High Temperature Tensile Properties Research Articles

High-temperature tensile rupture property of (Nb,W) co-alloying TiAl-based alloys

In order to explore whether (Nb,W) co-alloying TiAl-based alloys with relatively higher W addition have better high-temperature tensile rupture property, Ti-44Al-4Nb-1 W-0.1B alloy is designed and prepared. Ti-44Al-8Nb-0.1B alloy and Ti-44Al-7.2Nb-0.2 W-0.1B alloy are also prepared for comparative study. The rupture property testing is carried out at 800 °C and different tensile stresses. The property data, macro/microstructure evolution, fracture surface, W content, crack failure behaviors are studied. The results show that the (Nb,W) co-alloying alloys have better rupture property than the pure Nb alloying alloy. For the (Nb,W) co-alloying alloys, the higher W contained Ti-44Al-4Nb-1 W-0.1B alloy has the better property under lower tensile stress, and the lower W contained Ti-44Al-7.2Nb-0.2 W-0.1B alloy has the better property under higher tensile stress. The relationships of rupture life t and stress σ for the three alloys are given. All the three alloys have a coupling fracture mode of ductile fracture and brittle fracture. The ductile fracture exhibits the typical dimple characteristics. The brittle fracture exhibits the typical trans-granular cleavage, river-like pattern and trans-lamella fracture characteristics. The higher the stress, the more brittle fracture characteristics there are. After rupture property testing, the (α2 + γ) lamella colony sizes of the three alloys all decrease, indicating that DRX and grain boundary slip occur not only along (α2 + γ) lamella colony boundary, but also inside it. The colony boundary regions have the stress concentration, where the B2 phase produces the better buffering and coordination, and as well as the dislocation tangles, DRX and grain boundary slip can be found by EBSD and TEM. EPMA results show that the more W added in the alloy, the more W content is in the (α2 + γ) lamella matrix, which is beneficial for the rupture property. However, more W addition will also lead to the formation of more B2 phase in the initial as-cast microstructure. So that, under higher tensile stress, when the stress intensity factor K is higher, the crack failure is more likely to occur.

Design of a Thermally Stable Heat-Resistant (Al2O3+Al3Ti)/Al Composite with Excellent High-Temperature Mechanical Properties: Multimechanism Synergistic Strengthening Strategy.

The effectiveness of the room-temperature strengthening strategy for aluminum (Al) is compromised at increased temperatures due to grain and precipitate phase coarsening. Overcoming the heightened activity of grain boundaries and dislocations poses a significant challenge in enhancing the high-temperature strength through traditional precipitation strengthening. This study presents novel strengthening strategies that integrate intergranular reinforcements, intragranular reinforcements, refined grain, and stacking faults within an (Al2O3+Al3Ti)/Al composite prepared using sol-gel and powder metallurgy technology. Excellent high-temperature tensile properties are achieved; also, a remarkable fatigue performance at increased temperatures that surpasses those of other existing Al alloys and composites is revealed. These superior characteristics can be attributed to its exceptionally stable microstructure and the synergistic strengthening mechanisms mentioned above. This work offers new insights into designing and fabricating thermally stable Al matrix composites for high-temperature applications.

Study on Microstructure and High-Temperature Mechanical Properties of Al-Mg-Sc-Zr Alloy Processed by LPBF

Al-Mg-Sc-Zr alloy processed via laser powder bed fusion (LPBF) is poised for significant application in aerospace, where its high-temperature capabilities are paramount for the safety and longevity of engineered structures. This study offers a systematic examination of the alloy’s high-temperature tensile properties in relation to its microstructure and precipitate phases, utilizing experimental approaches. The LPBF-processed Al-Mg-Sc-Zr alloy features a bimodal microstructure, with columnar grains in the melt pool’s interior and equiaxed grains along its boundary, conferring exceptional properties. The application of well-calibrated processing parameters has yielded an alloy with an impressive relative density of 99.8%, nearly fully dense. Following a thermal treatment of 350 °C for 4 h, the specimens were subjected to tensile tests at both room and elevated temperatures. The data reveal that the specimens exhibit a tensile strength of 560.6 MPa and an elongation of 11.1% at room temperature. A predictable decline in tensile strength with rising temperature is observed: at 100 °C, 150 °C, 200 °C, and 250 °C; the respective strengths and elongations are 435.1 MPa and 25.8%, 269.4 MPa and 20.1%, 102.8 MPa and 47.9%, 54.0 MPa and 72.2%. These findings underpin the technical rationale for employing LPBF-processed Al-Mg-Sc-Zr alloy in aerospace applications.

