High Temperature Tensile Properties Research Articles

Study on the High Temperature Tensile Properties and Strengthening Mechanism of Nitrogen Containing Nickel‐Based Deposited Metals

This article investigates the tensile properties and strengthening mechanism of nitrogen‐containing nickel‐based flux cored welding wire deposited metal from room temperature to 900 °C. The results showed that the high‐temperature strength of the deposited metal increased with the addition of Tungsten and Nitrogen. When the temperature reaches 700 °C, M23C6 carbides begin to decompose. The alloying elements dissolve back into the matrix, and the solid solution strengthening effect minimizes the plasticity of the alloy. More carbonitrides are precipitated within the crystal with temperature. During high‐temperature deformation, carbonitrides fractures at the interface with the substrate due to difficulty in coordinating deformation. Therefore, the crack source formed greatly reduces the strength of the material. In addition, the stacking faults present in the low‐temperature zone have a significant impact on the work hardening of materials. The main deformation mechanism is the unit dislocation a/2 < 110> cutting precipitation phase. It can be observed that the dislocation cutting precipitation mechanism system has transformed into a dislocation bypassing precipitation mechanism system at intermediate. Finally, the anomalous yield strength (YS) and intermediate temperature brittleness phenomenon are reasonably explained. The main deformation mechanism gradually transforms into dislocation slip and climbing with temperature.

High-Temperature Creep and Microstructure Evolution of Alloy 800H Weldments with Inconel 625 and Haynes 230 Filler Materials

Alloy 800H stands as one of the few code-qualified materials for fabricating in-core and out-of-core components operating in high-temperature reactors. Welding is a common practice for assembling these components; however, the selection of a suitable filler material is essential for enhancing the high-temperature creep resistance of Alloy 800H weldments in high-temperature applications. In this study, Inconel 625 and Haynes 230 filler materials were used to weld Alloy 800H plates by employing the gas tungsten arc welding technique. The high-temperature tensile and creep rupture properties, microstructural stability, and evolution of the weldments after high-temperature exposure were investigated and compared with those of Alloy 800H. The results show that both weldments exhibit enhanced tensile and creep behavior at 760 °C. The creep rupture times of the weldments with Inconel 625 filler and Haynes 230 filler materials were about two and three time longer, respectively, than those of Alloy 800H base metal when tested at 80 MPa and 760 °C. Carbides (MC and M23C6) were commonly observed in the microstructures of both the weld and base metals in the two weldments after high-temperature creep tests. However, the Inconel 625 filler weldment displayed detrimental δ and Laves phases in the fusion zone, and these precipitates could be potential sites for initiating cracks following prolonged high-temperature exposure. This study shows that the weldment with Haynes 230 filler material exhibit better phase stability and creep rupture properties than the one with Inconel 625, suggesting its potential for use as a candidate filler material for Alloy 800H for further investigation. This finding also emphasizes the critical consideration of microstructural evolutions and phase stability in evaluating high-temperature materials and their weldments in high-temperature reactor applications.

Effect of the subsolvus and supersolvus solution treatments on the basket-weave microstructure, room and high temperature properties of TC21 alloy

In this study, two different microstructures were obtained after subsolvus solution treatment (910 °C + 550 °C) and supersolvus solution treatment (1010 °C + 550 °C) in TC21 alloy. The relationship of microstructure with room and high temperature properties was studied. The results showed that at room temperature, both samples after two treatments had high hardness. At room temperature, the subsolvus sample had high tensile strength of 1070 MPa and moderate plasticity and impact toughness, while the supersolvus sample was hard and brittle. The high strength and toughness of subsolvus sample was owing to its clear basket-weave structure within finer β grains which contributes to fine grain strengthening and the increase of crack tortuosity. Poor plasticity and toughness of supersolvus sample could be mainly attributed to its incomplete basket-weave structure, coarse β grains, Widmannstatten α and some coarse α-phase in the grain boundary. Both samples showed excellent high temperature tensile properties and stability at 400 °C, the tensile strength was still as high as 1000 MPa while plasticity was significantly improved. With the tensile temperature increasing to 600 °C, the alloys showed obvious softening as the tensile strength significantly decreased and elongation increased.

