Elevated Temperature Tensile Properties Research Articles

Role of TiC on the microstructure, tensile property and thermal stability of laser powder bed fusion fabricated AlSi10Mg alloy

The incorporation of ceramic particles is frequently employed to enhance the printability of high-strength aluminum (Al) alloys in laser powder bed fusion (L-PBF). However, their influence on the long-term thermal stability and elevated temperature mechanical properties of the Al alloy is seldom studied. This study aims to address this gap by investigating the role of micron-sized TiC particles in the microstructure, long-term thermal stability, and elevated temperature tensile properties of an L-PBF-fabricated AlSi10Mg alloy. The results indicate that highly dense TiC/AlSi10Mg samples can be fabricated, featuring fine equiaxed grains rather than the coarse columnar grains typically formed in the AlSi10Mg alloy. This columnar-to-equiaxed transition is attributed to the residual TiC and the in-situ formation of Al3Ti particles, which act as nucleating agents. Moreover, the incorporation of TiC significantly enhances the long-term thermal stability of the AlSi10Mg alloy by improving the stability of the eutectic network and retarding the coarsening of Si particles by inhibiting Si diffusion. Compared to the AlSi10Mg counterpart, the TiC/AlSi10Mg composite exhibits a higher hardness retention ratio (56 % versus 45 %) after thermal exposure at 400 °C for 192 h. The residual TiC and in-situ formed Al3Ti have high thermal stability and can impede dislocation motion, thereby contributing to enhanced long-term thermal stability. This study offers insights into the design of L-PBF ceramic-reinforced Al alloys with improved thermal stability for high-temperature applications.

Unusually high room and elevated-temperature tensile properties observed in direct aged wire-arc directed energy deposited Inconel 718

Wire-arc directed energy deposition (DED) processed Inconel (IN) 718 is known to have coarse columnar grains, strong texture, and significant chemical and microstructural inhomogeneity in the as-fabricated condition. Homogenization treatment is commonly used prior to aging to eliminate the inhomogeneity and detrimental precipitation for better mechanical properties. In this study, however, direct aging (DA) at 700 °C without homogenization has resulted in room-temperature yield strength, ultimate tensile strength (UTS), and elongation that are comparable to wrought condition and among the highest reported properties for wire-arc DED IN718. The DA samples at between 650 and 750 °C aging also demonstrates remarkable ductility when deformed at elevated temperatures. In addition, when aged below 750 °C the DA IN718 possesses significantly higher UTS compared to those with homogenization treatment. These superior mechanical properties are highly likely due to the non-uniform and hierarchical precipitation consisting of disk-shaped γ″ in diameter from a few to tens of nm in the dendritic core area and micron-sized Laves phase and carbides in the inter-dendritic region.

Suppression of texture and enhancement of high-temperature tensile property in heavily deformed gradient Ti2AlNb alloy

Hot isostatic pressed Ti2AlNb alloys with trapezoid-shaped sections were hot rolled at 1000 °C to obtain the specimens with the gradient of deformation. The effect of the rolling reduction on the microstructure of the Ti2AlNb alloys was investigated by this high throughput method, and the mechanical properties of the gradient alloys were studied. With the increasing rolling reduction, the morphology of the orthorhombic (O) phase changed from well-arranged herringbone and palisade structures to a randomly distributed lamellar structure. By the electron backscatter diffraction characterization, the textures of the B2 and O phases changed with the increasing rolling reduction, and the texture of the O phase was depressed. The elevated-temperature tensile properties of the Ti2AlNb and Mo-modified Ti2AlNb gradient specimens were measured, and the deformation gradient was 36.0–43.0% and 43.0–50.0%, respectively. The heavily deformed gradient specimens exhibited higher strength and ductility than the lightly deformed ones, due to the increasing low-angle grain boundary and uniform distribution of local strain.

