High Temperature Tensile Properties Research Articles

Enhanced mechanical properties of a near-α titanium alloy by tailoring the silicide precipitation behavior through severe plastic deformation

The microstructure evolution, tensile properties, and strengthening mechanisms of a near-α high-temperature titanium alloy with high Zr and Si content during isothermal multi-dimensional forging (IMDF) at the β-phase region were systematically investigated. The results show that the alloys exhibit a basket-weave microstructure after IMDF, with the silicides diffusely distributed in the matrix. As the forging temperature decreased, the intragranular primary α laths became more refined and the volume fraction of silicides increased, while the average size of silicides gradually decreased. The dynamic spheroidization of α laths occurs preferentially at the prior β grain boundary and extends into the grains as the deformation temperature decreases. The IMDF-1100 alloy possesses excellent high-temperature tensile properties and moderate room-temperature tensile properties, with ultimate tensile strengths (UTS) of 738.4 MPa and 1124.8 MPa at 650 °C and room temperature, respectively, which makes the alloy have tremendous potential for aerospace applications. The strengthening of the alloy at room temperature is primarily attributed to microstructure refinement and the thermal mismatch between silicide and matrix. However, owing to the weakening of grain boundaries at 650 °C, grain refinement leads to a decrease in tensile strengths. When tensile at 650 °C, the fragmentation and decohesion of large-size silicides tend to cause premature fracture of the alloy, and the microstructure with small-size silicide distribution presents better ductility.

Dynamic recrystallization-dependent high-temperature tensile properties and deformation mechanisms in Al-Mg-Sc-Zr alloys

This research elucidates discontinuous dynamic recrystallization (DDRX)-dependent high-temperature tensile properties and deformation mechanisms in simply extruded Al-7Mg alloys tailored by Sc/Zr ratios. The bimodal-grained Al-7Mg-0.4Sc alloy presents a high elongation to failure of ∼540% at 400 °C and 5 × 10−4 s−1. However, such superplastic behavior has not been observed in both coarse-grained Al-7Mg-0.1Sc-0.3Zr and Al-7Mg-0.3Sc-0.1Zr alloys. Thermally stable dispersed nano-sized Al3(Sc,Zr) particles strongly retard DDRX, accompanied by the retention of heterogeneous grain structure in Al-7Mg-0.1Sc-0.3Zr till fracture. The predominance of dislocation slip is proved by analyzing the evolution of texture and dislocations. In contrast, the bimodal grain structure evolves into a homogeneous fine one in Al-7Mg-0.4Sc with tensile deformation proceeding since coarsening Al3Sc precipitates play a weak role in restricting DDRX. The superplasticity in Al-7Mg-0.4Sc is achieved by cooperated mechanisms, i.e., grain boundary sliding (GBS) and dislocation slip as dominant mechanisms, which is accommodated by DDRX in the initial tensile deformation stage, followed by dislocation slip-accommodated GBS in the late stage.

High-temperature tensile and creep properties of TiB-reinforced Ti6Al4V composite fabricated by laser powder bed fusion

High-temperature tensile and creep properties of TiB-reinforced Ti6Al4V composite fabricated by laser powder bed fusion

Effects of Fe and Ni on the Microstructure and High Temperature Tensile Properties of Al-Si Aluminium Alloys

The effects of varied contents of Ni (1.2 wt.%, 1.6 wt.%) and Fe (0.6 wt.%, 0.8 wt.%) on the microstructure and high temperature mechanical properties of Al-Si alloy were studied using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and tensile testing machine. The experimental results demonstrate that Ni element plays a crucial role in modifying the Fe-rich phase type, morphology and distribution in the Al-Si alloy. The addition of 1.2 wt.% Ni and 0.6 wt.% Fe could generate a Chinese script Fe-rich strengthening phase in Al-Si alloy. Further increasing to 1.6 wt.% Ni and 0.8 wt.% Fe, the long needle-shape Fe-rich phase was detected. High temperature tensile properties of the alloy were significantly improved, because of the Chinese script Fe-rich strengthening phase in the Al-Si alloy containing 1.2 wt.% Ni and 0.6 wt.% Fe. The ultimate tensile strength (UTS) of Al-Si alloy with 1.2 wt.%Ni-0.6 wt.% Fe is up to 229 MPa, 174 MPa and 139 MPa at 250 °C, 300 °C and 350 °C, respectively.

