Solution-treated Condition Research Articles

High temperature creep properties of a linear friction welded newly developed wrought Ni-based superalloy

AD730™ Ni-based superalloy specimens in solution-treated conditions were linear friction welded. Then, post-weld heat treatment (PWHT), consisting of γ′ sub-solvus solution treatments followed by aging, was conducted on the linear friction welded samples. High temperature creep tests were performed on the as-welded and PWHTed joints at two different temperatures: 700°C under 600 and 750MPa stress levels, and 850°C under 100 and 200MPa stresses. The creep resistance of the PWHTed joints was higher than that of the as-welded samples. The PWHTed joints exhibited better ductility than that of the base material at 850°C, while they showed slightly lower creep life at 700°C in comparison to the base metal. Microstructure examination showed that cracks initiated at the interface of oxidized particles at 700°C. The decrease in creep resistance of the AD730™ Ni-based superalloy at 850°C was related to a combination of the formation of precipitate-free zones (PFZ) in the vicinity of the grain boundaries (GBs) and microcracking assisted by oxidation. The Larson-Miller Parameter (LMP) was used to correlate the creep strength, temperature and time to failure for the as-welded and PWHTed samples. LMP values varied between 21.5 × 103 and 24.5 × 103. It was found that in the investigated temperature range, the PWHTed AD730™ has similar creep characteristics as Udimet™720 Li and Inconel 738LC at low values of LMP and better creep properties than those of the Inconel 617 alloy at higher LMP values.

High-tensile-strength and ductile novel Ti-Fe-N-B alloys reinforced with TiB nanowires

In this study, we designed and fabricated high-performance Ti-Fe-N-B alloys by sintering a blend of Ti powder, Fe powder and BN nanopowder using spark plasma sintering. During sintering, TiB nanowires nucleated from the surfaces of Ti powder particles on which the BN nanoparticles were dispersed, and then grew into the nearby Ti matrix forming a three-dimensional (3D) network-woven architecture throughout the Ti matrix. The TiB nanowires were about 10–30µm in length and 50–200nm in diameter after sintering. Their existence suppressed the formation of the continuous α-Ti phase along the β-Ti grain boundaries and refined the microstructure of the Ti matrix. A large quantity of α-Ti nanoplates precipitated along the planes (110)β-Ti in the Ti-Fe-N-B alloys. The as-sintered Ti-4.5Fe-0.14N-0.11B alloy achieved a high tensile strength of 1176MPa with a significant tensile elongation of 10.4%, which satisfied the requirements for the tensile properties of mill-annealed Ti6Al4V in the solution-treated and aged (STA) condition. The TiB nanowires, α-Ti nanoplates, Fe solute atoms, and N solute atoms in the matrix all contributed to the high tensile strength.

Mechanical Performance of Cold-Sprayed A357 Aluminum Alloy Coatings for Repair and Additive Manufacturing

Cold-sprayed coatings made of A357 aluminum alloy, a casting alloy widely used in aerospace, underwent set of standard tests as well as newly developed fatigue test to gain an information about potential of cold spray for repair and additive manufacturing of loaded parts. With optimal spray parameters, coating deposition on substrate with smooth surface resulted in relatively good bonding, which can be further improved by application of grit blasting on substrate’s surface. However, no enhancement of adhesion was obtained for shot-peened surface. Process temperature, which was set either to 450 or 550 °C, was shown to have an effect on adhesion and cohesion strength, but it does not influence residual stress in the coating. To assess cold spray perspectives for additive manufacturing, flat tensile specimens were machined from coating and tested in as-sprayed and heat-treated (solution treatment and aging) condition. Tensile properties of the coating after the treatment correspond to properties of the cast A357-T61 aluminum alloy. Finally, fatigue specimen was proposed to test overall performance of the coating and coating’s fatigue limit is compared to the results obtained on cast A357-T61 aluminum alloy.

Optimization of heat treatment of gravity cast Sr-modified B356 aluminum alloy

Abstract In recent years, certain foundry processes have made it possible to obtain products with very thin parts, below the 4 mm threshold of the permanent mold casting technology. The safety margins of these castings have been reduced, so the T6 heat treatment conditions adopted for the Al–7Si–Mg alloys need to be investigated to identify the best combination of strength and ductility. Furthermore, the cost and the production time associated with T6 heat treatment have to be optimized. In the present work, an experimental study was carried out to optimize the solution treatment and artificial aging conditions in gravity cast thin bars of B356 aluminum alloy modified with Sr. Two solution temperatures were selected, 530 °C and 550 °C, respectively, with solution time ranging from 2 to 8 h, followed by water quenching and artificial aging at 165 °C with aging time from 2 to 32 h. The results of hardness and tensile tests were correlated with differential scanning calorimetry (DSC) analysis. The best combination of mechanical properties and heat treatment duration was obtained with 2 h solutionizing at 550 °C and 8 h aging at 165 °C. DSC analysis showed that the alloy's mechanical properties reach the maximum value when the β″ phase is completely developed during the artificial aging.