Tailoring the microstructure and mechanical properties of IN718 alloy via a novel scanning strategy implemented in laser powder bed fusion

The microsegregation of the brittle Laves phase at the interdendritic boundaries during additive manufacturing of IN718 leads to microvoid formation under tensile loads, thus, the mechanical properties are negatively affected. Recent advances have shown that extensive control over microstructural evolution is possible by modifying the additive manufacturing processes. Herein, it is aimed to tailor the final microstructure, managing the morphology of Laves phase, via implementing a novel scanning method, called time-homogenization (TH), in the laser powder bed fusion processing. Direct aging, solutionizing + direct aging, and homogenization + solutionizing + direct aging heat treatments were applied to increase the microstructural stability of additively manufactured IN718 at elevated temperatures. The modified microstructural features, microhardness, room and elevated temperature (550 °C and 650 °C) tensile properties of as-built and heat-treated specimens were systematically investigated considering the precipitation strengthening mechanism. Compared to the samples built by the standard scanning strategy (SP), fine and granular Laves phases were observed in TH specimens while SP specimens have coarse and chain-like Laves phases. Moreover, TH specimens after direct aging heat treatment exhibited an excellent combination of strength and ductility at room and elevated temperature.

Correction: On the Room- and Elevated-Temperature Tensile Properties of Hot-Rolled 6082 Alloys Containing Thermally Stable Dispersoids

Correction: On the Room- and Elevated-Temperature Tensile Properties of Hot-Rolled 6082 Alloys Containing Thermally Stable Dispersoids

On the Room- and Elevated-Temperature Tensile Properties of Hot-Rolled 6082 Alloys Containing Thermally Stable Dispersoids

On the Room- and Elevated-Temperature Tensile Properties of Hot-Rolled 6082 Alloys Containing Thermally Stable Dispersoids

Significant enhancement in high-temperature tensile strength of trace nano-Y2O3-reinforced TiAl alloy prepared by selective electron beam melting

In this study, the effect of 0.2 wt% Y2O3 nanoparticles addition on the microstructure and elevated-temperature tensile properties of TiAl alloy prepared by selective electron beam melting (SEBM) were investigated. The results indicated that the microstructures of Ti–48Al–2Cr–2Nb and Ti–48Al–2Cr–2Nb–0.2Y2O3 alloys were similar, except for the homogeneous distribution of Y2O3 nanoparticles, which were mainly composed of equiaxed γ, blocky B2, and a few (α2/γ) lamellar colonies. The nano-Y2O3 particles induced a large number of dislocations and twins around the reinforcing particles due to the thermal mismatch caused by rapid heating and cooling during SEBM layer-by-layer fabrication, and the density of geometrically necessary dislocations increased from 5.70 × 1013 to 4.92 × 1014 m−2. The high-temperature ultimate tensile strength increased significantly from 539 ± 2 MPa to 680 ± 3 MPa at 750 °C. The fracture elongation of Ti-48Al-2Cr-2Nb (66 ± 3%) was much larger than that of Ti-48Al-2Cr-2Nb-0.2Y2O3 (19 ± 1%) when tested at 750 °C. The ultimate tensile strength and fracture elongation of Ti-48Al-2Cr-2Nb-0.2Y2O3 were 539 ± 6 MPa and 56 ± 1%, respectively, when tested at 800 °C. Finally, the strengthening mechanism attributed to the added Y2O3 nanoparticles was discussed. These findings provided us an important reference for enhancing high-temperature mechanical properties of TiAl alloys.

Microstructures and High Temperature Tensile Behaviours of Laser Powder Bed Fusion Fabricated Al-Mn-Sc Alloy

The introduction of Sc/Zr inoculates to aluminium (Al) alloys for laser powder bed fusion (LPBF) provides numerous benefits, including laser processability improvement, solidification microstructure control and mechanical property enhancement. Though great efforts have been put into tailoring the microstructure and room temperature mechanical properties via process parameter optimisations, the potential roles of Sc/Zr inoculate modified Al alloys for high-temperature applications were still underexplored. In this study, the microstructural stability and the elevated temperature tensile behaviours of LPBF-processed Al-Mn-Sc alloy were systematically evaluated. The alloy demonstrated high microstructural stability after both heat treatment and high-temperature tensile testing for up to 573 K. The applied tensile testing temperature and strain rate played significant influences on the elevated temperature tensile properties and deformation behaviours. Unusual intermediate temperature embrittlement (also known as ductility dip) and yield drop behaviours were observed under certain testing temperature and strain rate regimes, and the underlying deformation mechanisms were elucidated in detail. The present study is expected to shed light on future high-performance, high-temperature Al alloy development for the LPBF process.

