scholarly journals Effect of Overheating Temperature on Thermal Cycling Creep Properties of K465 Superalloy

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1458
Author(s):  
Xiaotong Guo ◽  
Zeshan Liang ◽  
Xiaobin Nan ◽  
Chunxu Jiang ◽  
Yong Li ◽  
...  
Keyword(s):  
Thermal Cycling ◽  
Grain Boundaries ◽  
Turbine Blades ◽  
Creep Property ◽  
Solution Treatment ◽  
Aircraft Engines ◽  
Creep Life ◽  
Creep Properties ◽  
Standard Solution ◽  
C 30

Turbine blades in aircraft engines may encounter overheating and suffer serious creep property degradation. In this study, the thermal cycling creep experiments were conducted on K465 superalloy under (900 °C/30 min–1100 °C/3 min)/50 MPa, (900 °C/30 min–1150 °C/3 min)/50 MPa and (1000 °C/30 min–1150 °C/3 min)/50 MPa. The investigated thermal cycling creep properties were dramatically degraded, and increasing the overheating temperatures significantly decreased the thermal cycling creep life. The secondary γ′ precipitates obviously dissolved and the area fraction decreased to around 35.2% under (900 °C/30 min–1150 °C/3 min)/50 MPa and (1000 °C/30 min–1150 °C/3 min)/50 MPa, which was almost half that after the standard solution treatment. The decline of the thermal cycling creep properties was mainly due to the significant dissolution of γ′ precipitates. The creep holes/cracks were mainly distributed at the M6C carbides and γ/γ′ eutectics interfaces, M6C carbides and γ′ film interfaces in the grain boundaries, and resulted in the final intergranular fracture.

Effective Portion of Sample Taken From USC Boiler Pipes to Consider Heat-to-Heat Variation of Creep

2018 ◽  
Author(s):  
Masatsugu Yaguchi ◽  
Masato Tomobe ◽  
Shin-ichi Komazaki ◽  
Akihiro Kumada
Keyword(s):  
Base Metal ◽  
Outer Surface ◽  
Welded Joint ◽  
Creep Property ◽  
Assessment Method ◽  
Life Assessment ◽  
Thickness Direction ◽  
Base Metals ◽  
Creep Life ◽  
Creep Properties

One of authors proposed a creep life assessment method for USC boiler pipes that can consider heat-to-heat variations of the creep property of each welded joint, where the creep property of the welded joint is estimated from that of each base metal. In the method, it is assumed that the creep property of each base metal in actual pipes is approximately constant in the thickness direction of the pipes, and test results with small samples cut from base metals at the outer surface of pipes are useful for representing the creep properties of the pipes. In this work, the assumption was examined for five pipes of Grade 91 steel, which had been used for longer than 100,000 h at USC power stations. The microstructure, chemical composition, hardness, void density and remaining creep life were investigated in detail in the thickness direction of the pipes. No difference was observed for these items, except in an area less than about 0.2 mm from the outer surface of the pipes, which means that the assumption in the assessment method is valid except in this area. Therefore, it is suggested that an effective portion of the sample taken from USC boiler pipes to consider heat-to-heat variations of the creep properties of base metals is the material excluding the area less than about 1.0 mm from the outer surface of the pipes.

scholarly journals Yttrium’s Effect on the Hot Cracking and Creep Properties of a Ni-Based Superalloy Built Up by Additive Manufacturing

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1143
Author(s):  
Santhosh Banoth ◽  
Thaviti Naidu Palleda ◽  
Sota Shimazu ◽  
Koji Kakehi
Keyword(s):  
Grain Boundary ◽  
Solution Treatment ◽  
Grain Morphology ◽  
Hot Cracking ◽  
Air Cooling ◽  
Creep Life ◽  
Hastelloy X ◽  
Creep Properties ◽  
Creep Anisotropy ◽  
Columnar Grain