Phase stability dependence of deformation mode correlated mechanical properties and elastic properties in Ti-Nb gum metal

The evolution of microstructure and deformation modes in metastable Ti-23Nb-0.7Ta-2Zr-0.8O (at%) alloys with accumulated strain to 0.15 are investigated, where different solution treatments were applied to control both elemental distributions and the bcc β-phase stability. Recent studies suggest that the occurrence of specific deformation mechanism of the β-phase is strongly linked with its chemical stability. In the present study, the Bo-Md phase stability diagram was used to evaluate the β-phase stability and to discuss the deformation modes as function of solution treatment conditions, resulting in different deformed microstructures. Analysis of the deformed microstructure using electron backscatter diffraction and X-ray diffraction revealed that deformation bands formed at the initial stage of strain were composed of not only mechanically induced {332}<112>β and {112}<111>β twinning, but also stress-induced martensite ⍺״ phase. It was observed that the number of deformation bands decreases with increasing homogeneity in the alloy, which is strongly dependent on the phase constitution, and directly impacts its final properties including hardness and elastic modulus. Based on the experimentally observed results, the β-phase stability dependence of deformation features can explain the possibility of manipulating the mechanical properties without the evident elastic properties variation in Ti-Nb Gum Metal.

Origin of Insignificant Strengthening Effect of CNTs in T6-Treated CNT/6061Al Composites

Carbon nanotube (CNT)-reinforced 6061Al (CNT/6061Al) composites were fabricated via powder metallurgy combined with friction stir processing (FSP). CNTs were dispersed after FSP and accelerated the precipitation process of the CNT/6061Al composites. However, the strengthening effect of CNTs on the T6-treated materials was insignificant, while the composites under the FSP and solution treatment conditions exhibited increased strength compared to the matrix. Precipitate-free zones (PFZs) were detected around CNTs in the T6-treated CNT/6061Al composites, and a model was proposed to describe the effect of PFZs on strength. The calculations indicated that the strength of PFZs was similar to that of the T6-treated 6061Al. As a result, the strengthening effect of CNTs on the T6-treated CNT/6061Al composites was insignificant.

Effect of solution treatment and aging conditions on tensile properties of Ti–Al–Fe–Si alloy

The effect of the solution treatment and aging (STA) conditions on the tensile properties of Ti–4mass%Fe–4mass%Al–0.25mass%Si alloy has been investigated in this work. The obtained results revealed that varying the solution temperature affected the stability of the β phase due to the Fe partitioning (which inhibited the β→α′/α″ reaction during water quenching), while the magnitude of the aging temperature determined the predominant products of the β→isothermal ω→secondary αrich→secondary αlean+TiFe phase transformation with distinct tensile characteristics. In addition, the relationship between the alloy microstructure and its tensile properties was discussed.

Galvanic Corrosion Behavior of Microwave Welded and Post-weld Heat-Treated Inconel-718 Joints

In the present study, corrosion behavior of microwave welded Inconel-718 at various conditions was investigated. Welding of Inconel-718 in 980 °C solution-treated condition was performed using microwave hybrid heating technique. The microwave welds were subjected to post-heat treatment for improving its microstructure and mechanical properties by solubilizing the Nb-enriched Laves phase. The microstructural features of the fabricated welds at various conditions were investigated through scanning electron microscopy. The electrochemical testing results revealed that Inconel-718 welds were galvanic corroded when they were anodically polarized in 3.5 wt.% NaCl solution at 28 °C. The difference in the corrosion potentials between the base metal (BM) and fusion zone (FZ) in an Inconel-718 weld was the main factor for galvanic corrosion. The highest corrosion was occurred in the as-welded/aged weldments, followed by 980 °C solution-treated and aged weldments, as-welded specimen, and 1080 °C solution-treated and aged (1080STA) weldments. The least galvanic corrosion was occurred in the 1080STA specimens due to almost uniform microstructure developed in the weldment after the treatment. Thus, it was possible to minimize the galvanic corrosion in the microwave welded Inconel-718 by 1080STA treatment which resulted in reducing the difference in corrosion potentials between the BM and the FZ.