Tensile properties of 2D-C/SiC composites at temperatures up to 1873 K at wide-ranging strain rates

We determined the tensile properties of 2D-C/SiC composites at temperatures up to 1873 K with a wide range of loading rates (10−3 s−1 and 400 s−1) in argon and air. We developed a high-temperature Hopkinson tensile bar with tensile strength based on the loading rate, temperature, and oxidation. Under high loading rates, tensile strength was influenced by the nucleation of multiple cracks and the improvement of C-fiber pull-out length and interface strength. In argon, material component performance and thermal residual stress influenced the 2D-C/SiC high-temperature tensile properties. In air, oxidation damage significantly affected the tensile properties of 2D-C/SiC regardless of loading rate or temperature. This led to lower tensile strength and higher strain rate sensitivity. Our observations can enhance the understanding of the failure mechanism of thermo-chemo-mechanical coupling in 2D-C/SiCs and will provide guidance for safe application in extremely high-temperature conditions.

Microstructure and Mechanical Properties of Cast Al-Si-Cu-Mg-Ni-Cr Alloys: Effects of Time and Temperature on Two-Stage Solution Treatment and Ageing

Ameliorating the high-temperature performance of cast Al-Si alloys used as engine components is essential. The effects of different T6 heat-treatment processes on the microstructure and mechanical properties of cast Al-Si-Cu-Mg-Ni-Cr alloys were investigated in the present study. The results demonstrate that, under the optimal solution treatment conditions of 500 °C for 2 h and 540 °C for 4 h, the T-Al9FeNi phase was present in the alloy, and the roundness of primary Si and the aspect ratio of eutectic Si in the alloy reached valley values of 1.46 and 2.56, respectively. With increasing ageing time at 180 °C, the tensile strength significantly improved, while the microhardness first increased and then decreased. When the ageing time was 4 h, microhardness reached a peak value of 155.82 HV. The fracture characteristics changed from quasi-cleavage to the coexistence of quasi-cleavage and dimples. After heat treatment, the high-temperature tensile properties of the alloy improved, which is a significant advantage compared to the as-cast alloy. The stable Al3Ni and Al9FeNi phases inhibited the cracking of the alloy at 350 °C.

Formation of dendrites and strengthening mechanism of dual-phase Ni36Co30Fe11Cr11Al6Ti6 HEA by directional solidification

In order to reveal the effect of solidification rate on microstructure and improve room and high temperature tensile properties, Ni36Co30Fe11Cr11Al6Ti6 high entropy alloys (HEAs) were prepared by directional solidification at different solidification rates (5, 10, 20, 50 and100 μm/s). Results show that two kinds of dendrite form in the directionally solidified process. One is primary solidified dendrite, which is composed of FCC1 phase enriched in Co, Cr and Fe. Another is secondary solidified dendrite, forming between the primary solidified dendrites and consisting of the FCC2 phase enriched in Ni, Al and Ti. As the solidification rate increases, the primary solidified dendrite spacing decreases, the solute enrichment layer overlaps, and the constitutional undercooling in the inter-dendrite region decreases, increasing the difficulty of the secondary solidified dendrite formation. Tensile results show that the strength of Ni36Co30Fe11Cr11Al6Ti6 HEAs gradually increases with the increase of solidification rate. The alloy with a solidification rate of 100 µm/s exhibits excellent comprehensive room temperature properties, the yield strength, fracture strength and tensile strain are 732 MPa, 1020 MPa and 34.9 %, respectively. Furthermore, the directionally solidified Ni36Co30Fe11Cr11Al6Ti6 HEA still remains high yield strength of 533 MPa at 900 ℃. Fine grain strengthening, solid solution strengthening, second phase strengthening and hysteresis diffusion effects play an important role in enhancing the mechanical properties. By comparing the mechanical properties of other HEAs at room and high temperature, the proposed directionally solidified Ni36Co30Fe11Cr11Al6Ti6 HEAs with excellent mechanical properties show great potential in industrial applications.