Microstructures and High-Temperature Mechanical Properties of Inconel 718 Superalloy Fabricated via Laser Powder Bed Fusion.

The Inconel 718 superalloy demonstrates the potential to fabricate high-temperature components using additive manufacturing. However, additively manufactured Inconel 718 typically exhibits low strength, necessitating post-heat treatments for precipitate strengthening. This study investigated the microstructures and mechanical properties of the Inconel 718 superalloy fabricated via laser powder bed fusion. The room-temperature and high-temperature tensile properties of the Inconel 718 alloy samples following various post-heat treatments were evaluated. The results indicate that the as-built samples exhibited columnar grains with fine cell structures. Solution treatment resulted in δ phase formation and grain recrystallization. Subsequent double aging led to finely distributed nanoscale γ' and γ″ particles. These nanoscale particles provided high strength at both room and high temperatures, resulting in a balanced strength and ductility comparable to the wrought counterpart. High-temperature nanoindentation analyses revealed that the double-aging samples exhibited very high hardness and low creep rates at 650 °C.

Investigation of microstructure evolution and its effect mechanism on high temperature tensile properties of 304L stainless steel processed by laser powder bed fusion

Laser Powder Bed Fusion (LPBF) 304L stainless steel has garnered significant attention due to its unique blend of strength and ductility at room temperature. However, there is limited understanding of its high-temperature tensile properties. In this study, we conducted tensile testing on LPBF 304L at temperatures ranging from 623K to 1023K in its as-built state. Additionally, we performed a comparative tensile test on traditionally hot-rolled (at 1433K) 304L stainless steel under equivalent test conditions. The results revealed that LPBF 304L steel exhibited high ductility at 973K (ultimate tensile stress (UTS) is 257.3 ± 3.6 MPa)-1023K (UTS is 218.7 ± 3.8 MPa), but its strength (yield strength (YS) decreased from 346.0 ± 4.5 MPa to 182.7 ± 3.8 MPa) and plasticity (UTS decreased from 405.7 ± 5.3 MPa to 218.7 ± 6.4 MPa) decreased slowly as the testing temperature increases. We also delved into the microstructure and its impact on high-temperature tensile deformation. The fine grains and ensuing dynamic recovery were found to be responsible for the reduced strength and ductility of LPBFed 304L samples at elevated temperatures. Furthermore, a sawtooth fluctuation emerged in the stress-strain curve at 873K, which could be attributed to dynamic strain aging (DSA) and the interaction between solute elements and dislocations.

Achieving back-stress strengthening at high temperature via heterogeneous distribution of nano TiBw in titanium alloy by electron beam powder bed fusion

Back-stress strengthening has been proven to be an effective strategy in breaking the room temperature strength–ductility dilemma in hetero-structural metals matrix composite materials (MMC). However, back-stress is difficult to achieve at high temperature because of grain boundary softening, grain boundary sliding, dislocation annihilation and grain rotation. Here, back-stress strengthening is exploited to improve the high temperature tensile properties of Ti-6Al-4 V (TC4) alloy by precipitating a heterogeneous distribution of nano TiB whiskers (TiBw). In this work, the rapid solidification associated with electron beam powder bed fusion (EB-PBF) generates heterogeneous in-situ nano TiBw at both grain boundaries and grain interiors. The nano-TiBw on the grain boundaries (GB nano-TiBw) not only refines the grains but can also pin the grain boundaries. The intragranular nano TiBw (IG nano-TiBw) significantly reduces the dislocation mean free path, inhibit dislocation movement, and dramatically enhances the dislocation storage density. Meanwhile, specimens are strengthened by high-density < a + c > dislocations induced by the precipitated nano TiBw. The heterogeneous distribution of nano TiBw achieved a 50 °C increase in the service temperature of TC4 alloy while also increasing stability. This strategy provides a new perspective for further improving the high-temperature mechanical properties of titanium alloys.