Ambient, elevated temperature tensile properties and origin of strengthening in friction stir welded 6 mm thick reduced activation ferritic-martensitic steel plates in as-welded and post-weld normalised conditions

Reduced Activation Ferritic-Martensitic (RAFM) steels are currently being considered for test blanket modules of International Thermonuclear Experimental Reactor. This study is aimed at understanding the microstructure and mechanical properties of Indian RAFM steel during friction stir welding (FSW) of 6 mm thick plates. The full penetration bead-on-plate welds were fabricated employing PcBN tool at a rotational speed of 200 rpm. The FSW joint consisted of stir zone, thermomechanically affected zone and BM. Microstructure, hardness and tensile properties were evaluated in as-received (base metal, BM), as-welded and post weld normalised + tempered states. The as-received microstructure was composed of Cr-rich M23C6 on prior austenite grain and tempered lath martensite boundaries with intra-lath V-and Ta -rich monocarbides. Substantial changes occurred during welding leading to destruction and dissolution of M23C6 and precipitation of Fe3C in SZ. The microstructure was restored to the BM level by giving a post weld normalising and tempering treatment. Comparative study on tensile properties has been carried out at room and elevated temperatures (up to 550 °C) in all the three states and the observed variations have been explained on the basis of initial microstructure and evolving substructures. The as-welded samples showed higher strength and low percentage elongation values. The ductility was minimum in all the states at an intermediate temperature and ascribed to the dynamic strain ageing. All the states revealed falling strength with increasing temperature up to 550 °C. Failure occurred in AW and PWNT states at the interface between TMAZ and BM. Irrespective of material state and tensile test temperature, the transgranular ductile fracture prevailed. The contribution of the different strengthening mechanisms to the yield strength of the SZ region has been estimated theoretically and it matches with the experimental results. The influence of low angle grain boundaries (LAGB) and high angle grain boundaries (HAGB) on the tensile behaviour of the SZ was well explained using the Electron Back Scattered Diffraction (EBSD) maps of these regions.

Heat treatment effect on the microstructure and elevated temperature tensile property of the Ti6242S alloy fabricated via laser powder bed fusion

The microstructural evolution and its consequence on the room and elevated temperature (500 °C) tensile properties of the Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti6242S) alloy fabricated via the laser powder bed fusion were investigated after the following heat treatments: solution treatment followed by aging (STA), super-transus heat treatment, and water quenching (WQ) after annealing at a sub-transus temperature (885, 925, 954, and 982 °C) in the (α + β) regime. The super-transus heat treatment results in the removal of columnar prior β grains and formation of equiaxed grains that consist of α colonies. The WQ triggers the formation of a bimodal microstructure of α and α´ phases, and the volume fraction of α´ phase increases with increasing the WQ temperature. The STA process leads to a high yield strength (σy: ~658 MPa) and an elongation to fracture (εf: ~14.8%) when tested at 500 °C. The super-transus heat treatment results in a lower yield strength at both room and elevated temperatures due to coarsening of the α laths. The WQ process allows for the tailoring of the tensile property in a broad window, and the yield strength increased with increasing WQ temperatures. Particularly, the 885 and 925-WQ samples showed a remarkably enhanced strain hardening behavior during tensile tests. The 925-WQ samples exhibited a high σy of ~706 MPa and an εf of ~11.0% at elevated temperature. The samples that underwent STA processing and 925-WQ showed a higher σy while maintaining a decent ductility relative to the conventionally fabricated counterparts at 500 °C, indicating the potential elevated temperature applications for the Ti6242S alloy fabricated via laser powder bed fusion coupled with heat treatment.