A performance comparison of additive manufactured creep-resistant superalloys

Creep-resistant nickel, cobalt based superalloys, selected for a high-speed flight application, deposited using Wire + Arc Additive Manufacturing (WAAM), was reported. Three different alloys, Haynes 188, Inconel 718, and Rene 41, were deposited, and tested for their high-temperature tensile properties, and the results compared with wrought data. The alloys were tested from ambient temperature to 1000°C in their as-deposited condition and after undergoing industry standard age-hardening and solutionising heat-treatments, to down select the best performing alloy under two different processing conditions. The mechanical strength of the alloys fell short of the maximum achievable in wrought condition. Precipitation-strengthened alloys, Inconel 718 and Rene 41 were found to have underperformed the most significantly, whereas solid-solution-strengthened Haynes 188 suffered the least due to WAAM.

Enhancing high-temperature tensile properties of Ni/Ni-W laminated composites for MEMS devices

There is an increasing demand for materials with excellent mechanical performance for Micro-Electro-Mechanical System (MEMS) devices serving at elevated temperatures. However, how to enhance the high-temperature strength of the materials without losing their plasticity is a pending problem. Here, the Ni/Ni-W laminated composites with different monolayer thicknesses and the same ratio of the constituent layer thicknesses were fabricated successfully by using the dual-bath electrodeposition technique. The microstructure stability and tensile properties of annealed Ni/Ni-W laminated composites with different monolayer thicknesses were investigated at 400 °C. The results show that the annealed Ni0.5/Ni-W0.05 laminated composites have both high yield strength (450 MPa) and excellent elongation to failure (25.1%) at 400 °C, being superior to that of the monotonic Ni (179 MPa and 17.7%). Such a high strength of the laminated composite at 400 °C results from the contribution of the intrinsically high strength of the Ni-W layers with excellent thermal stability, the thickness-constrained effect on grain growth of Ni layers and the interface coupling effect of heterogeneous structures. The good plasticity may be derived from the heterogeneous laminated structure and the decrease in the constituent layer thickness, providing a good co-deformation ability. Basic mechanisms for the high tensile strength and good plasticity of the Ni/Ni-W laminated composites at 400 °C were analyzed theoretically. The findings reveal a potential strategy to fabricate MEMS components with excellent high-temperature tensile properties through tailoring the microstructure thermal stability and the constituent layer scale.

High-Temperature Tensile Properties of a Cobalt-Based Co-20Cr-15W-10Ni Superalloy with a Bimodal Grain Structure

Cobalt-based superalloys are common materials for the manufacturing of various components used in aerospace applications. Conventional cobalt-based superalloys with a unimodal grain structure generally exhibit low strength and ductility at high temperatures. A bimodal grain structure of a cobalt-based superalloy, Co–20Cr–15W–10Ni (CCWN), was designed to achieve both high strength and ductility at high temperatures. The deformation behavior and tensile properties of a CCWN alloy with unimodal fine-grain (FG), coarse-grain (CG), and bimodal (FG/CG) structures were investigated at 900 °C. The microstructures and substructures after high-temperature deformation were examined via electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) to determine the deformation mechanisms. The microstructural observation showed that the bimodal grain structure consisted of FG and CG domains. During high-temperature deformation at 900 °C, the FG structure was mainly deformed by dynamic recrystallization (DRX), maintaining a similar FG structure. The CG structure was mainly deformed by DRV, resulting in a small amount of DRX grains and a large amount of dynamic recovery (DRV) grains. However, the bimodal grain structures were mainly softened via DRX and transformed into a new bimodal structure, ultrafine grain (UFG) and FG. The FG domains tended to deform via dislocations, and the CG domains via twinning. The high-temperature tensile tests revealed that the bimodal-structured alloy exhibited both higher strength and ductility than those of the alloy samples with unimodal FG or CG structure. This is associated with the newly developed UFG/FG structures in the bimodal grain-structured samples during high-temperature deformation. This work may provide new insight into the development of high-temperature alloys with bimodal grain structures.