Characterization of the microstructure, texture, and tensile behavior of additively manufactured Hastelloy X superalloy: Insights into heat treatment at 900 °C

This research aimed at the microstructural characterization and elucidation of room- and high-temperature tensile properties of additively manufactured Hastelloy X Ni-based superalloy heat-treated at 900 °C. The samples were fabricated via the laser powder bed fusion method utilizing two scan strategies known as island and meander types. The results indicated that the cellular structure embedded in the columnar grains of the as-built microstructure disappeared after applying the heat treatment, linking to the reduction in dislocation density while keeping the former morphology of the grains unchanged. However, the intensities of the Brass, Goss, Goss-Brass, and rotated Goss texture components were reduced, leading to the generation of more homogenous fibers in the heat-treated microstructure. Additionally, it caused the formation of a Mo-rich phase on the grain boundaries, which improved the room temperature's ultimate tensile strength. However, it was elucidated that the Mo-rich phase-induced void formation and intergranular cracking failure caused a slight decrease in hot ductility. Overall, the obtained results revealed that the heat-treated island samples showed superior hot tensile behavior than the meander sample due to having a larger grain size.

Effect of Heat Treatment Temperature on Microstructure, Tensile Properties and δ-Precipitate Phase in Ni-based Superalloy

Here, we investigated the influence of δ-precipitate (orthorhombic D0a Ni<sub>3</sub>Nb-ordered phase) on the room- and high-temperature tensile properties in wrought nickel-based Inconel 625 superalloys subjected to solution and aging heat treatment. Typically, solution heat-treatment temperatures in these alloys affect the solid-state precipitation of δ-phase, which governs high-temperature tensile properties. While precipitation of fine D0<sub>a</sub> δ-phase is known to have beneficial effects on the mechanical properties owing to the retardation of grain coarsening, Widmanstätten δ precipitation plays a deleterious influence on the fracture toughness, tensile ductility, and fatigue resistance. Therefore, to enhance the mechanical properties of this alloy series, it is key to generate a high number density of fine D0<sub>a</sub> δ precipitate by adjusting solid solution treatment temperatures. In this study, solution heat treatments were conducted above and below δ-phase solvus temperatures. By applying solution heat treatment at 900°C and 970°C, this alloy was confirmed to have a Widmanstätten δ phase and is composed similarly to the annealed microstructure. This Widmanstätten δ precipitate was densely distributed at both intergranular and intragranular grains. On the other hand, when solution treatment was applied at 1040 and 1100°C, more coarse particles (approximately 30 μm) with a significant reduction of Widmanstätten type δ phase were obtained. We found that grain size and Widmanstätten δ-phases have an important role in the high-temperature tensile properties of Inconel 625 superalloy series.

Effect of variation in Zr content on microstructure and high-temperature tensile properties of a γ-TiAl alloy

A series of Ti-46Al-xZr (x = 0, 1, 2, 3, 4, 5 at.%) alloys were prepared to systematically investigate the effect of variation in Zr content on the microstructure and high-temperature tensile properties. The results show that the addition of Zr intensifies the solidification segregation and promotes the formation of blocky γ phase in TiAl alloys. With the increase in Zr content from 1 to 5 at.%, the volume fraction of the blocky γ phase increases from 0.2 to 12.8 %, and the solidification microstructure is transformed from a fully lamellar to a nearly lamellar microstructure composed of the blocky γ phase and lamellar colonies. Because Zr stabilises the γ phase, continuous and discontinuous coarsening occur simultaneously; the former is observed inside the colony, whereas the latter occurs between two adjacent lamellar colonies. The high-temperature tensile results show that the ultimate tensile strength at 800 °C of the Ti-46Al-4Zr alloy (692 MPa) is significantly greater than that of the Ti-46Al alloy (351 MPa), which is attributed to solid solution strengthening and the coordinated deformation of blocky γ phase.