High temperature tensile properties and deformation behavior of CoCrFeNiW0.2 high entropy alloy

High entropy alloys (HEAs) have been a new-type of structural materials, which show good performance in various extreme conditions. In the present study, we systematically investigated the high temperature deformation behavior of as-cast CoCrFeNiW0.2 HEA under different temperatures from 298 to 1173 K and various strain rate of 1 × 10−4 s−1 to 5 × 10−3 s−1. An obvious temperature dependence of yield strength can be found with a remarkable decrease from 362 MPa at 298 K to 119 MPa at 1173 K. The normal Portevin–Le Chatelier (PLC) effect was presented in the intermediate temperature range of 673 K to 1073 K, the serrated flow transformed in the sequence of A → A + B → A + C → B + C → C with the increasing temperature, which is caused by dynamic strain aging (DSA). W atoms played an important role in the interaction between solute atoms and dislocations. Fractography analysis suggests the failure mode transition from transgranular fracture to intergranular fracture. Electron backscatter diffraction (EBSD) demonstrates that the high temperature deformation mechanism of the HEA is dominated by dynamic recovery (DRV). Additionally, transmission electron microscopy (TEM) was performed to observe the dislocation configurations and the interaction between dislocations and μ phase precipitates at various temperatures, and these results further identify the high temperature deformation mechanism. To summarize, this study indicates the proposed HEA has excellent high temperature mechanical properties and a wide range of potential applications in many fields.

High-temperature tensile properties of Cu-modified AlSi10Mg alloy fabricated by selective laser melting

In this study, an AlSi10Cu4Mg alloy was prepared by selective laser melting (SLM) using a mixture of pre-alloyed AlSi10Mg and elemental Cu powders, followed by aging at 180 ℃ for 2 h. The high-temperature tensile properties of both the SLMed and SLM-aged samples were tested in the temperature range of 200–400 ℃, and the microstructure changes during deformation were compared. At the temperature of 200 ℃, the SLMed sample exhibits outstanding tensile properties with an ultimate tensile strength (UTS) of 327±2 MPa and an elongation (EL) of 25.5±0.5 %. This is mainly related to the strain hardening that caused by the accumulation of anomalous dislocations near the high-volume fraction of Si nano-particles within the grains. For the SLM-aged sample, the aging treatment is found to further increase the strength, yielding a UTS of 381±3 MPa. The metastable transition of the Al2Cu phase indirectly promotes the precipitation of the nano-sized Si phase during the aging process. As the testing temperature increases, the strength increment of the SLM-aged sample gradually diminishes, while the elongation increment increases. Due to the limited intrinsic thermal stability of Si nano-particles and θ′ phase, the coarsening of the precipitates can weaken the strengthening effect. The dynamic recrystallization process can be accelerated by the aging treatment, thereby helping to improve the elongation.

High-temperature tensile properties and deformation behavior of a multi-phase FeNiCrAlTi alloy

Single-phase multi-principal elements alloys (MPEAs) within the elevated temperature experience particularly severe strength loss, and even a distinct ductile-to-brittle transition. Herein, we report on a non-equiatomic, multi-phase FeNiCrAlTi MPEA which possesses remarkable combinations of mechanical properties across a wide range of temperatures from 400 °C to 800 °C, especially its specific yield strength possesses nearly 100 MPa/g∙cm−3 at 600 °C. The excellent mechanical behavior benefits from the synergistic effect of the special phase structure and precipitation strengthening by the ordered Ni (Al, Ti) B2 nanoparticles. The transformation of deformation mode at 600 °C should be considered the dominant of the resistance to intermediate or high-temperature embrittlement. This work provides a new methodology for regulating mechanical properties of superior alloys that involve high-temperature conditions.

