Elevated Temperature Tensile Properties Research Articles

Effects of thermal exposure on the microstructure and mechanical properties of Al-12Si-4Cu-1Ni-1Mg-2Mn piston alloys

ABSTRACT The effect of thermal exposure on the elevated-temperature mechanical properties of heat-treated Al-12Si-4Cu-1Ni-1 Mg-2Mn piston alloys was investigated using optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM), and tensile tests at elevated temperatures. The results showed that coarsening of the strengthening precipitates following a prolonged exposure at 350°C had a deleterious effect on the elevated-temperature tensile properties. Further thermal exposure up to 50 h did not result in even a slight reduction in the strength. After exposure at 350°C, the value of elevated-temperature ultimate tensile strengths of Al-12Si-4Cu-1Ni-1 Mg-2Mn piston alloys were 92, 80, and 73 MPa for 0 h, 10 h, and 100 h of thermal exposure, respectively, which are superior to those of the commercial piston alloys. The high-performance, elevated-temperature mechanical properties of Al-12Si-4Cu-1Ni-1 Mg-2Mn piston alloys can be attributed to the high thermal stability Mn-rich intermetallics and Al3CuNi.

Effect of heat treatment on the microstructure and elevated temperature tensile properties of Rene 41 alloy produced by laser powder bed fusion

The microstructure and elevated temperature mechanical properties of a precipitation hardenable Nickel based superalloy, Rene 41, fabricated by laser powder bed fusion followed by two different heat treatment regimes were studied. The as-built (AB) microstructure consists of γ columnar grains aligned in <100> direction. No γ′ precipitates were observed in the AB condition. Following to a sub-solvus solutionizing and aging heat treatment, the AB grain morphology was maintained. The development of fine γ′ precipitates within the grains along with the discrete carbide particles on the grain boundaries occurred. Heat treatment above the solvus temperature of γ’ resulted in the formation of a random equiaxed grain morphology. The γ′ and carbide precipitation was also observed in this heat treatment regime, but their distribution and morphology were different. Uniaxial tensile tests were conducted at 760 °C. Average yield strength values for AB, sub-solvus and super-solvus heat treated alloys were 879, 824 and 855 MPa respectively. The three tested conditions showed similar strength values that are comparable with a wrought alloy at the testing temperature. However, the elongation and deformation behaviors were different for each condition. Sub-solvus heat treatment lead to the highest elongation at break with 22% whereas super-solvus heat treatment resulted in the highest work hardening rate during deformation.

Effect of Heat Treatments on Microstructural Evolution and Tensile Properties of 15Cr12MoVWN Ferritic/Martensitic Steel

In this study, the phase transformation temperature of 15Cr12MoVWN ferritic/martensitic steel was determined by differential scanning calorimetry to provide a theoretical basis for the design of a heat treatment process. An orthogonal design experiment was performed to investigate the relationship between microstructure and heat treatment parameters, i.e., normalizing temperature, cooling method and tempering temperature by evaluating the room-temperature and elevated-temperature tensile properties, and the optimum heat treatment parameters were determined. It is shown that the optimized heat treatment process was composed of normalizing at 1050 °C followed by air cooling to room temperature and tempering at 700 °C. Under the optimum heat treatment condition, the room-temperature tensile properties were 1014 MPa (UTS), 810.5 MPa (YS) and 18.8% (elongation), while the values are 577.5 MPa (UTS), 469 MPa (YS) and 39.8% (elongation) tested at 550 °C. The microstructural examination shows that the strengthening contributions from microstructural factors were the martensitic lath width, dislocations, M23C6, MX and grain boundaries of prior austenite grain (PAG) in a descending order. The main factors influencing the tensile strength of 15Cr12MoVWN steel were the martensitic lath width and dislocations.