High-temperature mechanical properties and dynamic recrystallization of Mo-14Re alloy

The Mo-14Re alloy is currently utilized as a candidate structural material in space nuclear reactors and exhibits significant potential in other high-temperature fields. However, due to the high cost of rhenium, limited research has been conducted on the high-temperature properties of Mo-14Re. This study aims to investigate the high-temperature tensile properties of the stress-relieved Mo-14Re within the temperature range of 1200 K to 1773 K, specifically focusing on the microstructure of dynamically recrystallized grains and their influence on high-temperature deformation. The results demonstrate that the ultimate tensile strength of Mo-14Re reaches 399 MPa, 358 MPa, 311 MPa, and 33 MPa at 1200 K, 1350 K, 1500 K, and 1773 K, respectively. Above 1350 K, the softening caused by dynamic recovery and dynamic recrystallization becomes more pronounced, surpassing the influence of work hardening on high-temperature deformation. Continuous dynamic recrystallization is identified as the primary mechanism driving the dynamic recrystallization. Moreover, a new texture emerges when Mo-14Re undergoes dynamic recrystallization above 1500 K. Notably, no precipitated phases or element segregation are observed in Mo-14Re following high-temperature deformation.

Enhancing high-temperature mechanical property of Ti4822 alloy with in-situ Ti2AlC precipitates

Ti4822/xC composites with excellent high-temperature performance were prepared by spark plasma sintering technique. As the carbon content increased from 0.5 wt% to 1.5 wt%, the volume fraction of the Ti2AlC precipitates increased from 6.5% to 14.0%. The average size of the lamellar colony decreased from 305.5 ± 5 µm to 76.5 ± 5 µm. When the carbon content was 0.5 wt%, the lamellar size reached the minimum value of 75.5 ± 5 µm. Meanwhile, the equiaxed γ phase precipitated at the grain boundaries. With the carbon content of 0.5 wt%, the tensile properties reached the maximum value of 582 MPa, and the fracture elongation of 7.2% at 800 ℃. Compared with Ti4822 alloy, the ultimate strength and elongation of the composite increased by approximately 28% and 1.9% correspondingly. The dominant mechanism for high-temperature tensile properties of the composites was the combination of grain refinement strengthening, second phase strengthening, and γ phase weakening.

Microstructural Characteristics and Material Failure Mechanism of SLM Ti-6Al-4V-Zn Alloy

This study focuses on the additive manufacturing technique of selective laser melting (SLM) to produce Ti-6Al-4V-Zn titanium alloy. The addition of zinc at 0.3 wt.% was investigated to improve the strength and ductility of SLM Ti-6Al-4V alloys. The microstructure and mechanical properties were analyzed using different vacuum heat treatment processes, with the 800-4-FC specimen exhibiting the most favorable overall mechanical properties. Additionally, zinc serves as a stabilizing element for the β phase, enhancing the resistance to particle erosion and corrosion impedance of Ti-6Al-4V-Zn alloy. Furthermore, the incorporation of trace amounts of Zn imparts improved impact toughness and stabilized high-temperature tensile mechanical properties to SLM Ti-6Al-4V-Zn alloy. The data obtained serve as valuable references for the application of SLM-64Ti.