Constructing high-density dislocations by primary (Nb,Ti)(C,N) to induce massive secondary precipitations in austenitic heat-resistant cast steel

The microstructural evolution and the high-temperature tensile properties of a novel Nb-Ti-N alloyed austenitic heat-resistant cast steel were investigated during the isothermal aging at 900 °C for up to 1000 h. The mechanisms of enhancing strength-ductility synergy and the high-temperature tensile fracture behaviors after the aging process were analyzed in detail through tensile tests at 900 °C. Obtained results show that the high-density dislocation regions and the Cr segregation, formed around the intragranular primary (Nb,Ti)(C,N), provided numerous nucleation sites for submicron-sized secondary M23C6 precipitates. The density of secondary M23C6 significantly increased, while the coarsening rate was notably reduced during the aging process. Simultaneously, the uniform dispersed precipitation of nano-sized secondary (Nb,Ti)C was promoted by massive dislocations, which exhibited high resistance to coarsening during long-term aging. The improvement of high-temperature strength was attributed to the precipitation strengthening effects induced by the submicron-sized M23C6 and nano-sized (Nb,Ti)C particles. Additionally, the enhancement of ductility during aging was mainly due to the more effective stress transmission and the ameliorated interface relationship between primary (Nb,Ti)(C,N) and austenitic matrix, which was facilitated by the abundant precipitation of secondary phases. The current findings indicate that high-density dislocations constructed by the intragranular primary (Nb,Ti)(C,N) induce the extensive dispersion of secondary strengthening phases, which enhanced both ultimate tensile strength of 158 MPa and elongation of 45.3% at 900 °C after isothermal aging for 1000 h.

Effect of fan-shaped structure on high temperature tensile properties of nickel-based deformed superalloys

GH4742 alloy is a kind of precipitation-hardened superalloy, which is widely used in turbine disc, compressor disc, bearing ring and other parts due to its excellent high temperature mechanical properties. In this paper, high-temperature tensile comparison experiments were carried out at four temperatures, 1050 °C, 1080 °C, 1110 °C and 1140 °C, between alloy A containing a fan-shaped structure and alloy B without a fan-shaped structure. The results show that the tensile strength and plasticity of alloy A at 1050 °C are superior to those of alloy B. With the increase of temperature, the difference of tensile strength and plasticity between alloy A and B decreases gradually. By analyzing the fracture, both alloy A and B were found to have a large number of tough dimples, which showed ductile fracture characteristics. But alloy B was found to have some icing-like fracture at 1050 °C, which showed some brittle fracture characteristics. After 1110 °C, the difference in tensile strength and plasticity between alloy A and B almost disappears because γ′ phase is completely dissolved in the matrix. TEM results show that dislocations gather around the large-size γ′ phase, and for the small-size γ′ phase, dislocations tend to cut into γ′ phase directly. The results show that the existence of fan-shaped structure is beneficial to the high temperature tensile properties of GH4742 alloy, which has a certain reference effect on the production of GH4742 alloy in the future.

Effect of pre-precipitation thermomechanical treatment on precipitation behavior of CLAM steel

China Low Activation Martensitic steel (CLAM) is a cladding material used in thermonuclear fusion reactors. Its high temperature performance is closely related to precipitation strengthening. The MX phase with strong thermal stability is the key to improving the high temperature performance of CLAM steel, and the M23C6 phase which is easy to coarsen under long-term high temperature service conditions is one of the important factors causing creep failure. In order to increase the content of MX phase and reduce the content of M23C6 phase, this paper first pre-precipitates near the precipitation temperature of M23C6 phase (which is also close to the maximum precipitation temperature of MX phase), which limits the precipitation of M23C6 phase and promotes the maximum precipitation of MX phase. Then the subsequent thermomechanical treatment (TMT) is carried out. The results show that the content of M23C6 phase in the samples after pre-precipitation TMT is greatly reduced, and the size is slightly reduced compared with the samples with only thermal deformation. The size of the MX phase is reduced by 10.6%, the volume density is increased by 88%, the volume fraction is increased by 34.1%, and the dislocation density is slightly increased. At the same time, it was found that a large number of MX phases precipitated at the lath boundary and pinned the boundary, which delayed the coarsening of the lath during tempering. The changes of these microstructures improve the precipitation strengthening, dislocation strengthening and boundary strengthening, so the room temperature tensile properties and high temperature tensile properties are improved, but the work hardening makes the total elongation and room temperature impact properties decrease.