Long-Term Gamma Prime Phase Stability after Various Heat Treatment Conditions with Temperature Dropping during Solution Treatment in Cast Nickel Base Superalloy, Grade Inconel-738

Cast nickel based superalloy, Grade Inconel 738, is a material for turbine blades. Its rejuvenation heat treatment usually consist of solution treatment condition with temperature range of 1125-1205 oC for 2-6 hours. Then it is following with double aging process including primary aging at 1055oC for 1 hour and secondary aging at 845oC for 24 hours. However, the various selected temperature dropping program were performed during solution treatment to simulate the possible error of heating furnace. The maximum number of temperature dropping during solution treatment is varied from 1-3 times From all obtained results, the various temperature dropping during solution treatment conditions showed extremely the significant effect on the final rejuvenated microstructures and long-term gamma prime stability after heating at temperature of 900oC for 200 hours.

Liquation cracking behavior and control in the heat affected zone of GH909 alloy during Nd: YAG laser welding

In this paper, we describe experimental laser welding of GH909 alloy. The forming mechanism of heat affected zone (HAZ) liquation cracking was investigated and improvements to the welding process are proposed. We determined that the occurrence of HAZ liquation cracking proceeds through three stages: intergranular liquation, crack initiation and crack growth. The presence of liquation cracking is associated with low melting eutectics and composition segregation that occurs at the grain boundaries. The segregation caused lattice distortion at the grain boundaries and inhibited the binding force at the solid/liquid interface. The susceptibility to HAZ liquation cracking can be reduced by the migration of a relatively thin liquid film that is produced by reducing the heat input at the grain boundaries during laser welding. GH909 alloy in solid solution treatment condition rather than standard aging treatment was adopted to facilitate laser welding, which results in significantly lower mechanical.

Modeling the precipitation kinetics and tensile properties in Al-7Si-Mg cast aluminum alloys

The extensive application of Al-7Si-Mg cast aluminum alloys in the automotive and aerospace industries raises the need to better understand the relationship between microstructures and properties. In present work, an integrated precipitation/strengthening/strain-hardening numerical model is developed in order to model the precipitation kinetics and tensile properties in Al-7Si-Mg alloys. The influence of solidification and solution treatment conditions on yield strength is reflected by a term ∆σ0. The strain hardening model takes into account the effect of Orowan loops on the dislocation storage and recovery as well as kinematic contributions. Application of this integrated model to various aging treatments of Al-7Si-Mg alloys is conducted and the predictions both for precipitate microstructure and yield strength are compared well with experimental results. The influence of aging temperature, solution treatment temperature as well as Mg concentration on yield strength is investigated. Using the strain hardening model, the stress-strain curves are predicted and the influence of aging treatment on k1 and k20 parameters as well as the strain hardening behavior is analyzed. Through combining with the empirical expression (σUTS−σYS)=m·σYS+n+f(Tss), the ultimate tensile strength and elongation for the samples in Al-7Si-Mg alloys aged at 160°C and 180°C are predicted. Finally, the limitations of present model and the factors influencing the prediction precision of tensile properties are discussed.

Microstructure and Mechanical Properties of Cryorolled Aluminum Alloy AA2219 in Different Thermomechanical Processing Conditions

In the present study, aluminum alloy AA2219-T87 bars were cryorolled to various amounts of deformation in two pre-deformation conditions: (1) without solution treatment i.e., as-received T87 (WST-CR) and (2) with solution treatment (ST + CR). The solution treated and cryorolled bars were further annealed leading to a third condition: (3) solution treated, cryorolled, and annealed (CR + Annealed). Room-temperature mechanical properties have been evaluated for all three cryorolled conditions. Significant improvement in the 0.2 pct YS and UTS values was obtained for bars cryorolled to cross-sectional area reduction of more than 50 pct in the solution-treated condition (ST + CR), whereas for bars cryorolled in the without solution-treated condition (WST-CR), only an improvement in the 0.2 pct YS was observed. Cryorolling did not enhance the precipitation kinetics nor did it increase the response of the alloy to aging. The mechanical properties were correlated to the microstructures obtained by optical and transmission electron microscopy. Microstructural evolution in the ST + CR condition indicated gradual progression of the principal restoration mechanism from dynamic recovery (DRV) to dynamic recrystallization with an increasing amount of plastic deformation. Transmission electron microscopy of WST-CR and ST + CR specimens showed an increase in dislocation density as a function of the amount of deformation indicating suppression of DRV at cryogenic temperatures. Cryorolling in the solution-treated condition to cross-sectional area reduction of more than 50 pct (ST + 70 pct CR) was found to impart an optimum combination of strength and percent elongation in the present study.