High Temperature Tensile Properties and Microstructure of Ni20Cr Alloy Fabricated by Laser Powder Bed Fusion

Additive Manufacturing (AM) brings about an array of modifications in microstructure with respect to conventional routes transforming mechanical performances. These new microstructure features depend on process parameters and especially on volume energy-density delivered by the laser on powder layer. Among the different alloys manufactured by AM, Ni-alloys exhibit high-strength at elevated temperature opening the way of fabrication of gas turbines and jet-engine parts. Ni-superalloys experience precipitation hardening due to the formation of γ′ and γ′′ phases leading to complex microstructures. To better study the influence of the AM microstructure on Ni-alloys mechanical properties, in particular at elevated temperatures, a theoretically monophasic and binary Ni20Cr-alloy manufactured by laser powder-bed fusion was studied in this work. Remarkable Yield Strength (400 MPa) and Ultimate Tensile Strength (UTS) (600 MPa) were observed at 500°C with hardly any loss of properties from room temperature, owing to the thermal stability of cellular dendrites till 700°C. Ductility drop was reported at 700°C due to anomalous brittle behaviour of Ni-alloys. Hardening behaviour vanished at 900°C signifying the deletion of dendrites, disappearance of dislocations, diffusion of Cr from dendritic walls and growth of oxides.

Microstructure and mechanical behaviour study of the dissimilar weldment of ‘IN82 buttered’ P92 steel and AISI 304L steel for ultra super critical power plants

This study examines the influence of the ERNiCr-3 (Inconel 82) butter layer on the microstructure and mechanical feature of the dissimilar weld joint (DWJ) of ferritic grade P92 and austenitic grade AISI 304 L steel, manufactured using gas tungsten arc welding (GTAW) method with IN82 filler. The butter layer aims to prevent the formation of a hard martensitic layer adjacent to the fusion line by mitigating the carbon migration from the P92 steel to the welding pool. The optical microscope, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electron probe microanalyzer (EPMA) were used to examine the microstructures of the buttered welded plate. The mechanical characteristics of the joints were assessed using the standard and sub-sized tensile and Charpy tests. The flat and round specimens underwent the tensile test to determine their relative tensile properties at room temperature and high temperature. The high-temperature tensile properties were assessed at 600 °C and 650 °C at 1 mm/min extension rates. Along the weldments, hardness profilometry was also performed. Microstructural analysis validated that the application of a buttering layer successfully eliminated the extensive martensitic layer on the P92 side. Nevertheless, in the vicinity of the interface between the buttering layer and P92, there was evidence of a narrow unmixed zone and macrosegregation. SEM/EDS and EPMA studies confirmed that the predominant phases identified in IN82 butter and weld metal are NbC and TiC. The butter layer, overall, improved elongation/ductility by 25 % without a noticeable reduction in tensile strength. During tensile testing, the specimen fractured from the IN82 butter layer, revealing the presence of dimples and voids on the fracture surface, along with the TiC/NbC phases, as confirmed by SEM analysis. Tensile specimens subjected to high-temperature testing exhibited failure at the base materials of AISI 304 L (tensile strength=404 MPa) and P92 (307 MPa), specifically at 550 °C and 650 °C, respectively, rather than at the buttering layer or weld metal. The results of the tensile tests met the minimum criteria specified for Ultra-Supercritical (USC) boilers. More importantly, the IN82 butter layer successfully serves as a protective barrier between the weld pool and the P92 HAZ. As a result, the dual hardness peaks on either side of the welding pool are eliminated. After adding the buttering layer, the peak hardness in the coarse-grained heat-affected zone (HAZ) of P92, which ranged from 450 to 500 HV in the unbuttered sample, dropped by 200 MPa. The relationships between microstructural characteristics and mechanical properties have been thoroughly examined and discussed.