We studied the effects of the rare earth element yttrium (Y) on the hot cracking and creep properties of Hastelloy-X processed by selective laser melting. We used two different alloys to study hot cracking in Hastelloy-X: one with 0.12 mass% yttrium added and one with no yttrium. Y-free Hastelloy-X exhibited less cracks, mainly due to the segregation of Si, W, and C resulting in SiC- and W6C-type carbides at the grain boundary and interdendritic regions. On the other hand, more cracks formed in the Y-added Hastelloy-X specimen because of segregation of Y, resulting in the formation of yttrium-rich carbide (YC). Post-heat treatment was conducted at 1177 °C for 2 h, followed by air cooling, to obtain good creep properties. We carried out a creep test along the vertical and horizontal directions. Despite having more cracks, the Y-added as-built Hastelloy-X specimen showed longer creep life and ductility than the Hastelloy-X specimen. This was mainly because of the formation of Y2O3 and SiO2 inside the grains. After solution treatment, the Y-added specimen’s creep life was eight times longer than that of the Y-free solution-treated specimen. This was mainly because of the maintenance of the columnar grain morphology even after solution treatment. In addition, the formation of M6C carbides, Y2O3, and SiO2 improved creep life. To summarize the effect of Y, Y addition promoted the formation of cracks, which brought about creep anisotropy; however, it improved creep properties through the stabilization of oxygen and the promotion of discrete carbide precipitation, which prohibited the migration and sliding of grain boundary.

Effect of Hafnium on the Microstructure and Creep Property of a Hot Corrosion Resistant Superalloy

2015 ◽  
Vol 816 ◽  
pp. 641-647 ◽  
Author(s):  
Jie Shan Hou ◽  
Jian Ting Guo ◽  
Chao Yuan ◽  
Yong An Guo ◽  
Gu Song Li ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Creep Property ◽  
Thermal Exposure ◽  
Boundary Phase ◽  
Primary Carbide ◽  
Bayesian Neural Network ◽  
Creep Life ◽  
Σ Phase

The effects of the selective addition of Hafnium (Hf) on the grain boundary, phase, carbides and creep properties of experimented nickel superalloy after standard heat treatment and long-term exposure were investigated. Predicted by the Bayesian neural network, the creep life is prolonged with Hf content of 0-0.6 mass%, which is more effective at low stresses. The decrease of creep life of Hf free alloy after long term exposure was pronounced. Comparative study showed that the mainly small, coherent, blocky and closely spaced MC(2)and M23C6carbides precipitated on the grain boundaries in the 0.4wt% Hf contained alloy, and that relatively larger, incoherent MC(1)carbides precipitated on the grain boundaries in the Hf free alloy. During long term thermal exposure, fine discrete M23C6carbides decomposed from primary carbide, inducing a layer along the grain boundary, and the coarsening of grain boundary in Hf free alloy is more pronounced. At high stresses, the Hf-free alloy exhibited a stronger tendency of rafting than the 0.4Hf alloy, while the tendency of appearance of rafting was very similar at low stresses. However, Hf can render the alloy prone to the formation of σ phase, according to D-electrons method. Thus, the Hf content needs to be controlled to a suitable level.

scholarly journals The Effect of Recrystallization on Creep Properties of Alloy IN939 Fabricated by Selective Laser Melting Process

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1016 ◽  
Author(s):  
Santhosh Banoth ◽  
Chen-Wei Li ◽  
Yo Hiratsuka ◽  
Koji Kakehi
Keyword(s):  
Heat Treatment ◽  
Cast Alloy ◽  
Solution Treatment ◽  
Low Density ◽  
Laser Melting ◽  
Creep Life ◽  
Creep Properties ◽  
Treatment Conditions ◽  
Temperature Heat ◽  
Temperature Heat Treatment