Effect of deposit thickness on microstructure and mechanical properties at ambient and elevated temperatures for Inconel 718 superalloy fabricated by directed energy deposition

The effect of deposit thickness on the microstructure and the mechanical properties of Inconel 718 (IN718) fabricated by directed energy deposition was systematically investigated in both as-deposited (AD) and homogenization + solution + aging (HSA) treated conditions. Results indicate that deposit thickness for thin parts has a more significant impact on the microstructure and subsequent room (RT) and elevated temperature (650 °C) tensile properties compared to thick parts. Applying HSA treatment can effectively homogenize the microstructure of thick builds with a microstructure transition from columnar-dendritic grain structure presented in the AD condition to recrystallized equiaxted grain structure, which results in almost similar yield strength, ultimate tensile strength and ductility of ~ 970 MPa, ~ 1237 MPa, ~ 20% at RT and ~ 816 MPa, ~ 954 MPa, ~ 12% at 650 °C, respectively. In contrast, thin parts maintaining columnar grain features during HSA treatment yield a higher yield strength of 1112 MPa (increased by 15%) at RT and 936 MPa (increased by 15%) at 650 °C, but much lower ductility of 9% (decreased by 54%) at RT and 6% MPa (decreased by 51%) at 650 °C. The remaining large amount of residual stress primarily contribute to the enhancement of yield strength, as well as large amount of δ phase responsible for the much worse ductility for thin parts after HSA treatment. In addition, the underlying thermal history evolution in various deposit thickness is elucidated by the thermal simulations with the use of Finite Element Method (FEM) method within 3DExperience software. The results present in the current study show the capability of the directed energy deposition process to manufacture homogeneous components with varying thickness for high temperature application after a proper heat treatment, with regard to their initial as-deposited materials.

Effect of gradient microstructure on elevated temperature mechanical properties of Ni-based superalloy ATI 718Plus

The effect of the ultrasonic surface rolling process (USRP) and post-treatment on the microstructure and elevated-temperature tensile properties of ATI 718Plus were investigated. The gradient distribution of the η-Ni3(Al0.5Nb0.5) phase and recrystallized grains was generated on the surface of the USRP-treated samples after heat treatment. The amount of η phase in the gradient layer decreased with increasing depth, whereas grain size showed the opposite trend. These η phase particles, distributed in the grain boundaries (GBs) of the gradient microstructure with refined grains, stabilized the trans-scale grain hierarchy at a high temperature of 704 °C. This heterogeneous microstructure promotes the accumulation of high-density geometrically necessary dislocations (GNDs) near the GBs and η phase during plastic deformation, resulting in additional hardening. The central coarse grains in the heterogeneous structure were subjected to the most plastic deformation and conserved ductility during the tensile tests. Compared with the standard sample, the yield strength (YS) and ultimate tensile strength (UTS) of the ultrasonically rolled samples increased by approximately 12% during tensile tests at 704 °C, without distinct plastic deterioration occurring. This study helps to improve the understanding of the functional mechanism of the equilibrium secondary phase in superalloys and the influence of the distribution state of the equilibrium phase on the mechanical properties.

Elevated temperature tensile properties of an extruded aluminium alloy reinforced with SiCp

Abstract Elevated temperature tensile properties of AlSi7Mg (Al-7 %Si– 0.7 %Mg) and its composites with 10 and 20 vol.% SiCp in the as-extruded form were investigated. The cast ingots of the matrix alloy and the composites were produced by the permanent die casting technique and extruded at 480 °C using an extrusion ratio of 10 : 1. The high-temperature tensile tests were carried out over the temperature range from 25 to 430 °C. Mechanical properties after extrusion show that the composite samples have strength values superior to that of the matrix alloy at ambient temperature. At elevated temperatures the results indicate that the composites exhibit good strength retention up to 300 °C, above which the strengthening effect of SiCp disappears as the temperature is increased. The strain rate sensitivity “m” was observed to be 0.11 for the matrix alloy, 0.13 and 0.07 for the composites with 10 and 20 vol.% SiCp, respectively, at a test temperature of 430 °C in the strain rate range from 4 × 10 –5 to 4 × 10– 2 s– 1.