Influence of aging heat treatment on microstructure and tensile properties of laser oscillating welded TB8 titanium alloy joints

Investigations were conducted on TB8 titanium alloy to assess the influence of aging heat treatment on microstructure and phase transformations induced by laser oscillating welding, and establish a correlation between tensile properties and microstructure. Low-temperature aging joint consists of ω phase and β phase, while high-temperature aging joint is comprised of α phase and β phase. The formation of poor and rich precipitation zone in weld area was due to segregation of major alloying elements like Al, Mo and Nb. Low-temperature aging deteriorates plasticity of joints, but high-temperature aging improved ambient-/elevated-temperature tensile properties. The effect of aging temperature and aging time were discussed in depth. After aging treatment at 450° Celsius for 1 h, intermediate ω phase in gathering place transformed to α phase, but dispersed ω phase still retained. With the increase of aging temperature and aging time, size of α precipitate increased. Note that there is a significant increase (85%) in tensile strength after high-temperature aging treatment and Portevin-Le Chatelier (PLC) effect can be avoided under thermo-mechanical loading conditions. It was found that after 1 h of aging treatment at 550° Celsius followed by air cooling, the welded joints owned the best tensile properties at both ambient and elevated temperature.

Elevated temperature tensile properties of a ternary eutectic Al–27%Cu–5%Si cast alloy

Eutectic alloys have several advantages when compared to single-phase systems. Moreover, the solidification characteristic and microstructural features of eutectic alloys have continued to gain more attention in recent years due to their impact on the properties and performance of such eutectic materials. In this study, a eutectic Al–27%Cu–5%Si ternary alloy was investigated to understand its microstructural formation and its influence on the hardness and high-temperature tensile properties of the alloy. The eutectic composite was produced through a rapid solidification technique and its microstructure characterized by an optical microscope as well as a scanning electron microscope coupled with energy dispersive spectrometry (SEM-EDS). The hardness of as-cast alloy was evaluated at room temperature while its tensile properties were investigated at temperatures ≤400 °C. The results revealed that the cast alloy consists of both binary and ternary eutectic microstructures with different length-scales, which has considerably contributed to the mechanical performance of the eutectic composite up to 300 °C when compared to the traditional Al–Si (A319) cast alloy. The alloy displays a high hardness value of 224HV and a relatively higher elevated-temperature tensile strength of 217 MPa at 300 °C. The tensile strengths of the ternary eutectic alloy are 54% and 139% higher than that of the reference A319 casting alloy at temperatures of 200 °C and 300 °C, respectively.

Ambivalent Role of Annealing in Tensile Properties of Step-Rolled Ti-6Al-4V with Ultrafine-Grained Structure

Step rolling can be used to mass-produce ultrafine-grained (UFG) Ti-6Al-4V sheets. This study clarified the effect of subsequent annealing on the tensile properties of step-rolled Ti-6Al-4V at room temperature (RT) and elevated temperature. The step-rolled alloy retained its UFG structure after subsequent annealing at 500–600 °C. The RT ductility of the step-rolled alloy increased regardless of annealing temperature, but strengthening was only attained by annealing at 500 °C. In contrast, subsequent annealing rarely improved the elevated-temperature tensile properties. The step-rolled Ti-6Al-4V alloy without the annealing showed the highest elongation to failure of 960% at 700 °C and a strain rate of 10−3 s−1. The ambivalent effect of annealing on RT and elevated-temperature tensile properties is a result of microstructural features, such as dislocation tangles, subgrains, phases, and continuous dynamic recrystallization.

选区激光熔化成形GH3536合金的高温拉伸性能及断裂行为分析

选区激光熔化成形GH3536合金的高温拉伸性能及断裂行为分析

Thermal exposure of Al-Si-Cu-Mn-Fe alloys and its contribution to high temperature mechanical properties

The effect of Cu and Ti contents and thermal exposure on the elevated temperature mechanical properties of T6-treated Al-Si-Cu-Mn-Fe alloys was investigated via optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM), and elevated temperature tensile tests. The mechanical properties at elevated temperature increased with the increase in Ti and Cu contents. These results can be attributed to the increased amounts of precipitated particles. Thermal exposure at 300°C for 10h had a deleterious effect on the elevated temperature tensile properties due to the coarsening of the strengthening precipitates. Further thermal exposure up to 100h only resulted in a little reduction in the strength. After thermal exposure at elevated temperature of 300°C, the 4Cu-0.5Ti demonstrated best mechanical properties and Quality Index (QI). The ultimate tensile strength (UTS) at elevated-temperature of 300°C were 170MPa, 92MPa, and 88MPa for 0.5h, 10h, and 100h after thermal exposure, respectively, which are superior to those for the commercial aluminum alloys.