Significant enhancement in high temperature performance of TiAl matrix composites by a novel configuration design

Ti5Si3/TiAl composites were successfully prepared by pressure infiltration and subsequent reactive annealing. Final microstructure of Ti5Si3/TiAl composites was dependent on the reactive annealing temperature, which varied from 1350 °C to 1420 °C, two typical microstructures could be achieved: (i) An unique core-shell structure (Core: fully lamellar α2-Ti3Al/γ-TiAl with in-situ synthesized Ti5Si3 particles predominantly distributed at the interfaces of α2/γ lamellar colonies; Shell: equiaxed γ-TiAl with Ti5Si3 particles distributed in γ grain boundaries); And (ii) A novel quasi-network structure composed of fully lamellar α2/γ and a majority of Ti5Si3 particles with a quasi-network distribution. The formation of the two microstructures could be attributed to the chemical composition heterogeneity which was caused by the difference in interdiffusion rate of Ti and Al elements in different annealing temperatures. The comparative investigations on high temperature tensile properties and creep behavior showed that the core-shell Ti5Si3/TiAl composites exhibited a better specific strength (165 MPa⋅g−1⋅cm3) and higher ultimate tensile strength (633 MPa) at 800 °C, which was 12 % higher than that of the quasi-network Ti5Si3/TiAl composites. While the creep behavior analysis showed that in compassion with equiaxed γ phase, the slip distance of dislocations in fully lamellar α2/γ phase was shorter, impeding the motion of dislocations more effectively. And core-shell Ti5Si3/TiAl composites possessed a large number of grain boundaries concentrating in the shell which became weaker in the high temperature, facilitating the formation of creep pores in the shell and the final premature fracture. Hence, the quasi-network Ti5Si3/TiAl composites containing a higher content of fully lamellar α2/γ exhibited a better creep resistance than that of core-shell Ti5Si3/TiAl composites. More importantly, the steady state creep rate at 750 °C under the fixed stress of 250 MPa of quasi-network Ti5Si3/TiAl composites was relatively low, only 3.305 × 10−8 s−1, comparable to that of third-generation TiAl alloys.

The effect of oxide scale and microstructural changes during cyclic hot corrosion on high-temperature tensile properties of Rene-80 superalloy

ABSTRACT The effect of oxide scale and microstructural changes during 10, 20, and 40 hot corrosion cycles on the high-temperature tensile properties of Rene-80 superalloy at 950 °C was investigated. Due to the formation of micro-cracks and micro-voids, compressive stresses produced from Cr2O3 and NiO growth, and tensile stresses stemming from NiMoO4 transformation and Al internal oxidation, the oxide scale spalled. By increasing the hot corrosion cycles, UTS (Ultimate Tensile Strength) and El.% (Elongation) first decreased and then increased due to the propagation of intergranular vertical cracks from the oxide scale to the Rene-80 after 20 cycles. During hot corrosion cycles, YS increased due to a rise in the density of near-surface intergranular cracks close to the Rene-80/oxide scale interface resulting from micro-void linkage and γ′-depleted zone. Due to the high area fraction and the small average size of secondary γ′, UTS and YS were the highest and lowest after ten cycles, respectively.

Significantly Improving the High-Temperature Tensile Properties of Al17Cr10Fe36Ni36Mo1 Alloys by Microalloying Hf.

Dual-phase high-entropy alloys with excellent room temperature and high-temperature properties have been widely studied as potential high-temperature structural materials. However, interface weakening causes its high-temperature performance to decline at higher temperatures, severely limiting further development. In this study, a series of Al17Cr10Fe36Ni36Mo1Hfx (x = 0, 0.03, 0.15, 0.3, 0.5, and 0.8 at%) alloys were prepared to study the effect of Hf content on the microstructure and mechanical properties of the matrix alloy. The results indicate that with the addition of the Hf, the Hf-rich phase began to precipitate at the interface and inside the B2 phase in the matrix alloy. In contrast, the morphology of both the FCC and B2 phases had no noticeable change. With the increase in Hf content, the high-temperature strength and ductility of the alloy first increased and then decreased, while the room temperature performance remained almost unchanged. Benefiting from the hindrance of the Hf-rich phase to grain boundary sliding and dislocation movement during high-temperature deformation, the tensile strength, yield strength, and plasticity of the matrix alloy increased from 474 MPa, 535 MPa, and 8.7% to 816 MPa, 923 MPa, and 42.0% for the Al17Cr10Fe36Ni36Mo1Hf0.5 alloys, respectively. This work provides a new path for designing a high-entropy alloy with excellent high-temperature mechanical properties.