Influence of shot peening on the microstructure and high-temperature tensile properties of a powder metallurgy Ni-based superalloy

Influence of shot peening on the microstructure and high-temperature tensile properties of a powder metallurgy Ni-based superalloy

High-temperature fatigue damage mechanism and strength prediction of vermicular graphite iron

The high-temperature tensile properties, high-cycle fatigue properties and related damage mechanisms of vermicular graphite iron (VGI) with different microstructures at 500 °C were investigated. It is found that compared with ferritic VGI, pearlitic VGI has higher tensile strength and fatigue strength. The tensile strength shows a linear increasing trend with the increase of pearlite content. For ferritic VGI, fatigue cracks initiate at the graphite/ferrite interface, the ferrite grain boundary softens at high temperature, and cracks propagate along the grain boundary. In pearlitic VGI, fatigue cracks can also initiate at the graphite/pearlite interface due to oxidative debonding, and oxidation accelerates the initiation and propagation of fatigue cracks. Considering the influence of microstructures and temperature, a new method for predicting the high-temperature fatigue strength of VGI was proposed. This method has high prediction accuracy and suits for VGI from the room temperature to the high-temperature.

Effect of Grain Boundary Morphology on the High Temperature Tensile Properties of Developed Ni-Based Superalloy (LESS)

In order to investigate the mechanical properties of the developed wrought γ'-hardened Ni-based superalloy, LESS alloy (Low Eta Sigma Superalloy), and to understand the deformation behavior, tensile tests were carried out from room temperature to 800oC in comparison with IN 740H alloy. Like other superalloys, the tensile properties of the LESS alloy were found to be dependent on temperature. As the temperature rose between room temperature and 700oC, the ultimate tensile strength (UTS) decreased slightly, and then decreased sharply. The yield strength (YS) of the LESS alloy was found to be about 40% higher than that of IN 740H alloy from room temperature to 700oC. On the basis of microstructure observations, the high yield strength of the LESS alloy is thought to result from the dense grain boundary, where the fine carbides (MC, M23C6) and the γ' phase form a continuous film structure, which more effectively suppressed dislocation movements during deformation. It was found that the deformation mode of the LESS alloy changed from γ'- shearing to mixed mode (γ'-shearing + climb) at around 700~800oC. Although the main fracture mode of the LESS alloy was ductile dimple fracture, elongation decreased with temperature due to the local brittle region caused by micro-twins.

Anisotropic tensile and fatigue properties of laser powder bed fusion Ti6Al4V under high temperature

Laser powder bed fusion (LPBF) Ti6Al4V has a great potential to be applied in high temperature vehicle structure. The columnar grains of the LPBF components grow along the build derection. Duo to the specific microstructures, the tensile and fatigue properties of LPBF components are anisotropic. So, the study on high temperature mechanical properties of LPBF Ti6Al4V need to be intestigated further. In this paper, high temperature tensile and fatigue samples were designed and manufactured by LPBF. Tensile tests were carried out at 350 °C, 450 °C and 550 °C. The effects of build direction and temperature on high temperature tensile properties were analyzed and compared. The fatigue tests were carried out at 450 °C, and the strain amplitude was in the range of ±1.5 %. The effects of build direction on the hysteresis loops and the fatigue fracture surfaces of fatigue samples were studied. The results showed that the build direction can affect the kinematic hardening significantly, but it has little effect on isotropic hardening.