Microstructure, tribological property and high temperature tensile property of Co-Cr-Ni-W alloy parts fabricated by laser directed energy deposition

In this study, Co-Cr-Ni-W alloy parts were fabricated on the surface of 304 stainless steel (SS) substrate by laser directed energy deposition (LDED). Microstructure, microhardness and tribological behavior of as-deposited samples and 750 °C–950 °C aging-treated samples were tested. Carbides precipitated from Co-Cr-Ni-W alloy, and martensite transformation from γ-Co (FCC) to ε-Co (HCP) occurred in high temperature. The changes of microstructure caused by aging treatment could increase the microhardness and change wear mechanism. Tensile property of Co-Cr-Ni-W alloy at 750 °C–950 °C was also investigated. Co-Cr-Ni-W alloy formed a hard-sliding structure under high temperature, leading to high tensile strength. The main fracture mode of Co-Cr-Ni-W alloy was brittle cleavage fracture.

Temperature dependence tensile behaviors of additively manufactured GH4099 Ni-based superalloy

Additive manufacturing was currently widely used to fabricate complex-shaped superalloy components for extreme environment applications. To replace the components prepared by the traditional approaches, it is crucial to ensure the reliability of AMed superalloys, especially in a thermal-stress environment. In this work, the high-temperature tensile properties of AMed GH4099 nickel-based superalloy are studied to establish the relationships among deformation temperatures, mechanisms, and failure responses. The results show that the deformation mechanisms at 600 °C are mainly cross-slip of the slip bands and arrays, which induced a ductile fracture. Increasing the tensile temperature will cause a shift of the dislocation movement from cross-slip to Orowan looping and stacking fault shearing to dislocation entangles-recovery-recrystallization, and the fracture mode transformed from pure ductile to mixed ductile-brittle. Additionally, the neighboring grain boundaries and the carbide-grain boundary bondings will also change with the temperature, which is further linked to the mediate-temperature brittleness and high-temperature abnormal plasticity of this superalloy.

Additive manufacturing Ti-22Al-25 Nb alloy with excellent high temperature tensile properties by electron beam powder bed fusion

Additive manufacturing of TiAl alloys remains challenging due to their poor high-temperature tensile properties. In this work, electron beam powder bed fusion (PBF-EB) was applied to fabricate Ti-22Al-25 Nb alloy with a high pre-heating temperature (830℃), achieving a breakthrough in improving the tensile properties of TiAl alloys by additive manufacturing. The microstructure and tensile properties of Ti-22Al-25 Nb fabricated by laser beam powder bed fusion (PBF-LB) and PBF-EB were investigated. Excellent tensile strength (803 MPa) at 650℃ was obtained by PBF-EB, which was attributable to the precipitation and growth of the O phase at a suitable pre-heating temperature. An in-depth microstructure analysis of the deformation and fracture mechanisms of the as-printed samples was performed via Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). The area fraction of the O phase in the PBF-EB sample was approximately 6 times higher than that of the PBF-LB sample. The PBF-EB sample exhibited transgranular fracture at 650 °C, in contrast to the PBF-LB samples. The shape and quantity of the O phase and β phase played an important role in improving the tensile properties of the Ti-22Al-25 Nb alloys at high temperature.

High temperature tensile and creep properties of the new cladding steel of 15-15Ti-Y

The 15-15Ti austenitic stainless steel is commonly used as a fast reactor cladding material due to its favorable comprehensive properties. To further enhance its high temperature strength, yttrium (Y) modified 15-15Ti (15-15Ti-Y) steel was developed. In this study, the tensile properties of 15-15Ti-Y were evaluated across the temperature range of 200–700 °C, and the constant load creep properties of 20 % cold worked (CW) 15-15Ti-Y were measured at temperatures of 550–700 °C under various applied stresses. The results indicated that Y addition led to enhanced intragranular precipitates and delayed intergranular precipitates, which resulted in a YS (YS) that was ∼ 100 MPa higher than that of Y-free steel at temperatures ranging from 200 to 600 °C, without compromising the plasticity and ductility. The creep fracture life of 15-15Ti-Y steel ranged from 21 to 5761 h, and the deformation and damage processes were found to adhere to the Norton power-law and Modified Monkman Grant relationship. The stress exponent revealed that the deformation was dislocation creep mechanism, while the creep damage tolerance parameter suggested that the creep fracture was caused by necking. These findings provide data and theoretical support for the application of Y-modified 15-15Ti steel as a fast reactor cladding material in high temperature environments.