The tensile creep behavior of a B4C-bearing high Nb containing TiAl alloy

In the present paper, the effect of B4C addition on elevated temperature tensile properties and creep resistance of as-cast Ti–43Al–6Nb–1Mo–1Cr alloy has been characterized. Experimental results reveal that 0.2 at. % B4C can improve the ultimate tensile strength and elongation of alloy at 800 °C. The steady-state creep rate of alloy with the addition of B4C decreases from 2.3 × 10−6 s−1 to 5.2 × 10−7 s−1 at 800 °C under 300 MPa. The stress exponent (n) and the apparent activation energy (QC) of alloy with the addition of B4C are measured to be 3.18 at 800 °C and 416.410 kJ/mol under 300 MPa, respectively. Combining microstructure observation, the dominant creep deformation mechanisms of Ti–43Al–6Nb–1Mo–1Cr-0.2B4C alloy at 800 °C under 300 MPa are mechanical twinning and dislocation slipping pinned by solute carbon atoms. During creep, the α2 lamellar dissolution and α2/γ interface migration occur simultaneously, and the dynamic recrystallization at colony boundary effectively alleviates the stress concentration resulting from dislocation pile-ups. In addition, the initiation of cavities as well as the propagation and coalescence of cracks are the main creep fracture features. Particularly, TiB can prevent dislocation motion and prolong the crack propagation path to increase creep resistance.

Microstructure Characteristics and Elevated-Temperature Tensile Properties of Al-7Si-0.3Mg Alloys with Zr and Hf Addition

Microstructure Characteristics and Elevated-Temperature Tensile Properties of Al-7Si-0.3Mg Alloys with Zr and Hf Addition

Microstructure and high temperature tensile properties of Al–Si–Cu–Mn–Fe alloys prepared by semi-solid thixoforming

The differences in the microstructure and elevated temperature tensile properties of gravity die cast, squeeze cast, and semi-solid thixoformed Al–Si–Cu–Mn–Fe alloys after thermal exposure at 300 °C were discussed. The results demonstrate that the elevated temperature tensile properties of semi-solid thixoformed alloys were significantly higher than those of gravity die cast and squeeze cast alloys, especially after thermal exposure for 100 h. The ultimate tensile strength (UTS) of semi-solid thixoformed alloys after thermal exposure at 300 °C for 0.5, 10 and 100 h were 181, 122 and 110 MPa, respectively. The UTS values of semi-solid thixoformed alloys were higher than those of heat resistant aluminum alloys used in commercial applications. The enhanced elevated temperature tensile properties of semi-solid thixoformed experimental alloys after thermal exposure can be attributed to the combined reinforcement of precipitation strengthening and grain boundary strengthening due to thermally stable intermetallic phases as well as suitable grain size.

Temperature and strain-rate dependence of the elevated temperature ductility of Inconel 718 prepared by selective laser melting

The elevated temperature tensile properties of SLM IN718 were measured as a function of strain rate and test temperature to better understand the time-dependent and thermal aspects of environmental sensitivity. SLM and wrought materials were solution treated, aged, and tested over the range of 550–750 °C and 10−3 to 10−6 s−1. The SLM material tested across all conditions had inferior strength and ductility compared to wrought material of the same heat treatment because of environmental sensitivity in the form of dynamic embrittlement. SLM samples show evidence of brittle intergranular fracture, crack growth, and oxidized NbC particles on the fracture surface, which all contribute to the observed poor ductility. These features, and subsequent embrittlement, are intensified with decreasing strain rate and increasing temperature. Higher strain rates and lower temperatures are shown to improve the ductility in SLM IN718 but despite this recovery it remains susceptible to environmental attack even in the extreme cases of the current study. The prevalence of NbC at grain boundaries in the SLM material is the principal source of dynamic embrittlement and environmental sensitivity.