Improving high-temperature mechanical properties of laser powder bed-fused Inconel 738 alloy by hot isostatic pressing: Tailoring precipitates and healing defects

Microscopic defects and inferior high-temperature mechanical properties that occur during laser powder bed fusion (LPBF) of Inconel 738 alloys can severely hinder their industrial applications. Hot isostatic pressing (HIP) is a promising method to overcome these issues. In this study, the effects of HIP on the defects, grain structure, precipitated phase behavior, room- and high-temperature mechanical properties of an as-built Inconel 738 alloy were investigated. The results showed that, after HIP treatment, the defect densities in the XY and YZ planes of the as-built Inconel 738 alloy decreased from 0.537% and 0.292% to 0.251% and 0.123%, respectively. Moreover, the grain morphology of the as-built Inconel 738 alloy changed from elongated columnar grains to coarse equiaxed grains after HIP treatment, and the grain size became six times larger than that of the original sample, which was attributed to recrystallization and grain growth. Moreover, HIP treatment eliminated cellular dendritic segregation and significantly reduced dislocation densities in the as-built Inconel 738 alloy. Consequently, fewer M23C6 carbides were formed, but block-like M23C6 carbides were uniformly distributed at the grain boundaries after a combination of HIP and standard heat treatments. The HIP treatment reduced the room-temperature tensile properties of the as-built Inconel 738 alloy because of grain growth, low dislocation density, and coarser precipitates. However, the high-temperature (800 °C) tensile properties of the HIP sample with standard heat treatment (σuts = 827.8 MPa, σy = 744.3 MPa, εf = 2.2%) increased significantly compared to those of the as-built sample with standard heat treatment (σuts = 715.6 MPa, σy = 653.3 MPa, εf = 0.6%) and alleviated the embrittlement fracture owing to the formation of uniform carbides and lower defect densities. These results indicate that HIP treatment can significantly improve the high-temperature mechanical properties of LPBF-built nickel-based superalloys with high Al and Ti contents.

Effects of hot rolling and annealing temperature on microstructure and tensile properties of a Zr-containing Ni-based ODS superalloy

A Ni-based ODS superalloy with composition of Ni-20Cr-0.5Ti-0.3Al-0.6Y2O3-0.6Zr (in mass%) was prepared by mechanical alloying and hot isostatic pressing. Hot rolling was carried out at 1100 °C with different reduction ratio (40 %, 50 % and 60 %) and different annealing temperature (1200 °C, 1250 °C and 1300 °C) to investigate their influence on nanoscale oxides, grain and high temperature tensile properties. The results showed that high-density nanoscale oxides Y4Zr3O12 are formed in the Zr-containing Ni-based ODS alloy. Hot rolling and annealing result in the slight increase of oxide size and decrease of oxide density. The growth rate of oxides obeys fifth-law, which is called pipe diffusion along dislocation. The diffusion activity energy is derived as 827 kJ/mol. Average oxide size decreases and number density increases by decreasing rolling reduction ratio or annealing temperature. The size of columnar grain and grain aspect ratio increase with increase of annealing temperature which results into enhanced ultimate tensile strength and improved ductility at 800 °C. In addition, increasing rolling reduction ratio refines grain size and reduces grain aspect ratio in the alloy. The strength of the alloy annealed at 1300 °C with a reduction ratio of 50 % is the highest which is approximately 300 MPa at 800 °C.

Exploration of homologous substitution element on phase ratio and high temperature properties in high Nb-containing TiAl alloy

To reveal homologous substitution and refined mechanisms, and improve mechanical properties, Ti42Al6Nb 2.5 CxTa alloys were prepared by arc melting. Element distribution, lamellar colony size, length-diameter radio of Ti2AlC phase, tensile properties, and the corresponding influence mechanism were studied. Results show that the relative contents of γ and Ti2AlC phase increase, the content of α2 phase decreases, when Ta content increases from 0 to 2.0 at%. The relative content of B2 phase increases among the lamellar colonies and the length-diameter ratio of Ti2AlC particle decreases. Lamellar colony size decreases from 24.9 to 10.6 µm. With the increase of Ta content, the supercooling at the front of the solid-liquid interface increases and the β phase is refined. The increase of the precipitated phase content leads to the increase of the number of α phase heterogeneous nucleation particles, which will refine the lamellar colony. Tensile results show that the strength increases from 238 to 513 MPa and strain increases from 2.7 % to 11.1 % of Ti42Al6Nb 2.5 C1.6Ta alloy when the tested temperature increases from 750 to 950 ℃. The high temperature tensile properties of the alloy with more Ta content are relatively higher. Ta forms large lattice distortion after solid solution into the matrix due to its large atomic size, and Ta makes more Nb dissolve into the collective to increase the effect of solid solution strengthening. Another reason is the refinement of microstructure.