Microstructural Evolution and Mechanical Properties of Simulated Heat-Affected Zones in Cast Precipitation-Hardened Stainless Steels 17-4 and 13-8+Mo

Cast precipitation-hardened (PH) stainless steels 17-4 and 13-8+Mo are used in applications that require a combination of high strength and moderate corrosion resistance. Many such applications require fabrication and/or casting repair by fusion welding. The purpose of this work is to develop an understanding of microstructural evolution and resultant mechanical properties of these materials when subjected to weld thermal cycles. Samples of each material were subjected to heat-affected zone (HAZ) thermal cycles in the solution-treated and aged condition (S-A-W condition) and solution-treated condition with a postweld thermal cycle age (S-W-A condition). Dilatometry was used to establish the onset of various phase transformation temperatures. Light optical microscopy (LOM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) were used to characterize the microstructures, and comparisons were made to gas metal arc welds that were heat treated in the same conditions. Tensile testing was also performed. MatCalc thermodynamic and kinetic modeling software was used to predict the evolution of copper (Cu)-rich body center cubic precipitates in 17-4 and β-NiAl precipitates in 13-8+Mo. The yield strength was lower in the simulated HAZ samples of both materials prepared in the S-A-W condition when compared to their respective base metals. Samples prepared in the S-W-A condition had higher and more uniform yield strengths for both materials. Significant changes were observed in the matrix microstructure of various HAZ regions depending on the peak temperature, and these microstructural changes were interpreted with the aid of dilatometry results, LOM, SEM, and EDS. Despite these significant changes to the matrix microstructure, the changes in mechanical properties appear to be governed primarily by the precipitation behavior. The decrease in strength in the HAZ samples prepared in the S-A-W condition was attributed to the dissolution of precipitates, which was supported by the MatCalc modeling results. MatCalc modeling results for samples in the S-W-A condition predicted uniform size of precipitates across all regions of the HAZ, and these predictions were supported by the observed trends in mechanical properties. Cross-weld tensile tests performed on GMA welds showed the same trends in mechanical behavior as the simulated HAZ samples. Welding in the S-W-A condition resulted in over 90 pct retention in yield strength when compared to base metal strengths. These findings indicate that welding these PH stainless steels in the solution-treated condition and using a postweld age will provide better and more uniform mechanical properties in the HAZ that are more consistent with the base metal properties.

Processing and Characterization of Sub-delta Solvus Forged Hemispherical Forgings of Inconel 718

In this paper, microstructure and mechanical properties of 200 mm diameter Inconel 718 hemispherical domes processed at 1025 °C through closed die hammer forging have been investigated. Microstructure and mechanical properties of the forgings in radial and tangential directions were characterized using optical microscopy, scanning electron microscopy, impact testing, and tensile testing. Grain size of the forgings at three different locations was fine with an average grain size of ASTM No. 8-9. The typical tensile properties of the forgings in solution-treated and aged condition were ultimate tensile strength-1450 MPa, yield strength-1240 MPa, and ductility-25%. The fine grain size achieved in forgings has been attributed to delta phase present at grain boundaries which pinned the grains during forging and prevented grain coarsening.

Effects of Zr and Mn additions on formation of LPSO structure and dynamic recrystallization behavior of Mg-15Gd-1Zn alloy

The effects of Zr and Mn additions to Mg-15Gd-1Zn alloy on the formation of long period stacking ordered (LPSO) structure under solution-treated (T4-treated) condition and the dynamic recrystallization (DRX) behavior alloy during extrusion have been investigated. The underneath mechanisms have also been proposed. The results indicate that Zr hinders the formation of LPSO structure by consuming Zn, while the Mn promotes it. On the other hand, Zr suppresses the grain growth by introducing Mg(Zn, Zr) precipitates during the DRX, while Mn effectively hinders the recrystallization process due to increasing LPSO structure. As the LPSO structure has dissolved in recrystallized grains, Mn addition affects little on suppressing grain growth in the grain growth step. Zr addition improves the mechanical properties of both the casting and extruded Mg-15Gd-1Zn alloys by refining grains and introducing Mg(Zn, Zr) precipitates. By contrast, the Mn addition is beneficial for the tensile properties of casting Mg-15Gd-1Zn alloy because of the LPSO structure with high ductility but harmful for the properties of the extruded alloys due to the coarse un-recrystallized grains.