Investigation of microstructure-tensile behavior relationship in Hastelloy X Ni-based superalloy processed by laser powder-bed fusion: Insights into the elevated temperature ductility loss

The microstructure-tensile response correlation in a crack-free laser powder-bed fusion (LPBF) Hastelloy X Ni-based superalloy is investigated. The LPBF process parameters in terms of volumetric energy density were optimized to obtain the maximum relative densities, as well as the lowest defect size. The microstructure and tensile behavior of samples were evaluated. Microstructural characterizations showed that the columnar grains of the austenite phase consisted of a submicron cellular microstructure with a weak texture along <100> direction. The as-built sample had an acceptable tensile behavior at the ambient temperature, as compared to the AMS 5536 N standard specification. However, at 760 °C, it was observed that the plastic deformation of the as-built sample was influenced by an intergranular brittle fracture, leading to the elevated temperature ductility loss. The results of fractography investigations, performed by means of electron backscatter diffraction analysis, indicated that grain boundaries were precipitation-free and the cracks were formed in the areas with a high Taylor factor value. The investigations also demonstrated that a high degree of grain-to-grain incompatibilities, especially in the grains having <110> parallel to the building direction orientation, resulted in the stress concentration in the grain boundaries, leading to inferior elevated temperature tensile properties.

Microstructure and elevated temperature tensile property of Ti–46Al–7Nb-(W,Cr,B) alloy compared with binary and ternary TiAl alloy

The newly developed high-Nb TiAl with a small amount of W, Cr, and B addition prepared by electromagnetic cold crucible has been investigated by comparing with the microstructure and elevated temperature tensile properties of binary and ternary high-Nb TiAl alloy. Results indicate that microstructures of the three alloys are fully lamellar (FL), near fully lamellar (NFL) and near fully lamellar alloy with TiB (NFL + TiB). The dispersed TiB particles in the alloy have the B27 structure and are highly enriched with Nb and W but depleted with Al by the characterization of transmission electron microscopy. The elevated temperature tensile test results show that the high-Nb TiAl alloy with NFL + TiB microstructure exhibits excellent mechanical properties compared with the other two alloys, and the tensile strength and elongation at 800 °C are 648 MPa and 5.73%, respectively. Fracture morphology shows the alloy has a mixed mode of trans-lamellar and inter-lamellar fracture. As the dispersed second phase particles, rod-like TiB can act as the obstacle to crack propagation and dislocation movement. The excellent mechanical properties of the alloy at elevated temperatures are attributed to the combined effects of dislocation block and nanotwins formation during deformation within the γ lamellae. Moreover, the probable generation and propagation mechanism of dislocations and twins in the γ lamellae are further discussed.

Microstructure and enhanced mechanical properties of hybrid-sized B4C particle-reinforced 6061Al matrix composites

In the present work, the microstructure and elevated-temperature tensile properties of 6061Al alloy and 6061 Al matrix composites reinforced with bimodal-sized (micron + nano) B4C particles or monomodal micro-sized B4C particles are investigated. The results demonstrate that nanoscale B4C (n-B4C) particles are present both at the grain boundaries and within the grains in the composite. Due to the presence of n-B4C particles, there is a decrease in matrix grain size and recrystallization region percentage, and an increase in proportion of low angle grain boundaries. The combined mechanical property and theoretical analyses reveal that n-B4C particles play a significant role in hindering the dislocation movement and limiting the grain boundary slip during tensile deformation, causing an increase in ultimate tensile strength of the annealed composite with bimodal-sized B4C particles at elevated temperatures. The analysis shows that dislocation glide and climb are responsible for the elevated-temperature strengthening mechanism associated with the n-B4C particle addition. For the annealed composites, the ductile fracture of matrix is the primary failure mode at elevated temperatures.