In this research, we studied the creep properties of a selective laser melting (SLM)-processed γ′-strengthened IN939 superalloy along the building direction compared to a conventional cast alloy as a reference specimen. In the as-built condition, high-density dislocations were formed as a result of the SLM process due to the generation of the larger thermal gradient. Post-heat treatment was necessary to obtain specific mechanical properties to match industrial requirements. Two heat treatment conditions were used: the first was lower temperature heat treatment (LTH: solution treatment at 1160 °C/4 h + aging at 850 °C/16 h). The second was higher temperature heat treatment (HTH: solution treatment at 1240 °C/6 h + aging at 850 °C/16 h). Creep tests were conducted at 816 °C/250 MPa. The first and second heat treatment conditions were used for the SLM specimens, but only the first condition was used for the cast alloy (cast-LTH). The SLM specimens in the as-built and LTH conditions showed very poor creep life but good elongation. The poor creep life of the as-built specimen was caused by high dislocation density and the small recrystallized grains formed during testing. In the LTH specimen, poor creep life was due to the formation of the undesirable η phase at the grain boundary, as well as the formation of small recrystallized grains during testing. The creep life of the HTH specimen was 2.7 times longer compared to the LTH specimen. This was because these specimens were covered with recrystallized grains that included low-density dislocations, columnar grain morphology with random orientation, improvement in γ′ precipitate size, and elimination of undesirable η phase. The cast LTH specimen showed longer creep life than SLM specimens because of coarser grains with low-density dislocations, γ′ precipitate coarsening during the creep, and the presence of carbides at grain boundaries. In addition, the cast LTH specimen exhibited lower creep strain rate than SLM specimens also helped in creep life improvement.

Parallel Glide: A Fundamentally Different Type of Dislocation Motion in Ultrathin Metal Films

2003 ◽  
Vol 779 ◽  
Author(s):  
T. John Balk ◽  
Gerhard Dehm ◽  
Eduard Arzt
Keyword(s):  
Thermal Cycling ◽  
Grain Boundaries ◽  
Film Surface ◽  
Metal Films ◽  
Geometric Constraints ◽  
Film Stress ◽  
Diffusional Creep ◽  
Creep Model ◽  
Substrate Interface ◽  
Film Substrate

AbstractWhen confronted by severe geometric constraints, dislocations may respond in unforeseen ways. One example of such unexpected behavior is parallel glide in unpassivated, ultrathin (200 nm and thinner) metal films. This involves the glide of dislocations parallel to and very near the film/substrate interface, following their emission from grain boundaries. In situ transmission electron microscopy reveals that this mechanism dominates the thermomechanical behavior of ultrathin, unpassivated copper films. However, according to Schmid's law, the biaxial film stress that evolves during thermal cycling does not generate a resolved shear stress parallel to the film/substrate interface and therefore should not drive such motion. Instead, it is proposed that the observed dislocations are generated as a result of atomic diffusion into the grain boundaries. This provides experimental support for the constrained diffusional creep model of Gao et al.[1], in which they described the diffusional exchange of atoms between the unpassivated film surface and grain boundaries at high temperatures, a process that can locally relax the film stress near those boundaries. In the grains where it is observed, parallel glide can account for the plastic strain generated within a film during thermal cycling. One feature of this mechanism at the nanoscale is that, as grain size decreases, eventually a single dislocation suffices to mediate plasticity in an entire grain during thermal cycling. Parallel glide is a new example of the interactions between dislocations and the surface/interface, which are likely to increase in importance during the persistent miniaturization of thin film geometries.

Thermal cycling creep properties of a directionally solidified superalloy DZ125

2022 ◽  
Vol 104 ◽  
pp. 269-284
Author(s):  
Wenrui An ◽  
Satoshi Utada ◽  
Xiaotong Guo ◽  
Stoichko Antonov ◽  
Weiwei Zheng ◽  
...  
Keyword(s):  
Thermal Cycling ◽  
Directionally Solidified ◽  
Creep Properties

scholarly journals Towards Damage Controlled Hot Forming

2018 ◽  
Vol 885 ◽  
pp. 56-63
Author(s):  
Markus Bambach ◽  
Irina Sizova ◽  
Aliakbar Emdadi
Keyword(s):  
Metal Forming ◽  
High Performance ◽  
Titanium Aluminides ◽  
Turbine Blades ◽  
Process Time ◽  
Jet Engines ◽  
Internal Damage ◽  
Creep Properties ◽  
Recent Developments ◽  
Ram Speed