Wire + Arc Additively Manufactured Inconel 718: Effect of post-deposition heat treatments on microstructure and tensile properties

Wire + Arc Additive Manufacturing (WAAM) can be used to create large free-form components out of specialist materials such as nickel-base superalloys. Inconel (IN) 718 is well suited for the WAAM process due to its excellent weldability. However, during deposition, WAAM IN718 is susceptible to micro-segregation, leading to undesirable Laves phase formation in the interdendritic regions. Further, the WAAM process encourages columnar grain growth and the development of a strong fibre texture, leading to anisotropy in grain structure. This unfavourable microstructure can be addressed through specialised post-deposition homogenisation heat treatments. A new modified heat treatment was found to be effective in dissolving Laves phase, whereas a standard treatment precipitated δ phase. Tensile test results revealed that Laves and δ phases lead to low ductility when present in a precipitation-hardened matrix. The modified heat treatment also reduced the anisotropy in grain structure, leading to almost isotropic elevated temperature tensile properties, which meet minimum specifications for conventional cast but not for wrought material. Specialised post-deposition heat treatments, which address the unique microstructure of WAAM IN718, are crucial to achieving optimal mechanical properties.

Precipitation behavior of dispersoids and elevated-temperature properties in Al–Si–Mg foundry alloy with Mo addition

Abstract

PHENIX U.S.-Japan Collaboration Investigation of Thermal and Mechanical Properties of Thermal Neutron–Shielded Irradiated Tungsten

The United States and Japan have collaborated on fusion materials research in a series of agreements reaching back to 1981. The PHENIX collaboration is the latest U.S.-Japan project which spans 2013 to 2019 and has the goal of assessing technical feasibility of tungsten-based, helium-cooled plasma-facing component concepts for a demonstration fusion power reactor (DEMO). Task 2 within the PHENIX project is focused on evaluating the neutron irradiation effects in tungsten. For tungsten, the transmutation to Re and Os is at least as important to determining its properties after irradiation as the displacement damage, and the transmutation rate depends on the energy spectrum of the reactor. A large-scale, instrumented irradiation capsule with thermal neutron shielding to better mimic fusion conditions was irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. The tungsten specimens were irradiated in different temperature zones between 500°C and 1200°C to doses of ~0.2 to 0.7 displacements per atom. More than 20 varieties of pure tungsten and tungsten alloys were included in the irradiation, and they were evaluated in the 3025E hot-cell facility and at the Low Activation Materials Development and Analysis Laboratory. The elevated temperature tensile, fracture toughness, hardness, thermal conductivity, electrical resistivity, density, elemental composition, and microstructure properties of the irradiated materials are being collected. This paper overviews the experimental design, specimen matrix, and the initial results of postirradiation examinations.

Experimental evaluation on elevated temperature fatigue and tensile properties of one selective laser melted nickel based superalloy

Additive manufacturing techniques show more and more utilization potentialities in today’s aviation industry. In order to ensure safe operation of additive manufactured parts, it is important to have their mechanical properties well-characterized and assessed. In this study, elevated temperature tensile and fatigue performances of one selective laser melting (SLM) fabricated nickel based superalloy named K536 are investigated. A series of tensile tests at room and 400–700 °C temperature range and stress-controlled fatigue tests at 400 °C and 600 °C are employed. Effects of building orientation and temperature on tensile and fatigue properties are analysed. Scanning electron microscopy is used to examine the fracture surfaces of fatigue specimens to qualify the failure mechanism and crack initiation sites. The SLM K536 exhibits higher tensile strength in contrast with the wrought alloy at different tested temperatures. It is found that the anisotropy of monotonic tensile and fatigue properties is not significant. The scatter of fatigue data in the near-fatigue limit region shows more serious at 400 °C than 600 °C, indicating that a more conservative life prediction method will be suitable to ensure safety at lower temperature. The surface slippage and the internal facet are the main characteristics of crack initiation at elevated temperatures to SLM K536 specimens with shorter fatigue life and longer fatigue life, respectively.