Influence of Solution and Aging Treatment Conditions on the Formation of Ultrafine-Grained Structure of CuFe2 Alloy Processed by Rolling with Cyclic Movement of Rolls

Abstract The effect of second phase particles on grain refinement in CuFe2 alloy has been investigated by using rolling with the cyclic movement of rolls (RCMR) method. Two different population of second phase particles of Fe: coherent, about 10 nm in diameter and about 100 nm in size were obtained by applying aging treatment followed at 500°C for 2 h and at 700°C for 24 h respectively. In addition, solution treated samples were deformed by RCMR method at the same parameters. The microstructures of the CuFe2 alloy were analyzed using light microscope (LM), electron backscattered diffraction (EBSD) microscope technique and scanning transmission electron microscope (STEM). The presence of high-density of coherent Fe particles in the matrix inhibits recovery process and in the result obtained grain/subgrain boundaries have diffused character and are weakly visible. The largest particles which are not coherent with the matrix act as an effective barrier against the boundary motion.

Effect of aging and oxidation on strain hardening behaviour of a nickel-free high nitrogen austenitic stainless steel

Effect of aging and oxidation on strain hardening behaviour of a nickel-free high nitrogen austenitic stainless steel has been investigated using room temperature tensile tests and TEM. The alloy in both oxidised and unoxidised conditions exhibits a transition in flow behaviour that can be described best by the Ludwigson flow relationship as evident from the lowest values of the sum of residual squares, χ 2, of the fit. The transition in macroscopic flow behaviour with strain has been correlated to change in deformation mechanism from planar slip in the low strain regime (LSR) to deformation twinning and slip in the high strain regime (HSR) in solution treated (ST) condition of the alloy. However, the LSR of the alloy aged for longer times (>100 h) is characterized by the formation of dislocation tangles, while the HSR is marked by the formation of well-defined finer dislocation cell structure. This difference in deformation sub-structures in low and high strain regimes between ST and long term aged samples has been correlated to the change in stacking fault energy due to the precipitation of Cr2N and σ-phases. Further, the alloy in ST condition exhibits the highest strain hardening rate, which then progressively decreases with aging time.

Influence of Microstructure on Scratch-Induced Deformation Mechanisms in AZ80 Magnesium Alloy

Indentation scratch-induced wear in Mg-8 wt% Al-0.5 wt% Zn (AZ80) alloy is investigated in this study for solution-treated and peak-aged conditions. Aged alloy exhibited higher wear resistance, with 12–14 % reduction in wear volume. This is attributed to enhanced microstructural resistance to scratch wear due to precipitate phase. Ploughing was found to be the dominating material removal mechanism for both solution-treated and aged specimens. Microcutting was also active in solution-treated alloy, but not in aged alloy due to the presence of brittle Mg17Al12 intermetallic particles in the microstructure. The localized stresses induced by indenter tip were found to exceed theoretical shear strength for magnesium crystal, resulting in intergranular as well as transgranular fracture phenomena. Cracks were more prominent in aged alloy, which is ascribed to the suppression of twinning activity in aged alloy, resulting in non-fulfilment of von Mises criterion of plastic deformation. Scratch-induced plastic flow was more pronounced in solution-treated alloy, with twinning as the major plasticity mechanism.

Effects of Zn additions on the microstructure and hardness of Mg–9Al–6Sn alloy

The effects of Zn additions on the age hardening response and microstructure of Mg–9Al–6Sn (wt.%) alloy have been investigated. It is found that the Zn additions can remarkably increase the alloy hardness in the as-quenched condition. The peak hardness value of the Mg–9Al–6Sn alloy increases from 90±0.87HV to 103±3.83HV, when the Zn addition is 3wt.%, which is the highest among the magnesium casting alloys that are free of rare-earth elements. The enhanced hardness in the Mg–9Al–6Sn–3Zn alloy is attributable to an increased volume fraction of smaller Mg2Sn particles in the solution-treated condition and the formation of [0001]Mg Mg17Al12 rods and Mg21(Zn, Al)17 precipitates in the peak-aged condition.

Microstructural Characterization and Thermodynamic Simulation of Cast Al–Zn–Mg–Cu Alloys

Wedge castings were produced using six Al–Zn–Mg–Cu aluminum alloys with zinc concentrations ranging from 8 to 15 wt%, Zn/Mg ratios ranging from 1.7 to 6.5, and copper ranging from 0.6 to 1 wt%. Thermal analysis and microstructural characterization of the samples in the as-cast, solution-treated, and aged conditions were performed and compared to Calculation of Phase Diagram simulations. The calculated phase stability in the alloys was overall remarkably accurate for both the solidification and equilibrium phase formation. Additional equilibrium calculations were made to determine the range of alloying concentrations that would not contain eutectic T or η phase. The phase stability in a total of 195 chemistries was calculated.