Different Heat-Exposure Temperatures on the Microstructure and Properties of Dissimilar GH4169/IC10 Superalloy Vacuum Electron Beam Welded Joint

Vacuum electron-beam welding (EBW) was used to join the precipitation-strengthened GH4169 superalloy and a new nickel-based superalloy IC10 to fabricate the turbine blade discs. In this study, a solid solution (1050 °C/2 h for GH4169 and 1150 °C/2 h for IC10) and different heat-exposure temperatures (650 °C, 750 °C, 950 °C and 1050 °C/200 h, respectively) were used to study the high-temperature tensile properties and microstructure evolution of welded joints; meanwhile, the formation and evolution of the second phases of the joints were analyzed. After EBW, the welded joint exhibited a typical nail morphology, and the fusion zone (FZ) consisted of columnar and cellular structures. During the solidification process of the molten pool, Mo elements are enriched in the dendrites and inter-dendrites, and that of Nb and Ti elements was enriched in the dendrites, which lead to forming a non-uniform distribution of Laves eutectic and MC carbides in the FZ. The microhardness of the FZ gradually increased during thermal exposure at 650 °C and reached 300–320 HV, and the γ′ and γ″ phases were gradually precipitated with size of about 50 nm. Meanwhile, the microhardness of the FZ decreased to 260–280 HV at 750 °C, and the higher temperature resulted in the coarsening of the γ″ phase (with a final size of about 100 nm) and the formation of the acicular δ-phase. At 950 °C and 1050 °C, the microhardness of FZ decreased sharply, reaching up to 170~190 HV and 160~180 HV, respectively. Moreover, the Laves eutectic and MC carbides are dissolved to a greater extent without the formation of γ″ and δ phases; as a result, the absent of γ″ and δ phases are attributed to the significant improvement of segregation at higher temperatures.

Effect of Mn/Ag Ratio on Microstructure and Mechanical Properties of Heat-Resistant Al-Cu Alloys.

This paper mainly investigated the effect of the Mn/Ag ratio on the microstructure and room temperature and high-temperature (350 °C) tensile mechanical properties of the as-cast and heat-treated Al-6Cu-xMn-yAg (x + y = 0.8, wt.%) alloys. The as-cast alloy has α-Al, Al2Cu, and a small amount of Al7Cu2 (Fe, Mn) and Al20Cu2 (Mn, Fe)3 phases. After T6 heat treatment, a massive dispersive and fine θ'-Al2Cu phase (100~400 nm) is precipitated from the matrix. The Mn/Ag ratio influences the quantity and size of the precipitates; when the Mn/Ag ratio is 1:1, the θ'-Al2Cu precipitation quantity reaches the highest and smallest. Compared with the as-cast alloy, the tensile strength of the heat-treated alloy at room temperature and high temperature is greatly improved. The strengthening effect of the alloy is mainly attributed to the nanoparticles precipitated from the matrix. The Mn/Ag ratio also affects the high-temperature tensile mechanical properties of the alloy. The high-temperature tensile strength of the alloy with a 1:1 Mn/Ag ratio is the highest, reaching 135.89 MPa, 42.95% higher than that of the as-cast alloy. The analysis shows that a synergistic effect between Mn and Ag elements can promote the precipitation and refinement of the θ'-Al2Cu phase, and there is an optimal ratio (1:1) that obtains the lowest interfacial energy for co-segregation of Mn and Ag at the θ'/Al interface that makes θ'-Al2Cu have the best resistance to coarsening.

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 &lt; 110&gt; 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.