Development of high Fe content squeeze cast 2A16 wrought Al alloys with enhanced mechanical properties at room and elevated temperatures

In this study, the evolution of iron-rich intermetallics and their effects on room and elevated-temperature tensile properties of gravity die cast and squeeze cast 2A16 wrought Al alloys with high Fe content of 0.5% after T7 heat treatment were investigated by various methods. Compared to gravity die-cast alloys, squeeze cast 2A16 wrought Al alloys showed superior tensile properties at both room and elevated temperatures, especially in terms of elongation. This can be attributed to refinement in grain size and iron-rich intermetallics, which decreased porosity and raised dispersoids in α(Al) matrix. However, the increase in mechanical properties at high temperature resulting from applied pressure was lower than that obtained at room temperature. The results were attributed to the refinement in grain size and the weakness of grain boundary at elevated temperature.

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.

High temperature tensile properties of centrifugally cast in-situ Al-Mg2Si functionally graded composites for automotive cylinder block liners

The effect of Mg content (2.5 and 7.5 wt%) on the development of centrifugally cast in-situ A356-Mg2Si composite functionally graded material (FGM) has been investigated. The secondary dendrite arm spacing (SDAS) has the effect on size and volume% of Mg2Si particles. FGMs are characterized by optical and scanning electron microscopy, X-ray diffraction analysis, measurement of hardness and room and elevated temperature tensile properties (UTS). The microstructural features are correlated with room temperature and high temperature tensile properties at 150 °C and 300 °C. Since the population of Mg2Si particles are maximum at inner zones, the tensile strengths at these zones are maximum among the three zones. The room temperature tensile strength of FGM with 7.5 wt% Mg shows maximum value however it decreases at higher temperatures. The peak UTS of both FG composites in all three zones are attained at around 150 °C. Maximum peak UTS of 178 MPa is obtained with A356–2.5%Mg at this temperature. As the test temperature is increased, the fracture mode is changed from mixed mode to ductile mode. Particle cracking and decohesion of particles from the softer matrix are responsible for these two modes respectively.

Experimental Evaluation of Fatigue Behaviors and Tensile Properties of Selective Laser Melted K536 Alloy at Elevated Temperatures

Additive-manufacturing techniques show more and more utilization potentialities in today’s aviation industry. In order to ensure safe operation of additive-manufactured parts, it is important to have their mechanical properties well-characterized and assessed. In this study, elevated temperature fatigue behaviours and tensile properties of a selective laser melting (SLM) fabricated K536 alloy are investigated for horizontal and vertical building orientation, respectively. A series of tensile tests at 20 ºC ~700 ºC temperature range and stress-controlled fatigue tests at 400ºC and 600ºC are conducted. Effects of building orientation and temperature on tensile and fatigue behaviours are analysed. Scanning Electron Microscopy (SEM) is used to examine the fracture surfaces of fatigue specimens to qualify the failure mechanism and crack initiation sites. K536 parts manufactured via SLM are shown to exhibit anisotropic tensile properties at different testing temperatures. Anisotropy of fatigue properties is not obvious at 400ºC and 600ºC. Cracks are likely to initiate at the surface sliding or subsurface crystallographic plane of fatigue specimens in middle life regime and at subsurface or central zone crystallographic plane in longer life regime. In shorter life regime, cracks are easy to initiate at un-melted zones of fatigue specimens.

High temperature tensile properties of laser-welded high-strength Mg-Gd-Y-Zr alloy in as-welded and heat-treated conditions

The high temperature tensile properties of fiber laser-welded Mg-Gd-Y-Zr alloy in the as-welded and heat-treated state were systematically studied. The elevated temperature tensile properties of as-welded and heat-treated joints declined slightly from room temperature to 200 °C. With the temperature reaching 300 °C, the strengths of the two types of joints plummeted. High temperature tensile properties can be enhanced significantly by the β′ precipitates in the fusion zone and heat-affected zone after heat treatment. The ultrafine grains and unstable divorced eutectic in the fusion zone of as-welded joints deteriorated the tensile properties at 300 °C. The deformation mechanism of the heat-treated samples at 300 °C is the dislocation slip with void growth at the grain boundaries due to the dissolution of precipitates.