Metal forming processes may induce internal damage in the form of voids in the workpiece under unfavorable deformation conditions. Controlling the amount of damage induced by metal forming operations may increase service performance of the produced parts. Damage is crucial in high-performance components of limited workability such as jet engine turbine blades. Recent developments have introduced forged titanium aluminides into commercial jet engines. Titanium aluminides are lightweight intermetallic compounds with excellent creep properties but very limited ductility. Their low workability requires isothermal forging at slow strain rates, which is typically kept constant in the process. This work explores the possibility of increasing the ram speed during the process so that the process time is reduced while the amount of damage introduced into the workpiece is controlled. The results show that a 25% reduction in process time seems viable without increase in damage by solving an optimal control problem, in which the ram speed profile is determined off-line by minimization.

scholarly journals Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5522
Author(s):  
Kai-Cheng Shie ◽  
Po-Ning Hsu ◽  
Yu-Jin Li ◽  
Dinh-Phuc Tran ◽  
Chih Chen
Keyword(s):  
Thermal Cycling ◽  
Grain Boundaries ◽  
Maximum Stress ◽  
Failure Mechanisms ◽  
Deep Understanding ◽  
Bonding Interface ◽  
Triple Junctions ◽  
Element Analysis ◽  
Resistance Change ◽  
Hybrid Joints

The failure mechanisms of Cu–Cu bumps under thermal cycling test (TCT) were investigated. The resistance change of Cu–Cu bumps in chip corners was less than 20% after 1000 thermal cycles. Many cracks were found at the center of the bonding interface, assumed to be a result of weak grain boundaries. Finite element analysis (FEA) was performed to simulate the stress distribution under thermal cycling. The results show that the maximum stress was located close to the Cu redistribution lines (RDLs). With the TiW adhesion layer between the Cu–Cu bumps and RDLs, the bonding strength was strong enough to sustain the thermal stress. Additionally, the middle of the Cu–Cu bumps was subjected to tension. Some triple junctions with zig-zag grain boundaries after TCT were observed. From the pre-existing tiny voids at the bonding interface, cracks might initiate and propagate along the weak bonding interface. In order to avoid such failures, a postannealing bonding process was adopted to completely eliminate the bonding interface of Cu–Cu bumps. This study delivers a deep understanding of the thermal cycling reliability of Cu–Cu hybrid joints.

scholarly journals Study on the Evolution of the γ′ Phase and Grain Boundaries in Nickel-Based Superalloy during Interrupted Continuous Cooling

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1464
Author(s):  
Haiping Wang ◽  
Dong Liu ◽  
Jianguo Wang ◽  
Yanhui Yang ◽  
Haodong Rao ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Short Distance ◽  
Creep Property ◽  
Maximum Amplitude ◽  
Matrix Diffusion ◽  
Cooling Rates ◽  
Continuous Cooling ◽  
Nickel Based Superalloy ◽  
The Matrix ◽  
Solute Atoms

The formation of the irregular γ′ precipitates in the nickel-based superalloy Waspaloy was investigated during the continuous cooling, which is relevant to the cooling rates and interrupted temperature. The morphology of the γ′ precipitates was observed to change from a dispersed sphere to the flower-like one with the decreasing of the cooling rates. It was found that there are three modes of transportation of the solute atoms involved in relation to the γ′ precipitates: dissolution from the small γ′ precipitates to the γ matrix, diffusion to the large γ′ precipitates from the matrix, and the short distance among γ′ precipitates close to each other. Meanwhile, the slower cooling rates tend to result in the serrated grain boundaries, and the wavelength between successive peaks (λ) and the maximum amplitude (A) are larger with the decreasing of the cooling rates. The content of the low ΣCSL boundaries increases with the decreasing of the cooling rates, which is of great benefit in improving the creep property of the Waspaloy.

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