Sub-rapid solidified high copper-bearing steel with excellent resistance to hot shortness

The removal of accumulated impurity elements during scrap refining has been regarded as the bottleneck to limiting scrap usage, among which copper is the crucial tramp element in scrap steel recycling, resulting in the final product's hot shortness and surface cracking. This study proposes sub-rapid solidification-based strip casting technology to eliminate the copper impurity introduced problems. The results reveal that strip casting could improve copper behavior in the as-cast sample. More importantly, the sub-rapid solidified sample has excellent high-temperature tensile properties and resistance to hot shortness. It suggested that strip casting technology could produce copper-bearing steel, which can tackle the hot shortness problem and provide a unique idea for steelmaking with scrap as raw materials.

High-temperature tensile properties of an aluminum quasicrystal-forming alloy manufactured by laser powder bed fusion

Normalized tensile samples of Al–4Fe–3Cr–2Ti (wt.%) alloy were successfully fabricated by laser powder bed fusion (LPBF) additive manufacturing. The alloy's tensile properties and microstructure were investigated at room and high-temperature (up to 500 °C). This Al–Fe–Cr–Ti alloy exhibits exceptional thermal stability and outstanding mechanical performance at temperatures of up to 500 °C. A particularly interesting feature is the alloy's yield strength values, which reach ∼300 MPa at 300 °C and ∼180 MPa at 400 °C. The outstanding mechanical behavior of this alloy at high temperatures is attributed to the in situ precipitation of ultrafine icosahedral quasicrystalline (i-QC) particles endowed with high thermal stability. These values are notably higher than those achieved for A319, 6061-T6 and Al-8%wt.Cu–Mg–Ag cast alloys – three of the most common heat-resistant Al alloys, and higher than commercially available Al-based alloys for LPBF. Based on hardness measurements and the bimodal composite microstructure, we propose a model to predict this alloy's yield strength. This model shows a good agreement with the experimental results and can be used to maximize the alloy's tensile strength. This work describes a lightweight aluminum alloy with outstanding high temperature tensile strength within a wide range of temperatures, in addition to being additively processable and affordable.

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.

Effects of the Growth Rate on the High-temperature Tensile Properties and Micro-organization of Directionally Solidified Ti-44Al-9Nb-1Cr-0.2W-0.2Y Alloys

In this experiment, Ti-44Al-9Nb-1Cr-0.2W-0.2Y alloy was prepared by the directional solidification method. The effect of different growth rates on tensile properties and microstructure orientation at high temperature was studied. Three kinds of alloys with different growth rates of 10 μm/s, 15 μm/s and 20 μm/s were prepared. The results show that the tensile properties of the alloy at 800 ℃ decrease with increasing growth rate, and recrystallization occurred at the position of intracrystal fracture in the microstructure. The size of columnar crystals decreases with the increase of the growth rate, increasing the number of grains and decreasing the orientation difference between the growth and axial directions as well as the preferred orientation of lamellar, and the anisotropy of the material, which leads to the obvious decrease of the tensile strength and plasticity. Combined with electron backscattering diffraction test results, the lamellar orientation of the effective parts of the three specimens after high temperature stretching was studied. It was found that the axial preferred orientation of the alloy specimens decreased obviously with the increase of the growth rate, and the orientation became disorderly and the uniformity of lamellar thickness decreased gradually with the increase of the growth rate. In addition, it was found that a new single-phase γ phase is formed in the microstructure after high temperature stretching, and the distribution range increased with the increase of the growth rate, which seriously degraded the axial preferred orientation of the alloy. It can be concluded that the directionally solidified alloy with a growth rate of 10 μm/s has better microstructure orientation and high temperature tensile properties.

