strain-hardening rate affect the formability during subsequent severe plastic deformation at low temperatures. We then discuss how the deformation temperature and velocity influence the occurrence of PLC effects and the homogeneity of the deformed ECAP billets. Besides the mechanical properties and these microstructural changes, we discuss technologically relevant processing parameters (such as pressing forces) and practical limitations, as well as changes in fracture behavior of the low temperature deformed materials as a function of deformation temperature.