Influences of laser remelting treatments on microstructure and tensile properties of multiphase Ni3Al-based intermetallic alloy

The microstructure control of multiphase Ni3Al-based intermetallic alloy by traditional heat treatment is still limited, especially size and volume fraction of interdendritic β phase cannot be effectively reduced, due to the limitation of interdendritic β phase dissolution temperature close to the melting point of the alloy. In present work, the temperature gradient and solidification rate of the alloy under different laser remelting parameters were calculated by the Rosenthal equation. Afterward, the as-cast multiphase Ni3Al-based intermetallic alloy (19.4 vol% of interdendritic β phase) was remelted under different laser parameters of 3000–4500 W laser power and 5–20 mm/s laser scanning rate. And the effects of different laser remelting parameters on the microstructure, room temperature, and 980 °C high-temperature tensile properties of multiphase Ni3Al-based intermetallic alloy were studied. The results show that laser remelting treatment with the appropriate parameters (4000 W laser power and 10 mm/s laser scanning rate) can effectively reduce the size and volume fraction of interdendritic β phase and the morphology and size of γ′ phase in the γ′+γ dendrite, and significantly refine the microstructure of alloy, thus effectively improving the room temperature and 980 °C tensile properties of multiphase Ni3Al-based intermetallic alloy. Under the optimum laser remelting parameters of 4000 W-10 mm/s, the tensile strength at room temperature and 980 °C of the corresponding laser remelting alloy can reach 1215 MPa and 280 MPa, respectively, and the elongations after fracture of the corresponding alloy are 14.09% and 6.41%, respectively.

Parametric Influences of Geometric Dimensions on High Temperature Mechanical Behaviors and Damage Mechanisms of Ceramic Matrix Composite and Superalloy Double Bolted Joints

Given multiple material performance advantages, ceramic matrix composite (CMC) material has become one of the most promising hot structural materials used for thermal protection system in hypersonic vehicles. Under harsh thermal exposure of vehicles in flight, the design of connection structure would be a critical issue in improving load-carrying efficiency and ensuring service safety of aircraft structures in service environments. However, little attention was paid on mechanical behavior and its factors affecting the mechanical property of CMC joining at elevated temperature. To address this concern, a 3D finite element model coupled with progressive damage analysis is carried out to predict high temperature tensile properties and failure behavior of single-lap, double-bolt CMC/superalloy joints assembled by two serial protruding-head bolts. In the implementation of progressive damage analysis of 2D plain-woven C/SiC composites, a user-defined subroutine UMAT including a nonlinear constitutive model, 3D Alvaro failure criterion and Tan’s material degradation rule were embedded into the general package ABAQUS® through Fortran program interface. A parametric study considering geometries of joints was performed to evaluate their resultant influence on high temperature tensile behavior and the associated damage mechanisms for the CMC/superalloy double-bolt joint. New findings were provided for full exploitation of high performance through geometric design of ceramic matrix composite hot structure for hypersonic aircraft.

Microstructure and its effect on high temperature tensile properties of T92/HR3C dissimilar weld joints

A T92/HR3C dissimilar metal weld joint, which is widely used in the boiler components of ultra-supercritical power plants, was fabricated by manual tungsten inert gas welding with Inconel 82 as the filler metal. This study reports the high-temperature tensile properties, deformation behavior, and fracture mechanism of dissimilar weld joints. The results of tensile tests at 640 °C show a severe strength mismatch between the weld metal and the heat-affected zone of the T92 steel (T92-HAZ). The serrated flow behavior of the T92/HR3C weld joint at different tensile rates was observed during plastic deformation. Based on the results of transmission electron microscopy, dynamic recrystallization and re-precipitation of Cr23C6 carbides both likely triggered the serrated flow behavior and enhanced the tensile strength of the weld metal. Additionally, the inter-critical T92-HAZ was the weakest zone in the weld joint because of the dissolution of a large amount of carbides and the transformation of martensite laths into equiaxed subgrains.