Introducing both chemical and structural gradients in AISI 321 stainless steel via aluminizing and laser shock peening for superior properties

Aluminizing is a diffusion based chemical surface treatment on materials to provide excellent protection against high temperature oxidation and corrosion, but is likely to be accompanied by a degradation in mechanical properties. Laser shock peening (LSP) is a superior laser based surface strengthening technique for enhanced mechanical properties. In this study, we focus on combining these two methods on the AISI 321 stainless steel to introduce both chemical and structural gradients for superior properties. Comparative investigation on both the microstructure and mechanical properties of the as received 321 steel, aluminized 321 steel and the aluminizing + LSP processed steel indicated that: (1) A three-layer protective coating was introduced on the surface of the aluminized steel and the concentration of Al decreased gradually from the outermost layer to a certain depth, forming B2-FeAl(Cr) solid solution and Al2O3 in Layer-I, B2-FeAl and DO3-Fe3Al phases in Layer-II and BCC-Fe(Cr,Al) solid solution phase in Layer-III, with B2-NiAl precipitates distributed in Layer-II and Layer-III. (2) After LSP treatment, a dislocation density gradient from the surface to the matrix, dislocation-precipitate interactions and a significant compressive stress were introduced. (3) Though the aluminized steel exhibited a decrease in the high temperature tensile properties compared to that of the as received 321 steel, the aluminizing + LSP processed steel achieved a striking enhancement. The formation of three-layer coating, dislocation density gradient, dislocation-precipitate interactions and the residual stress contribute jointly to gain the yield strength, ultimate strength and fracture elongation up to 265 MPa, 430 MPa and 37.5 % at 620 °C, respectively.

High-temperature mechanical properties and microstructure of welded joint in GH4169/IC10 dissimilar nickel-based superalloys by vacuum electron beam welding

Jointing precipitation-reinforced GH4169 and newly-developed IC10 nickel-based superalloy through vacuum electron beam welding (VEBW) has become increasingly attractive for aeroengine's blade and disc. In this study, solution treatments (GH4169 for 980 °C/1.5 h and IC10 for 1180 °C/2 h) was chosen before welding, and different aging treatments (900 °C, 950 °C, 1000 °C, 1050 °C and 1100 °C for 6 h, respectively) were used for eliminating uneven compositions and structures of the GH4169/IC10 welded joint after VEBW method. Through optical microscopy (OM) observations, there are distinct morphological differences between the base metal (BM) and fusion zone (FZ) regions, with the BMs regions mainly being equiaxed and the FZ region mainly being dendritic grains after VEBW. Through scanning electron microscopy (SEM) observations, the carbides are mainly distributed at grain boundaries in BMs, and Ni–Cr–Nb phases are the dominant second phases in the FZs after VEBW. Moreover, the grain orientation is obviously strong in FZs with adjacent {001} orientation by electron backscattered diffraction (EBSD) characterizations. while grain orientation chiefly of BMs presents anisotropy. After heat treatments, the maximum microhardness of the welded joint was obtained after aging at 900 °C (242–258 HV), and the minimum microhardness was obtained after aging at 1050 °C (183–190 HV). Besides, among the aged welded joints, the 900 °C aged welded joint has the best high-temperature mechanical properties (tensile strength for 559 MPa and elongation for 19.3%) through high-temperature tensile tests, owing to the strengthening effect of numerous γ′ and γ′′ precipitates, nevertheless, 1050 °C aged welded joint has lower tensile strength than solution treated welded joint, mainly resulting from the numbers of δ precipitates isolating matrix. Moreover, combined with transmission electron microscopy (TEM) observations, the carbides, γ′, γ′′, and δ precipitates lead to different high-temperature tensile properties of welded joints, the transformation of γ′′ precipitates and coarsening of γ′ precipitate promote fracture crack initiation and propagation along grain boundaries.