Effect of differential speed rolling on the room and elevated temperature tensile properties of rolled AZ31 Mg alloy sheets

Cast-rolling AZ31 Mg alloy sheets were manufactured at four rolling speed ratios of 0.8, 1.0, 1.2 and 1.3. The results show that the basal texture can be weakened by differential speed rolling (DSR). The AZ31 alloy sheet manufactured at a speed ratio of 1.2 exhibits a fine microstructure with an average grain size of 10.3μm. The yield strength, ultimate tensile strength and elongation-to-failure at this speed ratio are 145MPa, 240MPa and 28.5% at room temperature, respectively. These parameters mainly benefit from the fine grains and weakened basal texture. The AZ31 alloy sheets processed by the DSR exhibit a remarkable improvement in elongation-to-failure compared with the AZ31 alloy sheets processed by equal speed rolling (ESR) primarily due to the weakened basal texture at room temperature. However, the difference in elongation-to-failure of the AZ31 alloy sheets processed by the ESR and DSR decreases at elevated temperatures, which can be attributed to the weakening of the influence of basal texture, with probable activation of non-basal slips and grain boundary sliding (GBS). The results obtained here will shed light on some DSR methods, which is critical to the development of Mg alloys with high mechanical properties.

Effects of warm laser peening on the elevated temperature tensile properties and fracture behavior of IN718 nickel-based superalloy

IN718 nickel-based superalloy specimens were treated by laser peening (LP) and warm laser peening (WLP) respectively. Tensile tests were performed on the matrix and treated specimens at both room (25°C) and elevated temperature (700°C). Tensile properties were examined by engineering stress-strain curves. The sectional micro-structural observations were carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in sequence to investigate the micro-structural evolution and precipitation strengthening mechanism. The fracture morphologies of untreated, LP and WLP treated specimens after tensile deformation at elevated temperature were also analyzed. The results show that LP process, in particular WLP process were found to have a remarkable effect on improving tensile properties of IN718 superalloy at both room and elevated temperatures. WLP treated specimens exhibited more stable high-temperature tensile properties. A serrated flow phenomenon was found in the stress-strain curves at elevated temperature. More δ precipitates dispersed in the grain boundaries after WLP treatment. Detailed TEM microstructural analysis showed that various typical microstructures including dislocation lines, dislocation tangles, dislocation arrays, mechanical twins and precipitated particles tangled together, forming the strengthening phase. A new formed substructure of submicron rhombic blocks with lengths in the range of 400–600nm was observed in the WLP treated specimens. In addition, the WLP treated specimens exhibited a ductile fracture mode, which was totally different with the ductile-brittle mixed fracture mode in untreated and LP treated specimens. WLP process is verified as an effective method to enhance the high-temperature properties of IN718 nickel-based superalloy.

Effect of heat treatment on elevated temperature tensile and creep properties of the extruded Mg–6Gd–4Y–Nd–0.7Zr alloy

The light and heavy rare earth elements are added to the magnesium alloys to improve the strengths and the creep resistance. The age hardening behaviors of the extruded Mg–6Gd–4Y–Nd–0.7Zr alloy aged at 200, 225 and 250°C were investigated. Tensile tests and creep tests of the extruded and extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr were carried out at 150–300°C. The relationship between the microstructure and the properties of the extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr alloy was studied. The result shows that the extruded Mg–6Gd–4Y–Nd–0.7Zr (contained less than 10wt% Gd) peak aged at 225°C for 72h has the excellent creep resistance and high strengths with the UTS more than 350MPa from room temperature to 200°C, which are correlative with the precipitates. The high dense and uniform distribution of β′ phase with good heat stability precipitates inhibiting the dislocation motion contributes to age hardening, accelerates the ageing hardening response and increases the creep resistance. The artificially aged (T5) at low temperature further creep tested and tensile tested at higher temperatures decreases the resistance to the dislocation motion and the grain boundary sliding, resulting in the reduction in creep properties and strengths of the extruded-T5 Mg–6Gd–4Y–Nd–0.7Zr alloy above 225°C.